scans day Flashcards
(25 cards)
CT indics and limits
indic: bone and soft tissue tumors, frx, intra-articular abnorms, bone fragment detection, bone mineral analysis, neuroimaging
benefits: less cost, less time, physcial barriers w/ mri
limit: unable to distinguish small areas of diff tissues (tumors and surrounding soft tissue), radiation exposure
CT mechanism
2D taken to localize structures, spiral slices taken continuously
radiodensities converted from digital signals into matrix - each pixel assigned a shade of gray
matrix-> image
CT variants
3D- multiplanar reconstruction
CT myelogram: contrast allows visual on structures that inpinge neuro structures
-distinguish osteophytes, lig infolding, disc material
Viewing CT
-radiodensity free of superimposed tissues
-denser=more white
sagittal: view L to R
coronal: view as if facing pt
Bone and neuroimaging findings
bone: subtle frxs, degen changes, serious trauma, spinal stenosis, IV disc patho, intra-artic loose bodies, osseous alignment in any plane
neuroimaging: acute trauma, SPECT, PET
MRI what is it
measurement of energy emitted by hydrogen as they respond to radiofrx signals
molecules align w/ external magnet field ( made by coils)
radiofrx wave pulse applied at right angle, aligning protons in transverse plain
as protons realign they release energy
contrast produced by diff T1 T2 and # hydrogen
T1 weighted
measure
colors
measure energy from structures that give up energy quick (fat)
good anatomic detail
tissues with high water content appear darker
T2 weighted
measure
colors
measure energy from structures that give up energy slowly (water)
fat=darker
grainier, less spatial
good for identifying inflam
Clinical application
-sensitive to changes in bone marrow (dx bone tumor, stress frx, AVN)
-soft tissue injury (lig/tendon, meniscus, alt to arthroscopic dx, disc patho/neuro impingement)
-tumor staging (not as effective as bone scan)
MR arthrography and myelography
MRI limits
-imaging bone
-time
-high cost
-contra metal
-hardware=distortion
-physical limits
STIR
fat suppressed, water/fluid has high signal intensity (bright)
ad: great contrast resolution, use with low field strength magnets
dis: hemmorrhage and protein fluid may be suppressed, cannot use after contrast injected, grainier
helpful spine, MSK, plexuses, abdomen, chest, tumor detection
FLAIR
-signal from CSF suppressed, high signal indics patho
free fluid appears dark, edematous tissue is bright
helpful w/ brain and spine imaging (infarction, demyelination, meningitis, TBI)
fat-high-bright
fluids-low-dark
PD
-tissues w/ high density of protons =higher signal
fat and fluids=high
helpful w. brain and MSK imaging in extremities (discriminates well between fluid and cartilages)
fluid/fat-bright, cartilages darker, moving blood/air dark
general indic of nuclear imaging
testing function of tissues (dx by physiologic change)
Nuclear mechanism
radionuclide (gamma rays) introduced
absorbed diff by tissues based on metabolic activity
gamma rays observed, computer converts to digital image
Methods used
static: single image of region
whole: AP (ex: bone scans)
dynamic: timed sequence (indic for cardiac, gastric,etc)
SPECT: 3D (bone, perfusion, brain, liver)
PET: biologic function of cells (CNS studies, tumors)
Clinical indics
-cancer: staging, observing (screen pts with high risk metastasis to bone)
-detection of metabolic bone diseases
-detect bone abnorm
MSK: GO, frx/stress, inflam/infec, complications of hardware, CRPS, PFPS, AVN
Scintigraphy
hot spots?
func
nuclear imaging of skeleton
=increased uptake
confirms disease, identifies extent
Bone scan
what is it
three phase
imaging study of skeleton
osteoblastic: increased uptake
osteoclastic: decreased
first few hours after injection
1: flow study (immediate)
2: blood pool(30 min)
3: delayed (2-4 hrs)
ad, dis, contras of bone scan
ad: high sensitivity for changes in bone metabolism
dis: low specificity, poor anatomic detail
contra: pregnancy, breast feeding
USI mechanisms
current applied to crystal cause oscillations creating US beam
beam applied through ST
intensity greatest at center of beam
focal zone: narrowest zone along long axis
doppler US
blood velocity measured
when moving toward transducer, sound waves arrive at transducer faster
when moving aaway, sound waves arrive slower
doppler provides info on
-presence bf
-direction bf
-gross circulation abnorms
blood flowing through narrowed foramen characterized by increased speed and turbulence
indics and limits
-identify MSK lesions
-real time assess (dynamic test)
-biofeedback
-cont monitoring
-lacks radiation
limits: limited ability to show joint surfaces and intrartic structures
bones: only show cortical outline
lung fields: cannot cross air/tissue interfaces
obese people poor visual
