A novel normalization for amide proton transfer CEST MRI to correct for fat signal–induced artifacts: application to human breast cancer imaging

Abstract

Purpose: The application of amide proton transfer (APT) CEST MRI for diagnosis of breast cancer is of emerging interest. However, APT imaging in the human breast is affected by the ubiquitous fat signal preventing a straightforward application of existing acquisition protocols. Although the spectral region of the APT signal does not coincide with fat resonances, the fat signal leads to an incorrect normalization of the Z-spectrum, and therefore to distorted APT effects. In this study, we propose a novel normalization for APT-CEST MRI that corrects for fat signal-induced artifacts in the postprocessing without the need for application of fat saturation schemes or water-fat separation approaches. Methods: The novel normalization uses the residual signal at the spectral position of the direct water saturation to estimate the fat contribution. A comprehensive theoretical description of the normalization for an arbitrary phase relation of the water and fat signal is provided. Functionality and applicability of the proposed normalization was demonstrated by in vitro and in vivo experiments. Results: In vitro, an underestimation of the conventional APT contrast of approximately −1.2% per 1% fat fraction was observed. The novel normalization yielded an APT contrast independent of the fat contribution, which was also independent of the | 921 ZIMMERMANN Et Al.

Clinical routine acquisition protocol for 3D relaxation‐compensated APT and rNOE CEST‐MRI of the human brain at 3T

“…In the future, the t acq could even further be reduced by replacing the WASABI scan for the quantification of field inhomogeneities by a faster technique. Instead of acquiring a B 0 map, the spectral position of the DS form the Lorentzian‐fit could be used to compensate for B 0 ‐field inhomogeneities 48 . Furthermore, a B 1 map could also be acquired in less than 30 s using the DREAM (dual refocusing echo acquisition mode) approach 49 .…”

“…Instead of acquiring a B 0 map, the spectral position of the DS form the Lorentzian-fit could be used to compensate for B 0 -field inhomogeneities. 48 Furthermore, a B 1 map could also be acquired in less than 30 s using the DREAM (dual refocusing echo acquisition mode) approach. 49 This would enable a t acq even below 5 min, even further facilitating the application of relaxation-compensated CEST-MRI in clinical F I G U R E 6 Reproducibility analysis of the MTR Rex APT contrast (B 1 = 0.7 µT) acquired in the same volunteer and in the same slice as in Figure 5.…”

Whole brain snapshot CEST at 3T using 3D‐EPI: Aiming for speed, volume, and homogeneity

“…CEST spectra can be strongly affected by direct saturation of fat signals 38,39 . Thus, a water excitation enables mitigation of this artifact.…”

“…CEST spectra can be strongly affected by direct saturation of fat signals. 38,39 Thus, a water excitation enables mitigation of this artifact. However, binominal water excitation pulses 9 are rather long (additional ≈ 1.1 ms per excitation for both GRE and EPI) and would prolong a GRE readout significantly.…”

Assessment of Early Response to Neoadjuvant Systemic Therapy in Triple-Negative Breast Cancer Using Amide Proton Transfer–weighted Chemical Exchange Saturation Transfer MRI: A Pilot Study

“…APT W CEST MRI has been investigated for tumor diagnosis as well as treatment assessment, primarily for brain cancer studies (13,17). APT W CEST MRI has also been developed for breast cancer studies (17)(18)(19)(20)(21)(22)(23)(24)(25), including a few studies that have investigated breast cancer treatment response to NAST (18,24,25). These studies have typically evaluated a variety of breast cancer types in the same study, have tested saturation powers ranging from 0.5 to 2.0 µT, and have used different analysis methods.…”