Study guide 9-11 Flashcards
The near zone is the region from
the transducer to the smallest cross-sectional area of a sound beam.
The Fraunhofer zone starts at the
beams smallest diameter and extends deeper.
Near zone & ____ have the same meaning.
Fresnel zone
Fraunhofer and ___ have the same meaning.
Far zone
Focus is the point or location where
a beam reaches its smallest dimension
The focal zone is the region of the sound beam where
focusing is most effective
The focus is at the
end of the near zone and the beginning of the Fraunhofer.
PZT crystal with small diameter/ low frequency will create a
beam with the shallowest focus.
PZT crystal with large diameter/high frequency will create
beam with the deepest focus
Ultrasound systems with a larger diameter crystal will have a deeper focus/higher frequency systems will have a
deeper focus
Terms that describe the shape of a sound wave created by a tiny fragment of PZT include:
spherical, Huygens’ wavelet and V-shape.
Huygens’ principle is based on
interference
Huygens’ principle explains the difference in
sound beam shape created by a disc-shaped crystal from that of a small chip of PZT.
A-mode
places time of flight information on the x-axis and echo amplitude on the y-axis accurately displays reflector depth.
displays a single jagged line of varying heights.
B-mode
strength of the reflection is put on the z-axis
places dots of dissimilar gray scale on the display.
M-mode
produces lines related to the changing positions of reflectors in the body with respect to time.
Axial resolution
accuracy visualizing two structures that are parallel to a sound beams main axis
An axial resolution of 0.3 mm (lower numerical value)
will produce a better quality image than an AR of 0.6 mm
The lower the numerical value of the longitudinal resolution
the better the picture
An ultrasonic pulse has a pulse repetition period of 1.9 msec, a spatial pulse length of 4.0 mm, and wavelength of 0.3 mm. What is the axial resolution of the system?
AR = spl/2 (2.0mm)
Higher frequency of the cycles within a pulse
the lower the numerical value of the axial resolution
The shorter the pulse length
the better the picture
The lateral resolution of an ultrasound system is 5 mm. Two structures are separated by 2 mm and lie side by side in relation to the sound beams main axis. What will most likely appear on the systems display?
one echo
Using an acoustic lens will
lower the value of an ultrasound systems lateral resolution
Using a curved crystal is an
internal focusing technique
The use of a lens is a technique for
external focusing
Both variable or multi-focusing are
electronic techniques for focusing
The diameter of a disc-shaped, unfocused piezoelectric crystal is 1.4 cm. The near zone length is 5 cm. What is the best estimate for the lateral resolution at a depth of 10cm?
1.4, at two near zone lengths the LR is again the same as the crystal width.
