Evaluation of the head attenuation compensation using an artificaial bone phantom

Recently, the evaluation of regional cerebral blood flow (rCBF) measured by single photon emission computed tomography (SPECT), has been developed. It is very important to make an effort to improve SPECT resolution and to differentiate the radioactive concentration in clinical use. It is related to the scatter and attenuation compensation. We evaluated the head attenuation conpensation using Chang method, about which were the SPECT without triple energy window (TEW), the one with TEW, and the one with TEW and the correction map ( ti -map) using Tc-99m gamma ray transmission computed tomography (TCT). An artificial bone phantom was filled with water and I-123-IMP solution (37 MBq) in the inner phase and the iodine solution (concentration: 0, 126, 300 mgl/m1) in the outer phase. The increase of iodine makes the more decrease of SPECT counts of the edge than the center of phantom. Thus, the value of attenuation coefficent for water to satisfy the uniformity in the phantom is less than the theoritical value of 0.146. This effect caused under-estimation of quantitative attenuation compensation and the inclination of radioacitve concentration line was lower