Flashcards in Medical Imaging Deck (77):
What two errors can be made in imaging?
Errors of observation, errors of interpretation
How is imaging important to PT?
diagnostics are a tool, not the answer. relate imaging to clinical care
enhances comprehensive exam, guides and informs treatment, improves communication between PT and Dr., PT is direct access
What is a true positive?
test detects something that is really there
What is a false positive?
test detects something that is not really there
What is a true negative?
test detects nothing, and there is nothing there
What is a false negative?
test detects nothing, but there is something there
What is sensitivity?
at test's ability to identify a true positive
negative test means you definitely don't have the condition
What is specificity?
test's ability to identify a true negative
positive test means you definitely have the condition
What is an example of a sensitive test?
HIV blood test. have low false negative but can have high false positives
What is an example of a specific test?
home pregnancy test. have low false positives but can have high false negatives
What are advantages of X-ray?
time and cost efficient
good for screening
What are disadvantages of x-ray?
may be normal when pathology actually exists
What is attenuation?
reduced strength or density of the x-ray beam as it passes through a medium
What is permeability?
ability of xray beam to pass through substance to reach film plate
What is radiodensity?
x-ray absorption capacity based on substance's composition, density, and thickness
How is radiodensity of an object related to radiodensity of the x-ray?
radiodensity of an object is inversely related to radiodensity (amount of blackening) on the radiograph
high object density results in lower density on film so the object appears whiter
What is a radiolucent substance?
easily penetrated by x-rays (low attenuation)
What is a radiopaque substance?
not easily penetrated by x-rays (high attenuation)
How is air shown on an x-ray? Where is it normally present?
least radiodense substance in the body.
Will show up black on film
normally present in trachea, lungs, stomach, digestive tract
How does fat and water show up on x-ray?
fat appears gray-black on film
water appears gray on film
How does bone, contrast, heavy metals show up on x-ray?
bone appears gray-white
contrast media appears as white outline
heavy metal appears solid white
What does "one view is no view" mean?
at least two views ideally at 90 degree angle to each other, are necessary to visualize an object in three dimensions
radiograph is two dimensional picture of a three dimensional object
What are two photographic qualities of imaging?
density: amount of blackening on radiograph dependent on distance, time, and current
contrast: differences between adjacent tissue densities
What are two geometric (clarity) qualities of imaging?
detail: aka sharpness or resolution; maximized by positioning patient so structure of interest is closest to film plate
distortion: usually occurs due to distance between beam source, patient, and image receptor, and from alignment and positioning issues
What to structures closest to the film plate look like?
they are more sharply defined and are imaged with less size distortion
What is foreshortening
image appears shorter and wider than the actual object or structure
What is magnification
objects or structures further from film appear larger than closer points
How are radiographs named?
named for beam direction relative to patient and patient's position
What is AP image?
x-rays travel through the patient from an A to P direction: the x-ray tube is in front of patient and the film plate is behind
What is lateral/oblique views?
named for side closer to film plate
What are some special x-ray positions?
oblique, open mouth: upper c spine, flexion/extension, sunrise or tangential: patellofemoral joint, upright weight bearing
How are AP/PA and lateral radiographs viewed?
AP/PA: viewed with patient facing viewer in anatomical position; hands, feet, and digits point upwards
Lateral: viewed in direction the x-ray beam traveled
What does the A in ABCs of radiology stand for?
Alignment: gross bone size, number of bones, shape and contour of cortical outline, joint position and alignment
What lines do you need to reference to with images of the spine?
anterior vertebral line
posterior vertebral line
posterior spinous line
What is the B in the ABCs of radiology?
Bone density: weight bearing surfaces should have higher density, cortical margin should be dense with lower density cancellous bone and medullary cavity, low contrast bone suggests osteoporosis, excessive sclerosis may suggest arthritic or rheumatic condition
What is the C in ABCs of radiology?
Cartilage: joint space width, subchondral bone, joint margins, epiphyses and growth plates
what is the s in the ABCs of radiology?
soft tissue: gross size of musculature, outline of joint capsules, periosteum
What is contrast enhancement?
injection or ingestion of radio-contrast medium prior to radiographic study
e.g.- arthrography, myelography, barium swallow studes, angiography, arteriorgraphy, cholecystography, urograms
What is a CT?
computed tomography: uses x-ray attenuation to produce cross sectional images
How is a CT set up?
x-ray tube and film move about a fulcrum
What does a CT provide an image of?
provides detailed anatomical imaging of bone
How are CTs read?
transverse images are read from the bottom looking up (feet to head)
What are advantages of CT?
sensitive and specific for fracture
useful for rapid assessment of brain or neurologic injury
What are disadvantages of CT
discriminates density, but limited in precise histologic differences
small volumes of tissue image as a uniform shade of gray
How does an MRI work?
uses pulses of radio frequency and a strong external magnet to generate an electromagnetic field
When the field is removed the nuclei realign to their resting state releasing resonance energy
this produces a radio frequency signal that can be captured and processed into an MRI
What is resonance?
alignment of atomic nuclei to the electromagnetic field
What are advantages of MRI?
images soft tissue well
little distortion, as images are obtained in one plane
What are disadvantages of MRI?
relatively low specificity
contraindicated if patient has a ferrous metal implant or exposure (orthopedic hardware is not ferromagnetic, but surgical clips usually are; pacemaker function can be compromised by magnetic field)
What is a T1 image?
longitudinal magnetization: how long it takes protons to 'relax' back to resting state following a RF pulse
has short repetition and echo times
What is a T2 image?
transverse magnetization: how long resonating protons remain 'in phase' following a RF pulse
has long repetition and echo times
How do T1 images show up on an MRI?
bone, fat, and hemorrhage have high (bright) signal
fluid and soft tissue have low (dark) signal
good gray/white matter discrimination
T1= 1ong bone is bright
How do T2 images show up on an MRI?
fluids and fluid filled structures are bright
fat and bone are dark
useful fro imaging CSP, edema
T2=H2O is bright
What are T2 images good for?
show soft tissue pathology and are ideal for acute trauma
What are T1 images good for?
weighted images reveals details of anatomy in high resolution
What is contrast MRI?
intravenous or intra-joint injection (arthrogram)
tissue enhancement is proportional to blood flow to the tissue
increased signal to T1 weighted images
before and after contrast image comparisons
What is a functional MRI?
technique based on increased blood flow that accompanies neural activity in the brain (BOLD technique)
What is contrast agent?
uses magnetic properties of deoxyhemoglobin as an endogenous contrast agent
What is DEXA used for?
widely used method of measuring bone mineral density
can also determine body composition
How does a DEXA work?
high and low energy x-rays are directed at bone from two different sources
difference in absorption between the beams is used to determine bone density
What is nuclear medicine used for?
use of radiopharmaceuticals for diagnosis, therapy, and research
How does nuclear medicin work?
radiopharmaceuticals are radioactive tracers that are absorbed according to the tissue's metabolic properties
detection of the location and concentration of radioactive elements is used to produce an image
What modalities fall under nuclear medicine?
single photon emission computed tomography (SPECT)
positron emission tomography (PET)
PET/CT and SPECT/CT
radionuclide scintigraphy (bone scan)
What is radionuclide scintigraphy used for?
detection of stress fractures and detection and follow up of metastatic bone disease
How is scintigraphy done?
labeled methylene is injected, scanning occurs 2-3 hours following injection
What does high uptake indicate in scintigraphy?
indicates areas of increased bone activity or mineral turnover
What are advantages of scintigraphy?
highly sensitive for early bone and joint disease
What are disadvantages of scintigraphy?
easily influenced by osteoblastic activity or blood flow of any etiology
What is ultrasonography?
anatomic images achieved through sound waves
different tissues have different acoustic qualities
What can ultrasonography be used for in PT?
during physical exam and with active functional activity
only be used to confirm diagnosis
Is ultrasonography easy to use?
operator dependent, good technique requires practice
What is the order of imaging done when evaluation a patient?
conventional radiographs are the first order modality
CT is used to visualize complex anatomy
MRI is used to assess soft tissue
What is the trauma survey?
diagnose and evaluate fracture or dislocation
match mechanism of injury to clinical presentation
assess treatment and monitor healing
In trauma what images are done?
possibly: x-ray of extremities, lateral views of T-L spine, CT of head, CT of C-spine, CT of thorax abdomen pelvis with/without contrast
What is Pittsburg decision rule for knee trauma?
x-ray ordered if history of blunt trauma or fall AND age under 12 or over 50 AND/OR inability to walk 4 weight bearing steps in ER
What is Ottawa knee rule?
x-ray ordered if age >55 years, tenderness at fibular head, isolated tenderness at patella, inability to flex knee to 90, inability to walk 4 weight bearing steps in ER
What is Ottowa ankle and foot rules?
ankle: pain in malleolar area AND tenderness at posterior aspect or tip of lateral malleolus, OR tenderness at posterior aspect or tip of medial malleolus, OR inability to WB immediately and in ER
foot: pain in midfoot area AND tenderness at base of 5th MT, OR tenderness at navicular bone, OR inability to WB immediately and in ER