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