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With ultrasound, how is frequency measured (units)?
What is the piezo-electric effect?
crystals in the transducer mechanically vibrate when stimulated by electrical current (electrical e* converted to sound waves)
What % of the time is the crystal emitting v. receiving information?
What is B mode?
brightness proportional to the strength of the echo
What is acoustic impedance? How does AI compare between air/gas, soft tissue and bone?
- resistance to transmission of sound
- = velocity x tissue density
- air (lowest) < soft tissue < bone
- *bone has high AI (transmits sound at higher velocity and hi tissue density)
T or F: Speed of sound does NOT depend on frequency.
Why does the transducer need to be perpendicular to object of interest?
to ensure maximal reflection of sound back to transducer
High frequency transducers have big or small wavelengths?
small (inverse relationship)
If you need the ultrasound to penetrate deep into tissues (ie. horse heart) do you want a high or low frequency transducer?
low frequency (long wavelength) transducer like 2.5MHz
Does hi or low frequency transducer give more detailed image?
hi frequency = detailed image but won't penetrate as deep
How does an ultrasound image differentiate between two soft tissue structures? (how are you able to see the kidney separate from the liver?)
different acoustic impedance sends different reflections back (appear w/different echogenicities)
what is acoustic shadowing?
when there is marked difference in acoustic impedance, nothing gets transmitted beyond the interface (ie bone makes a hyperechoic edge beyond which there are no echoes)
do fluid filled or soft tissue structures cause more attenuation (weakening) of the beam?
soft tissue requires more transmission, so more attenuation/weaking
What is acoustic enhancement?
beam is relatively stronger when exits a fluid filled structure surrounded by soft tissue (making it appear brighter where beam passed through gall bladder in liver)
what is lateral resolution? do hi or low frequencies allow greater lateral resolution?
- ability to discern two objects close together in a lateral plane
- hi frequencies are better at distinguishing adjacent points
How do you get better axial resolution?
use short pulse sequences (need higher frequency transducer)
When is M mode utilized? What about A mode?
- motion mode for cardiology
- amplitude mode for eyes
What is B mode? How many dimension can you see with this?
- brightness mode
- 2D images that appear to move bc its constantly updating
do you need a faster frame rate for cardiac or abdomen?
What is term for tissues that do no produce echoes? How do they appear on screen?
- anechoic or echolucent
How does a hypoechoic tissue appear on screen?
- shades of gray
- (hyperechoic is bright/white)
For abdominal radiology of a puppy, is it normal/common to see to increased or decreased serosal detail?
decreased (poor serosal detail-not much fat to highlite)
For abdominal rads of cats, how does their normal post-prandial stomach positioning differ from dogs?
cat stomach can distend significantly into abdomen (normal for cat, not for dog)
If fluid in the abdomen is suspected, how can definitive diagnosis be made?
abdominocentesis for cytology
How does peritoneal fluid appear on radiology?
- poor abdominal contrast
- indistinct serosal detail
- (can be local or generalized)
Is radiology or US the tool of choice if peritoneal fluid is suspected?
US-easy to identify fluid with US and then use as guide for aspirate
How does peritoneal fluid appear on US?
- anechoic area
- can have "snowy/swirling" appearance
- can have fibrin strands floating
What are rad signs of peritonitis?
- poor serosal detail
- w/intestine perforation or pancreatitis, usually localized
- free intra-abdominal air
What are US signs of peritonitis?
- hyperechoic fluid w/lots of fibrin strands
- adhesions btwn organs
- may see focal hyperechoic areas
What should be suspected when abdominal structures like kidneys are displaced ventrally on rads?
retroperitoneal mass or fluid
If intraabdominal air/gas is suspected, a horizontal beam should be directed toward the pt in which position? What are you looking for?
- left lateral recumbency (lateral decubitus view)
- gas (darkness) under costal arch in Rt cranial abdomen
What is expected on rads with ruptured bladder?
widespread lack of serosal detail
When evaluating rads, when do you suspect hepatomegaly?
liver lobe protrudes well beyond the costal arch
How does cholelith (gall bladder stone) show up on US?
hyperechoic region in GB and casts an acoustic shadow (dark field extending beyond the stone)
When choosing sedatives for rads of abdomen, what should be considered?
- should not enlarge the spleen or cause GIT distension
- should adequately relax the muscles
Where is the center point for abdominal films?
- lateral: half way between top of last rib and iliac crest
- VD: umbilicus
From inside-out, what are the 5 layers of intestine to identify on US?
lumen - mucosa - submucosa - muscularis - serosa
What is the visual appearance of cat's empty stomach on cross section on US?
What are the 2 types of ileus?
- mechanical- severe focal distention dt FB, neoplasia, intussuception
- functional - moderate generalized distention w/cause more difficult to identify
what is gravel sign on rads?
mineralized material seen proximal to obstruction indicating chronic situation
US of inflammation v neoplasia: which case usually preserves layering pattern?
inflammation thickened but pattern preserved
US of inflammation v neoplasia: which is usually focal v. diffuse? which causes obstruction?
- inflammation diffuse w/o obstruction
- neoplasia usu. focal and can cause obstruction
What is spalding sign?
radiograph shows overlapping sutures in fetus skull, indicating fetal death (brain shrinks)
What is physometra?
gas in uterus, seen in rads with fetal death
If a retrograde cystogram shows a reflux of contrast into prostatic cavitations, what are 2 things on your differential?
infection and neoplasia