Novel Cadmium Zinc Telluride Based detector General Purpose Gamma Camera: Initial Evaluation and Comparison with a Standard Camera

Objectives To prospectively compare the first of its kind Cadmium Zinc Telluride (CZT) based general purpose gamma camera (CZT-camera), with a standard NaI based camera (NaI-camera) in patients referred for scintigraphic investigations. The CZT-camera (Discovery NM/CT 670 CZT, GE Healthcare) has a pixelated detector of a size of 2.46 mm/pixel and energy resolution of 6.3% while the NaI-camera (Discovery NM/CT 670, GE Healthcare) has an energy resolution of 9.8%.

Methods Nineteen patients (9 men, age range 18 - 84y) who were referred for Nuclear Medicine (NM) imaging procedures as part of their clinical assessment were prospectively recruited. The studies included Tc99m-MDP bone scintigraphy (7), one day, single isotope Tc99m-MIBI myocardial perfusion imaging (MPI) (3), Tc99m thyroid (3), Tc99m-MAA lung (2), Tc99m-DMSA renal (2) and Tc99m-MIBI parathyroid (2) scans. First, the patients underwent the standard scintigraphic procedure according to the specific routine protocol using the dual head NaI-camera (Discovery NM/CT 670, GE Healthcare). Immediately after the completion of the study on the NaI-camera, patients were rescanned with the CZT-camera (Discovery NM/CT 670 CZT, GE Healthcare) using the same acquisition protocol. Images generated by the CZT-camera were reconstructed to be displayed using full and 75% acquisition times. Two readers independently scored all studies using a 5-point scale (1=non-diagnostic to 5=excellent) for perceived image quality and spatial resolution. The scores obtained for the two devices were further compared using the Mann-Whitney test with p<0.05 considered as indicating significant difference.

Results Overall, 29 scans were performed on each device including 18 planar and 11 SPECT studies. The average image quality and spatial resolution scores in the full time CZT-camera studies were 4.83 and 4.83 respectively. These values were significantly higher than the scores obtained with the NaI-camera (4.64 and 4.43, p<0.05). All CZT-camera scores were either higher or equal to NaI-camera scores. Furthermore there was no statistically significant difference in image quality and spatial resolution scores between CZT-camera images obtained at 75% acquisition time as compared to NaI-camera full time studies (4.64, 4.59 vs. 4.64, 4.43 respectively).

Conclusions These preliminary results suggest that the CZT-based general purpose gamma camera provides higher diagnostic performance as compared to the standard NaI-based camera when using the same acquisition parameters. A 25% decrease in acquisition time can be implemented on the CZT-based camera without any compromise in image quality and resolution. Future studies will assess whether time reduction can potentially interchange with lower injected dose.