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Diagnostic Imaging: Notes Summary

Types of Imaging:
--plain film radiography, aka x-ray
--tomography
--computed axial tomography (CT or CAT)
--magnetic resonance imaging (MRI)
--bone scan/nuclear medicine
--discography
--myelography
--positron emission tomography (PET)

PLAIN FILM RADIOGRAPHY
--1st choice for most cases
--indications: risk factors/history suggest clinical Q's that could alter Tx, ex: trauma, wt loss, nt pain, neuromotor deficit, inflam arthritis, hx of malignancy, FUO, abn blood, deformity, failure to respond to tx, therapeutic risk assess, monitor response to tx, medicolegal (CYA), over 50 yo, systemic dz, recent immigration, drug/alc abuse, corticosteroid use, unavailable other imaging, lost/old previous images
--NON-indicators: pt educ, routine screen, habit, discharge status assessment, routine biometric analysis, pre-employment, physical limitation of pt, non-trained personnel, financial gain, recent radiation exposure, preg
--advantages: cost effective, minimal radiation exposure, widely available
--disadvantages: not sensitive (30-50% bone dstx needed to see on film), no axial images, quality VERY depending on positioning/technique of doc/tech doing the image

PLAIN FILM OR CONVENTIONAL TOMOGRAPHY
--"you're never gonna order one of these"
--takes radiographic "slices" of bony anatomy with moving camera and film-->blurry image
--indications: visualize specific area hard to see on plain film: kidney w/ IV, TMJ
--advantages: slice view of bony anatomy, minimal radiation exposure, cheaper than CT
--disadvantages: can only see small area, blurry, sort tissues are seen as well in plain film, nobody uses it anymore

COMPUTED TOMOGRAPHY (CT)
--ADVANTAGES: quick, great for osseous detail & good soft tissue image, image can be manipulated, 3D reconstruction from planar images
--advantages: fast and readily available, better for trauma or claustrophobic pt, great for osseous structures
--DISADVANTAGES: high radiation dose, high cost, reformatted images not as good as original
--RADIATION: varies by resolution, anat, orient of beam, slick thickness, overlap, # of slices, kVp, MAs
--planar imaging (usu axial; coronal & sagittal pics depend on body part fitting in tube)
--looks like x-ray with shades of gray, contrast resolution 100x better than x-ray
--has no film-based image receptor, instead a detector collects info on remnant radiation after body
--computer compiles 3D data (voxel) matrix & contructs series of 2D images through pixel encoding on monitor
--voxels have numerical value in each dimension, range: -/+ 1000 HU (Hounsfield Units)
--image of thin slice of anatomy obtained
--tech controls contrast & brightness: fat in soft tissue window is black, bone & contrast chems are whit
--CONTRAST: barium swallow for GI, myelogram = contrast in CSF
--BONE WINDOW shows different shades for cortical and medullary bone
--SOFT TISSUE WINDOW gives better view of soft tissues, bone looks solid white
--OTHER WINDWS: lung, mediastinal (lung is black), etc
--CONTRAINDICATIONS: metallic objects-->artifact, radiation, sensitivity to iodine as contrast agent, claustrophobia (though it isn't as small as MRI tunnel), pt too large for gantry opening
--INDICATIONS: *axial view of bone, *often best way to go for chest and abdoomen because it is FASTER than an MRI, also: trauma w/ complex bone strx, calcifications or fresh blood, infx w/ cortical violation, vascular, neoplasms (better w/ MRI but sometimes CT is more available), arthridities (DJD in spinal canal = stenosis), disc herniation (also better w/ MRI), subarachnoid hemorrhage, sinusitis, Graves, foreign body, tumor of H or N, chest xray abn, fibrosis of lung, pulm embolism, liver dz, bone fx
--IMAGES: T6 burst fx vertebra looks too big, rib fx, clay shoveller's fx = SP popped off, adomen: kidney & liver concentrate contrast-->whiter than muscle, lumbar spondylophyte-->central canal stenosis, disc bulge (MRI better), type II dens fracture

MAGNETIC RESONANCE IMAGING = MRI
--ADVANTAGES: uses no ionizing radiation, great soft tissue detail, edema, multiplanar imaging
--DISADVANTAGES: expensive, slow (must lie still 30min-1 hour), maddening noise, effects unknown, complicated to interpret, claustrophobia, metal in pt bodies
--1977 first images produced
--bone cortex black on MRI, white on CT
--INDICATIONS: soft tissue abn, intracranial non-0acute, spinal cord, disc, marrow replacement, neoplasm
--CONTRAINDIC: 1st trim preg, over 300 lbs, metal in body,
--IMAGES seen in class: stress fx of sacrum in 37 yo female
--big magnet must be kept cool
--energy in Teslas, 1.5 T classic closed unit, open is .7 T-->grainy image, OHSU has 10 Tesla unit
--LITTLE OR NO KNOWN BIOLOGICAL EFFECT
--works by aligning body's atoms then releasing, looking at signal released when returning to "relax"ed, sees hydrogen density, sees T1 and T2 (diff relaxation times), sees motion (aorta black dt flow), sees diff btw fat and water protons
--MRI best for disc herniation
--T1: fat is white, CSF darker than cord, precise anatomy
--T2: water/CSF is white, CSF lighter than cord, less precise detail, normal discs bright
--ligaments dark on both, also fast moving blood, and air
--cortical bone is black on both
--scout image = vert bars that tell you where you are in pt
--CONTRAST: gadolinium is used, goes to vascular areas, good with T1 images only, ca, trauma, infx

MYELOGRAPHY
--has been largely replaced by MRI, only used when MRI or CT unavailable or contraindicated
--xray or CT scan with contrast in CSF
--to indirectly visualize lesion in spinal canal
--disc hern, tumor, hematoma, osteophyte, inflam, developmental abn
--ADVANTAGES: availability only
--DISADVANTAGES: invasive (needle), infx risk, rxns: ha, arachnoiditis, allergy, pt needs monitoring

NUCLEAR MEDICINE = BONE SCAN = SCINTIGRAPHY
--uses IV injx of radionuclide selectively absorbed by tissue w/ increased metabolic rate/vascularity
--radionuclides emit gamma radiation as decay
--radionuclides: technetium-99 for musculoskel, gallium-67 for infx, indium-111 for tumor
--geiger counter-like gamma camera measures emissions-->full body image
--INDICATIONS: inffx, malig in bone, stress fx (MRI best esp w/ bursitis/tendonitis), occult fx
--IMAGES seen in class: low back stress fx in 15 yo gymnast
--image of whole skel ant & post images
--ADVANTAGES: whole body seen, very sensitive (3-5% bone dstx needed to see)
--DISADVANTAGES: not specific, hot areas do not specify process, invasive injection and radiactivity risk
--multiple myeloma does not show up
--inject, wait 2-3 hours, come back for scan
--SEE: mets to bone (axial)
--IMAGES: patella, DJD, AC joint, bladder shows up too

DISCOGRAPHY
--inject radiopaque contrast into intervertebral disc, PROVOCATIVE test for LBP
--not often used, controversial, big needle in back
--some spine docs use it when deciding where/how to operate

SPECT = SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY
--similar to scintigraphy but uses CT to display tracer in selected images
--ANOTHER TYPE OF NUCLEAR MEDICINE
--multiple gamma cameras on rotating gantry
--can do slices
--results in better localization of lesion
--appears almost identical to planar bone scan
--yellow
--part of skel image w/ hotspots
--any plane
--100 images in one page
--use to confirm fatigue fx in pars interarticularis (seen: C5)

PET
--uses radiopharmaceuticals that emit positrons
--positron collides w/ electron, both particles annhilated producing gamma rays
--greater resolution than SPECT or scintigraphy
--great for tumor localization, ascertaining treatment success, esp LN's
--DISADVANTAGES: high cost, low availability
--visualize brain function, activity, using glucose tracer

DIAGNOSTIC ULTRASOUND
--INDICATIONS: preg, DVT, soft tissue, fibroids, ovaries, breasts, gallbladder, heart, thyroid, rot cuff, carpal tunnel, liver, scrotum/prostate, guide needle biopsy
--ADVANTAGES: cheap and easy, no radiation, noninvasive
--DISADVANTAGES: can't see a whole lot, just see masses when surrounded by softer tissue

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