Ultrasound Flashcards
Tell me the principles of how an image is formed on U/S
electrical impulses sent to transducer (probe) vibrate piezoelectric crystals in the probe, which send out high frequency sound waves. these sound waves go into the tissues. the sound waves are reflected back to the probe when they encounter differences in tissue density or a reflector surface (echo). the crystals pick up these sound waves and vibrate, sending back an electric signal.
what is attenuation?
progressive weakening of sound waves as they pass through tissues (lower quality the further through the tissues)
what is acoustic impedance?
resistance of tissues to propagation of sound waves (bone has high impedance
what is reflection? what direction are they?
proportion of waves that return to the transducer; perpendicular
occurs when there’s a change in acoustic impedance
(most with bone and air)
what is refraction? what direction are they?
bending of sound waves around interface; not perpendicular
causes shadows to appear under curved structures
what is scatter?
when sound waves encounter an irregular surface
what is absorption?
tissues capturing energy of waves
most with fluid
what are the common U/S artifacts?
- specular reflector
- non-specular reflector
- shadow
- enhancement
- reverberation
- beam width artifact
- electrical interference
what is a specular reflector?
parallel white line produced when beam strikes a smooth interface wider than beam
picture: diaphragm is acting as a specular reflector
what is a non-specular reflector?
white line when interface is irregular or narrower
what is a shadow?
from blockage of bone, FB, gas, etc or deviation of beam
what is enhancement?
bright echoes under a structure due to enhanced transmission through fluid
what is reverberation?
series of parallel white lines equidistant due to echo bouncing between 2 strong interfaces
what is beam width artifact?
fuzzy edges of large fluid-filled structures due to partial fill-in of a non echoic area with echodense artifact
what is electrical interference?
caused by an external electrical source interring (ex. motor running)
what do follicles look like on US? how are they measured?
black, round, fluid filled structures
(W+H)/2
what is a cystic follicle? how can you tell the difference between a follicular cyst and a luteal cyst?
large follicule ≥25mm, no CL present (no ovulatory crown)
follicular = thin walled
luteal = thick walled
what does a CL look like?
When can you detect it on US?
black central cavity irregularly shaped filled with tissue
detectable 1-2 post-ovulation until next ovulation
P4 levels are highly correlated to what in the bovine ovary?
area of lutenized tissue
_____ regression of the CL occurs before _____ regression
functional, morphologic
uterine coiling is most problematic when? and least problematic when?
most: diestrus
least: estrus
tell me about the fluid in the uterus of a cow for US
what does it look like on US?
begins to increase 3-4 days pre-estrus, peaks during estrus, then declines 3 days post estrus
uterine edema = black on US
tell me about cow pregnancy dx using US. like what’s happening on what day?
- 20d: embryo first detectable, surrounded by a small circular area of fluid
- 25d: embryo detectable at base of first uterine curl or between 2nd and 3rd curl; detection of chorioallantoic fluid
- 40d: fetal heartbeat = most reliable preg dx
what is the difference between cows and horses in terms of what the early embryo does to alert the mother of its presence?
cow: elongates to fill horn and signal presence while fixed
horse: expands to become larger and actively migrates to signal presence
