Ch. 12 Physics Flashcards
The two characteristics of sound to make 2D images are
sound travels in a straight line and sound beams must be narrow to optimize LATERAL resolution
Mechanical transducers have what kind of active element
single circular/disc shaped
Mechanical transducer sector shape
fan
Mechanical transducer type of steering
mechanical
Mechanical transducer beam focusing type
fixed focus (conventional or mechanical)
Mechanical transducer beam INTERNAL focusing uses
curved active element
Mechanical transducer beam EXTERNAL focusing uses
acoustic lens
Mechanical transducer damage to PZT crystals causes
entire image to be lost
What we use today
Transducer arrays
Transducer arrays contain
multiple active elements
Array transducers comprise of a slab of PZT cut into a collection of separare pieces called
elements
Array transducers each ACTIVE element is
connected by a wire to its own electronic circuitry
Array transducers: a combination of the active element, the wire and the systems electronics
a channel
Array transducers: generally all have ______ active elements (except annular phased arrays)
100-300
Array transducer types
linear phased, annular phased, linear sequential, curvilinear, vector
The time difference between electrical spikes when steering is about
10 nanoseconds
Linear phased array footprint
small
Linear phased array image shape
sector
Linear phased array beam steering
electronic steering or phasing
Linear phased array beam focusing
focused electronically
Linear phased array damage to PZT crystal results in
inconsistent or erratic beam steering and focusing
Linear phased array all the active elements in the probe are fixed to create
each sound pulse
Linear phased array each sound pulse creates
wavelets
Linear phased array wavelets interfere constructively and deconstructively creating a
single sound pulse
Linear phased array: The overall pattern of the electrical signals determines the sound beams
steering direction and focus
Linear phased array: specific electrical patterns create a sound beam which are
all active elements fired at the same time straight across the transducer, time delayed electric spikes (phased delays) create beam steering to the right or left
Time delayed electric spikes create beam steering to the right or left or in other words
the sound beam is steered if the spike line has a slope
When all active elements are fired at the same time straight across the transducer, the sound beam is directed
straight down
If the right electrical spike excites the right active first, then the next, and then the next, beam will be
steered to the left (and vice versa)
Linear phased array: the electrical within the ultrasound system that creates these patterns is called the
beam former
Linear phased array: focusing during transmission has a ____ pattern that creates a focused sound beam during _______
curved, transmission
Linear phased array: focusing during transmission has a straight line pattern that creates an _____ sound beam
unfocused
Linear phased array: focusing during receiving is called
dynamic receive focusing
Linear phased array: dynamic receive focusing, a more accurate image can be created when the US receiver introduces variable time delays to some of the electrical signals during _______. The time delays used during receive focusing depends upon the depth of the ______ created. Therefore, the delayed patterns during receive-focusing change ______. Allows for focusing at _____ depths.
reception, reflection, continuously, multiple
Annular phased array has multiple ____ shaped elements arranged like a ________
disc, bull’s eye target
Annular phased array beam steering
mechanical steering
What is not possible with Annular phased arrays
electronic steering
Annular phased array beam focusing is called ____ and has multiple _____
multi-focusing, transmit focal zones
Annular phased array: remember, ____- diameter crystals create shallow focus beams, and _____ diameter crystals create deeper focus beams
smaller, larger
Annular phased array image shape
sector
Annular phased array damaged PZT crystal
only a portion of the image is lost, side-to-side band of dropout at a particular depth
Linear sequential array active elements arranged in
a line
Linear sequential array beam steering
a small group of crystals are fired simultaneously to create each sound beam
Linear sequential array can also be steered in a
slop pattern phase delay
What does lope pattern phase delay create
parallelogram shaped image
Linear sequential array beam focusing types
electronic transmit focusing and receiving focus
Linear sequential array electronic transmit focusing is achieved with a
curved excitation pattern of the active elements
Linear sequential array receiving focus is achieved by
introducing electrical delays in the signals returning from the transducer
Is focusing the beam at many depths possible with Linear sequential array
yes
Linear sequential array image shape
rectangular
Linear sequential array damaged PZT crystal
only a portion of the image directly below the damaged element is affected (band/linear dropout)
Curvilinear array (convex or curved) crystals are arranged
side-by-side in a bowed line
Curvilinear array (convex or curved) beam steering, beam is directed
straight out of the crystals, and pulses travel in different directions as they radiate out from the transducer
Curvilinear array (convex or curved) beam focusing is
focused electronically
Curvilinear array (convex or curved) beam focusing during transmission is acheived by
exciting the active element in a fixed group with a curved spike like pattern
Curvilinear array (convex or curved) beam focusing, dynamic receive focusing acheived by
introducing varying phase delays in the signals returning from the transducer
