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magnetic resonance imaging (MRI, diffusion-weighted MRI)

Also see principles of magnetic resonance imaging Indications: clinical indications for MRI 1) structural diseases of the brain (MRI is the imaging modality of choice) a) primary brain tumor, metastatic brain tumor b) meningeal tumors c) acoustic neuromas d) pituitary tumors e) cerebral hemorrhage f) cerebral ischemia detected within a few hours of vascular occlusion g) multiple sclerosis h) radiation injury 2) structural diseases of the spine & spinal cord a) spinal cord neoplasm, meningeal neoplasm b) syringomyelia c) osteomyelitis of the spine d) degenerative disc disease e) herniated nucleus pulposis f) nerve root compression with radiculopathy g) cervical spine pannus h) spinal cord compression 3) suspected dissecting aortic aneurysm 4) *pelvic tumors a) endometrial carcinoma b) cervical carcinoma c) prostate cancer 5) structural musculoskeletal disorders a) bone tumors b) joint disease, especially knee osteoarthritis c) avascular osteonecrosis d) rotator cuff tear/injury e) useful for detecting soft tissue pathology, inflammation, & fluid collections [2] 6) soft tissue masses 7) pulmonary a) pulmonary neoplasm, lung cancer b) *assessment of superior sulcus tumors c) *small hilar tumors d) *tumor invasion of the chest wall (metastases) e) *tumors that involve the aortopulmonary window f) mediastinal tumors - mediastinal lymphadenopathy g) 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 a) *infection b) *inflammation c) *neoplasm d) *stroke * gadolinium is the enhancing agent commonly used for MRI superparamagnetic iron oxides is another enhancing agent [6] Contraindications: (contraindications for MRI) [5] 1) metal (any ferromagnetic material) a) aneurysm clips b) intraorbital of intraocular metallic fragments c) mechanical cardiac valves - Star-Edwards valve (caged ball valve) d) dental alloys, wires, splints & prosthesis do not appear to pose risk to patient, but may result in artifactual changes e) skin contact with metal objects can result in cutaneous burns - neurosurgical halo pins, pulse oximetry probes, nicotine patch f) tattoo reactions rare (& mild) [15] 2) electronic or magnetic implanted devices [7] a) pacemaker, AICD b) may be safe with modified protcols [8,9] c) nonthoracic MRI may be safe with conventional pacemakers or implantable cardioverter-defibrillators (ICDs) [12] d) no cardiac device has been FDA-approved for MRI compatibility [7] e) risk of MRI in patients with abandoned cardiac electronic implanted device leads is low, including thoracic MRI [17] f) cochlear implant [9] relatively contraindicated - MRI often painful - complications with implant magnet not uncommon [9] 3) 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] 4) unstable patient 5) 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 6) claustaphobia, sedation may mitigate 7) 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] Procedure: 1) patient is advanced into bore of magnet in supine position on floating table 2) ear-plugs or ear-music systems are commonly used because of high noise level 3) entire exam takes 20-45 minutes a) multiple imaging sequences in multiple planes b) imaging sequences range from 1 second to 10 minutes 4) patients asked to remove jewlery, metallic objects, including cutaneous metal devices (nicotine patch) 5) patients to wear face mask with no metal during MRI exams [16] during COVID-19 pandemic Advantages: 1) high sensitivity 2) sectional images in multiple planes a) transverse sections b) longitudinal sections: coronal & sagital 3) can show fluids in motion 4) no ionizing radiation 5) imaging of structure surrounded by bone 6) better for imaging of the spinal cord & posterior fossa (cerebellum) * advantages of MRI over CT Disadvantages: 1) small bore & long hollow tube of the magnet excludes: a) obese patients b) patients with claustrophobia c) critically ill patients on life-support equipment 2) strong magnetic field excludes: a) patients with pacemakers b) patients with ferromagnetic appliances 3) changes in calcified tissue are not revealed a) pathologic changes in cortical bone b) calcification of tissues: tumors, vasculature, etc. 4) long imaging times & motion artifact makes MRI less useful than CT for assessing lung parenchyma [2] * limitations of MRI Notes: - introduction of the 1.5 Tesla whole-body superconducting scanner in 1983 - scanners are mostly found in specialized radiology departments & large imaging centers with radio frequency (RF)-shielded rooms [18] - 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]

Related

gadolinium [Gd] magnetic resonance images (clinical) MRI cerebral white matter lesion (white matter hyperintensity) principles of magnetic resonance imaging (MRI)

Specific

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)

General

radiography (roentgenography)

References

  1. Introduction to Clinical Imaging, Radiology Syllabus, UCSF, 1993
  2. Medical Knowledge Self Assessment Program (MKSAP) 11,16,17. American College of Physicians, Philadelphia 1998,2012,2015.
  3. Harrison's Principles of Internal Medicine, 14th ed. Fauci et al (eds), McGraw-Hill Inc. NY, 1998, pg 2289
  4. Veterans Affairs (VA) National Center for Patient Safety Magnetic Resonance Imaging (MR) Hazard Summary http://www.patientsafety.gov/mrihazardsummary.html
  5. UpToDate 14.1 http://www.utdol.com
  6. 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: 16641352
  7. 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: 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: 16966586
  8. 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: 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: 21969346
  9. Kim BG et al Adverse Events and Discomfort During Magnetic Resonance Imaging in Cochlear Implant Recipients. JAMA Otolaryngol Head Neck Surg. November 20, 2014 PMID: 2541181 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 PMID: 25412437 http://archotol.jamanetwork.com/article.aspx?articleid=1936463
  10. 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 PMID: 27599330 http://jama.jamanetwork.com/article.aspx?articleid=2547756
  11. 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. 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 PMID: 28225684 http://www.nejm.org/doi/full/10.1056/NEJMoa1603265
  13. FDA News Release. July 20, 2017 FDA clears first neonatal magnetic resonance imaging device. https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm567840.htm
  14. FDA News Release. Oct 12, 2017 FDA clears first 7T magnetic resonance imaging device. https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm580154.htm
  15. 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: 30699316 https://www.nejm.org/doi/full/10.1056/NEJMc1811197
  16. 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. 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: 33595595 https://jamanetwork.com/journals/jamacardiology/fullarticle/2776350
  18. 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: 38723062 https://www.science.org/doi/10.1126/science.adm7168