Figure 1:Un-subtracted axial VIBE image of left breast demonstrates patchy areas of hyperintensity

Figures 2 and 3: Axial and sagittal subtracted images demonstrate a large enhancing mass in left superior medial breast with spiculated margins, morphologically suspicious for malignancy. Sagittal image also demonstrates loss of fat plane between the enhancing mass and anterior surface of the pectoralis muscle, suggesting possible extension of the mass into the pectoralis muscle. This large mass correlates with the patchy areas of hyperintensity in the left breast seen in Figure 1.

Figure 4: Post-contrast enhanced T1-weighed fat saturated images were taken at 3 time points after contrast administration: 20 seconds, 2 minutes, and 3.5 minutes. Regions of interest were drawn:

ROI 1: Enhancing breast lesion
ROI 2: Air
ROI 3: Background fat

Figure 5: Enhancement curves demonstrate that the background fat (ROI 3) and air (ROI 2) show very little enhancement as expected. The breast lesion curve demonstrates a quick wash in and wash out pattern which is suspicious for malignancy.

Ductal carcinoma in situ and infiltrating ductal adenocarcinoma of the left breast.

The potential for MRI for evaluating breast disease has increased over the past decade concurrently with advances in MRI technology. Overall, the existing data prove that MR imaging techniques have a high sensitivity (85-100%) for detection of breast malignancy. Breast MRI is generally performed with the patient in the prone position with dedicated surface coils to minimize image artifacts caused by respiratory motion and to optimize the signal-to-noise ratio. The heterogeneous nature of the breast and the overlap in T1 and T2 relaxation times between different normal and abnormal breast tissue types frequently renders conventional non-contrast breast MR images ambiguous. Various techniques have been applied to improve the sensitivity of MRI to diagnose breast disease including hybrid imaging approaches combining T1 and T2-weighting with fat suppression and magnetization-transfer (MT) contrast techniques. However, to provide clinically useful information a contrast enhanced dynamic MRI study must be used to increase the sensitivity of MRI in differentiating benign and malignant breast lesions.

For contrast enhanced studies the optimal dose of Gd-DTPA may range from 0.1 to 0.2 mmol per kg body weight depending of the sequence used. A variety of MR sequences for contrast-enhanced breast imaging can be used and should provide for adequate temporal resolution in dynamic studies of contrast enhancement. Most commonly, gradient-echo (GRE) sequences are used including 3D-FLASH (Fast Low Angle Shot) which using a very short TR and TE and a relatively low excitation angle provides for rapid acquisition of a large number of thin T1-weighted images. . Small lesions are better detected with three dimensional sequences than with two dimensional sequences because two dimensional sequences can produce gaps between slices that can miss small lesions. T2-weighted sequences acquired before the pre- and post-enhancement sequences allow for distinguishing blood products from fluid or fibrosis. On gradient-echo imaging high signal intensity can represent both fat and an enhancing lesion. Methods of eliminating fat from MR images include frequency selective fat suppression, chemical-shift imaging techniques, e.g. RODEO (Rotating Delivery of Excitation Off-Resonance), and image subtraction of the pre-contrast images from the post-contrast images.

There have been two major approaches for MRI breast image interpretation: evaluation of enhancement kinetics following contrast agent administration and evaluation of lesion morphology. Studies evaluating the enhancement kinetics of breast lesions following contrast agent administration have demonstrated that malignant breast lesions consistently enhance after contrast administration and tend to enhance earlier and to a greater degree than benign lesions. Both quantitative and qualitative methods have been studied to evaluate the enhancement kinetics. Quantitative methods include calculating several empiric measurements of enhancement including the maximum rate of enhancement (slope of enhancement uptake) and increase in signal intensity after contrast administration. The intervals at which these measurements should be performed and the optimal threshold above which enhancement should be suggestive of a malignancy vary widely and are being studied. The qualitative method for evaluating enhancement kinetics looks at the overall shape of the enhancement curve following contrast administration. Three types of time-intensity curves have been described:

Type I (Steady Enhancement): curve demonstrates a persistent increase in signal intensity beyond 2 minutes after contrast administration
Type II (Plateau): curve demonstrates a maximal signal intensity is achieved within the first 2 minutes after contrast administration and then remains fairly constant.
Type III (Washout): curve demonstrates a maximal signal intensity is achieved in the first 2 minutes after contrast administration and then decreases over time.

Studies have shown that benign lesions tend to exhibit type I curves, where as malignant lesions tend to exhibit type III curves. Contrast enhancement in tumors likely reflects the degree of vascularity, tumor angiogenesis, capillary permeability, and extracellular space. Variations in these factors can explain the overlap seen between the enhancement patterns of malignant and benign lesions. Approximately 10% of breast carcinomas do not show the characteristic rapid enhancement. For example, there have been reports of several infiltrating lobular carcinomas, malignant phylloides tumors, tubular carcinoma, and colloid and mucinous carcinomas showing a slow enhancement pattern. In addition, benign lesions such as certain fibroadenomas, papillomas and other proliferative lesions may show the characteristic enhancement curves of carcinoma. Since studies have shown that degree of contrast enhancement is related to proliferative activity within a given lesion, contrast enhancement patterns can also vary with the menstrual cycle. Studies have suggested that that maximum enhancement of the normal breast tissues occur during the luteal phase, the week prior to menstruation, as well as in the first week of the cycle. This cyclic enhancement is not uniform and can also be nodular with some tissues demonstrating rapid enhancement patterns similar to malignant processes. To reduce the risk of false positive results, MRI examinations of the breast should be performed in the second or third week of the menstrual cycle. For both the quantitative and qualitative approaches for evaluating enhancement kinetics acquisition of images promptly after contrast administration and accurate placement of a region of interest (ROI) over the area(s) of most rapid and intense enhancement is critical to differentiate between benign and malignant lesions.

The second major approach to MRI breast image interpretation has been the evaluation of lesion morphology. Morphological features that have been reported to suggest a malignant lesion include: a mass with irregular or spiculated borders, a mass with peripheral enhancement, and ductal enhancement. Morphological features that have been reported to suggest a benign lesion include: a mass with smooth or lobulated borders, a mass demonstrating no contrast enhancement, a mass with non-enhancing internal septa, and patchy parenchymal enhancement. In the future an integrated strategy combining both the evaluation of enhancement kinetics and morphologic features will be used for MRI image interpretation.

References:

1. Kopans DB. Breast Imaging, 2nd Edition. Philadelphia: Lippincott, 1998. pp. 626-634.
2. Kim EE and Jackson EF. Molecular Imaging in Oncology: PET, MRI, and MRS. Berlin: Springer-Verlag, c1999. pp. 147-150.
3. Orel SG and Schnall MD. MR Imaging of the Breast for the Detection, Diagnosis, and Staging of Breast Cancer. Radiology. 2001; 220: 13-30.