Orthopedic - Radiology Flashcards
What are 3 major factors of Radiopacity?
Radiopacity (how an image will show up on an x-ray film
1) Atomic number (hight the # the more radiopaque)
2) Physical density (Air, Fluid, Bone)
3) Thickness (Thicker= more white/radiopaque)
What is fats opacity compared to bone or soft tissue or gas?
What does fat allow you to see?
- Fat is more radio opaque than bone or soft tissue but more opague than gas.
- Fat allows you to view the organ outline since most organs are encased in fat.
What can gas opacity allow you to see?
Gas it the most radiolucent material visible on a film and thereby provides contrast to allow visualization of various structures
How does an X-ray machine work?
Free electrons generated from heated cathode collide with tungston atom - knocking an electron out of a lower orbit. A higher orbital electron fills the empty gap releasing excess energy as a photon (x-ray)
- 5% of electron energy is deposited as an X-ray
What unit measures the amount of radiation in an x-ray?
Roentgen
How does digital radiography work?
- uses photostimulable plate and an image reader- writer. Screen absorbs X-rays and converts them to light energy. Light is used to create a digital image.
What are the advantages of digital radiography?
Cost
Chemicals
Digital transfer of information
Modifiable
What are the most common digital X-ray sensors used in hospitals?
FDP (flat panel detectors)
- Amorphous silicon - converts x-ray radiation into light and light is converted to a digital output signal (indirect)
- Amorphous Selenium - x-ray photons are converted directly into charge on sensor (direct)
What are 3 ways to ensure radiation protection?
1) Reduce time of exposure
2) Increase distance from radiation source
3) Provide radiation shielding (ex. lead aprons, thyroid shields)
What are radiographs?
- X-ray beam passed through tissue onto photographic film. The image recorded represents the radiation that passs through the patient.
What are scanograms?
Used to compare leg length. Used allot in children to determine whether long or short leg . If yes than can adjust the epiphyseal growth
What are comparison x-rays?
Usually done to verify a fracture in a pediatric patient. Used in kids due to variation of growth.
When are stress x-rays used?
-usually done to assess ligamentous stability.
Why are tomography radiographs not used?
Because of CT scanners
When are arthrogram contrast used?
- They are used to analyze bone and tears - such as in the rotator cuff.
When are Myleograms used?
Used to identify pressure and whats going on in it. Ex. hypertrophy in ligamentum flavum and stenosis
When are arteriograms used?
To assess blood supply, ex. can be put in at the groin to assess peripheral vascular disease.
What are venograms used?
To assess the compliance of a veins. Veins are much more tortous than arteries
What are discograms?
To assess the spinal cord discs. When applying contrast the needle is put into the nucleus pulposus, not the annulus. Can be diagnostic if you inject and symptoms are reproduced.
What is the importance of an orthogonal view?
To view more than one side of a 3-D structure
What is Computed tomography (CT)?
- Fanned X-Ray beam rotated around a patient. Exit transmissions of x-rays measured by a series of detectors. Image densities the same as conventional X-ray. Density and contrast varied by varying amount of radiation and time of exposure.
What is the best type of radiography for viewing fractures?
- CAT scans**
What is the best type of radiography for viewing bony edemas?
MRI
What is ultrasonography?
- Use of acoustic properties of tissue, sound waves are sent through a patient - returning echo converted into images, Resolution of images depends on wavelength and frequency of waves.
What are the two types of ultrasound and what are each used for?
- Low frequency US: longer wavelengths, less resoultion, greater depth of penetration
- High frequency: smaller wavelength, greater detail, superior for orthopedic images of tendons and ligaments.
What is the process that an MRI is used?
Proton the origin of signal used in the generation of MRI images, magnetic field is applied, response of excited proton is measured after a second signal is applied.
What are the disadvantages of an MRI?
extremely noisy, reuquires a large room and a small bore, there is a weight limit, takes, longer than CT, patients with claustrophobia may not tolerate well
What is a disadvantage of an open scanner MRI?
- Lower field strength and therefore a lower resolution.
What are the advantages of using the MRI?
- Excellent soft tissue contrast
- Good for evaluating bone marrow, cartilage, soft tissues
- No ionizing radiation ideal for children
- Can be more effective than CT for dx of osteomyelitis, malignancy, and stress
What are some limitations for MRI?
- Relatively long scan time, sedation needed for kids and crazy people, cannot be used in pts with implants or pacemakers, cannot be used in patients with orthopedic implants located close to area being scanners,
What is T1 and what does it measure?
T1 measures energy released as proton exposed to Rf signal realigns to magnetic orientation
What is T2 and what does it measure?
T2 measures energy transmitted by the wobbling effect of protons that have been exposed to Rf signal. T2 images show water density and fluid.
What is unique about T1 and T2?
Every tissue will have a unique T1 and T2 property. Different tissues may have same T1 but will have different T2 images or vice versa
What type of radiation is produced by radioisotopes that are localized in the skeleton?
Gamma radiation
How long is it before technetium is excreted into the urine? What causes increased presence of the radioisotope in specific areas?
- 4 hours
- areas with increased circulation will have more than areas that do not.
What is indium 111 used for?
to tag WBC’s and assess uptake in areas of infection
What is gallium 67 used for?
- impregnates into calcium hydroxyapatite crystals uptake in neutrophils and bacteria. Doesn’t necessarily mean an infection - just indicative
What are the factors affecting the uptake of isotopes?
- Bone turn over rate
- Blood flow to area
- trauma
- Time isotope is in system
What types of tissues is PET scans good for?
What type of tracer does it use?
What does it measure?
- Soft tissue neoplasms or osseous metastasis
- Tracer- 2-deoxy-2-Fluoro-D-Glucose
- pet scan measures glucose utilization by tissue
For nuclear medicine - the use of FDG is based on what?
- What does high grade malignancies tend to have as opposed low grade malignancies?
- increased glycolytic rate in pathologic tissues
- high grade malignancies tend to have higher rates of glycolysis than low-grade malignancies and have greater uptake of FDG than low grade or benign lesion
What are the advantages of Nuclear medicine?
- High sensitivity for bone pathology
- allows imaging of metabolic activity
- white cell scinitgraphy can be used ot dx osteomyelitis
- Scintigraphy can be used to dx metastasis, stress fx, occult fx
What are the disadvantages of nuclear medicine?
- Lack of detail***
- Limited early sensitivity to detect acute fx. in pt with slow bone metabolism
- Low sensitivity can occur with lytic diseases such as multiple myeloma
- Low specificity for bone pathology
How do dexa scans work?
Used to evaluate bone density, they shoot 2 beams of radiation into area, compare results, and calculate T-scores and use them to ID whether they have osteopenia or osteoporosis
What T-scores are representative of Osteopenia, osteoporosis, severe osteoporosis, and normal?
- Osteopenia: T-score between -1 and -2.5
- Osteoporosis: T-score at or below -2.5
- Severe Osteoporosis: T-score at or below -2.5 and a history of one or more fractures
- Normal: BMD T-score -1 and above
What percentage of women 20-40 have normal BMD
85%
What restraints might be imposed on choosing an imaging modality?
- Needs of individual patients
- Insurance
- Availability of equipment
- Availability of radiologist
What is the best choice of imaging modality for:
- Cross sectional capability:
- Early detection of fracture or infection and degree of involvement
- Bone contusion, articular cartilages, relationships of neurovascular structures to other anatomy:
- Fluid filled tissue and vascular supply:
- CT scan
- Bone Scan
- MRI
- Ultrasound
Bone scan can be obvious how many hours after fracture?
- 48 hours
