The biological application of small animal PET imaging

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Abstract

The short history of small animal PET is reviewed in the context of its application in the laboratory. Early work has demonstrated a role for the technique in both drug development and in the in vivo monitoring of neuroreceptor function with time. As spatial resolution approaches 1 mm, challenges in quantification remain. However, the ability to carry out animal PET studies that are analogous to human PET will form an important bridge between laboratory and clinical sciences.

Section snippets

A brief history of small animal PET

Many contributors to this volume will begin with reflections on the state of the art in their particular field at the time of the Receptor 1980 meeting, 20 years ago. At that time, Positron Emission Tomography (PET) was still in its infancy. From the point of view of PET technology, the limitation to small animal PET imaging was the spatial resolution achievable with the available detectors, although, even then, external coincidence detection was being used to determine kinetic rate constants

Early applications of dedicated small animal scanners

The RATPET scanner at the MRC’s Cyclotron Unit, developed in collaboration with CTI, Knoxville, TN, was the first dedicated, small diameter positron tomograph to move beyond the development and validation process to produce what could be considered ‘routine’ experimental data. The resolution of the system, although better than any other at the time, was still limited. Comprising an 11.5 cm ring of bismuth germanate (BGO) crystals its full width at half maximum (FWHM) value for transaxial

Practical issues

In each of the applications described above, the generation of even semi-quantitative experimental data represents the solving of a number of practical issues common to small animal PET scanning. The animal, like a human subject in a clinical scanner, must remain still and, the higher the resolution of the system, the smaller the movement which can be tolerated. Anaesthetic alone may not be sufficient since even breathing may cause systematic movement of the head. For rat brain, the problem has

The role of small animal PET in the biology laboratory

The latest developments in small animal scanner technology represent important and exciting advances in the field of PET and have attracted considerable interest. At the time of writing, orders are in place for around 20 dedicated small animal PET scanners. Before embarking on an animal PET scanning project, it is important, however, to consider what the scanner is realistically capable of achieving and to bear in mind that, in experimental biology, alternative techniques already exist to do

Resolution

The current phase of PET technology development has not yet run its course. The potential of the latest generation of microPET and HIDAC scanners has yet to be explored, let alone fully exploited, and it would be foolhardy to suggest that further dramatic enhancements are not in the pipeline. It can, however, reasonably be predicted that future improvements in spatial resolution will not be of the same magnitude as those seen over the last few years. In the mid-1970’s, for example, scanner

In conclusion

It has been clear for some time that small animal PET has the capacity to make a valid and unique contribution to basic and applied science. The ability to carry out analogous studies in small animals and in patients forms an invaluable bridge between laboratory and clinical science. Now, finally, with the delivery of the first commercially available systems, the full potential of this technique can be explored in a variety of environments around the world. It is intriguing indeed to speculate

Acknowledgements

The author gratefully acknowledges the help and advice of a number of colleagues at the MRC Cyclotron Unit including Peter Bloomfield, Ella Hirani, Terry Jones and, most especially, Sue Hume who helped to finalise the manuscript.

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    Current address: Imaging Research Solutions Ltd., Cyclotron Building, Hammersmith Hospital, Du Cane Road, London W12 ONN, UK.

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