Knowledge Base

CatWalk XT10 Technical Specifications

CatWalk™ XT is an easy-to-use and highly sensitive tool for the detailed assessment of gait changes in laboratory rodents. CatWalk is a plug-and-play system and consists of the following components:

• The walkway: consists of a hardened glass plate, a spring-operated corridor, an illuminated ceiling, a control unit, and a goal box.
• A 100 frames per second (fps) high-speed color camera that records the footfalls and body contour.
• The CatWalk XT software, version 10, for the recording and analysis of the footprints and gait of rodents traversing the walkway.
• Top-of-the-line computer equipment for running the software.

Part 1 - Hardware

The Walkway

The CatWalk XT walkway consists of a scratch-resistant hardened glass plate that is essential for the detection of the footprints and outline of an animal. Usually, a rodent walks from left to right, toward the goal box located on the right side while being constrained in its lateral movement by a corridor. It thus facilitates the recording of footprints and limits unwanted behaviors to elicit uniform runs. Since the paws are detected by the light they reflect, it is best to record in a low-light environment. However, a dim red indirect light source can be used to illuminate the environment. The dimensions of the walkway are 130 x 68 x 152 cm (51.2" x 26.8" x 59.8").

Illuminated Footprints Technology

The Illuminated Footprints™ technology is based on total internal reflection. Green LED light is injected into the glass plate from the side and is completely internally reflected, except for those areas where the animal makes contact with the glass plate. At points of contact, typically the animal's paws, light escapes and is reflected toward the camera. The high-speed color camera (100 Hz) positioned underneath the glass plate captures the illuminated paws, and their position in space and time is determined by the CatWalk XT software.

The Illuminated Footprints™ technology assures that the actual footprints of the rodent can be captured with a high-speed video camera while the rodent traverses the walkway. This ensures maximal spatial and temporal resolution and is why CatWalk XT is able to produce such high-quality data. The captured video is processed by the CatWalk XT software. Based on the timing, dimensions, position, dynamics, and intensity of each footfall, numerous parameters are calculated for qualitative and quantitative analysis of footfalls and gait.

The Glass Plate

The glass plate is made of clear, hardened, scratch-resistant safety glass with polished edges. This type of glass is less contaminated than standard glass to ensure evenly distributed lighting conditions along the length and width of the walkway. Each plate is hand-selected for clarity and the absence of blemishes or inclusions introduced during the manufacturing process. A replacement glass plate can be ordered from the Noldus website when necessary. Dimensions of the glass plate are 130 x 20 x 0.5 cm (51.2" x 7.9" x 0.2").

Spring-Operated Corridor

The corridor consists of two matted black walls to limit and direct an animal's movement over the glass plate. The width of the corridor can be adjusted, making the system suitable for both mice and rats. The left edges are bent outwards so animals can be easily inserted. On top of the corridor walls, an extra diffusion plate is mounted to provide stability and prevent animals from peeking over the corridor. If necessary, the diffusion plate can be removed to allow, for instance, tethered animals to traverse the walkway.

For cleaning purposes and to remove a rodent from the glass plate, the corridor can be effortlessly lifted with just two fingers due to the spring-operated lifting mechanism situated at the back of the corridor.

Goal Box

The goal box is located at the right end of the corridor. It consists of a platform with a hole in the middle. On this platform, a lightweight box can be positioned that covers the hole and has an opening at the side of the corridor to allow entry from the corridor. This box can easily be lifted with one hand for access to an animal inside. Once inside the box, the animal has the option to jump through the hole into its home cage located below. The goal box design accommodates the most commonly used rack-based cages, and various inserts are provided for a precise fit.

Illuminated Ceiling

The illuminated ceiling on top of the walkway creates a red background so that the contour of the animal can be visualized. This contour is used to determine the position of the illuminated paw relative to the body contour and assign its identity. Furthermore, it is used to detect the position of the animal so a trial can be started and stopped, or the speed of the animal can be determined.

Power Supply

The 24V power supply unit can be operated worldwide using mains voltage from 100 to 240V AC and 50 to 60 Hz.

CatWalk XT Control Unit

The CatWalk XT Control Unit takes power from the power supply and distributes it to the camera, green LED rail, and illuminated ceiling. The voltages to the green and red light rails can be controlled by the CatWalk software via a USB connection.

Camera and Mount

The high-speed color camera (100 fps) captures video of the animal traversing the CatWalk. The time limit for capturing a run is determined by numerous factors, such as image light noise level and computer memory. The camera is connected via a CAT-6 UTP cable to a network card inside the computer running the CatWalk XT software. To view a smaller or larger portion of the glass plate, the camera can be moved up or down on the slider. Having approximately 60 cm of the glass plate in view results in capturing approximately five to six strides of gait in rats. Decreasing the distance between the camera and the glass plate to approximately 35 cm in view allows you to acquire the same number of strides for a mouse while increasing image resolution and light sensitivity.

Part 2 - Software

Navigation

Startup

When you start the CatWalk XT software, a task dialogue will appear that guides you through the application. The dialogue allows you to easily navigate to relevant parts of the software that are often accessed when starting up CatWalk XT.

Task Dialogue

Further task dialogue windows will guide you through the application and offer functions depending on the position in the workflow.

Menu Bar

The menu bar located at the top of the user interface allows you to navigate anywhere in the application, independent of the task dialogues.

Experiment Explorer

The left pane of the user interface displays the experiment explorer, which contains the workflow from top to bottom. Double-clicking allows you to quickly jump to different positions in the workflow. It also shows the acquired trials and runs and their status, including selection by the data segmentation profile, classification, and whether a run is compliant with the run criteria.

Quick Links

The bottom of the user interface offers links to the previous and subsequent phases in the workflow.

Setup

Define and Calibrate the Walkway

In this part of the software, the camera view needs to be cropped to omit all redundant parts in the video image. The image also needs to be calibrated to match real-world dimensions.

Detection Settings

The detection settings allow you to define the optimal intensity range for footprint detection and for filtering out background noise. The detection settings dialogue includes an auto-detection function that suggests optimal detection settings, from which you can fine-tune detections by adjusting the camera gain, intensity threshold, and green and red light intensity.

Experiment Settings

In the experiment settings, you can define experiment groups and time points, which can later be used as independent variables in data selection and analysis. Run criteria can also be defined to set thresholds for run duration and speed variation. These criteria become read-only for the entire experiment once the first run is acquired. Runs that comply with these criteria are labeled accordingly, while runs that do not comply are not discarded and can still be used for data segmentation. The minimum number of runs required to comply with these criteria can also be set in this dialogue.

On average, three compliant runs per animal per time point are necessary when using five or six gait cycles per paw per run. When using fewer gait cycles per run due to time limitations or motivational issues, more than three compliant runs are advised to ensure enough repeated measures are taken.

Trial List

The trial list allows you to automatically build a list of trials to acquire for each time point and treatment group. A trial is a unique identifier that contains the treatment group, time points, animal ID, and several runs. A trial is finished when the number of compliant runs set in the run criteria is acquired.

Acquisition Settings

The acquisition settings dialogue allows you to set several standard operations regarding runs. For instance, you can determine after what duration runs should be automatically aborted. The default is set at 10 seconds.

Acquisition

Trial Selection

Prior to acquisition, the trial that matches the animal being tested must be selected. Alternatively, a new trial can be created for the animal. In the experiment explorer, you can see how many runs have been performed in each trial and how many of them are labeled compliant.

Run Acquisition

Before starting a run, you need to refresh the background for optimal detection fidelity. After the animal is placed on the walkway, its image is captured automatically during the entire time it is in view, until it either leaves the camera's view or the maximum run duration is exceeded. Feedback is provided after each run regarding the run's compliance with the defined run criteria.

Run Footprint Classification

Manual Footprint Classification

The software automatically identifies the parts of the animal that have made contact with the glass plate, which are typically the animal's footprints. The footprints can then be labeled manually through a click-and-select function. Once a footprint is manually labeled, the software automatically jumps to the next unlabeled print. Recognition of the footprints is facilitated by dragging the video slider back and forth or by zooming into the video image.

The Automatic Footprint Classification Module

With Automatic Footprint Classification™, the classification of each print is performed automatically by the built-in classification algorithm. Atypical prints are automatically highlighted for manual classification, and any labeling conflicts are automatically detected. These conflicts can be accessed via a dropdown menu. Once labeling is completed, both qualitative and quantitative data are automatically generated by the software.

Adjusting the Intensity Threshold

In the Adjust Intensity Threshold dialogue, you can change the intensity threshold set in the detection settings. This change applies only to the selected run, whereas the value set in the detection settings is applied to all runs yet to be acquired. Changing the intensity threshold may be necessary for individual runs when there is a large variation in background noise between runs, trials, or time points. Please revisit the detection settings when this is the case.

Source: Technical specs - CW XT 10.7, Noldus Information Technology