Hypoperfusion Asymmetry IndexThe Hypoperfusion Asymmetry Index (HAI) measures the volume of significant hypoperfusion voxels based on p-values and extent thresholds in each hemisphere of the brain. This is a powerful tool for lateralizing seizure onset to the correct hemisphere for post-ictal injections. Calculating the HAIIn order to calculate the hypoperfusion asymmetry index follow the steps below:
Interpreting HAI
A positive HAI indicates more hypoperfusion in the left hemisphere,
while a negative HAI indicates more hypoperfusion in the right hemisphere.
For purposes of reviewing the calculations, let us pretend that the sample patient data were from a post-ictal injection. The HAI would then be calculated as follows: HAI = kleft – kright) / (kleft + kright)Since the HAI is positive, this would lateralize seizure onset to the left hemisphere. Based on McNally et al., 2005, this lateralization is expected to be correct in approximately 80% of patients if the injection occurred in the post-ictal period (which it did not for this patient). Back to Interpreting Results || Jump to Top || Return to ISAS Home |