magnetic resonance imaging (MRI, diffusion-weighted MRI)
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Introduction
Also see principles of magnetic resonance imaging
Indications
clinical indications for MRI
- structural diseases of the brain (MRI is the imaging modality of choice)
- primary brain tumor, metastatic brain tumor
- meningeal tumors
- acoustic neuromas
- pituitary tumors
- cerebral hemorrhage
- cerebral ischemia detected within a few hours of vascular occlusion
- multiple sclerosis
- radiation injury
- structural diseases of the spine & spinal cord
- suspected dissecting aortic aneurysm
- pelvic tumors
- structural musculoskeletal disorders
- bone tumors
- joint disease, especially knee osteoarthritis
- avascular osteonecrosis
- rotator cuff tear/injury
- useful for detecting soft tissue pathology, inflammation, & fluid collections[2]
- soft tissue masses
- pulmonary
- pulmonary neoplasm, lung cancer
- assessment of superior sulcus tumors
- small hilar tumors
- tumor invasion of the chest wall (metastases)
- tumors that involve the aortopulmonary window
- mediastinal tumors
- long imaging times & motion artifact makes MRI less useful than CT for assessing lung parenchymal disorders
*indications for contrast MRI imaging with gadolinium:*
- suspected process interrupting blood brain barrier
- infection
- inflammation
- neoplasm
- stroke
* gadolinium is the enhancing agent commonly used for MRI superparamagnetic iron oxides is another enhancing agent[6]
Contraindications
(contraindications for MRI)[5]
- metal (any ferromagnetic material)
- aneurysm clips
- intraorbital of intraocular metallic fragments
- mechanical cardiac valves
- Star-Edwards valve (caged ball valve)
- dental alloys, wires, splints & prosthesis do not appear to pose risk to patient, but may result in artifactual changes
- skin contact with metal objects can result in cutaneous burns - neurosurgical halo pins, pulse oximetry probes, nicotine patch
- tattoo reactions rare (& mild)[15]
- electronic or magnetic implanted devices[7]
- pacemaker, AICD
- may be safe with modified protcols[8][9]
- nonthoracic MRI may be safe with conventional pacemakers or implantable cardioverter-defibrillators (ICDs)[12]
- no cardiac device has been FDA-approved for MRI compatibility[7]
- risk of MRI in patients with abandoned cardiac electronic implanted device leads is low, including thoracic MRI[17]
- cochlear implant[9] relatively contraindicated
- implantable infusion pumps vary by make & model
- serious adverse events, including patient death due to dosing inaccuracies & other mechanical pump problems
- only implantable infusion pumps labeled as MR Conditional may be safely used as specified by the manufacturer[11]
- unstable patient
- pregnancy, risk to fetus unknown (relative contraindication)
- MRI during 1st trimester safe
- gadolinium enhancement risky during any trimester & should be avoided[10]
- 4-fold increase risk for stillbirth or neonatal death
- claustaphobia, sedation may mitigate
- obesity, devise has size limitations
Contrast MRI imaging with gadolinium:*
- risk for nephrogenic fibrosing dermopathy with glomerular filtration rates < 30 mL/min/1.73 m2
- use alternative forms of imaging in patients with low GFR if possible
- hemodialysis: perform dialysis promptly after gadolinium administration[11]
Advantages
- high sensitivity
- sectional images in multiple planes
- transverse sections
- longitudinal sections: coronal & sagital
- can show fluids in motion
- no ionizing radiation
- imaging of structure surrounded by bone
- better for imaging of the spinal cord & posterior fossa (cerebellum)
* advantages of MRI over CT
Disadvantages
- small bore & long hollow tube of the magnet excludes:
- obese patients
- patients with claustrophobia
- critically ill patients on life-support equipment
- strong magnetic field excludes:
- patients with pacemakers
- patients with ferromagnetic appliances
- changes in calcified tissue are not revealed
- pathologic changes in cortical bone
- calcification of tissues: tumors, vasculature, etc.
- long imaging times & motion artifact makes MRI less useful than CT for assessing lung parenchyma[2]
* limitations of MRI
Procedure
- patient is advanced into bore of magnet in supine position on floating table
- ear-plugs or ear-music systems are commonly used because of high noise level
- entire exam takes 20-45 minutes
- multiple imaging sequences in multiple planes
- imaging sequences range from 1 second to 10 minutes
- patients asked to remove jewlery, metallic objects, including cutaneous metal devices (nicotine patch)
- patients to wear face mask with no metal during MRI exams[16] during COVID-19 pandemic
Notes
- introduction of the 1.5 Tesla whole-body superconducting scanner in 1983
- 1st MRI FDA-approved for neonates July 2017[13]
- 7 tesla device doubles magnetic field strength facilitating better visualization of smaller structures & subtle pathologies[14]
- 0.05 Tesla whole body MRI, including T1-weighted, T2-weighted, & diffusion-weighted imaging augmented by deep learning AI[18]
- no protective shielding is needed
- patients & bystanders can safely use smart phones
- scanner is safe for patients with implanted devices, inlcuding cochlear implant or pacemaker
- metal on body or clothes also ok
- no hearing protection is required, scanner is quiet
- not yet FDA-approved
- may be commercially available in a few years[18]
- helium is used in cooling MRI scanners[19]
More general terms
More specific terms
- cardiac magnetic resonance imaging (CMR imaging)
- diffusion-weighted imaging (DWI)
- dobutamine stress MRA
- functional magnetic resonance imaging (fMRI)
- magnetic resonace imaging breast
- magnetic resonace imaging head & neck
- magnetic resonance angiography (MRA)
- magnetic resonance cholangiopancreatography (MRCP)
- magnetic resonance imaging abdomen
- magnetic resonance imaging bone marrow
- magnetic resonance imaging chest
- magnetic resonance imaging lower extremity
- magnetic resonance imaging pelvis
- magnetic resonance imaging spine
- magnetic resonance imaging temporomandibular joint (TMJ)
- magnetic resonance imaging upper extremity
- magnetic resonance neuroimaging (brain & brainstem)
- magnetic resonance venography (MRA)
- MR enterography; magnetic resonance enterography
- MRI of abdomen
- MRI of abdomen & pelvis
- MRI of adrenal gland
- MRI of ankle
- MRI of breast
- MRI of cervical spine
- MRI of chest; MRI of thorax
- MRI of elbow
- MRI of foot
- MRI of forearm
- MRI of hand
- MRI of head;
- MRI of hip
- MRI of kidney
- MRI of knee
- MRI of liver
- MRI of lower extremity
- MRI of lower leg
- MRI of lumbar spine
- MRI of neck (soft tissues)
- MRI of pancreas
- MRI of pelvis
- MRI of sella turcica & pituitary
- MRI of shoulder
- MRI of spine; MRI of vertebral column
- MRI of spleen
- MRI of thoracic spine
- MRI of upper extremity
- MRI of wrist
- open MRI (includes standing MRI)
Additional terms
- gadolinium [Gd]
- MRI cerebral white matter lesion (white matter hyperintensity)
- principles of magnetic resonance imaging (MRI)
References
- ↑ Introduction to Clinical Imaging, Radiology Syllabus, UCSF, 1993
- ↑ 2.0 2.1 2.2 Medical Knowledge Self Assessment Program (MKSAP) 11,16,17. American College of Physicians, Philadelphia 1998,2012,2015.
- ↑ Harrison's Principles of Internal Medicine, 14th ed. Fauci et al (eds), McGraw-Hill Inc. NY, 1998, pg 2289
- ↑ Veterans Affairs (VA) National Center for Patient Safety Magnetic Resonance Imaging (MR) Hazard Summary http://www.patientsafety.gov/mrihazardsummary.html
- ↑ 5.0 5.1 UpToDate 14.1 http://www.utdol.com
- ↑ 6.0 6.1 Aguirre DA, Behling CA, Alpert E, Hassanein TI, Sirlin CB. Liver fibrosis: noninvasive diagnosis with double contrast material-enhanced MR imaging. Radiology. 2006 May;239(2):425-37. PMID: https://www.ncbi.nlm.nih.gov/pubmed/16641352
- ↑ 7.0 7.1 7.2 Sommer T et al, Strategy for safe performance of extrathoracix magnetic resonance imaging at 1.5 tesla in the presence of cardiac pacemakers in non-pacemaker-dependent patients: A prospective study with 115 examinations. Circulation 2006, 114:1285 PMID: https://www.ncbi.nlm.nih.gov/pubmed/16966587
Nazarian S et al, Clinical utility and safety of a protocol for non-cardiac magnetic resonance imaging of patients with permanent pacemakers and implantable-cardioverter defibrillators at 1.5 tesla. Circulation 2006, 114:1277 PMID: https://www.ncbi.nlm.nih.gov/pubmed/16966586 - ↑ 8.0 8.1 Nazarian S et al. A prospective evaluation of a protocol for magnetic resonance imaging of patients with implanted cardiac devices. Ann Intern Med 2011 Oct 4; 155:415 PMID: https://www.ncbi.nlm.nih.gov/pubmed/21969340
Reynolds MR and Zimetbaum P. Magnetic resonance imaging and cardiac devices: How safe is safe enough? Ann Intern Med 2011 Oct 4; 155:470. PMID: https://www.ncbi.nlm.nih.gov/pubmed/21969346 - ↑ 9.0 9.1 9.2 9.3 Kim BG et al Adverse Events and Discomfort During Magnetic Resonance Imaging in Cochlear Implant Recipients. JAMA Otolaryngol Head Neck Surg. November 20, 2014 <PubMed> PMID: https://www.ncbi.nlm.nih.gov/pubmed/2541181 <Internet> http://archotol.jamanetwork.com/article.aspx?articleid=1936465
Kanal E Magnetic Resonance Imaging in Cochlear Implant Recipients. Pros and Cons. JAMA Otolaryngol Head Neck Surg. November 20, 2014 <PubMed> PMID: https://www.ncbi.nlm.nih.gov/pubmed/25412437 <Internet> http://archotol.jamanetwork.com/article.aspx?articleid=1936463 - ↑ 10.0 10.1 Ray JG, Vermeulen MJ, Bharatha A et al Association Between MRI Exposure During Pregnancy and Fetal and Childhood Outcomes. JAMA. 2016;316(9):952-961 <PubMed> PMID: https://www.ncbi.nlm.nih.gov/pubmed/27599330 <Internet> http://jama.jamanetwork.com/article.aspx?articleid=2547756
- ↑ 11.0 11.1 11.2 FDA Safety Communication. Jan 11, 2017 Safety Concerns with Implantable Infusion Pumps in the Magnetic Resonance (MR) Environment. http://www.fda.gov/MedicalDevices/Safety/AlertsandNotices/ucm536518.htm
- ↑ 12.0 12.1 Russo RJ, Costa HS, Silva PD et al Assessing the Risks Associated with MRI in Patients with a Pacemaker or Defibrillator. N Engl J Med 2017; 376:755-764. February 23, 2017 <PubMed> PMID: https://www.ncbi.nlm.nih.gov/pubmed/28225684 <Internet> http://www.nejm.org/doi/full/10.1056/NEJMoa1603265
- ↑ 13.0 13.1 FDA News Release. July 20, 2017 FDA clears first neonatal magnetic resonance imaging device. https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm567840.htm
- ↑ 14.0 14.1 FDA News Release. Oct 12, 2017 FDA clears first 7T magnetic resonance imaging device. https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm580154.htm
- ↑ 15.0 15.1 Callaghan MF, Negus C, Leff AP et al Safety of Tattoos in Persons Undergoing MRI. N Engl J Med 2019; 380:495-496. Jan 31, 2019 PMID: https://www.ncbi.nlm.nih.gov/pubmed/30699316 https://www.nejm.org/doi/full/10.1056/NEJMc1811197
- ↑ 16.0 16.1 FDA Safety Communication. Dec 7, 2020 Wear Face Masks with No Metal During MRI Exams. https://www.fda.gov/medical-devices/safety-communications/wear-face-masks-no-metal-during-mri-exams-fda-safety-communication
- ↑ 17.0 17.1 Schaller RD, Brunker T, Riley MP et al Magnetic Resonance Imaging in Patients With Cardiac Implantable Electronic Devices With Abandoned Leads. JAMA Cardiol. Published online February 17, 2021 PMID: https://www.ncbi.nlm.nih.gov/pubmed/33595595 https://jamanetwork.com/journals/jamacardiology/fullarticle/2776350
- ↑ 18.0 18.1 18.2 18.3 Szalinski C 'Big Breakthrough': New Low-Field MRI Is Safer and Easier. Medscape. May 20, 2024 https://www.medscape.com/viewarticle/big-breakthrough-new-low-field-mri-safer-and-easier-2024a10009hb
Zhao Y, Ding Y, Lau V, Man C, Su S, Xiao L, Leong ATL, Wu EX. Whole-body magnetic resonance imaging at 0.05 Tesla. Science. 2024 May 10;384(6696) PMID: https://www.ncbi.nlm.nih.gov/pubmed/38723062 https://www.science.org/doi/10.1126/science.adm7168 - ↑ 19.0 19.1 Nature. 2024. Dec 12.