Feasibility of diffusion weighting with a local inside‐out nonlinear gradient coil for prostate MRI

Abstract

Purpose Prostate cancer remains the second leading cancer killer of men, yet it is also a disease with a high rate of overtreatment. Diffusion‐weighted imaging (DWI) has shown promise as a reliable, grade‐sensitive imaging method, but it is limited by low image quality. Currently, DWI quality image is directly related to low gradient amplitudes, since weak gradients must be compensated with long echo times. Methods We propose a new type of MRI accessory, an “inside‐out” and nonlinear gradient, whose sole purpose is to deliver diffusion encoding to a region of interest. Performance was simulated in OPERA and the resulting fields were used to simulate DWI with two‐compartment and kurtosis models. Experiments with a nonlinear head gradient prove the accuracy of DWI and apparent diffusion coefficient (ADC) maps encoded with nonlinear gradients. Results Simulations validated thermal and mechanical safety while showing a 5‐ to 10‐fold increase in gradient strength over prostate. With these strengths, lesion contrast to noise ratio in ADC maps approximately doubled for a range of anatomical positions. Proof‐of‐principle experiments show that spatially varying b‐values can be corrected for accurate DWI and ADC. Conclusions Dedicated nonlinear diffusion encoding hardware could improve prostate DWI.

Quantitative diffusion MRI of the abdomen and pelvis

“…For these reasons, the current emergence of modern low‐field systems (e.g., 0.55 T or lower) offers intriguing possibilities 190 . Other hardware innovations, such as localized nonlinear gradient systems, 191 also offer fascinating opportunities.…”

Identifying potential imaging markers for diffusion property changes in a mouse model of amyotrophic lateral sclerosis: Application of the continuous time random walk model to ultrahigh b‐value diffusion‐weighted MR images of spinal cord tissue

“…Although the magnetic field and gradient strength used in this study are not available on clinical scanners, this technical obstacle may be overcome in the future 54,55 . In addition, a recent study has reported the application of a nonlinear gradient insert to achieve high b‐values for prostate imaging 56 . When comparing spin echo sequences with STE sequences, the STE sequence enables a wide range of diffusion times because the T 1 is usually much longer than the T 2 .…”

Multi‐shot Diffusion‐Weighted MRI With Multiplexed Sensitivity Encoding (MUSE) in the Assessment of Active Inflammation in Crohn's Disease

“…Further comparative studies on the optimal choice of b ‐value for CD diagnosis are thus needed. Lastly, we did not include either advanced DWI based on multi‐echo fast spin‐echo 39 or the use of local inside‐out gradient coil for efficient DWI 40 . Potential impact of these novel DWI concepts on the effectiveness of MRE for CD diagnosis awaits further investigations.…”

“…Lastly, we did not include either advanced DWI based on multi-echo fast spin-echo 39 or the use of local inside-out gradient coil for efficient DWI. 40…”