A parameterized gamma-variate function can describe the temporal response of cerebral blood flow after Acetazolamide injection in Moyamoya patients

Background: Quantitative modelling of the temporal response of cerebral blood flow (CBF) following Acetazolamide (ACZ) may be performed using a parameterized gamma-variate function with physiologically interpretable parameters. When combined with sequential CBF measurement before and after administration of ACZ, such a model could enable assessment of cerebrovascular reserve (CVR) while accounting for regional differences in the timing of the vascular response between steno-occlusive and unaffected territories. To evaluate this approach, we applied the model to patients with moyamoya disease (MMD). Methods: Twenty-four MMD patients underwent MRI including structural- and sequential multi-delay arterial spin labeling acquisitions before and after ACZ injection. Non-linear least squares curve fitting was performed on CBF values extracted from vascular regions. Root mean squared error (RMSE), absolute and relative CVR (CVR_diff and CVR_rel) and time to maximum CBF response (t_max) were compared between the anterior circulation (affected) and posterior circulation (unaffected). Results: Twenty-one patients were evaluated (age range 10-61; 16 females), three was excluded due to technical issues. Median RMSE ranged between 2.8 and 3.8 ml/100 g/min. CVR_rel was lower in anterior regions compared to posterior regions (mean differences 10.4-29.2%), whereas, CVR_diff differences were in general similar (0.8-6.9 ml/100 g/min). Median difference in t_max of 2.3-6.8 min was observed in affected compared to unaffected regions. Reversible intracerebral steal was found in two patients and successfully modelled using an extended gamma-variate function. Conclusion: This parameterized gamma-variate function framework provides physiologically interpretable parameters for modelling the CBF response to ACZ in MMD.