What do medical imaging and astronomy have in common? Whether it is detecting tumors or observing colliding neutron stars, both fields can benefit from the same sensor technology. When observing radiation in the MeVband (0.1-100 MeV) from celestial sources, one faces challenges like low flux, limited interaction probability, three energy loss processes, and a high background radiation rate. Present MeV-band observatories suffer from poor sensitivity, and new state-of the-art detector technology will be a key contributor to improve sensitivity of future observatories. The detector group at DTU Space has developed a 3D CdZnTe drift strip detector technology to meet the demands of future high-energy detectors. This advancement also shows potential application for emerging Low Dose Molecular Breast Imaging (LD-MBI) systems for breast cancer diagnosis. In this study, we present the results of the novel large area 3D CZT drift strip detectors (4×4×0.5 cm3) developed in a collaboration between DTU Space and Kromek. We find the spatial resolution of these modules to be < 0.6mm in the x- and z-axis, and we measure the spectral resolutions to be < 7% FWHM at 122 keV, < 1.4% FWHM at 661.6 keV, and 1% FWHM above 1460 keV.
PURPOSE
Pixelated CdZnTe (CZT) detector arrays are used in molecular imaging applications that can enable precision medicine, including small-animal SPECT, cardiac SPECT, molecular breast imaging (MBI), and general purpose SPECT. The interplay of gamma camera, collimator, gantry motion, and image reconstruction determines image quality and dose-time-FOV tradeoffs. Both dose and exam time can be minimized without compromising diagnostic content.
METHODS
Integration of pixelated CZT detectors with advanced ASICs and readout electronics improves system performance. Because historically CZT was expensive, the first clinical applications were limited to small FOV. Radiation doses were initially high and exam times long. Advances have significantly improved efficiency of CZT-based molecular imaging systems and the cost has steadily declined. We have built a general purpose SPECT system using our 40 cm x 53 cm CZT gamma camera with 2 mm pixel pitch and characterized system performance.
RESULTS
Compared to NaI scintillator gamma cameras: intrinsic spatial resolution improved from 3.8 mm to 2.0 mm; energy resolution improved from 9.8% to <4 % at 140 keV; maximum count rate is <1.5 times higher; non-detection camera edges are reduced ~3-fold. Scattered photons are greatly reduced in the photopeak energy window; image contrast is improved; and the optimal FOV is increased to the entire camera area.
CONCLUSION
Continual improvements in CZT detector arrays for molecular imaging, coupled with optimal collimator and image reconstruction, result in minimized dose and exam time. With CZT cost improving, affordable whole-body CZT general purpose SPECT is expected to enable precision medicine applications.
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