Technetium-99m-HMPAO, technetium-99m-ECD and iodine-123-IMP cerebral blood flow measurements with pharmacological interventions in primates.
Technetium-99m-bicisate ethyl cysteinate dimer (ECD) presents a different pattern from cerebral blood flow (CBF) in the subacute phase of cerebral infarction, as measured by PET, perhaps due to lack of oxygen and enzyme activity; this pattern is contrary to that of hexamethyl-propyleneamine oxime (HMPAO) but similar to that of N-isopropyl-[123I]beta-iodoamphetamine ([123I]IMP). This study explores possible CBF differences among HMPAO, ECD and IMP, with various relevant drug interventions.


METHODS
Anesthetized adult baboons were used in these SPECT studies. Four studies (n = 6 baboons for each study), one control study and three intervention studies involving intravenous acetazolamide, nimodipine infusion and intramuscular sumatriptan, were followed with 99mTc-HMPAO, 99mTc-ECD and [123I]IMP. The split-dose method was used as follows. For each tracer, intervention data from the second SPECT (SPECT-2) after the second tracer injection (444 MBq) reflected a change in CBF with respect to the baseline SPECT (SPECT-1) data from the initial injection (222 MBq). These changes as a ratio, R (R = SPECT-2/SPECT-1), for each study, and the R values for each tracer were compared to R values from the corresponding control studies, yielding a quantitative estimate of drug effects.


RESULTS
There were no significant differences (p > 0.05) between HMPAO and ECD for the control, acetazolamide and sumatriptan studies, but there was indeed a difference between the two for the nimodipine study, indicating a nimodipine-dependent underestimation of CBF with ECD (and also with IMP), with respect to HMPAO. A further significant difference was that larger CBF increases were observed with acetazolamide, as measured with [123I]IMP.


CONCLUSIONS
This is a crucial observation for the clinical interpretation of CBF SPECT data and should direct the choice of tracer for a specific examination.
Dormehl
I C
IC
AEC Institute for Life Sciences, University of Pretoria, South Africa.
Oliver
D W
DW
Langen
K J
KJ
Hugo
N
N
Croft
S A
SA
D000086:Acetazolamide / Q000494:pharmacology; D000662:Amphetamines; D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002560:Cerebrovascular Circulation / Q000187:drug effects* / Q000502:physiology; D003545:Cysteine / Q000031:analogs & derivatives*; D004347:Drug Interactions; D007457:Iodine Radioisotopes; D020367:Iofetamine; D008297:Male; D009553:Nimodipine / Q000494:pharmacology; D015609:Organotechnetium Compounds; D010215:Papio; D019275:Radiopharmaceuticals; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D018170:Sumatriptan / Q000494:pharmacology; D019690:Technetium Tc 99m Exametazime; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
D000662:Amphetamines; D002121:Calcium Channel Blockers; D007457:Iodine Radioisotopes; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; D017366:Serotonin Receptor Agonists; D019690:Technetium Tc 99m Exametazime; D009553:Nimodipine; D018170:Sumatriptan; D020367:Iofetamine; C059659:technetium Tc 99m bicisate; D003545:Cysteine; D000086:Acetazolamide