Ultrasound Physics, Terminology, and Knobology Flashcards
What does POCUS stand for and what specific questions does it answer?
POCUS = Point Of Care Ultrasound
To answers questions like
is there pericardial effusion
is there intraperiotneal fluid
are there glasstones
is there hydronephrosis
Advantages of POCUS (ultrasound)
- no ionizing radiation
- noninvasive
- portable
- easy to use - FAST
- inexpensive
- easily repeated at bedside, thereby enhancing clinicians’ ability to perform serial reassessments of pts
Disadvantages of POCUS (ultrasound)
- operator dependent
- limitations = poor image quality with fat and air
Physics: wavelength and frequency relationship and effect on tissue penetration
Wavelength is INVERSELY related to frequency
HIGHER frequency = SHORTER wavelength = don’t penetrate deeply into tissue
lower frequency = longer wavelength = CAN penetrate deeply into tissue
Low frequency vs high frequency probes -what can be viewed, what are disadvantages
LOW frequency probes:
- good for DEEP structure imaging ( long wavelengths)
- penetrate deeply but POOR RESOLUTION
- for ABDOMINAL structures = aorta, kidney, gallbladder
HIGH frequency probes:
- good for SUPERFICIAL structure imaging (short wavelength)
- poor penetration but GOOD RESOLUTION
- for SUPERFICIAL structures = blood vessels, breast tissue, thyroid tissue
Compare the different types of probes
- LINEAR (aka “vascular”) probe
- higher frequencies and resolution
- for superficial scanning and procedural guidance
- preserved lateral resolution - Sector/phased array (aka “cardiac”) probe
- lower frequencies
- small footprint for intercostal scanning
- high frame rates - Curvilinear (aka “curved array” or “abdominal”) probe
- ever lower frequencies
- large field view
- large footprint
What is FAST scan and what is it used to detect?
FAST = Focused Assessment with Sonography for Trauma
It’s a standard set of ultrasound examinations for the evaluation of injured patients
Purpose: detect free intraperitoneal fluid, pericardial fluid, pleural fluid, hemothorax/ pneumothroax in trauma pts
*not a definitive test = can NOT rule out intraabdominal injury
What structures are shown in the image; what area would you scan to see this?
Liver top, Kidney bottom, separated by morrison’s pouch (white line); diaphragm very top of image (white lines)
Scan RUQ at edge of lower lateral thoracic cage
Define echogenicity and list the three types w/description
Echogenicity = ability of structure to reflect sound waves or echoes
- Anechoic - complete absence of returning sound waves; looks black; ex. fluid
- Hypoechoic - structures that have few echoes and appear darker than surrounding tissue
- Hyperechoic - echogenic structures, appear brighter than surrounding tissue
What is the image and viewing what structure causes this?
ACOUSTIC SHADOWING!
- common artifact; occurs when sound waves encounter reflective surface
- hyperechoic or anechoic area appears deep to structure
- occurs b/c few sound waves can get behind or around structure ex. gallstones
What is the image, you see it with viewing what structure
POSTERIOR ACOUSTIC ENHANCEMENT
- common artifact; deep to an anechoic structure
- inc in echogenicity posterior to an anechoic structure b/c sound waves lose very little energy traveling through a fluid filled structure
- ex. bladder
What is the image, you see it with viewing what structure
EDGE ARTIFACT
- sound bent by structure in parallel with ultrasound beam and does not return to probe, resulting in appearance of shadow behind the surface
- arrowheads show edge artifact from wall of gallbladder
- seen w/imaging fluid-filled structures (ex. gallbladder)
What is the image
MIRROR ARTIFACT
- you see the “mirror image” of structure you’re imaging; distal in relation to the probe
- usually seen at the bottom or periphery of the scree
What is the image
REVERBERATION ARTIFACT
- seen w/ line placement
- multiple intermittent line “echoes” running parallel to actual needle
Describe movements of the probe
Sliding: moving along skin w/o changing angles
Rocking/ “heel toe”: tilt probe along axis of indicator (indicator is the notch the prob)
Fanning/sweeping : title problem perpendicular to axis of indicator
Rotating/twisting: rotate probe about axis of the cord w/o tilting
Is ultrasound safe for fetal imaging at all gestational ages?
YES!
Explain ALARA
As Low As Reasonably Achievable Exposure
– so you expose pt to as low amt of ultrasound as possible for the given test
What is the alignment of the probe marker during longitudinal vs transverse scanning? Why is cardiac an exception?
Longitudinal scanning = probe marker (the notch) towards the head
Transverse scanning = probe marker facing pt’s right so image will look similar to orientation of CT scan
**Cardiac exception = screen marker is on LEFT
