Colocalization encounters of the Session Arithmetic kind

Session Arithmetic is the new tool in Volocity 2 that allows you analyze the relationship between different measurement sessions.

We will use it to look at Colocalization

Let us begin with a simple dataset I have created to demonstrate the possibilities.
Below is a view of an image sequence in Volocity. There are 2 channels, with randomly distributed red objects in the first channel and likewise there are randomly distributed green objects in the second channel.

What I want to achieve is a measure of the amount of Colocalization between the 2 channels.

You can visualize this quite easily with Volocity by viewing both channels simultaneously in the image view.

However when measuring with Volocity you must remember to target a specific channel using the target button on the Navigation palette.

Firstly I will make a classifier to identify all of the green objects. See last month's tip for help with making Classifiers

I will then use this classifier to measure all of the green objects, putting the measurements into a new measurement session called green.

I will now repeat this for the red objects putting the measurements into a new session called red.

So we now have two measurement sessions containing the red and green measurement respectively.

Now click on the Measurements tab at the top of the window to see the measurement sessions that you have created.

Go to the "Measurements" menu and select "Session Arithmetic".

In the Session Arithmetic dialog select the "Colocalize sessions" operator.


Now click on the OK button, this will produce a total of four new measurement sessions.

1. "green touching red" - this session will contain objects from the green session that touch any objects in the red session, and objects from the red session that touch any objects from the green session.

2. "green not touching red" - this session will contain objects from the session green that do not touch any objects from session red. It will not contain any objects from the red session.

3. "red not touching green" - likewise this session will contain objects from session red that do not touch objects from session green.

4. Finally the session "green overlapping red" will give a measure of the amount of overlap between the two sessions.

By selecting the measurements in the Measurement Session you can view them in the Image view.

For your viewing pleasure I have selected the measurements in the "green overlapping red" session below.

And there we have it, another highly useful application of Volocity made simple by yours truly!