[Investigation of discrepancy between 99mTc-HMPAO and 133Xe rCBF SPECT; a comparative study with X-ray CT findings]

To investigate the discrepancy between 99mTc-hexamethylpropyleneamine oxime (HMPAO) and 133Xe rCBF SPECT, the findings of thirty patients with reasonable rCBF reduction on 133Xe SPECT were compared with HMPAO SPECT and X-ray CT. The subjects did not include the cases of acute and subacute CVD. Both SPECT were performed within two weeks by ring-type dynamic SPECT (HEADTOME, Simadzu, Japan). In comparison between the SPECT findings by 133Xe and 99mTc-HMPAO, the subjects were classified into three groups as follow. Group A: Similar findings in the both SPECT were noted in 6 cases (20%). Group B: Smaller findings on HMPAO SPECT than that by 133Xe were in 11 cases (37%). Group C: No findings of rCBF reduction on HMPAO SPECT were in 13 cases (43%). The rCBF of the lesion measured by 133Xe SPECT in the group C was 24-35 ml/100 g/min. The density of HMPAO in the lesion did not correlate with the rCBF value. Only the severity of CT findings tend to correlate with the density of HMPAO. These results suggest that the reduction of HMPAO density depends directly on some kind of neural injury rather than the rCBF value. The injury may be caused by the flow reduction under the threshold of each neural cell. So the correlation between HMPAO density and actual rCBF might show like sigmoid curve. Then the HMPAO SPECT might directly reflect the regional extraction and fixation ratio, and the reduction of blood flow cause the minute neural-injury in the lesion of moderately reduced rCBF.