radiology 1 Flashcards
Bayesian analysis
posttest odds = pretest odds * likelihod ratio
degree of attenuation of xray beams based on 3 things
- density
- thickness
- energy of xray beam
radiolucency -> radiodensity of common materials (6)
- air = most radiolucent- looks black
- fat
- water
- bone
- contrast
- heavy metals= most radiodense - looks white
digital storage systems for info
PACS
DICOM
RIS
HIS
PACS= picture archiving and communication systems
DICOM= digital imaging and communication in medicine
RIS= radiology information system
HIS= hospital information system
orienting an image on xray
AP/PA view
lateral
hands/feet
hang anatomically- like u are looking at the person
laterals are hung in same direction they are taken
hands and feet hand so you are looking at dorsal surface and digits face up
satisfaction of search (2)
can lead to false negative
when detection of 1 radiologic finding interferes w/ that of another
hounsfied units
def
3 common #s to know
def: measure of how much attenuation occurs in each pixel of CT scan
air = -1000
water = 0
bone = 1000
artifacts in CT
why they are caused
3 things that can cause them
caused by partial volume average of each voxel (less of a problem with new machines with thinner slices)
caused by:
- motion (eg cardiac motion)
- metal artifacts- distorts tissue around it
- beam hardening = algorithm filters out areas of low energy - which is high density places
risks of CT contrast (3)
- allergic reactions
can be mild (rash ) => severe -HTN, swelling, CV collapse*
- renal failure (creatinine >1.5-1.8)**
diabetics, dialysis pts, multiple myelomas
- contrast extravasation = contrast in soft tissue instead of vein
what type of contrast is okay for pts on dialysis?
what type of contrast is not okay for pts on dialysis?
OKAY: IV CT contrast
NOT OKAY: MRI contrast
3 advantages of CT
- fast
- high resolution
- multiplanar reformatting (3D)
3 disadvantages of CT
- radiation**
- possible risks
- possible artifacts
ionizing radiation
def
why we care
- electromagnetic waves that have the potential of creating an ion by knocking an electron out of its valence shell
- can damage DNA
radiation safety
acronym
trade-off
ALARA- as low as reasonably achievable
trade off btwn dose and quality of image
2 biological effects of radiation
examples of each
linear no threshold model (assumption)
- deterministic effects - means its dose dependent and there is threshold below which there is no effecteg; epilation, permanent sterility, cataracts
- stochastic effects= random = not dose dependent and no lower threshold
a. k.a. cancer from radiation (leukemia, breast, thyroid)
** linear no threshold model (assumption)= risk is directly proportional to dose at all levels. sum of several small exposures can = 1 large exposure
MRI pulse sequences
what is MRI contrast material?
risks of MRI contrast (3)
material = gadolinium
risks:
- nephrogenic systemic fibrosis = fibrosis of skin, joints, eyes, organs (= fatal)
- pts with severe kidney failure or on HD - contraind EGFR <30
- contraI for pregnant women
advantages of MRI (6)
- no ionizing radiatio
- lots of info on soft tissue
- sensitive to contrast enhancement
- ability to obtain 3d dataset
- get angiograms w/o contrast
- gadolinium is not as allergenic as iodinated compounds (CT)
disadvantages of MRI (6)
- long scan times
- motion artifacts
- artifacts- eg surgical hardware
- expsensive
- many pts have contra I
- claustrophobia
MRI safety
4 zones
the magnet is always on full strength*
zone 1: public accessible
zone 2: supervised access, where screening by MRI staff occurs
zone 3: restricted area, prescreened pts and staff
zone 4: magnet room
MRI dangers (7) (first 4 are **)
- missile effect*
- field interatcion w/ medical devices*
- torque on implanted devices*
- gadolinium risks*
- thermal effect
- cryogens
- acoustic noise
MRI safety signage
MR in a box = MR safe
device/ implant non-magnetic, non-electrically conductive, non-RF reactive = safe for MRI
MR in a triangle= MR conditional
device/implant may contain magnetic, electrically conductive or RF reactive components- but is safe in the proximity of the MR
MR circle w/ line= unsafe
device/implant significantlly ferromagnetic
general rules to follow for ordering films (1)
for fx: order
soft tissue
infection
always order plain films first
fx: 1. plain films
2. CT
3. bone scan and MRI
soft tissue injury
- MRI
- US
infection
- xray
- MRI w/ & w/o contrast
- bone scane
- indium WBC scan
