JPS5850313Y2 - radiation sensing device - Google Patents

Description

[Detailed description of the invention] Diagnosis of tumors and other pathological tissues has become significantly easier with the advent of nuclear medicine.

For example, small amounts of radioisotopes concentrate in different concentrations in diseased and healthy tissues after being administered to a patient.

Thus, the different concentrations of radiation, usually gamma rays, emitted by healthy and diseased tissue can be distinguished and detected.

Instruments used to detect radiation typically utilize collimators to direct or transmit the radiation to scintillation crystals, which convert the radiation into visible light during scintillation.

A photomultiplier tube detects light and various means are used to locate scintillation in a scintillator and thus indirectly locate a tumor or other abnormality in a patient.

Radiographic imaging equipment includes dynamic and stationary equipment, sometimes referred to as scanners and cameras, respectively.

Both devices have their own limitations.

The scanner moves slowly over the patient and is believed to have better resolution and field uniformity.

However, scanners take a relatively long time to detect radiation, which can be uncomfortable for some patients.

On the other hand, a still image device shoots a single still image, so it is relatively fast.

Although still image devices are faster than scanners, they do not provide as good resolution and uniformity of image plane as scanners.

Resolution is used here to mean the ability of an instrument to distinguish between two distant points or sources.

An example of a still image device is Anger Patent No. 3.
, No. 011,057, the contents of which are incorporated by reference.

Unger's device operates by moving the photomultiplier away from the scintillator so that it sees overlapping regions of the crystal.

However, such separation results in some photons not being detected by the photomultiplier, resulting in a loss of resolution.

This invention is based on the patent application filed in Japan in 1982-76 by the present applicant.
This is an attempt to further improve the radiation sensing device disclosed in No. 116 (Japanese Patent Publication No. 56-51312).

The radiation sensing device of this patent application No. 48-76116 uses a plurality of photomultiplier tubes, no fewer than three, typically 19 or 37, arranged in a hexagonal arrangement immediately adjacent to a scintillator. ing.

Although this arrangement allows the photomultiplier tubes to receive the maximum number of photons, it does present some problems.

By placing the photomultiplier tube close to the scintillator,
This causes the photomultiplier tube to shift the spatial location where scintillation occurs toward the center of the nearest photomultiplier tube.

This results in spatial distortions and non-uniformities that appear as a mottled hexagonal mesh or open hexagonal visible pattern in the visual display.

In order to correct such spatial distortion and non-uniformity, the photomultiplier tube is moved backward from the crystal in the aforementioned U.S. Pat. No. 3,011,057; In the '76116 invention, such spatial distortions and non-uniformities are electronically corrected using diodes.

In the invention of Japanese Patent Application No. 76116/1984, a diode was used to electronically correct spatial distortion and non-uniformity, but the use of such a diode caused irregularities in field uniformity. has appeared.

Such irregularities in field uniformity are caused by sharp conduction points, which serve as reference points at which diodes conduct and non-conduct.

These irregularities appeared in the image as scintillation and scintillation occurrence increasing in the region directly below the photomultiplier tubes, and scintillation occurrence decreasing in the region between the photomultiplier tubes. .

Therefore, if there is an outline of the photomultiplier tube, it may be observed in the displayed image.

The present invention solves the problem caused by the sharp conduction point of the diode by using a pulsating bias means that pulsates the conduction point of the diode.

The invention provides means for forming a visible response from radiation, means for converting the visible response from the radiation into electrical impulses, and means for producing a signal with the electrical impulse giving an indication of the relative position of the radiation. and a radiation sensing device comprising means for operating the radiation sensing device.

The means for correcting the distortion includes a non-linear response device that provides an output that is not directly proportional to the human input signal.

This correction means includes a non-linear device having human power and an output;
pulsating bias means connected to the non-linear device to pulsate the conduction point.

As shown in FIGS. 1 and 2, the means for creating a visible response from the radiation includes a straight hole collimator 10 and a scintillator 11 directly above it.

Different types of collimators may be used, such as pinhole collimators.

As can be seen in detail in FIG. 2, the scintillator 11 has a thickness of approximately 1.27 m (1/2 m) and is bonded to a thin glass plate 14 such as Pyrex with epoxy 13.
2 inch) relatively thin circular scintillation crystal 1
Contains 2.

It has been found that a thickness of 0.635 cIIL (1/4 inch) to 1.27 CIIL (1/2 inch) should be satisfactory for this glass plate.

Scintillation crystals convert invisible radiation, such as gamma rays, into visible light (photons).

The glass plate 14 has an annular right-angled groove 1 forming an annular platform 18.
The scintillation crystal 12 is supported by a metal ring 16 on which the glass plate rests.

A coupling agent 20 such as epoxy connects the glass 14 to the metal ring 16.
and maintain contact with each other to form a hermetic seal.

The bottom surface of the crystal 12 is protected by a thin aluminum plate 15.

This aluminum plate 15 has an upwardly extending outer periphery flange which is epoxy bonded to a recess formed in the metal i16.

This aluminum plate 15 is far away from the plane of the crystal.

Gamma rays from outside the field of vision are filtered out by lead shielding.

Another lead shield around the entire interior of the head assembly prevents the introduction of stray radiation.

A case 26 surrounds and supports the entire lead shield.

Scintillators are of a commercially available type from a variety of manufacturers.

Glass plate and metal ring supports are required by the manufacturer to provide sufficient structural support.

However, as yet unknown future designs may allow this glass support to be removed.

Any support between crystal 14 and collimator 10 will block the gamma rays.

Moreover, the crystal is fragile and cannot be supported by its outer periphery alone.

The means for converting radiation into electrical impulses include a hexagonal array of photomultiplier tubes 28.

In this hexagonal array, shown in cross section in FIG. 1, there are 37 2-inch photomultiplier tubes viewing the scintillator 11.

The photomultiplier tubes 28 are arranged in a hexagonal configuration because the hexagonal configuration allows the maximum number of photomultiplier tubes to be placed on a circular crystal.

The array of photomultiplier tubes is surrounded by a cylindrical light shield 29 made of sheet metal.

A press plate 27 is removably connected to the top of this light shield 29.

As noted in FIG. 1, photomultiplier tube 28 is placed immediately adjacent to scintillator 11 with only standard optical coupling grease 21 in between.

In this way, the photomultiplier tube senses the maximum number of photons emitted by the scintillator 11.

1 glass plate with a thickness of approximately 0.635 (1 m (1/4 inch)
Only 4 has a scintillation crystal 12 and a photomultiplier tube 28.
separated from the surface.

This 0.635 cIrL glass plate is only needed to support the crystal and is required by the crystal manufacturer.

A glass plate is not intentionally placed between the photomultiplier tube and the scintillation crystal 12 to provide spacing.

However, it should be understood that the present invention can also be used to modify image plane uniformity in other geometries of scintillation crystals and photomultiplier tubes.

Depending on the size of the scintillator, fewer or more photomultiplier tubes can be used.

Photomultiplier tubes are commercially available from RCA or Space Research Corp.
orat 1on) can be done manually.

In addition, one having one photocathode and a plurality of electron multipliers
It is also possible to use two photomultiplier tubes.

The photomultiplier tubes are placed parallel to each other and look at one side of the scintillator 11.

Since those surfaces are placed immediately adjacent to the scintillator, little or no overlap area of the scintillator 11 is seen.

The photomultiplier tubes only need to be placed so that three of them see a common scintillation.

That is, each scintillation must be viewed by at least three photomultipliers to provide the necessary basis for determining its position.

As previously explained, this arrangement of placing the photomultiplier tube immediately adjacent to the scintillator allows maximum photon reception and thus the best possible resolution.

Means operating by electrical response produce a signal giving an indication of the relative position of the radiation and generally refer to all of the circuitry involved.

This circuit includes a preamplifier, voltage divider, amplifier, and all of the circuits described below.

It should be understood that variations thereof will be apparent to those skilled in the art.

The block diagram of FIGS. 3A and 3B showing the major components shows that the photomultiplier tube 28 is connected to a resistive voltage divider network 34 supplied by a high voltage source 36. .

This high voltage source can vary depending on the isotope used with the camera or otherwise called still imaging device.

Preamplifier 30 receives the signal from the photomultiplier tube and is attached to a low voltage source 38.

Preamplifier 30 provides signals to delay line amplifiers 39 ~1~ to ~37~.

The incoming pulse to the delay line amplifier is about 3 volts and about 750
It has a relatively fast rise time of nanoseconds and a power decay time on the order of about 35 microseconds.

Delay line amplifier 39 shapes the pulse to have a flat top with a duration of approximately 2 microseconds.

The height of the top of the square wave is directly proportional to the peak of the original pulse.

Delay line amplifiers are used to give the circuit time to operate with pulses and reduce the effects of pulse stacking at high pulse repetition rates.

Delay amplifiers have been found to be preferred in simple pulse stretchers because they reduce dead time.

Dead time is defined as the time between signals to which the circuit can respond.

By using a delay amplifier, the dead time can be reduced to about 2 microseconds.

An initial attenuator 40, shown in detail in FIG. 4, is operatively connected to the output of the delay amplifier.

Diode 40a is placed in series with the line signal and resistor 4
It is grounded by 0b and placed in parallel with resistor 40C.

Diode 40a in combination with resistor 40C attenuates small signals and, in effect, provides discrimination against noise or very small signals.

The threshold voltage of a diode prevents any signal from passing through the diode until the signal reaches a predetermined value.

Discriminating against small signals ensures that only relatively strong signals are utilized that can be used to accurately determine the location of scintillation within the scintillator.

A mottling effect or chicken-wire on the image plane as a result of the sharp cut-off of diode 40a
To avoid the effect, bypass resistor 40C in parallel with it
is used.

Diode 40a reduces the low part of the signal so sharply that its effect is visible and reduces the uniformity of the image plane.

To reduce the severe effects of conduction of diode 40a, a resistor 40G is placed in parallel with it to pass a small signal.

This resistor 40c has a resistance value approximately equal to that of the resistor 40b, and is 1000 ohms.

It is expected that other resistances will also be acceptable.

Means are operatively connected to the first discriminator 40 to correct for distortions resulting from placing the photomultiplier tube adjacent or near the scintillator or from other sources.

This means 42 for correcting distortion is particularly shown in FIG. 5 and includes a human resistor 43 of about 100 ohms, a diode 41 with a threshold voltage of about 0.6 volts, and a bias voltage of about 0.3 volts. It includes a resistor 41a of about 60 ohms that connects the DC voltage and an AC bias voltage with a peak-to-peak value of about 0.8 volts at 60 hertz.

The values given are typical values, but may vary.

To increase the uniformity of the image plane, a pulsating voltage that is a combination of a DC bias voltage and an AC bias voltage is used.

It has been found that a pure DC bias voltage makes the diode conduction point too steep.

When the diode begins to conduct, an artificial or false active area under the photomultiplier tube appears in the pattern.

Using an AC bias voltage and a DC bias provides a range of threshold values at which the diode begins to conduct.

In this way, the conduction effect of the diode is expanded, so
The uniformity is greatly improved and the area under the photomultiplier does not appear as an area of increased activity.

This bias improvement is extremely important because it improves uniformity.

A sign of pathological tissue is precisely the inhomogeneity of the radioactive pattern.

If not clear, it is critical to yield the exact area of increased radioactivity based on tissue characteristics.

A diode 41 and a resistor 41a are placed in parallel with the output from the diode of the bias unit.

Any voltage in the human power will cause current to flow through resistor 43.

If that voltage is not greater than the bias and threshold voltage combined, no current will flow through the diode.

In this respect, output is directly proportional to human power.

As the input terminal increases, a value is reached where the diode becomes forward biased.

At this point, current flows through diode 41 and resistor 41a, and the output voltage is not directly proportional to the input terminal.

Therefore, diode 41 and resistor 41a become attenuation factors in the circuit.

The bias voltage is adjustable and may be used to vary the output of the photomultiplier tube delivered in the circuit.

By using an alternating current bias voltage, spatial distortion and image plane non-uniformity can actually be eliminated whether the photomultiplier tube is adjacent to or remote from the scintillation crystal.

Non-linear response devices other than diode bias can be used to correct for distortion and image plane non-uniformity.

Another non-linear response device is shown in Figure 5a,
This device is transistor 40'.

This acts to discriminate against small signals or noise and to attenuate signals above a predetermined level.

This is an alternative to the image components shown in FIGS. 4 and 5.

It has a base 41' with a resistor 41a' in series.

The collector 42' has a resistor 42a' in series with it, and the emitter 43' has a resistor 43a' in series with it.

Base resistor 41a' is approximately 100 ohms, collector resistor 42a' is approximately 600 ohms, and emitter resistor 43a' is approximately 65 ohms, although these values may vary.

An alternating current bias voltage is applied to the collector with a peak-to-peak value of approximately 300 millivolts.

A DC voltage bias of approximately 200 millivolts is also applied to the collector.

No signal appears at the emitter output for a signal that is less than the manually applied threshold bias value.

The transistor thus acts as a discriminator for small signals or noise.

After the bias voltage is exceeded in human power, the emitter output has a signal equal to human power minus the bias value.

The transistor acts as an emitter-follower in the human power range.

As the input voltage increases further and approaches the bias voltage, the collector 42' of the transistor can no longer supply current and the human input signal is attenuated by the voltage dividing action of resistors 41a' and 438'.

This last phenomenon is similar to the operation of the diode bias circuit of FIG.

Pulsating bias voltages with AC and DC bias voltages act essentially the same way as described above for diodes.

That is, they change the conduction point of the transistor, thereby avoiding the non-uniformity experienced with DC bias only.

Other configurations utilizing diodes and transistors may also achieve the desired effect.

It is through this addition to the circuitry that the invention described herein utilizes the maximum number of photons to obtain the best resolution and eliminate distortion and image plane non-uniformity.

A summing circuit 44 is operatively connected to diode biasing device 42 .

Summing circuit 44 includes a small group summing amplifier 45 having an input resistor 46 having a value of about 5 to 40 kilohms and a resistor 48 having a value of about 5 kilohms.

For example, the small group summing amplifier 45 for the Y1 signal includes input from a photomultiplier tube on one side of the X axis.

For convenience, this will be shown as a ¥11 addition add-on.

A summing amplifier for the ¥2 signal, the X1 signal and the X2 signal is representatively shown.

These small group summing amplifiers receive signals from photomultiplier tubes on either side of the X and Y axes.

In particular, the Y1 and Y22 summing amplifiers receive signals from photomultiplier tubes on either side of the X axis.

The X1 and X2 summing amplifiers receive signals from the photomultiplier tubes on either side of the Y-axis.

The term small group summing amplifier is generally used to refer to summing amplifiers 45, 47, 49 and 51 collectively.

In addition to the element shown generally as 50, these elements include inverters 52, 53 and summing amplifiers 60, 62.

Inverter 52 simply converts the Y2 and X2 signals to negative values before applying them to Yl and Xl, respectively.

Resistors 56 and 58 of conventional type are used in the summing amplifier and have a value of approximately 5 kilohms.

Summing amplifiers 60 and 62, respectively, further combine signals in the coordinate signals of the Y and X positions of scintillation occurring in scintillator 11.

The central photomultiplier tube of the hexagonal array is not operatively connected to the subgroup summing amplifier.

Additionally, any photomultipliers on the X axis are not used to determine the Y coordinate position.

The electrically responsive means further includes first and second summing amplifiers.

The first summing amplifier 64 is similar to the other summing amplifiers described above, except that it is operatively connected to all of the photomultiplier tubes.

The first summing amplifier sums all the signals after they have been modified by the diode biasing device but before they are passed to the small group summing amplifier.

The composite signal is called a two-signal. A second summing amplifier 66 similarly sums all of the outputs from all photomultiplier tubes and provides the z2 signal.

This second summing amplifier 66 receives the signal from the point before the first discriminator 40 and after the delay line amplifier.

Separate diode devices 68 and 70 (similar to those previously described as 40 and 42) are used in conjunction with the second summing circuit.

As shown in Figure 3b, the Y, X, Z, and Z2 signals are transmitted to the circuit.

In particular, the Y and X signals are transmitted to a divider circuit.

A divider circuit is a well-known device that takes two forces and divides them.

The purpose of this divider circuit is to standardize the coordinate signals; they are referred to here as a means of standardizing the Y and X signals and making them independent of the scintillation strength.

As shown in FIG. 3, the Y and X signals are divided by the output of the first summing amplifier, which is the z1 output signal.

In this way, the Y and X signals are divided by a denominator proportional to the total energy of scintillation and are normalized or made independent of that energy.

From the divider circuit, the standardized coordinate signals are then passed to plate 78 for the X-axis and plate 18 for the Y-axis.
The signal is transmitted to the X-axis and Y-axis of an oscilloscope 76 with

The Z2 signal, which is proportional to the total energy level of the signal seen by the photomultiplier tube, is passed through a pulse height analyzer 82.

The pulse height analyzer 82 determines the energy level at which the pulses are received and is operatively connected to the oscilloscope 76.

If the signal is accepted by the pulse height analyzer, the signal passes to a well-known two-axis driver 84 which provides a specific time connection to the accepted signal.

If desired, the circuit may be provided with a logic controller 86 to provide a specific amount of time for the circuit to operate or to count the number of scintillations before they disappear.

This 22 signal is then directed to an oscilloscope 76.

The oscilloscope receives the signal and turns it into a point on the scope, giving the scintillator its relative position.

In operation, a radioisotope is delivered to the patient to form a radioactivity pattern.

Radiation, usually gamma rays, is passed through collimator 10 to scintillator 11 .

Thereby, gamma radiation is converted into visible radiation,
Detected by an adjacent photomultiplier tube.

The photomultiplier tube, due to its close proximity to the scintillator, provides an electrical signal that is somewhat shaped as a function of position.

Means for operating with an electrical response include suitable amplifiers and diode biasing, particularly to provide a non-linear response to human power.

This diode bias is adjustable and is used to eliminate extra distortion and image field uniformity.

A small group summing circuit is operatively connected to the diode biasing means to provide a coordinate signal of the location of the scintillation in the scintillation crystal.

The coordinate signals are normalized by dividing by the combined output of the summing amplifier.

It will be appreciated and understood that other well known means for summing the outputs of photomultiplier tubes and standardizing them may be used.

A second summing amplifier is used as a pulse height analyzer so that only the desired signal is utilized to trigger the oscilloscope.

In the present invention, by using a radiation sensing device, an image placed on a scintillation crystal can be reproduced as an image on an oscilloscope.

It will be further appreciated that various electronic devices other than oscilloscopes may be used to display.

Other variations in circuitry and display means will be apparent to those skilled in the art and should be considered as part of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the head of the static imaging device of the present invention, FIG. 2 is an enlarged view of the circled area in FIG. 1, and FIGS. 3A and 3B are block diagrams of the circuit. Figures (two figures are line a)
-a and line b-b), Fig. 4 shows a discriminator for attenuating small signals, Fig. 5 shows a diode bias device for modifying electrical signals, and Fig. 5A shows a transistor for attenuating electrical signals. be. 10...Collimator, 11...Scintillator, 12...Scintillation crystal, 28
...Photomultiplier tube, 30...Preamplifier, 34...Voltage dividing network, 36...High voltage source, 39... ...Delay line amplifier, 40...
...First attenuator, 42... Diode bias device, 44... Addition circuit, 72, 74...
...divider, 76...oscilloscope.

Claims (1)

[Claims for Utility Model Registration] Visible response forming means for forming a visible response from radiation; and converting means for converting the visible response from the radiation into electrical impulses, and the visible response forming means is substantially connected to the converting means. transducing means for producing a distortion in the relationship of the electrical impulses to the position of the radiation; and actuating means for producing a signal which is actuated by said electrical impulse and gives an indication of the relative position of the radiation; actuating means including a distortion correction means for correcting the input signal, the distortion correction means having a non-linear response position for providing an output that is not directly proportional to the input signal, the non-linear response device including a non-linear device; The linear device causes the non-linear response device to provide an output proportional to the human input signal with a first gain in the non-conducting state, but in the conductive condition in response to a human input signal of a certain magnitude, the non-linear response device provides an output proportional to the human input signal with a first gain. The non-linear response device provides an output proportional to the human input signal with a second gain, and a pulsating bias means is connected to the non-linear device for pulsating the conduction point of the non-linear device. A radiation sensing device characterized by: