Magnetic Resonance Imaging (MRI)
MRI is a superior technique than X-ray mammography and ultrasound and can detect otherwise occult breast cancers. MR images are created by recording the signals generated after radiofrequency excitation of hydrogen nuclei (or other elements) in tissue exposed to a strong static magnetic field. The signals have characteristics that vary according to the tissue type (fat, muscle, fibrotic tissue, etc.).
The method has minimal hazards from magnetic field effects and does not use ionizing radiation. The first MRI results of the human breast were disappointing, but subsequent use of an intravenous gadolinium based contrast agent has offered a clear advance and increased sensitivity. Reportedly, the sensitivity of contrast-enhanced MRI in detection of suspicious breast lesions varies from 88% to 100% (average reported sensitivity of about 95%). However the specificity of the contrast-enhanced MRI has been quoted as rather variable, ranging from 37% to 100%. This is mainly because of considerable exceptions and overlaps in contrast agent uptake and kinetics between benign and malignant tumors. The prevalence of cancer by MRI screening in high risk women is significantly greater than that reported in a similar population screened by ultrasound (4% vs. 1.3%). However, neither the technique nor the interpretive criteria are standardized as of to date, leading to variability in performance and in results interpretation. In addition, MRI can only be performed in a setting in which it is possible to perform biopsy of lesions detected solely by MRI.
Despite its high accuracy in detecting malignancies in breast, MRI is not recommended as a routine examination for the differentiation of benign and malignant lesions/tumors. MRI is a prohibitively expensive modality and it is unsuitable for large-scale screening programs. A US survey conducted by market research firm IVM has revealed that not more than 17% of US imaging facilities provide MRI imaging on site. Nonetheless, where available, MRI can be used as a complementary methodology to assist in differential diagnosis of uncertain lesions.
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