Direct radiofrequency saturation corrected amide proton transfer tumor MRI at 3T.

Purpose: Amide proton transfer (APT) imaging has been increasingly applied in tumor characterization that complements diffusion and dynamic contrast-enhanced MRI. However, quantification of in vivo APT effect is challenging because of concomitant semisolid magnetization transfer (MT) and nuclear overhauser enhancement effects. A direct saturation corrected (DISC) chemical exchange saturation transfer (CEST) analysis has been recently proposed that simplifies the determination of in vivo CEST effects. Our present study aimed to extend the DISC analysis to pulsed radiofrequency CEST MRI and evaluate it at 3T. Methods: Nine adult male SpragueDawley rats implanted C6 gliomas underwent multiparametric MRI of T-1, T-2, CEST, and T-1-weighted gadolinium-enhanced imaging 1 day before and 3 days after chemoradiotherapy. The routine MT asymmetry, 3-point method, and the extended DISC analysis were compared in tumor characterization with histology as a reference. Regional variations were assessed by 1-way analysis of variance. Results: T-1, T-2, and MT asymmetry and the DISC CEST effects showed significant alterations in tumor/necrosis with respect to the contralateral reference (P < 0.05). The resolved APT effect revealed a significant difference among the contralateral reference (2.42 +/- 0.24%), necrosis (2.86 +/- 0.19%), and tumor (3.25 +/- 0.15%) regions after chemoradiotherapy (P < 0.05), consistent with histological observations. Conversely, the MT asymmetry did not show tumor regional variation post-treatment (P > 0.05), whereas the 3-point method detected no regional alteration at both time points (P > 0.05). Conclusion: Our study translated DISC CEST MRI to 3T, evaluated it in glioma rat models, and confirmed its advantages in resolving tumor heterogeneity over the routine asymmetry and 3-point analyses.