Chapter 3 Physics

what do ultrasound transducers do?

convert electric energy into ultrasound energy

some materials when deformed by an applied pressure produce a voltage

piezoelectric principle

what do ultrasound transducers operate on?

piezoelectric principle

common material in ultrasound transducers, not naturally piezoelectric

lead zirconate titanate

what is the abbreviation for lead zirconate titanate?

PZT

where are piezoelectirc properties lost if they exceed this?

Curie point

ceramics combined with a nonpiezoelectric polymer

composites

what do composites offer?

lower impedance, bandwidth, sensitivty, resolution

contain miniature elements comprised of two electircally conducting layers facing each other, one fixed and one flexible

capacitive micromachined ultrasonic transducers

what form do single element transducers take?

disk

contain multiple elements, each with a rectangular shape

linear array

piece of piezoelectirc equipment, also known as crystal

element

how many cycles of ultrasound pulse do single cycle use?

2-3

how many cycles of ultrasound pulse do Doppler use?

5-30

preferred frequency of operating for element determined by propagation speed of material and thickness of element

operating frequency

operating frequency equation

ct/2xth

what is the typical thickness of diagnostic ultrasound elements?

.2-1 mm

what is the typical propagation speed of diagnostic ultrasound elements?

4-6 mm/microsecond

do thinner elements correspond to higher or lower frequency?

higher frequency

attached to near face, reduce number of cycles in each pulse

damping material

what does damping material decrease?

pulse duration, spatial pulse length, amplitude, efficiency, sensitivty

what does damping material increase?

resolution, bandwidth

what is the bandwidth of modern transducers (percentage)?

50-100%

helps with intermediate impedance to reduce reflection and improve transmission, typically made up of two layers

matching layer

how much of sound intensity would be reflected without matching layer?

80%

what does coupling medium do?

eliminate air layer

avoid intervening tissues like bowel or lung, reduce sound transmission path length

invasive transducers

what do invasive transducers decrease?

path length, attenuation

what do invasive transducers increase?

frequency, detail resolution

width of a pulse as it travels away form the transducer

beam

what does the width of a scan plane determine?

lateral resolution

what does lateral resolution determine?

section thickness artifact

concentration of the sound beam into a smaller beam area than would exist otherwise

focus

what does increased focus correspond to?

decreased beam width

region of minimum beam diameter and area

focal region

area between the transducer and focal region

near zone

area after the focal region

far zone

what is another name for near zone?

Fresner zone

what is another name for far zone?

Fraunhoefer zone

distance from transducer to center of focal region

focal length

distance between equal beam widths that are some multiple of the minimum value at the focus

focal zone length

size of a transducer element or group of elements

aperture

all points on a wave front or at a source can be considered as point sources for the production of spherical secondary wavelets

Huygens principle

what does Huygens princple explain?

formation of beam form aperture

occurs when a wave passes an obstacle or small aperture

deviation of wave direction not attributed to reflection, scattering, or refraction

diffraction

what is the beam width equal to at the end of the NZL?

½ transducer width

what is the beam width equal to at 2 x the NZL?

transducer diameter

what does the beam width increase in proportion to at beyond 2 x the NZL?

distance

what happens to the width as a pulse travels through the near zone?

decreases

what happens to the width as a pulse travels through the far zone?

increases

what is the range of diagnostic sonography?

2-20 MHz

useful for increased depth (obesity) and high attenuation (transcranical)

low range

useful when little penetration is needed (breast, thyroid, superficial vessels, pediatrics)

high range

if the aperture or frequency increase, what else increases?

resolution

what happens to the focus as aperture and frequency increase?

narrow focus

is the focus deeper or shallower with increased frequency?

deeper

is the focus deeper or shallower with increased diameter?

deeper