ATTENUATION Flashcards
Other term for acoustic boundaries
tissue interface
Difference between acoustic impedance from one to another
acoustic boundaries
Position within the tissue where the values of acoustic impedance change.
acoustic boundaries
Weakening of the sound as it propagates through a medium
attenuation
factors affecting attenuation
medium and frequency
unit of attenuation
decibel
↑ densely packed = _ attenuation
high
low frequency = _ penetration = _attenuation
high, low
unit of attenuation coefficien
dB/cm
For soft tissues, the typical value for attenuation coefficient is
0.5 db/cm
Process by which energy in the ultrasound beam is transferred to the propagating medium
absorption
converted to heat
absorption
concepts that affect attenuation
absorption, reflection, refraction, scattering, divergence
The major interaction of interest for diagnostic ultrasound
reflection
Occurs when two large structures of significantly different acoustic impedance form an interface
reflection
sound that hits an acoustic interface
incdent energy
reflected beam is called
echoes
factor of strength of reflection
size of reflector
small difference on the acoustic impedance makes _ echoes
small
two types of reflectors
speculative and diffuse
occurs when the boundary is smooth and larger than the beam.
specular reflector
in specular reflector, the angle of incidence is equal to
the angle of reflection
Terms to describe when the beam is perpendicular to the interface
normal incidence
Denotes a direction of travel of the incident ultrasound that is
not perpendicular to the boundary between two media
oblque incidence
- Incident beam is reflected in many different directions.
diffuse reflector
reflecting interface is irregular in shape and its dimensions are smaller than the diameter of the ultrasound beam.
diffuse reflector
Is responsible for providing the internal texture of organs in the image
scattering
Occurs when an ultrasound wave strikes a boundary or interface between 2 small structures and the wave is scattered in different directions
scattering
scatter in equal direction
rayleigh scattering
redirection of beam
refraction
what happens to refraction when angle of incidence is 90 °
none
gives the relationship between the angle of incidence and the angle of refraction when a beam of sound passes through an interface between two tissues where the speed of sound is different
snell’s law
what happens when p2>p1?
angle of transmission is higher than the angle of incidence
two requirements for refraction
- Oblique incidence
- Different propagation speed on either side of the boundary
Power spread over a large area
divergence
↑area = _ divergence = _ intensity
high, low
transducers convert _ energy to _ energy
electrical to ultrasound
general compositions of transducer
physical housing, electrode, piezoelectric element, backing material, matching layer
Contains all the individual components including the crystals, electrodes, matching later, and backing material.
physical housing
Provides structural support and acts as an electrical and acoustic insulator.
physical housing
o Protects patients from electric shock.
outside electrodes
other term for outside electrons
grounded electrode
inside electrodeis also
live electrode
o Abuts against a thick backing block
inside electrode
are connected to the UTZ machine which generates the short burst of electrical pulses to excite the crystals
electrodes
size of piezoelectric element
6-19mm diameter, 0.22mm thickness
most commont type of pizeoelectric element
lead zirconate titanate PZT
piezo means
to press
Eliminate the vibrations from the back face and to control the length of vibrations from the face of the crystals.
backing material
Sandwiched between the piezoelectric crystal and the patient
matching layer
Region nearest the transducer face, characterized by a highly collimated beam with more uniform intensity
near field
aka nearfield
fresnel zone
aka far field
fraunhofer zone
Region farthest from the transducer and characterized by the divergence of the beam with great variation in intensity.
far field
The location where the beam reaches its minimum diameter
focus points
Energy from the transducer that radiates at various angles from the transducer face
Side lobes
The arrangement of crystals within the transducer
array
types of electronic array
linear, curvilinear, phased
PROBE REFERS TO THE PHYSICAL SIZE OF THE PART OF THE ULTRASOUND THAT CONTACTS THE PATIENTS.
foot print
THE WIDTH OF THE IMAGE THAT IS SEEN ON THE SCREEN.
field of view
Produces parallel scan lines and has
a rectangular field of view
linear
linear array is Used to image superficial structures and vessels and therefore operate at frequencies above
4MHz
Extensively used for vascular, small parts and musculoskeletal applications.
linear
other term for curvilinear
sector
Similar to the linear array but the transducer face is formed into a curve (convex in shape) which provides a wide field of view which diverges with depth
curvilinear
Operate at lower frequencies, typically around 3.5 MHz and are best suited to image deep lying structures
curvilinear
Main application are in
abdominal and obstetric scanning
curvilinear
commonly used in echocardiography
phased
similar to curvilinear transducers, they are used to image deep-lying structures and perform trans-cranial investigation
phased
smaller and flatter footprint, which allows the users to maneuver more easily between the ribs and small spaces
phased
Transducers designed to enter the body via the vagina, rectum, esophagus or a blood vessel (catheter-mounted type)
invasive
use __ for cleaning
transeptics
Improves sound transmission into and out of the patient by eliminating air reflection.
coupling medium
coupling medium is also referred to as
aqueous gel
