Ultrasound Flashcards
Ultra sound is a mechanical, longitudinal wave with a frequency that
Exceeds the upper limit of human hearing
20000 Hz
Sound is a mechanical, ______ wave that travels in a _____. It requires a ____ through which to travel
Longitudinal wave
Straight line
Medium
How many Hz (oscillations/second) is medical ultrasound? What about the transducers for UGRA?
2 to 16 MHz
4-13 MHz
Ultrasound is produced by passing an alternating electrical current through a
Piezoelectrical crystal
Ultrasound relies on ______ to image the body and diagnose and identify different structures in the body. They oscillate back and forth to produce a series of
High frequency sounds
Compressions and refractions
Why are high frequencies used for scanning areas of the body close to the surface? Frequencies generally range between
Higher frequencies have shorter wavelengths that are absorbed easily so not as penetrating
1-50 MHz
How does the resolution of the image produced by a lower frequency transducer compare to that of a higher frequency?
Lower resolution but can penetrate deeper (longer wavelengths)
What is the formulas for velocity?
V = frequency x wavelength Velocity = speed of wave Frequency = oscillations per second Wavelength = distance between two compressions or refractions
What is the difference between a compression and refraction?
Particles in compressions are close together and there is high pressure. Refractions have particles that are far apart with low pressure
What are the components of an ultrasound transducer?
Metal outer casing Backing block Plastic nose Electrodes that apply an alternating potential difference Piezoelectric crystal Acoustic insulator Power cable
Running an alternating current through the piezoelectric crystal causes it to _____ depending on the voltage running through it. The ultrasound is produced when the crystal vibrates at ______. This conversion of electrical to mechanical energy is known as the
Grow and shrink
Vibrates at high speed
Piezoelectric effect
When the ultrasound produced from the transducer hits the object under investigation, it bounces back off and hits the piezoelectric crystal, causing
The reverse effect to happen
Mechanical energy is converted back into electrical
What interactions does ultrasound have with tissue?
Reflection
Refraction
Transmission
Attenuation
Targets for UGRA are based on _____ and
Reflection
Impedance - tendency of a medium to conduct ultrasound
When a sound travels through an object and contacts an adjacent object with a different impedance, a _____ is formed. At the interfaces between objects with different impedances, _____ occurs. Greater reflections are formed from ____ difference in acoustic impedance.
Demarcation
Reflection
Greater
The ultrasound image is formed from
Reflected echoes
Objects that are highly reflective are displayed as
White or hyper echoic
Examples include facial planes, bones, and some nerves, tendons, diaphragm
Objects that are weakly reflected are
Darker or hypo echoic
Examples include muscle, fat, and some nerves
How do blood vessels appear on the ultrasound?
Anechoic and black
What is the fundamental clinical challenge in UGRA? Give an example?
Many neural structures lie in close proximity to one another with similar acoustic impedances so making a positive identification is challenging since the structures appear similar.
An example of this is distinguishing tendon from nerve in the distal arm or leg
Why is cardiac imaging much easier?
Clear demarcation between blood filled chambers (black) on myocardium (whiter)
The loss of ultrasound wave energy as it travels through tissue is known as _____. Lower frequency waves will _____ in comparison to a higher frequency wave.
Attenuation
Attenuate less
The deeper the wave travel in the body, the weaker it becomes (attenuation) by three processes:
Reflection
Absorption
Refraction
Balanced gain settings are important to obtaining adequate images.
Ok.
Most solid organs on the ultrasound are? What about thick fluid?
Gray, weaker reflections
Thick fluid is iso echoic
What structure a have no reflections?
Fluid within cysts, urine, blood
They are black dots, hypo echoic
What determines how far the ultrasound waves travel?
FREQUENCY if the transducer
Attenuation is directly related to frequency
The ultrasound beam comes out as a ____ that is ____ thick. The depth displayed is _____. The image produced is
Slice
1 mm thick
2D - tomographic slice that assumes no thickness
The ultimate goal of the ultrasound is to make
Like tissues look the same and unlike tissues look different.
This is some tautology shit right here.
Regional anesthesiologist prefer to use which axis to image nerves and blood vessels? Why?
Short axis
Simultaneous view of the anterior/posterior and lateral/medial perspective
A short axis view can become long when the transducer is turned ____. Which perspective is lost in the long acid view?
90 degrees either direction
Lateral/medial perspective is lost
Ten steps of peripheral UGRA are to
1 visualize key landmark structures
2 identify the nerves or plexus on short axis imaging
3 confirm normal anatomy or recognize variations
4 plan for safest and most effective needle approach
5 use aseptic needle insertion technique
6 follow the needle under real time visualization toward the target
7 consider a secondary confirmation technique such as nerve stimulation
8 when needle tip is assumed to be in correct position, inject small volume of test solution
9 make necessary needle adjustments to obtain optimal peri neural spread of local anesthesia
10 maintain traditional safety guidelines
What is the PART maneuver in the ASRA recommended scanning techniques?
PRESSURE - varying degrees of pressure on the skin
ALIGNMENT - sliding movement to define lengthwise course of the nerve
ROTATION - in clockwise or counter to optimize the image
TILTING - in both directions to maximize angle of incidence
All those pictures
Just look at it
Different approaches to ultrasounds…?
Supra clavicle lateral to medial approach Supra clavicular medial to lateral in plane approach Interscalene block Infraclavicular block Auxiliary block Femoral block Subgluteal approach of sciatic nerve Popliteal fossa sciatic nerve block
