Measurement error Flashcards
In modern calliper systems, measurements can be done offline/on stored image dependent on…
apprioprate placement
What are the 2 main measurements taken?
- Linear
- Volume (area)
Which ones are more sensitive to error
non-linear
C is assumed at 1540m/s by machine to calculate….. & with variety of algorithms can calculate…. of each echo in memory
- axial distance
2. final location
measurements are made from pixel centre to pixel centre and converted into mm or cm. The conversion is dependent on
- depth of selected area
- scale
- magnification settings
Talk about track and ball calliper control?
- it’s user friendly (like using a computer mouse)
- maybe very sensitive and sometimes;
- hard to accurately control
What does non-linear mean?
irregular circumferences
non-linear, circumference and area are calculated how?
track ball, plots around the ROI. Calculating the Sum & length of the trace
How is area calculated (structure perimeter)? This method is not often used. But….
multiplying the number of pixels enclosed per area pixel.
- more accurate and reproducible than circumference
Define ellipse fitting
Used in truly elliptical structures. Measuring circumference and area
When is the circumference calculated? (averaging long and short axis)
When ellipse is fixed.
Whats the equation for the circumference of a circle?
circumference = π × (d1 + d2)/2 = 1.57 × (d1 + d2)
3 linear calculation is required when measuring what?
Volume
What is required to measure volume?
2 images 90 degrees to each other @ sagital and transverse
How is Volume calculated?
multiple diameters together and multiplying by the constant value (K).
Volume = k . x . y . z
(k often chosen as 0.52)
