# Ultrasound Physics

## 95 terms

### pulse duration

time it takes to complete one pulse

### pulse repetition period

time from the start of one pulse to the start of the next pulse

### PRP formula

PRP=1/PRF; PRP=(13microsec)(cm)

### pulse repetition frequency

number of pulses that occur per time

PRF=1/PRP

### pulse duration formula

PD=(Period)(# of cycles)

DF=PD/PRP * 100%

### duty factor

percentage of time that a system transmits sound

### directly proportional

increase in one variable results in increase in the related variable

### inversely proportional

increase in one variable results in decrease in the related variable

### distance formula

Distance=rate x time

### attenuation

decrease in wave amplitude due to the mechanical wave interaction with the medium

### absorption

conversion of energy from the sound wave into heat

### attenuation depends on:

viscosity-higher the viscosity the higher absorption; frequency-higher f the higher absorption

### reflection

change in energy propagation direction such that some energy returns in the general direction

### attenuation coefficient

the amount of attenuation per cm; dB/cm

### calculating attenuation:

soft tissue .5dB/(cm-MHz)
muscle 1.0 dB/(cm-MHz)
blood .125 dB/(cm-MHz)

### attenuation formula

.5dB/(cm-MHz) x depth x frequency

### time of flight

time needed for US "pulse" to travel to reflector and return t transducer

### angle of incidence

angle formed between the wave front and the interface of the reflecting structure; must be 90 degrees; perpendicular to reflector

### normal incidence

PORN; Perpendicular; Orthogonal; Right angle; normal/ninety degrees

### angle of transmission

all waves will have some transmission and some reflection

### types of reflection

specular; scattering; Raleigh scattering

### specular reflection

mirror like reflection
smooth surface
large comparing to wavelength

rough surface

### Raleigh scattering

small in comparison to wavelength

### acoustic impedance (Z)

Z=Density x Propagation velocity
units: Rayls

### impedance mismatch

difference in impedance determine the amount that is reflected or transmitted

### conservation of energy

reflected energy plus transmitted energy will equal total energy 100%

### refraction

bending of the wave at an interface of two media

### refraction occurs

change in propagation speed
must have oblique incidence and difference in propagation speed

### Snell's law

predicts the amount of refraction

### continuous wave

"on" all the time
2 crystals
unable to locate depth
range ambiguity

### pulse

collection of cycles that travel together

"on" and "off"
range resolution

### resolution

ability to image accurately

dependent on SPL
aka LARRD

longitudinal
axial
range
depth

### axial resolution

ability to distinguish two objects that are close together and parallel to sound beam

### axial resolution formula

axial resolution=SPL/2

### pulsed wave (2-D imaging)

any modality that turns the transmitter on and off to reduce range ambiguity

### acoustic line (2-D imaging)

a single sound beam transmitted in a specific direction

returning echoes registered by a system from a single line

### display line (2-D imaging)

data displayed on the screen

### frame time

amount of time it takes to complete one frame

### frame rate

amount of frames per sec

### frame time formula

FT=PRP x (# of lines/frame)

### SPL formula

SPL=wavelength x # of cycles

### compressions

area of high concentration of an acoustic variable

### amplitude

maximum variation of an acoustic variable from its mean value

pressure
density
particle motion

### wavelength

distance from the beginning of a cycle to the end of the cycle

### attenuation is determined by

pathlength and frequency

### sound wave is considered as

mechanical and longitudinal

### frequency

how often an event occurs

### period

time required to complete a single cycle

media

### scanned modality

acquire information over a plane

### non-scanned modality

acquire information only along a line

### damping

SPL decreases
better axial resolution

### bandwidth

range of frequencies over which a device can operate

### piezoelectric effect

converts electrical energy into mechanical energy and mechanical energy into electrical

large wavelength
lower frequency

small wavelength
high frequency

### PW operating frequency equation

f(MHz)= C/2 x thickness

### CW operating frequency equation

f=Drive voltage freq.

focus

### matching layer

increases impedance mismatch between PZT and skin

### backing material

damping material
shortens SPL to get better axial resolution
reduces amount of ringing

### annular phased array

mechanically steered
electrical focus

### linear seq. array

steered: no steering
focus: external/fixed

### linear phased array

steered: electrically
focus: electronic
trapezoid phased

### convex seq array

steered: no steering
focus: external

### convex phased array

steered: no steering
focus: electronic

### 1.5 D array

elevation
more crystals side to side than up and down

### 2 D

3 D
same amount of crystals side to side and up and down

### NZL formula

NZL=D2(mm) x frequency (MHz)/6

LATA

Lateral
Azimuthal
Transverse
Angular

### transducer

any device that converts energy from one form to another

very repeatable characteristics
high frequency
highly efficient

high impedance compared to tissue-30-40Mrayls
great amount of reflection

### poling

increases efficiency of PZT
extreme heat is applied
magnetic field is introduced
allows "+" and "-" to line up

### curie point

point at which the material loses piezoelectric properties
300 C or 572 F

can operate at different frequencies
operate at high or low frequencies
dynamic frequency tuning
-optimizes both resolution and penetration

### PD and Bandwidth

reciprocals
long pulse-narrow bandwidth
short pulse-wide bandwidth

### focus

location where the sound beam reaches its minimum diameter

### focal zone

region surrounding the focus
where the beam is narrow and the picture is good

### focal depth

distance from transducer to focus (focal length, NZL)

### effects of frequency on focal depth

larger frequency-deeper focus
smaller frequency-shallower focus

### near zone

Fresnel zone
region between transducer face and focus
beam converges

### far zone

Fraunhofer zone
region beyond focus
beam diverges

### convergence

occurs in near field
at the end of near zone, the beam is 1/2 the diameter

### divergence

occurs in the far field
at the twice the near zone length the beam will e as wide as the crystal