week 5 probes and scanning types Flashcards
How does the Linear Array Probe work?
large probe (150) with small flat rectangular footprint that sends a parallel US beam
has a HIGH FREQ
small subsets of crystals are activated to sweep the beam across the entire area
Produces a rectangular image that can be electronically steered (widened) into a trapezoid by pushing a button
used for superficial structures and vascular doppler
Pros and cons of linear array probe
pros
- high res bc high freq
- small footprint
cons
- low pen bc high freq
-narrow sector width bc parallel beam
what is the hockey stick probe
a small linear array probe
eg used on very small structures like a tendon
curvilinear array probe - how does it work
large convex footprint (500) with a diverging beam
steer beam by activating subsets of crystal at a time
produces a trapezoid image
used for assessing large areas like abdominal, gynecological, obstetrical
pros and cons of curvilinear array probe
pros
- good pen (lower freq)
- wide sector width (div beam)
cons
- large footprint
- bad lat res in far field (bc div beam)
phased array probe - how does it work
smaller footprint (128) than curvilinear so it fits btw ribs
steer using electronic time delays to each indiv crystal
produces the pizza image
used for cardiac, intercostal spleen and liver, neonatal heads
phased array probe pros and cons
pros
- good pen
- smaller footprint
cons
- narrower near field
- poor far field res (bc beam diverges)
What is the minimum acceptable frame rate
15 fps
What are the 4 factors affecting frame rate?
- LPF = lines per frame (determined by sector width)
- PRF = pulse rep freq (determined by depth)
- SLD = scan line density (SLD = LPF/sector angle)
minimum is 1 scan line per degree - # focal zones (2 focal zones = 2 pulses per scan line = 1/2 PRF)
What is frame rate (defn and formula)
number of frames (images) per second that make up the moving clip
FR = PRF/LPF
What is strain elastography
in general,
push up and down with probe on patient over area of interest and machine colour codes the amount displacement.
Hard tissue is a different colour than soft tissue
What is sheer wave elastography
in general,
machine sends high intensity pulse into patient which creates a sheer wave that travels laterally. The velocity of the sheer wave correlates to tissue elasticity.
increase tissue stiffness = increase sheer wave velocity
what is Tissue doppler
in cardiac (not reliable so not used today),
put tissue doppler box over walls of LV to track the movement of the walls
get graph of velocity of the selected walls over time
what is Strain
in cardiac
machine tracks a certain speckle and determines its deformation (not movement) through out the cycle
used to predict heart failure in cancer patients so they can stop taking meds before EF drops
What is 3D ultrasound used for
3D = 4D
used in cardiac to calculate EF
what is fusion imaging
fuse two diff imaging modalities on one screen
eg cath lab overlays fluoroscopy (xray) and TEE
What is tissue harmonic imaging (THI)
tissues produce harmonics
if harmonics are on, the machine only listens to the 2nd harmonic freq
improves image quality
in cardiac, harmonics always on
in general, switch btw harmonics (fluid filled) and fundamental (large patient)
pros and cons of THI
pros
- better lat, elev, and axial res (bc higher freq and 2nd harmonic comes from center of beam)
- better contrast res (bc less noise)
- less artifacts (bc no side lobe noise)
cons
- decr pen (bc incr freq)
What is spatial compound imaging
obtain sonographic info from several angles and combine it into a single image (averages and smooths)
if the machine receives info back from more than 1 angle, it assumes the structure is real
used in breast, liver, soft tiss masses (NOT in kidney stones bc overestimate size)
pros and cons of spatial compound imaging
pros
- decr noise (bc only shows structures from more than 1 angle)
- decr grey speckle (bc smoothing and ave)
cons
- low frame rate - cant use in cardiac
- may miss small structures (bc smoothing and averaging)
what is panoramic imaging
can get an image wider than the probe capabilities by sliding the probe parallel to the image plane.
