Stim-CODE: PNS and CNS Constraint Optimized Diffusion-Encoding for Neuroimaging on 200 mT/m Whole-Body Gradients

AI Summary

Stim-CODE uses the GrOpt toolbox to design diffusion-encoding gradients constrained by CNS and PNS envelopes, enabling full hardware utilisation.
It reduces echo time and increases SNR, with larger gains at higher resolution, greater Gmax and for M1 nulled waveforms.
Validated in simulations and in vivo, Stim-CODE provides equivalent diffusion weighting, lower ADC uncertainty, and similar DTI metrics despite minor global ADC differences.

TL;DR (AI Generated)

METHODS: Stim-CODE uses the gradient optimization (GrOpt) toolbox to optimally design diffusion-encoding gradient waveforms subject to a CNS or PNS "constraint envelope" based on other gradient events in the sequence.

Healthy volunteers (N = 10) underwent neuro DWI at b = 1000 s/mm 2 with Monopolar, Stim-CODE- M 0 , Bipolar, and Stim-CODE- M 1 encoding.

CONCLUSION: Stim-CODE maximizes hardware capabilities to achieve time-optimized diffusion-encoding while respecting CNS and PNS, enabling similar diffusion-weighting as conventional approaches with reduced TE and higher SNR.

Basic summary

Magn Reson Med. 2026 Nov 9. doi: 10.1002/mrm.70639. Online ahead of print.

ABSTRACT

PURPOSE: Ultra-high-performance whole-body MRI gradients ( $G_{\max}$ $\geq$ 200mT/m, $S_{\max}$ $\geq$ 200 T/m/s) can reduce echo times (TE) in diffusion-weighted imaging (DWI), improving SNR. However, full hardware utilization is limited by cardiac (CNS) and peripheral (PNS) nerve stimulation thresholds. This work demonstrates Stimulation Constraint Optimized diffusion-encoding (Stim-CODE) for neuro diffusion.

METHODS: Stim-CODE uses the gradient optimization (GrOpt) toolbox to optimally design diffusion-encoding gradient waveforms subject to a CNS or PNS “constraint envelope” based on other gradient events in the sequence. Stim-CODE was evaluated in simulations and in vivo protocols with in-plane resolutions of 1.5 $\times$ 1.5 mm $^{2}$ and 1.0 $\times$ 1.0 mm $^{2}$ across G $_{\max}$ = [45, 80, 200] mT/m and $S_{\max} = 200$ T/m/s. Healthy volunteers (N = 10) underwent neuro DWI at b = 1000 s/mm $^{2}$ with Monopolar, Stim-CODE- $M_{0}$ , Bipolar, and Stim-CODE- $M_{1}$ encoding. SNR, apparent diffusion coefficient (ADC) maps, and ADC uncertainty were quantified. One volunteer underwent DTI with the same encoding schemes acquired at $b$ = [1000, 3000]s/mm $^{2}$ .

RESULTS: Stim-CODE reduced TEs across all $b$ -values, with larger gains for higher resolutions, greater G $_{\max}$ , and $M_{1}$ -nulled waveforms. Phantom and in vivo experiments confirmed equivalent diffusion-weighting with TE savings and SNR improvements. Stim-CODE- $M_{1}$ had significant SNR gains over Bipolar scans, but some differences in global ADC were observed. DTI metrics were similar across scans, with Stim-CODE showing lower uncertainty.