Thursday April 05 2007
CEA/ SHFJ
First complete simulation of a whole body human PET scan
Communiqué de presse
CEA/ SHFJ
The interpretation of data from positron emission tomography (PET), a medical imaging method increasingly used for examinations in hospitals, is still complex. To optimise data analysis and extract the most relevant physiological information from scans, researchers are working on digital simulation programmes to support PET. However, long computing times have held up progress in this area.
CEA-SHFJ (Frédéric Joliot Hospital Service) has set up a simulation facility, called GATE , to model PET scans using the Tera 10 supercomputer located at CEA DAM at Bruyères-le-Châtel. The simulation made it possible to very realistically reproduce the distribution of a tracer used in PET for diagnosis in oncology in a very short time. This first simulation result should, in the medium term, allow a finer use of data provided by imaging and closer adjustment of scans to individual patients.
CEA-SHFJ (Frédéric Joliot Hospital Service) has set up a simulation facility, called GATE , to model PET scans using the Tera 10 supercomputer located at CEA DAM at Bruyères-le-Châtel. The simulation made it possible to very realistically reproduce the distribution of a tracer used in PET for diagnosis in oncology in a very short time. This first simulation result should, in the medium term, allow a finer use of data provided by imaging and closer adjustment of scans to individual patients.
Positron emission tomography (PET) involves administering a tracer, in the form of a substance labelled with a radioactive isotope, by the intravenous route, to observe the normal or pathological function of an organ by external detection. Using appropriate detection tools, the radiation emitted by the tracer makes it possible to construct an image on which the distribution of the labelled substance in the body can be visualised. Some diseases react to the substances used. This is the case for glucose, for example, which concentrates in cancerous tumours where metabolism is more intense.
To optimise the detectability of tumours according to the radioactive dose injected into the patient, and to circumvent factors that interfere with the analysis (e.g., the patient’s breathing during the scan or the reaction of other organs that naturally have a high metabolism), researchers use simulations as a correction tool. These simulations are carried out using the Monte-Carlo method, which is based on probability theory. However, the analysis comes up against the limits of computer processing times: for a classical human ‘whole body’ PET scan a Monte-Carlo simulation has to process the emission pattern of several billion positrons and gamma photons, requiring at least 10,000 hours or some 400 days of computing time on a standard PC.
To reduce computing time, researchers at the SHFJ and the DAM conducted a simulation on the Tera 10 supercomputer. After modelling a patient’s body, based on a real scan, the researchers simulated the injection of a tracer for a realistic activity of 264 megabecquerels (MBq) and an acquisition time similar to that of a standard PET scan. This first simulation required less than 3 hours of computing on 7000 processors. Comparison of the real scan and the simulation shows a practically identical tracer distribution. Quantitatively, the comparison of the volume of a tumour located under the patient’s left armpit gives a discrepancy of 6%, considered very low for a first simulation. This result is thus an important first step towards the development of methods to correct real data from PET scans and ultimately make possible the patient-tailored specification of PET acquisition and analysis protocols. It also illustrates the usefulness of high-powered computing in the life sciences.
See the comparison of images obtained below
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Left: PET image of a real ‘whole body’ scan. Right: the result obtained by simulation on Tera 10.
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Press contact: Stéphane Laveissière – 01 64 50 27 53
[1]The SHFJ is one of the four research facilities of the Institute of Biomedical Imaging (CEA-I²BM). The others are NeuroSpin (Saclay), MIRCen (Fontenay-aux-Roses) and Ci-NapS (Caen).
[1]GATE: Geant4 Application for Tomographic Emission – Geant4 is an international simulation programme developed at the CERN (Switzerland).
[1]DAM: Military applications division