骨等価溶液を用いた骨SPECT評価用ボディファントムの開発

摘要

核医学分野で使用されるファントムは，検査技術の改善や技術的精度の検証に極めて有用であり，それぞれの検査に対応する薬物動態や解剖学的な特徴が必要とされる.なかでも心筋シンチグラフィ，脳血流シンチグラフィなどのファントムは種々の目的に応じて比較的早い段階から市販され，多くの研究成果によって技術的なエビデンスの構築に貢献している.%We developed a custom-designed phantom for bone single photon emission computed tomography (SPECT)-specific radioactivity distribution and linear attenuation coefficient. The aim of this study was to evaluate the accuracy of the phantom. The lumbar phantom consisted of the trunk of a body phantom (background) containing a cylinder (vertebral body), a sphere (tumor), and a T-shaped container (processus). The vertebral body, tumor, and processus phantoms contained a K_2HPO_4 solution of bone equivalent density and 50, 300 and 50 kBq/mL of ~(99m)Tc, respectively. The body phantom contained 8 kBq/mL of ~(99m)Tc solution. SPECT images were acquired using low-energy high-resolution collimation, a 128 × 128 matrix and 120 projections over 360° with a dwell time of 15 sec/view × 4 times. Thereafter, CT images were acquired at 130 kV and 70 ref mAs using adaptive dose modulation. The SPECT data were reconstructed with ordered subset expectation maximization with three-dimensional, scatter, and CT-based attenuation correction. Count ratio, linear attenuation coefficient (LAC), and full-width at half-maximum (FWHM) were measured. Count ratios between the background, the vertebral body, and the tumor in SPECT images were 463.8: 2888.0: 15150.3 (1: 6.23: 32.7). The LAC of the background and vertebral body in the CT-derived attenuation map were 0.155 cm~(-1) and 0.284 cm~(-1), respectively, and the FWHM measured from the processus was 15.27 mm. The precise counts and LAC indicated that the phantom was accurate and could serve as a tool for evaluating acquisition, reconstruction parameters, and quantitation in bone SPECT images.