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(Cr(III)-labeled RBC's) Chromium labeled red blood cells have paramagnetic properties and potential as an intravascular MRI contrast agent. The labeling with chromium decreases the relaxation times of packed red blood cells (RBCs). The use of RBCs in nuclear medicine suggests a low toxicity.
See also Contrast Agents, Intravascular Contrast Agents, Blood Pool Agents. | | | | | Further Reading: | Basics:
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Coherent gradient echo sequences can measure the free induction decay ( FID), generated just after each excitation pulse or the echo formed prior to the next pulse. Coherent gradient echo sequences are very sensitive to magnetic field inhomogeneity.
An alternative to spoiling is to incorporate residual transverse magnetization directly into the longitudinal steady state.
These GRE sequences use a refocusing gradient in the phase encoding direction during the end module to maximize remaining transverse (xy) magnetization at the time when the next excitation is due, while the other two gradients are, in any case, balanced.
When the next excitation pulse is sent into the system with an opposed phase, it tilts the magnetization in the - a direction. As a result the z-magnetization is again partly tilted into the xy-plane, while the remaining xy-magnetization is tilted partly into the z-direction.
A fully refocused sequence with a properly selected and uniform f would yield higher signal, especially for tissues with long T2 relaxation times (high water content) so it is used in angiographic, myelographic or arthrographic examinations and is used for T2* weighting.
The repetition time for this sequence has to be short. With short TR, coherent GE is also useable for breath hold and 3D technique. If the repetition time is about 200 msec there's no difference between spoiled or unspoiled GE. T1 weighting is better with spoiled techniques.
The common types include GRASS, FISP, FAST, and FFE.
The T2* component decreases with long TR and short TE. The T1 time is controlled by flip angle. The common TR is less than 50 ms and the common TE less than 15 ms
Other types have stronger T2 dependence but lower SNR. They include SSFP, CE-FAST, PSIF, and CE-FFE-T2.
Examples of fully refocused FID sequences are TrueFISP, bFFE and bTFE. | | | | • View the DATABASE results for 'Coherent Gradient Echo' (6).
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Contrast enhanced MRI is a commonly used procedure in magnetic resonance imaging. The need to more accurately characterize different types of lesions and to detect all malignant lesions is the main reason for the use of intravenous contrast agents.
Some methods are available to improve the contrast of different tissues. The focus of dynamic contrast enhanced MRI (DCE-MRI) is on contrast kinetics with demands for spatial resolution dependent on the application. DCE- MR imaging is used for diagnosis of cancer (see also liver imaging, abdominal imaging, breast MRI, dynamic scanning) as well as for diagnosis of cardiac infarction (see perfusion imaging, cardiac MRI). Quantitative DCE-MRI requires special data acquisition techniques and analysis software.
Contrast enhanced magnetic resonance angiography (CE-MRA) allows the visualization of vessels and the temporal resolution provides a separation of arteries and veins. These methods share the need for acquisition methods with high temporal and spatial resolution.
Double contrast administration (combined contrast enhanced (CCE) MRI) uses two contrast agents with complementary mechanisms e.g., superparamagnetic iron oxide to darken the background liver and gadolinium to brighten the vessels. A variety of different categories of contrast agents are currently available for clinical use.
Reasons for the use of contrast agents in MRI scans are:
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Relaxation characteristics of normal and pathologic tissues are not always different enough to produce obvious differences in signal intensity.
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Pathology that is sometimes occult on unenhanced images becomes obvious in the presence of contrast.
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Enhancement significantly increases MRI sensitivity.
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In addition to improving delineation between normal and abnormal tissues, the pattern of contrast enhancement can improve diagnostic specificity by facilitating characterization of the lesion(s) in question.
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Contrast can yield physiologic and functional information in addition to lesion delineation.
Common Indications:
Brain MRI : Preoperative/pretreatment evaluation and postoperative evaluation of brain tumor therapy, CNS infections, noninfectious inflammatory disease and meningeal disease.
Spine MRI : Infection/inflammatory disease, primary tumors, drop metastases, initial evaluation of syrinx, postoperative evaluation of the lumbar spine: disk vs. scar.
Breast MRI : Detection of breast cancer in case of dense breasts, implants, malignant lymph nodes, or scarring after treatment for breast cancer, diagnosis of a suspicious breast lesion in order to avoid biopsy.
For Ultrasound Imaging (USI) see Contrast Enhanced Ultrasound at Medical-Ultrasound-Imaging.com.
See also Blood Pool Agents, Myocardial Late Enhancement, Cardiovascular Imaging, Contrast Enhanced MR Venography, Contrast Resolution, Dynamic Scanning, Lung Imaging, Hepatobiliary Contrast Agents, Contrast Medium and MRI Guided Biopsy. | | | | | | | | | | | • View the DATABASE results for 'Contrast Enhanced MRI' (14).
| | | • View the NEWS results for 'Contrast Enhanced MRI' (8).
| | | | Further Reading: | | Basics:
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News & More:
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FDA Approves Gadopiclenol for Contrast-Enhanced Magnetic Resonance Imaging Tuesday, 27 September 2022 by www.pharmacytimes.com | | |
Effect of gadolinium-based contrast agent on breast diffusion-tensor imaging Thursday, 6 August 2020 by www.eurekalert.org | | |
Artificial Intelligence Processes Provide Solutions to Gadolinium Retention Concerns Thursday, 30 January 2020 by www.itnonline.com | | |
Accuracy of Unenhanced MRI in the Detection of New Brain Lesions in Multiple Sclerosis Tuesday, 12 March 2019 by pubs.rsna.org | | |
The Effects of Breathing Motion on DCE-MRI Images: Phantom Studies Simulating Respiratory Motion to Compare CAIPIRINHA-VIBE, Radial-VIBE, and Conventional VIBE Tuesday, 7 February 2017 by www.kjronline.org | | |
Novel Imaging Technique Improves Prostate Cancer Detection Tuesday, 6 January 2015 by health.ucsd.edu | | |
New oxygen-enhanced MRI scan 'helps identify most dangerous tumours' Thursday, 10 December 2015 by www.dailymail.co.uk | | |
All-organic MRI Contrast Agent Tested In Mice Monday, 24 September 2012 by cen.acs.org | | |
A groundbreaking new graphene-based MRI contrast agent Friday, 8 June 2012 by www.nanowerk.com |
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| | | Searchterm 'relaxation' was also found in the following services: | | | | |
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A contrast medium (or contrast agent) is a chemical substance introduced to the anatomical or functional region being imaged, to increase the differences between different tissues or between normal and abnormal tissue, by altering the relaxation times.
The chemical composition of the contrast media determines the specific usage. Similar to nuclear imaging is the intention in development of MR contrast media a high affinity to different organs or even tumors (e.g. necrosis avid contrast agent).
In 'contrast' to nuclear imaging contrast agents MR contrast media do not contain radiopharmaceuticals and the concentrations are about 100 times higher. Nuclear imaging contrast agents are direct contrast agents;; they are directly visible caused by their radioactivity. MR contrast agents affect the targeted tissue; they are indirect contrast agents.
See also Contrast Agents, the info sheet gives an overview and more in-depth information about different types of MRI contrast medium. | | | | | | • View the DATABASE results for 'Contrast Medium' (26).
| | | • View the NEWS results for 'Contrast Medium' (2).
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| | | | • View the DATABASE results for 'Correlation Time' (2).
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