Flow Measurement Using Arterial Spin Labeling with Flow Discrimination by Cumulative Readout Pulses

Yi Wang^1,2, Allison Payne³, Seong-Eun Kim³, Edward DiBella³, Dennis L. Parker³

The Pennes bioheat transfer equation (BHTE) is the most widely used equation to model the effects of heat deposition and dissipation in tissues. The formulation includes terms for thermal conductivity and an effective perfusion, which represents the rate at which blood flow removes heat from a local tissue region. MR thermometry has allowed accurate estimations of these subject-specific thermal properties. Using these estimated parameters enables more accurate treatment planning. However, tissue properties, particularly perfusion, are known to change over the course of a thermal therapy treatment. Detecting perfusion changes during a thermal therapy treatment would allow for the adjustment of treatment parameters to achieve a more efficacious therapy. In this work, we present a method to use arterial spin labeling to determine the rate at which flow passes through a point. The pulse sequence combines the turbo-FLASH imaging and Look-Locker-like readout at multiple inversion times in a single scan. The data obtained from this newly developed sequence approximates the average velocity of blood (fluid) passing through a thin slice, providing a surrogate for the Pennes perfusion term. This method is independent of MR thermometry, decoupling the blood flow measurement from the MR temperature maps, allowing the perfusion changes to be monitored throughout the thermal therapy session.