Week 4- Basic US principles, measurements and views

echocardiography Hz range

1-10 MHz

AE TTE Frequency

2 - 5 MHz

Pediatric Probe Frequency

3.5 - 5 MHz

TEE Echo Probe frequency

2-10 MHz

what happens with increased acoustic impedance

increased sound return

What incidence is best for 2D imaging

Perpendicular

Examples of tissue producing impedance in the heart

walls, valves, blood

What incidence is best for doppler

Parallel

scattering occurs when

structures are less than 1 wavelength in lateral dimension

refraction occurs when 2 structures have different

impendance

refraction results in

“double image” artifacts

attenuation is concerted into (3)

1. heat

2. reflection

3. scattering

how to avoid airs high acoustic impednace (4)

1. Air has a high acoustic impendace

2. gel elimates air between skin and xducer

3. placing pt. on left side will help reduce lung interferance

4. move heart beyond the sternum

poor lateral resultion in far field causes

“blurring”

how does frequency affect lateral resolution

higher = better

how does frequency affect axial resolution

higher = better

how to make measurements for accurate

get cardiac structures perpendicular to xducer

temporal resolution limited by

sweep speed

what improves spatial resolution

increased frequency

spatial res def

ability of the system to image strucuter’s close together

penetration vs. resolution

cant have increased resoluition with optimal penetration- there is a tradeoff

optimal resoltion =

poorer penetration

patients that require deeper penetration and less optimal resolution

COPD, Body habitus, etc.

near field aka

fresnel zone

far field aka

fraunhaufer zone

MC type of xducer

phased array

pencil probe (pedoff, non-imaging probe) pros

1. small footprint for getting between ribs

2. superior at detecting high velocities, mainly aortic valve stenosis

3. 2 crystals 1 send-1receive

pedoff cons

no image,

anatomical sound guidance only which can be difficult to obtain

image quality and resolution depend on

scan-line density

ways to improve scan line density / frame rate

• decrease sector width

• use zoom

• decrease sector width

X_axis m mode

time

y_ axis m ode

depth

sampling rate of m-mode

1800 times per second

m-mode can aid in visualization of

• endocardium

• high frequency fluttering on valve leaflets

m-mode for measurements

should ONLY be used if perpendicular to structure

harmonic imaging

bypasses tissue frequencies and only looks at the harmonic frequencies

harmonic imaging originally used for

was originally to be used with contrast but tissue also produces different frequencies (harmonic frequencies) which was thought to be noise

harmonic frequency realted to transmitted frequency

harmonic is double the hz as transmitted

S:N ratio with harmonic imaging

increased

what resolutions are increased with harmonic imaging

contrast and spatial

harmonics used with

contrast

harmonics improve visualization of

endocardium in 2D imaging

ALARA

Minimized scan time and power

As Low As Reasonably Achievable

who discovered the doppler effect

johann Christian Doppler (1803-1853)

doppler frequency when fluid moving toward xducer

positive

doppler frequency when fluid moving toward xducer

negative

a sound wave refelcted from a moving object changes _______ in proportion to ________

frequency, velocity

doppler records

velocity and direction of blood flow

doppler allows measurement of

pressure gradient -

pressure gradient measured by -

Bernoulli principle

can be visualized as (3)

color

spectral (PW & CW)

doppler interrogation, uses (6)

Various windows

views (traditional and non-traditional)

Planes,

tools

color

patient adjustment

sound

etc.

intercept angle Θ (theta)

Must be parallel to flow as possible for increased accuracy of velocity

intercept angle degrees

less than 20 = good

more than 20 = underestimation of velocity

color doppler uses PW or CW?

PW, Has range resolution

color doppler can be overlayed on

2D or M-mode

large area or minute area (color doppler)

large

color doppler has limited

temporal resolution

color doppler use

very good at determining extent and area of regurgigation

color doppler can distinguish between

laminar and turbulent flow

color doppler angle

parallel to flow

color doppler scale setttings

50-60 cm/s

color maps

velocity (2color) variance (4 color)

how to set solor doppler gain

turn up unitl speckling appears then lower until speckling is gone

3 parts of the color doppler jet

vena contracta

PISA

jet area

vena contracta

narrowest part of the stream where the velocity is the highest

PISA Stands for

Proximal Iso-velocity Surface Area

PISA def

(flow convergence) - The hemispheric - shaped flow formed when fluid flows towards a flat surface.

PISA used for

calculating diameter of an oriface

Jet Area

The area of the regurgitant jet into the downstream oriface

examples of velocities CW can resolve that PW can not

AS (Aortic stenonsis)

MR (Mitral regurgitation)

AI (Aortic insufficiency)

what is spectral doppler used for

measuring velocities and assessing timing

what 2 dopplers create a spectral doppler

CW and PW

temporal res of spectral doppler

excellent

“zero” line or baseline is adjusted how?

up or down

x-axis spectral doppler

time

y-axis spectral doppler

direction and velocity (frequency shifts)

how is flow towards displayed on spectral doppler

above “0” line

how is flow away displayed on spectral doppler

below “0” line

how to determine turbulence with CW?

Envelope if filed in

how to determine turbulence with PW?

will vary depending on interogration style

spectral broadening: what is it?

possible causes

The broadening or filling of a PW waveform due to various velocities, non-laminar flow (sample volume/gate is too large

VTI Stands for

velocity time integral

VTI AKA

Flow velocity integral

VTI / FVI definiton

distance blood travels in each stroke (cm)

How is VTI / FVI Calculated

by the machine by tracing the doppler spectral curve

nyquist limit =

FRF/2

How to improve your nyquist limit

adjust depth (higher PFR = Better nyquist limit)

How created the bournoulli equation

Daniel Bernoulli (1700-1782)

Bernouli equation:

ΔP = 4V² (V = Doppler velocity) is Simplified Bernoulli Equation

explain bernoulli equation in words

Change in pressure across a small oriface is proportional to the square of the velocity of the fluid flowing through the oriface

3 steps to obtaining Pulmonary artery pressure (PAP) or Right ventricular systolic pressure (RVSP)

1. Obtain peak velocity of the tricuspid reguigitant jet

2. Change the velocity to a pressure gradient using the bernoulli equation

3. then add the estimated right atrail pressure by assessing the degree of collapse of the IVC

PAP=

PVSP In the absense of pulmonic stenosis

Right atrail pressure is estimated by

size and collapability of the IVC

Application of Bernoulli equation

changes velocity (m/s) into pressure gradient (mmHg)

bernoulli equation uses

peak velocity of TV regugitent jet

RVSP or PAP =

4(Tricuspid regigitation veloctity)² + right atrial pessure

PAP or RVSP =

ΔP_RV-RA + RAP

How is RAP (right atrial pressure) estimated

by evaluating the degree of collapse of the IVC