Projects / Programmes
Advanced detector for Time-of-Flight PET based on Cherenkov radiation
| Code |
Science |
Field |
Subfield |
| 2.06.09 |
Engineering sciences and technologies |
Systems and cybernetics |
Medical physics |
| Code |
Science |
Field |
| B140 |
Biomedical sciences |
Clinical physics, radiology, tomography, medical instrumentation |
| Code |
Science |
Field |
| 2.06 |
Engineering and Technology |
Medical engineering
|
positron emission tomography, time-of-flight, picosecond photo detector, MCP-PMT, SiPM,
Cherenkov radiation
Researchers (10)
Organisations (2)
Abstract
Positron emission tomography (PET) is one of the most important diagnostic tools in medicine, allowing three-dimensional imaging of functional processes in the body. It is based on detection of two gamma rays originating from the point of annihilation of the positron emitted by a radio-labelled agent. Standard PET scanners have an axial length of about 20 cm and can only use a fraction of the activity in the body. This fraction may be increased by extending the axial length of the device, which is associated with a significant increase in its price, which, in turn, is largely determined by the cost of the scintillator. Development of devices for imaging of the whole body is one of the hottest trends in functional and molecular imaging.
The contrast of the image can be improved by reducing the fraction of background combinations, mostly from random coincidences, and from events where gamma rays scatter in the tissue, in special PET devices, measuring the time of flight of gamma rays (TOF-PET, Time-Of-Flight PET). Their accuracy is between 250 ps and 400 ps, which can already significantly improve the contrast in imaging of large objects. One of the major limitations to further improvements of the timing resolution is the response time of the scintillator crystal. The search for new materials and mechanisms of light emission is another direction of intensive development.
The purpose of the presently proposed project is to develop an ultra-fast module for detecting annihilation gamma rays, which will allow a measurement of the difference in the time-of-flight with an accuracy around 100 ps or better. This can be achieved by detecting Cherenkov light emitted by electrons, produced in the interaction of gamma rays in the detector. Lead fluoride (PbF2), which is suitable as Cherenkov radiation medium for such a detector, is also potentially less expensive than scintillator materials; this makes it also interesting as a material for full body scanners. In addition, lead fluoride has a shorter attenuation length for gamma rays, which means that the crystals can be shorter, leading to a reduction of the parallax error, of particular importance for long scanners for full body imaging.
A preliminary study, which we conducted jointly with research groups from several European universities and companies, has shown that a Cherenkov-PET scanner using Lead fluoride with the same size of detector elements and the same ring geometry as a standard PET scanner will have a 20% improved spatial resolution. Sensitivity will be about one half, but noise equivalent count rate (NEC) can be expected to be as good as in a standard PET scanner, if TOF resolution is 200 ps or better. The simulation study also showed that, due to the smaller attenuation length (and therefore shorter crystals and smaller parallax errors), a detector module with PbF2 is also very promising for a 1m long scanner. Our pioneering experimental study has shown that this type of detector is feasible, and is actually very fast. Using PbF2 crystals and photomultiplier tubes with microchannel plates (MCP-PMT, Micro-Channel Plate photomultiplier tube), we have achieved a time resolution of 95 ps (FWHM).
To use this method in a PET device the efficiency of gamma ray detection needs to be improved because relatively few Cherenkov photons are emitted per interaction. Silicon photomultiplier (SiPM) is a very suitable sensor, which has a considerably better detection efficiency, but somewhat lower timing resolution and relatively large dark count rate, that needs to be reduced by cooling.
Within the proposed project we would develop a detector module based on silicon photomultiplier, which can in principle operate in a magnetic field (important for simultaneous MRI-PET imaging), and which would - due to a lower material cost and shorter crystals – allow a construction of a full/half body imaging device and imaging the patient would receive a smaller dose.
Significance for science
Existing devices for Time-of-flight PET (TOF-PET) imaging are based on the detection of gamma rays through the scintillation light, which limits the timing resolution of the system. The originality of our approach is the use of Cherenkov light, emitted promptly after the interaction of the gamma ray in the detector material. After our first publication on the promising results achieved with this new method, this topic has become a hot topic in TOFPET imaging, and an important discussion topic at conferences and workshops on PET imaging (e.g., MEDAMI 2016, Ajaccio, 2016, FAST Workshop, Trento, 2016 and Ljubljana 2018, etc.). In this new research area our group has been playing a leading role, which could be further strengthened with the proposed project.
With our first measurements using a Cherenkov based TOF-PET method, we managed to attract
considerable attention in the scientific community; the first presentation at one of the main conferences in this field (IEEE Nuclear Science Symposium and Medical Imaging Conference) in 2011, was in the most prestigious section, the joint session of the simultaneous conferences, Nuclear Science Symposium and Medical Imaging Conference. Since then, our research in this area has continued to attract a constant attention.
An increased interest of the scientific community in the use of Cherenkov light for PET imaging has been observed in the recent years. Only in Europe there are at least three other groups (groups from CERN, Switzerland; CEA, France; TU Delft, Netherlands) currently perusing research of Cherenkov based TOF-PET detectors. After many clinical trials demonstrating the benefits of TOF measurement in PET the demands from the users for an improved resolution are increasing. Since there has been no breakthrough relating to the development of improved scintillators, the attention of the research community is becoming increasingly focused on alternative methods of improving the TOF resolution, such as the use of Cherenkov light.
The detection method first developed by our group and the use of which is foreseen for the proposed research project does not only bring the benefits in terms of an improved TOF resolution, but also enables the use of lower cost of materials, necessary for construction of the whole PET device. Instead of scintillators, which represent a major fraction of the cost for the whole device, we would use a lead fluoride Cherenkov radiator crystal, which will be significantly less expensive than currently used LSO scintillator, especially in case of a large volume production. This would enable production of longer devices with at least 1m axial coverage, and with this, simultaneous imaging of the whole or at least a majority of the body. With this, new medical research, such as the complex influence that the digestive tract has on the hormones and the central nervous system, would become possible.
Significance for the country
Existing devices for Time-of-flight PET (TOF-PET) imaging are based on the detection of gamma rays through the scintillation light, which limits the timing resolution of the system. The originality of our approach is the use of Cherenkov light, emitted promptly after the interaction of the gamma ray in the detector material. After our first publication on the promising results achieved with this new method, this topic has become a hot topic in TOFPET imaging, and an important discussion topic at conferences and workshops on PET imaging (e.g., MEDAMI 2016, Ajaccio, 2016, FAST Workshop, Trento, 2016 and Ljubljana 2018, etc.). In this new research area our group has been playing a leading role, which could be further strengthened with the proposed project.
With our first measurements using a Cherenkov based TOF-PET method, we managed to attract
considerable attention in the scientific community; the first presentation at one of the main conferences in this field (IEEE Nuclear Science Symposium and Medical Imaging Conference) in 2011, was in the most prestigious section, the joint session of the simultaneous conferences, Nuclear Science Symposium and Medical Imaging Conference. Since then, our research in this area has continued to attract a constant attention.
An increased interest of the scientific community in the use of Cherenkov light for PET imaging has been observed in the recent years. Only in Europe there are at least three other groups (groups from CERN, Switzerland; CEA, France; TU Delft, Netherlands) currently perusing research of Cherenkov based TOF-PET detectors. After many clinical trials demonstrating the benefits of TOF measurement in PET the demands from the users for an improved resolution are increasing. Since there has been no breakthrough relating to the development of improved scintillators, the attention of the research community is becoming increasingly focused on alternative methods of improving the TOF resolution, such as the use of Cherenkov light.
The detection method first developed by our group and the use of which is foreseen for the proposed research project does not only bring the benefits in terms of an improved TOF resolution, but also enables the use of lower cost of materials, necessary for construction of the whole PET device. Instead of scintillators, which represent a major fraction of the cost for the whole device, we would use a lead fluoride Cherenkov radiator crystal, which will be significantly less expensive than currently used LSO scintillator, especially in case of a large volume production. This would enable production of longer devices with at least 1m axial coverage, and with this, simultaneous imaging of the whole or at least a majority of the body. With this, new medical research, such as the complex influence that the digestive tract has on the hormones and the central nervous system, would become possible.
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