JPH0463554B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation sensor, particularly a medical radiation CT.
The present invention relates to a radiation sensor array for scanner equipment.

More specifically, the present invention relates to a sensor array in which a large number of thin-film solid-state sensors for radiation CT scanners are arranged in an annular configuration in which an amorphous thin film having X-ray sensitivity is sandwiched between two metal electrodes.

The importance of X-rays in medicine is a well-known fact. For X-ray diagnosis, there are two-dimensional imaging methods that use X-ray film, and computer topography, an X-ray CT scanner method that makes full use of the functions of a computer and displays sliced images of the human body. be.

X-ray CT scanners require an X-ray sensor that can detect X-rays that have passed through the object with high sensitivity and high performance, and various X-ray sensors have been developed to improve the performance of the equipment. has been put into practical use.

FIG. 1 is an overview of an X-ray CT scanner.

In the figure, 1 is the subject (for example, a human body), 2
is an X-ray tube, and 3 is a collimator. 4 is a collimator, and 5 is an X-ray sensor, which constitute a detector 8. Further, 6 is an X-ray beam, and 7 is a computer.

The detector 8 of the X-ray tube 2 is placed facing the subject 1 as shown in the figure, and while irradiating the subject 1 with X-rays called a thin pencil beam, linear movement and rotation are combined, as shown by the arrow. Move around the subject as shown.

After acquiring X-ray absorption data from all directions of the subject 1 in this manner, the computer 7 processes these data to reconstruct a tomographic image of the subject 1. In this case, the X-ray sensor 5 is
Conventionally, NaI scintillation detectors with high detection efficiency have been used.

In this method, the time required for one photographing time - that is, the time required to make one rotation around the subject 1, is
I have a problem that takes a few minutes. As a countermeasure for this,
Improvements have been made, such as changing the pencil beam to a fan beam (X-rays focused and shaped into a fan shape), increasing the number of detectors, and shortening the imaging time.

In its final form, as shown in Figure 2,
A large number of detectors 9 are arranged side by side to form an array, and the object 1 is
A method has been considered in which the X-ray tube 2 is fixedly arranged around the X-ray tube 2 and rotated at high speed. In this method,
It becomes possible to reduce the shooting time to several seconds or less.

In order to realize such an array type detector, a method of arranging a large number of conventional scintillation detectors can be considered, but it is difficult to realize high density with this method.

That is, even if conventional scintillation detectors were arranged closely together, the pitch would be approximately 2 mm or more, which was considered to be the practical limit of resolution. Furthermore, although X-ray sensors using semiconductor crystals such as silicon and cadmium/tellurium are under consideration, they have not yet been put to practical use.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a radiation sensor arranged in high density (array type).

Another object of the present invention is to provide a thin film radiation sensor array that can be easily miniaturized.

Still another object of the present invention is to provide a radiation sensor array with high detection efficiency.

Still another object of the present invention is to provide a radiation sensor array whose shape can be freely processed.

In order to achieve the above object, in the present invention, a large number of strip-shaped electrodes are provided on one surface of a radiation photoreceptor, and a photosensitive portion is formed on the other surface by overlapping with the strip-shaped electrodes. A large number of radiation sensors, each of which has a counter electrode and is entirely formed into a thin film, are arranged in a ring.

The present invention will be described in detail below with reference to the drawings. In addition, although the case where the present invention is applied to an X-ray sensor will be described below, the present invention is not limited to this, and can be applied to the detection of radiation in general.

FIG. 3 is a plan view of an embodiment of the thin film type X-ray sensor of the present invention, and FIG. 4 is a sectional view taken along the - line.

In these figures, 10 is a substrate, 11 is a large number of strip electrodes formed on one surface of the substrate, 12 is an X-ray photoreceptor provided on the strip electrode 11, and 13 is an X-ray photoreceptor 12. This is a counter electrode provided on top of the . Then, a photosensitive portion 14-
1, 14-2, . . . 14-n are formed.

Such a thin film type X-ray sensor can be manufactured as follows.

As the substrate 10, glass, ceramic, or a metal plate with an insulating layer formed on its surface can be used.

For example, a Cr-Au thin film formed on a glass substrate 10 with good smoothness is processed by known means to form the strip electrode 11, and an X-ray sensitive material such as a Se thin film is deposited thereon to a thickness of 10 to 100 μm. Apply to thickness.

Although the Se deposited film has the advantage of being highly sensitive to X-rays, it has the disadvantage that it is an unstable material and easily crystallizes. In order to improve this drawback, it is known to dope with As. In the present invention, 2 to 5% As
It is effective to use a vapor deposited Se-As film doped with .

The reason why the As doping concentration is limited to the above range is to achieve both high X-ray response speed and prevention of crystallization. X-ray response speed is CT
It has to be as fast as possible to shorten the scanning time.

A Se-As thin film with an As doping concentration of 5% or less has a high hole mobility, so it has an extremely fast response speed to X-rays. 20 μm thick Se
When a voltage of 100 V is applied to the -As thin film, both the rise and fall times of the response are 0.5 msec or less. This performance is sufficient for use in high-speed CT scanners.

On the Se--As thin film 12, an X-ray transparent metal electrode layer, such as a thin film of Al, Ag, Be, etc., is formed by vapor deposition or sputtering to form the counter electrode 13. The thickness of the counter electrode 13, that is, the metal electrode layer is 0.05~
It is preferably in the range of 0.5 μm.

As mentioned above, the area where the strip electrode 11 and the counter electrode 13 face each other is the portion 14- which acts as a photosensitive area.
1, 14-2, . . . 14-n, and the size and pitch of this region are closely related to the resolving power of the radiation sensor.

In CT scanners, focusing and collimating the x-ray beam with sufficient precision and maintaining that precision during rotation can be extremely complex and expensive. In order to avoid such a situation, in this embodiment, the photosensitive parts 14-1, 1 of the sensor
4-2, . . . 14-n are rectangular in shape.

An example of a typical arrangement and shape of the photosensitive parts is that the pitch is 1.2 mm, the width of the strip electrode is 0.9 mm, and the length in the direction perpendicular to the array is 3.0 mm. Therefore, according to the present invention, compared to the conventional method of arranging individual scintillation detectors in an array, an extremely high-density arrangement is possible.

Next, the operating principle of the X-ray sensor of this example is as follows.
This will be explained with reference to FIG.

Photodiode symbols 14-1, 14- in the figure
2,... are the photosensitive parts 14-1, 14-2... in FIG.
...and represents an X-ray sensor. Each photosensitive section is equipped with one semiconductor switch 15-.
1, 15-2, . . . are connected in series, and each switch is sequentially scanned in time series by the shift register 18.

In addition, each photosensitive section (photodiode) 14
-1, 14-2, . . . are connected in series to the power supply 16 and the operational amplifier 20 to form a closed circuit when the corresponding semiconductor switches 15-1, 15-2, .

For example, first, the switch 15-1 is closed, and the power supply ₁₆
A charge Q ₀ is charged from. When charging is complete, open the switch. In this state, the X-ray photosensitive section 14-1
Assume that a beam with an X-ray intensity L ₀ is incident for a time T ₀ .

Here, if the effective X-ray gain is η, charges of ΔQ=ηL ₀ T ₀ are discharged from the X-ray photosensitive section 14-1. Therefore, at this time, a charge of Q=Q ₀ -ΔQ=Q ₀ -ηL ₀ T ₀ remains in the X-ray photosensitive section 14-1.

When the switch 15-1 closes at the next moment, the power supply 16
A large current flows from the This current is detected and amplified by the operational amplifier 20 and outputted from the output terminal 17 as a detection signal.

Through the above operations, a signal that quantitatively matches the amount of X-rays received by the X-ray photosensitive section during T ₀ time can be obtained. In the case of a detection method like this example, the accumulation time
Since detection sensitivity can be increased by increasing T ₀ , even extremely weak X-rays can be detected.

In addition, according to such a detection method, the X-ray intensity
When L ₀ is high, the dynamic range of the X-ray intensity can be apparently widened by reducing the storage time T ₀ and reading out at high speed. X
In the case of radiographic diagnosis, especially when there is a demand for precise diagnosis, the above-mentioned system in which the dynamic range can be adjusted is particularly effective.

According to the present invention, as detailed above, (1) it is possible to provide a thin film X-ray sensor array that enables a high-density detector array type X-ray CT scanner.

(2) A thin film X-ray sensor array with a wide X-ray dynamic range can be provided.

(3) An X-ray sensor array whose shape is easy to process can be provided.

It is possible to achieve excellent effects such as

The present inventors have conducted numerous experiments on the radiation (X-ray) sensor configured as shown in Figures 3 and 4, and found that particularly good results were obtained when the following numerical values were selected. Obtained.

As shown in Figure 6a, 5.1cm (2″) x 7.6cm
(3″) rectangular glass substrate 10 with 800% Cr.
Å, Au was deposited to a thickness of 400 Å, and this Cr-Au composite film was deposited with a pitch of 1.2 mm, a conductor width of 0.9 mm, and a flow rate of 30 mm.
Photographing was carried out so that 40 strip-shaped electrode arrays 11 could be obtained. At this time, the extraction terminal 23 of the counter electrode 13 was also provided close to the electrode array 11 at the same time.

On this substrate 10, a
A Se-As thin film was deposited to a thickness of 20 μm. At this time, as shown in FIG. 6b, the Se-As thin film 12 is
A portion of the band-shaped electrode 11 was vapor-deposited so as to cover a portion of the band-shaped electrode 11 except for the upper counter electrode lead-out terminal 23.

Note that the evaporation method uses pure Se as an evaporation source.
A co-evaporation method using two components, As ₂ Se ₃ , was employed, and the evaporation rate of both was controlled to adjust the composition. Also,
In this example, the As concentration was set to 5 wt%.

On top of this, a Cr film with a thickness of 1000 Å was formed as the upper electrode or counter electrode 13. in this case,
It goes without saying that the counter electrode 13 should cover the counter electrode lead terminal 23 as shown in FIG. 6c. The readout circuit (not shown) was externally connected, and a normal multi-pin connector was used for connection.

A sensor array was fabricated by arranging a large number of the X-ray sensors configured as described above in a ring shape in the longitudinal direction of the sensors, as shown in FIG. In addition,
Although X-rays cannot be detected at the butt portions of the respective X-ray sensors, and therefore no video signals can be obtained, this portion is adjusted by image processing by a computer.

The X-ray sensor with the above configuration has an average energy of 60 KeV and 3×10 ² to 6
When X-rays of ×10 ⁵ photon/0.9 mm × 3 mm were applied, not only was a signal proportional to the amount of X-ray irradiation obtained, but the resolution was also higher than that of conventional ones.

Regarding resolution, it is also possible to achieve a strip-shaped electrode pitch of about 4 to 12 electrodes/mm using microfabrication technology, making it possible to inspect details that are not possible with conventional methods. You will be able to do this.

Furthermore, if a semiconductor chip for a detection circuit is mounted on the substrate of the radiation sensor of the present invention, or if the same chip is provided as an IC, particularly favorable results can be obtained in terms of miniaturization of the device and ease of processing the shape. can bring.

[Brief explanation of drawings]

Figures 1 and 2 show conventional X-rays, respectively.
A schematic perspective view of a CT scanner, FIG. 3 is a plan view of a radiation sensor according to an embodiment of the present invention, FIG. 4 is a sectional view taken along the - line in FIG. 3, and FIG. Basic circuit diagram of radiation sensor readout,
6a to 6c are plan views showing the manufacturing process of the radiation sensor of the present invention. 1... Test object, 2... X-ray tube, 3, 4... Collimator, 5... X-ray sensor, 6... X-ray beam,
7... Computer, 9... X-ray sensor array,
DESCRIPTION OF SYMBOLS 10... Substrate, 11... Strip electrode, 12... X-ray photoreceptor, 13... Counter electrode, 14... Photosensitive part.

Claims (1)

[Scope of Claims] 1. A radiation CT scanner device in which a radiation source is rotated around a subject and radiation transmitted through the subject is detected by a radiation sensor array arranged in a ring around the subject. The radiation sensor array used includes: a substrate; a plurality of strip-shaped electrodes arranged on the substrate at right angles to the longitudinal direction thereof; and a radiation-sensitive electrode formed thereon so as to cover the plurality of strip-shaped electrodes. and a counter electrode formed to overlap the plurality of band-shaped electrodes in the longitudinal direction on the radiation photoreceptor, and the radiation sensors are arranged side by side in the longitudinal direction. Features: Radiation sensor array for radiation CT scanner equipment. 2 Se− in which the radiation photoreceptor contains 5wt% or less of As
The radiation sensor array for a radiation CT scanner device according to claim 1, characterized in that it is an As thin film.