Practical Considerations for Serial Computed Tomography Angiography in Cerebral Blood Flow Assessment During Legal Brain Death Determination

Background: The 2024 revision of the Japanese legal brain death determination manual newly incorporated cerebral blood flow testing as a supplementary and alternative test. However, clear criteria regarding the timing and implementation of these tests remain undefined in clinical practice. We investigated patients who underwent serial computed tomography angiography (CTA) after reaching a clinical state consistent with brain death to characterize serial CTA findings during the progression toward cerebral circulatory arrest and to explore practical considerations regarding CTA timing and interpretation.Methods: We retrospectively analyzed three patients who underwent serial CTA during the clinical course of brain death determination. Imaging timing, delayed-phase acquisition timing, contrast injection rate, and cerebral blood flow findings were evaluated.Results: According to current diagnostic criteria, absence of cerebral blood flow was confirmed only on follow-up CTA in Patient 3 performed 10 days after confirmation of fixed dilated pupils, whereas cerebral blood flow remained detectable in all early examinations performed within 1–5 days. A contrast injection rate of 3 mL/s and delayed-phase imaging approximately 40 seconds after the arterial phase appeared to provide clearer venous-phase assessment. Evaluation of peripheral arterial branches and deep veins, rather than only proximal arterial visualization, contributed to cerebral blood flow assessment.Conclusions: Cerebral circulatory arrest findings suggest temporal evolution of CTA findings, suggesting that CTA assessment may be difficult during the early phase of clinical progression. Delayed-phase imaging approximately 40 seconds after the arterial phase may represent useful practical imaging conditions for cerebral blood flow assessment during brain death determination. These observations should be regarded as hypothesis-generating and require validation in larger prospective studies.