GB2117900A - Radiation detector - Google Patents

Abstract

A radiation detector includes a detection probe containing a crystal A sensitive to radioactivity surrounded by a radiation shield 3 which has a small port 2 protected by a window 4 of aluminium through which radiation can pass. When radiation impinges upon the crystal A an electrical pulse is created which is passed to preamplification means B. The amplified pulse is passed, over a cable 8, to counting means where the pulse may be further amplified and is converted into a radiation count. <IMAGE>

Description

SPECIFICATION Radiation detector This invention relates to a gamma ray detector and in particular relates to a gamma ray detector for use in surgical applications.

Gamma ray detectors play a very important part in medicine particularly in the fields related to the detection of carcinoma.

If a radioactive isotope is injected into the body, it will tend to accumulate around areas of carcinogenic activity. The presence and position of carcinoma can be determined by finding the areas of high density of the radioactive isotope using the gamma ray emmissions.

There are certain surgical operations, for instance the treatment of bone cancer, where it is necessary to effect the detection of gamma rays on a continuous basis throughout the operation. It is also necessary to determine the position of the gamma ray source extremely accurately (perhaps to within 1 mm). X-rays may be used to locate radioactive isotopes within the body but obviously these cannot feasibly be applied during surgery.

There are prior devices available for the detection of gamma ray emmissions during surgery. For example, optical devices are available for such use, but these are usually bulky and not very reliable.

It is an object of the present invention to provide a lightweight, reliable electronically operated detector of gamma ray emmissions which can accurately locate the source of such emmissions.

According to one aspect of the invention there is provided a radiation detector comprising a detection probe having a radiation shield within which a crystal responsive to radiation is located, said radiation shield having a port through which electromagnetic radiation can enter to impinge upon the crystal thereby producing an electrical pulse, pre-amplification means to amplify said electrical pulse and counting means adapted to convert said amplified electrical pulse into a radiation count.

Advantageously the radiation which is detected is gamma radiation and the crystal is a cadmium telluride crystal. The radiation shield is desirably a lead shield.

The radiation count may be displayed on, for example an LED (light emitting diode) display, an analogue ;ether and/or a printer. Also there may be a two wire current loop transmitter for interface to a microprocessor or computer. Further multiplexed outputs may be available which can be used via a microprocessor to create colour graphics on a visual display unit.

The count rate or range may be varied from 0.01 seconds to 10 seconds. The LED in normal mode may count the radiation in counts per second, and may update the count every 0.2 seconds.

Desirably the detector is powered at a maximum of 36 V.

Reference is now made to the accompanying drawings in which: Figure 1 is an elevation of a detector probe and pre-amplifier case according to the invention; Figure 2 is a schematic biock diagram of one embodiment of a gamma ray detector according to the invention; Figure 3 is a circuit diagram of an embodiment of the pre-amplification means; Figure 4 is a circuit diagram of one embodiment of an amplifier for use within the counting means; Figure 5 is a circuit diagram showing one embodiment of means to filter out low energy pulses; Figure 6 is a circuit diagram showing one embodiment of means to filter out high energy pulses; Figure 7 is a circuit diagram of one embodiment of a logic gate system; Figure 8 is a circuit diagram of one embodiment of a monostable unit; Figure 9 is a circuit diagram showing an embodiment of means to scale down the radiation count;; Figure 10 is a circuit diagram of a pulse counter; Figure 11 is a circuit diagram of a multivibrator unit; Figure 12 is a schematic block diagram of an alternative embodiment of a gamma ray detector according to the invention; Figure 13 is a circuit diagram of an alternative embodiment of an amplifier for use within the counting means; Figure 14 is a circuit diagram showing an energy pulse amplifier for use within the counting means; Figure 1 5 is a circuit diagram showing a further energy pulse amplifier within the counting means; Figure 16 is a circuit diagram showing an alternative embodiment of means to filter out high and low energy pulses; Figure 17 is a circuit diagram showing a potential divider network for a pulse height window; Figure 1 8 is a circuit diagram showing an alternative embodiment of a logic gate system;; Figure 19 is a circuit diagram showing an alternative embodiment of a monostable unit; Figure 20 is a circuit diagram showing an integrator scaler; Figure 21 is a circuit diagram showing a microprocessor interface unit; Figure 22 is a circuit diagram showing a pulse rate to audible converter; Figure 23 is a circuit diagram showing a switch matrix; Figure 24 is a circuit diagram showing a decade counter, digital display and multiplexed output; and Figure 25 is a circuit diagram showing an arrangement of a power supply for the system.

In Figure 1 a detector probe generally designated 10 is shown in more detail. A CdTe crystal A is contained within a lead shield 3.

Incident radiation, for example gamma radiation shown by arrows 1, falls on to the probe 10. A small amount of radiation 1 reaches the CdTe crystal A through port 2. There is an aluminium window 4 press-fitted into the end of the probe.

This may be secured by an anaerobic adhesive.

The probe is held by the case generally designated 5. Case 5 also serves to contain the preamplifier B.

The stalk of the probe 6 and the probe head 7 are designed according to the particular use for which the detector is required. In the embodiment shown the detector is intended for use in surgical applications and hence must be able to access objects at awkward locations.

The output from the pre-amplifier B is fed through a wire 8 to the counting means (not shown). The wire 8 may be a four core individually screened PVC cable of 5 mm diameter cable which is secured to the probe case 5 by adhesive lined heat shrinkable sleeving.

Referring now to Figure 2 incoming gamma radiation indicated by arrows 1 falls on lead shieiding 3 which surrounds the CdTe crystal A.

The CdTe crystal responds only to gamma radiation 1 which passes through port 2 in the lead shielding.

When gamma radiation strikes the CdTe crystal a pulse is created which is passed to pre-amplifier B. Here, the pulse is amplified at a gain of 10000.

The amplified pulse is fed to the operational amplifier C', which has a gain of about 20.

The output from amplifier C1 is fed to the operational amplifiers D1 and E1.The input to amplifier D1 is set by the high level "window" F1.

This is used to set the maximum value of pulse which will be detected by the system. If the output from amplifier C1 is greater than the value set by the high level "window" then there will be no output from amplifier D1.

The input to amplifier El is set by the low level "window" G 1. This is used to set the minimum value of pulse which will be detected by the system. If the output from amplier C1 is less than the value set by the low level "window" then there will be no output from amplifier El. The low level "window" is used to calibrate the system in order to eliminate noise by background radiation and by the CdTe crystal itself. The high level "window" is used to eliminate random high voltage pulses which occur from time to time. An LED H 1 flashes every time the voltage of pulse exceeds the setting of the high level "window". A further LED display J1 flashes every time a pulse exceeds the setting of the low level "window".

The output from amplifiers D1 and El are fed into a gating circuit K1 which is basically a "D" flip flop. There will be an output from gating circuit K1 provided that there is an output from amplifier El and no output from amplifier D1.

The output from gating circuit K1 is fed to a monostable L1.The monostable L1 is used to calibrate the system for particular radioactive isotopes. The isotope which it is most suitable for this embodiment is Technesium 99 M. The monostable should produce an output which is approximately a square wave pulse.

The square wave pulse is fed to a clock input on a "/10 counter" Mi. This enables the radiation count to be divided by a factor from 1 to 10. The purpose of this reduction is to facilitate easier reading of an LED radiation count display R1.

The output from '710 counter" M1 is fed to a counter Ni. This counts the number of pulses that it is receiving from the "/10 counter" My. A multivibrator Q1 is calibrated at a frequency of 1 Hz so that the count N1 will give a reading in counts per second. The output from the counter is fed to the LED radiation count display R1. Each second the counter stores the radiation count and holds the figure until the next second.

Consequently the count of display Rl gives a different reading at one second intervals corresponding to the number of counts in the immediately preceding second.

The counter N1 also has facilities for connection to the printer P 1 for hard copy output.

The output from the "/1 0 counter" M1 is also fed to a loudspeaker circuit S1 for an audible representation of the count.

Figures 3 to 11 show in more detail the circuitry for the embodiment of the gamma ray detector shown in Figure 2.

Figure 3 shows the circuitry for the preamplification and the CdTe detector. The CdTe detector 300 emits an electrical pulse when struck by gamma rays. This pulse is amplified by 3 operational amplifiers 301,302 and 303 at an overall gain of 10000.

The output voltage Vault corresponds to the input voltage V,n to operational amplifier 400 shown in Figure 4. The gain of this amplifier is 20.

The variable resistor generally designated 403 enables the circuitry to be balanced. There are also variable resistors 505 and 609 shown in Figures 5 and 6 respectively which serve a similar function.

The output from the circuit along wires 401 and 402 are fed to the circuits shown in Figure 5 and Figure 6.

Figure 5 shows the circuitry for the low level "window". Here the pulse is fed to operational amplifier 500, which is on open loop gain. The variable resistor generally designated 503 sets the low level "window" at the required value. The output from amplifier 500 is fed along wire 504 to the circuitry generally designated 501 which has an LED which flashes whenever the voltage of a pulse exceeds the setting of the low level "window". The output from amplifier 500 is also fed along wire 502 to the gating circuit shown in Figure 7.

Figure 6 shows the circuitry for the high level "window". Here the pulse is fed along wire 401 to operational amplifier 600, which is on open loop gain. The variable resistor generally designated 607 sets the high level "window" at the required value. Variable resistor 607 may be switched between a "normal" position 601 and a "window" position 602. In the normal position there is no cut off of high level pulses. The output from amplifier 600 is fed along wire 608 to the circuit generally designated 605 which has an LED which flashes whenever the voltage of a pulse exceeds the setting of the high level "window". The output from amplifier 600 is also fed along wire 606 to the gating circuit shown in Figure 7.

Both amplifiers, 500 and 600 will not have an output unless the size of the pulse from amplifier 400 is at least 12 volts.

The output wire from amplifier 600 is fed along wire 606 to a "clock" input 705 of a dual "D type" flip flop 701, shown in Figure 7. The output from amplifier 500 is fed along wire 502 to a "data" input 704 of flip flop 701. Wire 502 is also fed through two NAND gates 707 and 708 to the "reset" input 706 of flip flop 701, and in addition is fed to AND gate 702. The output from the flip flop 701 is fed to AND gate 702. The output from AND gate 702 is fed to NAND gate 703. The output from NAND gate 703 is fed to the monstable shown in Figure 8.

The monstable 800 converts the pulse into a square wave, then the output is fed along wire 801 to the "/10 counter" 901 shown in Figure 9.

The variable resistor 802 is used for the calibration of the monostable.

The "/10 counter" 901 may be used to divide the size of the count by a factor from 1 to 10. The output from the "/10 counter" 901 is fed along wire 905 to the loudspeaker circuit generally designated 902. This gives an audible representation of the count through loudspeaker 904.

The output is also fed along wire 903 to a counter shown in Figure 10.

The counter in Figure 10 is generally designated 1 000. The counter has 7 segments numbered from 1005 to 1011. Each of the segments is connected to an LED and then to one of segment drivers numbered from 1012 to 1018.

For convenience only one segment 1005, one segment driver 1012, and one LED 1003 is shown. The segment drivers form part of a darlington driver 1004 the main purpose of which is to prevent flicking of the LED display. The counter also has a "bcd" output for connection to a printer for hard copy output. This output is numbered 1019 to 1022.

There are wires 1001 and 1002 which are connected to the multivibrator shown in Figure 11. Wire 1001 is a "store" line and wire 1002 is a "clear" line.

The multivibrator is generally designated 1100 and consists of a standard dual timer package (No: NE556).

Referring now a further embodiment of the invention shown in Figure 12, a cadmium telluride crystal A and pre-amplifier B are identical to the crystal A and preamplifier B described above for the first embodiment.

The amplified pulse from the preamplifier B is fed to an operational amplifier C2 which has a gain of about 20.

The output from amplifier C2 is fed to energy pulse amplifier T2 the input resistance/capacitor time constant and gain of which can be adjusted for varying isotopes. The amplifier T2 provides a coarse adjustment.

The output from the energy pulse amplifier T2 is fed to another energy pulse amplifier U2, the input resistance/capacitor time constant and gain of which can also be adjusted for varying isotopes.

The amplifier U2 provides for the fine adjustment of the output from pulse amplifier T2.

The output from amplifier U2 is fed to operational amplifiers D2 and E2 which act as high and low level windows respectively. The window level is adjusted by a potential divider network V2 which provides a channel percentage window width which can be varied in six discrete steps up to 60%. This channel width provides a bias voltage to both D2 and E2 operational amplifiers. If an input from amplifier U2 is less in voltage value than a preset lower window width then no pulse output occurs from E2. If a pulse is higher in voltage value than a preset higher window then no pulse output occurs from D2. The output from amplifiers D2 and E2 are fed to a gating circuit K2 which comprises two D-type flip flops and will produce an output provided the pulse from the output of amplifier U2 is within the window levels.

The output from gating circuit K2 is fed to a monostable L2 and to a switch matrix W2.

The monostable L2 is used to provide an accurate pulse width.

The switch matrix W2 is used to switch from normal pulse counts to "pulse interval time". The output is then fed to a decade counter M2. This is a universal counter integrated circuit which is ujsed to decode the input pulses from switch matrix W2 into counts per second and provides multiplexed outputs for computer interface and printer. The output from monostable L2 is fed into the Integrator Scaler X2 which can be adjusted for various isotopes. The output from the integrator scale X2 feeds to a pulse rate to audible converter S2 which provides an audible representation of the pulse rate, and to a Microprocessor Interface Y2, which provides an output port to Interface with a microprocessor.

Figures 13 to 24 show in more detail the circuitry for the embodiment of the gamma ray detector shown in Figure 12.

The output voltage VOUT from pre-ampiifier B (Figure 12, Figure 3) corresponds to the input voltage VIN to operational amplifier 400 shown in Figure 1 3. The gain of this amplifier is 20. A variable resistor generally designated 1 301 enables the circuitry to be balanced. Variable resistors 1401 and 1 501 shown in Figures 14 and 1 5 respectively serve a similar function with respect to operational amplifiers 1 400 and 1 500.

The output from the circuit 1 3 passes along wire 1302 to the circuit shown in Figure 14.

Figure 14 shows the circuitry for the first energy pulse amplifier, where the various pulse widths from different isotopes are widened and amplified by operational amplifier 1 400. The amplifier 1400 has a gain of between 1 and 20.

The output from amplifier 1400 is fed along wire 1402 to operational amplifier 1 500 (Figure 15).

Figure 1 5 shows the circuitry for the second energy pulse amplifier, where the various pulse widths from different isotopes are widened and amplified by operational amplifier 1 500. The amplifier 1500 has a gain of between 1 and 10.

The output from amplifier 1 500 is fed along wire 1 502 to operational amplifiers 1600 and 1 610 shown in Figure 1 6.

Resistor 1 620 sets the bias level to both amplifiers 1 600 and 1 610. This bias voltage cuts out all the noise level created by the CdTe crystal and by the operational amplifiers 301, 302, 303, 1300,1400 and 1500.

Figure 1 7 shows the potential divider network V2 (see Figure 12). This sets a bias voltage level or window width to both operational amplifiers 1600 and 1610 at points 1621 and 1622 (see Figure 16).

The outputs from operational amplifiers 1 600 and 1 610 are fed along wires 1 623 and 1 624 respectively to two D-type edge triggered flipflops 1800 and 1 810 shown in Figure 18. The output from the flip-flops are fed to logic gating circuits which provide a pulse output when the pulse is within the window level.

The output from the logic gating circuit is fed along wire 1 820 to a Monostable 1900 shown in Figure 1 9. This unit provides an accurate pulse width output. The output from monostable 1 900 is fed along wire 1 901 to an integrator scaler shown in Figure 20.

Figure 20 shows the circuit for the integrator scaler. This unit integrates the incoming pulses and provides an anologue output, depending on the rate of incoming pulses received. The output of the integrator scaler is fed along wire 2000 to a microprocessor interface shown in Figure 21.

This circuit is a two wire current loop transmitter, and generally provide an output in the range 4MA to 20MA.

Also, the output from the integrator scaler (see Figure 12) is fed along wire 2000 to a pulse rate to audible converter shown in Figure 22, which essentially is a frequency to voltage converter, whose output changes from low frequency to high frequency as the pulse input repetition increases.

A loudspeaker 2200 provides an audible representation of the pulse.

Also the output from the logic gating circuit (see Figure 18) is fed along wire 1 820 to a switch matrix shown in Figure 23.

This circuit provides a pulse along wire 2300 for complete counting, or alternate pulses out along wires 2300 and 2301. This gives the correct logic to count the interval between pulses. The output from the switch matrix wires 2300 and 2301 are fed to a decade counter shown in Figure 24.

This is a fully integrated counter which provides various on-chip functions as specified by the manufacturers. An 8 digit display shows the pulses to be counted and updates the display every 0.2 seconds.

The decade counter integrated circuit has "bcd" multiplexed outputs which may be used for an external printer and/or a computer to produce a colour graphics display of the radiation being monitored.

Figure 25 shows the arrangement of the power supply to the various parts of the circuitry. The power may be supplied by 36 Volts 1201 or by 12 Volts 1203.

All parts of the detector except for the CdTe crystal itself use this supply.

Although the gamma ray detector of the present invention is principally to be used in surgical applications it is clear that there are widespread uses for the detector.

The detector has many advantages over the prior art which include increased portability and increased reliability. Furthermore the detector is capable of accessing more awkward locations than prior detectors.

Claims (20)

1. A radiation detector comprising a detection probe having a radiation shield within which a crystal responsive to radiation is located, said radiation shield having a port through which electromagnetic radiation can enter to impinge upon the crystal thereby producing an electrical pulse, pre-amplification means to amplify said electrical pulse and counting means adapted to convert said amplified electrical pulse into a radiation count.

2. A radiation detector according to Claim 1 in which the radiation detected is gamma radiation, and the crystal is a cadmium telluride crystal.

3. A radiation detector according to Claim 1 or 2 in which the radiation shield is a lead shield.

4. A radiation detector according to Claim 1,2 or 3 in which the cross sectional area of the port through which radiation can flow is less than 1 cm.

5. A radiation detector according to Claim 4 in which the cross sectional area of the port is less than 0.3 cm.

6. A radiation detector according to Claim 5 in which the cross sectional area of the port is less than 0.1 cm.

7. A radiation detector according to any preceding Claim in which the preamplification means and the detection probes are constructed as an integrated unit.

8. A radiation detector according to any preceding claim in which the counting means includes means to amplify the electrical pulse from the preamplification means.

9. A radiation detector according to any preceding claim in which the counting means has a high level window and a low level window to filter out electrical pulses above and below a preset value.

10. A radiation detector according to Claim 9 in which the counting means includes a logic gate system for determining whether the electrical pulse is within the range defined by the high and low level windows.

ii. A radiation detector according to any preceding claim in which the counting means includes a monostable to enable the detector to be calibrated for use with different isotopes.

12. A radiation detector according to any preceding claim in which the counting means includes an integration scaler.

13. A radiation detector according to any preceding claim in which the counting means includes a pulse rate to audible converter.

14. A radiation detector according to any preceding claim in which the counting means includes a microprocessor interface circuit.

1 5. A radiation detector according to any preceding claim in which the counting means includes a switch matrix.

1 6. A radiation detector according to any preceding claim in which the counting means includes a decade counter, a digital display and multiplexed output.

1 7. A radiation detector according to any of Claims 1 to 11 in which the counting means includes means to scale down the radiation count.

1 8. A radiation counter according to Claim 1 7 in which the counting means includes a pulse counter.

1 9. A radiation detector according to Claim 1 8 in which the counting means includes a multivibrator unit.

20. A radiation counter substantially as herein described with reference to and as shown in the accompanying drawings.