US Physics-Unit 5 & 6

reflection

reflection provides the _____ of the organs

contour (capsule)

scattering provides the _______ of the tissues (organ parenchyma)

texture

echoes are created when the sound waves reach interfaces between tissues with __________

different acoustic properties

a specular reflector is an interface that is:

larger than the wavelength of the ultrasound wave,

smooth, mirror-like

specular reflection is responsible for the

bright appearance of fibrous structures

if 2 tissues have similar stiffness, most of the energy transmits into the next

tissue

if the stiffness of two tissue are very different most of the energy will be

reflected

requirements for specular reflection in dmu

acoustic impedance (Z) mismatch

perpendicular incidence

the larger the mismatch the

stronger the echoes

specular reflection is non-

frequency dependent

acoustic impedance (Z)

determines the amount of reflection at the interface

the larger the difference in impedance at the interface, the ______ the intensity

greater

if impedance values of media in both sides of interface are equal, the whole incident beam is transmitted with

no relfection

reflection coefficient

R= (Z1-Z2/Z1+Z2)2

transmission coefficient equation

T=1-R

thickness has ______ to do with reflection

nothing

air=

reflection

solids=

absorption

how do we reduce the amount of air

coupling gelc

coupling gel

has an impedance closer to soft tissue, which increases the intensity of transmitted ultrasound

ansiotrophy

the effect that makes a tendon appear bright when it runs at 90 degrees to the ultrasound beam, but dark when angle is changed

scattering gives rise to the characteristic _______ of the image seen within soft tissue

texture

diffuse reflection

kind of scattering, produced by reflectors with dimensions larger than the wavelength of the ultrasound and rough surfaces

Rayleigh scattering

small boundaries compared to wavelength

small amounts of energy are absorbed and retransmitted in all directions

backscatter

echo that returns to the transducer on the same path of the incident ultrasound wave

backscatter is usually a

weak echo

back scatter is not

angle dependent

backscatter is dependent on

frequency

because of backscatter, blood vessels appear

anechoic

diffuse reflection and Rayleigh scattering contributes to

attenuation

rayleigh scattering alternate between

constructive and destructive interferences, which result in a speckle

speckle contains useful

information and noise

contrast harmonic imaging

uses the enhancement of backscatter produced by Rayleigh scattering by exposing very small particles to high frequencies (harmonics)

micro bubble-based contrast agents

enhance ultrasonic backscatter signals and produce strong harmonic frequencies to improve imaging

properties of contrast agents

capable of easy administration, nontoxic, stable for sufficient exam time, small enough to pass through capillaries, echogenic enough with low attenuation to improve ultrasound

attenuation is higher in bone than in soft tissue.

true

when ultrasound encounters a boundary with perpendicular incidence, the _______ of the tissues must be different to produce a reflection

impedances

with perpendicular incidence, two media ___ __and the incident__ ____ must be known to calculate the reflected intensity

impedances, intensity

with perpendicular incidence, 2 media _____ must be known to calculate the intensity reflection coefficient

impedances

if the impedances of the media are equal, there is no reflection.

true

with perpendicular incidence, the reflected intensity depends on the

impedance difference and sum

reflection of sound in many directions while is encounters rough media junctions or particles suspensions is called

scattering

backscatter helps make echo reception less dependent on the incident angle

true

what must be known to calculate the distance to a reflector

travel time and speed

no reflection will occur with perpendicular incidence if the media _______ are equal

impedances

scattering occurs at smooth boundaries and within homogenous media

false

in general, gas content is eliminated by ______

lungs

perflurocarbons and sulfur hexafluoride do not undergo

metabolism, instead is excreted through lungs from exhalation

in general, shell components are filtered by the

kidney and liver

galactose dissolves quickly and undergoes

metabolism by liver

microbubble backscatter

rayleigh scattering

how do microbubbles produce enhanced echoes

backscatter, and production of harmonic frequency

contrast harmonic imaging can be used to:

enhance left ventricle opacification and endocardial border detection

improve lesion detection when echogenecity is similar

improve doppler detection when signals are weak

what is the most common site for metastatic spread of cancer?

the liver

renal perfusion

assessment of blood flow throughout kidney uising contrast harmonic imaging

aids in diagnosis of renal artery stenosis and urinary obstruction

regional myocardial blood flow

detection of coronary stenosis

high intensity transient signals

sharp spikes of strong echoes on doppler spectrum caused by microbubble bursts or clusters of macrobubbles

blooming

presence of color or power doppler signal outside the vessels

how do we fix blooming?

reducing color gain, or increasing PRF to decrease sensitivity

fluids are

liquids and gasses

viscosity

the resistance to flow offered by a fluid in motion

units: poise

Pressure

driving force behind fluid flow

a pressure _______ is required for flow to occur

difference

the greater the pressure difference, the ______ will be the flow rate

greater

gradient means

change, difference

Equation for pressure

force/area

Volumetric flow rate (Q)

the volume of blood passing a point per unit of time

unit: mL/s

Equation for volumetric flow rate

Q=Pressure difference/R

Volumetric flow rate is used for

long straight tubes

Resistance in a long tube depends on

kinematic viscosity, tube length, tube radius

Resistance equation

8L(viscosity)/pie(r4)

Poiseuille’s equation

Q=DeltaP(pie)(r2)/8(l)(viscosity)

only in long, straight tubes

if pressure difference or the diameter of the tube increases, flow rate _______

increases

if viscosity or the length of the tube increases, flow rate

decreases

flow spatial categories

plug, laminar, parabolic, disturbed, turbulent flow

flow temporal categories

steady, pulsatile

plug flow

the speed of the fluid is essentially constant across the tube

laminar flow

streamlines are straight and parallel to each other

flow speed is max at the center of the tube and minimum or 0 at the tubes walls

parabolic flow

a form of laminar flow

the average flow speed across the vessel is equal to one half the max flow speed (center)

disturbed flow

form of laminar flow

occurs when the parallel streamlines are altered from their straight line form

occurs in the region of a stenosis or bifurication

turbulent flow

non laminar flow with random and chaotic speeds and directions

forward net flow is still maintained

steady flow

pressures, flow speeds and flow patterns do not change over time

typically refers the venous systems

pulsatile flow

non steady flow with acceleration and deceleration over the cardiac cycle

arterial diastolic flow reveals much concerning the state of the downstream arterioles

stenosis

abnormal narrowing of a passage in the body

continuity rule

volumetric flow rate must be constant proximal, within and distal to a stenosis

applies only to a short segment of a vessel-stenosis

continuity rule equation

Q=va(area)

In order to maintain constant Q in a stenosis (decrease area) average velocity must

increase

Bernoulli effect

a drop in pressure associated with high flow speed at a stenosis

with the Bernoulli effect, if flow speed increases, pressure will_______

decrease

the largest pressure drop occurs at the

arterioles

Post-stenotic turbulence

turbulence occurs distal to stenoses because of

increased velocity and vessel widening

post-stenotic turbulence results in

bruit

bruit

sounds on auscultation from turbulence

Doppler provides info about motion:

presence, speed, direction, character of blood flow

doppler effect

the change in frequency (wavelength too) caused by motion of a sound source, receiver, or reflector

Doppler effect involves a

source, reflector, and receiver

Doppler shift (fD)

is the difference between the frequency of the received sound wave (fR) and the frequency of the emitted sound wave (fT)

Doppler shift equation

fD=fR-fT

Doppler shift can be used to determine

velocity and speed of the reflector due to the directional component