WO1999061880A9

WO1999061880A9 - Integrated radiation detector probe

Info

Publication number: WO1999061880A9
Application number: PCT/US1999/008974
Authority: WO
Inventors: Bo Pi; Timothy C Collins; Richard L Conwell; Jerome Gormley; Clinton L Lingren
Original assignee: Digirad Corp
Priority date: 1998-04-24
Filing date: 1999-04-23
Publication date: 2000-07-27
Also published as: AU5896499A; WO1999061880A2; WO1999061880A3

Abstract

An integrated radiation detector system that integrates at least one silicon photodiode detector (2) (with or without a scintillation assembly (1)) with amplifiers (3), interface electronics (4), and radiation shielding into one compact radiation probe assembly. The probe assembly uses relatively low voltages, has relatively few electrical connections (9, 10), is relatively easy to manufacture, and is low-cost and thus disposable. The invention provides a radiation detection probe particularly useful for detecting radionuclides during lymphatic mapping.

Description

INTEGRATED RADIATION DETECTOR PROBE

TECHNICAL FIELD

This invention relates to an integrated radiation detector system for radiation detection probe applications.

BACKGROUND

Nuclear medical imaging systems provide powerful diagnostic and prognostic tools. By designing a radio-pharmaceutical to be preferentially concentrated in an organ in a metabolically meaningful way, very specific information may be obtained about the condition of the organ long before structural changes or defects can otherwise be detected. An advantage of nuclear medical imaging systems is that they permit relatively non-invasive investigation and testing of a variety of organ and tissue functions. Specifically, lymph nodes can now be imaged for diagnostic and prognostic testing of tumor metastasis by lymphatic mapping to detect "sentinel nodes".

Sentinel node biopsy is a less invasive alternative to lymph node dissection to determine metastasis of breast cancer tumors. The principle of sentinel node biopsy is that neoplastic cells detaching from the primary tumor are most likely to be held by the "sentinel node," which is the first lymph node to receive lymph from the involved area and the most likely site of early metastasis. If the sentinel node is free of tumor, it is highly probable that all of the other nodes are free of cancer cells. This knowledge helps the physician in staging the treatment.

Detection of a sentinel node may be achieved by using a gamma ray detection probe intra-operatively to assist surgeons in locating cells tagged with radioactive material (e.g., technetium 99m). From the condition of the sentinel node, axillary lymph node status in almost all patients in whom a sentinel node is identified can be accurately predicted. Thus, in the large majority of patients with breast cancer, lymphoscintigraphy and gamma radiation detection-guided surgery can be used to locate the sentinel node in the axilla and can avoid general resection of lymph nodes, thus substantially reducing trauma and cost.

There have been a number of prior art gamma ray detector probes. However, most designs use a sodium-iodide (NaT) scintillation crystal coupled with a small photo multiplier tube, or a high-Z semiconductor detector (such as CdZnTe or CdTe) as the detection unit (see, e.g., U.S. Patent No. 5,732,704). These designs are large in size and expensive to make. Such probes typically include a limited amount of electronics (typically preamplifiers) integrated within the probe. These designs may require supply voltages as high as hundreds or sometimes thousands of volts. They also require numerous electrical connections.

Because of the cost of the detector, interconnection cables and connectors, all known existing probes are designed to be reusable, thus requiring costly re-sterilization.

Accordingly, the inventor has determined that it would be useful to have a gamma radiation-detecting probe that uses relatively low voltages, has relatively few electrical connections, is relatively easy to manufacture, and is low-cost and thus disposable.

SUMMARY

The invention includes an integrated radiation detector system that integrates at least one silicon photodiode detector (with or without a scintillation assembly) with amplifiers, interface electronics, and radiation shielding into one compact radiation probe assembly. The probe assembly uses relatively low voltages, has relatively few electrical connections, is relatively easy to manufacture, and is low-cost and thus disposable. The invention provides a radiation detection probe particularly useful for detecting radionuclides during lymphatic mapping.

More particularly, each silicon photodiode radiation detector can detect radiation directly or after "down-conversion" of the radiation by means of a scintillation material (either single element or array) mounted to the radiation detector to enhance detection efficiency for high-energy g£imma rays. The radiation detector preferably uses a scintillation assembly that is wavelength-matched to the detector in order to "down-convert" radiation to a wavelength range more efficiently detected by the detector. The radiation detector is preferably connected to a printed circuit board (PCB) on which an application specific integrated circuit (ASIC) with amplification and interface circuits is mounted. A discrete or a hybrid amplifier and interface electronics can also be used. Each radiation detector generates an output signal indicative of an electrical pulse amplitude when the radiation detector is exposed to a radiation event. The probe includes one or more collimators of a high-density material and one or more preamplifiers coupled to the radiation detectors, for amplifying the output signal from each radiation detector. The probe also has a simple connector for connecting the probe to an electronic instrument.

The details of one or more embodiments of the invention are set forth in the accompa- nying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWING

FIG. 1 is a cross-sectional view of a stylized example of one implementation of the invention.

DETAILED DESCRIPTION

Overview

The invention is based on the inventor's realization that substantial benefits can be achieved in a radiation detector probe by utilizing at least one silicon PIN photodiode as the radiation detector element. While a silicon photodiode may be used alone, in a preferred embodiment, the radiation detector element uses a scintillation assembly that is wavelength- matched to a silicon PIN photodiode in order to "down-convert" radiation to a wavelength range more efficiently detected by the photodiode. A preferred scintillation material is thallium-activated cesium iodide (CsI(Tl)), which more closely matches the wavelength detection sensitivity of a silicon PIN photodiode than does sodium iodide (Nal).

Thus, in a typical embodiment, a single high-energy gamma radiation photon interacts in the material of the scintillation assembly and creates multiple low-energy photons. The number of low-energy photons created is proportional to the energy of the incoming high-energy photon. The silicon PIN photodiode detects these low-energy photons and produces an electrical signal proportional to the number of such photons. This electrical signal is electronically amplified, processed, and output to a connector. For economy of implementation, the electronics is preferably embodied in an application specific integrated circuit (ASIC), or a combination of an ASIC with discrete or hybrid amplifier and interface electronic elements. The output from the probe circuitry is typically in the form of a digital signal, although an analog signal (e.g., a frequency modulated signal) may be used if desired. Such circuits are well known in the art. The output connector is typically coupled to a monitoring system having a display or other output element.

Using an ASIC to provide all the amplification and interface circuitry for a radiation detector probe greatly simplifies the probe-to-control monitor interface. Such an ASIC also provides support for a multi-pixel radiation detector in the probe, because an ASIC can provide highly integrated multi-channel electronics.

The result is that the energy of each incoming radiation photon can be transformed to an electronic signal and sent to a monitoring system for display or further processing. Other interface circuits, like switches and display, can be connected to the ASIC to send signals to a control station or to display status information.

Advantages

The invention provides numerous advantages over existing probes, including the following: • A scintillation material that is wavelength-matched to a silicon PIN photodiode provides an optimized solution for wide ranges of radiation ray detection, from gamma rays to beta rays. In particular, CsI(Tl) matches the wavelength sensitivity range of typical silicon PIN photodiodes more closely than Nal (for which the optical response peaks near the blue end of the wavelength spectrum). A silicon PIN photodiode detector may be operated at a voltage of no more than about 70V, and preferably no more than about 20V, and eliminates the need to supply very high voltages to the detector probe. Lower voltages means that less expensive electronic components may be used and less interference of the signal due to power supply interference. €sI(Tl) is less toxic than CdZnTe or CdTe and is thus safer for use in the body and during disposal (e.g., by incineration). CsI(Tl) is easier to shape (for example, into cylinders) than CdZnTe or CdTe, thus lowering cost of manufacture of radiation detector probes. Shaping the scintillator to better match the configuration of the photodiode may result in a smaller outer-diameter probe with the same sensitivity as prior probes (or higher sensitivity with the same diameter as prior probes). Importantly, CsI(Tl) does not exhibit significant piezoelectricity characteristics, unlike CdZnTe or CdTe. Thus, striking or even just moving the probe will not generate a piezoelectric voltage "noise" signal. Further, CsI(Tl) is less fragile than CdZnTe or CdTe, and photodiodes are more rugged than photomultiplier tubes, making a probe in accordance with the invention more durable.

Illustrated Embodiment

FIG. 1 is a cross-sectional view of a stylized example of one implementation of the invention. Shown is a scintillation assembly 1 optically coupled to a silicon PIN photodiode detector 2. The detector 2 may be a single photodiode, or may be a "pixel" array of photodiodes. One embodiment of an array of photodiodes is shown in Gruber et al, "A Discrete Scintillation Camera Module Using Silicon Photodiode Readout of CsI(Tl) Cyrstals for Breast Cancer Imaging", publication LNBL-41034 by Lawrence Berkeley National Laboratory, presented at IEEE NSS/MIC, Nov. 9- 15 1997 and submitted to IEEE Trans. Nucl. Sci. , the teachings of which are hereby incorporated by reference. The scintillation assembly 1 may comprise a single crystal of scintillation material, or multiple crystals of scintillation material matching an array of photodiodes. The scintillation assembly 1 may also include one or more collimators of a high-density material (e.g., lead or tungsten) to limit the field of view of the probe and minimize interference from scattered radiation. As noted above, the preferred scintillation material is CsI(Tl), preferably in a thickness (relative to high-energy photon impingement) range of about 1 mm to about 10 mm. The thickness of the scintillation material will vary with the energy of the photons that are to be captured and downconverted for sensing by the detector 2, but in general should have a thickness optimized to interact with a selected photon energy level. The optimized thickness can be determined from known data relating photon energy to interaction probabilities of the selected scintillation material. Alternatively, an optimum thickness may be determined empirically. For some applications, the silicon PIN photodiode detector 2 may be used without a scintillator, for example, when detecting gamma radiation below 50 keN or beta radiation. In the illustrated embodiment, the output of the detector 2 is coupled to one or more discrete electronics components 3 (e.g., preamplifiers) and/or one or more ASICs 4 that condition the electronic signal. An example of such circuitry is described in allowed U.S. Patent Application No. 08/672,831, entitled SEMICONDUCTOR GAMMA-RAY CAMERA AND MEDICAL IMAGING SYSTEM, filed 6/28/96, and assigned to the assignee of the present invention, the teachings of which are hereby incorporated by reference. The scintillation assembly 1, detector 2, discrete electronics components 3, and

ASICs 4 are preferably mounted as an integrated unit on a printed circuit board (PCB) 5. One or more optional switches 6 may be coupled to the PCB 5 to perform such functions as selection of measurement ranges or modes. These components are preferably mounted within a probe-like housing 7, which is preferably fabricated of a sterilizable, bio-compatible material that provides suitable electronic shielding (and optionally, radiation shielding) surrounding the PCB 5, the components mounted on the PCB 5, and/or the detector 2. A suitable material would be shaped (e.g., extruded) aluminum or steel, or a molded or extruded plastic lined with a conductive coating. A radiation-transparent window 8 (e.g., a bio-compatible plastic) is provided at the distal end of the housing 7 that preferably seals the contents of the housing 7 from body fluids and other contaminants. The probe housing 7 preferably has dimensions suitable for intra-operative use, and preferably in the range of about 10-25 cm in length and about 0.5-25 mm in diameter.

A connector cable 9 connects the electronics on the PCB 5 to a connector element (e.g., plug or socket) 10 located at or outside of the proximal end of the housing 7. The connector element 10 permits signals and electrical power to be coupled between the electronics on the PCB 5 and an external monitor system (not shown). In the preferred embodiment, the connector element 10 is an inexpensive telephone-type socket (e.g., RJl 1 or RJ12 socket).

A number of embodiments of the present invention have been described. Neverthe- less, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the probe may be powered by internal batteries, and thus need no external power source. Accordingly, other embodiments are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. An integrated radiation detector probe, including: (a) a probe housing dimensioned for intra-operative use; (b) a silicon PIN photodiode detector mounted within the probe for converting received photons to an electronic signal; (c) electronic circuitry mounted within the probe and coupled to the silicon PIN photo- diode detector, for conditioning the electronic signal into an output signal; and (d) a connector, coupled to the electronic circuitry and accessible from outside the probe housing, for coupling the integrated radiation detector probe to an external monitor- ing system and transmitting the output signal to such external monitoring system.

2. The integrated radiation detector probe of claim 1 , further including a scintillator assembly optically coupled to the silicon PIN photodiode detector, for downconverting high-energy photons to low-energy photons detectable by the silicon PIN photodiode detector.

3. The integrated radiation detector probe of claim 2, wherein the scintillator assembly is wavelength-matched to the wavelength detection sensitivity of the silicon PIN photo- diode detector.

4. The integrated radiation detector probe of claim 2, wherein the scintillator assembly includes a collimator.

5. The integrated radiation detector probe of claim 2, wherein the scintillator assembly includes thallium-activated cesium iodide as a scintillator.

6. The integrated radiation detector probe of claim 2, wherein the scintillator assembly has a scintillator having a thickness optimized to interact with a selected photon energy level.

7. The integrated radiation detector probe of claim 6, wherein the scintillator has a thickness in the range of about 1 mm to 10 mm.

8. The integrated radiation detector probe of claim 1 , wherein the housing is fabricated of a sterilizable, bio-compatible material.

9. The integrated radiation detector probe of claim 1 , wherein the housing includes elec- tronic shielding.

10. The integrated radiation detector probe of claim 1 , wherein the housing includes radiation shielding.

11. The integrated radiation detector probe of claim 1 , wherein the silicon PIN photodiode detector and the electronic circuitry are mounted on a printed circuit board.

12. The integrated radiation detector probe of claim 1 , wherein the electronic circuitry is implemented in an integrated circuit.

13. The integrated radiation detector probe of claim 1 , wherein the integrated radiation detector probe is sterilizable, bio-compatible, and disposable.

14. The integrated radiation detector probe of claim 1, wherein the silicon PIN photodiode detector is operated at a voltage of no more than about 70 V.

15. The integrated radiation detector probe of claim 14, wherein the silicon PIN photodiode detector is operated at a voltage of no more than about 20V.

16. The integrated radiation detector probe of claim 2, wherein the silicon PIN photodiode detector includes an array of silicon PIN photodiodes.

17. The integrated radiation detector probe of claim 16, further including a scintillator assembly optically coupled to the array of silicon PIN photodiodes, for downconverting high-energy photons to low-energy photons detectable by the array of silicon PIN photo- diodes.

18. The integrated radiation detector probe of claim 1 , wherein the probe housing has dimensions in the range of about 10-25 cm in length and about 0.5-25 mm in diameter.

19. An integrated radiation detector probe, including: (a) a probe housing dimensioned for intra-operative use; (b) a silicon PLN photodiode detector mounted within the probe for converting received photons to an electronic signal; (c) a scintillator assembly mounted within the probe and optically coupled to the silicon PIN photodiode detector, wherein the scintillator assembly is wavelength-matched to the wavelength detection sensitivity of the silicon PLN photodiode detector, for downconverting high-energy photons to low-energy photons detectable by the silicon PIN photodiode detector; (d) electronic circuitry mounted within the probe and coupled to the silicon PIN photo- diode detector, for conditioning the electronic signal into an output signal; and (e) a connector, coupled to the electronic circuitry and accessible from outside the probe housing, for coupling the integrated radiation detector probe to external an external monitoring system and transmitting the output signal to such external monitoring system.

20. The integrated radiation detector probe of claim 19, wherein the scintillator assembly includes a collimator.

21. The integrated radiation detector probe of claim 19, wherein the scintillator assembly includes thallium-activated cesium iodide as a scintillator.