It is essential to obtain a very fast sequence under two minutes with contrast enhanced MRI rapid scans. The initial rise in signal intensity of any latent breast cancer can be missed. After a few minutes, the breast cancer is really not distinguishable from the normal enhancing breast parenchyma which enhances diffusely over time. Unfortunately, on T1 weighted sequences used in dynamic breast scans, fat will appear hyperintense just like the Gadolinium injection.
Therefore it becomes very important to suppress the fat signal in order to discriminate between a contrast enhance breast cancer lesions and the breast background, which contains variable amounts of fat. Fat suppression is an important aspect of breast MRI, even though younger woman screening for breast cancer will tend to have a decreased proportion of fat tissue. Breast stromal tissue tends to be replaced by fat tissue as women age. High fat density can obscure areas of contrast enhancement, and therefore certain methods are typically used to suppress the fat tissue signal.
Subtraction, subtracting the precontrast image from the postcontrast image can be helpful in subtracting the fat signal, but requires absolutely no patient movement between precontrast and postcontrast scans. The selection of a more specific fat suppression technique will generally depend on the purpose of the fat suppression whether it is contrast enhancement vs tissue characterization and the r elative amount of fat in the tissue being analyzed.
In the two breast MR images above and below, one notes how the fat suppression technique has revealed two distinctive areas of increased contrast intensity , suggestive of a suspicious lesion. The three main MRI techniques for fat suppression of contrast enhanced breast tissue scans are fat saturation, inversion-recovery imaging, and opposed-phase imaging. But a drawback of this technique is the sensitivity to magnetic field nonuniformity, unrealiability when used with low-field-strength magnets, and misregistration artifacts.
However, this technique is not specific for fat, and the intensity of the signal in breast tissue with a long T1 or a short T1 can be ambiguous. The main drawback of the opposed-phase technique is that the detection of small tumors embedded in fatty tissue is somewhat unreliable.
In a contrast-enhanced MRI scan of normal non-cancerous breast tissue, the radiologist will be looking for certain consistent features. Normal fibroglandular breast tissue will demonstrate enhancement, but this enhancement is rather easily recognized as it is visible in the lateral part of both breasts.
Normal fibroglandular breast tissue enhancement will also be simultaneous in both breasts, symmetrical, and with show a slow and continuous signal increase. This patient also has breast implants, but otherwise contrast enhancement MRI shows breast tissues to be normal. So, it is important to remember that enhancement contrast enhancement indicates increased vascularity. Since increased vascularity is not specifice to malignant tumors , as many benign tissues will also exhibit enhancement to varying degrees, the radiologist has to carefully analyze the type of enhancement in order to differentiate benign from malignant lesions.
When a contrast enhancement MRI technique is administered for breast cancer screening and diagnosis, there will usually be slow and gradual enhancement of the nipple-areola complex as well.
Many premenopausal women will demonstrate patchy or irregular enhancement to various degrees, dependent upon the timing of the menstrual cycle and the MRI scan.
This can complicate the use of MRI breast cancer screening for premenopausal high-risk women. Hormonal fluctuations during the menstrual cycle have been known to cause an uptake of gadolinium in normal breast tissue that can make dynamic breast MRI scans challenging to interpret.
These can be confusing signals to a radiologist looking for breast cancer. So, it is suggested that the best time to perform a contrast-enhanced MRI breast scan is just after menses is finished , when the hormonal effects should be lowest. Some radiologists working in the area of breast cancer have now started testing for serum progesterone concentrations. There are premenopausal women who lack cyclic menses due to a variety of reasons, and testing for serum progesterone can help determine the follicular phase of a normal menstrual cycle, and aid in scheduling the optimum time for a contrast-enhanced breast MRI.
But on the whole, scheduling breast MRI scans around menstrual cycle days usually turns out to be impractical and of little or no benefit, because when the breasts are dense and fibrocystic and have lots of enhancing areas, those cause uncertainties for the radiologist, no matter what part of the cycle the scan is done. In the contrast enhanced breast MRI below , one can see that basically all of the fibroglandular breast tissue is enhancing.
Unfortunately, this means that any breast cancer lesions, if present, would be hidden from view. It is quite likely that this particular breast MRI scan was performed with too-long a delay after the injection of the contrast agent. The longer the delay time before the scan, the more likely it becomes that normal fibroglandular breast tissue will also enhance.
However, an experienced breast cancer radiologist, aware of the timing sensitivities involved in contrast enhanced MRI, particularly for women with dense breasts, will not mistake enhanced fibroglandular tissue for breast cancer.
Objective: The purpose of this study was to assess and compare contrast-enhanced ultrasound and MRI patterns in the diagnosis of soft-tissue masses. Materials and methods: Two hundred fifty-five consecutively registered patients with histologically confirmed soft-tissue masses were included in this retrospective study. The diagnostic properties of four predefined contrast enhancement CE patterns were assessed, and logistic regression analysis was performed to determine the correlation between diagnosis and CE pattern, lesion size, and patient age and sex.
Contrast enhancement. Reference article, Radiopaedia. URL of Article. Promoted articles advertising. Loading more images Close Please Note: You can also scroll through stacks with your mouse wheel or the keyboard arrow keys.
Loading Stack - 0 images remaining. By System:. GBCAs can be classified by clinical use as extracellular fluid space, liver-specific, or blood pool. GBCAs share a minute half-life and are predominantly if not completely excreted in the urine. Because extracellular fluid space agents are used for neuroimaging, they will be the focus of this article.
Gadolinium-based contrast agents have been used around the world for about 20 years and are very safe and well tolerated. Serious adverse reactions are significantly less common than those caused by the iodinated agents used in CT scans. All agents release some free gadolinium, a toxic heavy metal, and none are entirely free of the risk of nephrogenic systemic fibrosis NSF. Magnetic resonance imaging is used routinely to image suspected cerebellopontine angle lesions, most commonly in the evaluation of patients with hearing loss and dizziness.
Contrast agents assist in the routine MR imaging of suspected pituitary lesions by highlighting the difference in appearance of the rapidly and floridly enhancing gland and the slower and less avidly enhancing lesion. Typical 2. Recently available 3D fast spin echo acquisitions overcome the limitations of older techniques and should be considered for routine use.
While perhaps less beneficial for the evaluation of macroadenomas, contrast is commonly used and may improve delineation of lesion borders with the adjacent optic apparatus and the presence of cavernous sinus invasion.
Contrast enhancement is an essential part of routine MR imaging protocols in patients with suspected metastatic disease, offering improved sensitivity especially with tiny nodular metastatic lesions which may elude detection without the use of contrast.
Leptomeningeal involvement is difficult to detect in on an unenhanced MR exam. Using contrast for this application improves sensitivity Figures 5 and 6. Postcontrast, 3-dimensional, T1-weighted techniques provide thin slices, which improve disease detection and the enhanced efficiency of three planes in a single scan. Perfusion imaging is an off-label use of contrast-enhanced MRI that can assist in characterizing primary brain tumors and can be essential in differentiating treatment related changes from tumor.
There are many versions of commercially available software which analyze data from the first pass of the contrast agent through the brain and deliver parametric images of blood flow and blood volume.
0コメント