assay report center of mass displacements

Sample Report

MetaVi Labs Chemotaxis Assay Reports provide numerous characteristics of moving cell behavior. This page will describe each of the analysis results.

User Input

In the Experiment-set edit page, choose 'Advanced Settings' to display the chemotaxis settings(Click on the image below to see full size).

Experiment-set edit page chemotaxis settings

Critical Settings for Chemotaxis Analysis

Microscopic Resolution Pixels/µm. This key factor is used by the image analysis algorithms to find and track the cells and all downstream calculations of distances and speeds.  For help calculating this important factor, see: Tech Note: Calculating Microscopic Resolution
Time Between Images The number of seconds between each image (the inverse of the frame rate). This factor is used in calculations of speed and results graphed with respect to time.
Minimum Track Duration Number of seconds a track should be exist (based on time-between-images) to be considered in the analysis. Tracks shorter than this time are excluded.
Evaluation Interval The time frame for calculating speed. For example, if the interval is 120 seconds, then the distance moved from in each 120 second interval  determines the speed in that interval.
Movement Threshold Minimum number of µm a cell must move to be considered as having moved. Cells that oscillate in position less than this threshold are excluded from the analysis.

Re-Doing Reports

redo report icon Look for the re-do-report icons on the experiment-set page next to each experiment-trial.  Make adjustments in the above settings then click the re-do-report.  Chemotaxis reports typically take 2 minutes to complete. Create as many reports as necessary to determine your preferred settings (there is no cost associated with generating reports). Then use these same settings for future experiments.

Interpreting the Results

Number Tracks in Interval.

In each evaluation interval, the number of tracks (that are longer than the minimum track duration) are plotted for each well in the experiment.

number tracks in interval chart

Number Tracks Starting in Interval

In each evaluation interval, the number of new tracks (that are longer than the minimum track duration) are plotted for each well in the experiment.

numbe tracks starting in interval chart

Number Tracks Ending in Interval

In each evaluation interval, the number of tracks which termited (that are longer than the minimum track duration) are plotted for each well in the experiment.

number tracks ending in interval chart

Forward Migration Index

The Forward Migration Index is a measure the cell's track directionality forward where forward is defined as toward the bottom of the view.  The calculation is a measure of Chemotactic Bias as Defined by Foxman et al. 1999 (please consult this paper for the calculation and a detailed explanation).   The first and final positions of cell cell track (Euclidean Distance) are used in the calculation.

forward migration index chart

Center of Mass Displacements

The first and final positions of each cell cell track (Euclidean Distance) are used to determine the magnitude of x,y vectors of the cell tracks.  All the vector X values are averaged and all the vector Y values are averaged to form average x,y vector for the well. This final average vector is the Center of Mass Displacement for the well.  This is an indicator of the average Chemotaxis Bias with distance and directionality.

center of mass displacements chart

Center of Mass Displacement Magnitudes

The first and final positions of each cell cell track (Euclidean Distance) are used to determine the magnitude of x,y vector of the cell track.  All the vector X values are averaged and all the vector Y values are averaged. The Euclidean distance of the average-X and the average-Y is the Center of Mass Displacement Magnitude for the well.  This is an indicator of the average Chemotaxis Bias as a distance only.

center of mass magnitude chart

Mean Cell Speed (both including and excluding non-moving cells)

In each evaluation interval, the cell speed is calculated by taking the distance it made in the interval divided by the interval duration (time).  The speeds over all intervals for each cell are averaged. Then the average speed for each cell track is averaged for the entire well.

This calculation is done for two cases a) including all cells and b) excluding non-moving cells. Non-moving cells are cell tracks shorted than the Minimum Track Duration.

The Movement Threshold applies to the calculation of all tracks - that is, all cells must move greater than the Movement Threshold in any given interval to be considered has having moved at all.

Mean Cell Speed in Interval includes both moving and non-moving cells.

Note: cells that move in circles and end up where they started can have cell speed but zero velocity. Refer to the Mean Cell Velocity explanation below.

mean cell speed in excluding non-moving chart

mean cell speed in interval chart

Mean Cell Velocity (both including and excluding non-moving cells)

The first and final positions of each cell cell track (Euclidean Distance) are used to determine the magnitude of x,y vector of the cell track.  The Velocity is calculated as the Euclidean Distance divided by the time duration of the track. Then the velocities for all cell tracks in the well are averaged for the entire well; this is the Mean Cell Velocity.

This calculation is done for two cases a) including all cells and b) excluding non-moving cells. Non-moving cells are cell tracks shorted than the Minimum Track Duration.

The Movement Threshold applies to the calculation of all tracks - that is, all cells must move greater than the Movement Threshold in any given interval to be considered has having moved at all.

Note: cells that move in circles and end up where they started can have cell speed but zero velocity.  The greater the final distance from the starting point, the greater the potential velocity (depending of course on the time required to make that distance).

mean cell velocity excluding non-moving chart

Average Directness

The directness represents a measure of the cell's tendency to travel in a straight line. It is the Euclidean distance divided by the accumulated distance for each cell. A value greater than or equal to 1 indicates straight-line migration.

average directness of cell paths chart

Mean Euclidean Distance

The first and final positions of each cell cell track (Euclidean Distance) are used to determine the magnitude of x,y vector of the cell track.  The the Euclidean Distance for all cell tracks in the well are averaged.

mean Euclidean distance chart

Accumulated Distance

In each evaluation interval, the cell distance is calculated. This distance is accumulated for all cell tracks in the well.

accumulated distance chart

Accumulated Euclidean Distance

The first and final positions of each cell cell track (Euclidean Distance) are used to determine the magnitude of x,y vector of the cell track. The magnitude of this distance is accumulated for all cell tracks in the well.

accumulated euclidean distance chart