Alan Jeavons

Dr Alan Jeavons, formerly a Senior Physicist at CERN, Switzerland, founded Oxford Positron Systems in 1985. The activities of the company are research, development and manufacture in wire chamber technology, in particular developing the scientific and commercial potential of the High Density Avalanche Chamber (HIDAC).

The Technology

A HIDAC consists of a Multiwire Proportional Chamber (MWPC) with the provision of laminated cathodes containing interleaved lead and insulating sheets and mechanically drilled with a dense matrix of small holes. Ionisation resulting from photons interacting with the lead is trapped by, amplified in, and extracted from, the holes by a strong electric field into the MWPC. On arrival at an anode wire, further avalanching occurs. Coordinate readout may be obtained from orthogonal strips on the cathodes. The result is precise, two dimensional localisation of the incident gamma rays. Every hole on the cathodes acts as an independent counter. By stacking these HIDACs, millions of these counters are integrated to form a large-area radiation camera with a high spatial resolution.

A second-generation prototype two-detector HIDAC-PET camera was assessed at the MRC Cyclotron Unit, Hammersmith Hospital, London, UK, during 1999.

This camera achieved:

*a field-of-view 10cm in diameter and 21cm axially;
*a 3D sub-millimetre spatial resolution;
*an absolute sensitivity of 8.9 Hz/kBq;
*a sensitivity of 918 Hz/kBq/ml for a phantom 55 mm diameter and 60 mm long.

Detailed physics results from this camera were presented at the 1998 IEEE Nuclear Science Symposium in Toronto.

A third-generation camera, quad-HIDAC, became available in June 2000. The first was purchased by Imperial College of Science, Technology and Medicine, London, UK and is installed at their newly established MRI/vPET Imaging Centre at Hammersmith Hospital, and the second camera was purchased by the Paul Scherrer Institute, Villigen, Switzerland and has been relocated in 2005 to ETH, Hoenngerberg, Zurich. Further units have been sold to the University Hospital, Münster, Germany for mouse cardiac imaging and to Manchester Molecular Imaging Centre, UK for pharmaceutical purposes. Quad-HIDAC cameras have also been used at Leeds General Infirmary, UK, for arthritis research and at the Royal Marsden Hospital, Surrey, UK for oncological investigations.