B-Mode and Doppler Measurement Tools Flashcards
What are the four measurements taken to estimate gestational age?
- Biparietal Diameter
- Head circumference
- Femur length
- Abdomen circumference
What is the approximate accuracy of a transducer taking vertical measurements?
0 +/- 1%
What is the approximate accuracy of a transducer taking horizontal measurements?
1 +/- 1%
What type of transducers cause the largest error in horizontal measurements?
Transvaginal - tight membrane curvature.
What is the expected error when using the ellipse tool to measure circumference?
0-1%
What is the expected error when using the ellipse tool to measure area?
-2 - +4%
How should a PW-Doppler trace be set up so as to measure blood flow in the carotid artery?
- Use a cine-loop, and scroll to give a good trace
- Adjust the angle correction to lie parallel to the sides of the vessel.
What tools are available on PW-Doppler trace and what do they do?
- Single caliper: Displays velocity values
- Heart rate tool: displays vertical line at start of r-wave
- Auto PW: Display max and mean velocity traces, and parameter values (e.g. RI)
- Time slope tool: gives the rise time of the R-wave (if sweep speed in increased)
- Volume flow tool: uses auto tools mean velocity trace, and radius measurement to estimate volume flow.
How can the volume of the left ventricle be measured using ultrasound?
- Take a apical four-chamber cine-loop and scroll to end diastole.
- Use the manual trace tool to draw around the circumference form the mitral valve annulus to the apex and back down.
- Scanner splits the area into 20 discs and uses Simpson’s rule, V=(pi/4)(L/20)Sigma[a_i^2]
How can ejection fraction be calculated?
- Calculate the volume at end systole and end diastole as usual.
- Stroke volume, SV = EDV-ESV
- EF = SV/EDV
- Normal ejection fraction is in the range 55-70%.
How can volume assessment be made more accurate?
- Bi-plane scanning: repeat area measurement at 90 deg.
- Simpson’s rule becomes:
V= (pi/4) (L/20) * Sigma[a_ib_i] - 4D imaging: auto contours heart and produces 3D data set. Volume is automatically contoured for each 3D frame.
How is a mitral valve regurgitation assessment performed?
- Flow from mitral valve back into left ventricle during systole converges as a series of hemispherical shells.
- Adjust the colour-Doppler baseline until aliasing occurs.
- Proximal iso-velocity surface area (PISA) = 2pir^2
- MV regurgitant flow rate - PISA x aliasing velocity.
How is fractional shortening measured using M-Mode ultrasound?
- Parasternal long axis view of the heart with m-mode cursor at MV leaflet tips
- LV volumes are calculated using the Teichholz equation.
- Left ventricular Internal dimensions (LVID) at systole (s) and diastole (d) measured.
- Fractional shortening , FS = (LVIDd- LVIDs)/LVIDd