Magnetic resonance imaging in breast diagnosis
Abstract: MRI of the breast has, since the introduction of gadolinium contrast agents, been increasingly used in breast investigations. MRI has been found to have a high sensitivity but a low specificity in cancer detection. The aim of this thesis was to study and establish the role of MRI in the clinical diagnosis of breast lesions. Which kind of lesions and which patients would benefit the most from MRI of the breast as an adjunct to other breast imaging modalities, and how should MRI be used in a clinical setting? In study I a comparison of the appearance of 27 lesions in two different T1-weighted 3D sequences regarding the contrast inherent in the sequences and following contrast enhancement was performed. Due to strong and widespread enhancement on the routine FLASH-sequence these lesions were examined with another T1 -weighted sequence. The FLASH-sequence was found to have a high sensitivity, revealing contrast-enhancing areas, and therefore remains the first choice for routine examinations. The MPRAGE-sequence was found to increase the specificity by downgrading false positive lesions to true negatives. In study II the histological changes caused by fine needle aspiration biopsy (FNAB) that theoretically might affect the evaluation of breast lesions on semidynamic MRI was evaluated in 17 lesions. According to our result MRI can be performed irrespective of the time interval to a performed FNAB, as the evaluations were not impaired. In study III dynamic contrast enhanced MRI (CE-MRI) was found to be a valuable adjunctive method to clinical examination, mammography and FNAB (triple diagnosis,TD) due to high sensitivity, but at the cost of a decreased specificity. This decrease was less pronounced in mammographically dense breasts, and hence these patients might benefit most from CE-MRI as an adjunctive investigation. In study IV lesion size at CE-MRI and mammography were compared to histopathological size. The size of a breast cancer is of importance in the choice of treatment, in particular when breast-conserving surgery is considered. CE-MRI and mammography were both good at measuring the size of detected invasive breast malignancies. The total sizes of malignant lesions were frequently underestimated by both methods. In study V the diagnostic accuracy of CE-MRI and scintimammography was compared, and the clinical value as an adjunct to mammography was evaluated. Dynamic CE-MRI and 99mTc-sestamibi scintimammography showed comparable diagnostic accuracy, but a better accuracy was found for the combination of CE-MRI and mammography when using ROC curves for evaluation. In lesions smaller than 10 mm in size 99mTc-sestamibi scinti mammography was found to be less reliable due to the low spatial resolution. In conclusion, MRI is a useful tool in breast diagnosis, in particular due to its high sensitivity, the ability to exclude multifocality/multicentricity and accuracy in determining size and extent of a lesion. Due to the low specificity MRI is not to be recommended as a general screening tool, but as an adjunctive method in selected cases.
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