Improved Delineation of Parathyroid Lesions in Patients with Chronic Renal Failure Using Magnified Pinhole Imaging

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...

Parathyroid adenoma localization with 99mTc-sestamibi SPECT/CT

“…Modifications to the technique have included pinhole collimation, which results in superior spatial resolution [9,42], oblique views to increase separation of posteriorly positioned parathyroid adenomas from overlying thyroid tissue, and 3D SPECT imaging, which increases sensitivity [43,44] by increasing the depth of information and removing radioactivity from overlying tissues [43,45,46]. Given the current surgical management strategy using a minimally invasive approach, it is essential to perform preoperative adenoma localization with the highest diagnostic accuracy possible.…”

Endocrine Scintigraphy with Hybrid SPECT/CT

“…Planar images are acquired with static views of the neck as well as the thorax to include the mediastinum. Pinhole collimation results in superior spatial resolution (50,220), and oblique angle views increase the separation of the posteriorly positioned parathyroid adenoma from overlying thyroid tissue. SPECT has superior sensitivity to planar imaging (221,222) improving object contrast, removing overlying tissues and increasing depth information from 3D images (221,223,224).…”

Parathyroid Scintigraphy in Renal Hyperparathyroidism

“…18,19,34 Pinhole imaging has been a standard for optimal thyroid scintigraphy. In our opinion, its role is even more crucial for parathyroid imaging.…”

“…99m Tc-MIBI single-tracer SPECT has higher sensitivity compared to planar imaging with a parallel-holes collimator, but still has lower sensitivity compared to pinhole imaging. 34 …”