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A quantitative approach to technetium-99m ethyl cysteinate dimer: a comparison with technetium-99m hexamethylpropylene amine oxime Abstract. To develop non-invasive regional cerebral blood flow (rCBF) measurements using technetium-99m ethyl cysteinate dimer (99mTc-ECD) and single-photon emission tomography (SPET), the same graphical analysis as was described in our previous reports using technetium-99m hexamethylpropylene amine oxime (99mTc-HMPAO) was applied to time-activity data for the aortic arch and brain hemispheres after intravenous injection of 99mTc-ECD. Hemispherical brain perfusion indices (BPI) for 99mTc-ECD showed a highly significant correlation (n = 22, r = 0.935, P = 0.0001) with those for 99mTc-HMPAO in 11 patients who underwent both tracer studies. Using both linear regression line equations between 99mTc-ECD BPI and 99mTc-HMPAO BPI and between 99mTc-HMPAO BPI and mean cerebral blood flow (CBF) values obtained from a xenon-133 inhalation SPET method in a previous study, 99mTc-ECD BPI was converted to 133Xe CBF values (y = 2.60x + 19.8). Then raw SPET images of 99mTc-ECD were converted to rCBF maps using Lassen's correction algorithm. In this algorithm, the correction factor tx was fixed to 1.5, 2.6 and infinite. In the comparison of rCBF values for 99mTc-ECD SPET with those for 99mTc-HMPAO SPET in 396 regions of interest in the aforementioned 11 patients, the fixed correction factor tx of 2.6 gave nearly the same rCBF values for 99mTc-ECD (50.1 -+ 16.9 ml/100 g/min, mean ___ SD) as for 99mTc-HMPAO (49.9 + 17.3 ml/100 g/rain). In conclusion, the same non-invasive method as has been used in 99mTc-HMPAO studies is applicable to a 99mTc-ECD study for the measurement of rCBF without any blood sampling.Key words: Technetium-99m ethyl cysteinate dimer -Technetium-99m hexamethylpropylene amine oxime -Single-photon emission tomography -Regional cerebral blood flow Eur J Nucl Med (1995) 22:633-637

A non-invasive, simple method for the quantitative evaluation of brain perfusion is presented using intravenous radionuclide angiography with technetium-99m hexamethylpropylene amine oxime (99mTc-HM-PAO). Graphical analysis was employed for the evaluation of the unidirectional influx constant (ku) of the tracer from the blood to the brain. The ku values were standardized to provide objective and comparable values, brain perfusion indices (BPI), among studied subjects by setting the ratio of ROIbrain size to ROIaorta size at 10. The whole-brain BPI values for the normal control subjects showed a significant negative correlation with advancing age (r = -0.632, P = 0.0204, n = 13). The mean of the whole-brain BPI of 7.0 (SD = 1.4) in 20 patients with cerebrovascular disorders was significantly lower than that of 10.6 (SD = 1.5) in 13 normal control subjects. The BPI measurements showed only minimal intra- and interobserver variability. Changes of the ratio of ROIaorta size and ROIbrain size did not significantly influence the BPI values. Hemispherical BPI values in 19 subjects (n = 38) showed highly significant correlations with the hemispherical mean cerebral blood flow values obtained from Xenon-133 single photon emission tomography (SPET) (r = 0.926, P = 0.0001 for the early picture method and r = 0.932, P = 0.0001 for the sequential picture method). This technique is easy to apply as an adjunct to SPET and may be helpful in the quantitative evaluation of brain perfusion in routine clinical studies.

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The previously reported method for quantitative measurements of whole-brain or hemispheric-brain perfusion using technetium-99m hexamethylpropylene amine oxime (HMPAO) radionuclide angiography is now further developed so that regional cerebral blood flow (rCBF) can be measured. Lassen's correction algorithm is used for the linearization of a curve-linear relationship between the radioactivity in the brain and blood flow as seen with single-photon emission tomography (SPET) images. In this algorithm, the cerebral hemisphere was chosen as the reference region and the correction factor alpha was adapted to rCBF in the reference region. This new method of measuring CBF from SPET has been validated in 33 normal subjects and 22 patients with cerebrovascular disease. Regional CBF values in 20 brain regions of the normal subjects were in good agreement with reported values measured by other methods. Regional CBF in the frontal cortex was greater than that in the temporal, parietal or occipital cortex for the entire age range. This hyperfrontal perfusion tended to be less pronounced with advancing age. Seventeen patients with unilateral brain infarction showed significantly lower rCBF than normal subjects. The infarct core showed a low rCBF value of 11.1 ml/100 g/min on average. An increase in rCBF after acetazolamide administration was observed and measured with this method in five patients with unilateral occlusive vascular pathology. These results suggest that this non-invasive method (without any blood sampling) permits the routine measurement of rCBF from HMPAO SPET tomograms of blood flow.