Intro to Radiology Flashcards
PA vs AP setups
Which setup makes the heart appear larger than it really is? AP, or PA?
AP makes the heart appear larger, since it is farther away from the screen.
Remember, AP is A Portable X-ray, which has the screen placed behind the patient while the patient is in bed.
Good inspiration on a CXR
Diaphragm should be between the 8th and 10th posterior rib
Dorsal vs ventral ribs on CXR
When placing a central line, where do you want it to end up?
The cavo-atrial junction (where the SVC meets the right atrium)
How do you find the cavo-atrial junction on a CXR?
It is approximately at the location where the right main stem bronchus meets the heart.
Endotracheal tubes should be placed. . .
. . . in the trachea, above the level of the carina.
If one is improperly placed, the lung it favors will likely be hyperinflated relative to the other lung.
How far should an NG tube be placed?
10 cm into the stomach beyond the approximate EG junction
“Danger zones” on CXR
Areas that are hard to see and often harbor pathology
The apices of the lungs and behind the heart
What is more dangerous? A left-sided pneumothorax, or a right-sided pneumothorax?
A right-sided pneumothorax, because the lower-pressure vascular systems are all on the right.
If you are having trouble telling whether or not an X-ray shows pneumothorax, the best place to look is the. . .
. . . intervertebral squares: the areas in-between the posterior and anterior rib shadows that should clearly show normal lung markings.
When you see an opacified hemithorax on imaging, think. . .
. . . atelectasis, pneumonia, or pleural effusion.
What finding suggests atelectasis on CXR with an opacified hemithorax?
Deviation of the heart towards the collapsed side.
What finding suggests pleural effusion on CXR with an opacified hemithorax?
- Deviation of the heart away from the opacified side
- Sharp line boundaries indicating a fluid-air interface
- Occupation of the costodiaphragmatic recess
What finding suggests pneumonia on CXR with an opacified hemithorax?
Lack of heart deviation
Straight line vs meniscus on pleural effusion
Meniscus = uncomplicated pleural effusion
Straight line = air-liquid-interface, ergo, hydropneumothorax
Most frequent cause of airway deviation
Thyroid goiter
If you see a rib fracture on CXR, you should always go back and double-check the area for. . .
. . . pneumothorax
Tissue-weight factors in radiation exposure
Accounts for density and replicative capacity of different tissues.
Used to noramlize “effective dose” of radiation
In radiology, radiation dosage is measured in. . .
. . . millisivierts (mSv)
Radiation exposure diagram
If in doubt, how do you determine what imaging protocol is appropriate for a given scenario?
The American College of Radiology Appropriateness criteria
Or, call your radiology team!
Whenever you image a patient with and without contrast. . .
. . . you are giving double the dose of radiation.
If you are ordering an abdominal CT, that is a LOT of radiation (~6 years worth of background radiation)
When fat is inflammed, . . .
. . . it appears brighter on CT!
Characteristics of contrast-induced nephropathy
- Serum creatinine elevated to ~50% above baseline 1-3 days after contrast injection
- Elevation peaks at ~7-10 days post-injection
- Usually returns to baseline within 2 weeks
Generally speaking, when is it safe vs unsafe to give contrast?
If creatinine is < 1.5, it is fine.
If cretinine is between 1.5 and 2, it might be okay with adequate hydration and monitoring.
If creatinine is > 2, absolutely not.
Contrast allergy
- Not well understood
- Not a true IgE-mediated effect
- Thought to be a direct effect of contrast on mast cells
Contrast and shellfish allergy overlap
IS A MYTH
This is BS, but some clinicians still believe it.
If a patient has questions about preparing for a study and what it will entail, where should you refer them?
radiologyinfo.org
This is a good reference for students as well. Includes info about dietary restrictions prior, protocols, etc.
The frequency of diagnostic ultrasound is on the order of. . .
. . . 106 Hz
Essential mechanism of ultrasound
Ultrasound devices utilize piezoelectric crystals such as quartz to create ultrasound waves (by applying a rapidly alternating current) and receive sound waves (by generating current from compression).
Over 128 crystals are measured spread over the face of the ultrasound tool. The received information is used to digitally reconstruct an image.
Static vs dynamic guidance
Static: Get imaging, then use this to figure out location and angle for needle insertion
Dynamic: Live imaging to guide insertion of needle with visualization of the needle tip in real time
In-plane vs out-of-plane ultrasound guidance
FAST exam sensitivity and specificity
Sensitivity of 73 to 99%, a specificity of 94 to 98%, and an overall accuracy of 90 to 98% for clinically significant intraabdominal injury in trauma
Angles examined in FAST exam
“Lung point” sign
Visualized on ultrasound and 100% specific for pneumothorax. The parietal and visceral pleura of the lung stops sliding at a certain point on ultrasound.
This correlates with a “barcode” or “stratosphere” sign on time-resolved ultrasound, also highly specific for pneumothorax.
B lines
Correlates with the presence of an air-liquid interface on ultrasound, and usually means fluid is present in the alveoli, often from alveolar edema or acute respiratory distress syndrome.
In the emergency care setting, the presence of B lines on pleural ultrasonography predicts fluid overload, adding diagnostic accuracy to the physical examination and measurement of brain natriuretic peptide
Low frequency vs high frequency in ultrasound
- Low frequency has a rounded top, travels farther, see more depth, used for cardiac and abdomen
- High frequency has a flat top, better resolution, but less depth, used for superficial visualization
A lines
Ultrasound artifact indicating the normal lung surface
The liver is normally slightly more dense on CT (higher Hounsfield units) relative to the spleen. What might cause this ratio to change?
If there is hepatic steatosis, increased fat content in the liver decreases the density by HU, making it less dense than the spleen.
Diatnostically, liver HU < 40 or liver HU < (Spleen - 10) are sufficient for diagnosing hepatic steatosis.
