A comparison of three-dimensional-ring CZT and NaI(Tl) single-photon emission computed tomography systems using 99mTc-methoxyisobutylisonitrile in patients with hyperparathyroidism, with concurrent phantom studies.

BACKGROUND: Previous research has shown that cadmium-zinc-telluride (CZT) crystals, as semiconductor detectors, provide higher spatial and energy resolution than thallium-activated sodium iodide [NaI(Tl)] crystals. This study aimed to evaluate the extent to which a full-ring CZT single-photon emission computed tomography/computed tomography (SPECT/CT) system could improve the image quality of 99mTc-methoxyisobutylisonitrile (99mTc-MIBI) parathyroid imaging, as well as its potential to enhance diagnostic accuracy and optimize imaging protocols.

METHODS: Two phantoms were acquired: (I) a uniform phantom to obtain the calibration factor; and (II) a National Electrical Manufacturers Association (NEMA) International Electrotechnical Commission (IEC) phantom containing different-sized spheres to compare the contrast-to-noise ratio (CNR) and recovery coefficients (RCs). A total of 85 patients who were diagnosed with hyperparathyroidism (HPT) were enrolled in this study. Two hours after injecting 99mTc-MIBI, delay-phase parathyroid scanning was performed sequentially on NaI(Tl) SPECT/CT in 8 minutes and full-ring CZT SPECT/CT in 6 minutes. List-mode data were used to reconstruct 3-minute CZT SPECT/CT images. A 10-mm diameter volume of interest (VOI) was used to delineate the lesion and reference regions. The coefficient of variation (CV) and CNR were calculated to quantitatively compare image quality and lesion contrast. The standardized uptake values (SUVs) of the lesions were calculated from the images acquired using the full-ring CZT SPECT/CT. Clinical and pathology information were collected through standardized pre-procedural medical history inquiry and subsequent patient follow-up.

RESULTS: The NaI(Tl) system exhibited a lower CNR than the full-ring CZT system when using the same injected activity and their respective recommended NEMA IEC phantom parameters. For the images acquired with the full-ring CZT system, those reconstructed using block sequential regularized expectation maximization (BSREM) 20i10s exhibited a higher CNR than those reconstructed using OSEM 4i10s. Compared with OSEM 20i10s, although the difference in the CNR was not statistically significant, the spheres appeared visually clearer, which may be attributed to a more uniform background (CV: OSEM 20i10s, 19.9%; BSREM 20i10s, 17.9%). In the clinical patients, all the three imaging conditions, including 8-minute NaI(Tl), 3-minute CZT, and 6-minute CZT imaging, identified the same positive lesions upon visual assessment. In the image quality comparison, the full-ring CZT system with the standard 6-minute imaging sequence demonstrated better performance than the NaI(Tl) system to varying degrees. Specifically, the CV was lower for the CZT system based on the thyroid (P=0.022) and mediastinal blood pool (P<0.001), but not significantly different based on the cervical muscles (P=0.599). Similarly, the CNR was higher for the CZT system when using the thyroid as the reference region (P=0.033) and mediastinal blood pool as the reference region (P=0.001), but not significantly different when using the cervical muscles as the reference region (P=0.223). The CNR values from the 3-minute CZT imaging were comparable to those from the standard 6-minute CZT imaging (thyroid, P=0.956; cervical muscles, P=0.265; mediastinal blood pool, P=0.182).

CONCLUSIONS: The full-ring CZT SPECT/CT system exhibited a higher CNR than the NaI(Tl) crystal-based system in the delay-phase scan of 99mTc-MIBI parathyroid imaging when using the thyroid and mediastinal blood pool as references. Additionally, it enables acquisition within a reduced time frame while maintaining comparable diagnostic sensitivity.