JPS6147539B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for inspecting an object to be inspected using radiation such as X-rays and γ-rays.

The device according to the invention can be used to capture images such as images on a cathode ray tube or other image forming device, photographs of such images, or maps of absorption coefficients generated by a digital computer and which can subsequently be contoured. can be used to facilitate the generation of any form of radiograph.

In the apparatus described in Japanese Patent Application No. 47-40330, a pencil beam of radiation from external radiation is caused to pass through a portion of the object to be inspected.
In that case, the beam is subjected to a superimposed scanning motion so that it adopts many different positions, and a detector is used to find out the magnitude of the absorption of the beam at each of those positions after the beam has passed through the test object. is used. In order to cause the beams to adopt their various positions, the radiation source and the detector are caused to reciprocate in a plane and orbitally about an axis perpendicular to that plane.
The various positions are thus in one plane in the object under examination, in which, by processing the beam absorption provided by the detector, the absorption coefficient distribution of the radiation is obtained. The processing in this case is such that the final displayed absorption distribution is the result of a series of approximations.

The device described in the said patent application has been found to be quite satisfactory for generating cross-sectional representations of parts such as the head of a human body as an object to be examined.

However, since the scanning operation of the apparatus configured as described above is relatively slow, a much faster scanning speed is desired depending on the portion of the object to be inspected. A device capable of realizing such a fast scanning speed is described in Japanese Patent Application No. 1986-63812, which describes a device that allows X-rays spread in a fan shape to pass through the object to be inspected, and scans other parts of the object to be inspected. Absorption data signals are generated by measuring the radiation transmitted along a set of beam paths within the sector with a side array of detectors. The fan-like extent is at an angle sufficient to encompass the entire area of interest in the plane of the object. Therefore, if the installation range of the detector is approximately the same as the fan-shaped spread of radiation, it is necessary to orbit both the radiation source and the detector around the object to be inspected. If is sufficiently larger than the fan-like spread of the radiation, it is only necessary to orbit the radiation source around the object to be inspected.

Further, Japanese Patent Application No. 49-47032 describes an apparatus for processing absorption data by a convolution method.
This method enables faster processing than the iterative method disclosed in Japanese Patent Application No. 47-40330.

According to one aspect of the present invention, there is provided an apparatus for inspecting an object to be inspected using penetrating radiation such as X-rays or gamma rays, the radiation irradiating the object to be inspected with radiation that spreads in a fan shape. detection means comprising a source means and a plurality of detectors adapted to detect radiation after the radiation has passed through the object to be examined and each adapted to receive radiation along a narrow but diverging beam path; and causing the radiation source means and the detection means to scan around the object to be inspected so as to scan the beam of the radiation source at a plurality of angular positions in the plane of the cross-sectional portion with respect to a planar cross-sectional portion of the object to be inspected. means for irradiating radiation along the beam obtained from the detector. A reconstruction of the absorption distribution of the radiation in the cross-sectional portion is caused to occur in response to the data signal, and substantially
By combining output signals for beam paths at angular positions 180° apart, an absorption data signal representative of absorption of radiation along a path having a substantially uniform width is generated;
A penetrating radiation inspection device is provided.

According to another aspect of the invention, the fan-shaped X
The object to be inspected is irradiated with penetrating radiation such as rays or gamma rays, and a detection means consisting of a radiation source and a plurality of detectors sensitive to the radiation is scanned around the object to be inspected. irradiating a planar cross-sectional portion along a radiation beam at a plurality of angular positions within the plane thereof, beam data provided by said sensing means in relation to radiation beams at angular positions 180° apart; the signals combined to generate other data signals relating to radiation along the beam path having a substantially uniform width, the other data signals generating a reconstruction of the absorption distribution of the radiation in the cross-sectional portion; A method is provided which comprises:

According to still another aspect of the present invention, a radiation source configured to irradiate a planar cross-sectional portion of an object to be inspected with radiation spread in a fan shape within the plane thereof, and a radiation source having an angle within the fan shape. a detection means comprising a plurality of detectors adapted to determine the absorbed absorption of the radiation after passing through the object to be inspected along a plurality of beam paths distributed over a plurality of beam paths, the radiation source and the detection means; means configured to scan around the object to be inspected and irradiate the cross section with radiation from a plurality of directions, the absorption beam given by the detector;
From the data signal, a reconstruction of the absorption distribution of radiation in the cross-sectional section is generated, and the signal from the detector is determined in relation to the corresponding position of the detector during the scanning movement. An inspection device is provided in which means are provided for selecting and generating a sequence of signals only for the parallel set of radiation beams.

Embodiments of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, an object 1 to be examined is shown lying on a support means 2, which is subjected to an examination by means of radiation indicated by dashed lines 3. In FIG. This radiation is generated by a radiation source 4 and forms a fan-shaped extension in a plane perpendicular to the plane of the drawing. It will be appreciated that the object support means must be of sufficient length to position any cross-sectional portion of the object in the plane of the x-ray.

In the field of scanning radiation, the body of the subject, ie the patient, is surrounded by a suitable medium (in this case water) which has an absorption coefficient for radiation closely similar to human tissue. The water is indicated at 5 in the drawing and it is placed in a bag 6. The bag 6 is placed within a ring-shaped structure 7 made of metal such as duralumin.

The ring-shaped structure 7 consists of two parts, as described in Japanese Patent Application No. 49-63812, and is fixed to the support means 2 in this embodiment. In this case, the ring-like structure 7 can be mounted in movable relation to the support means 2 if desired, and the support means 2 can be used for the same purpose, in order to facilitate the admission of the patient. It should be noted that it can be made movable with respect to other parts of the device for correct positioning with respect to the X-ray beam.

The support means 2 is positioned at one end by a support 8 and at the other end by a fixed bracket 9. The bracket 9 is in the form of a shaft member having an axis around which the orbital movement of the X-ray source 4 takes place, as will be clear from the description below.

When the patient is positioned in position within the device, around his body is a surrounding member or frame 10 which is longitudinally cylindrical and has a longitudinal axis that is the axis of the bracket 9. is located. The surrounding member 10 is a bracket 9
The end adjacent to the bearing 11 is closed, and the bearing 11
Supported by. The bearing 11 is supported by the shaft of the bracket 9. The enclosure member 10 is open at its other end to permit positioning of the patient therein, and is supported at its open end on rollers 12 having suitable fixed bearings. These rollers allow the enveloping member 10 to rotate freely on its own axis along which the orbital movement of the X-ray source 4 takes place. The radiation source 4 is mounted on the enclosure 10 by means of a support 13 . Directly opposite the radiation source 4 , detector means 15 are mounted on the enclosure 10 by means of a support 14 and detect radiation absorption data from the patient's body in the plane of the radiation from the radiation source 4 . It is designed to give

The shaft of the bracket 9 is supported by a support 16, and a bobbin 17 is provided near the support to surround the shaft of the bracket.
A bobbin 17 is fixed to the support 16 and is wound with a cable 18 which transmits the absorption data from the sensing means 15 to the processing unit. Those cables and connections 1
9 supplies power, control signals, and cooling fluid to the X-ray source 4. As the radiation source and the detection means orbit, the cable will correspondingly wrap around and unwind from the bobbin. Those cables are
Guides G18 and G1 attached to member 10
9 and then sent to the bobbin. Cables and other connections are fixed to the bobbin and lead to each connection unit, including the data processing unit, and to the power supply unit.

For the purpose of performing an orbital movement, the surrounding member 1
Gear teeth 20 are provided on the peripheral surface of the open end of the gear. Engaged in these teeth is a toothed wheel 21 mounted on the shaft by bearings 22. The gear wheel 21 is connected to a reversible motor 23 via a gearbox 24.
driven by. It will be appreciated that gear teeth 20 may be provided at any desired location on member 10. A scan timing signal unit 40 provides a signal representative of the rotational progress of the radiation source 4. This could be a combination of a light source and a photocell or a scale on the axis of toothed wheel 21 in cooperation with a suitable cam mechanism.

FIG. 2 is an end view of the apparatus shown in FIG. 1, with reference numbers indicating the same parts as in FIG. In FIG. 2, 25 indicates the location of the trajectory axis and 26 indicates the profile of the cross-section of the patient's body in the plane of the search radiation.

Furthermore, in FIG. 2, 27 and 28 indicate opposite sides of the fan-shaped radiation from the radiation source 4. It will be seen that the detection means 15 extends over the entire sector of radiation between lines 27 and 28. As explained in Japanese Patent Application No. 49-94561, means may be provided for further detailed examination of desired areas of the patient's body, but such means are not provided in this embodiment. . Details of the ring-shaped groove body 7 and its related holding means are described in the aforementioned Japanese Patent Application No. 49-63812.

FIG. 3 schematically shows the entire processing arrangement for the apparatus shown in FIGS. 1 and 2. FIG.

In this figure, point X is the point of emission of X-rays from the radiation source 4, point 25 is the location of the orbital axis, 7 is the location of the ring-shaped groove, and 15 is the location of the absorption data for processing. It is a detection means that gives.

The detection means 15 includes a plurality of detectors and corresponding collimators defining individual radiation beams as described in the aforementioned applications. During the course of orbital motion of the device, absorption data is obtained as an output current from a secondary electron multiplier associated with the detector. Data is amplified by each amplifier 29. The gains of these amplifiers are individually adjusted to compensate for the different sensitivities of the various scintillation crystals of the detector. If desired,
The gains of these amplifiers can be controlled in common to compensate for possible changes in the emission intensity of the X-ray source X. The amplified currents are each passed through the Miller integration circuit 3.
It is integrated by 0. These integrator circuits operate in response to timing signal unit 40 during the period during which each beam corresponding to the detector extends over an angle of approximately 2/15 degrees in this embodiment due to orbital motion. It is made to be. Correspondingly, the beams are spaced apart from each other about the point source X such that the center lines of their beams are substantially 2/15 degrees apart. The output of the integrating circuit is converted from analog to digital by converter 31.

The final image reconstruction represents the distribution of the absorption coefficient over the area of the cross-sectional section under examination (in this case, the absorption coefficient is the absorption per unit length in the vicinity of a given point of the search beam passing through that point). It is desirable to express it. In order to achieve the desired result, it is necessary that the output signal obtained from the sensing means 15 is transformed into its logarithm. For the purpose of
A logarithmic converter 32 operates on the digital data from A/D converter 31. Logarithmic converter 32 consists of a logarithm table in known usage. Data is written to memory 34 in response to address selector 33 in the manner described below and then to unit 35 before being displayed on display and control unit 36.
undergoes convolution processing and interpolation at . The operation and characteristics of processing unit 35 are described in detail in Japanese Patent Application No. 49-47032. The technique described in that application can be described as producing a corrected layergram, and it is a set in which the data each relate to a set of substantially parallel radiation beams. and in that case,
Requires that each set of data be provided term by term. Address selector 33 and memory 34, which form part of a suitably programmed digital computer, are therefore programmed so that the data are arranged in such "parallel" sets. Here, the address selector 33 functions as a sorting circuit that performs a sorting operation such as sequentially selecting addresses of a memory storing a group of data signals and reading out and combining the data signals.

In the device now being described, the integrator 30
Considering the orbital motion during the integration period, the effective divergence of the beam path is 2/15°, so each 2/
It operates for a time such that an output signal is obtained after 15° of movement. Additionally, the spacing of the beams within the fan is arranged such that the centerlines of adjacent beams are substantially 2/15 degrees apart. Thus, each time the rotation increases by this amount, each beam will assume a position parallel to the position occupied by one of its neighboring beams before this rotational increment. Thus, by appropriate selection of data from memory 34, it is possible to generate signals corresponding to a set of parallel beams spaced 2/15 degrees apart.

This is illustrated in Figure 4, which shows a sector of three beams spaced 15 degrees apart from the centerline. These beams represent the center and side beams of a 30° fan, but momentarily they can be thought of as if they were only three beam fans. These three beams a,
b and c for the position _of point source (not shown) in Figure 4a. When the radiation source 4 is caused to orbit by ₁₅ ° to a position become parallel. Beam c takes on a new slope. 15 more
When it moves, beam a becomes beam c.
etc., and thus a set of parallel beam positions is being formed.

In view of this, once the data from the transducers are entered into the memory 30 to the point where the angular position for the corresponding beam is indicated, they can be extracted as a data set for each such angle.

This is the fifth beam for an exemplary set of five beams.
As shown in the figure. This figure corresponds to a matrix of locations in memory 34, each location being identified by the angle with respect to any zero of the beam at which data is obtained. Each detector provides data to the elements in the columns designated a, b, or c, corresponding to FIG. The center beam (b)
A 360° rotation causes all of the beams to rotate through a series of angles, including the angles shown. The 360° position, which is the same as 0°, is not shown. It will also be appreciated that -180° is the same as +180° and therefore positive angles greater than 180° are shown for the corresponding angle. The data is entered into memory in rows as it is derived, with each row corresponding to the average angular position for one reading from each detector. For clarity of illustration, not all lines are shown. It can be seen that diagonal sets of locations give data for beams at the same angle and therefore parallel. It should be noted that beams at the same angle are parallel, but not identical. The 0° set of beams shown by the real diagonals form a perfectly parallel set, but data must be obtained from the first and last rows. Therefore, the set will only be complete when all the data is obtained. Data from locations for such parallel sets are stored in memory 34.
Processor 35 for convolution processing selected from and described in Japanese Patent Application No. 49-47032.
will be transferred serially. The data can be transmitted to processor 35 after all data has been derived and stored, or, if desired, as soon as each "parallel" data set is completed. In the embodiment of FIG. 5, the 15° set is completed first.

In the embodiment of the device shown in FIGS. 1-3, the memory 34 naturally has much more space than shown in FIG. 2/15° row for each orbit position and detection means 15
There is a column for each detector.

It should be noted that with regard to the beam arrangements considered in Japanese Patent Applications No. 49-47032 and No. 49-94561, it is the case that the beams are treated as having uniform width. however,
In the apparatus of FIGS. 1 and 2, the beam defined by the detector does not have this character, but is narrower on the X-ray source side of the searched area and wider on the detector side. This uneven effect limits the orbital motion to 180°, which is theoretically sufficient in this device, but only continues for 360°.
For every beam position with the first 180° of a scan, a second scan whose direction of nonuniformity is the same as that first except for the fact that the direction of passage of the radiation is reversed. exist and be kept to a minimum. By calculating the average value of the absorption amount of the two beams and considering the angular spread of each beam as the minimum width at the center position of the beam, a more uniform width can be obtained compared to the width of each beam itself. It is designed to generate data corresponding to the beam path.

The use of two beams 180° apart to illuminate a single beam path means that the "skin dose" of radiation resulting from the total required x-ray intensity for that path is substantially It has the further advantage that it is not concentrated but is equally divided between the surfaces at both ends of the passage.

However, it should be understood that the data for each beam is only combined with data for beams that have a substantially 180 degree relationship during scanning. For a fan of beams as shown in Figures 4 and 5, only the data for the center beam (b) is combined with the data for the same beam inverted, thus forming a 180° set (shown in dashed lines). The data for the 0° set are combined with the data for the 0° set.

The position relative to the other beams of the set is shown in Figure 4b. Three positions of point source X are shown identified with symbols representing the corresponding angular positions of central beam b. It will be seen that for X ₁₅₀ , beam c shares the beam path with beam a of X ₀ , so they can be combined to give a uniform width beam. Similarly, c at X ₀ is
It shares a passage with a in X ₁₅₀ . Considering this in relation to the memory locations of FIG. 5, it can be seen that if the 180 beam set data and the 0 data are retrieved from the memory in reverse order, the former data can be combined with the latter data. The combinations are as follows.

(a ₀ +c ₁₈₀ ), (b ₀ +b ₁₈₀ ) and (c ₀ +c ₁₈₀ ) For this purpose, the digital calculator forming the address selector 33 and the memory 34 in FIG. to retrieve data from a location,
It is arranged to combine them and transfer them to a processor 35. For this purpose of combination, an adder 41 is provided between the memory 34 and the processor 35. This can also be included within a digital computer. Address selector 33 provides data for the two pairs to be combined. Adder 41 has storage locations for one beam data signal to retain the first of each pair and add the second to the first before sending the combined new data to processor 35. It is provided. It will be appreciated that other means for combining data may also be used. For example, the "opposite" parallel set of each pair (e.g. 180° and 0
Individual reconstructions of the absorption coefficients can be derived for .degree.) and the two images can be combined on display or in other ways. The term "combination of data" encompasses all combinations of this type.

As stated in Japanese Patent Application No. 49-47032,
The processor 35 shown in FIG. 3 may be implemented as a suitably programmed digital computer.
In an embodiment of the invention, devices 33, 34, 4
All 1 and 35 functions can be provided by one digital computer. However, they are shown as separate units in FIG. 3 to clearly identify their functions.

Instead of using a general purpose digital computer to perform the function of storing data in "parallel" sets, a special purpose digital computer may be used. An example of such a configuration is shown in FIG.

Ignoring the plurality of conductors 39, which are divided into five categories, conductor 39k carrying the output signal from detector k may be considered as typical of all conductors from such a detector.

As previously mentioned, the sampling period for each detector output, such as k, is such that the effective beamwidth resulting from the orbital motion is the desired one. In reality, the ``aperture effect''
effect) makes the beam width larger than this, and therefore some weight is generated. The output is amplified by amplifier 29k controlled by gain control unit 37. Analog memory 30k is the previously mentioned Miller integrator, which performs the well-known function of an analog memory used to sample and hold and then be reset for further sampling in the same manner. It works like this. A/D converter 31k also operates as in FIG. Responsive to the address selector 33, the data is in this case portions 1, 2, 3, . . .
. . . are distributed to storage units 34 divided into n. All data from conductors such as k are also distributed in these parts of memory 34. However, in this embodiment, each portion of memory 34 holds one "parallel" set of data corresponding to the diagonal of FIG. Therefore, this circuit differs from the circuit of FIG. 3, which receives the desired data and sorts it into parallel sets at a timing separate from the timing of the scan. The circuit of FIG. 6 requires that data be distributed over portions of memory 34 and in "parallel" sets as it is obtained, so its timing must be coordinated with the scan. For this purpose,
Address selector 33 is controlled by timing unit 38 which receives input signals from scan timing signal unit 40.

For the purpose of combining data for beams that are 180° apart during the scan, the first 180° of the scan
The data for the second 180° (i.e. of the parallel set, rather than the scan position) are provided in the reverse order, as shown in FIG. 4b. Realizes the combinations mentioned above. For this purpose, the address selector 33 is suitably programmed. Once any portion of storage 34 has received all the data for its parallel set, the data is transferred serially to composition unit 35 for processing as described above.

A logarithmic converter 32 is provided in this embodiment between converter 31 and selector 33 as in FIG. However, it is shown as cooperating with memory 34 to extract data from each memory location, convert it to logarithms, and replace them at the same location. In this way it is possible to provide a logarithmic converter that operates on one signal at a time, rather than on several signals simultaneously as in the case of FIG.

Considering the outputs from the sensing means 15 in Figure 6, it will be seen that they can be divided into five categories. This feature (which is optional) allows the number of categories to be reduced by a factor of five, but then each channel must still have its own amplifier. . In this configuration, the detectors are category 1, such as the first, sixth, and eleventh detectors.
The second and seventh detectors, etc. are classified as Category 2, the third detector, etc. are classified as Category 3, the fourth detector, etc. are classified as Category 4, and the fifth detector, etc. is classified as Category 5. Split as assigned. Thus, the five categories of detectors are interlaced. Data is obtained from these detectors in relation to a 2/15° orbital motion as follows. the first
At 2/15°, all category 1 detectors are sampled. Category 2 at next 2/15°
all detectors are sampled for a beam path parallel to the beam path used by the category 1 detectors. At the next 2/15°, category 3 detectors are sampled, and so on. At number 6, 2/15°, the category 1 detector is sampled again for a beam path displaced by 2/15° from the previously used beam path for all five categories. . Data are thus obtained for parallel sets separated by 2/3, where the number of beams is five times the number of beam paths that would otherwise be possible for a given number of integrators. For this purpose,
Each integrator takes one corresponding beam from each category (eg, all fifth position beams). Each amplifier is gated by a timing unit 38 to provide data only to the required integrators. This gating effect can also be provided in other ways if required. Thus, for example, the detector secondary electron multiplier may be gated as such, or a separate gate or switch may be provided.

It will be appreciated that the features of the present invention may be utilized with any signal processing such as that described in Japanese Patent Application No. 47-40330. Furthermore, the present invention can be used for scanning mechanisms other than those described above.
For example, the rotation need not be a simple rotation as described above, but may be a more complex movement if desired for other purposes. With respect to the scanning mechanism described above, the given beam widths and spacings may be varied as desired as long as the correct relationships are maintained. Additionally, each beam can be inspected by one or more detectors, if desired.

[Brief explanation of the drawing]

1 is a side elevational view schematically showing an apparatus according to the invention; FIG. 2 is an end view of the apparatus; FIG. 3 is a schematic diagram showing parts relevant to the processing of absorption data;
Figures a and 4b are explanatory diagrams for explaining the present invention, Figure 5 is a diagram showing the arrangement of absorption data in the pre-processing unit, and Figure 6 is a diagram showing the arrangement of absorption data in a form particularly suitable for composition processing. FIG. 3 is a diagram showing a special circuit for 1...Object to be inspected, 2...Supporting means, 3...Radiation, 4
...Radiation source, 7...Groove body, 8...Support body, 10...Surrounding member, 15...Detection means, 20...Gear, 21...Dentil, 23...Reversible motor, 26...Patient, 29...Amplifier, 30...Mirror amplifier , 31... converter, 32...
Logarithmic converter, 33... Andres selector, 34... Memory device, 35... Composition processing unit,
36...Display control unit, 40...Scanning timing signal unit.

Claims (1)

[Claims] 1. A radiation source arranged to irradiate a radiation surface distributed in a fan shape in one plane to a tomographic part of a living body, and a plurality of detection elements, and detecting means for generating a data signal representative of the absorption of radiation passing through the living body along a plurality of beam paths distributed at predetermined angles within said sector; scanning means 10, 20 for locating the fan-shaped distribution range in a plurality of angular directions by scanning around;
21, 23, and a timing circuit 3 arranged to regulate and control said scanning means and detection means to provide data signals at predetermined time intervals.
8, and a processing means 35 adapted to generate a signal representing the absorption distribution of radiation generated in the tomographic section from the data signal generated by the detection means. A radiation biological examination apparatus for examining a living body using radiation, comprising: a storage device 34 connected before the processing means; and a sorting device arranged to control a storage device in the storage device in which data signals are stored. a circuit 33, said sorting circuit for storing data signals from said detection means in said storage device during a sequence in which a group of signals relating to a fan-like distribution of radiation is generated during a number of small angular steps of said scanning means; a data signal generation sequence adapted to receive and store data signals, and the sorting circuit is configured to detect the detecting means at different times in relation to mutually parallel beam paths through the living body. 2. A radiation biopsy apparatus, characterized in that the timing information provided by the timing circuit is used to output an output data signal from a storage location corresponding to the parallel beam path in a group of data signals generated from the parallel beam path. 2. The radiation source rotates about an axis of extension perpendicular to the radiation surface, and a timing circuit is configured such that the orbital movement of the scanning means at each time interval is adjusted between adjacent beams in a fan-shaped distribution of radiation. 2. The method of claim 1, further comprising controlling the operation of the sorting circuit and the scanning means so as to extract data signals collected in the storage device from the detection means in a sequence of time intervals equal to the angular interval. radiation biopsy device.