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Topic Title: Volocity Measurement Parameters
Topic Summary: Looking for more information about analysis parameters carried out in selected ROI for z-stacks.
Created On: 8/15/2018 8:21 AM
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 8/15/2018 8:21 AM
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Zoe H Smith

Posts: 2
Joined: 8/15/2018

Does anyone know (or know where I can find out) how volocity calculates the following parameters from an object within an ROI from the measurement tab:

1. Bounds

2. Skeletal Length

3. Longest Axis

4. Polarity

I have been able to find the relevant information otherwise in the manual but it includes 'bounds' and 'skeletal length' without further descripction.

 8/16/2018 10:35 AM
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RAH

Posts: 73
Joined: 5/16/2014

Have you had a look in the Volocity 'Help' section? I've sometimes found more information here compared with the Userguide. For instance in the Help menu, Skeletal length is deinfed as:

''This is the maximum length of the object. The selection is eroded evenly from its border inwards until it consists of a one-voxel thick, skeletal representation along its entire length. This ’skeleton’ is then measured.''

 8/16/2018 10:39 AM
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Zoe H Smith

Posts: 2
Joined: 8/15/2018

I have not but I will try that, thank you - this is very useful! Thanks for the information.

 8/16/2018 10:42 AM
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RAH

Posts: 73
Joined: 5/16/2014

Skeletal length is calculated by first thinning or skeletonising the object from all sides until a single voxel line is left. This measurement is best suited to elongated shapes. The direction of the line is elongated to meet the edges of the object and the length of this line is the skeletal length. For objects where the skeleton branches the skeletal length is measured as the longest traverse across the object without crossing a point more than once.

Skeletal diameter is the diameter of a cylinder if it had a length equal to the skeletal length of the object determined as above and a volume equal to the object's measured volume.

Derived using the equation for the volume of a cylinder.

V = Pi r2 *l

Measure skeletal length populates the measurement columns skeletal length and skeletal diameter for each measured object. For each skeletal length a measurement row is added. This row is a line measurement representing the skeletal length for the purpose of viewing feedback. The parent ID column of the row representing the skeleton will reflect the ID of the source object

 8/16/2018 10:45 AM
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RAH

Posts: 73
Joined: 5/16/2014

Polarity is calculated by finding the longest axis of an object, and dividing the object into two halves based on the midpoint of the longest axis. Each half is then compared using the equation below. Objects that are polar have a value close to 1, objects that are non-polar have a value close to 0. This gives you an indication as to whether the intensity is distributed evenly within your object, or heavily towards one pole.

polarity = 1 - sum of Intensities from the darkest half of the object / the sum of intensities from the brightest half of the object

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