Role of MR Spectroscopy in Characterization of Breast Masses

Abstract

D espite the improvement in the detection of breast cancer with the widespread application of mammography and ultrasound, some breast lesions still remain difficult to diagnose and characterize, especially in dense fibroglandular breasts. Contrast material–enhanced breast MR imaging is currently accepted as the most sensitive imaging technique for the diagnosis and staging of breast cancer especially in the dense fibroglandular breasts. However, several studies have noted that conventional breast MR imaging, including T2-weighted imaging and contrast-enhanced T1- weighted imaging, is limited in terms of specificity in the assessment of breast tumors. Con¬sequently, there has been considerable interest in the development of adjunct MR imaging methods to improve the specificity of dynamic contrast-enhanced breast MR imaging, and proton MR spectroscopy (¹H MRS) imaging is being investigated for its potential to improve breast disease diagnosis at the cost of a small increase in examination time. Magnetic resonance spectroscopy (MRS) offers unique possibilities for non-invasive clinical studies of human biochemistry in vivo. Chemical shift, which refers to the variation in the resonance frequency due to the chemical environment, can be explained by the fact that the moving electrons surrounding the protons can generate their own local magnetic field. With its ability to identify different compounds by their chemical shifts, MRS is especially useful in studying metabolism to detect cancer cells. Rather than generating an image, MRS produces a graph of the resonance amplitudes of various metabolites on the y-axis (in arbitrary units) versus the resonance frequencies on the x-axis (in Hz or ppm). The resonance amplitudes and frequencies are determined by the relative concentrations and the chemical structures of the metabolites respectively.