ultrasonography ch19 Flashcards
The creation of sonographic image (sonogram) depends on three major components:
- the production of high-frequency sound waves
- the reception of a reflected wave or echo
- conversion of that echo into actual image
The body surface that can be scanned can be
external (transabdominal)
internal (transvaginal, transösophageal, endovascular, transrectal)
A tissue that reflects more echoes is depicited ___ on the sonogram
brighter/whiter
hyperechoic
A tissue that transmits more echoes (resulting in less echoes reflected back to the transducer) is depicted __ on the image
darker
hypoechoic
sonloucent
A tissue that transmits all the echoes id sepicted as __ on sonogram
black
anechoic
Posterior acoustic shadowing
when a very dense structure, such as a gallstone or bone, reflects so many echoes that virtually no sound waves are transmitted, the tissue deeper to this structure is displayed as hypoechoic and this phenomenon is called posterior acoustic shadowing.
Posterior acoustic enhancement
when a structure transmits more echoes that the surrounding tissues, such as a cyst in the liver, the sound waves deeper to this structure (compared with surrounding structures) are depicted as hyperechoic and this phenomenon is called posterior acoustic enhancement
two common imaging planes used in ultrasonography
sagittal or longitudinal
transverse
small differences in acoustical impedance will result in:
greater sound transmission
greater differences in acoustical impedance will result in
greater sound reflection
Appearance of commonly encountered tissues on ultrasound: fluid
hypoechoic or anechoic (depending if the fluid is simple or complex (containging debris, pus, blood); may have posterior acoustic enhancement
example: cyst, abscess, gallbladder…
Appearance of commonly encountered tissues on ultrasound: calcium
hyperechoic, may have posterior acoustic shadowing
example: renal stones, bones, calc. in soft tissues
Appearance of commonly encountered tissues on ultrasound: air
hyperechoic foci; may cause posterior acoustic shadowing
examples: gas-forming infections (abscesses, fournier’s gangrene, endometritis),
intraperitoneal air, necrotizing enterocolitis
By convention, two common imaging planes are used:
- saggital or longitudinal plane (long axis)
2. transverse plane (perpendicular to long axis)
What influences resolution of images?
frequency of the soundwaves
higher frequency = higher resultion, more detail BUT shorter penetration
and vice versa
advantages of ultrasonography
no ionizing radiation no known long term side effects real-time images produces little or no patient discomfort small, portable, inexpensive, ubiqutous
disadvantages of ultrasound
difficulty penetrating through bone
gas-filled structures reduce its utility
obese patients may be difficult to penetrate
dependent on the skill of the operator
list types of ultrasound
A-mode B-mode M-mode Doppler Duplex ultrasonography
What is A-mode US
simplest type of US
spikes along a line represent the signal amplitude at a certain depth
used mainly in ophthalmology
what is B-mode US
mode most often used in diagnostic imaging; each echo is depicited as a dot and the sonogram is amde up of thousands of these dots; can depicit real-time motion
(basically US we use)
What is M-mode US
it is used to show moving tructures, such as blood flow or motion of the hear valves
what is doppler US
used to asses blood flow.
pulsed doppler devises emit short bursts of energy that allow for an accurate localization of the echo source
what is duplex ultrasonography
it is used in vascular studies;
it referst to the simultaneous use of both gray-scale (or color doppler) to visualize the structure of, and flow within, a vessel and spectral (waveform) doppler to quantgative flow
Doppler: the direction of flow is represented by colors red and blue.
____indicates flow towards and ____ indicates flow away from transducer.
red towards (higher frequency) , blue away (lower frequency)
appereance of normal gallbladder on US
fluid-filled sonolucent (dark) lumen surrounded by echogenic wall (whitish wall)
4x10cm in size, wall normally no thicker than 3 mm
where will gallstone be impacted
in the neck of the gallbladder or cystic wall
how to differentiate biliary sludge from gallstones
sludge does not produce acoustic shadowing
how to recognize acute cholecystitis on US (3 points)
- thickened gllbladder wall (>3mm)
- pericholecystic fluid
- positive sonographic Murphy sign
HIDA scans include radioactive traces which will show obustrction.
What does it mean when
a) the tracer does not appear in the gallbladder, and
b) when it does not appear in small intestine?
a) obustrction of cystic duct = no tracer in gallbladder
b) obustrction of the common bile duct = no tracer in small intestine
common bile duct (CBD) lies ___ to the portal vein and ___ to the hepatic artery in the porta hepatis
anterior to portal vein
lateral to hepatic artery