Evaluation of a small cadmium zinc telluride detector for scintimammography

Abstract

The purpose of this study was to evaluate a small semiconductor-based gamma camera that may have applications in scintimammography.

Methods: A small cadmium zinc telluride (CZT) detector was evaluated. The detector had a field of view of 20 x 20 cm with detector elements of 2.5 x 2.5 mm in size. Both short-bore (35 mm) and long-bore (50 mm) collimators, matched to the geometry of the detector elements, were evaluated. The imaging performance of the CZT detector was compared with that of a conventional gamma camera equipped with all-purpose and ultra-high-resolution collimators. The performance of both systems with respect to breast imaging was evaluated using a water tank containing small glass spheres, 1.8-9.8 mm in diameter. The effects of variations in breast thickness, tumor depth, and tumor-to-background ratio were all simulated in this phantom model. Total counts per image were adjusted to approximate the count density observed in clinical scintimammographic studies.

Results: Sensitivity of the CZT detector was 76% that of the equivalent NaI system. The system demonstrated excellent integral uniformity. The energy resolution of the CZT system was 6.5% for (99m)Tc. Spatial resolution with the long-bore collimator was superior to that of a conventional large field-of -view gamma camera equipped with an ultra-high- resolution collimator, over the range 0-6 cm from the collimator face. A blinded review of breast phantom images showed that small spheres (< or =7 mm in diameter) were better seen and had a better tumor-to-background ratio with the CZT system than with the conventional gamma camera.

Conclusion: A small CZT detector offers superior performance to a conventional gamma camera and should permit reliable detection of breast tumors <1 cm in size.