# 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* f _{opt}* 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 ‘**f _{opt}’ **parameteris 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

*f*is kept.

_{opt }The *f _{opt }*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

*f*which gives the smallest spread in the resulting locations.

_{opt}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.