Blind Adaptive Local Denoising for CEST Imaging

TL;DR

This paper introduces BALD, a novel blind adaptive local denoising method for CEST MRI that effectively reduces complex, heteroscedastic noise without prior noise knowledge, improving quantitative imaging accuracy.

Contribution

BALD is the first denoising approach tailored for CEST MRI that adaptively stabilizes noise and preserves molecular signals using self-similarity and local SVD transforms.

Findings

BALD outperforms existing denoisers in quantitative metrics.

Improves accuracy of molecular concentration maps.

Enhances cancer detection in CEST imaging.

Abstract

Chemical Exchange Saturation Transfer (CEST) MRI enables molecular-level visualization of low-concentration metabolites by leveraging proton exchange dynamics. However, its clinical translation is hindered by inherent challenges: spatially varying noise arising from hardware limitations, and complex imaging protocols introduce heteroscedasticity in CEST data, perturbing the accuracy of quantitative contrast mapping such as amide proton transfer (APT) imaging. Traditional denoising methods are not designed for this complex noise and often alter the underlying information that is critical for biomedical analysis. To overcome these limitations, we propose a new Blind Adaptive Local Denoising (BALD) method. BALD exploits the self-similar nature of CEST data to derive an adaptive variance-stabilizing transform that equalizes the noise distributions across CEST pixels without prior knowledge of noise characteristics. Then, BALD performs two-stage denoising on a linear transformation of data to disentangle molecular signals from noise. A local SVD decomposition is used as a linear transform to prevent spatial and spectral denoising artifacts. We conducted extensive validation experiments on multiple phantoms and \textit{in vivo} CEST scans. In these experiments, BALD consistently outperformed state-of-the-art CEST denoisers in both denoising metrics and downstream tasks such as molecular concentration maps estimation and cancer detection.