Improvement of brain SPECT by stabilization of Tc-99m-HMPAO with methylene blue or cobalt chloride. Comparison with Tc-99m-ECD.
OBJECTIVE
This present study was carried out to investigate whether stabilization of Tc-99m-HMPAO with methylene blue (MB) or cobalt chloride (CC) causes a sensible improvement in image quality and how cerebral to noncerebral activity ratios compare with those of Tc-99m-ECD.


METHODS
30 minutes after preparation 400-600 MBq unstabilized Tc-99m-HMPAO (N = 35 patients), Tc-99m-HMPAO added with MB (N = 24 patients), added with CC (N = 30 patients) or Tc-99m-ECD (N = 28 patients) were injected. Radiochemical stability was measured in vitro with three chromatographical methods. Image quality was assessed quantitatively using two ratios, one of them determined by count densities of brain/scalp (Os), the other one by count densities of brain/nose (QN). In addition, image quality (0 = bad, 3 = excellent) and background activity (0 = high, 3 = no) were visually assessed by three independent observers.


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 only by a few percent during a period of 2 hours after reconstitution (66.8 +/- 9.9 vs. 93.0 +/- 2.5, 91.8 +/- 1.9 and 96.9 +/- 1.4%, p < 0.001). Qs and Qn (m.v. +/- SD) differed significantly between studies using unstabilized 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 using Tc-99m-ECD (4.3 +/- 0.7 and 4.8 +/- 1.4, p < 0.05 and < 0.001). Stabilization with CC or MB resulted in significant higher scoring of image quality and lower scoring of background activity in comparison to that of unstabilized Tc-99m-HMPAO, without reaching the scores obtained with Tc-99m-ECD.


CONCLUSIONS
It is concluded that stabilization of Tc-99m-HMPAO with MB or CC 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 extracerebral activity.
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001921:Brain / Q000000981:diagnostic imaging*; D002561:Cerebrovascular Disorders / Q000000981:diagnostic imaging; D003035:Cobalt; D003545:Cysteine / Q000031:analogs & derivatives*; D003863:Depression / Q000000981:diagnostic imaging; D004355:Drug Stability; D005260:Female; D006801:Humans; D008297:Male; D008751:Methylene Blue; D008875:Middle Aged; D019636:Neurodegenerative Diseases / Q000000981:diagnostic imaging; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; D012535:Scalp; D012680:Sensitivity and Specificity; D012891:Sleep Apnea Syndromes / Q000000981:diagnostic imaging; D019690:Technetium Tc 99m Exametazime; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*