Abstract
1347
Objectives Brain death is clinically diagnosed by deep coma, no brainstem reflex, and no spontaneous breathing. No effective CBF associated with residual skull blood flow was found in such patients reported as hollow skull sign with gamma-camera and Tc-99m pertechnetate. We aimed to examine whether zero CBF and 1% residual CBF can be distinguished by means of SPECT with Tc-99m solution.
Methods Hoffman phantom was employed for mimicking zero or 1% CBF brain. Approximately 4% of 740 MBq Tc-99m HMPAO administered accumulated in brain. By assuming brain volume to be 1200ml, brain radioactivity is 24.7 kBq/ml. Gray matter (GM) and white matter (WM) CBF ratio was assumed to be 4:1, and volume ratio to be 1:1, GM and WM radioactivity in normal state (100%CBF) is 31.9 kBq/ml and 17.5 kBq/ml, respectively, after washout correction. In 1% CBF phantom, GM and WM radioactivity is 0.528 kBq/ml and 0.290 kBq/ml, respectively, after washout correction. In zero CBF phantom, cylindrical phantom filled with water was set instead of GM and WM compartments. Mean skull to brain matter radioactivity ratio was 1:2.9 in 10 patients. Therefore, skull radioactivity is 8.56 kBq/ml in both phantoms. To mimic skull attenuation, CuSO4 (42 g) was added to skull compartment solution. The SPECT-CT scanner used was Siemens Symbia-T6.
Results When data acquisition was 30 min, OSEM-based reconstruction with both CT- and Chang-based attenuation correction distinguished between zero and 1% CBF. FBP-based reconstruction showed much noise activity in the water phantom.
Conclusions The present SPECT scanner can visualize tomographic “hollow skull sign” in zero CBF state and detect 1% residual CBF when OSEM-based reconstruction algorism and Tc-99m labeled flow tracers are employed.
Research Support Grant-in-aid for Diagnosis of Brain Death, Ministry of Health, Welfare, and Labor, Japan