Relaxation-compensated CEST (chemical Exchange Saturation Transfer) Imaging in Breast Cancer Diagnostics at 7T

Purpose: To investigate whether fat-corrected and relaxation-compensated amide proton transfer (APT) and guanidyl CEST-MRI enables the detection of signal intensity differences between breast tumors and normalappearing fibroglandular tissue in patients with newly-diagnosed breast cancer. Method: Ten patients with newly-diagnosed breast cancer and seven healthy volunteers were included in this prospective IRB-approved study. CEST-MRI was performed on a 7 T-whole-body scanner followed by a multiLorentzian fit analysis. APT and guanidyl CEST signal intensities were quantified in the tumor and in healthy fibroglandular tissue after correction of B-0/B-1-field inhomogeneities, fat signal contribution, T-1- and T-2-relaxation; signal intensity differences of APT and guanidyl resonances were compared using Mann-Whitney-Utests. Pearson correlations between tumor CEST signal intensities and the proliferation index Ki-67 were performed. Results: APT CEST signal in tumor tissue (6.70 +/- 1.38%Hz) was increased compared to normal-appearing fibroglandular tissue of patients (3.56 +/- 0.54%Hz, p= 0.001) and healthy volunteers (3.70 +/- 0.68%Hz, p= 0.001). Further, a moderate positive correlation was found between the APT signal and the proliferation index Ki-67 (R-2= 0.367, r= 0.606, p= 0.11). Guanidyl CEST signal was also increased in tumor tissue (5.24 +/- 1.85%Hz) compared to patients' (2.42 +/- 0.45%Hz, p= 0.006) and volunteers' (2.36 +/- 0.54%Hz, p< 0.001) normal-appearing fibroglandular tissue and a positive correlation with the Ki-67 level was observed (R-2= 0.365, r= 0.604, p= 0.11). APT and guanidyl CEST signal in normal-appearing fibroglandular tissue was not different between patients and healthy volunteers (p= 0.88; p= 0.93). Conclusion: Relaxation-compensated and fat-corrected CEST-MRI allowed a non-invasive differentiation of breast cancer and normal-appearing breast tissue. Thus, this approach represents a contrast agent-free method that may help to increase diagnostic accuracy in MR-mammography.