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Subtraction SPECT for Parathyroid Scintigraphy Based on Maximization of Mutual Information

¹ Department of Radiological Technology, Sumitomo Hospital, Nakanoshima, Kita-ku, Osaka, Japan; ² Department of Health Sciences, Graduate School of Medical Sciences, Kanazawa University, Kodatsuno, Kanazawa, Japan; ³ Department of Ultrasonic Examination, Sumitomo Hospital, Nakanoshima, Kita-ku, Osaka, Japan; ⁴ Department of Urology, Sumitomo Hospital, Nakanoshima, Kita-ku, Osaka, Japan; and ⁵ Department of Internal Medicine, Sumitomo Hospital, Nakanoshima, Kita-ku, Osaka, Japan

Correspondence: For correspondence or reprints contact: Narihiro Hara, RT, Department of Radiological Technology, Sumitomo Hospital, Nakanoshima, Kita-ku, Osaka, Japan. E-mail: hara-narihiro{at}sumitomo-hp.or.jp

Our objective was to investigate the feasibility of subtraction for SPECT images of ^99mTc-MIBI double-phase parathyroid scintigraphy. Methods: Fourteen patients with hyperparathyroidism were enrolled in the present study. Histopathologically, excised tissue specimens showed hyperplasia in 11 patients and adenoma in 3 patients. Both ultrasonography and ^99mTc-sestamibi (MIBI) SPECT images were obtained from all patients. As standard lines to ensure that patient positioning remained identical between the different phases, we used the cross-marker produced by a pair of laser pointers, the orbitomeatal line, and the vertical midline through the patient's nose. Data processing was performed with software that enables image registration by maximization of mutual information. The results of subtraction SPECT imaging were compared with those of ultrasonography. Results: The registration of double-phase SPECT images was successful in all patients when the salivary glands were excluded from the image reconstruction region. The overall sensitivities of scintigraphy and ultrasonography were 90.9% (40/44) and 70.5% (31/44), respectively, with respective specificities of 83.3% (10/12) and 75.0% (9/12). Scintigraphy and ultrasonography showed accuracies of 92.8% (52/56) and 71.4% (40/56), respectively. Conclusion: The new technique used in the present study allowed the subtraction for SPECT images. The sensitivity of parathyroid lesion detection using this technique was superior to that of ultrasonography.

Key Words: hyperparathyroid; SPECT; subtraction; double-phase imaging; laser pointer