T. Waelbers; K. Peremans; S. Vermeire; K. Piron; I. Polis
Introduction
In dogs, the regional cerebral blood flow (rCBF), which is a measure for the regional brain activity, can be measured with single photon emission computed tomography or SPECT with the use of the perfusion tracer Technetium 99m-Ethyl Cysteinate Dimer (99mTc-ECD). Alterations of the rCBF have already been reported in dogs with behavioral problems or epilepsy. The distribution of 99mTc-ECD, a lipophilic tracer which becomes rapidly trapped in the brain, thus creating a "fixed image", represents the rCBF at the moment of tracer injection. Due to this property, it is possible to administer the tracer in the awake animal and performing the acquisition afterwards, under general anaesthesia.
Aim
The aim of this study was to look at the in vivo stability of the regional cerebral distribution of this tracer in the canine brain and to derive the optimal interval between tracer administration and acquisition from the results of this study.
Methods
Three serial acquisitions were performed 15 (T15), 40 (T40) and 65 (T65) minutes after tracer injection. Semi-quantification, resulting in the calculation of perfusion indices, was performed by normalizing the regional counts to the counts of the total brain and to the counts of the cerebellum. Total counts were measured and perfusion indices, normalized to the total brain (PIT) and to the cerebellum (PIC) were calculated for 11 brain regions.
Statistics
One-way ANOVA was used with post hoc comparisons of the group means using the Tukey test. Significance was defined as P < 0,05.
Results
At T65, total counts decreased by approximately 30% and significant regional differences in the perfusion indices occurred compared to T15.
Conclusion
This study shows that in dogs both the "entire brain" as well as the cerebellum can be used as a reference region for semi-quantification purposes and that regional differences in the clearance of 99mTc-ECD, resulting in significant alterations of the perfusion indices, occur from 65 minutes after tracer injection onwards. As a result of these findings, it can be recommended to start the acquisitions between 15 and 40 minutes post injection, when 99mTc-ECD-SPECT is used for brain perfusion studies in dogs.