Cadmium zinc telluride (CdZnTe, or CZT) is a room-temperature semiconductor radiation detector that has been
developed in recent years for a variety of applications. CZT has been investigated for many potential uses in medical
imaging, especially in the field of single photon emission computed tomography (SPECT). CZT can also be used in
positron emission tomography (PET) as well as photon-counting and integration-mode x-ray radiography and computed
tomography (CT). The principal advantages of CZT are 1) direct conversion of x-ray or gamma-ray energy into
electron-hole pairs; 2) energy resolution; 3) high spatial resolution and hence high space-bandwidth product; 4) room
temperature operation, stable performance, high density, and small volume; 5) depth-of-interaction (DOI) available
through signal processing. These advantages will be described in detail with examples from our own CZT systems. The
ability to operate at room temperature, combined with DOI and very small pixels, make the use of multiple, stationary
CZT "mini-gamma cameras" a realistic alternative to today's large Anger-type cameras that require motion to obtain
tomographic sampling. The compatibility of CZT with Magnetic Resonance Imaging (MRI)-fields is demonstrated for
a new type of multi-modality medical imaging, namely SPECT/MRI. For pre-clinical (i.e., laboratory animal) imaging,
the advantages of CZT lie in spatial and energy resolution, small volume, automated quality control, and the potential for
DOI for parallax removal in pinhole imaging. For clinical imaging, the imaging of radiographically dense breasts with
CZT enables scatter rejection and hence improved contrast. Examples of clinical breast images with a dual-head CZT
system are shown.
The interest in the use of CdZnTe room-temperature, solid-state detectors for Nuclear Medicine applications continues to grow. Efforts are underway at several companies and institutes to develop CdZnTe detector systems to compete with existing scintillator-based Large Field of View (LFOV) gamma cameras. eV PRODUCTS is focusing on the development of Small Field of View (SFOV) gamma cameras using monolithic CdZnTe detector arrays coupled to custom designed, low noise analog read-out electronics. Electronic noise in the ASIC's has been minimized, and is typically less than 100 e- rms (0pF). The detector readout system has the capability to perform automatic energy calibration, gain setting and discrimator level setting, along with a comprehensive self-diagnostic routine. The complete integrated unit includes a bias voltage generator, counters and communication control. A first prototype 256-channel device has been developed and constructed, with pixel dimensions of 1.8 x 1.8 mm2, on a 34 x 34 x 5mm3 monolithic CdZnTe detector. Results obtained from this system will be presented, showing both the energy resolution and uniformity data for several arrays. The energy resolution has been demonstrated to be 3-5% FWHM 140 keV, with photopeak efficiencies of 70-80%.
A linear CdZnTe pad detector array with approximately 1 mm2 pad area has been developed. The detector has a wide energy range from about 20 to 200 keV. To read out these detector arrays, a fast, low-noise monolithic mixed signal ASIC chip has been developed. A prototype x-ray imaging system consisting of the CdZnTe detector array and the monolithic ASIC chip has been fabricated and tested. In this system, the detectors are abutted against each other to form an approximately 1 m long linear array. The system has been used to take preliminary scanned images of complex objects at various energies. New results from this system will be presented.
Recently, much has appeared in the literature concerning methods to improve the resolution and photopeak efficiency of CdZnTe radiation detectors operating at or around ambient temperature. THese methods generally involve either the use of modified electrode structures or pulse processing techniques, both of which add complexity, and hence cost, to the production and operation of such devices. In this paper, we will report on results obtained with a simpler, modified two-terminal device. The detector structure combines a planar anode with an extended surface cathode, and relies on a standard, single channel preamplifier/shaping amplifier system. The results obtained demonstrate that the charge collection efficiency of the device, as shown by the Peak- to-Valley ratio, is significantly improved when compared to the standard planar geometry, especially at higher photon energies.
Conference Committee Involvement (1)
Penetrating Radiation Systems and Applications V
7 August 2003 | San Diego, California, United States
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