Toward Semiautomated Analysis of Cerebrovascular Reserve: Enhancing Objective Comparisons Using 99mTc-HMPAO SPECT With Acetazolamide in Moyamoya.

Background and objectives: Cerebrovascular reserve (CVR) is a key physiological mechanism allowing the brain to adapt to fluctuating perfusion, particularly relevant in the management of neurovascular disorders such as idiopathic (iMM) and syndromic moyamoya (sMM). Although 99mTc-HMPAO SPECT with acetazolamide is commonly used for CVR assessment, it faces limitations including low spatial resolution, artifacts, and variability in interpretation. This study primarily aims to evaluate a novel, semiautomated, and more objective method for interpreting HMPAO SPECT in CVR assessment. As a secondary objective, the method is applied to a cohort of patients who underwent revascularization surgery for iMM or sMM.

Methods: A retrospective analysis was performed on prospectively collected data from a tertiary neuroscience center, including 20 adult patients with iMM (n = 9) or sMM (n = 11). Clinical and imaging data were reviewed. 99mTc-HMPAO SPECT images were assessed independently by 2 nuclear medicine physicians blinded to clinical details. Images were registered to T1-weighted MRI and overlaid with an arterial territory atlas. Territories classified as healthy by experts were defined as true negatives; all others as altered. Statistical comparisons were made using Student's t-tests with false discovery rate correction.

Results: Among the 20 patients (12 females), patients with sMM were older and had more cardiovascular risk factors. The proposed method significantly discriminated between altered and healthy perfusion territories. Compared with expert interpretation, the method demonstrated specificities of 93% (iMM) and 92% (sMM), with negative predictive values of 80% and 75%%, respectively.

Conclusion: Although 99mTc-HMPAO remains a validated modality for CVR assessment, its interpretation is operator-dependent. The proposed semiautomated method offers high specificity and greater objectivity, supporting its integration into clinical workflows. Further multicenter validation is warranted.