Introduction to breast MRI
Breast MRI (magnetic resonance imaging), also known as magnetic resonance mammography, is a noninvasive technique for imaging the breasts. It creates high-quality images of the breasts and has better sensitivity and specificity for detection of breast cancer than the other currently available technologies. Breast MRI is also used in evaluation of integrity of breast implants. (See the images below.)
See Breast Lumps in Young Women: Diagnostic Approaches, a Critical Images slideshow, to help identify and manage palpable breast lumps in young women.
See Breast Cancer for complete information on this topic.
Development of MRI-based breast examination
The breast was one of the first organs studied with MRI for the detection of cancer, albeit initially in vitro.  The breast was also the first organ in which the detection of invasive tumor neovascularity was highlighted through the application of rapid serial imaging after an injection of contrast agent.
With the clinical application of nonenhanced breast MRI, the value of T1-weighted (T1W) and T2-weighted (T2W) spin-echo imaging rapidly became clear, through the analysis of characteristics such as lesion morphology, signal intensity, and tissue relaxation times.
It also became clear that the T2 relaxation rates of benign tissues and malignant tissues overlap  and that in situ cancers could not be reliably detected at all. The development of a dedicated breast coil, rapid 2D gradient-echo (GRE) imaging, high field strength (>1T) magnets that enabled spectral fat-suppression, new methods of k-space filling to increase resolution and speed, and bolus injection of gadolinium dimeglumine created the technique of dynamic contrast-enhanced breast MRI. This technique showed an extremely high sensitivity for breast malignancy, higher than conventional methods of breast imaging.
Although dynamic contrast-enhanced breast MRI was initially limited to a single section location, it was soon modified with newly developed multisection, spoiled GRE sequences. This thin-section dynamic contrast-enhanced technique formed the foundation of modern breast MRI. MRI-guided breast biopsy and localization methods have been developed to investigate abnormal areas seen on breast MRI. (See the image below.)
Prerequisites for the performance and interpretation of breast MRI
Breast MRI is a highly specialized diagnostic technique that complements clinical assessment and conventional imaging with mammography and ultrasound (US). It does not replace these techniques, except in certain unusual situations. In general, breast MRI should not be performed without conventional imaging performed first.
When breast MRI is performed for screening or evaluation of breast cancer, administration of an intravenous gadolinium-based contrast agent is a must. If the patient has a contraindication to gadolinium administration, breast MRI should not be performed for evaluation of breast cancer. Non-contrast MRI of the breast should only be performed for assessment of integrity of breast implants.
Breast MRI is best performed in a multidisciplinary setting with access to additional breast imaging, as well as close collaboration between the surgeon, radiologist, oncologist, and pathologist.
Radiologists experienced in MRI but without a strong knowledge of breast disease and diagnosis often have major difficulties with the interpretation of breast MRI studies. The radiologist interpreting breast MRI must (1) have a thorough understanding of breast pathology and diagnostic workup of breast diseases, (2) work closely with a breast surgeon and pathologist, (3) be experienced in the interpretation of mammograms and breast sonograms, and (4) be experienced in image-guided breast biopsy techniques.
Role of breast MRI in detection and evaluation of breast disease
Breast MRI is used as an adjunct to conventional mammographic assessment.
It provides additional information in the following ways:
Finding breast cancer not detected by other imaging modalities in women with dense breasts.
Finding additional disease in recently diagnosed breast cancer cases (multifocal, multicentric, or bilateral disease).
Finding an invasive component in ductal carcinoma in situ lesions.
Breast MRI relies on detection of abnormal enhancement caused by neoangiogenesis associated with malignancy. The increasing use of breast MRI has inevitably been accompanied by increased detection of incidental enhancing abnormalities that were not detected by conventional imaging. These apparent lesions may represent normal or dysplastic tissues, cyclic hormonal changes, benign tumors, or unexpected malignant foci. The nature of such foci must be clarified so that a cancer is not missed and small cancers are identified.
Three strategies are commonly used to diagnose these lesions: performing MRI-guided repeat US (second-look ultrasound), repeating breast MRI at another suitable time, or performing MRI-guided needle biopsy.
Indications for performing breast MRI
Breast MRI is costly, is not as widely available as mammography, and needs injection of contrast medium. Optimal MRI imaging of breasts is performed between days 7 and 14 of a woman's menstrual cycle to avoid the confounding background parenchymal enhancement. It can give rise to a larger number of false positives leading to unnecessary biopsies. Therefore, there are guidelines for performing breast MRI. [6, 7, 8, 9]
According to the American Society of Cancer guidelines for screening breast MRI, women who are at high risk for breast cancer based on certain factors should get an MRI (and a mammogram) every year. This includes women who have a lifetime risk of breast cancer of about 20-25% or greater, according to risk assessment tools that are based mainly on family history (such as the Claus model); have a known BRCA1 or BRCA2 gene mutation; have a first-degree relative (parent, brother, sister, or child) with a BRCA1 or BRCA2 gene mutation and have not had genetic testing themselves; had radiation therapy to the chest when they were between 10 and 30 years of age; and have Li-Fraumeni syndrome, Cowden syndrome, or Bannayan-Riley-Ruvalcaba syndrome or have first-degree relatives with one of these syndromes.
The American Cancer Society recommends against MRI screening for women whose lifetime risk of breast cancer is less than 15%.
There is not enough evidence to make a recommendation for or against yearly MRI screening for women who have a moderately increased risk of breast cancer (a lifetime risk of 15-20% according to risk-assessment tools that are based mainly on family history) or who may be at increased risk of breast cancer based on certain factors, such as (1) having a personal history of breast cancer, ductal carcinoma in situ (DCIS), lobular carcinoma in situ (LCIS), atypical ductal hyperplasia (ADH), or atypical lobular hyperplasia (ALH) or (2) having dense breasts (“extremely” or “heterogeneously” dense) as seen on a mammogram.
If MRI is used, it should be in addition to, not instead of, a screening mammogram. This is because although an MRI is a more sensitive test (it’s more likely to detect cancer than a mammogram), it may still miss some cancers that a mammogram would detect.
For most women at high risk, screening with MRI and mammograms should begin at age 30 years and continue for as long as a woman is in good health. However, because the evidence is limited about the best age at which to start screening, this decision should be based on shared decision-making between patients and their health care providers, taking into account personal circumstances and preferences.
Indications for breast MRI in a diagnostic setting include the following:
Evaluation of extent of disease in a patient with recently diagnosed breast cancer (multifocal or bilateral disease).
Evaluation of invasive lobular carcinoma.
Characterization of an indeterminate lesion after a full assessment with mammography, ultrasonography, and physical examination.
Detection of occult primary breast carcinoma in the presence of carcinoma in axillary lymph node or metastatic adenocarcinoma of unknown origin.
Monitoring of the response to neoadjuvant chemotherapy.
Evaluation in postoperative patients with positive margins.
See the image below.
Contraindications to performing breast MRI
Contraindications to breast MI include the following:
Patient's inability to lie prone.
Marked kyphosis or kyphoscoliosis.
Extremely large breasts.
Inability to use gadolinium-based contrast media (history of allergy to contrast media or pregnancy).
Other general contraindications to MRI.
Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent.
Advantages of breast MRI
The advantages of breast MRI include the following:
No ionizing radiation.
Capability of imaging the entire breast volume and chest wall.
3-dimensional (3D) lesion mapping with techniques such as maximum intensity projection (MIP) slab 3D reconstruction.
Detection of occult, multifocal, or residual malignancy.
Accurate size estimation for invasive carcinoma. 
Good spatial resolution.
Ability to image regional lymph nodes (axillary as well as internal mammary).
In a study by Wasif et al, MRI was found to be more accurate than ultrasonography or mammography in the determination of the size of breast cancer masses. Out of 61 lesions, MRI-based tumor size was within 1 cm of pathologic size in 44 (72%) tumors, more than 1 cm above pathologic size in 6 tumors, and more than 1 cm below pathologic size in 11 tumors. 
Weinstein et al concluded that the addition of MRI to mammography in patients with a high risk of breast cancer has the greatest potential to detect additional, mammographically occult cancers. The investigators prospectively compared breast cancer detection of digital mammography (DM), whole-breast US (WBUS), and contrast-enhanced MRI in a high-risk screening population that previously screened negative with film screen mammography (FSM). 
In the Weinstein study, the cancer yield by modality was evaluated, and 20 cancers were diagnosed in 18 patients (9 ductal carcinomas in situ and 11 invasive breast cancers). The overall cancer yield on a per-patient basis was 3% (18 of 609 patients). The cancer yield by modality was 1% for FSM (6 of 597 women), 1.2% for DM (7 of 569 women), 0.53% for WBUS (3 of 567 women), and 2.1% for MRI (12 of 571 women). Of the 20 cancers detected, some were detected on only one imaging modality (FSM, 1; DM, 3; WBUS, 1; MRI, 8). 
Moy et al evaluated breast MRI in cases in which mammographic or ultrasonographic findings were inconclusive, and they found that MRI had a sensitivity of 100% and a significantly higher specificity than mammography (91.7% vs 80.7%, respectively). MRI also had greater positive predictive value (40% vs 8.7%) and overall accuracy (92.2% vs 78.3%). 
(See the images below.)
Limitations of breast MRI
There are several factors that limit the widespread use of breast MRI, such as the following:
High equipment cost.
Limited scanner availability.
Need for the injection of a contrast agent.
No standard technique.
Poor throughput compared to that of US or mammography.
Large number of images.
Relatively long learning curve for interpretation.
False-positive enhancement in some benign tissues (limited specificity).
Variable enhancement of in situ carcinoma.
An incidence of slowly or poorly enhancing invasive carcinomas of about 5%. 
Breast MRI and mastectomy
There has been concern that because breast MRI has greater sensitivity in cancer detection than mammography and US, its increased use will lead to an increased rate of mastectomy in women with early stage breast cancer. However, Dang et al found that from 2003 to 2007, although the annual number of breast MRI scans ordered by their institution rose from 68 to 358, the percentage of women who underwent mastectomy did not change over that period. 
Differential diagnosis of lesions seen with breast MRI
If early rapid enhancement due to neovascularity were unique to malignant tissues, breast MRI would be the standard in clinical practice today. Unfortunately, such enhancement is not specific, and several benign conditions may enhance in a fashion similar to cancer. Conversely, a small percentage of malignancies either enhance identically to benign breast parenchyma or, rarely, do not enhance at all.
Benign pathologies that may mimic malignant enhancement include the following (false positive):
Cyclical physiologic parenchymal enhancement
Florid epithelial hyperplasia
Lobular carcinoma in situ
Posttreatment scarring and/or granulation tissue
Radial scar and/or complex sclerosing lesion
Malignancies that may show benign-type enhancement include the following (false negative):
Highly scirrhous invasive ductal carcinoma (IDC)
Invasive lobular carcinoma
MRI-guided ultrasonography (second-look US)
When a suspicious finding is seen on breast MRI, high-resolution targeted US is performed to detect and evaluate the lesion, as well as to provide guidance for biopsy as needed. It is frequently possible to perform an ultrasound-guided biopsy instead of a more expensive and time-consuming MR-guided biopsy. However, one should be careful, because a malignant lesion detected by MRI may be subtle and less specific in appearance on US; therefore, careful ultrasound scanning is required.
MRI-guided biopsy or localization
MRI-guided biopsy is an inevitable consequence of performing breast MRI, because it can depict lesions that are occult on all other forms of breast imaging and on clinical examination. A number of research centers have confirmed that MRI-guided biopsy is at least practical and that it can be used to verify a malignant diagnosis of otherwise occult neoplasms. [47, 48]
Early breast coils had a completely closed design that precluded needle-based interventions in the breast. Breast coils that have an open design have been developed for routine imaging. These permit free access to the breast for biopsy. Unilateral, dedicated biopsy coils allow complete access to the breast and much of the chest wall and axillae.  Several investigators have developed various techniques for MRI-guided fine-needle biopsy or localization. [41, 50, 51, 52, 53, 54, 55, 56] Biopsy needles and hookwires made specifically for breast MR interventions are commercially available. Typically, these devices are non-ferromagnetic, compress the breast mediolaterally, have a perforated needle-guide compression plate, have MRI-visible markers, and use mechanical needle positioning.
User preference and familiarity with conventional image-guided breast biopsy are critical factors for success, regardless of the device and choice of needle-biopsy technology.
Typically, imaging is performed with gentle, mediolateral compression by using compression plates to stabilize the breast. It is important not to apply too much pressure, because this may reduce lesion enhancement, sometimes markedly. 
After contrast enhancement and appropriate targeting, the suspicious lesion is biopsied with an MRI-compatible needle. Alternatively, a biopsy clip can be placed or a hookwire can be deployed for subsequent surgical excision.
It is important to determine concordance of the histologic results with biopsied MRI findings. In benign concordant biopsies, a 6-month follow-up breast MRI is recommended.
Synonyms, Keywords and Related Terms
Breast MRI, Magnetic Resonance Mammography, breast cancer imaging
For breast MRI, most facilities use a 1.5T or higher-strength magnet. Narrow separation of fat and water peaks at mid and low field strengths, which precludes effective fat suppression. Although image subtraction techniques can overcome this to some extent, motion artifacts remain a major limitation of this postprocessing method for the removal of fat signal. Sensitivity to gadolinium enhancement is reduced at lower field strengths because of the inherently shorter T1 of all tissues. The signal-to-noise ratio (SNR) of all MRI methods is directly proportional to the field strength: at 1.5T, the SNR is 3 times greater than the SNR at 0.5T.
A dedicated double breast surface coil is essential, because it permits simultaneous high-resolution and high-quality imaging of one or both breasts. Such a coil is shown in the image below.
A phased-array design is considered ideal today. Sixteen channel coils have recently been introduced. Newer designs are open on the sides, permitting access during hookwire localization and needle biopsy.
The patient lies prone, with both breasts freely suspended in the coil. A symmetrical coil platform design gives the patient the option of entering the magnet bore feet first or head first. Because of claustrophobia concerns, it may be preferable to perform these studies with the patient entering feet first.
In general, the available gadolinium-based intravascular contrast agents have virtually identical pharmacokinetics and contrast-enhancement characteristics. They are equally suitable for breast MRI. All of these agents shorten T1 and increase tissue relaxation rates, increasing the signal intensity on T1W or spoiled GRE images. Suitable agents include gadolinium dimeglumine, gadoteric acid, gadoteridol, gadodiamide, and gadobenate dimeglumine.
The administration of contrast material should be by means of a rapid bolus injection. The authors routinely use an MRI-compatible power injector at a rate of 2 mL/sec, followed by a 20-mL isotonic sodium chloride flush. Although they are less convenient, hand injections are also successful.
For 2D GRE sequences, a dose of 0.16 mmol/kg appears to provide better sensitivity for lesion detection than the standard dose of 0.1 mmol/kg at field strengths less than 1.0T.  However, good evidence suggests that with 3D gradient echo sequences at higher field strengths, the standard dose of 0.1 mmol/kg does not reduce the sensitivity of the test,  and the authors routinely use this dose successfully.
Injection timing is important for breast MRI. To capture the peak contrast enhancement, it is recommended that scanning should start within 1 to 2 minutes of contrast injection. Each post-contrast scan duration should be between 1 to 2 minutes.
Patients undergoing breast MRI are often anxious either because they have a known diagnosis of breast cancer or because they are expecting one. In anxious or claustrophobic patients, the physician and technologist can use the following strategies:
Provide a good explanation of the examination.
Use a calm, relaxed approach during the examination.
Allow the patient to enter the magnet bore feet first.
Intermittently move the patient out of the tunnel if needed.
Appropriately shorten the sequences as appropriate.
Extremely anxious patients may require IV sedation. Midazolam, 3-5 mg, via slow IV injection is effective.
Numerous breast MRI protocols have been published, and the inexperienced reader can easily be confused as to which to follow. All of the published techniques are similar in the detection of breast malignancy. Therefore, it is more important for a radiologist to be comfortable and familiar with a specific protocol to ensure a high level of diagnostic accuracy than to try to always update to the latest sequence or technique.
The ideal contrast-enhanced breast MRI sequence has the following parameters:
Temporal resolution of less than 30 seconds.
Volumetric acquisition with at least 28 sections and no intersection gaps.
Isotropic spatial resolution of less than 1 mm.
High sensitivity with the contrast agent.
Perfect removal of the fat signal.
Capability to image both breasts entirely in one pass.
Because of current hardware limitations, no current sequence has all of these characteristics. However, novel methods for k-space filling, such as spiral 3D imaging, may allow this ideal sequence to be achieved in the near future.
In general, repeated scans are performed through the breasts after contrast administration, with each one lasting between 1-2 minutes. All post-contrast imaging should be completed within 7-10 minutes, because the diffusion of contrast material into normal tissues limits diagnostic characterization after this time. This technique is called dynamic contrast-enhanced breast MRI (DCE-MRI).
To detect suspicious contrast enhancement, imaging times shorter than 10-60 seconds are generally unnecessary; as many as 5-10% of carcinomas enhance relatively slowly, reaching peak enhancement at 3 minutes or even longer.
Rapid serial, double-breast scanning with 2D multisection GRE imaging may be performed after the injection of contrast material, with or without image subtraction. This method is almost unchanged from the initial technique described by Kaiser and Zeitler. 
Slower, high-resolution, single-breast, fat-suppressed 3D imaging may be performed, with acquisitions in the first 3 minutes after the injection. High-resolution analysis of lesion architecture and enhancement is used. [17, 19] The use of 3–time-point, 3D, high-spatial-resolution acquisitions with these sequences has been described for additional low-temporal-resolution information.
A hybrid technique using a rapid serial 3D or 2D sequence for the first 2-3 minutes after the administration of contrast agent, followed by 2- to 3-minute high-resolution, fat-suppressed imaging in 1 plane, yields similar results.  Optionally, one may also add a rapid serial, dynamic, washout-phase acquisition after high-resolution imaging to increase diagnostic specificity for some invasive cancers.
The acquisition plane has a significant impact on the pulse sequence. Phase-direction motion artifacts due to breathing and heart motion are minimized by ensuring that the frequency-encoding direction is in the anteroposterior direction for axial and sagittal imaging. In the coronal plane, switching the phase direction craniocaudally allows the use of a rectangular field of view with reduced phase encoding, reducing the acquisition time. However, intramammary mapping of lesion location can be difficult in the coronal plane; respiratory motion may produce unpredictable variations in signal across the images; and some coils and sequences generate unwanted moiré-like image artifacts at the edges of the breast because of variations in bulk tissue susceptibility.
For these reasons, the authors prefer the axial and sagittal planes. These are also generally easier to correlate with the mammographic projections. Despite the problems with coronal imaging, the International Multicentre Breast MRI Study used the coronal plane for dynamic acquisitions, with excellent results.  Again, this testifies to the overall robustness of breast MRI as a technique, even with major differences in acquisition methods.
Removal of fat signal
In general, T1W sequences of any type that are sensitive to contrast enhancement are also highly sensitive to other intrinsic short-T1 substances, the most common of which in the breast is fat. Four major approaches have been used to reduce or remove fat signal to show enhancement more clearly: GRE technique, digital image subtraction, spectral fat saturation, and magnetization transfer suppression (MTS). 
GRE imaging can be performed with a carefully chosen repetition time (TR), echo time (TE), and flip angle to minimize the (in-phase) fat signal while remaining sensitive to the presence of gadolinium enhancement. This approach was initially developed with field strengths of less than 1T, and it tends to be less suitable with high field strengths, where the T1 of fat is longer. Because this method is usually a 2D technique with relatively thick sections, the risk of missing a small lesion is significant.
Pixel-by-pixel digital image subtraction with precontrast and postcontrast images is the only reliable method of fat suppression with low field strengths. This method permits the short imaging times required for breast MRI. Inversion recovery and Dixon techniques tend to be slow at low field strengths, largely because of the poor SNR.
Subtraction is the best means of canceling signal inhomogeneity across the breast at any field strength. However, it is time-consuming and susceptible to motion artifacts. Worse, misregistration due to patient motion may cause a lesion to become less visible. Therefore, if subtraction is used, the source images must be carefully reviewed.
Spectral fat saturation using frequency-selective pulses is another technique. At less than 1T, the spectral separation of fat and water resonances is too narrow for this technique to be reliable. Successful application requires careful shimming; a good coil design; and, frequently, manual preimaging tuning. Even so, homogeneous fat suppression may not be possible with large breasts. Nevertheless, this technique remains the best method of obtaining high-spatial-resolution 3D scans without resorting to subtraction.
The MTS method reduces the glandular tissue signal by using detuned saturation pulses before the imaging sequence; this shortens the water relaxation by coupling it to macromolecular motion. This technique, as either an adjunct to or a substitution for spectral fat suppression, achieves high sensitivity in terms of contrast-enhancement sensitivity. [23, 24, 25] However, the technique has not been formally studied to determine whether it is consistently superior to other methods.
Of all of these approaches, image subtraction and spectral fat suppression are the 2 most commonly used strategies for improving enhancement detection.
Quantification of enhancement
Morphology of a lesion is the most important criterion for distinguishing between benign and malignant lesions. Breast MRI specificity may be improved by analyzing the pattern of contrast enhancement on dynamic images. Breast cancers tend to enhance early, whereas normal breast tissue enhances slowly.
The enhancement curves obtained by DCE-MRI are divided into 2 phases of enhancement: early (between contrast injection and second postcontrast minute) and delayed (after second postcontrast minute).
The American College of Radiology Breast Imaging Reporting and Data System (BIRADS) lexicon describes 3 types of early phase enhancement: slow, medium, and rapid. Most malignant lesions show faster early enhancement, as compared to normal breast tissue and benign lesions. The delayed phase of enhancement is also characterized into 3 types:
Progressive (type I): enhancement continues to increase throughout the dynamic scans.
Plateau (type II): peak enhancement is reached at the end of the early phase and then does not change significantly in the delayed phase.
Washout (type III): enhancement decreases after the early phase peak enhancement.
A lesion may contain many different kinetic patterns. The most suspicious pattern within a lesion is usually considered for characterizing it.
These 3 basic curve shapes were described by Kuhl and co-investigators  .
In a study to determine the value of using such signal-time measurements with dynamic 2D MRM, Kuhl et al found that lesions with type I enhancement were more likely to be benign than malignant, whereas lesions with a type II or III enhancement curve were more likely to be malignant. The investigators studied 266 lesions.  These were subsequently excised, and 101 were proven to be malignant.
The researchers showed that 9% of breast cancers had a type I enhancement curve; 33.6%, type II; and 57.4%, type III. Conversely, 83% of benign lesions had a type I curve; 11.5%, type II; and 5.5%, type III. In this analysis, the sensitivity, specificity, and diagnostic accuracy were 91%, 83%, and 86%, respectively.
The use of computer-aided detection (automated, pixel-by-pixel, color parametric map analysis of the enhancement rate and intensity) is useful for improving reliability of assessment of the large number of images typically obtained with dynamic breast MRI.  This technique can also be used to instantly graph the time-enhancement curve as the cursor is moved across the dataset; this information adds to the diagnostic confidence in assessing the nature of an enhancing area. (See the image below.)
These maps are arbitrary, but typically, lesions that are strongly and/or rapidly enhancing appear red, whereas slowly or weakly enhancing lesions appear blue or green. Intermediate lesions usually are orange or yellow. These have been developed and commercialized to simplify the analysis of the large amount of image data.  These maps are helpful for the rapid evaluation of multiple foci of enhancement.
Even if such a workstation is lacking, all MR consoles have ROI measurement capabilities. The detection of suspicious foci depends, then, on visual analysis, with ROIs placed over each suspect area and the mean signal intensity being read off the screen. These data can be entered into standard software programs, such as spreadsheet programs, for further analysis and charting.
High-resolution spatial analysis of lesion architecture
Nunes et al published a somewhat complex, but comprehensive and, most importantly, validated, image-analysis decision model to improve the classification of enhancing lesions depicted on low-temporal-resolution, high-spatial-resolution, 3D fat-suppressed (3D FSPGR) images.  This detailed method yields high diagnostic accuracy and has formed the basis for subsequent studies of architectural-feature assessment.
This model was further validated, updated, and slightly modified. The resultant values for sensitivity, specificity, negative predictive value (NPV), positive predictive value (PPV), and accuracy were 96%, 80%, 96%, 78%, and 87%, respectively.  These diagnostic performance indicators are slightly more sensitive than, but otherwise similar to, those obtained by enhancement–time course analysis using dynamic 2D MRM.
Combined qualitative and quantitative analysis
Liu et al studied the diagnostic performance of combining enhancement quantitation with qualitative feature analysis and obtained sensitivity, specificity, and accuracy statistics of 93%, 74%, and 85%, respectively.  These results are essentially identical to those obtained with time-enhancement–curve analysis and with high-resolution spatial analysis.
Diagnostic criteria for malignant and benign processes
The following summary tables show the diagnostic criteria that permit characterization of an enhancing lesion as either malignant or benign. The data have been collated from a variety of publications and represent pooled approximations of published results.
Table 2. Breast MRI Criteria for Malignant Processes (Open Table in a new window)
|Peak enhancement < 60-90 s after the injection||Sensitivity||>90|
|Peak enhancement >50% above baseline||Sensitivity||>90|
|Peak enhancement >80% above baseline||Sensitivity||70-80|
|Washout after peak with falling enhancement over 5 min||Specificity||>90|
|Peripheral washout of enhancing mass*||Specificity||100|
Note–Values are from various authors and the architectural interpretation model developed by Nunes et al in 1997. PPV indicates positive predictive value.
Table 3. Breast MRI Criteria for Benign Processes (Open Table in a new window)
|Mild regional enhancement||NPV||92|
|No enhancing lesion||NPV||99|
|Lobulated enhancing nonseptate mass with low T2 intensity||NPV||100|
|Lobulated mass with minimal enhancement||NPV||100|
|Lobulated mass with non-enhancing internal septations||NPV||98|
|Note–Values are from various authors and the architectural interpretation model developed by Nunes et al in 1997. NPV indicates negative predictive value.|
Appearance of normal tissues
Fat and fibroglandular tissue
Normal fat appears moderately bright on non–fat-saturated images. For all practical purposes, normal fat does not enhance after the administration of gadolinium-based contrast material. With fat suppression, normal fat typically appears dark gray, except in areas where either paradoxical water suppression or poor fat suppression occurs; both are usually due to field inhomogeneity or incorrect preimaging tuning.
The amount of fibroglandular tissue is assessed on the noncontrast non–fat-saturated T1W images. This correlates with the amount of fibroglandular tissue seen on mammography. The descriptors to describe fibroglandular tissue on MRI are added to the new BI-RADS edition, as follows:
Almost entirely fatty
Scattered fibroglandular tissue
Heterogeneous fibroglandular tissue
Extreme fibroglandular tissue
Background parenchymal enhancement (BPE)
BPE has been officially added to the new BI-RADS MRI lexicon and the MRI report. There are four terms that describe the BPE: minimal, mild, moderate, and marked.
BPE does not directly correlate with amount of fibroglandular tissue seen on mammography.
These patterns and the intensity of enhancement depend on the patient's age and menstrual-cycle stage, as well as the relevant prior medical treatment. Normal parenchyma enhances more strongly in the 35-50 year age range. The enhancement is least in the second and third weeks of the menstrual cycle.  Nonspecific, focal areas of enhancement may resolve or fluctuate in size from month to month. [35, 36]
Nipple and areola
Normal nipples usually show a smooth thin rim of enhancement and are symmetrical bilaterally.
The normal nipple may enhance intensely and rapidly. Retroareolar ducts may enhance normally, though usually not as intensely. These changes can make the interpretation of nipple enhancement problematic in cases of malignancy, especially in the subareolar area.
(See the image below.)
In contrast, the areola does not normally enhance, and it appears only slightly thicker than adjacent skin; this characteristic permits the detection of areolar infiltration by a malignancy. Comparison with the contralateral side may be helpful, as shown in the image below. Asymmetrical enhancement in the presence of DCIS may indicate the presence of nipple involvement, even in the absence of clinically obvious Paget disease.
Appearance of intramammary and axillary lymph nodes
Normal intramammary and axillary nodes may enhance moderately intensely, either slowly or rapidly. They may even show a washout curve in the absence of malignancy. Therefore, the enhancement pattern is generally not useful for distinguishing benign nodes from involved nodes.
A node may be diagnosed with confidence on MR images by the presence of a fatty hilum and a sharply defined smooth contour. Careful comparison with the matching mammograms sometimes increases the diagnostic confidence if the typical mammographic appearance of the node can be demonstrated in the corresponding position.
Benign abnormalities seen on MRI
Simple cysts appear as circumscribed, uniformly T2 hyperintense, nonenhancing masses. There may be mild enhancement surrounding the cyst because of inflammation or because of compression of normal parenchyma.
Fibrocystic changes (FCC)
FCC includes cysts, apocrine metaplasia, epithelial hyperplasia, stromal fibrosis, and adenosis. On MRI, FCC may show regional, segmental, or focal non-mass enhancement or may appear as a mass with spiculated or smooth margins with varying types of enhancement.
Duct ectasia may be visible on precontrast T1W images as hyperintense, dilated, retroareolar ducts because of proteinaceous secretions and hemorrhagic contents. They can mimic prominent enhancing ducts and can be potentially misleading. The use of subtraction images can prevent this pitfall.
Sclerosing adenosis is typically indistinguishable from glandular parenchyma. On MRI, it can present as a mass (nodular sclerosing adenosis) with variable enhancement characteristics.
Fibroadenomas have varied MRI appearances. They typically appear as circumscribed, oval masses and are isointense or hypointense on T1W images. On T2W images, the signal intensity depends on the amount of myxoid (bright) and fibrous (dark) tissue within the mass. They may have dark internal septations. Postcontrast enhancement varies with the cellularity and sclerosis of the mass.
When fibroadenomas are hyalinized (usually in older women), they generally enhance more slowly and weakly. Densely hyalinized fibroadenomas show minimal or no enhancement. Larger fibroadenomas may appear moderately bright on T2W precontrast imaging, whereas almost 90% of larger carcinomas have a signal intensity lower than that of normal parenchyma.  (See the images below.)
Lipoma and hamartoma
Lipomas and fibroadenolipomas (hamartomas) are benign, mesenchymal lesions, and they are usually readily diagnosed with conventional imaging. Characteristically, the lesions have internal fat. Hamartomas can show varying enhancement on MRI because of the glandular component.
In acute infectious mastitis, conventional assessment is usually sufficient, and MRI has a limited role. The main differential diagnosis is inflammatory carcinoma. If MRI is performed for the assessment of infections, strong, rapid enhancement may be present, usually with a poorly defined regional or diffuse pattern.
Granulomatous mastitis is a rare inflammatory condition that may mimic acute infectious mastitis or invasive breast cancer. It is usually idiopathic, but it may be caused by various mycobacteria or Actinomyces species. It has also been described in association with sarcoidosis and Wegener granulomatosis. The patient experiences recurrent bouts of breast sepsis, with formation of sinus tracts that may discharge purulent material. Cultures of the material are usually negative, and biopsy shows granulomatous inflammation. (See the image below.)
MRI shows areas of strong, irregular enhancement around fluid-filled pockets. MRI can be useful in mapping the full extent of disease in this condition. This mapping helps in planning and monitoring therapy for this condition, which is notoriously difficult to treat. Surgery or corticosteroid therapy is the treatment of choice.
Atypical ductal hyperplasia
Atypical ductal hyperplasia (ADH) is a well-recognized, high-risk condition that may progress to DCIS and, eventually, to invasive carcinoma. Moreover, ADH can get upgraded to malignancy in 16-50% cases, which usually justifies surgical excision. On MRI, ADH can appear like a mass or nonmass enhancement.
Proliferative dysplasias, including florid epithelial hyperplasia, usually appear as foci or regions of slow to moderate enhancement after the administration of contrast material. Generally, this enhancement is indistinguishable from that of normal parenchyma or other abnormalities, and the diagnosis is made at pathologic examination.
Radial scar or complex sclerosis lesion
These lesions may be associated with tubular carcinoma, other invasive carcinoma, DCIS, LCIS, and ADH. They have variable MRI appearances and can present as an MRI-occult lesion, mass, architectural distortion, or nonmass enhancement. The enhancement characteristics are also variable. (See the images below.)
Papillomas are typically isointense on T1W images and isointense to slightly hyperintense on fat-suppressed T2W images. They enhance rapidly with contrast and can show variable delayed kinetics. High-resolution ultrasonography may be useful to determine whether the lesion is intraductal. (See the image below.)
Juvenile papillomatosis is an uncommon condition seen in young women. It may produce an appearance of multiple masses with marked distortion on mammograms. On MRI, this may appear as a network of enhancing, beadlike nodules that are connected by enhancing ducts. Alternatively, they may appear as a lobulated, enhancing mass with small internal cysts. (See the image below.)
Lobular carcinoma in situ
Lobular carcinoma in situ (LCIS) is a nonmalignant, proliferative condition that is a marker for an increased risk of breast malignancy. It is usually indistinguishable from benign parenchyma on MRI.
Malignant conditions of the breast on MRI Scans
Ductal carcinoma in situ (DCIS)
DCIS is a biologically diverse disease. It may be low grade, intermediate grade, or high-grade. The most common morphologic feature of DCIS on MRI is nonmass enhancement (NME). NME is described in the ACR BI-RADS lexicon as enhancement that is not a mass but is still distinct from the surrounding normal breast tissue.
DCIS mostly presents as NME. Segmental and ductal patterns of enhancement are more suspicious than regional and diffuse enhancement. Clumped NME is the most common type of NME seen with DCIS. Clustered ringlike enhancement has been described as a type of NME that is strongly suspicious for DCIS. In a smaller number of cases, DCIS may be seen on MRI as a mass with irregular margins.
DCIS frequently shows slower initial and plateau or persistent delayed-phase enhancement. It is well known that DCIS may not show kinetic features that are regarded as typical for malignancy.
The variability of enhancement of DCIS is due to variations in neoangiogenesis, which in turn is somewhat related to the histologic grade.  Between 15 and 40% of DCIS cases show minimal to moderate enhancement that is indistinguishable from that of normal glandular tissues. This pattern tends to occur in low-grade DCIS,  but it has also been described in comedocarcinoma.  DCIS of a high nuclear grade tends to have stronger enhancement than that of a lower-grade DCIS. Note that 40% of DCIS cases are not calcified, even when they are high grade  .
Paradoxically, although breast MRI is unsuitable for an evaluation of microcalcifications, it sometimes shows the extent of DCIS (calcified or noncalcified) better than mammography. Because this information has the potential to change the type and extent of surgical excision, breast MRI can prove useful for the local staging of DCIS, particularly when the noncalcified component is significant.
Invasive ductal carcinoma
On breast MRI, invasive ductal carcinoma (IDC) most often appears as an irregular, spiculated, or multilobulated mass with strong, rapid contrast enhancement that is at least 60% above baseline. Rim or inhomogeneous, centripetal enhancement on dynamic scans may be present. Typically, either a type II or type III enhancement curve is observed. Surrounding architectural distortion may be noted. About 5% of IDCs enhance slowly and/or less strongly, particularly if they are highly scirrhous. 
Surrounding enhancement of variable intensity may represent DCIS; florid dysplasia; or benign, parenchymal enhancement. Breast MRI may show multifocal lesions or nipple/chest-wall involvement, which may not be otherwise evident. Multifocal IDC may show moderate, segmental, ductal enhancement connecting the masses; such masses are thus seen to be part of the same breast segment, even if they are not close to one another. Internal, enhancing septa are sometimes seen in invasive carcinomas; these should be distinguished from nonenhancing septations, which are typical in fibroadenomas.
Invasive lobular carcinoma
Invasive lobular carcinoma (ILC) accounts for 10-15% of breast carcinomas. ILC lesions can be mammographically occult or subtle in 20-40% of cases. [42, 43] As many as 85% are isointense relative to glandular parenchyma, and a minority have malignant microcalcifications.  The incidence of multifocal, multicentric, and bilateral, synchronous or metachronous involvement is much higher with ILC than with IDC.
Mammography and ultrasonography tend to underestimate the extent of ILC. Breast MRI has been shown to be more accurate, correctly demonstrating the extent of disease in about 85% of cases.  In the authors' center, breast MRI is routinely used in all women with a preoperative diagnosis of ILC.
In most cases, ILC shows focal, irregular, strong, rapid enhancement typical of a malignancy. Single or multiple masses in one or more quadrants may be demonstrated. However, ILC occasionally has weak or moderate enhancement, and it may be difficult to distinguish from glandular parenchyma with this criterion alone.  Recognizing this problem is easier if the diagnosis is already known from needle biopsy results. In these cases, a masslike contour or associated architectural distortion is usually present. Despite this limitation, breast MRI is better than conventional imaging for preoperative staging of breast ILCs.
Other breast malignancies
Mucinous or colloid carcinoma may be well defined, with a lobulated border and homogeneous enhancement. Superficially, these tumors may resemble a large fibroadenoma. However, these lesions are typically round rather than oval. Enhancing internal septa may be visible; if present, malignancy can be correctly diagnosed.  In rare cases, if an excess of mucin is present with relatively little malignant tissue, enhancement may be unremarkable or even absent.
Papillary and tubular carcinomas may enhance strongly and rapidly. However, some of these tumors have weak angiogenesis, which reflects their relatively low biologic aggression. These lesions may then enhance relatively slowly and/or weakly. 
Non-Hodgkin lymphoma of the breast is rare and usually secondary to involvement elsewhere in the body. Primary lymphoma may be synchronously or metachronously bilateral; in some cases, it grows rapidly and forms a large mass. These tumors can be occasionally confused with an invasive carcinoma, particularly if only needle-biopsy specimens are examined. Breast MRI can help in determining the intramammary extent of disease and may be useful for monitoring the response to chemotherapy.
In the breast, sarcomas are rare. Metaplastic carcinomas are also rare, but they may undergo sarcomatous transformation, most typically to osteosarcoma. These generally appear as a nonspecific mass with enhancement. Sometimes, they are remarkably rounded with circumscribed margins. However, they may have markedly heterogeneous enhancement secondary to tumor necrosis.
Phyllodes tumors are usually diagnosed with mammography, ultrasonography, and needle biopsy. Breast MRI adds little other than a true size measurement of large lesions. These lesions appear as large, circumscribed masses with rapid, strong enhancement; they often have internal lobulation and cystic spaces. [41, 46, 28, 29]
Repeat breast MRI examinations
In premenopausal patients, cyclic hormonal enhancement is a common cause of false-positive enhancement. Although efforts to image premenopausal women in midcycle usually reduce the incidence of such foci, repeat midcycle MRM can show whether an apparent lesion changes from one cycle to the next. This is characteristic of hormonally influenced, benign tissue.
If a repeat examination shows a persistent abnormality with suspicious features that cannot be localized with US, the choice is to either continue to observe the lesion or perform breast biopsy to achieve a definitive diagnosis. The decision should be based on the level of suspicion of the MRI findings in context of the breast cancer risk in that particular patient; the options should be presented to and discussed with the patient.
Post image-guided biopsy changes on MRI scans
Normal tissues do not significantly alter their enhancement after routine needle biopsy. Foci of hemorrhage or a focal hypointense ferromagnetic metal artifact are occasionally seen at the biopsy site, particularly on GRE images. The biopsy clip is best visualized on T1 non-fat saturation images. Postbiopsy changes, including the biopsy tract, may be visualized in cases with recent biopsy.
Postoperative changes on MRI scans
Hematoma and seroma
Hematomas and seromas are usually seen shortly after surgery. However, in some cases, they may persist for months or years. Seromas appear as fluid-intensity, nonenhancing masses with smooth margins. Hematomas may be hyperintense or hypointense on T1W images, depending on the age and oxygenation state of the blood products. Chronic hematomas may have a low-intensity hemosiderin rim.
Both may show a rim of enhancing granulation tissue. This enhancement may be intense, potentially masking residual malignancy at the boundary of the collection. Focal nodular rim enhancement raises suspicion of residual disease. This reactive postsurgical enhancement decreases over time. A delay of at least 28 days after surgery is needed to achieve a reasonable specificity (75%) and an NPV (86%) for the detection of residual tumor. 
Fat necrosis can be seen with any trauma to the breast, including image-guided or surgical interventions. The MRI appearance of fat necrosis can be variable. Fat necrosis can present as oil cyst, calcification, spiculated mass, and architectural distortion. The enhancement pattern on MRI can be very variable. Correlation with the site of surgery and mammography is important. Central T1 hyperintensity within an abnormal enhancing area helps confirm the diagnosis of fat necrosis. If the lesion has suspicious morphology and enhancement, biopsy may be required to differentiate fat necrosis from cancer.
Scar tissue, as shown in image below, generally appears as a low-signal-intensity, linear irregularity with variable enhancement, which largely depends on the interval since treatment. In the first few months after surgery, the borders of the surgical cavity may have strong enhancement, particularly if hemorrhage or fat necrosis has occurred.
This reactive enhancement gradually subsides. At 6 months after surgery without radiation therapy, most cases show slow, minimal, or no enhancement. In such cases, the appearance of abnormal enhancement at the scar after 6 months should raise the suspicion of a recurrent malignancy.  Again, tiny ferromagnetic, hypointense, sucker-tip and instrument artifacts may be evident at the site of surgery, particularly if the native, unsubtracted GRE images are reviewed.
Alloderm is a human acellular tissue matrix that is being increasingly used in breast reconstruction. It is hypointense to glandular tissue on T2W images and isointense on T1W images. It does enhance after contrast administration.
Post-radiation therapy changes on MRI scans
Diffuse skin thickening, fibrosis leading to a smaller breast, and trabecular thickening are common findings after radiation. Fibrosis can have a spiculated masslike appearance but shows no or minimal enhancement.
In the first 12 months after radiation therapy, a diffuse increase in capillary permeability occurs. This change can cause marked parenchymal enhancement that later becomes patchy. In most women, this enhancement gradually declines after 18 months because of fibrosis.  As a result, after radiation, there is usually minimal background enhancement, less than the normal contralateral breast. Any enhancing lesion on this background is suggestive of a recurrent tumor. 
Some patients may need breast MRI soon after surgery and radiation therapy, if the presence of residual disease is strongly suspected. Although diffuse parenchymal enhancement is of little diagnostic value, the demonstration of typically malignant enhancement in a focal lesion should prompt repeat excision.
Post-chemotherapy changes on MRI scans
Breast MRI is a useful tool to assess the tumor response to neoadjuvant chemotherapy. It has been shown that breast MRI correlates better with pathologic response after neoadjuvant chemotherapy than a clinical exam and conventional imaging methods. Chemotherapy does not produce the initial edema response seen with radiation therapy.