Improvement of brain SPECT by stabilization of Tc-99m-HMPAO with methyleneblue or cobalt chloride - Comparison with Tc-99m-ECD

Aim: This present study was carried out to investigate whether stabilizatio n of Tc-99m-HMPAO with methylene blue (MB) or cobalt chloride (CC) causes a sensible improvement in image quality and how cerebral to noncerebral acti vity ratios compare with those of Tc-99m-ECD. Methods: 30 minutes after pre paration 400-600 MBq unstabilized Tc-99m-HMPAO (N = 35 patients), Tc-99m-HM PAO added with MB (N = 24 patients), added with CC (N = 30 patients) or Tc- 99m-ECD (N = 28 patients) were injected. Radiochemical stability was measur ed in vitro;with three chromatographical methods. Image quality was assesse d quantitatively using two ratios, one of them determined by count densitie s of brain/scalp (Q(S)), the other one by count densities of brain/nose (Q( N)) In addition, image quality (0 = bad, 3 = excellent) and back-ground act ivity (0 = high, 3 = no) were visually assessed by three independent observ ers. Results: In contrast to unstabilized Tc-99m-HMPAO the integrity of the complexes of MB-Tc-99m-HMPAO, CC-Tc-99m-HMPAO and Tc-99m-ECD decreased onl y by a few percent during a period of 2 hours after reconstitution (66.8 +/ - 9.9 vs. 93.4 +/- 2.5 91.8 +/- 1.9 and 96.9 +/- 1.4%, p <0.001). Q(s) and Q(n) (m.v. +/- SD) differed significantly between studies using unstabilize d Tc-99m-HMPAO (3.0 +/- 0.4 and 2.1 +/- 0.3), MB-Tc-99m-HMPAO (3.4 +/- 0.4 and 2.3 +/- 0.3) CC-Tc-99m-HMPAO (3.6 +/- 0.6 and 2.6 +/- 0.4) and those us ing Tc-99m-ECD (4.3 +/- 0.7 and 4.8 +/- 1.4; p < 0.05 and < 0.001). Stabili zation with CC or MB resulted in significant higher scoring of image qualit y and lower scoring of background activity in comparison to that of unstabi lized Tc-99m-HMPAO, without reaching the scores obtained with Tc-99m-ECD. C onclusions: It is concluded that stabilization of Tc-99m-HMPAO with MB or C C definitely improves image quality in rCBF-SPECT, without reaching that of Tc-99m-ECD. Improvement of image quality results from the reduction of the amount of decomposition products that contribute to considerable extracere bral activity.