Improving magnetic field homogeneity in prostate MR imaging and spectroscopy using an add-on local external shim coil array.

OBJECTIVE: To improve B0 field homogeneity in prostate MR imaging and spectroscopy using a custom-designed 16-channel external local shim coil array.

METHODS: In vivo prostate imaging was performed in seven healthy volunteers (mean age: 40.7 years) without bowel preparation. A simulation study determined the most robust configuration of the add-on shim coil together with shim coils from the MR system. The combination of the add-on shim coil array with 1st-order shims of the MR scanner was used and compared to the MR system's reference standard of conventional 1st and 2nd-order shimming. Performance was evaluated using the standard deviation (SD) of off-resonance frequencies (ΔB0) from B0-maps, the distortion of diffusion-weighted images (DWI) by the Dice similarity coefficient (DSC) with reference to T2W images, and the citrate linewidths of 1H-MR spectroscopic imaging (1H-MRSI) of the prostate.

RESULTS: Overall, improvements were made with the combination of coils, with DSC rising from 0.90 ± 0.02 to 0.92 ± 0.02 (p = 0.01), a reduction in the SD of ΔB0 from 18.5 ± 4.7 Hz to 16.5 ± 3.6 Hz, and a decrease in citrate linewidths from 8.3 ± 5.7 Hz to 7.9 ± 3.6 Hz (p = 0.018), all compared to the reference standard of conventional 1st and 2nd-order shimming.

CONCLUSION: A dedicated external shim coil array can improve B0 homogeneity in the prostate, enhancing image quality and precision in multi-parametric MRI.