Elizabeth Vera Gadwood MD, Presenter: Nothing to Disclose

New MRI techniques are being developed to quantitatively evaluate breast tumors in the diagnostic and prognostic settings. One such method is amide proton transfer (APT), a type of chemical exchange saturation transfer (CEST) imaging. APT provides information about protein content and distribution in tumors. Studies have shown that APT can distinguish healthy tissue from tumor and may be sensitive enough to detect subtle changes related to chemotherapy. This study aims to evaluate APT-CEST-MRI in relation to diffusion weighted MRI (DW-MRI) and dynamic contrast enhanced MRI (DCE-MRI) in breast cancer patients.

12 patients with invasive mammary carcinoma underwent MR imaging prior to therapy, which included DW-, DCE-, and APT-CEST-MRI. Analysis of the DCE-MRI data returned the volume transfer constant (Ktrans), extravascular extracellular volume fraction (ve), efflux constant (kep), and blood plasma volume fraction (vp). The apparent diffusion coefficient (ADC) was estimated from the DW-MRI data, while the mean APT was calculated from the CEST data. The Spearman’s rank correlation coefficient was calculated to test for a significant statistical relationship between all of these parameters at the whole tumor region of interest level. 

APT and Ktrans demonstrated a strong and significant correlation (r2=0.82, p=0.002) while a modest but non-significant correlation was seen between APT and vp (r2=0.6, p=0.051). There was no correlation between APT and ADC (r2=0.08, p=0.8).

The significant correlation between APT and Ktrans, a marker of tumor vessel perfusion and/or permeability, suggests that protein synthesis may be related to tumor associated angiogenesis. This hypothesis is strengthened by the positive correlation between APT and vp. Lack of correlation between APT and ADC suggests that APT is a stronger marker of extracellular protein, rather than intracellular protein, as it appears to be independent from tumor cell density.

Initial results suggest APT is independent from DW-MRI and complimentary to DCE-MRI. If this can be validated in a larger patient set, measurements of APT could impact standard MRI breast protocols.

Gadwood, E, On the Statistical Relationships Between Quantitative DCE-, DW-, and APT-CEST-MRI: A Hypothesis Generating Study.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14001589.html