L2 Flashcards
Unfocussed beams have 2 areas
near field and far field
What are unfocussed beams used for
low resolution imagery; soft tissue injury treatment and targeted drug delivery
Explain what is near field
all the pulse waves maintian constant diameter
Near Zone Length (NZL) relates to
diameter and wavelength
As frequency increases (wave decreases), NZL
increases at the cost of penetration
Towards the end of the near zone, the beam decreases
to half its diameter of crystal and then diverges (huygen’s principle)
Far Field is where
the beam diverges and has less intensity
Higher US freq produce beams that
are less divergent thus producing better detail
As diameter increases,
divergence decreases (at cost of lateral resolution)
As frequency increases,
divergence decreases, at cost of penetration
Why is a focussed beam better
smaller cross sectional diameter, better lateral resolution, better visibility of detail of image
Best detail is obtained in
focal zone
Describe the focal point
smallest beam area; most intense part; max resol; adjustable
Describe the lateral resolution
best at focus, changes with distance, beam diverg worse than focal point
Axial resolution (up/down)
function of pulse frequency and is same at all depths
Slice Thickness
is how wide beam is at max depth
Grating lobes are side lobes where
spatial aliasing cause side lobes to be larger in ampl; causing image artifacts by sending beams in unwawnted directions
What are th types of transducer arrays
Curilinear, linear, phased array and endocavity
Endocavity is used for
transrectal US and gynaecological - curved face - wide field of view - high freq - more resolution - elogonated shape
Phased array transducer
most common - aligned linear/curved; beam creation is done electronically - reduces need to move probe
What imaging does phased array transducer do
cardiac imaging, and imaging for the ribs
Curvilinear transducer arrays
aligned along a curved surface resulting in a wide field of view - for lower freq/deeper struc - abdominal/pelvic
Linear Transducer
Used for superficial imaging and higher freq - less penetration
What are the diff in transducers
piezoelectric crystal arrangement
aperture (beam footprint)
frequency
