Knowledge Base

Introduction

1.1 An Introduction to CatWalk XT

This section gives a general overview of what the CatWalk program does. We recommend that all first-time users of CatWalk read this section.

Principle of Operation

The heart of the CatWalk system consists of an enclosed walkway on a glass plate that is traversed by a rat or mouse from one side of the walkway to the other. Green light enters at the long edge of the plate and is completely internally reflected. Light is able to escape only at those areas where the animal's paws make contact with the glass plate; as a result, the light is scattered. Thanks to our Illuminated Footprints™ technology, paws are captured by a high speed video camera that is positioned underneath the walkway. The video camera transforms each scene (the area in front of the lens) into a digital image composed of discrete pixels of digital brightness values. The digital images are transferred to the computer through an Ethernet connection. The brightness of a pixel depends on the amount of light received from such an area by the camera. The Illuminated Footprints™ technology enables intensity differences to be detected between animals' paws.

Paw Detection

In order to be able to classify paw prints in the video, you first need to set the CatWalk program to distinguish between paw prints and background noise. For this you can adjust the Camera Gain and Green Intensity Threshold to set the Maximum and Minimum Green Intensity, respectively, of the pixels that comprise a paw print.

Classifying Runs

The video images with paw prints are used in the footprint classification. You assign labels (for example, right hind paw, left front paw) manually or automatically to illuminated paw prints in each video image. You can also determine (Intermediate) Toe Spread, Print Length and Paw Angle with the interactive footprint measurements module. Once classification is done, the CatWalk software automatically calculates a wide number of parameters in each of the following categories:

• Parameters related to individual footprints: for example, initial contact of each placement of a paw, the duration of contact of a paw print with the glass plate, the width and length of a complete paw print, the intensity of a paw, the time the animal stands on a single hind paw or both hind paws, etc.
• Parameters related to the position of footprints: for example, stride length, base-of-support, relative print positions.
• Parameters related to time-based relationships between footprints: for example, footfall patterns, phase dispersions, support formulas.
• The Sciatic Functional Index, which is commonly used as a tool for the evaluation of the recovery of the sciatic nerve.