PEPT data processing

The PEPT cameras collect raw data as a series of 2D locations of pairs of gamma rays. These raw data are then processed using a programme that applies an algorithm to remove corrupt data and create a series of locations in the form (t, x, y, z) representing the path of the tracer. Two parameters, N and fopt control the performance of the algorithm.

Factors which affect the parameters include; tracer velocity, system geometry and tracer activity which declines throughout the day. Value selection for the parameters is a trade-off between having enough data points and having good enough data points for an accurate location.

In the algorithm raw data are divided into slices, the slices are sequential events recorded by the camera. The ‘events per slice’ (N)parameter determines the number of recorded events in each slice to use. Generally speaking the faster the particle is travelling, the fewer events should be selected; as the faster the particle moves, the further it travels in a time period. Thereby selecting fewer events reduces that time period and so should give a more accurate location.

The ‘foptparameteris the percentages of data that is retained. The algorithm identifies events which lay furthest from a point and discards them as corrupted. This reconstruction repeats until only the fopt is kept.

The fopt is independent of speed; therefore determination of a good value can be obtained from measuring data for a stationary particle in the system and then finding the value of fopt which gives the smallest spread in the resulting locations.

Once the data have been processed, the locations of the tracer are in the form (t, x, y, z) and the data can then be analysed to reveal useful information.