Imaging Flashcards
Errors of Observation/Interpretation
Errors in detecting and diagnosing pathologies in imaging that are there but are missed, or saying something is there that is not.
True Positive
Detects something that really IS there
False Positive
Detects something that really it NOT there
True Negative
Detects nothing when nothing is there
False Negative
Detects nothing when something is there
Specificity
Ability for test to detect true negatives. Example - if X-ray detects a fracture, there really is a fracture there. (SPIN)
Sensitivity
Ability for test to detect true positives. Example - MRI does not detect soft tissue injury so there is no soft tissue injury. (SNOUT)
X-ray Advantages
- Time/cost effective
- Non-invasive
- Low exposure risk
- Good for initial screening
X-ray Disadvantages
- May miss diagnosis of pathology that really is there.
X-ray Attenuation
Reduction of X-ray beam’s density/strength as is it passes through a medium.
X-ray Permeability
Ability of the X-ray beam to pass through a medium and reach the film plate.
Example - Air is more permeable than bone.
X-ray Radiodensity
- Ability for X-rays to be absorbed by a structure.
- Based on structure’s density, composition and thickness
Radiodensity relationship
- Radiodensity of an object is inversely related to the amount of blackening on X-ray film
- Example - bone is more radiodense (shows up white on film) than air (shows up black on film)
Photographic Qualities
Refers to the visibility of an image
-Density, contrast
Geometric Qualities
Refers to the clarity of an image
- Detail, distortion, foreshortening, magnification
Density
Amount of blackening on the film.
Contrast
Differences in color (density) of nearby structures.
Detail
Sharpness or resolution of image. Structures closest to the film plate have more detail.
Distortion
- Structures farther from the film plate or beam source have clarity issues.
- Occurs due to distance between the beam source, patient and image receptor (film)
- May also be caused by alignment and patient positioning issues
Foreshortening
Image appears shorter and wider than it actually is.
Magnification
Structures farther from the film appear larger than structures closer to the film.
X-Ray Views
- Anterior/Posterior (AP)
- Lateral/Oblique
- Special
Radiology ABCs
A - Alignment
B - Bone Density
C - Cartilage
S - Soft tissue
A - Alignment
- Gross size of bones
- # of bones
- Shape of cortical bone outline
- Joint position/alignment
B - Bone Density
- Cortical bone = dense; Medullary/Cancellous bone = less dense
- Weight bearing surfaces are more dense
- “Washed out” bone indicates osteoporosis
- Sclerosis (hardening/thickening of bone) indicates arthritis or RA
C - Cartilage
- Joint space
- Subchondral bone integrity
- Joint margins (smooth or rough)
- Epiphyses and growth plates (esp. children)
S - Soft tissue
- Size of musculature/soft tissue
- Outline of joint capsules
- Periosteum integrity
CT Advantages (2)
- Sensitive and specific for fractures
- Useful for quick brain/neurological injury assessment
CT Disadvantages (3)
- Radiation exposure
- Issues with diagnosing histological problems
- Small amounts off tissue show up uniformly gray
MRI
Magnets cause protons of all cells to align according to electromagnetic field (resonance) that then return to their resting state after EMF is removed.
MRI Advantages (4)
- Good sensitivity
- Great for soft tissue images
- No radiation exposure
- Little distortion of images
MRI Disadvantages
- Expensive
- Low specificity
- Can’t be done on patients with ferrous (iron based) materials in their body (implants, exposure to metal)
T1 Images
- How long it takes excited protons to return to resting state
- Fat, bone, and hemorrhage are BRIGHT
- Fluid/fluid filled structures are DARK
T2 Images
- How long excited protons remain “in phase” or aligned with EMF
- Fat and bone are DARK
- Fluid/fluid filled structures are BRIGHT
Contrast MRI
- Contrast media injected intravenously or into joint
- Where contrast travels to depends on blood flow
- Increased T1 image signals
- Compares images before and after contrast administration
fMRI
- MRI done to determine which area of the brain is being utilized when the patient is asked to perform or think about specific tasks
- Contrast media is deoxyhemoglobin
- Dependent on blood flow (increased blood flow to brain area means that area is primarily being used to perform the task)
DEXA
- Type of X-ray used to determine bone density and body composition.
- Considered the Gold Standard for bone density
Nuclear Medicine
- Imaging done with radiographic tracers to diagnose patients
- Includes PET, SPECT, and radionuclide scintigraphy
Radionuclide Scintigraphy
- Uses label methylene injections
- Scan taken 2-3 hours after injection
- Looks at areas of bone activity/mineral turnover
- Gold standard for stress fracture diagnosis
Radionuclide Scintigraphy Advantages (3)
- Very sensitive for early bone and joint diseases (stress fractures, metastatic bone disease)
- Fast
- Reasonable cost
Radionuclide Scintigraphy Disadvantages
- Poor specificity
- Easily tricked by areas of high osteoblast activity and blood flow
Ultrasound
- Sound waves used to produce image
- Most commonly used in OBGYN settings
- Can be used by PTs but should be used for confirmation of diagnosis only
- Requires a lot of training, technique mastery, and practice to get accurate results
Pittsburgh Knee Trauma Decision Rule
X-ray ordered if:
- Patient has history of fall or blunt trauma AND…
- Age < 12 or >50 AND/OR…
- Inability to walk 4 steps in ER
Ottawa Knee Rule
X-ray ordered if:
- Age >55
- Tenderness at fibular head
- Isolated tenderness to patella
- Inability to flex knee to 90 5.
- **Inability to walk 4 steps after injury or in ER
Ottawa Ankle Clinical Decision Rule
- Patient must have pain in the malleolar area AND
- Point tenderness of posterior aspect/tip of medial malleolus OR
- Point tenderness of posterior aspect/tip of lateral malleolus OR
- Inability to walk 4 WBing steps after injury and in ER
Ottawa Foot Clinical Decision Rule
- Patient must have pain in the midfoot area AND
- tenderness at the base of 5th metatarsal OR
- tenderness at the navicular bone OR
- Inability to WB for 4 steps after injury and in ER
