physics exam 2

what produces electrical waveforms that drive the transducer

pulser (transmitter)

how is the amplitude of a signal controlled

directly by the transmit power knob

2 requirements of diagnostic ultrasound

preparation and transmission, reception

all subsystems in ultrasound machine are controlled by

master synchronizer

2 components of pulse ultrasound

transmit talking (time on), receive listening (time off)

primary objective of an ultrasound scanner

produce a unidirectional beam

pulse duration (pd) def

time from start of a pulse to end of that pulse

are shorter or longer duration pulses better for imaging

shorter

in clinical imaging, a pulse is how many cycles

2-4

pulse duration units

microseconds

pd formula using frequency

pd = cycles/frequency

pd formula using period

pd = p x cycles

pulse repetition period def (prp)

time from start of one pulse to start of next

prp units

seconds or milliseconds

prp is only related to

depth of view

how is prp related to prf

inversely (reciprocal)

prp is determined by

sound source only

can a sonographer adjust prp

yes (by adjusting depth)

how does depth affect pulse repetition period

deep imaging = longer prp

what a sonographer alters depth and changes prp, what portion of the prp was changed

listening time

pulse repetition frequency (prf) def

number of pulses occurring in one second

units for prf

hz and khz

equation for prf

prf = c/2r

prf is determined by

sound source

spatial pulse length def (spl)

distance of pulse from start to end of pulse

range of ppl in soft tissue

0.1-1 mm

spl is determined by

both source and medium

spl formula

spl = wavelength x cycles

are short or long spatial pulse lengths more desirable

short

axial resolution def

ability to separate structures parallel to the ultrasound beam

what is necessary for good axial resolution

short spatial pulse duration

duty factor def

fraction of time (percentage) the ultrasound unit is transmitting a pulse

duty factor formula

pd / prp

duty factor relationship to depth

inversely related

piezoelectric effect def

property of certain materials to create a voltage when mechanically deformed or when pressure is applied to them

2 materials that produce a voltage when deformed by an applied pressure (piezoelectric effect)

ceramics and quartz

piezoelectric effect material commonly used in ultrasound

lead zirconate titanite

7 parts of the transducer

-case

-electrical shield

-acoustic insulator

-pzt or active element

-wire

-matching layer

-backing material/damping element

the electrical shield of the transducer helps prevent

noise

the acoustic insulator in the transducer prevents

vibrations in the case

resonance frequency of transducer crystal is determined by

thickness of piezoelectric element

resonant frequency relationship to crystal thickness

proportional

most effective crystal thickness for us transducers

one half the wavelength

resonant frequency def

natural frequency where a medium vibrates at highest amplitude

how can you be sure of the purity of the frequency of ultrasound emission

more cycles present in an ultrasound pulse

how are pzt thickness and frequency related

inversely related

what 2 characteristics of the active element determine the frequency of sound created by a pulsed wave transducer

speed of sound in the pzt, thickness of the pzt

speed of sound in pzt and frequency of sound relationship

directly related

matching layer is how thick

¼ wavelength

purpose of the matching layer

reduce reverberations and provide efficient transmission of sound waves

what does matching layer do

decreases reflections at pzt/skin boundary, increasing transmitted sound

what does damping material do

damp the ultrasound pulse (reduce vibrations and shorten pulses)

damping and q value relationship

inversely related

damping material reduces _ and enhances _

ringing, axial resolution

damping _ sensitivity of the transducer bc it _ intensity of output signal

reduces, lowers

damping material and crystal should have what difference in acoustic impedance to get max absorption and ensure a short duration pulse

similar

consequences of backing material (3)

decreases sensitivity, wide bandwidth, low quality factor (q)

broad or wide bandwidth transducers have a _ range of transmitted frequencies

larger

cw has narrow or broad bandwidth with lower or higher frequency

narrow bandwidth, higher frequencies

pw has narrow or broad bandwidth with lower or higher frequency

broad bandwidth, more frequencies

q factor def

purity of vibration of piezoelectric crystal

bandwidth and quality factor relationship

inversely related

long ring down time/high q is good for (2)

therapy ultrasound or cw

q factor relationship to pulse length

directly related