Key Terms Week1/Lecture1 Flashcards
Analog Scan Converter
first type of scan converter
made grayscale imaging possible
no longer used in modern equipment
B-Mode
brightness mode
A-mode signal converted to dots that vary in brightness depending on the strength of the returning echo
stronger echo=brighter dot
Cavitation
the formation of gas-or vapor-filled cavities
Digital Scan Converter
uses computer memory to digitize the image and transfer it to the display monitor
Doppler Effect
when a source of wave motion moves, the apparent frequency of the emitted wave changes
Grayscale Imaging
varying shades of gray that are produced from an analog scan converter
M-Mode
series of B-Mode dots that are displayed on a moving time base to graph moving structures
formed the basis of echocardiography before real-time scanning
today it is used in conjunction with real-time imaging
Piezoelectric Effect
a mechanical deformation results when an electrical field(voltage) is applied to the crystal, the crystal resonates mechanically
when the crystal resonates mechanically, it produces a voltage
material most commonly used is lead zirconate titanate
Real-Time Imaging
recording moving structures
real-time B-mode ultrasound systems use a transducer, which contains a crystal that can convert ultrasound impulses into electrical impulses
signals are integrated by a computer(scan converter)
Therapeutic Ultrasound
between .5MHz and 3MHz
beam intensities results in tissue temperature rises as high as 4 degrees Celcius and up to depths of about 5cm
used to increase blood flow and manage several soft tissue conditions
3D Imaging
like a 2D image, except instead of sound waves being sent vertically, they are sent from many angles, and the returning echoes can be used to build and display a volume image in 3D
4D Imaging
3D image with real-time imaging
Diagnostic Ultrasound
2MHz-12MHz
frequencies below 2MHz has poor resolution
frequencies above 12MHz does not penetrate deep into the patient
Transverse Waves
particles move in a direction that is perpendicular (at right angles) to the direction that the wave propagates (moves)
Longitudinal Waves
particles move in the same direction that the wave propagates (moves)
Compression
squeezed together
Rarefaction
stretched apart
Medium
tissue
some type of material
Acoustic variables-pressure
concentration of force in an area
units: pascals(Pa), kg/m2
compression phase-pressure increases
rarefaction phase-pressure decreases
Acoustic variables-density
concentration of mass in a volume
units: kg/cm3
compression phase-density increases
rarefaction phase-density decreases
this leads to nonlinear imaging technique-harmonic imaging
Acoustic variables-distance
measure of particle motion
units: cm, feet, mile, etc.
Acoustic parameters-period
the time it takes a wave to vibrate a single cycle
the time from the start of one cycle to the start of the next cycle
units: microseconds, seconds, hours, days
not adjustable
Acoustic parameters-frequency
number of cycles that occurs in one second
units: hertz(Hz)
Hertz equals per second
not adjustable
Acoustic parameters-amplitude
the “bigness” of a wave
the difference between the maximum value and the average or undisturbed value of an acoustic variable
the difference between the minimum value and the average value of the acoustic variable
units: units of any of the acoustic variables
Acoustic parameters-power
the “bigness” of a wave
rate of energy transfer or the rate at which work is performed
units: watts
It is adjustable
Acoustic parameters-intensity
the “bigness” of a wave
the concentration of energy in a sound beam
units: watts(W), W/cm2
It is adjustable
Acoustic parameters-wavelength
the distance or length of one complete cycle
units: mm, meters, other units of length
not adjustable
Acoustic parameters-propagation speed
the rate at which a sound wave travels through a medium
units: m/sec, or any other distance/time
not adjustable
Hertz
events per second
units that frequency is measured by
Infrasound
sound waves with frequencies lower than 20Hz
Audible sound
between 20Hz and 20,000Hz
Hertz(Hz): standard unit of frequency equal to 1 cycle per second
Ultrasound
between 1 and 30MHz (1,000,000-30,000,000Hz)
do not exist in a vacuum
movement in gases is poor because the molecules are widely separated
the closer the molecules are, the faster the sound wave moves through the object
A-Mode
Amplitude Mode
the distance between the transducer and the structure determines where an echo is seen along the time axis
(Obsolete)
