Convex optimized diffusion encoding (<scp>CODE</scp>) gradient waveforms for minimum echo time and bulk motion–compensated diffusion‐weighted <scp>MRI</scp>

Abstract

Purpose To evaluate convex optimized diffusion encoding (CODE) gradient waveforms for minimum echo time and bulk motion–compensated diffusion‐weighted imaging (DWI). Methods Diffusion‐encoding gradient waveforms were designed for a range of b‐values and spatial resolutions with and without motion compensation using the CODE framework. CODE, first moment (M 1 ) nulled CODE‐M 1 , and first and second moment (M 2 ) nulled CODE‐M 1 M 2 were used to acquire neuro, liver, and cardiac ADC maps in healthy subjects (n=10) that were compared respectively to monopolar (MONO), BIPOLAR (M 1 = 0), and motion‐compensated (MOCO, M 1 + M 2 = 0) diffusion encoding. Results CODE significantly improved the SNR of neuro ADC maps compared with MONO (19.5 ± 2.5 versus 14.5 ± 1.9). CODE‐M 1 liver ADCs were significantly lower (1.3 ± 0.1 versus 1.8 ± 0.3 × 10 −3 mm 2 /s, ie, less motion corrupted) and more spatially uniform (6% versus 55% ROI difference) than MONO and had higher SNR than BIPOLAR (SNR = 14.9 ± 5.3 versus 8.0 ± 3.1). CODE‐M 1 M 2 cardiac ADCs were significantly lower than MONO (1.9 ± 0.6 versus 3.8 ± 0.3 x10 −3 mm 2 /s) throughout the cardiac cycle and had higher SNR than MOCO at systole (9.1 ± 3.9 versus 7.0 ± 2.6) while reporting similar ADCs (1.5 ± 0.2 versus 1.4 ± 0.6 × 10 −3 mm 2 /s). Conclusions CODE significantly improved SNR for ADC mapping in the brain, liver and heart, and significantly improved DWI bulk motion robustness in the liver and heart. Magn Reson Med 77:717–729, 2017. © 2016 International Society for Magnetic Resonance in Medicine