Conditions and Treatment Flashcards
Error rate in interpretation
As high as 20-40%
Errors of Observation
Doesn’t look like it’s there
Errors of Interpretation
Missed something
True Positive
Test detects something that is really there
False Positive
Test detects something that is not really there
True Negative
Test detects nothing, and nothing is there
False Negative
Test detects nothing, but there is something there
Sensitivity
Refers to test’s ability to identify a true positive
“SPOUT”
HIV blood test - very sensitive
Specificity
Refers to test’s ability to identify a true negative
“SPIN”
Home pregnancy tests - very specific
Radiograph
First-order diagnostic modality
Named for the beam direction relative to patient and patient’s position
Radiograph Advantages
Time/cost efficient
Low risk
Radiograph Disadvantages
May be normal although pathology exists
Attenuation
Reduced strength or density of the x-ray beam as it passes through a medium
Permeability
Ability of the x-ray beam to pass through substance to reach the film plate
Radiodensity
X-ray absorption capacity, based on substance’s composition, density, and thickness
Radiograph Image Quality
At least two views, ideally at 90 degree angle to each other, are necessary to visualize an object in three dimensions
Density
Amount of blackening on the radiograph dependent on distance, time, and current
Contrast
Differences between adjacent tissue densities
Detail
“Sharpness/Resolution”
Maximized by positioning patient so structure of interest is closest to film plate
Distortion
Occurs due to distance between beam source, patient, and image receptor, and from alignment and positioning issues
Foreshortening
Image appears shorter and wider than the actual object or structure
Magnification
Objects or structures further from the film appear larger than closer points
ABCs of Radiology
Alignment
Bone Density
Cartilage
Soft Tissue
Alignment
Gross bone size
Shape and contour of cortical outline
Joint position/alignment
Bone Density
Cortical - dense
Cancellous - lower density
Low contrast - “washed out” (osteoporosis)
White showing up - sclerosis
Contrast Enhancement
Injection
Ingestion of radio-contrast medium
CT
X-ray and film move about a fulcrum
Detailed imaging of bone
CT Advantages
Sensitive/Specific for fracture
Useful for brain/neurologic injury
CT Disadvantages
Radiation
Limited in precise histologic differences
MRI
Uses pulses of radio frequency and a strong external magnet to generate an electromagnetic field
Resonance
Water molecules align in body
Atomic nuclei align to electromagnetic field
Field is removed, image is formed
MRI Advantages
Good sensitivity
Images soft tissue well
No radiation
MRI Disadvantages
Relatively low specificity
Expensive
Contraindicated with metal implant
T1 Image
“Longitudinal”
How long it takes protons to “relax”
Reveal details of anatomy in high resolution
T1 High Signal (Bright)
Bone
Fat
Hemorrhage
T1 Low Signal (Dark)
Fluid
Soft Tissue
T2 Image
“Transverse”
How long resonating protons remain “in phase”
Show soft tissue pathology and ideal for acute trauma
T2 High Signal (Bright)
Fluid
Fluid-filled structures
T2 Low Signal (Dark)
Bone
Fat
Contrast MRI
IV or intra-joint injection
Increased signal to T1 weighted images
Functional MRI
Based on increased blood flow accompanying neural activity (Oxygen/glucose uptake) (BOLD)
Uses deoxyhemoglobin as contrast agent
BOLD
Blood Oxygen Level Dependent
DEXA
“Dual Energy X-ray Absortiometry”
Gold measure for body composition
Measuring bone mineral density
Difference in absorption between beams determine density
Nuclear Medicine
Use radioactive tracers absorbed according to metabolic properties of tissue
Nuclear modalities
SPECT
PET
Radionuclide scintigraphy
Radionuclide scintigraphy
Methylene injected, scan every 2-3 hours
Best choice for detection of stress fracture or metastatic bone disease
RS Advantages
Highly sensitive for early bone/joint disease
Fast
Reasonable cost
RS Disadvantages
Poor specificity
Influenced by osteoblastic activity or blood flow
Ultrasound
Images through sound waves
Useful with musculoskeletal tissue