[^99mTc]Tc-Sestamibi/[^99mTc]NaTcO₄ Subtraction SPECT of Parathyroid Glands Using Analysis of Principal Components

The aim of the study was to validate a new method for semiautomatic subtraction of [^99mTc]Tc-sestamibi and [^99mTc]NaTcO₄ SPECT 3-dimensional datasets using principal component analysis (PCA) against the results of parathyroid surgery and to compare its performance with an interactive method for visual comparison of images. We also sought to identify factors that affect the accuracy of lesion detection using the two methods. Methods: Scintigraphic data from [^99mTc]Tc-sestamibi and [^99mTc]NaTcO₄ SPECT were analyzed using semiautomatic subtraction of the 2 registered datasets based on PCA applied to the region of interest including the thyroid and an interactive method for visual comparison of the 2 image datasets. The findings of both methods were compared with those of surgery. Agreement with surgery was assessed with respect to the lesion quadrant, affected side of the neck, and the patient positivity regardless of location. Results: The results of parathyroid surgery and histology were available for 52 patients who underwent [^99mTc]Tc-sestamibi/[^99mTc]NaTcO₄ SPECT. Semiautomatic image subtraction identified the correct lesion quadrant in 46 patients (88%), the correct side of the neck in 51 patients (98%), and true pathologic lesions regardless of location in 51 patients (98%). Visual interactive analysis identified the correct lesion quadrant in 44 patients (85%), correct side of the neck in 49 patients (94%), and true pathologic lesions regardless of location in 50 patients (96%). There was no significant difference between the results of the 2 methods (P > 0.05). The factors supporting lesion detection were accurate positioning of the patient on the camera table, which facilitated subsequent image registration of the neck, and, after excluding ectopic parathyroid glands, focusing detection on the thyroid ROI. Conclusion: The results of semiautomatic subtraction of [^99mTc]Tc-sestamibi/[^99mTc]NaTcO₄ SPECT using PCA had good agreement with the findings from surgery as well as the visual interactive method, comparable to the high diagnostic accuracy of [^99mTc]Tc-sestamibi/[¹²³I]NaI subtraction scintigraphy and [¹⁸F]fluorocholine PET/CT reported in the literature. The main advantages of semiautomatic subtraction are minimum user interaction and automatic adjustment of the subtraction weight. Principal component images may serve as optimized input objects, potentially useful in machine-learning algorithms aimed at fully automated detection of hyperfunctioning parathyroid glands.