Ultra-high gradient connectomics and microstructure MRI for human brain circuits

• An ultra-high gradient connectomics and microstructure MRI scanner enables imaging of human brain circuits across scales (Nature, July 2025).^{1 1}

Weekly enrichment (2026-07-20)

• The scanner is “Connectome 2.0,” described by Ramos-Llordén, Lee et al. in Nature Biomedical Engineering (published 16 July 2025; 2025, 10(2):309–324; PMID 40670720), developed at the Athinoula A. Martinos Center for Biomedical Imaging, MGH.²³
• Its 3-layer head-only gradient coil reaches a gradient strength of 500 mT m⁻¹ and slew rate of 600 T m⁻¹ s⁻¹, about a 5-fold gradient-performance gain over state-of-the-art research systems (including the original Connectome 1.0) and roughly an 18-fold improvement over clinical scanners.²³
• The coil geometry was explicitly optimized to minimize peripheral nerve stimulation, allowing this performance to be operated safely in living human subjects.²
• Radiofrequency hardware includes a 72-channel in vivo head coil and a 64-channel ex vivo whole-brain coil with built-in field monitoring; the 72-channel coil gives ~1.5× peripheral SNR over a standard 32-channel coil, and the 64-channel ex vivo coil outperforms the in vivo coil by ~1.73× on average.²
• Higher gradient strength shortens echo time by 13–50% versus Connectome 1.0 (and at least 77% versus a clinical protocol at b = 5,000 s mm⁻²), yielding SNR gains up to 2-fold at b = 40,000 s mm⁻².²
• With the improved SNR, 1 mm isotropic diffusion-weighted images were acquired in 30 minutes and diffusion tractography resolved fine diencephalic pathways (e.g., the mammillo-tegmental tract) that were recoverable only on the Connectome 2.0 protocol.²
• Microstructure modeling (AxCaliber-SMT) estimated axonal diameters of 2.45 ± 0.15 μm on Connectome 2.0 versus 4.04 ± 0.48 μm on Connectome 1.0 in the posterior corona radiata, showing sensitivity to smaller axons with tighter variance.²
• Overall the system delivers at least a 30% sensitivity improvement over Connectome 1.0 and up to 40% better diffusion resolution for axonal and cellular-size estimation, approaching near-single-micron scales in vivo.²
• The work was funded in part by the NIH BRAIN Initiative under the BRAIN Connectivity Across Scales (BRAIN CONNECTS) program, aimed at building multi-scale whole-brain wiring diagrams relevant to disorders where microstructure is disrupted.³

Footnotes

1. https://news.google.com/rss/articles/CBMiX0FVX3lxTFBFUlZGemt2MUIyYm5rWUlBajgyaVlVZGRVTEVSeWtnSURPTEV6ZEhBYTJXLWpYc1RQQzlIWmx5WENQamo1NWE1Q2UtbnVhTUg0by05RUoxTm9JMmd2S1h3?oc=5 ↩ ↩²

2. https://www.nature.com/articles/s41551-025-01457-x ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸

3. https://www.martinos.org/another-leap-forward-in-connectome-imaging-of-the-brain/ ↩ ↩² ↩³