4 Basic MRI TechnologyThe basic MR system is composed of a main magnetic field, gradient fields, RF pulse generators, radiofrequency antennas to receive the signals returning from the tissues, and computer systems to control the system and to convert the information into readable images.
5 Some favor evaluating images in the axial planes, others choose to interpret in the sagittal plane. A dedicated breast coil, at least 1.5-Tesla magnet strength, and dynamic contrast administration are absolute requirements for the performance of breast MRI.
6 Many early breast imaging systems used a single coil and only one breast could be imaged at a time. We have always preferred a double coil that allowed bilateral simultaneous imaging because it has permitted a direct comparison between the two breasts.
8 The fat have faster relaxation times (greater interaction between molecules), so their T1 signal is shorter than pure water; thus, fat has the shortest T1 relaxation time. By convention, tissues with short T1 are presented as bright signals on T1 images.
9 Signals from Water: tissues with a long T2 are presented as bright signals on T2-weighted images. Thus, cysts (that contain fluid) with long T1 are dark on T1-weighted images and those with long T2 are bright on T2-weighted images.
10 On MRI this cyst had a characteristically low signal intensity (black) on this T1-weighted image (A) and a high signal intensity (white) on the T2-weighted image (B).
11 FAT Suppression :Because of the high signal intensity of fat on T1 images, it is often difficult to appreciate enhancing lesions on gradient-echo images from the high signal produced by fat on T1-weighted images. Consequently, methods have been devised that eliminate the high signal from fat so that the tissues that enhance following contrast administration are more easily appreciated .
12 Most MRI includes sequences that suppress the signal from fat Most MRI includes sequences that suppress the signal from fat. To optimize the chemical-shift fat-suppression techniques, maximizing the homogeneity of the field of the imaging volume is necessary. Shimming before imaging is needed to reduce the field in homogeneities that commonly occur in breast imaging.
13 Automated shimming is available Automated shimming is available. One effective method of fat suppression that is used in the one dedicated breast MRI system being sold uses RODEO (rotating delivery of excitation off-resonance) pulse sequence.
14 Fat suppression makes enhancing lesions easier to appreciate Fat suppression makes enhancing lesions easier to appreciate. Fat has low signal intensity on this fat-saturated T1-weighted image (A) prior to the IV administration of contrast. The cancer in the left breast is more evident on the first fat-saturated set of images following contrast injection (B). The lesion is more evident on this maximum intensity contrast subtraction 3D display (C) and on this single-slice subtraction image (D).
15 The most important advantage of breast MRI at this time is that contrast enhancement makes lesions stand out from the background tissues (high signal to background).Unlike mammography and US, where the signals generated by cancer may be similar to the background tissue, thus making the lesion difficult to perceive or even invisible on those tests.
16 Using contrast enhancement, MRI of the breast has become an increasingly useful clinical test. MRI of the breast requires the use of an (IV) contrast agent to define areas of possible malignancy.There is no data to support the use of MRI as a screening tool.Screening mammography generally used to detect breast cancer in the general population. while breast MRI has been shown to detect an increased rate of small cancers in women at high risk for breast cancer.
18 Fibroadenomas are usually round or oval, with sharply defined margins, on contrast-enhanced MRI.
19 The normal axillary lymph nodes also routinely enhance . The lymph nodes are usually clearly defined.Solitary enhancing lesions should be biopsied unless they are less than 5 mm or have clearly nonenhancing internal septations.
20 Breast MRI should not be used instead of mammography; it is a complementary study to other breast imaging modalities.Both mammography and USG have limitations in the evaluation of the chest wall. MRI is able to visualize the entirety of the chest wall. Enhancement of the pectoralis and intercostal muscles is indicative of chest wall invasion in patients with a posterior breast tumor.
21 Breast MRI indications 1-Preoperative evaluation of patients with newly diagnosed breast cancer:when combined with mammography and clinical breast exam, has been shown to provide sensitivity of 99% for the preoperative assessment of the local extent of disease in patients with newly diagnosed breast cancer.
22 The purpose of MRI is to detect the presence of multifocal and multicentric disease as well as to detect bulky residual disease at the lumpectomy site in order to allow directed re-excision.malignancies may enhance at much more rapid initial rates than benign lesions.
23 Breast cancer staging is based on the extent of local-regional disease in the breast and axilla, which has predictive value regarding the patient's prognosis and dictates treatment options.MRI sensitivity rates for the detection of invasive breast cancer are estimated to be as high as %.
24 Breast cancers are usually irregular in shape and heterogeneous in their enhancement on MRI.
25 2- evaluation of breast cancer patients treated with neoadjuvant chemotherapy. MRI has been used to monitor treatment response to neoadjuvant chemotherapy in patients with locally advanced cancer.Change in tumor vascularity/enhancement appear to explain changes in functional dynamic contrast assessment and can be seen after only one cycle of chemotherapy.
26 Neoadjuvant chemotherapy Neoadjuvant chemotherapy. Sagittal post contrast fat suppressed T1W image prior to chemotherapy shows an enhancing mass correlating to a biopsy-proven invasive ductal carcinoma (A). Following chemotherapy, a comparable image shows only a small area of residual enhancement (B)
27 3- evaluation of patients with metastatic axillary lymphadenopathy and an unknown primary malignancy.4- evaluation of breast cancer patients with positive surgical margins following breast conservation therapy.MRI can be useful in determining the extent of residual disease when margins are positive and the mammogram is not helpful.
28 Postsurgical MRI can demonstrate residual malignant disease Postsurgical MRI can demonstrate residual malignant disease. The postoperative MRI shows the seroma cavity on both the T2 images
29 5- determination of silicone breast implant integrity. (A) Retropectoral and (B) retroglandular placement of implants on MRI. Sagittal T1-weighted images of two different patients with silicone implants.
30 6-breast cancer screening in high risk women. 7- use of breast MRI as a problem-solving tool for equivocal mammographic findings and for 3-dimensional localization of a lesion seen.
31 8- Evaluation of occult breast cancer In patients with an occult primary presenting with axillary lymphadenopathy or Paget's disease, MRI has been shown to identify the primary in many patients, thus allowing for conservative surgery rather than mastectomy.
32 Detection of occult malignancy Detection of occult malignancy. This patient had a positive axillary lymph node with a negative clinical examination
33 9-small breast (MRI) is well suited to the investigation of breast cancer by virtue of its noninvasive nature and its multiplanar imaging abilities.10-Post surgical scar vs. recurrent tumorIn cases where mammography and ultrasound are inconclusive in patient suspected of recurrent disease, MRI can be helpful.Breast tissue can show enhancement for up to 18 months following radiation therapy.
34 Invasive breast cancer visible on T1-weighted image because of the surrounding fat.
35 Cysts are bright on T2. In this mammogram of the right breast (A), the dense tissues obscure the cysts that are easily seen on the T2-weighted MRI examination (B).
36 Blood in the ducts can be bright on T1 Blood in the ducts can be bright on T1. This patient had a bloody nipple discharge on the right. The blood in the duct is bright on the precontrast T1 image.
37 11-Breast MRI has consistently been found to detect additional unsuspected malignancy within the ipsilateral breast(in 10% to 27% of patients).
39 C. Inappropriate Use of Breast MRI 1. Screening of general populationAt present there is no data to support the use of MRI as a screening tool.To date, there are no studies demonstrating decreased mortality by the use of MRI. Not all cancers seen on mammography can be identified in MRI.
40 2. Differentiation of benign & malignant lesions Because of an overlap between the enhancement and morphological characteristics of benign and malignant lesions, MRI cannot be used as a substitute for biopsy.