Ultra-high field magnetic resonance imaging of breast cancer

Abstract

Dynamic contrast-enhanced (DCE) breast MRI plays an important role in the detection and staging of breast cancer. It has a high sensitivity of approximately 0.90 for the detection breast cancer, although the specificity of 0.72 is relatively low. Therefore, research has focused on improving specificity. One of the areas of interest is the use of a higher magnetic field strength. In the past decade 7T MRI has become available for whole-body imaging. 7T MRI offers possibilities that may improve the diagnostic accuracy of breast MRI. In the first part of the thesis we investigated the feasibility of 7T breast MRI. In a patient case it was shown that 7T breast MRI is technically feasible, and may allow for analysis conform the BI-RADS-MRI lexicon. Following this first experience, a dedicated patient study was conducted to investigate clinical feasibility. 7T examinations of twenty patients with suspicious breast lesions were assessed by two radiologists. The radiologists identified all histopathological proven malignant lesions, and classified them BI-RADS-MRI 4 or 5. A benefit of ultra-high resolution imaging was illustrated as it increased reader confidence in the majority of cases. Third, an intra-individual comparison study was performed were patients were imaged at both 3T and 7T MRI. Two radiologists equally identified malignant lesions at both field strengths and determined an overall good imaging quality for the dynamic scans acquired at 7T. In the second part we focused on improved or new breast imaging techniques that benefit from the ultra-high field strength. Magnetic Resonance Spectroscopic Imaging (MRSI) is one of the techniques that benefits from moving to 7T. To answer the question whether 31P (phosphorus) MRSI results are influenced by the menstrual cycle, seven females with a regular menstrual cycle were measured each four equidistant times. It was shown that 31P MRSI examinations can be performed at any point during the menstrual cycle, without a significant effect on the phosphorus metabolic ratios. Ductal carcinoma in situ (DCIS) presents itself as microcalcifications on mammography in up to 79% of cases. However, microcalcifications are also often associated with benign or high-risk lesions instead of with malignancy. Therefore, careful evaluation is needed. First, the added value of 3T breast MRI in patients presenting with suspicious microcalcifications on mammography was investigated. It was shown that 3T MRI in addition to conventional imaging has an added value, as the AUC showed a significant increase in multivariate analysis. However, 3T MRI does not exclude DCIS lesions of all grades sufficiently. The diagnostic accuracy of MRI may be improved when detection and morphologic characterization of microcalcifications becomes feasible. Therefore, a new technique sensitive for the susceptibility property of calcifications was investigated for its potential to visualize calcifications with 7T MRI. Ex-vivo whole-breast specimens were subjected to gradient echo sequences of which the phase derivative was examined. A specific pattern in the phase derivative allowed microcalcifications to be discriminated from other field perturbers, which showed the feasibility of the technique. Furthermore, the first steps towards automated detection were presented by using a template matched algorithm.