JP7693382B2 - MRI machine - Google Patents

Description

Applicable under Article 30, Paragraph 2 of the Patent Act. Presented at the ISMRM & SMRT Virtual Conference & Exhibition (online) from August 8 to 14, 2020.

The present invention relates to MRI devices, and more particularly to coil inserts for use with MRI systems, MRI system apparatus including MRI systems including coil inserts or other components, echo planar spectroscopic imaging systems including MRI system apparatus, and methods of operating MRI systems.

Magnetic Resonance Imaging (MRI) systems are widely used for imaging subjects and, in the case of Magnetic Resonance Spectroscopy Imaging (MRSI), for acquiring spectral information. MRI systems typically include a magnet arrangement that creates a large static magnetic field _B0 , a set of radio frequency coils or antennas that generate an alternating magnetic field _B1 and acquire magnetic resonance signals (i.e., acquire magnetic resonance data), and a set of gradient coils that allow spatial encoding in the _B0 field to allow tomographic imaging. Additionally, in the case of MRSI, gradient coils are also used to allow spectroscopic encoding.

Spatial encoding of magnetic resonance signals is typically achieved by rapid switching of three magnetic field gradients (X, Y, Z) produced by gradient coils positioned around the scanner bore, within which the subject being examined is located.

Typically, in existing systems, gradient coils are driven in the 0-10 kHz range. Because gradient coils are driven in the audible range (20 Hz-20 kHz), considerable effort has been expended on reducing the noise generated by the switching gradients and the Lorentz forces induced thereby. This includes using materials that attenuate the resulting noise.

To enhance the spatiotemporal resolution of MRI, gradient systems can be driven "faster" and "stronger", i.e. with larger gradient slew rates (T/m/s) and larger gradient strengths (mT/m). Current gradient performance may be limited primarily by unpleasant peripheral nerve stimulations (PNS) induced by too rapid switching of strong magnetic field gradients. Gradient switching can induce electric fields and currents in conductive tissues such as muscles and nerves, resulting in nerve depolarization and ultimately nerve stimulation.

It would therefore be desirable to develop MRI machines and methods of operating MRI machines that can improve performance without increasing the physical discomfort to the patient due to auditory effects and/or peripheral nerve stimulation. Similarly, it would be desirable to create MRI machines and methods of using MRI machines that can reduce auditory effects and/or peripheral nerve stimulation and/or other sources of discomfort, with or without improving the performance of the MRI process itself. It would also be of interest to be able to complete scans more quickly, minimizing patient discomfort and/or obtaining results that are less affected by the time it takes to acquire the scan.

According to a first aspect of the present invention, there is provided a coil insert for an MRI system for use within a bore of the MRI system, the coil insert comprising at least one gradient magnetic field coil arranged to produce a spatially varying magnetic field along a respective axis and to be electrically driven at ultrasonic frequencies.

This allows the functionality of the main MRI system to be used in combination with the insert to perform the examination. There are various advantages to using ultrasonic frequencies. Firstly, there is less time for the Lorentz forces to dominate, so less force can be exerted on the coil itself. This means that the coils can be lighter than when driven at more conventional frequencies, so they can be physically different and the structures that support them can be different. Secondly, the switching of the gradients becomes inaudible to the patient. Thirdly, it has been found that when ultrasonic frequencies are used, there can be less peripheral nerve stimulation (PNS) in the patient undergoing the examination. This is thought to be because there is not enough time for the nerves to react to the switching magnetic field.

The coil insert may have a central region that is free of gradient field coil windings. This may allow for the insert to have a window through which the patient can see when their head is positioned within the insert. This may be facilitated by using lighter weight coils/less force on the coil.

The insert may be generally cylindrical. The insert may have a major axis. The major axis may be arranged to align with a major axis of a bore of a primary MRI system in which the insert is used. In such a case, the axes of the insert and the primary MRI system may be aligned by being parallel to one another or coincident with one another.

The at least one gradient coil may comprise a Z-gradient coil that produces a spatially varying magnetic field along a major axis of the insert. The at least one gradient coil may comprise an X-gradient coil or a Y-gradient coil that produces a spatially varying magnetic field transverse to the major axis of the insert.

The coil insert may include a first gradient coil for producing a spatially varying magnetic field along a first respective axis, and a second gradient coil for producing a spatially varying magnetic field along a second respective axis.

The first gradient coil may be a Z-gradient coil that creates a spatially varying magnetic field along the major axis of the insert, and the second gradient coil may be an X-gradient coil or a Y-gradient coil that creates a spatially varying magnetic field transverse to the major axis of the insert.

When the coil insert comprises a first gradient coil and a second gradient coil, the coil insert may still have a central region that does not have gradient coil windings.

The coil insert may also include a third gradient coil that creates a spatially varying magnetic field along a third respective axis that is transverse to the first and second axes. However, it is generally preferred to provide one or two gradient coils and no third gradient coil, as this makes it easier to provide a central region that does not have gradient coil windings.

The main MRI system will have its own gradient coils, which may be used in conjunction with the gradient coils of the insert during operation. Thus, for example, if the insert does not have gradient coils to create a spatially varying magnetic field along a particular axis, spatial encoding in that axis may be accomplished using the gradient coils of the main MRI system.

The Z-gradient magnetic field coil may have at least one set of windings.

The Z-gradient coil may include a first set of windings provided at a first end of the insert and a second set of windings provided at a second end of the insert. In one set of embodiments, the area between the first and second sets of windings may be free of Z-gradient coil windings.

Creating a central region free of windings can result in a less linear magnetic field, but has been found to be acceptable for this type of insert, especially when the insert is used for examinations involving the patient's head, where it is not necessary for the insert to have a long length.

In some examples, the Z-gradient coil may have more than two sets of windings. For example, four or more sets of windings may be provided.

The windings may be arranged to allow for providing a segmented gradient on the Z axis. That is, rather than providing a continuous or linear gradient along the Z axis, a series of gradient sections along the axis are provided. This means that a smaller maximum absolute magnetic field may be used to set the gradient along the entire Z axis. This in turn may help to minimize peripheral nerve stimulation (PNS) of the patient being examined. This arrangement is more useful for longer inserts, i.e., when the Z axis is longer. Such an insert may be for examining a longer area of the patient, or may be a whole body insert.

In other words, the windings may be arranged in a manner that allows for providing a spatially non-monotonic gradient along the Z axis.

The windings may be arranged in a manner that allows for providing a spatially multi-lobed gradient along the Z axis.

The windings may be arranged to allow for providing a spatially oscillating gradient along the Z axis.

The windings may be arranged to allow for providing a gradient having a polynomial-like or sinusoidal-like spatial variation along the Z axis.

It will be understood that when referring to these gradient patterns, we are referring to the variations in amplitude/size of the magnetic field as viewed along the Z axis.

The windings of the Z-gradient coil may be provided in two layers, with the windings of the first of the two layers not aligned with the windings of the second of the two layers. This may help improve the spatial encoding that can be achieved.

The first set of windings of the Z-gradient coil may be provided in two layers, with the windings of the first of the two layers being misaligned with the windings of the second of the two layers. The second set of windings of the Z-gradient coil may be provided in two layers, with the windings of the first of the two layers being misaligned with the windings of the second of the two layers.

The X-gradient magnetic field coil or the Y-gradient magnetic field coil may have at least one set of windings.

The X-gradient magnetic field coil or the Y-gradient magnetic field coil may comprise a pair of windings provided on radially opposite sides of the insert. Each winding of the pair may comprise a plurality of helically wound turns, each full turn having an inner arcuate segment, a first end segment extending outwardly to an outer arcuate segment, and a second end segment extending inwardly from the outer arcuate segment to a corresponding inner arcuate segment of the next turn. Each inner arcuate segment may conform to a sidewall of the insert. Each outer arcuate segment may conform to a sidewall of the insert.

When a Z-gradient magnetic field coil is provided with first and second sets of windings as described above, an X or Y-gradient magnetic field coil may be provided and disposed within the insert axially between the first and second sets of windings of the Z-gradient magnetic field coil.

The X or Y gradient coil may comprise a third set of windings and a fourth set of windings provided on radially opposite sides of the insert and axially between the first and second windings of the Z gradient coil. Thus, the third and fourth sets of windings may be provided in areas where there are no Z gradient coil windings. Note that the third and fourth sets of windings are the same windings described above as a pair of windings, and in this set of examples are third and fourth in the sense that the first and second windings are defined in relation to the Z gradient coil.

A circumferential gap may be provided between the third and fourth sets of windings such that there is an area of the insert that is free of Z-gradient coil windings and X- or Y-gradient coil windings. This area may be arranged as a window through which the patient can see when the patient's head is disposed within the insert.

The third set of windings and the fourth set of windings may each comprise a plurality of helically wound turns, each full turn having an inner arcuate segment, a first end segment extending outwardly to an outer arcuate segment, and a second end segment extending inwardly from the outer arcuate segment to a corresponding inner arcuate segment of the next turn.

Each inner arcuate segment may conform to a sidewall of the insert. Each outer arcuate segment may conform to a sidewall of the insert.

Such an arrangement may help maximize the axial length of the insert over which the X or Y gradient coils can generate linear magnetic fields. It may also allow for maximizing the circumferential gap between the ends of the third and fourth sets of windings, allowing for the creation of a window for the patient.

The insert may include a partial shielding coil for at least one gradient magnetic field coil, or may even include no shielding coil. If the insert includes a first gradient magnetic field coil and a second gradient magnetic field coil, the insert may include a partial shielding coil for the first gradient magnetic field coil and the second gradient magnetic field coil, or may even include no shielding coil.

The insert may comprise at least one capacitor electrically connected to at least one gradient coil to resonate the respective gradient coil at a predetermined ultrasound frequency. This helps to drive the gradient coils efficiently at the predetermined frequency. It also means that the gradient coils can be driven using low current from a high impedance signal source, which reduces inductive coupling to other coils/metal objects in the area.

When the insert includes a first gradient magnetic field coil and a second gradient magnetic field coil, at least one first capacitor may be electrically connected to the first gradient magnetic field coil to resonate the first gradient magnetic field coil at a first predetermined ultrasonic frequency, and at least one second capacitor may be electrically connected to the second gradient magnetic field coil to resonate the second gradient magnetic field coil at a second predetermined ultrasonic frequency.

The first predetermined ultrasonic frequency may be the same as the second predetermined ultrasonic frequency.

However, preferably, the first predetermined ultrasonic frequency is different from the second predetermined ultrasonic frequency.

This makes it easier to operate the two gradient coils at different frequencies, which in turn can lead to sampling more spatial frequencies during imaging, as this combination produces Lissajous encoding rather than circular or spiral encoding. This in turn can increase the potential for accelerating imaging.

It has been determined that there is a potential problem with using two frequencies that could result in an audible sound. This has been determined to be due to a "beat" occurring between the sounds produced by the two frequencies.

Preferably, the frequency difference between the first and second predetermined ultrasonic frequencies is an inaudible frequency, i.e., either an infrasonic frequency or an ultrasonic frequency. Typically, in practice, the first and second predetermined ultrasonic frequencies are selected such that the frequency difference between them is an infrasonic frequency.

According to another aspect of the present invention, there is provided a coil insert device for an MRI system comprising a coil insert as described above and a signal generator device for electrically driving at least one gradient coil at ultrasonic frequencies.

When the at least one gradient coil comprises a Z-gradient coil, the coil windings and signal generator arrangement may be arranged to provide a gradient segmented on the Z axis.

The windings and signal generator arrangement may be arranged to provide a spatially non-monotonic gradient along the Z axis.

The windings and signal generator arrangement may be arranged to provide a spatially multilobal gradient along the Z axis.

The windings and signal generator arrangement may be arranged to provide a spatially oscillating gradient along the Z axis.

The windings and signal generator arrangement may be arranged to provide a gradient having a polynomial-like or sinusoidal-like spatial variation along the Z axis.

When the insert comprises a first gradient coil and a second gradient coil, the signal generator device may be arranged to drive the first gradient coil at a first selected ultrasonic frequency and to drive the second gradient coil at a second selected ultrasonic frequency. The first and second frequencies may be the same as each other. The first and second frequencies may be different from each other.

Preferably, the frequency difference between the first selected ultrasonic frequency and the second selected ultrasonic frequency is an inaudible frequency, i.e., either an infrasonic frequency or an ultrasonic frequency. Typically, in practice, the first selected ultrasonic frequency and the second selected ultrasonic frequency are selected such that the frequency difference between them is an infrasonic frequency.

The first selected frequency may be the same as the first predetermined frequency. The second selected frequency may be the same as the second predetermined frequency.

Thus, the first and second coils may be driven at a selected frequency with or without a capacitor being provided to cause the coils to resonate at the selected frequency, although it is noted that it is preferred that a capacitor is provided and the coils are driven at their respective resonant frequencies.

According to another aspect of the present invention, there is provided an MRI system apparatus comprising an MRI system having a main bore and a coil insert for the MRI system as described above for use within the bore.

According to another aspect of the present invention, there is provided an MRI system apparatus comprising an MRI system having a main bore and a coil insert apparatus for an MRI system as described above, with a coil insert disposed for use within the bore.

Although the above features have been described in the context of a coil insert for an MRI system, the above features and ideas can be used in the MRI system itself, where the context permits.

Thus, according to another aspect of the present invention, there is provided an MRI system comprising a coil arrangement, the coil arrangement comprising at least one gradient magnetic field coil arranged to produce a spatially varying magnetic field along a respective axis and to be electrically driven at ultrasonic frequencies.

In general, any feature described above is also an optional feature for this aspect of the invention, where the context permits. For the sake of brevity, not all are repeated here, but some are explicitly described as examples.

The MRI system may include a signal generator device that electrically drives at least one gradient coil at ultrasonic frequencies.

In one set of embodiments, the at least one gradient coil comprises a Z-gradient coil, the coil windings and signal generator arrangement being arranged to provide a segmented gradient on the Z axis.

In other words, the windings and signal generator arrangement may be arranged to provide a spatially non-monotonic gradient along the Z axis.

The windings and signal generator arrangement may be arranged to provide a spatially multilobal gradient along the Z axis.

The windings and signal generator arrangement may be arranged to provide a spatially oscillating gradient along the Z axis.

The windings and signal generator arrangement may be arranged to provide a gradient having a polynomial-like or sinusoidal-like spatial variation along the Z axis.

The MRI system may include at least one capacitor electrically connected to at least one gradient coil to resonate each gradient coil at a predetermined ultrasound frequency.

The coil device may include a first gradient magnetic field coil and a second gradient magnetic field coil, and at least one first capacitor may be electrically connected to the first gradient magnetic field coil to resonate the first gradient magnetic field coil at a first predetermined ultrasonic frequency, and at least one second capacitor may be electrically connected to the second gradient magnetic field coil to resonate the second gradient magnetic field coil at a second predetermined ultrasonic frequency.

The first predetermined ultrasonic frequency may be the same as the second predetermined ultrasonic frequency.

However, preferably, the first predetermined ultrasonic frequency is different from the second predetermined ultrasonic frequency.

Preferably, the frequency difference between the first and second predetermined ultrasonic frequencies is an inaudible frequency, i.e., either an infrasonic frequency or an ultrasonic frequency. Typically, in practice, the first and second predetermined ultrasonic frequencies are selected such that the frequency difference between them is an infrasonic frequency.

When the coil arrangement comprises a first gradient coil and a second gradient coil, the signal generator arrangement may be arranged to drive the first gradient coil at a first selected ultrasonic frequency and to drive the second gradient coil at a second selected ultrasonic frequency. The first and second frequencies may be the same as each other. The first and second frequencies may be different from each other.

Preferably, the frequency difference between the first selected ultrasonic frequency and the second selected ultrasonic frequency is an inaudible frequency, i.e., either an infrasonic frequency or an ultrasonic frequency. Typically, in practice, the first selected ultrasonic frequency and the second selected ultrasonic frequency are selected such that the frequency difference between them is an infrasonic frequency.

The first selected frequency may be the same as the first predetermined frequency. The second selected frequency may be the same as the second predetermined frequency.

According to another aspect of the present invention, there is provided a method for operating an MRI system apparatus as described above.

According to a further aspect of the present invention there is provided an echo planar spectroscopic imaging system comprising an MRI system apparatus having an acquisition unit for acquiring magnetic resonance data and a reconstruction unit for reconstructing image and spectroscopic information from the acquired magnetic resonance data,
The acquisition department,
an RF transmitter arranged to output single-band or multi-band RF pulses;
a first gradient coil arranged to be driven at ultrasonic frequencies to produce a spatially varying magnetic field along a first respective axis; and a second gradient coil arranged to be driven at ultrasonic frequencies to produce a spatially varying magnetic field along a second respective axis.
a signal generator device for electrically driving the first gradient coil at a first selected ultrasonic frequency and for driving the second gradient coil at a second selected ultrasonic frequency;
the signal generator apparatus is configured to apply a plurality of chirp pulses to a first gradient coil and a plurality of chirp pulses to a second gradient coil during a readout period as part of acquiring the magnetic resonance data to achieve spectral and spatial encoding in the first and second respective axes;
An acquisition unit is arranged to read out magnetic resonance data during said readout period, and a reconstruction unit is arranged to reconstruct an image and spectral information relating to the image from the magnetic resonance data read out during said readout period.

This allows spatial encoding over the duration of each chirp, and over the duration of the readout period. By using ultrasonic frequencies and a series of chirps, it is possible to obtain MRI data, i.e. MRI images and associated spectral data, associated with a significantly shorter examination period than is achieved with existing techniques. This avoids information being lost or confounded by changes over time, e.g. metabolite flux or metabolite chemistry changes in the subject during the examination period.

Each chirp pulse may have a length of less than 100 milliseconds, preferably less than 10 milliseconds. In one embodiment, each chirp pulse has a length on the order of 1 millisecond. In another embodiment, each chirp pulse has a length on the order of 0.5 milliseconds.

The signal generator device may be configured to apply at least 10 chirp pulses during the readout period, preferably at least 50 pulses. In one embodiment, 200 chirp pulses may be applied during the readout period.

It can thus be seen that the readout period may be, for example, on the order of 100 ms, e.g. 200 chirp pulses of 0.5 ms each, or 200 ms, e.g. 200 chirp pulses of 1 ms each. This in turn may lead to bandwidths of 2 kHz and 1 kHz, respectively, and resolutions of the spectral data on the order of 10 Hz and 5 Hz, respectively.

The acquisition unit may be arranged to acquire magnetic resonance data during multiple readout periods to generate a set of magnetic resonance data.

The acquisition unit may be arranged to cause the RF transmitter to output a single-band or multi-band RF pulse before the start of each readout period, and the acquisition may be configured to apply a respective plurality of chirp pulses to a first gradient coil and a respective plurality of chirp pulses to a second gradient coil during each readout period to achieve spectral and spatial encoding in each of the first and second axes.

The reconstruction unit may be arranged to reconstruct an image and spectral information relating to the image from a set of magnetic resonance data read out during the multiple readout periods.

The first selected ultrasonic frequency and the second selected ultrasonic frequency may be the same frequency.

Preferably, the first selected ultrasonic frequency is different from the second selected ultrasonic frequency.

Preferably, the frequency difference between the first selected ultrasonic frequency and the second selected ultrasonic frequency is an inaudible frequency, i.e., either an infrasonic frequency or an ultrasonic frequency. Typically, in practice, the first selected ultrasonic frequency and the second selected ultrasonic frequency are selected such that the frequency difference between them is an infrasonic frequency.

The acquisition unit may include at least one first capacitor electrically connected to the first gradient magnetic field coil to resonate the first gradient magnetic field coil at a first predetermined ultrasonic frequency, and at least one second capacitor electrically connected to the second gradient magnetic field coil to resonate the second gradient magnetic field coil at a second predetermined ultrasonic frequency.

The first predetermined ultrasonic frequency may be the same as the second predetermined ultrasonic frequency.

However, preferably, the first predetermined ultrasonic frequency is different from the second predetermined ultrasonic frequency.

Preferably, the frequency difference between the first and second predetermined ultrasonic frequencies is an inaudible frequency, i.e., either an infrasonic frequency or an ultrasonic frequency. Typically, in practice, the first and second predetermined ultrasonic frequencies are selected such that the frequency difference between them is an infrasonic frequency.

The first selected frequency may be the same as the first predetermined frequency. The second selected frequency may be the same as the second predetermined frequency.

The acquisition section may further comprise a third gradient coil arranged to be electrically driven to create a spatially varying magnetic field along the third respective axis. The signal generator device may be arranged to electrically drive the third gradient coil, in particular to provide spatial encoding in the third respective axis to allow for selecting a slice of the subject under examination for which the above-mentioned magnetic resonance data or set of magnetic resonance data is acquired during a respective readout period or during a respective readout period.

The acquisition unit may be arranged to acquire further magnetic resonance data or further sets of magnetic resonance data in a subsequent step to facilitate improving the signal-to-noise ratio of the acquired data.

The acquisition unit may be arranged to acquire further magnetic resonance data or further series of magnetic resonance data in a subsequent step so that different slices of the subject under examination are selected using spatial encoding in the third respective axis.

The MRI system device may include an MRI system having a main bore and a coil insert device for the MRI system for use within the bore.

The insert may include a first gradient magnetic field coil and a second gradient magnetic field coil.

The insert may comprise a coil insert according to the first aspect of the invention.

The third gradient coil may be the gradient coil of the MRI system itself, allowing it to be moved away from the patient to help keep the window of the insert unobstructed.

Typically, the MRI system also includes further respective gradient coils arranged to produce a spatially varying magnetic field along a first respective axis and a spatially varying magnetic field along a second respective axis. However, in at least some instances, these further respective gradient coils may remain unused when performing magnetic resonance data acquisition in accordance with the above-described further aspects of the invention.

In other implementations, there may be no insert, and instead the first and second gradient coils of the above-described further aspect of the invention may be provided in the main body of the MRI system.

In other implementations, gradient coils may be utilized in both the main MRI system and the insert, even on the same axis. Thus, for example, Z gradient coils in the insert and in the main MRI system may both be used for encoding.

According to another aspect of the present invention, there is provided a method of echo-planar spectroscopic imaging using an MRI system having an acquisition unit for acquiring magnetic resonance data and a reconstruction unit for reconstructing image and spectral information from the acquired magnetic resonance data, comprising:
The method is:
applying a single-band or multi-band RF pulse to a subject being examined;
electrically driving a first gradient coil at a first ultrasonic frequency to produce a spatially varying magnetic field along a first respective axis; and electrically driving a second gradient coil at a second ultrasonic frequency to produce a spatially varying magnetic field along a second respective axis;
applying a plurality of chirp pulses to a first gradient coil and a plurality of chirp pulses to a second gradient coil during a readout period as part of acquiring the magnetic resonance data to achieve spectral and spatial encoding in the first and second respective axes;
reading out magnetic resonance data during said readout period;
and reconstructing an image and spectral information relating to the image from the magnetic resonance data read out during said readout period.

It should be noted that in general terms and with necessary modifications of wording, all further features defined above according to any aspect of the invention defined above are applicable as further features of all other aspects of the invention defined above. These further features are not restated after each aspect of the invention for the sake of brevity.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an MRI system. 2 is a schematic diagram illustrating a coil insert for an MRI system of a type that may be used in the MRI system apparatus shown in FIG. 1 and having a Z-gradient magnetic field coil; FIG. FIG. 2 is a schematic diagram of a portion of an alternative coil insert for an MRI system showing only the Z-gradient field coil, as well as the X or Y-gradient field coils of the insert. FIG. 4 is a diagram showing in more detail the winding pattern of the X or Y gradient coil shown in FIG. 3 in comparison with a portion of a conventional X or Y gradient coil. FIG. 13 illustrates an alternative set of windings of a Z-gradient field coil in an alternative MRI system coil insert that produces a segmented Z-axis gradient. 2 is a timing diagram illustrating an echo planar spectroscopic imaging technique that may be implemented using an MRI system apparatus of the type shown in FIG. 1.

Figure 1 shows a schematic diagram of an MRI system apparatus, in this example comprising a main MRI system 1 and a coil insert 2 for the MRI system. In this example, the structure and operation of the main MRI system 1 is largely conventional. Thus, while various aspects of the main MRI system are shown in the drawings and described below, other aspects of the MRI system 1 are not shown or described in detail, although it will be appreciated that these details are well known and understood in the field of MRI testing.

The MRI system insert 2 is arranged to be supplied and used in conjunction with an existing MRI system. Of course, this is commercially advantageous as it means that existing MRI systems may be adapted to utilise the ideas of the present invention, rather than having to develop an entirely new MRI system. That is, in the alternative, the MRI system arrangement shown in Figure 1 may be fabricated from scratch, and in a further alternative, the features and functionality of the insert 2 may be incorporated into the main body of the MRI system 1, if so desired.

In FIG. 1, the MRI system coil insert 2 is shown external to the main MRI system 1 for clarity. However, in operation, the insert 2 is moved to a position within the main bore B of the main MRI system 1, to a position shown in dotted lines in FIG. 1. FIG. 2 shows diagrammatically an insert 2 of the type shown in FIG. 1 mounted on the bed 3 of the MRI system 1 such that the insert 2 is slidably movable between a position shown in FIG. 2 corresponding to the position shown in FIG. 1, which is external to the bore B of the MRI system 1, and a position inside the bore B of the MRI system 1.

A variety of different insert configurations may be provided.

The insert 2' shown in FIG. 2 includes an insert Z gradient coil 2z having a first set of windings 2z1 and a second set of windings 2z2, one at each end of the insert 2.

Although the fact that the Z coil winding is not in the central region between the first set of windings 2z1 and the second set of windings 2z2 may lead to a less than optimal magnetic field, it has been determined that in at least some circumstances these imperfections are acceptable. As an example, the space between the first set of windings 2z1 and 2z2 in inserts used in examining human heads is relatively small, making these imperfections acceptable.

The insert 2 shown in FIG. 1 includes a similar insert Z gradient coil 2z with first and second sets of windings 2z1 and 2z2, and further includes an insert X gradient coil 2x with first and second sets of windings 2x1 and 2x2. These sets of windings are shown more clearly separated in FIG. 3.

In both the insert 2 of Figures 1 and 3 and the insert 2' of Figure 2, each set of Z-windings 2z1, 2z1 itself comprises two sets of helically wound turns 2z1a, 2z1b, 2z2a, 2z2b. The second layers 2z1b, 2z2b are wound on top of, but slightly out of alignment with, the respective first layers 2z1a, 2z2a so that the outer set of conductors can provide opposite current directions. This has been found to improve shielding of the gradient magnetic field and minimize eddy currents in the surrounding conductor material.

The winding pattern of the windings 2x1, 2x2 of the X-gradient coil 2x in the insert 2 of Figures 1 and 3 can be seen more clearly by considering Figure 4 in combination with Figure 3.

Figure 4 shows the winding set 2x1, 2x2 of the X insert gradient coil 2x in comparison with the inner layer of a more conventionally wound X gradient coil (labeled "Prior Art" in Figure 4). Each winding set 2x1, 2x2 is wound helically, with each full turn comprising an inner arcuate segment 2x1a, 2x2a connected to an outer arcuate segment 2x1c, 2x2c via a first end segment 2x1b, 2x2b. The turn is completed by a second end segment 2x1d, 2x2d, which returns inward toward the beginning of the next turn. The next turn begins with the corresponding inner arcuate segment 2x1a, 2x2a of the succeeding turn, and so on.

It can be seen that the arc of each inner arcuate segment has the same radius as the other inner arcuate segments. Similarly, the arc of each outer arcuate segment has the same radius as the other outer arcuate segments. The radius of the arc of the inner segments is less than the radius of the arc of the outer segments.

This winding arrangement results in a longer linear region in the axial direction of the insert than prior art winding arrangements, and allows for a larger circumferential gap between the ends of the two sets of windings 2x1, 2x2 than prior art patterns. Although there may be compromises in the nature of the magnetic field produced by such windings, it has been found that the benefits of the system of the present invention outweigh these problems.

The insert 2 shown in Figures 1 and 3 is designed for use in performing examinations of a patient's head, and of course in particular the brain. The insert 2 is therefore arranged so that the patient's head is disposed within the bore of the insert. The arrangement of the Z-gradient and X-gradient magnetic field coils 2z, 2x in the insert makes it possible to provide the insert 2 with a window W (shown diagrammatically in Figure 3 and the position of which is shown diagrammatically in Figure 1) through which the user's head can be seen when inserted into the insert 2. This window W may be an opening in the insert if desired, or it may be an opening filled with a transparent material.

Furthermore, in an insert 2' of the type shown in FIG. 2, which does not have an X-gradient field coil, it is still possible to create one or more windows W through which the user can see when their head is within the insert 1. Naturally, providing such windows helps counteract the patient's sense of claustrophobia.

The MRI system device includes a signal generator device 4 provided to drive the gradient magnetic field coils 2z, 2x of the insert 2.

In commercial terms, this signal generator device 4 may be provided with the insert 2 and together they may be considered a coil insert device for an MRI system that may be used with an existing MRI system 1. Of course, again in other alternatives, if a complete system is developed, a separate signal generator device may not be necessary and instead it may be incorporated into the system provided within the main MRI system.

The signal generator device 4 is arranged to drive the gradient coils 2z, 2x of the insert 2 at ultrasonic frequencies, i.e. frequencies above the audible range.

When there are two or more gradient coils in the insert 2, such as the type of insert 2 shown in Figures 1 and 3, in some examples the same ultrasound frequency may be used to drive each of the gradient coils 2z, 2x.

Alternatively, and preferably, if there are two gradient coils in the insert 2, e.g. two gradient coils 2z, 2x, the signal generator device 4 is arranged to drive each of these at a different ultrasonic frequency.

As an example, in some embodiments, a single ultrasound frequency is used, which may be set at 20.2 kHz. In other embodiments, where two different frequencies are used, these may be, for example, 22 kHz on the one hand and 19.9 kHz on the other hand, one used to drive the X-gradient magnetic field coil 2x and the other used to drive the Z-gradient magnetic field coil 2z. In practice, as will be appreciated, there is a great deal of freedom as to which frequencies may be selected.

However, it has been determined to be particularly advantageous, firstly, for two different frequencies to be selected, and secondly, for the difference between these two different frequencies to itself be an inaudible frequency. This is because, as mentioned in the introduction, a good spatial coding can be achieved when the two frequencies are different, and having a frequency difference in the inaudible range avoids the generation of an audible "beat" signal created between sounds occurring at the two selected inaudible frequencies. In general, the two frequencies may be selected such that the frequency difference is below the range of human hearing, i.e. the frequency difference is less than or equal to 20 Hz.

As shown diagrammatically in FIG. 1, a signal generator device 4 is arranged to drive each gradient coil 2x, 2z of the insert via a respective capacitor Cx, Cz. The values of these capacitors are selected to resonate each gradient coil 2x, 2z at the frequency at which it is driven by the signal generator device 4. This facilitates the use of a high impedance signal generator to deliver lower currents to the gradient coils 2x, 2c, which in turn can help reduce coupling between them.

Note that the idea of making the gradient coil resonate at a given frequency encompasses the situation where the gradient coil is one electrical entity driven by one signal generator, as well as the situation where the gradient coil is made up of several separate electrical entities that may be driven individually. Thus, for example, if the gradient coil has several separate windings, each is made to resonate by providing an appropriate capacitor.

In the apparatus of the present invention, no RF shielding is provided at the insert 2 or between the insert 2 and the main MRI system. This helps to minimize losses due to the generation of eddy currents, as would otherwise occur when the insert gradient coils 2x, 2z are driven at ultrasonic frequencies. At the same time, the insert, and in particular the gradient coils 2x, 2z, are relatively transparent to signals transmitted and received by the main MRI system. Thus, operation of the main MRI system may continue with the insert 2 in place within the bore B of the main MRI system.

In general terms, minimizing the amount of conductive material in the vicinity of the insert gradient coils 2x, 2z (or any gradient coils operating at ultrasonic frequencies) helps improve efficiency by minimizing the effects of eddy currents. The greater the separation between the ultrasonically driven gradient coils and the metal objects, the less of a problem there is. Thus, in the device of the present invention, active gradient shielding is not optimal or even nonexistent for the main MRI system, and the fact that other metal objects are in the main MRI system is acceptable. This requirement to minimize metal in the vicinity of ultrasonically driven gradient coils makes it i) less obvious that such frequencies are practical to use, and ii) more convenient in at least some circumstances to include them in the insert rather than in the main MRI machine.

Figure 5 shows, in a schematic way, an alternative form of Z-gradient coil that may be provided in an alternative form of insert. Similarly, in the alternative, this form of Z-gradient coil may be provided in the main body of the newly constructed MRI machine 1.

Here, the Z-gradient coil comprises four sets of windings 2z1-2z4, each having the same structure as the Z-winding sets 2z1, 2z2 described above. Again, these windings are arranged to be driven by a signal generator device 4, and are arranged to resonate at a selected drive frequency by including one or more capacitors (not shown).

In this case, instead of monotonically varying the Z-gradient field set in the insert by the Z-gradient field coils as in the conventional case and in the insert described above with respect to Figs. 1-4, a segmented Z-gradient is now created. That is, instead of monotonically varying the Z-gradient field, the insert of Fig. 5 is arranged to create a more complexly varying Z-gradient field. In particular, it may be set to be multi-lobed and to have, for example, a polynomial-like or sinusoidal variation along the Z axis. This in turn means that the maximum amplitude of the difference in the gradient field from one end of the axis to the other can be controlled while still providing an appropriate variation of the gradient per unit length along the insert. It has been determined that providing a segmented Z-gradient field can be advantageous, especially when longer inserts are used, i.e. when examining areas longer than just the head, for example when the insert is used for a full-body examination or when the gradient windings are incorporated into a full-body MRI machine. It has further been determined that the SENSE (sensitivity encoding) reconstruction technique, as is well known in the field of MRI, can successfully reveal information obtained in acquiring magnetic resonance data using segmented Z-gradients of the type produced by the insert shown in FIG. 5. It has further been determined that the use of such segmented Z-gradients can reduce the onset of PNS in the examined subject or allow the use of stronger Z-gradients before onset of PNS is obtained.

Following a brief introduction to the main MRI system 1, the operation of the MRI system device is described below.

In general terms, the main MRI system 1 comprises an acquisition section I for acquiring magnetic resonance data and a reconstruction section R for reconstructing images and spectroscopic information relating to those images from the acquired magnetic resonance data. In the arrangement shown in FIG. 1, the insert 2 and the signal generator device 4 form part of the acquisition section I, i.e. they cooperate with the acquisition section I of the main MRI machine to acquire magnetic resonance data, which may then be reconstructed by the reconstruction section R.

The elements of the acquisition section I of the main MRI machine 1 comprise, in general terms, a magnet and coil arrangement 5 and a control system 6. The control system 6 has an output 61 which controls the operation of the magnet and coil arrangement 5, and a receiver 62 which receives information returning from the magnet and coil arrangement 5. In the apparatus of the present invention in which a coil insert 2 is used, the output 61 also issues control signals to the signal generator arrangement 4, and in some embodiments the receiver 62 also receives an output from the insert 2, although this is optional. In the apparatus described here, the reception of the magnetic resonance data is performed in the main MRI machine 1 itself.

As suggested above, in an alternative embodiment, the insert 2 and components of the signal generator device may be incorporated into the MRI machine itself.

It will be appreciated that an MRI machine will typically include one or more "computers" that control operation and process received data. Each such computer may include a processor, memory, and at least one data storage device. The control system 6 may be computer implemented. The reconstruction unit R may be computer implemented.

The magnet and coil device 5 includes a main magnet 51 that creates a static magnetic field, X, Y, and Z gradient magnetic field coils 52, a high-frequency transmit coil 53, and a high-frequency receive coil 54.

In operation, the output section 61 delivers a drive current to the gradient coil 52 causing appropriate high frequency transmit pulses to be output by the transmit coil 53, and the receive section 62 receives an input from the receive coil 54.

In an embodiment of the present invention, the output 61 also provides a control trigger signal to the signal generator device 4 to enable proper timing of generating the gradient drive signals that drive the insert gradient field coils 2x, 2z.

In principle, any combination of gradient coils 52 of the main MRI system 1 and gradient coils 2x, 2z of the insert 2 may be used to produce the desired encoding effect.

Most commonly, perhaps, if the insert 2 includes an X-gradient coil 2x and a Z-gradient coil 2z, these may be used in combination with a Y-gradient coil 52y in the main MRI machine 1.

Thus, in a particular example, the gradient coil 52y of the main MRI machine 1 may be used for spatial encoding to select and examine a particular slice of the subject, and the Z and X gradient coils 2z, 2y of the insert 2 may be used for spatial encoding within that slice.

In situations where the insert includes only a Z-gradient coil (e.g., the insert shown in FIG. 2), the X- and Y-gradient coils 52x, 52y of the main MRI machine 1 may be used in cooperation with the Z-gradient coil 2z of the insert 2.

In other situations, both gradient coils on one particular axis of the main MRI machine 1 and the insert 2 may be used together.

For example, the insert shown in FIG. 2 may be used in a situation where the X, Y, and Z gradient coils 52x, 52y, 52z from the MRI machine 1 are used in conjunction with the Z gradient coil 2z of the insert. This can provide different options for spatial encoding.

In the above situation, the gradient coils 52 of the main MRI machine 1 are driven at a conventional frequency, while the gradient coils of the insert 2 are driven at an ultrasonic frequency.

Figure 6 illustrates a timing diagram for an echo planar spectroscopic imaging (EPSI) technique that may be implemented using an MRI system apparatus of the type described above. In particular, the MRI system apparatus of Figure 1, when used in conjunction with an insert of the type described with respect to Figures 1-3 above, may be used as an echo planar spectroscopic imaging system and operated according to the timing diagram shown in Figure 6.

In this technique, the Z-gradient coil 2z of the insert 2 is used in conjunction with the X-gradient coil of the insert 2x and the Y-gradient coil 52y of the main MRI machine 1. Timing diagram 6 shows, in a simplified manner, the signals applied to these gradient coils when implementing the technique of FIG. 6. As will be appreciated, "Gz insert" refers to the signals applied to the Z-gradient coil 2z of the insert, "Gx insert" refers to the signals applied to the X-gradient coil 2x of the insert, and "Gy body" refers to the signals applied to the Y-gradient coil 52y of the main MRI machine.

Furthermore, in the timing diagram, RF indicates a signal applied using the transmit coil 53 of the main MRI machine 1.

At the beginning of each repetition period (TR), a multi-band pulse is applied by the RF transmit coil 53 and a slice selection pulse is applied to the Y-gradient coil 52y of the MRI machine 1. Then, during the following readout period, a respective plurality of chirp pulses are applied to the Z-gradient coil 2z of the insert 2 on the one hand and the X-gradient coil 2x of the insert 2 on the other hand. In an embodiment of the present invention, each chirp has a duration of 500 microseconds, and a total of 200 such chirps are applied to the Z-gradient coil and the X-gradient coil 2z, 2x, respectively, during the readout period.

In an embodiment of the invention, each chirp is of the same waveform as each of the other chirps, and the chirps of the Z-gradient coil 2z and the chirps of the X-gradient coil 2x are applied in phase with each other. However, other possibilities are available.

The purpose of applying chirp is to obtain a large K-space (the amplitude per axis defines the spatial resolution of that axis) and the distance between points/circles in K-space (the decaying amplitude defines the field of view).

Using this technique, all spatial encoding can be defined in each chirp, while the spectral information is encoded across the group of chirps, i.e., 200 chirps in this example. The number of chirps and their length, as well as the total length of the chirps, determine the spectral bandwidth and resolution. Thus, in this example, if each chirp is 500 microseconds long, the bandwidth is 2 kHz and the total length of the chirps is 100 milliseconds, which gives a resolution of the order of 10 Hz (excluding the effects of relaxation and other small units).

In another embodiment, each chirp may be 1 millisecond long. In such an example, if 200 chirps are still applied, this would result in a bandwidth of 1 kHz and a resolution on the order of 5 Hz, rather than 10 Hz as in the example above.

Each chirp consists of a limited, time-varying amplitude application of an ultrasound frequency at which the respective insert gradient field coils 2z, 2x are configured to operate. In this example, the two ultrasound frequencies are the same, but in other examples, they may be different, providing the additional benefits described above.

In this embodiment, four shots are used to improve the accuracy of the results as shown in the timing diagram. A second multiband pulse in MB2 is provided at the start of the second shot, and a suitable slice selection signal is applied to the Y gradient coil 52y of the main MRI machine 1. Following this, a second sequence of chirps is applied to the Z gradient coil and the X gradient coil 2z, 2x of the insert 2 during the readout period of this second shot. The whole process is repeated again with the third and fourth shots, so that the acquired magnetic resonance data may be fed to a reconstruction unit R for reconstructing the image and the spectral data associated with the image. The reconstruction system R may be configured under software to perform SENSE (sensitivity encoding) reconstruction.

If desired, further steps as described above may be performed to obtain more data in order to improve the signal-to-noise ratio.

Alternatively, or in addition, further processing may be performed for different "Y slices" of the subject. That is, a different set of slice-select offset frequencies may be applied to the RF coil 54 of the MR machine 1, such as to select a second batch of slices for examination.

It is noted that with this technique, spatial coding is performed on each chirp, and complete spatial and spectral coding for a set of slices may be performed in a total of around 100 ms if only one shot is used, or around 400 ms if four shots are used as in the example shown in Figure 6.

This means that image and spectral data collected over a very short period of time can be considered. This can help avoid loss of information or confusion in the results that would occur with more traditional techniques that require much longer encoding times. In more traditional echo-planar spectroscopic imaging techniques, data is encoded one voxel at a time across the entire volume of interest, and spatial encoding actually involves first selecting a particular voxel, then spectroscopic sampling is performed on that voxel before moving on to the next voxel. This leads to much longer examination periods, on the order of a few seconds.

Claims (30)

1. A coil insert for an MRI system for use within a bore of a primary MRI system, comprising:
The main axis and
at least one gradient coil configured to generate a spatially varying magnetic field along each of an axis parallel to, coincident with, or at an angle to the primary axis, and configured to be electrically driven at an ultrasound frequency of 19.9 kHz or greater ;
the MRI system coil insert comprises a first gradient coil and a second gradient coil, at least one first capacitor electrically connected to the first gradient coil to resonate the first gradient coil at a first predetermined ultrasonic frequency, and at least one second capacitor electrically connected to the second gradient coil to resonate the second gradient coil at a second predetermined ultrasonic frequency;
A coil insert for an MRI system, wherein the first predetermined ultrasonic frequency is different from the second predetermined ultrasonic frequency . The coil insert for an MRI system according to claim 1, having a central region free of gradient coil windings. The MRI system coil insert of claim 2, wherein the MRI system coil insert has a window through which the patient can see when the patient's head is positioned within the MRI system coil insert. The coil insert for an MRI system according to any one of claims 1 to 3, further comprising a Z-gradient coil for producing a spatially varying magnetic field along the major axis of the coil insert for an MRI system. The MRI coil insert of claim 4, wherein the Z-gradient coil comprises a first set of windings provided at a first end of the MRI coil insert and a second set of windings provided at a second end of the MRI coil insert. The coil insert for an MRI system of claim 4, wherein the Z-gradient magnetic field coil comprises more than two sets of windings, the windings arranged to enable providing a segmented magnetic field gradient on the Z-axis. The coil insert for an MRI system according to any one of claims 1 to 6, comprising an X-gradient coil or a Y-gradient coil for producing a spatially varying magnetic field transverse to the main axis of the coil insert for an MRI system. A coil insert for an MRI system according to any one of claims 1 to 7, comprising a first gradient coil for producing a spatially varying magnetic field along a first one of the axes, and a second gradient coil for producing a spatially varying magnetic field along a second one of the axes. 6. The coil insert for an MRI system of claim 5, further comprising an X-gradient magnetic field coil or a Y-gradient magnetic field coil for producing a spatially varying magnetic field transverse to said major axis, said X-gradient magnetic field coil comprising a third set of windings and a fourth set of windings provided on diametrically opposed sides of said MRI system coil insert with respect to said major axis and axially between said first and second sets of windings of said Z-gradient magnetic field coil with respect to said major axis of said MRI system coil insert. The coil insert for an MRI system according to claim 9, wherein a gap is provided around the circumference of the coil insert for an MRI system between the third and fourth sets of windings such that there are areas of the coil insert for an MRI system that are free of the windings of the Z-gradient coil and the windings of the X- or Y-gradient coils. The coil insert for an MRI system according to claim 9 or 10, wherein the third set of windings and the fourth set of windings each comprise a plurality of helically wound turns, each full turn having an inner arcuate segment, a first end segment extending outwardly to an outer arcuate segment, and a second end segment extending inwardly from the outer arcuate segment to a corresponding inner arcuate segment of the next turn. 12. A coil insert for an MRI system as claimed in any one of claims 1 to 11, wherein a frequency difference between the first predetermined ultrasonic frequency and the second predetermined ultrasonic frequency is an inaudible frequency outside the audible range of 20 Hz to 20 kHz. 13. A coil insert arrangement for an MRI system, comprising: a coil insert for an MRI system according to any one of claims 1 to 12 ; and a signal generator arrangement for electrically driving the at least one gradient coil at an ultrasonic frequency of 19.9 kHz or higher. 14. The coil insert apparatus of claim 13, wherein the signal generator apparatus is arranged to drive the first gradient coil at a first selected ultrasonic frequency and to drive the second gradient coil at a second selected ultrasonic frequency. 15. The coil insert device for an MRI system of claim 14 , wherein a frequency difference between the first selected ultrasonic frequency and the second selected ultrasonic frequency is an inaudible frequency outside the audible range of 20 Hz to 20 kHz. 17. A coil insert device for an MRI system as described in claim 14 or claim 15, wherein the first selected ultrasonic frequency is the same as the first predetermined ultrasonic frequency and the second selected ultrasonic frequency is the same as the second predetermined ultrasonic frequency. 14. A coil insert device for an MRI system as described in claim 13 when dependent on claim 6, wherein the windings of each set of the Z-gradient magnetic field coils and the signal generator device are arranged to provide a magnetic field gradient segmented on the Z axis. 13. An MRI system comprising an MRI system having a main bore and a coil insert for an MRI system according to any one of claims 1 to 12 for use within said main bore. 17. An MRI system apparatus comprising an MRI system having a main bore and a coil insert apparatus for an MRI system according to any one of claims 13 to 16 including a coil insert for the MRI system arranged for use within the main bore. 1. An echo-planar spectroscopic imaging system comprising an MRI system apparatus having an acquisition unit for acquiring magnetic resonance data and a reconstruction unit for reconstructing image and spectroscopic information from the acquired magnetic resonance data,
The acquisition unit,
an RF transmitter arranged to output single-band or multi-band RF pulses;
a first gradient coil arranged to be driven at an ultrasound frequency of 19.9 kHz or greater to produce a spatially varying magnetic field along a first axis; and a second gradient coil arranged to be driven at an ultrasound frequency of 19.9 kHz or greater to produce a spatially varying magnetic field along a second axis.
a signal generator device for electrically driving the first gradient coil at a first selected ultrasonic frequency and for driving the second gradient coil at a second selected ultrasonic frequency;
the signal generator apparatus is configured to apply a plurality of chirp pulses to the first gradient coil and a plurality of chirp pulses to the second gradient coil during a readout period as part of acquiring the magnetic resonance data to achieve spectral and spatial encoding in the first and second axes;
the acquisition unit is arranged to read out magnetic resonance data during the readout period, and the reconstruction unit is arranged to reconstruct an image and spectral information relating to the image from the magnetic resonance data read out during the readout period;
An echo planar spectroscopic imaging system , wherein the first selected ultrasound frequency is different from the second selected ultrasound frequency . 21. The echo-planar spectroscopic imaging system of claim 20 , wherein each chirp pulse has a length of less than 10 milliseconds. 22. The echo-planar spectroscopic imaging system of claim 20 or 21 , wherein the signal generator device is configured to apply at least 10 chirp pulses during the readout period. 23. The echo planar spectroscopic imaging system of claim 20, wherein the acquisition unit is arranged to acquire magnetic resonance data during a plurality of readout periods to generate a set of magnetic resonance data, the acquisition unit is arranged to cause the RF transmitter to output single-band or multi-band RF pulses before the start of each readout period, and the acquisition is configured to apply a respective plurality of chirp pulses to the first gradient magnetic field coil and a respective plurality of chirp pulses to the second gradient magnetic field coil during each readout period to achieve spectral and spatial encoding in the first and second axes. 24. The echo planar spectroscopic imaging system of claim 20, wherein a frequency difference between the first selected ultrasonic frequency and the second selected ultrasonic frequency is an inaudible frequency outside the audible range of 20 Hz to 20 kHz. 25. The echo planar spectroscopic imaging system of claim 20, wherein the acquisition unit comprises at least one first capacitor electrically connected to the first gradient coil to resonate the first gradient coil at a first predetermined ultrasound frequency, and at least one second capacitor electrically connected to the second gradient coil to resonate the second gradient coil at a second predetermined ultrasound frequency. 26. The echo-planar spectroscopic imaging system of claim 25, wherein the first selected ultrasound frequency is the same as the first predetermined ultrasound frequency and the second selected ultrasound frequency is the same as the second predetermined ultrasound frequency. 27. The echo planar spectroscopic imaging system according to claim 20, wherein the acquisition section further comprises a third gradient coil arranged to be electrically driven to create a spatially varying magnetic field along a third axis, and the signal generator device arranged to electrically drive the third gradient coil to provide spatial encoding in the third axis and to enable selection of a slice of the subject under examination from which the magnetic resonance data or a set of magnetic resonance data is acquired during the respective readout period or respective readout periods . 28. The echo planar spectroscopic imaging system of claim 20, wherein the MRI system comprises an MRI system having a main bore and an MRI system coil insert apparatus for use within the main bore , the MRI system coil insert comprising the first gradient magnetic field coil and the second gradient magnetic field coil. 28. An echo planar spectroscopic imaging system as claimed in any one of claims 20 to 27 , wherein the MRI system comprises an MRI system having a main bore and a coil insert for an MRI system as claimed in any one of claims 1 to 12 for use within the main bore. 1. A method of echo-planar spectroscopic imaging using an MRI system having an acquisition unit for acquiring magnetic resonance data and a reconstruction unit for reconstructing image and spectral information from the acquired magnetic resonance data, comprising:
applying a single-band or multi-band RF pulse to a subject being examined;
electrically driving a first gradient coil at a first ultrasonic frequency to produce a spatially varying magnetic field along a first axis, and electrically driving a second gradient coil at a second ultrasonic frequency to produce a spatially varying magnetic field along a second axis;
applying a plurality of chirp pulses to the first gradient coil and a plurality of chirp pulses to the second gradient coil during a readout period as part of acquiring magnetic resonance data to achieve spectral and spatial encoding in the first and second axes;
reading out magnetic resonance data during said readout period;
reconstructing an image and spectral information relating to the image from the magnetic resonance data read out during the readout period ;
The method , wherein the first ultrasonic frequency is different from the second ultrasonic frequency .