This site is devoted to mathematics and its applications. Created and run by Peter Saveliev.

# Medical testing device

This came from a scientist at a medical equipment company:

We are analyzing images of a red dye in a plastic window and would like to measure the width (measured vertically in the attached picture) of the white stripe at the bottom of the window. It would be best if we were also able to measure the overall height of the window so that we could report the width of the white stripe in mm - we know that the window should be 2.54 mm high... The photos are taken of the sensing device of a serum testing system that we are developing. The red color development is specific for the presence of CRP reactive protein ... produced by the liver in response to infection or other stress (like cardiovascular disease). Our device allows physicians to measure CRP levels in a single drop of blood - the test takes about 5 minutes and can be run by a physician's assistant.

The white and red rectangles are the windows and the whitish bands at the bottom of the red rectangles is what we want to measure.

Pixcavator is well suited for this task.

First, an important step in analysis of color images is to choose the color channel. The fact that some rectangles are red suggests that Red should NOT be chosen. I chose Green (at the Analysis tab). To make it quick I left the shrink factor at 3x (if you make it 1, the accuracy will be much higher). Then I pushed Run.

At the Output tab, I moved the two main sliders (size and contrast) to 210 and 40 respectively. That gave me the bands (the first image below). Under "Dim." thickness and length are shown in the table. The four bands have thicknesses 7,7,7,8.

To calibrate I used the white rectangles. I moved the first slider to 4662 and the last rectangle was captured (the second image). The thickness is 90 pixels. So, 1 pixels = 2.54 mm.

Therefore, the thickness of the white band is 7*2.54/90 = .20 mm.