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Knee MRI, with its high soft tissue contrast is one of the m ain imaging tools to depict knee joint pathology. MRI allows accurate imaging of intra-articular structures such as ligaments, cartilage, menisci, bone marrow, synovium, and adjacent soft tissue.
Knee exams require a dedicated extremity coil, providing a homogenous imaging volume and high SNR to ensure best signal coverage.
A complete knee MR examination includes for example sagittal and coronal T1 weighted, and proton density weighted pulse sequences +/- fat saturation, or STIR sequences. For high spatial resolution, maximal 4 mm thick slices with at least an in plane resolution of 0.75 mm and small gap are recommended. To depict the anterior cruciate ligament clearly, the sagittal plane has to be rotated 10 - 20° externally (parallel to the medial border of the femoral condyle). Retropatellar cartilage can bee seen for example in axial T2 weighted gradient echo sequences with Fatsat. However, the choice of the pulse sequences is depended of the diagnostic question, the used scanner, and preference of the operator.
Diagnostic quality in knee imaging is possible with field strengths ranging from 0.2 to 3T. With low field strengths more signal averages must be measured, resulting in increased scan times to provide equivalent quality as high field strengths.
More diagnostic information of meniscal tears and chondral defects can be obt ained by direct magnetic resonance arthrography, which is done by introducing a dilute solution of gadolinium in saline (1:1000) into the joint capsule. The knee is then scanned in all three planes using T1W sequences with fat suppression. For indirect arthrography, the contrast is given i.v. and similar scans are started 20 min. after injection and exercise of the knee.
Frequent indications of MRI scans in musculoskeletal knee diseases are: e.g., meniscal degeneration and tears, ligament injuries, osteochondral fractures, osteochondritis dissecans, avascular bone necrosis and rheumatoid arthritis. See also Imaging of the Extremities and STIR. | | | | | | | | | | | Further Reading: | | Basics:
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| | | | • View the DATABASE results for 'Low Field MRI' (8).
| | | • View the NEWS results for 'Low Field MRI' (5).
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Safety of Bedside Portable Low-Field Brain MRI in ECMO Patients Supported on Intra-Aortic Balloon Pump Friday, 18 November 2022 by www.mdpi.com | | |
Researchers at the University of Tsukuba develop a portable MRI system specifically for identifying wrist cartilage damage among athletes, providing a convenient means of early detection and treatment of injuries Tuesday, 26 April 2022 by www.tsukuba.ac.jp | | |
This bizarre looking helmet can create better brain scans Friday, 11 February 2022 by www.sciencedaily.com | | |
A low-cost and shielding-free ultra-low-field brain MRI scanner Tuesday, 14 December 2021 by www.nature.com | | |
Portable MRI provides life-saving information to doctors treating strokes Thursday, 5 August 2021 by news.yale.edu | | |
Synaptive Evry, an MRI for Any Space, Cleared by FDA Thursday, 30 April 2020 by www.medgadget.com | | |
World's First Portable MRI Cleared by FDA Monday, 17 February 2020 by www.medgadget.com | | |
Introducing a point-of-care MRI system Tuesday, 29 October 2019 by healthcare-in-europe.com | | |
Opportunities in Interventional and Diagnostic Imaging by Using High-performance Low-Field-Strength MRI Tuesday, 1 October 2019 by pubs.rsna.org | | |
Portable 'battlefield MRI' comes out of the lab Thursday, 30 April 2015 by physicsworld.com | | |
Portable MRI could aid wounded soldiers and children in the third world Thursday, 23 April 2015 by phys.org |
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| | | | | | | | • View the DATABASE results for 'Lung Imaging' (7).
| | | • View the NEWS results for 'Lung Imaging' (3).
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Chest MRI a viable alternative to chest CT in COVID-19 pneumonia follow-up Monday, 21 September 2020 by www.healthimaging.com | | |
CT Imaging Features of 2019 Novel Corona virus (2019-nCoV) Tuesday, 4 February 2020 by pubs.rsna.org | | |
Polarean Imaging Phase III Trial Results Point to Potential Improvements in Lung Imaging Wednesday, 29 January 2020 by www.diagnosticimaging.com | | |
Low Power MRI Helps Image Lungs, Brings Costs Down Thursday, 10 October 2019 by www.medgadget.com | | |
Chest MRI Using Multivane-XD, a Novel T2-Weighted Free Breathing MR Sequence Thursday, 11 July 2019 by www.sciencedirect.co | | |
Researchers Review Importance of Non-Invasive Imaging in Diagnosis and Management of PAH Wednesday, 11 March 2015 by lungdiseasenews.com | | |
New MRI Approach Reveals Bronchiectasis' Key Features Within the Lung Thursday, 13 November 2014 by lungdiseasenews.com | | |
MRI techniques improve pulmonary embolism detection Monday, 19 March 2012 by medicalxpress.com |
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The MRI device is located within a specially shielded room ( Faraday cage) to avoid outside interference, caused by the use of radio waves very close in frequency to those of ordinary FM radio stations.
The MRI procedure can easily be performed through clothing and bones, but attention must be paid to ferromagnetic items, because they will be attracted from the magnetic field. A hospital gown is appropriate, or the patient should wear clothing without metal fasteners and remove any metallic objects like hairpins, jewelry, eyeglasses, clocks, hearing aids, any removable dental work, lighters, coins etc., not only for MRI safety reasons.
Metal in or around the scanned area can also cause errors in the reconstructed images ( artifacts). Because the strong magnetic field can displace, or disrupt metallic objects, people with an implanted active device like a cardiac pacemaker cannot be scanned under normal circumstances and should not enter the MRI area.
The MRI machine can look like a short tunnel or has an open MRI design and the magnet does not completely surround the patient. Usually the patient lies on a comfortable motorized table, which slides into the scanner, depending on the MRI device, patients may be also able to sit up. If a contrast agent is to be administered, intravenous access will be placed. A technologist will operate the MRI machine and observe the patient during the examination from an adjacent room. Several sets of images are usually required, each taking some minutes. A typical MRI scan includes three to nine imaging sequences and may take up to one hour. Improved MRI devices with powerful magnets, newer software, and advanced sequences may complete the process in less time and better image quality.
Before and after the most MRI procedures no special preparation, diet, reduced activity, and extra medication is necessary. The magnetic field and radio waves are not felt and no p ain is to expect.
Movement can blur MRI images and cause cert ain artifacts. A possible problem is the claustrophobia that some patients experience from being inside a tunnel-like scanner. If someone is very anxious or has difficulty to lie still, a sedative agent may be given. Earplugs and/or headphones are usually given to the patient to reduce the loud acoustic noise, which the machine produces during normal operation. A technologist observes the patient during the test. Some MRI scanners are equipped with televisions and music to help the examination time pass.
MRI is not a cheap examination, however cost effective by eliminating the need for invasive radiographic procedures, biopsies, and exploratory surgery. MRI scans can also save money while minimizing patient risk and discomfort. For example, MRI can reduce the need for X-ray angiography and myelography, and can eliminate unnecessary diagnostic procedures that miss occult disease. See also Magnetic Resonance Imaging MRI, Medical Imaging, Cervical Spine MRI, Claustrophobia, MRI Risks and Pregnancy.
For Ultrasound Imaging (USI) see Ultrasound Imaging Procedures at Medical-Ultrasound-Imaging.com.
See also the related poll result: ' MRI will have replaced 50% of x-ray exams by' | | | | | | • View the DATABASE results for 'MRI Procedure' (11).
| | | • View the NEWS results for 'MRI Procedure' (6).
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The subacute risks and side effects of magnetic and RF fields (for patients and staff) have been intensively examined for a long time, but there have been no long-term studies following persons who have been exposed to the static magnetic fields used in MRI. However, no permanent hazardous effects of a static magnetic field exposure upon human beings have yet been demonstrated.
Temporary possible side effects of high magnetic and RF fields:
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Varying magnetic fields can induce so-called magnetic phosphenes that occur when an individual is subject to rapid changes of 2-5 T/s, which can produce a flashing sensation in the eyes. This temporary side effect does not seem to damage the eyes. Static field strengths used for clinical MRI examinations vary between 0.2 and 3.0 tesla;; field changes during the MRI scan vary in the dimension of mT/s. Experimental imaging units can use higher field strengths of up to 14.0 T, which are not approved for human use.
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The Radio frequency pulses m ainly produce heat, which is absorbed by the body tissue. If the power of the RF radiation is very high, the patient may be heated too much. To avoid this heating, the limit of RF exposure in MRI is up to the maximum specific absorption rate (SAR) of 4 W/kg whole body weight (can be different from country to country). For MRI safety reasons, the MRI machine starts no sequence, if the SAR limit is exceeded.
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Very high static magnetic fields are needed to reduce the conductivity of nerves perceptibly. Augmentation of T waves is observed at fields used in standard imaging but this side effect in MRI is completely reversible upon removal from the magnet. Cardiac arrhythmia threshold is typically set to 7-10 tesla. The magnetohydrodynamic effect, which results from a voltage occurring across a vessel in a magnetic field and percolated by a saline solution such as blood, is irrelevant at the field strengths used.
The results of some animal and cellular studies suggest the possibility that electromagnetic fields may act as co-carcinogens or tumor promoters, but the data are inconclusive.
Up to 45 tesla, no important effects on enzyme systems have been observed. Neither changes in enzyme kinetics, nor orientation changes in macromolecules have been conclusively demonstrated.
There are some publications associating an increase in the incidence of leukemia with the location of buildings close to high-current power lines with extremely low-frequency (ELF) electromagnetic radiation of 50-60 Hz, and industrial exposure to electric and magnetic fields but a transposition of such effects to MRI or MRS seems unlikely.
Under consideration of the MRI safety guidelines, real dangers or risks of an exposure with common MRI field strengths up to 3 tesla as well as the RF exposure during the MRI scan, are not to be expected.
For more MRI safety information see also Nerve Conductivity,
Contraindications, Pregnancy
and Specific Absorption Rate.
See also the related poll result: ' In 2010 your scanner will probably work with a field strength of' | | | | • View the DATABASE results for 'MRI Risks' (9).
| | | • View the NEWS results for 'MRI Risks' (3).
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