On camera

Carol Lewis gets to grips with imaging techniques and the benefits of two into one The cost may be prohibitive, but a combined PET/CT scanner greatly increases patient throughput and aids diagnosis.PET/CT is a combination of two scanning technologies in one machine.

CT (computed tomography) is an x-ray technique in which highly detailed anatomical images are obtained from a series of cross-sectional slices.

PET (positron emission tomography) looks at activity rather than anatomy.The patient is given a radioactive compound, such as glucose, which is metabolised more rapidly by tumour-containing cells.The scan then shows radioactive accumulation in tumours.

In a PET/CT scanner, the two types of image are fused to enable activity to be placed in an accurate anatomical context.

PET/CT is a highly sensitive method of detecting occult disease, early tumour recurrence and chemotherapy response.

Studies have shown the combined scan has several important advantages over two separate scans:

It provides more accurate definition of lesions.

It gives a more precise anatomic location.

It reduces the need for further scans or diagnostic procedures.

The combined scan is also fast - the fastest systems can now do a whole body oncology scan in seven to 10 minutes (opposed to 30 minutes previously).This means less time in the scanner for the patient, less radiation exposure for everyone involved and the chance to scan far more patients.

PET/CT also has potential applications in Parkinson's disease, stroke, cardiac disease, epilepsy and Alzheimer's disease.

Disadvantages

Cost is the major problem with scanners, as they are approximately£1.2m each.The costs of accessories, staff and running also need to be factored in.

There is also the problem that very few people in the UK are trained to use and interpret PET scans, and the few centres that currently offer a clinical PET service are too stretched to offer training.Some centres have already looked at overseas training as an option.

What are the implications

A strategy for provision of PET in the UK was published earlier this year. It recommends that PET scanners be established in at least 15 UK sites during the next three to five years, and this figure should rise to 35-60 within the next 10 years. It recommends that funding should be provided by the government with operating costs included in the budget of cancer networks/primary care trusts.

Clearly, if your trust is going to invest in a new PET scanner, it is best to buy a combined machine with all its advantages - so most centres are expected to invest in PET/CT.There are currently just three sites offering PET/CT in the UK and 13 offering PET (six for clinical use, seven for research). l Further information lPositron emission tomography: a strategy for provision in the UK.Royal College of Physicians.£15.

www. rcplondon. ac. uk

Strategy for the provision of positron emission tomography in the UK.Editorial by Professor Peter Ell.Nuclear Medicine Communications,2003, 24,229-231. www. nuclearmedicinecomm. com