Design of a nonlinear double-breast single-axis gradient coil with controlled anterior-posterior gradient variation for diffusion-weighted imaging.

INTRODUCTION: High-performance whole-body gradient systems show promise for breast diffusion-weighted imaging, but their performance is constrained by physiological limits. Although local nonlinear gradient coils can provide stronger gradients while remaining within these limits, they often exhibit a substantial reduction in the gradient amplitude of the z-component of the magnetic field near the chest wall. METHODS: We introduced an optimization framework incorporating a constraint on the anterior-posterior variation in the encoding gradient amplitude. A figure of merit combining coil efficiency and minimum wire width was defined to assess performance. A prototype was constructed to validate the design methodology. RESULTS: The optimized coil achieved a 2.35-fold efficiency increase over standard linear coils. Compared to previous nonlinear designs, the new constraint reduced spatial variation by 35.7% and improved minimum efficiency near the chest wall by 2.6-fold. Experimental field maps matched simulations with errors under 8%. DISCUSSION: The proposed method effectively mitigates the trade-off between gradient strength and spatial uniformity along anterior-posterior direction. By enhancing performance in the posterior breast region, the design addresses a critical limitation of previous local coils. CONCLUSION: This framework enables the development of high-performance, robust local gradient coils, facilitating the clinical implementation of advanced DWI protocols for breast cancer screening.