Specific Absorption Rate Comparisons of Multiphoton Excitation, PINS and MultiPINS for Simultaneous Multislice Imaging

Motivation: Elevated specific absorption rate (SAR) levels pose a significant challenge for simultaneous multislice (SMS) imaging especially at high field strengths. Goal(s): Multiphoton excitation has recently been proposed for reduced-SAR SMS applications. We aim to evaluate the SAR benefit of multiphoton SMS imaging compared to PINS and MultiPINS. Approach: We show how pulse parameters affect the efficiencies of multiphoton SMS, PINS, and MultiPINS compared to conventional SMS through simple calculations and simulations. Additionally, we implement a multiphoton SMS spin-echo sequence in vivo at 3T. Results: Multiphoton SMS is more SAR-efficient than PINS and MultiPINS for short pulse durations and thin slices under slew-rate constraints. Impact: Multiphoton excitation makes short pulse durations and thin slices possible for SMS applications under SAR and slew-rate constraints. This subsequently enables the acquisition of high-quality imaging data for both scientific and medical purposes while reducing scan times.