Amide proton transfer imaging of high intensity focused ultrasound-treated tumor tissue

Purpose: In this study, the suitability of amide proton transfer (APT) imaging as a biomarker for the characterization of high intensity focused ultrasound (HIFU)-treated tumor tissue was assessed. Methods: APT imaging was performed on tumor-bearing mice before (n=15), directly after (n=15) and at 3 days (n=8) after HIFU treatment. A control group (n=7) of nontreated animals was scanned at the same time points. Histogram analysis of the tumor APT-weighted signal distributions was performed to assess HIFU-induced changes in the tumor APT contrast. Results: Distinct regions of decreased APT-weighted signal were observed at both time points after HIFU treatment. Analysis of the tumor APT-weighted signal distribution showed a pronounced shift toward lower APT-weighted signal values after HIFU treatment. A significantly increased fraction of pixels with an APT-weighted signal value between-10 and-2% was observed both directly (0.37±0.16) and at 3 days (0.49±0.16) after HIFU treatment as compared to baseline (0.2260.16). Conclusion: The presented results show that APT imaging is sensitive to HIFU-induced changes in tumor tissue and may thus serve as a new biomarker for monitoring the response of tumor tissue to HIFU treatment.