Earlobe Inferior Margin as a Landmark for Cerebellar Visualization in Brain Perfusion SPECT

Consistent inclusion of the cerebellum is essential for accurate interpretation of brain perfusion SPECT. However, the anatomic validity of external head landmarks for patient positioning has not been quantitatively evaluated. This study assessed spatial relationships between external landmarks and the cerebellar inferior margin using CT images. Methods: We retrospectively analyzed 100 preoperative brain tumor CT studies and measured z-coordinates of the eyeball center, inferior margin of the earlobe, nasal base, external auditory meatus, and inferior margin of the cerebellum. Differences between z-coordinates of landmarks and a tilt index were calculated. Results: The inferior margin of the earlobe was consistently located caudal to the cerebellum with low variability and showed the weakest association with neck posture. Conclusion: The inferior margin of the earlobe is a stable landmark for reproducible craniocaudal head positioning and may support consistent cerebellar coverage in brain perfusion scintigraphy.