Module 4 : Pulsed Ultrasound Flashcards
in a pulsed ultrasound can a crystal transmit and receive at the same time
- no
- must listen to create an image
what are the 2 ways that a pulse is generated
- electrical output from a generator is gated to apply a rapidly alternating voltage to a crystal
- a charged capacitor is discharged through the crystal which is stimulated to vibrate at a resonance frequency
what are the 5 wave parameters with pulsed ultrasound
- pulse duration
- spatial pulse length
- pulse repetition frequency
- pulse repetition period
- duty factor
what does ring down mean
- cycles in a pulse
what is pulse duration
- time it takes for one pulse to occur
what is the pulse duration equation
PD = T (period) x Ring Down
does pulse duration include the dead time ? and what units is it represented in
- no
- microseconds
what is spatial pulse length
- length of the pulse
what is the spatial pulse length equation
- SPL = wavelength x RD
what are the units of SPL
- mm
why is SPL important in ultrasound
- decreasing spatial pulse length improve image resolution (axial)
what two things decrease SPL
- increasin g frequency decrease wavelength which will decrease SPL
- decreasing number of cycles in a pulse
what is pulse repetition frequency
- number of pulses emitted in one second
- limited by depth
what are the units of PRF
Hz kHz
what is the pulse repetition period
- time from the beginning of one pulse to beginning of the next
- also go return time
what is the PRP equation as the go return time
PRP = D / c
what is the relationship between the PRF and PRP
PRF = 1 / PRP
what is the PRF equation using the range equation
PRF = c / d
what is the duty factor
- fraction of time that the pulsed ultrasound is on
- a higher PRF or PD increases the DF
what is the DF equation using PRP and pD
DF = PD / PRP x 100
what properties of the medium determine the acoustic velocity
- density and compressibility
what is density
- mass of medium per unit volume
- concentration of matter
how does density affect velocity
- if all other factors remain constant an increase in density will impede the rate of sound travel
what is compressibility
- indicates fractional decrease in volume when pressure is applied to material
- how squishy it is
how does compressibility affect velocity
- easier to compress the material the slower the velocity
what is the relationship between compressibility and density
- usually dense materials have low velocity and therefore have high velocity
what is bulk modulus
- reciprocal of compressibility or the negative ratio of stress and strain
- stiffness
characteristics of elasticity
- ability of object to return to its original shape and volume after a force is no longer acting on it
characteristics of temperature an velocity
- temperature increases the velocity of sound increases
- human body has little temperature variation so not very important
