P2-08-06: Improved Spatial Resolution Diffusion-Weighted Imaging for Characterizing Tumors and Treatment Response in Patients with Invasive Breast Cancer.

Abstract

Background: Diffusion weighted magnetic resonance imaging (DWI) is a non-invasive technique that is sensitive to tissue microstructure. Previous studies have shown that DWI adds positive predictive value in diagnostic studies of breast cancer and it has been shown to predict tumor response to neoadjuvant chemotherapy. While DWI shows promise for evaluating breast cancer, the technique suffers from limitations. Specifically, image distortion is common with the echo planar sequence available for DWI on clinical scanners, and spatial resolution is lower than that of other MRI sequences. Our group has optimized a high-resolution reduced field-of-view DWI acquisition, originally developed for the spine by Saritas et al., for breast imaging. The goal of this work was to compare high resolution (hr)-DWI) to standard resolution (std)-DWI for characterizing breast tumors. Methods: Patients undergoing neoadjuvant chemotherapy were scanned with MRI before, during and after neoadjuvant chemotherapy as part of IRB-approved studies at our institution. Nine women were scanned with both hr-DWI and std-DWI before and after one cycle of chemotherapy. Apparent diffusion coefficient (ADC) maps were calculated from hr-DWI and std-DWI data using previously described methods. One tumor region of interest (ROI) was defined on the hr-DWI slice estimated to contain the largest tumor area. This tumor ROI was then applied to the corresponding slice and location on the std-DWI and hr-DWI ADC maps. Mean tumor ADC as well as 15th, 25th, 50th, 75th, and 90th percentile ADCs were calculated for both DWI acquisitions for all subjects. Results: The mean tumor ADC values measured prior to treatment were similar for the hr-DWI and std-DWI acquisitions, however there was a significant difference between hr- and std-DWI 15th and 25th percentile ADC values (p= 0.0495, p=0.0717) For the early treatment time point, significant differences between the two DWI acquisitions were found for: mean tumor ADC, 15th, 25th, and 50th percentiles (p=0.0302, 0.0075, 0.0212, and 0.0488, respectively), with the most significant difference found for the lowest (15th) percentile measured. Tumor hr-DWI ADCs were consistently lower than std-DWI ADCs. Discussion: These data show that although the mean ADC values calculated from the pre-treatment hr-DWI and std-DWI are similar, the lower percentile (15th, and 25th) ADC values are significantly lower for the hr-DWI acquisition. Our results also showed larger difference in lower percentile ADC values between the two sequences after one cycle of chemotherapy. The differences in the lower percentile ADC values calculated from the hr-DWI are consistent with reduced partial voluming between viable tumor tissue, which is characterized low ADC values, and normal fibroglandular tissue. This may be particularly important for post-treatment ADC measurements where tumor size may decrease, potentially making partial volume effects more pronounced. Continuing studies are evaluating the relationship between low percentile ADC values from hr-DWI and tumor stage and response to treatment. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-08-06.