Assessment of the arterial input curve for [99mTc]-d,l-HM-PAO by rapid octanol extraction.
The in vitro conversion of the lipophilic molecule [99mTc]-d,l-hexamethylpropyleneamine oxime [( 99mTc]-d,l-HM-PAO) to a hydrophilic form was studied in saline, plasma, and blood at 37 degrees C by paper chromatography and by octanol extraction. The octanol:saline ratio was 79.9. From this value and the corresponding octanol: plasma and octanol:blood partitioning values, an estimate of the transport of the lipophilic compound by various components of blood was made: 20% is carried in hemoglobin, 53% by the plasma proteins and 27% by the water phases of the red blood cell and plasma. Octanol extraction provided a rapid method for measuring the radiochemical purity (RCP) of lipophilic [99mTc]-d,l-HM-PAO. In saline, the RCP declined with a half-life of more than 1 h. In human plasma and whole blood, the conversion of [99mTc]-d,l-HM-PAO was biexponential due to the differences in the conversion rates of the d and l isomeric forms. The initial half-life representing the conversion rate of the l form was 1.7 min in blood and 1.4 min in plasma, while the conversion half-life of the d form was 7.4 and 24.4 min, respectively. In vivo, the RCP of arterial blood sampled after an i.v. bolus injection showed an initial peak value of 75% (68-79%) during the initial, first passage of the bolus. It declined to approximately 35% (29-40%) after 1.5 min and reached very low levels (about 1%) at 6 to 10 min. Quantitative measurements of cerebral blood flow using [99mTc]-d,l-HM-PAO necessitates a rapid method for RCP determination in arterial blood such as the one described here.
Andersen
A R
AR
Department of Neurology, Rigshospitalet, Copenhagen, Denmark.
Friberg
H
H
Lassen
N A
NA
Kristensen
K
K
Neirinckx
R D
RD
D001158:Arteries / Q000378:metabolism*; D002845:Chromatography; D000442:Octanols / Q000032:analysis*; D009942:Organometallic Compounds / Q000032:analysis* / Q000378:metabolism; D010091:Oximes / Q000032:analysis* / Q000378:metabolism; D012995:Solubility; D013667:Technetium / Q000032:analysis* / Q000378:metabolism; D019690:Technetium Tc 99m Exametazime
D000442:Octanols; D009942:Organometallic Compounds; D010091:Oximes; D019690:Technetium Tc 99m Exametazime; D013667:Technetium