UltrasoundTheory, Technique, and Knobology
Jerry Jones M.D.
Assistant Professor
Director, Acute Pain Service
Division Chief, Regional Anesthesia & Acute Pain Medicine
UTHSC/Regional One Health
Memphis, Tennessee
Disclosures
▪ Honoraria/Speakers Bureau – B Braun Medical, Avanos, Pacira
▪ CPNB Consulting LLC – Owner
▪ Cal Tenn Innovation Inc – CEO/patent holder
What is ultrasound …?The transmission of mechanical sound energy
If there is no material, nothing can vibrate → NO SOUND
Air/gas is NOT dense enough to transmit ultrasound waves
SOUND = vibrations passing through a conducting medium
• Electrical field applied to crystals
• Mechanical distortion of crystals results in
vibration and production of sound waves
(mechanical energy)
• Each piezoelectric crystal produces an US
wave → summation of all waves forms US
beam
• Also coverts reflected, incoming sound
waves to electrical energy
Lead Zirconate
Titanate (PZT)
D
I
Generation of US wave
• Ultrasound waves are generated in PULSES
- Each pulse commonly consists of 2-3 sound cycles of same frequency
• Pulses MUST be spaced with enough time to permit sound to reach target
and return to transducer before next pulse is generated
Frequency
• Frequency = rate of vibration
• Hertz (Hz) is the basic unit used to specify frequency, # of cycles per second
• 1 Hz = 1 vibration/sec.
• Ultrasound is anything > 20,000 Hz
• Most diagnostic ultrasound falls into the
range of 2-20 MHz (million cycles/sec)
1 cycle
How does it work again …?US transducer emits and receives signals
• Emits a short ultrasound pulse when electrical field applied to it.
• Listens a “LONG” time for returning echoes.
• Can only do ONE at a time
• Converts returning echoes to electrical energy → processed into an
image = PIEZOELECTRIC EFFECT (Pierre Currie 1880)
Speed of Ultrasound
Luckily, the speed of
US is nearly the same
for most body parts
Types of ultrasound
▪ B-mode (brightness mode)
▪ 2D, grey scale image that can be manipulated by adjusting GAIN.
▪ M-mode (motion mode)
▪ Monodimensional view
▪ Common in cardiology and thoracic imaging
▪ Time motion display of ultrasound wave along a chosen line.
▪ Doppler
▪ For imaging motion, specifically flowing blood
▪ RED = TOWARDS and BLUE = AWAY
Acoustic Impedance= the resistance of a tissue to the passage of ultrasound
The degree of acoustic impedance mismatch between two tissues → extent of reflection
The HIGHER the impedance mismatch, the GREATER the amount of reflection
Degree of reflection for air is high d/t VERY LOW acoustic impedance → AIR ARTIFACT
Echoes = bright spots
Produced by surfaces/boundaries between two tissue types
No reflecting
surfaces within fluid
–
ANECHOIC
Grey scale image (sometimes called a “B mode” image) is
due to the “mixture” of different tissue types within an
anatomic area
HYPERECHOIC
HYPOECHOIC
Which one do I pick …?
Sector/phased – crystal
arrangement in footprint is
bundled around the center and
fans out creating a pie-like
image on US screen.
Curvilinear
Linear
Intracavity
Selection is largely based upon:
• Imaging modality
• Depth and/or type of target
structure
• Desired field of view
Curvilinear Transducer
= Wider Field of View
8 MHz Transducer12 MHz Transducer
Interscalene block at approximately 1-2 cm depth.
Higher frequency transducer provides superior image resolution for superficial structures.
Linear Transducer
= Superior Image (higher frequency)
Modern transducers are broad
bandwidth – generate > 1 frequency
HIGH Frequency = HIGH spatial resolution but limited depth of penetration
LOW frequency = LOW spatial resolution but GREATER depth of penetration
- Superficial blocks (interscalene, supraclavicular, axillary, …)
• High frequency transducer 10-15 MHz preferred
- Intermediate depth blocks (infraclavicular and popliteal-sciatic)
- Lower frequency transducer less than or equal to 7 MHz
- Deep blocks (lumbar plexus, sciatic, …)
• Curvilinear transducer 2-5 MHz
Compound Imaging
• Reduces speckle artifacts
• Improves contrast resolution
Impact of the Depth Setting on Image Quality
• Median nerve in the forearm
(arrowhead) gets smaller and
smaller as depth is increased.
• Important to select
appropriate depth!!!
Impact of Gain Setting on Image Quality
• Gain compensates for attenuation
as sound travels deep
• Intensity of returning signals
amplified to brighten image
• Excessive gain → “NOISE”
Impact of Focus Setting on Image Quality
ATTENUATION = ENERGY LOSS
• Absorption → heat production
- Accounts for 80% of attenuation
• Reflection
• Scattering at interfaces
• Varies with frequency of US wave
- High frequency wave = high attenuation
Time Gain Compensation (TGC)
Increases overall image brightness, including
background noise
Gain = receiver amplification, ONLY amplifies returning signal
Preferably, TGC is adjusted to selectively
amplify the weaker signals returning from
deeper structures
Practical Introduction to CPNB & US
US BASICSWhat SHOULD the structures look like?
Nerves
Muscle, Fat, Bone
Artery & Vein
Pleura/Peritoneum
Skin/Fascia
Local Anesthetic
Practical Introduction to CPNB & US
US BASICS Nerve Appearance is due to Connective Tissue content
Supraclavicular Image Femoral Nerve Popliteal Sciatic
White (hyperechoic) Shell with Completely White (hyperechoic) Honeycomb Appearance
Black (Hypoechoic) Center Confused with muscle/tendon
Can be confused with artery or vein
Practical Introduction to CPNB & US
US BASICS Fat vs Muscle, Artery vs Vein, Bone
Saphenous Nerve Block Anterior Sciatic Approach
Fat has long wavy lines. Muscle appears ‘marbleized’ like steak Bone is hyperechoic and casts a dark Bone ‘Shadow’
Arteries pulse & Veins are compressible.
Practical Introduction to CPNB & US
US BASICS Pleura & Peritoneum
Thoracic Paravertebral/Intercostal Supraclavicular Image TAP with II/IH
Pleura & Peritoneum are bright white with Comet Tail Effect below and are moving
Notice Bone Shadow below Rib in picture to far left
Practical Introduction to CPNB & US
US BASICS Fascia & Local Anesthetic
Fascia Iliaca – longitudinal images
Fascia is hyperechoic. Sartorius Muscle seen to Right of first image. L.A. is hypoechoic
Cephalad direction is to the left in first two images.
Practical Introduction to CPNB & US
US BASICS - Tools
Tissue Distraction by needle
Needle is near. Move PROBE to find it
Hydro-dissection using local anestheticUse to find/follow needle tip with steep angles
Leave LA ‘marker’, confirm crossed into next tissue plane
Enhancement when local anesthetic injected(Greater difference in Echogenic interface than with adjacent muscle)
Helps confirm that needle tip is accurate & spread is correct
Practical Introduction to CPNB & US
US BASICS - Pitfalls
Air (USUALLY an enemy)Can’t see through air, but spread pattern of air can confirm needle position.
Oh, I thought THAT was the LATERAL side…..Confirm which side needle will approach EVERY time!
Needle direction on screen should be SAME as direction you are driving the needle.
Is that an Artery? Nerve? Muscle? Can appear similarly. Confirm structure: pulsing? Compresses easily? Or use color doppler
Move through space to confirm
Is THAT my Needle Tip?MUST always be aware of needle tip location!
Needle shaft may appear the same as needle tip.
Practical Introduction to CPNB & US
US BASICS - Odd Visual Effects
Contact Artifact
Anisotropy
Reverberation
Shadows (Bone & Steep Needle)
Posterior Acoustic Enhancement
Contact (air) artifact
Poor probe patient interface. Remember acoustic impedance of air is
MUCH LESS than any other body tissue → limits penetration
Anisotropy
Nerves are not seen well as they are seen at a greater (or lesser) than 90 degree angle to the
probe, so tilting the probe slightly will make nerves appear better or worse.
Reverberation
Sound bounces off deepest aspect of needle and returns to probe to display an image. When at a 90 degree angle to probe, some of that sound bounces back off of most shallow aspect of needle and hits deepest aspect again, returning later. This appears as a deeper structure. Multiple bounces creates the repeating image below the needle.
Needle shadow
Posterior acoustic enhancement
Supraclavicular Femoral Infraclavicular
Blood returns sound signals much less than adjacent structures do, so there is a relative overabundance of sound at deeper end
of blood vessel which is seen as exaggerated hyperechogenicity of the underlying tissues
▪ Global Rating Scale for Ultrasound
▪ Frame/Reframe Image & Target (“Frame it up”)
▪ How/Why to Avoid touching the nerve
▪ Avoid excessive needle passes
▪ Steady Speed & Intentional Path of Needle
▪ Use sense of FEEL as advance needle
▪ Move slightly off needle to see injection pattern
▪ Elbows in tight, neutral wrist position, finger tips
▪ STABILIZE YOUR HANDS!!!
▪ SMALL ADJUSTMENTS (Fine motor skills)
▪ Air (USUALLY an enemy)
▪ Avoiding secondary failure
▪ Minimize needle passes
▪ The GOOD Assistant!
▪ Ultrasound Artifacts
▪ Helping & Helped by the ALERT Patient
▪ Completely set up first
▪ Archetypal Images
▪ Ergonomics
▪ Orient needle direction to screen
▪ Sidedness: Left/Right screen errors
▪ Probe hand ‘drift’
▪ Never use needle to find probe
▪ Nerve Stimulation as Confirmation/Alarm
▪ Only redirect Needle for Optimal Spread of Local
▪ Use Ultrasound like a VIDEO, not as a picture…
▪ Using Tissue Distraction by needle
▪ Hydro-dissection using local anesthetic
▪ Find/follow needle even if tip with steep angles
▪ Leave a LA ‘marker’
▪ Enhancement when local anesthetic injected
▪ Looking ‘downstream’ or laterally
▪ Overcome Obstacles, Poor Image & Reorienting
▪ Needle +’s & -’s
▪ Gel, condoms and Probe selection
▪ Know EXACTLY where you’re putting your Probe!
Ultrasound Technique Lessons
The Language of Probe Movement
‘tilt’
‘rock’ or
‘dig in heel of probe’
*
*
*
*
US probe manipulation maneuvers “PART” mnemonic for Pressure,
Alignment, Rotation and Tilt as fundamental probe manipulation maneuvers
Int J Shoulder Surg. 2010 Jul-Sep; 4(3): 55–62. Ultrasound: Basic understanding and learning the languageBarys Ihnatsenka and André Pierre Boezaart
Angle of Incidence
Schematic illustration of improving the angle of incidence by
tilting the probe. By tilting the probe from position 1 to position 2,
we obtained the true axial short-axis view of the artery and the
nerve. The shape of the image of the artery and the nerve got
more rounded, and the image of the nerve is much more defined
in position 2 due to a more favorable angle of incidence. Note
the changes in A1 and A2 distance as well.
“The angle at which the US waves
encounter the surface of the
structure, termed, the angle of
incidence, affects the way it is
presented on the screen. If the angle
is perpendicular, or close to
perpendicular, more US waves will
be reflected back to the transducer
and fewer will be “scattered” away,
resulting in a better image. If the US
waves are more parallel to the
surface of the object (more than a
45° angle of incidence), the image
will have less definition. The operator
can improve the image of the target
by tilting or rotating the probe, thus
adjusting the angle of incidence.”
Int J Shoulder Surg. 2010 Jul-Sep; 4(3): 55–62.
Ultrasound: Basic understanding and learning the language
Barys Ihnatsenka and André Pierre Boezaart
Improving needle visualization during “in plane” needle
placement. To improve needle visualization, one can change the
US probe position (from 1 to 2) and the needle approach (from 1
to 2 to 3) to optimize the angle of incidence between US waves
and the needle
YOUR APPROACH & YOUR HANDS:
“Pause for Pulsation” (Look for Arteries)
Compress/Decompress to identify Veins
Optimize View of Target & Choose Entry Anisotropy
Minimize Depth/Adjust Gain/B-steer
Tilt Probe for better needle angle
Choose as Shallow a Needle Angle as possible
Select a Safe Needle Path
Practical Introduction to CPNB & US
Novice BehaviorsCharacterizing Novice Behavior Associated With Learning Ultrasound-Guided Peripheral Regional Anesthesia Sites et al, Regional Anesthesia & Pain Medicine: March/April 2007 - Volume 32 - Issue 2 - p 107–115
Error 1 (43.7%) = needle not visualized while being advanced.Error 2 (11.6%) = inadequate equipment preparation. Error 3 (4.7%) = neural target mal‐positioned on ultrasound screen. Error 4 (26.9%) = unintentional probe movement. Error 5 (3.5%) = awkward needle holding.Error 6 (1.7%) = watching hands instead of ultrasound image. Error 7 (7.8%) = poor ergonomics.
Novice vs Expert SkillsScanning Phase:
Locate & identify key anatomic landmarks
Obtain optimal plane for needle insertion
Requires familiarity of gross and sonoanatomy &
the ability to manipulate probe to obtain desired images
Needling Phase:
Safely guide needle tip to appropriate location
Subsequently redirect needle for adequate local spread
Maintaining continual needle-beam alignment found to be
the most demanding skill in either phase
Chin et al, Regional Anesthesia and Pain Medicine & Volume 36, Number 3, May-June 2011 Hand Motion Analysis in Ultrasound-Guided PNB
Novice vs Expert SkillsScanning Phase:
Residents: 1 - 6 minutes
Early Fellow: 1 – 5 minutes
Late Fellow: 54 sec – 1 min 36 sec (had performed >50 SS supraclavicular blocks)
Consultants: 24 sec - 1 min 48 sec
Consultants 3x better ‘Dexterity’ scores (time, total distance of path, total movements)
Consultants similar # movements/minute but made shorter movements with probe hand
Needling Phase:
Residents: 4 min 54 sec - 13 min 30 sec
Early Fellows: 6 – 10 minutes
Late Fellows: 3 min 30 sec – 8 minutes
Consultants: 3 min 24 sec – 8 min 12 sec
Consultants 40% better (shorter) all ‘Dexterity’ scores
Consultants made significantly fewer movements of probe hand/minute and made
smaller amplitude movements with probe and needle hand
(Best to worst possible Total Times for block: 3 min 48 sec to 19 min 30 sec)*
Novice vs Expert SkillsNOVICES:
1. When scanning, probe movements are inappropriately large (Use Gross motor skills)
2. When needling, needle movements are inappropriately large (Use Gross motor skills)
3. When needling, unintentional probe movements (Hand positions not secured)
EXPERTS:
1. Make fewer probe movements to obtain image (Use Fine motor skills)
2. Smaller probe movements with scanning and needling (Use Fine motor skills)
3. Able to obtain and maintain alignment of needle & beam (Hand positions secured)
* MY ANALYSIS
Similar number of probe- & needle-hand movements per minute both phases
Practical Introduction to CPNB & US
YOUR APPROACH & YOUR HANDS:Frame/Reframe Image & Target (“Frame it up”)
Do NOT use excessive needle passes
Steady Speed & Intentional Path of Needle
Use sense of FEEL as advance needle
Move slightly off needle to fully see injection pattern
Keep elbows in tight, neutral wrist position
STABILIZE YOUR HANDS!!!
SMALL ADJUSTMENTS with Fingertips (Fine motor skills)
Practical Introduction to CPNB & US
YOUR APPROACH & YOUR HANDS:Nerve-Stimulation as Secondary Confirmation (& Alarm)
Redirect Needle for Optimal Spread of Local
Use Ultrasound like a VIDEO, not as a still picture…
scan through space to recognize patterns of change, orientation of structures
Images provided by:
Dr Jerry Jones
Scan option 1
Feel the Biceps Femoral
Tendon proximally until
it feel like a muscle
Set the lateral edge of
the probe on that
location
This will orient you as to
which muscle is which
Images provided by:
Dr Jerry Jones
Scan option 1
Scan distally & look for
the nerve to split into
the common peroneal &
tibial nerves, the
decrease in muscle size
and the appearance of
the popliteal vessels
Images provided by:
Dr Jerry Jones
Scan option 2
Set the probe in
the popliteal
crease, and locate
the pulsation of the
popliteal artery
The tibial nerve will
be just superficial
to it
Images provided by:
Dr Jerry Jones
Scan option 2
Scan proximally,
watching for the
common peroneal
nerve to join it
from the lateral
aspect while the
artery descends
away
Thank You!