Disclosure Statement of Financial Interest

ULTRASOUND BASICS Christian R. Falyar, CRNA, DNAP Department of Nurse Anesthesia Virginia Commonwealth University

Disclosure Statement of Unapproved/Investigative Use

• I, Christian Falyar, DO NOT have a financial interest/arrangement or affiliation with one or more organizations that could be perceived as a real or apparent conflict of interest in the context of the subject of this presentation.

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I, Christian Falyar, DO/DO NOT anticipate discussing the unapproved/investigative use of a commercial product/device during this activity or presentation.

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WHAT IS SOUND?

WHAT IS SOUND? Rarefactions (low pressure)

A

Transducer λ

Compressions (high pressure)

PROPAGATION VELOCITY

ROLE OF FREQUENCY... High frequency

Low frequency

•  More cycles per second

•  Fewer cycles per second

•  Images are higher

•  Greater tissue penetration

resolution •  Increased attenuation •  Imaging limited to shallow depths

but lower resolution •  Less attenuation allows

for imaging of deeper structures

ROLE OF FREQUENCY High frequency

Low frequency

BEAM PROPERTIES

IMAGE CREATION

 



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TRANSDUCER BASICS

•  It’s all in the math •  Depth of the echo is

  

 
 






 


 


determined by time from when the echo was sent to when it was received •  The brightness of an echo is results from differences in acoustic impedance between adjacent tissues

ACOUSTIC IMPEDANCE

IMAGE CREATION Transducer Incident Wave

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Reflected Wave

Incident Wave

Incident Wave

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Impedance Z1

Impedance Z1

Impedance Z2

Impedance Z2

Refracted Wave

Attenuated Wave





 






























  



































  




















 


REFLECTION Specular

REFRACTION Diffuse

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RAYLEIGH SCATTERING

ATTENUATION •  The decreasing intensity of a sound wave as it

•  Rayleigh scattering occurs

at interfaces involving small structures (red blood cells). •  This creates a low uniform amplitude reflection in all directions.

ATTENUATION COEFFICIENTS

passes through tissue. •  The attenuation coefficient is the relation of

attenuation to distance; it is dependent on the tissues traversed and ultrasound frequency. •  Higher frequencies are attenuated more than lower frequency waves.

ATTENUATION

Attenuation

TISSUE APPEARANCE •  Nerves – in cross section appear as round “honeycomb” structures

NERVES Popliteal Fossa

Brachial Plexus

•  Tendons – appear similar to nerves at the joint, but become flat and

disappear when followed toward the muscle belly •  Vascular Structures – anechoic circular structures in cross-section;

appear tubular in longitudinal view •  Fat – hypoechoic areas with streaks of irregular hyperechoic lines •  Fascia – thin linear hyperechoic structures marking tissue boundaries •  Muscle – feather-like in longitudinal view; “starry night in cross-

section •  Pleura and Air – pleura appears as thin hyperechoic lines, while lung

parenchyma appears hypoechoic; reverberation artifact present •  Cysts – similar vascular structures, however appear as hypoechoic

circles in longitudinal view •  Bone – hyperechoic linear structures with shadowing underneath

NERVES AND TENDONS

•  Nerves and tendons can

both appear as hyperechoic circles near joints •  They can be differentiated by following their course into the muscle

ADIPOSE TISSUE

•  Adipose appears as hypo-

echoic areas with streaks of irregular hyperechoic lines •  It is the most superficial layer imaged

Adipose

FLUID-FILLED STRUCTURES

ARTERIES Arteries •  Round in short-axis, and

tube-like in long-axis view •  Pulsatile in nature •  Difficult to compress •  Display color on Doppler

•  Arteries, veins, and cysts

all appear as circular anechoic structures in short-axis

VEINS

MUSCLE Veins •  Muscle appears •  Ovoid in short-axis and

tube-like in long-axis •  Easily compressible •  Valves may be visible •  Display color on Doppler

heterogeneous on ultrasound due to the different acoustic impedances between cell structures, the water content within the cells, and the fascia

BONE

PLEURA Pleura appears as a hyperechoic line with “comet tails” beneath it

•  Bone is a significant

DOPPLER EFFECT

DOPPLER EFFECT

reflector, creating a hyperechoic area with significant shadowing beneath it

"Über das farbige Licht der Doppelsterne und einige andere Gestirne des Himmels Versuch einer das Bradleysche Theorem als integrirenden Theil in sich schliessenden allgemeineren Theorie"

Christian Andreas Doppler 1803-1853

DOPPLER EFFECT

DOPPLER EFFECT

•  Doppler is not used to

create an image •  Doppler is dependent on the angle of insonation •  Either the sender or receiver must be moving

ARTIFACTS

AIR ARTIFACT

•  Any phenomenon that affects the acquisition or

interpretation of an ultrasound image •  Artifacts occur because: •  properties of sound •  tissue •  created by the provider

•  The most common artifacts are air artifact,

shadow artifact, acoustic enhancement, mirror image and reverberation

•  Transducer does not fully

contact the skin •  Commonly occurs when imaging smaller structures •  Add gel and apply even pressure to correct this

SHADOW ARTIFACT

•  When ultrasound contacts

tissue that is a strong reflector, the amplitude of the beam distal to structure is diminished, resulting in a hypoechoic

ACOUSTIC ENHANCEMENT

•  When sound passes

through tissue with low acoustic impedance and contacts tissue with a much higher impedance, making it appear more echogenic than it actually is

REVERBERATION MIRROR IMAGE •  When sound reflects off

Sound trapped between two highly reflective surfaces

two strong specular reflectors separated by a thin layer of air or fluid an illusion of “multiple” structures are displayed below the actual one

SCANNING BASICS

TRANSDUCERS

•  Successful procedures begin with choosing the

•  The transducers used for USRA are either linear

correct transducer and holding it properly •  Several basic functions will improve outcomes as well. These include:

or curved linear array transducers •  Transducers are the link between the ultrasound system and the tissue. They play a significant role in determining the resolution and accuracy of an image •  Transducer selection is determined by the depth of the structures to be imaged

•  Depth •  Contrast adjustment (gain) •  Color-flow Doppler

LINEAR ARRAY

CURVED ARRAY

HANDLING

HANDLING •  Notch to the anesthetist’s

left or the patient’s head •  Hold the transducer flat against the skin for maximal contact •  Hold the transducer like a pencil •  Support the scanning arm; rest it on a firm surface •  Apply firm, but gentle pressure

HANDLING Transducer Perpendicular

Correct Hand Position

Improper Hand Position

B-MODE IMAGING Transducer Angled

Cross-Section/Short-Axis

Longitudinal/Long-Axis

DEPTH

DEPTH – MEDIAN NERVE Proper depth

•  Depth determines how far

into tissues echoes are interpreted •  Increasing the depth, decreases resolution •  The structure of interest is kept in the center of the screen

GAIN

GAIN – JUST RIGHT •  Gain compensates for

attenuation •  It amplifies RETURNING

echoes •  Gain can be adjusted

either in the near field, far field, or overall image •  Gain is adjusted so that the image is uniform

Too deep

GAIN

COLOR-FLOW DOPPLER

•  Color-flow allows you to

confirm the presence or absence of vascular structures •  Doppler is super-imposed over the B-mode image

COLOR-FLOW DOPPLER

COLOR-FLOW DOPPLER

MOVEMENTS

SLIDING

•  In 1999, the American Institute for Ultrasound

Medicine (AIUM) established terminology to describe transducer movements. •  These terms do not include specification of direction (i.e. proximal, distal, clockwise) •  In general, a transducer can be manipulated in five ways: sliding, tilting, rocking, rotating and compressing.

ROCKING

•  Rocking can be used to

correct air artifact and increase contact of the transducer

•  Sliding allows the provider

to find the appropriate level to perform the block

TILTING

•  Tilting improves nerve

image by accounting the effect of anistropy

ANISTROPY Transducer Tilted

ROTATING Transducer perpendicular •  Rotating allows the

provider to optimize all structures in the image on the same plane

COMPRESSING

ORIENTATION •  Proper placement of the transducer in relation to

•  Compressing can be used

to decrease space from the skin to the desired structure

the patient is key to obtaining a correct image •  The transducer should be oriented to the anesthetist’s left in cross-section or toward the patient’s head in longitudinal view •  When the transducer is not properly oriented, a “mirror-image” will result

ORIENTATION

PROPER ORIENTATION

IMPROPER ORIENTATION

ERGONOMICS •  Appropriate bed height •  Ultrasound in line with the

provider and patient •  Scanning arm supported •  Assistant (if available) •  Proper transducer handling

ERGONOMICS Poor Ergonomics

WHAT NOW? Good Ergonomics

OPTIMIZE THE IMAGE •  Use PLENTY of gel. Gel acts as a coupler

between the transducer and the skin, and improves the image quality •  Ensure your transducer is initially perpendicular and flat against the skin •  Optimize your depth so the structures you wish to image are in the center of the screen •  Adjust your gain to make picture look uniform

•  You have the right patient, discussed the

proposed anesthetic technique, obtained consent, verified the site, and gathered your supplies •  Select the appropriate frequency transducer •  Imagine how the image should appear on the monitor •  Use good ergonomics •  Apply sufficient gel to the transducer •  Jump in!

NEEDLE VISUALIZATION In-Plane

NEEDLE VISUALIZATION Out-of-Plane

SAFETY STRATEGIES •  Ultrasound itself is non-invasive •  Ultrasound-guided procedures introduce a needle

and/or local anesthetic into the patient increasing the potential for complications •  Needle insertion should first be practiced using a phantom numerous times, with emphasis placed viewing the entire needle as it passes through the tissue •  Strategies such as wiggling, or hydro-location can be used to verify the location of the needle tip

ANATOMY •  Know it. Most nerves blocked using regional

anesthesia are in close proximity to arteries, veins, or other vital organs (i.e. the lungs) •  Anticipate what you will be seeing before you start scanning. •  Proper orientation of the picture make your picture appear correctly

QUESTIONS?

REFERENCES •  • 

•  • 

•  • 

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