# radiology 1a

 really basic idea behind Bayesian Analysis pretest probability affects post-test probability what should the clinical history look like in a radiology report/request one sentence, like a tweet, includingchief complaintrelevant medical historyrelevant exam findings (localize, lateralize)what are you trying to rule out ex: HIV c 2 days acute back pain at L5 and fever, R/O DJD, DDD Bayesian analysis formula post-test odds = pretest odds x likelihood ratio ex: was the employee who tested positive on the drug test using drugs? = 0.5% prevalence of drug use in the company x 99% specificity and sensitivity of test .67 = .0005 x .99  -- so there's a 67% chance the person isn't using drugs the .0005 would increase if the person has bloodshot eyes or needle marks in the arm volar vs dorsal means what? palmar vs dorsal how are radiographic views named? for the lower body part, the one closer to the cassette -- so, a R lateral side has the pt laying on her right side, RAO, LAO, RPO, LPO  (anterior/posterior oblique) -- has pt laying on front or back but on an angle what's a voxel? it's a 3-d pixel (vo stands for volume) attenuation of x-rays is based on what 3 things? thickness of material/bodymarterial density (fxn of atomic number)energy of the x-ray beam two variables that determine the amount of radiation mAs (milliamperes per second) - volume of x-rayskVp (peak kilovoltage) - energy of x-rays (like the height of a waterfall) radiolucency def allowing passage of x-rays or other radiation, not opaque radiodensity def opposite of radiolucency not allowing the passage of x-rays or other radiation spectrum of materials in order of increasing radiodensity (decreasing radiolucency) air, fat, water, bone, contrast, heavy metals air lets the x-rays pass thru, so it'll look blackbone contrast catches the x-rays, so it looks white basics on how distortion and magnification happens in x-rays the closer to the source of light (further from the x-ray cassette/film), the more the object gets magnified, (the bigger it'll look) so you need to have objects flat on the screen, or be aware of why distortion is happening 3 points on how to hang x-ray films hang anatomically - like you're looking at someone (their L is on your R)laterals are hung in same dir as when image is taken, otherwise facing to the Rhands and feet are hung so you're looking at dorsal surface and digits point up ABCs of x-rays (just what each letter stands for) alignmentbonescartilagesoft tissue things to look for under the A of the ABCs ALIGNMENTfracturesdislocation/sublucations things to look for under the B of the ABCs BONEScortical erosions (cortical is the outside of a Crunchie, cancelous is inside)mineralizationosteophytesdegenerative changesradiodense or radiolucent lesions things to look for under the C of the ABCs CARTILAGEjoint spacesjoint effusions things to look for under the S of the ABCs SOFT TISSUEmassesforeign bodiessubcutaneous airulcers where's the pedicle? btwn the vertebral body and the superior articular process where's the lamina? btwn TP and SP superior vertebral notch and inferior vertebral notch locations? posterior to the vertebral body, the indentations before the sup/inf articular processes what's Satisfaction of Search? You look at an x-ray, find one pathology, say, "ahah!" and stop looking. The phenomenon in which detection of one radiographic finding interferes with that of others .... results in false negative interpretation CAT scan aka CT scan is made how? x-ray beam and dectector are rotated around the patient who's laying in a tubeintense math happensa measure of attenuation (Hounsfield Units) is given for each pixel, and the end result is a cross-sectional image of the pt based on the attenuation of the x-ray beam Hounsfield units these are for measuring the attenuation of the x-ray beam in CT scanswater = 0 Hounsfield unitsair = -1000 super cool thing about helical CTs volume data at <1mm thickness can be reconstructed in any plane with very high resolution - you can have diff materials (bone, fat, soft tissue) in focus how many grayscale values in CT? how many can a human eye detect? how does this impact CTs? 4,00060-80we adjust the window and level to select the part of the scale we want to see (lung, mediastinal, fat, bone....) motion artifact in CT scans motion blurring the pic - the machine moves fast but we, or our heart beats, can move faster artifacts in CTs complications that make the image a less good representation of the body - motion, partial volume averaging, metal, beam hardening partial volume averaging artifact in CT if the blip of color is directly over one voxel, it's fine, but if it lies on a cross section, each voxel will average the darkenss in with the lightness on those squares, and you'll lose the fact that there was one concentrated spotthis is more of an issue with thicker slices, less with smaller voxels metal artifact in CTs some metal in the body - it's super dense (high radiodensity), a bright white spot, and it limits the eval of soft tissue directly adjacentthe metal radiates white off it in a star shapethis effect can be minimized with tweaks to imaging techniques beam hardening artifact a less dense area between much more dense areas may appear esp less dense (a darker line) "as x-rays pass thru substances that are dense, it filters out the low energy portion of the spectrum and "hardens" the beam" 4 types of CT contrast oralrectalnegativeintravenous how does intravenous contrast work? iodinated compounds are injected into a vein as scan is performed, usually approx 100mlscan is timed to get images in desired phase - arterial, venous, excretory, delayedevaluates blood pool structures (arteries and veins) and vascularity (infection, tumor, inflammation) why IV contrast is good at id-ing a tumor contrast leaks into tumor, and also the angiogenesis of a tumor (new blood vessels) draw in blood and contrast from the nearby vein or artery allergy & CT contrast mild: rash - not a contraindication, just an inconveniencesevere: hypotension, laryngeal swelling, CV collapse (contraindications, of course) renal failure & CT contrast renal failure (creatinine > 1.5-1.8) can be triggered in pts w diabetes, multiple myeloma, -- decreased risk w non-ionic iso-osmolar contras agents BUTonce you're on dialysis it's fine to do contrast - it won't hurt you now! contrast extravasation a leakage of contrast material into the fatty tissue around a vein. Extravasation happens in one out of every 250 to 500 procedures. 3 advantages of CT fast (seconds)high resolutionmultiplanar reformatting (MPR) - 3D dataset can be reconstructed in any plane 3 disadvantages of CT artifactsrisks of trouble from the IV contrastradiation!! spectrum of things that give increasing amounts of electromagnetic radiation radiofrequencymicrowavesinfraredvisible lightUV lightx-rays (x-rays, CT)gamma rays (nuc med -used for destroying tissue) can ionizing radiation result in damage to DNA? yes what is ionizing radiation? electromagnetic waves w the energy to knock an outer shell electron out of its valence shell --> an ioncan --> damage to DNA the Inverse Square Law of Radiation and Distance radiation dose decreases as a function of distance from the source, squaredie. double the distance, get a quarter of the radiation ALARA as low as reasonably achievable - how much radiation you want to use but it's a compromise btwn dose and quality of image depends on rate of exposure, tissue exposed, strength of radiation, etc deterministic effects health effects caused by radiation (erythema, sterility, chateracts...) stochastic effects neg effects that happen years after radiation exposure - cancer "linear no threshold model" it's an assumption - risk is directly proportional to the dose at all dose levels - so you need to look at the sum over time, not just at some one-time high level tx Authorshmvii ID197387 Card Setradiology 1a Descriptionradiology spring 2013 Updated2013-02-02T21:45:10Z Show Answers