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MRI stand for what?
magnetic resonance imaging
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the magnet in MRI
- 0.5-3 Tesla, 1.5 is most common
- this is 10,000-60,000x stronger than the earth's magnetic field
- it's always on
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real basics on how MRI works
it organizes your hydrogen atoms so you can detect disorganization in each voxel
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T1 FSE MRI shows what for water, fat, muscle, cartilage, cortical bone
- T1 FSE
- water: dark
- fat: bright
- muscle: intermediate
- cartilage: dark
- cortical bone: dark
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T2 FSE MRI shows what for water, fat, muscle, cartilage, cortical bone
- T2 FSE
- water: bright
- fat: bright
- muscle: intermediate
- cartilage: dark
- cortical bone: dark
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diff btwn T1 FSE and T2 FSE
water is bright in T2
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PD (proton density) MRI shows what for water, fat, muscle, cartilage, cortical bone
- PD
- water: intermediate
- fat: bright
- muscle: intermediate
- cartilage: dark
- cortical bone: dark
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PD vs T1 vs T2
water is dark for T1, bright for T2, intermediate for PD
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Stir/T2 Fat Stat, and T1 Fat Stat
they're like T1 and T2, but the fat is saturated and darkened (in this case, saturation darkens it!)
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what do you use for MRI contrast?
- gadolinium, not iodine like in CTs
- looks bright in imagine
- approx 20cc
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risks of MRI contrast
- gadolinium
- no significant allergy risk
- not nephrotoxic
- risk of nephrogenic systemic fibrosiscontraindicated for pregnant women
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nephrogenic systemic fibrosis
- people with kidney disease are at risk
- fibrosis of skin, joints, eyes, organs --> fatal
- gadolinium is absolutely contra-ind for pts w EGFR (estimated glomelular filtration rate) <30. 30-60 is borderline
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advantages of MRI
- no ionizing radiation
- lots of info about soft tissue
- very sensitive to contrast enhancement
- ability to obtain 3D datasets
- can get angiograms w/o contrast
- gadolinium isn't as allergenic
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disadvantages of MRI
- time (upt ot an hour)
- motion artifact
- artifacts of nearby surgical hardware
- expensive
- many pts have contra-ins
- claustrophobia
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MRI dangers
- missile effect on magnetic stuff in the room
- field interaction w medical devices
- torque on implanted devices
- gadolinium risks
- noise
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contraindications to MRI
- pacemaker
- nonremovable cochlear implant
- metal in eye
- non-compatible aneurysm clip
- any implanted electronic device (insulin pump, neurostimulatro units, etc)
- pregnant
- kidney disease
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possible problems for MRI pts (not contra-ind necessarily)
- metalic stnets, previous projectile injry
- penile implants
- artificial limbs
- tattoos
- medication patches w metal
- claustrophobia
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generally, what should you order for a fracture
- plane films
- CT
- bone scans and MRI for occult fractures
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occult fracture
- a fracture that cannot be detected by radiographic standard examination until several weeks after injury. The break is most likely to occur in the ribs, tibia, metatarsals, hip, or navicular. It is accompanied by the usual signs of pain and trauma and may produce soft tissue edema.
- Magnetic resonance imaging or a bone scan may be used to confirm a suspected occult fracture.
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generally, what should you order for a soft tissue injury
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generally, what should you order for an infection
- MRI w/wo contrast
- Indium WBC scan
- bone scan
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wondering what test to order...?
try www.acr.org
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nontraumatic knee pain -- what to order?
- first, x-ray
- if x-ray shows typical DJD, stop
- if x-ray is non-diagnostic, shows osteochondritis, avascular necrosis, second fracture, or deep lateral femoral notch (signs of lig injury) consider ordering an MRI
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summary of what to order
x-ray first, then non-contrast MRI
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when to give contrast?
- most musculoskeletal CTs and MRIs don't require it
- if you're looking for tumor or infection, MRI > CT, give contrast
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if an x-ray's not helpful and you suspect the osseous or surrounding soft is abnormal, order___
MRI w/o contrast
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if you suspect osteonecrosis and ordered an x-ray already...
MRI w/wo contrast
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if you suspect labral tear
MR arthography
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if you suspect referred pain...
joint injection
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if x-ray shows arthritis...
maybe MRI
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if x-ray shows PVNS or osteochondromatosis (benign bone tumor)...
MRI w/o contrast
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3 severe alergic reactions to CT contrast
- hypotension
- laryngeal swelling
- CV collapse
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what's the creatinine # for renal failure?
- > 1.5-1.8
- (0.6-1.3 is the norm)
- seen in diabetics and multiple myeloma
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if you want to do a CT on a pt with diabetes or multiple myeloma, how can you reduce the risk of triggering renal failure?
use nonionic iso-osmolar contrast agents
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a bunch of deterministic effects that can come form CTs
- epilation
- erythema
- dry desquamation
- wet desquamation
- (desquamation = loss of bits of outer skin by peeling or shedding or coming off in scales)
- permanent sterility
- cataracts
- blood, GI, or neurovascular syndromes
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which procedure has nephrotoxic contrast?
- CT (idiodine)
- not MRI, with gadolinium
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for whom is gadolinium contraindicated?
- preggers
- pts w esteimated glomelural filtration rates < 30 (30-60 is borderline)
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nephrogenic systemic fibrosis
- fibrosis of skin, joints, eyes, organs --> it's fatal
- gadolinium can triger this in pts w sever kidney falure or on hemodialysis
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basics on when to order MRI
for soft tissue injury or infection
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3 basic rules on when to give contrast
- 1) most msk CTs don't require IV contrast
- 2) most msk MRIs don't require IV contrast
- 3) if you're looking ofr tumor or infection, use MRI > CT .... and probably should give contrast
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