DarkSPARC: Dark-Blood Spectral Self-Calibrated Reconstruction of 3D Left Atrial LGE MRI for Post-Ablation Scar Imaging

TL;DR

DarkSPARC is a novel, training-free spectral reconstruction method that transforms routine bright-blood 3D LA LGE MRI into dark-blood images, significantly improving scar visualization and quantification accuracy in post-ablation atrial fibrillation patients.

Contribution

It introduces a self-calibrated spectral reconstruction technique that enhances dark-blood imaging without additional scans or training, improving scar detection and quantification.

Findings

DarkSPARC increases CNR, SNR, and eCNR up to 30-fold in phantom studies.

Reduces bias in scar percentage estimation from -37% to -5%.

Improves in vivo metrics significantly, with p<0.001.

Abstract

Purpose: To develop DarkSPARC, a retrospective, training-free, self-calibrated spectral reconstruction method that converts routine bright-blood 3D left atrial (LA) late gadolinium enhancement (LGE) MRI into a dark-blood image, and to quantify its impact on LA scar-pool CNR, SNR, effective CNR (eCNR), and scar quantification accuracy. Methods: DarkSPARC embeds bright-blood LA LGE into a calibrator-conditioned (N+1)-dimensional spectral domain and reconstructs a dark-blood-like image using scan-specific spectral landmarks. A scan-specific 3D numerical phantom framework was built from LAScarQS post-ablation LGE by cloning remote myocardium into the LA wall and imposing controlled scar burden. Five baseline cases spanning the 5th-95th percentiles of native scar-pool CNR, each with multiple scar burdens and 10 CNR degradation levels, yielded 200 phantoms. For every phantom, LA scar-pool CNR, SNR, eCNR, and Scar% were measured on bright-blood and DarkSPARC images. In vivo performance was evaluated in 60 public post-ablation scans of atrial fibrillation patients. Results: In scan-specific phantoms, DarkSPARC increased LA scar-pool CNR, SNR, and eCNR over bright-blood in all 200 experiments, with DarkSPARC/bright-blood ratios up to about 30-fold for CNR and about 6-fold for SNR in the lowest-CNR conditions. At 70% CNR degradation, bright-blood underestimated ground-truth LA Scar% by -37% to -54%, whereas DarkSPARC reduced bias to about -3% to -5%. In vivo, DarkSPARC similarly improved metrics: median scar-pool CNR, SNR, and eCNR increased from 20.0 to 135.9 (6.8x), 70.6 to 200.6 (2.8x), and 0.22 to 0.75 (3.4x), respectively (all p<0.001), and LA Scar% increased from 3.9% to 9.75%. Conclusion: DarkSPARC is a self-calibrated, training-free reconstruction that yields dark-blood 3D LA LGE, boosting CNR/SNR/eCNR and stabilizing reliable scar quantification without extra scans.