Intro - Radiology - Goldschmidt Flashcards
Two types of effects from radiation?
Deterministic effects result from cell death such as skin erythema, epilation, radiation burns or cataracts
These are easier to document and predict
Exposure threshold
For example: 0.5 to 2 Gy dose to lens leads to risk of cataract
The other is stochastic Effects: Cancer or Leukemia
This is much more difficult to predict
There is no threshold level below which do not occur
May or may not occur, after a long delay, at a rate nearly imperceptible above baseline
Possibility of these effects supports practice of exposure levels being kept as low as reasonably achievable (ALARA)
Why are pediatric patients at higher risk for radiation exposure?
Greater risk for these stochastic effects because they generally occur many years after the exposure
Higher proportion of rapidly dividing and therefore radiosensitive cells
Harder to shield due to small size
Average Yearly radiation exposure?
Standard person in US—3mSv per year
Varies across globe—Mountains vs sealevel (Mountain—1.5 mSv more/year)
Largest source is radon gas in homes (2 mSv/year)
Cross country airplane flight (0.03 mSv)
Average doses of radiation from different CT scans?
Head or Facial Bones: 2 mSv C-spine or neck: 2 mSv Chest or PE: 8 mSv Abdomen: 7.5 mSv Pelvis: 7.5 mSv Renal or A/P: 15 mSv Extremity: 0.5 mSv
ATOMIC BOMB SURVIVORS WERE EXPOSED TO 50-150 mSv
When during pregnancy is fetus at highest risk for exposure to radiation?
First trimester ( time of organ formation) is felt to be particularly critical and we try to avoid exposure After the first 2 gestational weeks, there is no appreciable risk of lethality with low dose exams (plain films) High dose during organogenesis will more likely cause congenital malformation than death Risk decreases with age, so prefer third trimester scanning
What are plain films?
These are the original X-ray studies.
These are the first line of study for evaluation of lungs, heart, and skeleton because of its availability, speed, and low cost.
These are electromagnetic energy that pass through body to expose the film/sensor.
Image generated based on the density of the structures.
X-rays absorbed by bone/metal -> white/radiopaque
X-rays pass through air/ay so -> black/radiolucent
Why do you usually do PA rather than AP for chest x-ray?
Posterior-anterior view minimizes distortion of the heart.
How does ultrasound work?
Medical imaging technique uses high frequency sound waves
Sound waves leave probe, travel into body and are reflected back to the machine to be analyzed
Location of structures is based on the time required for sound waves to return to the probe
Intensity of the echoes on the image is dependent on composition of structures
No ionizing radiation with ultrasound - so no risk of that.
What situations are best to use ultrasound in?
Ultrasound is the primary way of evaluating pregnancy
US is the best way to evaluate the gallbladder
US is the best way to assess abdominal or pelvic pain in a woman, because it is so good at evaluating the uterus and ovaries
US should be considered to evaluate abdominal pain in children and thin females
Ultrasound is useful for evaluating veins for DVT
How does Computed Tomography work?
What is it used for?
Electromagnetic energy (ionizing radiation)
Gantry moves around patient, scanning from many angles
Computer generates a 3D image
in Brain it is best test for screening the brain for acute hemorrhage
This is the best test for almost all imaging of the chest, including PE, tumor, and interstitial lung disease, urinary tract disease (including stones)
How does MRI work?
Tissues are mostly water, with two hydrogen atoms or protons
Inside the magnet, the dipoles of the protons line up with direction of the magnetic field
A radiofrequency pulse is applied to flip the spins
Protons then relax as electromagnetic field is turned off
Allows exquisite anatomic images of brain, spine and musculoskeletal system
Typically is a problem solving technique in the chest, abdomen, and pelvis
Images take longer to acquire than CT and there are issues with motion artifact (both with the patient and with internal moving structures such as bowel peristalsis or cardiac motion)
What type of contrast can cause renal damage?
CT scan with contrast can be nephrotoxic.
MRI with contnrast is not nephrotoxic
What is Nephrogenic Systemic Fibrosis (NFS)?
Rare condition caused by gadolinium based contrast agents
Causes multisystem fibrosis—esp in skin and SQ tissues
Risk factors include chronic renal insufficiency, chronic hemodialysis, and multiple exposures to contrast
Screen for renal disfunction
GFR <30 try not to use
GFR 30-60 at physician discretion
What is nuclear medicine?
Nuclear medicine is not used very much anymore.
It is done by injecting radioactive substances into the body.
Unlike other exams that look at the anatomy, nuclear medicine will look for function.
Most commonly used to look for GB disease, Bone scans
Barium examination?
Utilizes x-rays
Contrast material placed into GI tract
Antegrade for upper GI tract (patient will drink the contrast)
Retrograde for colon (tube inserted into patient rectum to put contrast in)
Much less common than in the past
CT has also replaced barium for many diagnoses, including diverticulitis and small bowel obstruction (SBO)
