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Chapter 2
January 2015
bk3000 User Guide
(16-01249-EN-01)
Figure 2-6. The dotted line indicates the convex hull of the non-convex figure.
Measuring volume using a stepping method produces an approximation caused by
the finite number of steps in the measurement. The user must always try to assess
how large an inaccuracy is introduced by the selected step size, that is, the distance
between organ cross sections.
Geometric Measurements
2D Measurements
The geometric measurements performed by BK Medical ultrasound systems are
distance, perimeter, area and ellipsoid volume. The accuracy of these measurements
is influenced by the following factors:
•
Transducer geometry
•
Rounding of results
•
Resolution of digital image memory
3D Measurements
The 3D volume is found by summing the marked area in the individual slices and
multiplying by a factor that includes the distance between the slices and their relat ive
orientation.
To obtain the accuracies listed in the table in the Technical Data (BZ2100), you must
ensure that the calculation is based on contributions from at least 10 slices for very
regular shapes and more for irregular shapes. It must also be possible to discriminate
the boundary of the object from the surrounding tissue.
Volume
accuracy
The volume accuracy in the table is given as a percentage of the capture d 3D volume
starting with the first slice and ending with the last slice that intersects the object of
interest.
If the 2D ROI (region of interest) is set to be much larger than the object, the accuracy
as a percentage of the object volume can be much worse (higher percent).
NOTE:
To ensure that the accuracy of your volume measurement is as high as
possible, make sure that the object you are interested in fills the region of interest as
much as possible.
Distance and
area accuracy
The accuracy of a distance measurement on a 3D image will never be better than 6%;
the accuracy of an area measurement on a 3D image will never be better than 6%.
