SPI Flashcards
Harmonic Imaging
Better resolution and less image noise due to processing the reflections at a higher frequency
Lateral Resolution
Beamwidth must be less than the distance between two objects for them to be viewed separately.
Axial Resolution
Higher frequency, shorter wavelength = improved resolution.
Elevational Resolution
AKA slice thickness.
Resolution; thinner slices = better elevational resolution.
Dynamic Range
Lower numbers for dynamic range indicate less shades of grey will be displayed. Increasing compression will lower the dynamic range.
Posterior Shadowing
Occurs posterior to highly attenuating structures. Plaque in the arterial wall is highly reflective. The posterior shadowing can limit color and PW Doppler evaluation of the arterial segment posterior to the plaque.
Posterior Enhancment
Occurs posterior to poorly attenuating structures. Fluid filled structures are non-reflective. The structures located deep to the fluid filled structure will demonstrate increased echogenicity.
Edge Shadowing
When the ultrasound beam strikes a rounded structure, sound waves are scattered and refracted, leading to energy loss and the formation of a shadow. It causes linear posterior shadowing on each side of the structure.
Mirror Image Artifact
Occurs when there is a highly reflective surface in the path of the primary beam. Places a second copy of the structure deeper on the image.
Contrast Evaluation
IV Contrast can be used to improve the visualization of the PW Doppler signal. The contrast material makes the blood more reflective, therefore the PW tracing is brighter.
Incident Angle for Color Doppler
Blood flow toward the probe will demonstrate a positive change in frequency which will be displayed on the top side of the Doppler baseline. Bllood flow away from the probe will demonstrate a negative change in frequency which will be displayed on the bottom side of the Doppler baseline.
Velocity Mode
Color varies from top to bottom of color bar to indicate mean velocity.
Variance Mode
Color varies from top to bottom and side to side of color bar to indicate mean velocity.
Smaple Size
The smaller the area of color evaluation, the better the color display will be on the image. A smaller color Doppler FOV offers a faster frame rate for improved flow evaluation and display
Electronic steering
The transducer will detect blood from that is moving toward or away from the probe. Steering the color box will make the flow in the vessel less perpendicular to the US beam, therefore improving the detection and display of the flow.
Ulceration
Power Doppler is much more sensitive to low velocity flow movement than color Doppler but in Most US systems the direction of lfow is not displayed with Power Doppler
Color Doppler
Imaging represntation of flow.
Demonstrates presence/ absence of flow.
Demonstrates direction of flow.
Average flow velocity.
Spectral Doppler
Graphic respresentation of flow.
Demonstrates presence/absence of flow
Demonstrates direction of flow.
Peak flow velocity
Pulsed Wave
One crystal transmits and receives sound waves, very low duty factor.
Use to localize points of stenosis.
Nyquist Limit imposes limitations on the depth of vessels that can be evaluated.
Aliasing possible.
Continuous Wave
Two crystals used, one to transmit and one to receive the sound wave 100% duty factor.
Cannot locate exact area of obstruction
Not limited by PRF (Nyquist Limit), good for deep or superficial evaluations.
No aliasing.
Sensitivity
True positives / total # positive tests proven positive by the gold standard test
Specificity
True Negative Tests/ Total # Negative Tests proven negative by the gold standard test
Postive Predictive Value
True positive tests/ Total # postive tests
Negative Predictive Value
True negative tests / Total # negative tests
Accuracy
True positive test + # true negative test / Total # of tests preformed.
