Ring-Configured CZT SPECT-CT System: Clinical Experience and Implementation

Since the first introduction of scintillation cameras in the 1950s, scintillation crystals with indirect conversion of gamma rays into an electrical signal have formed the basis for clinical nuclear medicine. The introduction of solid-state cadmium zinc telluride (CZT) detectors enables a direct conversion of gamma rays to signal within the crystal material. CZT detectors are more compact, facilitating smaller and more diverse camera architectures, for example C-shaped dedicated cardiac cameras and, more recently, ring-configured CZT cameras. Studies have shown that such systems demonstrate improved sensitivity and energy resolution compared with scintillation cameras, thereby enabling reduced scan time and/or administered activity. The ring-configured CZT camera is a single-photon computed tomography (SPECT) system with 12 detectors that follow a sweeping motion that can collect data from an entire field of view (FOV). The sweeping motion can be adjusted to a focus acquisition over a smaller FOV to locally boost the signal-to-noise ratio. At the maximal field of view, the sensitivity is similar to conventional two-headed cameras. In smaller patients, such as children, where the 12 detectors can move in a smaller FOV, like brain scans, the sensitivity can increase by a factor of 2 to 4 times that of a conventional camera. When the sweep is adjusted to an even smaller FOV, such as the heart or a single point, the sensitivity approaches the maximal factor of 6. The 360° detector configuration enables dynamic SPECT with frame times down to 1 second, which is very difficult at standard systems. The CZT characteristics, new architecture, camera features and related reconstruction algorithms require an adjustment of calibrations, quality controls and clinical examinations to guarantee safe clinical implementation. Validation into clinical routine requires scan-rescan studies of patients to verify that an equal and, if possible, improved image quality and diagnostic outcome is obtained.