There are different shapes of transducers:
- curvilinear (good for mashing down fat)
- linear (legs, arms, whatever)
- hockey stick (good for thyroid, breast, and superficial structures)
- endocavital (mouth, rectum, vaginal)
- cardiac (for TEE)
If you REALLY want to get into the nitty-gritty, this article goes into more detail about different ultrasound probes.
Different frequencies are good for different purposes:
- 1 is good for fat
- 8 is soft tissue range, like liver or kidney
- 15 is like breast, thyroid
- You can increase the “gain” on the ultrasound, and make proteinaceous material move around 😀
There are certain organs that tend to get over-imaged. See this editorial that argues for fewer thyroid ultrasounds.
On CT physics:
the Hounsfield unit describes the radiodensity of objects. The higher, the more radiodense it is, the lower, the less radiodense it is.
-400——- -50——0——- 80 —————————-800
air———– fat– water— soft tissue—————— bone
BAM–I didn’t even have to go far to find an answer to this question. RadConsult has made a super-helpful chart organized by rule-out diagnosis:
||Best with IV contrast
||No IV contrast needed
|-any CT angiography (aorta, PE study, carotids/vertebrals, brain)
-adrenal mass assessment*
-cardiac CT (except calcium scoring)
-liver mass assessment*
-pancreatic mass assessment*
-renal mass assessment*
|-abdominal pain generally
-anytime infection is suspected
-followup malignancy exam (usually)
-mediastinal mass (usually)
|-aortic aneurysm size assessment (for intraluminal detail, contrast needed)
-pulmonary nodule followup
-fractures and many osseous lesions
-brain (nearly always; talk to your radiologist if you have questions)
-suspicion for intra-abdominal, retroperitoneal, or other large hemorrhage
-ventral hernia (oral contrast may be helpful)
* Be sure to understand that for these studies, a non-contrast scan is usually part of the protocol, exposing your patient to at least double the radiation dose.
Don’t worry, it’s not the “whiff” test.
“Sniff test” can actually refer to two different phenomena. It could be a test used to see in real-time if a patient has unilateral diaphragm paralysis–sniffing is essentially the opposite of a Valsalva maneuver and you would expect both halves of the diaphragm to flatten appropriately. If they don’t, that’s a problem.
It can also refer to duplex ultrasound, and trying to identify the subclavian vein. Eyeballing veins can be tricky. But if you ask the patient to do a “sniff test,” the subclavian should collapse, which can be a helpful way to identify it. Conversely, if you ask the patient to Valsalva, the subclavian should expand.
At some point in your outpatient clinic, you will have a patient with an ankle injury. Maybe they tripped on the curb. Maybe they stepped wrong on a stair. Anyway, they’re here in your office, and the #1 thought on their mind is probably: is it broken?
Their ankle looks kind of swollen and bruised on exam, and they wince when you so much as put your fingertip on their skin. So do you get an x-ray? Or not?
Luckily, there are rules to guide us. The Ottawa Ankle Rules have a sensitivity of virtually 100% and okay specificity. This is what it boils down to: if they can’t bear weight on that leg AND they have pain around their ankle or the 5th metatarsal, get an x-ray.
What you do next depends on what the x-ray shows. If there was no fracture–only a sprain–I would have told her to move around to the best of her ability and RICE it. (RICE=rest, ice, compression, elevation) If there was a fracture, I would have made an urgent orthopedics appointment so that she could get a cast.