Volumetric MRI thermometry using a three‐dimensional stack‐of‐stars echo‐planar imaging pulse sequence

Abstract

Purpose To measure temperature over a large brain volume with fine spatiotemporal resolution. Methods A three‐dimensional stack‐of‐stars echo‐planar imaging sequence combining echo‐planar imaging and radial sampling with golden angle spacing was implemented at 3T for proton resonance frequency‐shift temperature imaging. The sequence acquires a 188x188x43 image matrix with 1.5x1.5x2.75 mm 3 spatial resolution. Temperature maps were reconstructed using sensitivity encoding (SENSE) image reconstruction followed by the image domain hybrid method, and using the k‐space hybrid method. In vivo temperature maps were acquired without heating to measure temperature precision in the brain, and in a phantom during high‐intensity focused ultrasound sonication. Results In vivo temperature standard deviation was less than 1°C at dynamic scan times down to 0.75 s. For a given frame rate, scanning at a minimum repetition time (TR) with minimum acceleration yielded the lowest standard deviation. With frame rates around 3 s, the scan was tolerant to a small number of receive coils, and temperature standard deviation was 48% higher than a standard two‐dimensional Fourier transform temperature mapping scan, but provided whole‐brain coverage. Phantom temperature maps with no visible aliasing were produced for dynamic scan times as short as 0.38 s. k‐Space hybrid reconstructions were more tolerant to acceleration. Conclusion Three‐dimensional stack‐of‐stars echo‐planar imaging temperature mapping provides volumetric brain coverage and fine spatiotemporal resolution. Magn Reson Med 79:2003–2013, 2018. © 2017 International Society for Magnetic Resonance in Medicine.