Ortho Introduction to Radiology Flashcards
X-Ray Properties
high energy electromagnetic waves that pass through a body part onto a film
Most of the radiation is passed through the body, but some is absorbed producing the image
3 factors of radio-opacity
- atomic number: higher is more radiopaque
- physical density: air (black), fluid and soft tissue (grey), bone (white)
- Thickness: thicker structures result in more attenuation, more radiopaque
Overlapping structures will be additive and appear more radiopaque than if they were separate
General Opacities
- Mineral opacity
- Soft tissue/fluid opacity
- Fat opacity
- Gas Opacity
- Metal Opacity
X-Ray Components
Electrode pair, glass vacuum tube in a lead case
Cathode generates electrons that strike the tungsten anode
Electron collides with tungsten atom knocks an e- out of a lower orbit
When a higher orbital electron falls to fill the gap, energy is released as a photon (x-ray)
95% of energy is deposited as heat, only 5% generates x-rays
Digital radiography
Photostimulable plate absorbs x-rays and emits light (flourescence) that is detected by an image reader
Flat Panel Detectors
most common
Amorphous silicon: x-ray converted to light, which is converted digital output signal (indirect image)
Amorphous selenium: x-ray photons converted directly into charge on a sensor (direct image)
High Density Line Scan Solid State Detectors
Phosphor detectors records X-ray energy during exposure
Radiation Protection
- Reduce time of exposure
- Increased distance from radiation source
- Radiation shielding (lead shields)
Scanograms
Measure leg lengths precisely
Used in children if correction is necessary to equalize growth of legs
Comparison X-Rays
When comparing left to right
Done to verify a fracture in a pediatric patient (compare epiphysis)
Stress X-Rays
Usually done to assess ligamentous stability
Arthrogram
Contrast is injected into a joint capsule and a radiograph is taken
If the contrast extraverts then the capsule has a tear in it
Myelogram
Image the subdural space
Useful in diagnosing spinal stenosis
How many views are needed when doing conventional x-ray exams?
Radiographs provide a 2D image
3D must be reconstructed mentally (from orthogonal projections, need at least 2 views)
Orthogonal projections
two radiographic projections made at right angles
X-Ray Naming
Direction primary beam enters and leaves the tissues being examined (AP)
Position of the patient (prone, supine, seated, standing) during exposure, left/right markers identified
Radiographic planes
- Median or midsagittal plane
- Coronal plane
- Axial or transverse cross-sectional plane
Computed Tomography
Fanned x-ray beam rotated around a patient is measured by a series of detectors
Measurement of transmission at different angles allows computation of an image
Image densities are the same as conventional X-rays
Density and contrast varied by varying amount of radiation and time of exposure
Good for viewing fractures
Ultrasonography
Displays an image based on acoustic properties of the tissue
Sound waves are sent into a patient and returning echo is converted into an image
Resolution depends on wavelength and frequency of waves
Types of Ultrasound
- Low frequency-longer wavelength, less resolution, greater depth of penetration
- High frequency-smaller wavelength, greater image detail, superior for images of tendons, ligaments and bone
High Frequency US
Better for tendons, ligaments and bone
Smaller wavelength
Greater image detail
MRI
Tissue in magnetic field causes magnetic moment spin of hydrogen nuclei to line up
Deflecting the nuclei from this orientation using RF signals causes protons to emit RF signals that are used to generate images
Good for soft tissue contrast
Good for bone marrow, cartilage, soft tissues, ligaments, muscle and fat
T1
Measures energy released as proton exposed to RF signal realigns to magnetic orientation
Fat and muscle appear different on T1 (visualize fluid better)
T2
Measures energy transmitted by the wobbling effect of protons that have been exposed to RF signal (they are out of phase and release energy as they become in phase “larmor frequency”
2nd RF blast is used
Normal muscle and striated muscle appear different on T2
Radio-isotope absorption
Tissues with increased circulation will receive more isotope
Strontium 85
1961
1st isotope used for bone scanning
Strontium 87
Shorter half life, poor soft tissue clearance
Technetium tc99
1971 Short half life Excreted into urine 4 hours post injection Administered as phosphate complex Binds with Ca2+ in bone
Indium 111
leukocyte scan
Used to tag WBCs and assess uptake into areas of infection (useful in osteomyelitis)
Gallium 67
impregnates into Ca2+ hydroxyapatite crystals
Uptake in neutrophils and bacteria
Track progression of treatment of infection
Factors that affect uptake of isotopes
- Bone turnover rate
- Blood flow to trauma
- Trauma
- Time isotope is in the system
PET
- metabolic imaging (good for diagnosing tumors)
- Tracer is used to measure the rate of glucose absorption by tissue
- Accumulation rate reflects glucose utilization in tissue
- Based on increased glycolytic rate in pathologic tissues
Advantages of PET
high sensitivity for bone pathology, allow imaging metabolic activity, white cell scintgraphy used to dx osteomyelitis, scintigraphy used to dx metastsis, stress fx, occult fx, etc
Disadvantages of PET
Lack of detail and special resolution
Limited early sensitivity to detect acute fx in patient with slow bone metabolism, low sensitivity with lytic diseases (multiple myeloma)
Low specificity for bone pathology
DEXA Scan
Dual energy X ray absorption
Measures absorption of 2 beams of radiation into hip and spine
Results are compared to standard
T-scores calculated and used to identify if patient has osteopenia or osteoporosis
Measures bone mineral density
Dexa scan values
Osteopenia-T-score at or below -2.5
Severe osteoporosis-T-score at or below -2.5 and history of one or more fractures
Normal T-score -1 and above
BMD differences
20-40 for healthy caucasian women
One standard deviation on either side represents 68% of population
85% of women 20-40 have normal BMD
CT Advantages
Better cross sectional capability
Bone Scan Advantages
Early detection of fracture
Stress fracture, can be positive as early as 48 hours post injury
Detection of infection and degree of involvement
MRI
Bone contusion
Articular cartilages
Relationships of neurovascular structures to other anatomy
Ultrasound advantages
Fluid filled tissue and vascular supply
