Direct quantification of optic nerve blood flow by 3D pseudo-continuous arterial spin labeling

Background: Blood perfusion of the optic nerve (ON) plays a key role in many optic neuropathies. Microvascular changes precede or accompany neuronal changes, and detecting these changes at an early stage may facilitate early treatment to avoid blindness. However, the quantification of ON blood perfusion remains a challenge. This study aimed to evaluate the viability of three-dimensional pseudocontinuous arterial spin labelling (3D-pCASL) MRI for the quantification of ON blood flow (BF). New method: The ON segmentation was performed using nnFormer on a cohort of ten participants (4 males, 6 females, 25-59 years old). Subsequently, the mean BF of each ON segment was calculated using whole brain 3DpCASL image data. Results: The average ON-BF values of the left and right intraorbital segments, left and right intracanalicular segments, left and right intracranial segments, optic chiasma, and left and right optic tract were 41.308 mL/100 g/min, 43.281 mL/100 g/min, 53.188 mL/100 g/min, 57.202 mL/100 g/min, 45.089 mL/100 g/min, 49.554 mL/100 g/min, 42. 326 mL/100 g/min, 43.831 mL/100 g/min and 45.176 mL/100 g/min, respectively. The ONBF correlated with cerebral BF (r = 0.503, p = 0.024). Comparison with existing method(s): The 3D-pCASL can measure tissue microvascular blood perfusion in absolute quantitative units with good test-retest repeatability over a wide field of view and without restrictions on depth. The use of the nnFormer makes the measurement easy, objective and reproducible. Conclusions: The study showed that, 3D-pCASL may be a promising tool for detecting abnormal ON-BF. In particular, 3D-pCASL coupled with the nnFormer provides an objective, reproducible, and reliable method to quantify BF in ON.