Magnetic Resonance Imaging (MRI) (Diagnostic)

Magnetic Resonance Imaging (MRI)

imaging technique that uses a strong magnetic field and radiofrequency waves to generate detailed images of the body

Does MRI use ionizing radiation (XR)?

no

MRI provides superior visualization of

soft tissues (e.g., brain, spinal cord, muscles, ligaments)

does MRI take a long or short time?

long time, sometimes hours

how does MRI work?

-strong magnetic field causes H protons in body (water and fat) to align in a specific direction

-radiofrequency (RF) pulses applied, temporarily disrupting alignment

--when RF turned off, protons return to their original alignment, releasing energy in form of signals

-signals are detected by receiver coils and processed by a computer to generate detailed images in multiple planes

2 main MRI sequences

T1: best for anatomy eval (fluid is dark)

T2: best for patho eval (fluid is bright)

Advanced MRI Sequences: DWI (Diffusion-Weighted Imaging)

highly sensitive for acute strokes, abscesses, and some tumors

Advanced MRI Sequences: FLAIR (Fluid-Attenuated Inversion Recovery)

helps to identify white matter lesions (e.g., multiple sclerosis)

Advanced MRI Sequences: STIR (Short Tau Inversion Recovery)

helps to identify tissue edema and inflammation

Advanced MRI Sequences: MRA (Magnetic Resonance Angiography)

noninvasive imaging of blood vessels; helps to detect aneurysms, AVMs, and stenosis

MRI with contrast

-uses gadolinium-based contrast given IV (metal)

-compared to iodinated contrast used in CT/XR, allergic rxns w gadolinium are rare

why should MRI w contact be used w caution?

in pt w severe renal impairment d/t risk of Nephrogenic Systemic Fibrosis

Common Indications of MRI

can be performed virtually any part of the body

-Brain: Detection of strokes, epilepsy, infection, tumors, MS, or trauma.

-Spinal cord: Detection of myelopathy, disk disease, cord compression, tumors, or trauma.

-Musculoskeletal (MSK): Joint and bone pathology, bone marrow abnormalities, ligament, tendon, and cartilage injuries.

-Abdomen and pelvis: Diagnosis of abdominal or pelvic pathology and congenital abnormalities.

-Pregnancy: Detection of placental position and invasion, fetal anomalies (particularly cerebral)

-Cardiac: Detection of ischemia, iron overload, infiltrative diseases, congenital malformation, and cardiomyopathy. MRI can complement cardiac CT, echocardiography, and other cardiac tests.

-Angiography (MRA): Evaluation of arteries and veins throughout the body for stenosis, aneurysms, or vascular malformations

absolute contraindications of MRI

-Implanted medical devices (e.g., pacemakers, neurostimulators). There are many MRI-safe devices on the market now. Still, each device needs to be verified for safety before scanning.

-Metallic foreign bodies (esp. in the eye). Often seen in foundry workers. These people require orbital X-rays prior to MRI scanning.

-Bullets or shrapnel near great vessels or vital organs.

Contraindications of MRI d/t metal

-strong magnetic field can attract ferromagnetic objects, causing them to move suddenly with significant force (projectile risk).

-For safety, all metallic items must be screened and removed prior to entering the MRI environment, unless confirmed to be MRI-safe or MRI-conditional.

-Metallic objects within the body may move, cause injury, or heat during scanning.

relative contraindications for MRI

-Obesity (large patients might not fit into the bore of the MRI + poor image quality).

-Inability to remain still (e.g., claustrophobia, pain, movement disorder), which is crucial for MRI. Motion degrades image quality and limits the accuracy of interpretation.

-Children can be scanned without sedation at the age when they understand the need to lie still; otherwise, they may need to be sedated

special considerations of claustrophobia and anxiety for MRI

common

Pt may feel trapped inside the MRI scanner and may require reassurance, anxiolytics, or mild sedation.

-companion may be allowed in

-Open MRI scanners are an alternative

special consideration of pregnancy

-generally safe

-should only be performed when it will provide important diagnostic information that cannot be obtained with other modalities (e.g., ultrasound).

-Gadolinium contrast is generally avoided in pregnancy.

special consideration of breast feeding

-does not affect breastmilk

-Gadolinium contrast is excreted into breast milk in very small amounts.

--amount absorbed by the infant is negligible.

--No interruption of breastfeeding is required after gadolinium administration.

benefits of MRI

-Noninvasive, painless.

-Provides excellent soft tissue contrast and more detailed evaluation than CT or X-ray.

-Evaluates anatomy AND function (fMRI).

-Highly sensitive for early ischemic stroke.

-Does not use radiation (safe for children and pregnant women).

risks of MRI

-generally very safe for the general population.

-strong magnetic field may cause implanted medical devices to malfunction or distort the images (image artifacts).

-Nephrogenic Systemic Fibrosis is a rare complication caused by gadolinium contrast in patients with severe renal impairment

cost of MRI

between $400 to 10,500