No abstract

99m Tc-sestamibi dual-phase scintigraphy is currently established for parathyroid localization. However, the imaging technique is not standardized, and the role of the pinhole collimator, especially, is not fully recognized in the imaging protocol. The aim of this study was to check whether the use of a pinhole collimator in parathyroid scintigraphy would enhance lesion detectability and delineation more than does a parallel-hole collimator or SPECT in patients with secondary hyperparathyroidism due to chronic renal failure with a mixed pattern of abnormalities. Methods: Thirty-five patients referred for a parathyroid scan were included. Imaging was performed at 10 min and 2 h after injection of 925 MBq (25 mCi) of 99m Tc-sestamibi using both a pinhole collimator and a high-resolution parallelhole collimator fitted to a scintillation camera. SPECT was also performed at 1.5 h after injection. The images were reviewed by 2 experienced nuclear medicine physicians, and the results were analyzed. In addition, the contrast of visualized lesions was evaluated. Results: Twenty-three patients (65.7%) had abnormal scan findings. The McNemar test revealed better detection of parathyroid lesions using pinhole imaging than with planar parallel-hole imaging and SPECT (P , 0.001 and P , 0.03, respectively). Both observers showed good agreement in evaluating different imaging techniques (k 5 0.76). Observers were in favor of pinhole imaging because SPECT suffered from noise. Lesion contrast was significantly higher in pinhole imaging than in parallel-hole imaging and SPECT (P , 0.05), with a 16% and 11% improvement in contrast, respectively. Conclusion: Pinhole imaging better delineates and detects lesions in parathyroid scintigraphy than does parallel-hole imaging and SPECT. Pinhole imaging increases confidence in image interpretation because of high lesion contrast and better magnification and resolution. The use of this technique is therefore recommended as part of the routine imaging protocol for 99m Tc-sestamibi parathyroid scintigraphy. Dual -phase scintigraphy using 99m Tc-sestamibi is an established procedure for detection and localization of parathyroid lesions in patients in whom the diagnosis of hyperparathyroidism has been confirmed (1-3).The mechanism of 99m Tc-sestamibi uptake is related to its chemical nature as a lipophilic cation diffusing passively into the cell and localizing more preferentially in the mitochondria. The main attribute of this agent in the context of parathyroid imaging is that it demonstrates slower washout from the functionally active parathyroid lesions than from adjacent thyroid tissue, thus permitting detection of parathyroid abnormalities by showing differential clearance over time-the so-called single-isotope dual-phase technique. In practice, early and late images are obtained after intravenous injection of the tracer, making this technique simple, easy to perform, and superior to the earlier technetium-thallium subtraction method (1,2,4).A review of 99m Tc-sestamibi methodology, howev...

A significant improvement in image quality can be achieved by simply applying different window widths over the different photopeaks. Our results indicated that two photopeaks with optimized window widths can significantly outperform three windows in terms of spatial and contrast resolution and lesion detectability with a relatively negligible reduction of count sensitivity.

No abstract