Intravascular Ultrasound
30MHz-40MHz
asses vessel walls characterize plaque morphology
transducer contained in a sheath attached to catheter
no air means high preq usable
Therapeutic Ultrasound
.5MHz-3MHz
beam intensity result in tissue temperature increases
4°C as deep as 5cm
increases blood flow
treats muscle spasms, tendonitis and bursitis
joint swelling
High Intensity Focused Ultrasound
HIFU
used for selective destruction of tissue volumes
cancerous lesions in liver, kidney, breast and prostate
focusing the beam allows energy concentration on affected area while sparing surround tissue
Wave Propagation
Worse in Gas
better in liquid
best in solids
Sound wave propagation
sound traveling pressure variation
regions of compression and rarefraction
particles vibrate back and forth
parallel to the directoin of travel
Mechanical Wave
needs physical interaction
must have medium
longitudinal
transverse
Electromagnetic Waves
travel in medium or vacuum
light, heat, X-rays, gamma rays TV rays
transer of energy through a varying electrical and magnetic field
Acoustic variables
Pressure
Density
Temperature
particle motion
Pressure
concentration of force
Pascals
varies cyclically as sound wave propagates
Density
p=mass/volume
compression increases
rarefraction decreases
non linear imaging Harmonic Imaging
units kg/m3
Temperature
any mechanical movement produces heat
sound wave vibrate the tissue and some wave energy is lost to heat with tissue
important in Bioeffects
Celcius
Kelvin
Fahrenheit
Particel Motion
particels of tissue being imparted with momentum and traveling into the locale of the nearest neighbors
osscillate back and forth about their original location allowing energy to propagate along the wave p[ath
particles DO NOT travel with the wave
ALARA
As Low As Resonably Achievable
short scan time
low power settings
short use of color and spectral
Attenuation
decrease in wave amplitude due to mechanical wave interaction wiht mnedium
units dB
absorption
reflection
refraction
Absorption
conversion of energy from wave to heat within medium
as Freq increases amount of energy lost increases
Reflection
sound wave changes direction and does not continue to travel forward
returns to source
foundtation for diagnostic ultrasound
Ultrasound based on processing these refelctions
Refraction
bending of wave
change in propagation velocity when angle of incidence is other than 0
Anechoic
without echoes
cysts
fluid filled organs
Hypoechoic
low level reflected signals
Hyperechoic
highly echogenic tissues
moderate to high reflected signals
calcified echoes
strongly echoic
usually with acoustic shadows
Complex
mixed echogenicity
with or without shadowing
Transducers
Device that converts energy from one form to another
Transducer components
Crystal
matching layers
Damping material
Transducer case
electronic cable
Crystal
diameter determines beam shape
like beam of flashlight
shape is region in the patient which sound travels
matching layers
provide an acoustic connection between crystals and skin
reduces amount of reflection from large acoustic mismatch
allows wave to travel into the body
gel
Damping material
decrease secondary reverberations of crystal with returning signals
reduces the ring time and results in an increase in depth resolution (axial)
Trasducer Case
provides housing for all internal components
Electronic cable
caontains bundle wires to cary electrical signals to and from the crytals
B-scan (Static scan)
uses series of B-mode images to biuld a 2 d image of tissue
transducer attached to articulated arm to provide system with position and orientation
no longer used due to numerous drawbacks
