Veriton Multi-CZT Detector SPECT/CT System Acceptance Testing

Objectives: The Veriton (Spectrum Dynamics, Israel) is a new generation SPECT/CT system comprising 12 individual Cadmium Zinc Telluride (CZT) detectors, coupled with a conventional CT system. The purpose of this study is to report our initial experiences in acceptance testing and validation of this new technology.

Methods: The Veriton system contains 12 independent detector arms 4 x 32 cm in size arranged in a circular pattern around the imaging table. Each detector is equipped with a tungsten collimator and can move in a radial direction and also swivel over a 180^o arc. The gantry has a rotational range of 25^o. The system is capable of imaging energies up to 200 keV. Acceptance testing of this system is unique as many NEMA tests cannot be applied to this design. Here, we describe the quality control tests that can be performed, their purpose, and performance measurements. Daily QC was performed with a provided Co-57 line source (45 cm) mounted on a jig arm to suspend the source in air in the center of the field of view. Focused scanning of this source provides information on detector uniformity, detector registration, energy resolution, and system sensitivity. A special application allowed assessment of high count rate performance and dead time loss. An additional tool was available to check if activity in the line source was uniform along its length. Multi-bed alignment was checked by repeatedly repositioning a line source on the imaging table while the system performed a whole body SPECT study. The Jaszczak phantom was imaged with both Tc-99m and In-111 (using only they 171 keV peak) as an overall determinant of image quality. A total of 32 Mcts were acquired as per ACR recommendation.

Results: The system demonstrated good detector uniformity, defined as regional homogeneity >90% and global homogeneity >85% across the 12 detectors. Energy resolution was 6%. System sensitivity was measured at 2581 cts/min/uCi, which is an order of magnitude higher than that of a conventional dual-detector system. High count rate performance exceeded 1.9 Mcts/sec. Images of the Jaszczak phantom demonstrated excellent resolution with good visualization of all cold rods (4.8 to 12.7 mm) and spheres (9.5 to 31.8 mm. Figure 1 compares images of the cold rod section of the Jaszczak phantom obtained on the Veriton with comparable images obtained on a conventional dual-detector SPECT/CT system.

Conclusions: The Veriton system represents the next generation in conventional SPECT/CT imaging, with sensitivity and resolution comparable to that observed with modern PET/CT systems. The improved sensitivity allows rapid whole body imaging (<20 minutes). The combination of improved spatial resolution and sensitivity is expected to yield improved diagnostic sensitivity and accuracy, although confirmatory studies are underway. A current limitation of this technology is that the CZT detectors, collimation and detector shielding are optimized for Tc-99m. While higher energy isotopes such as In-111, Lu-177, etc. can be imaged, this will be at a lower sensitivity compared to Tc-99m, and will require correction for high energy penetration through the shielding and collimation.

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