Determination of conversion factors of SPECT hot images respect to hot objects in bone medium: preliminary study using in house phantom

Abstract

The purpose was to determine conversion factors (CF) of SPECT hot images respect to the original size of hot objects in the bone medium. In house phantom has been made in the form of a cubical acrylic (37cm x 15cm x 15cm) provided with cylindrical channel filled with bovine bone powder with the diameter (1.5; 3.5; 5.4; 7.4 cm). As hot objects, a mixture of bone powder and 99mTc source with various activity and diameter were embedded in filled bone channels. Image acquisitions were carried using Intevo Symbia E Siemens SPECT/CT and LEHR collimator, with surface collimator distance 9.6 cm. There were 6 different in activities and diameter of hot objects in each channel. Conversion factor (CF) was defined as the ratio between FWHM of hot object image profile and the original hot object size. CF value for each diameter channel was varied with the activity and size of the object diameter. The source activities used were 0.1-0.2 mCi and the observed object diameters were 7-12 mm. For hot object size less than resolution stated in SPECT specifications (4 mm), CF values were in the range 1.7-3.4 for 1.5 cm and 3.5 cm channel diameter. For hot objects diameter, 7.5-12 mm, CF value was mostly independent of channel diameters, with the value of (1.1 ± 0.2). This preliminary study informs that CF values of SPECT hot images independent with the size of the host bone medium. Whereas for object diameter ≤ 7.5 mm very relatively higher and influenced by the size of the host bone medium.