The present invention relates to a process for locating the position of a radionuclide emitting positrons during its disintegration and whereof the child core emits at least one photon by de-excitation.
A field of application is locating radioactive markers for example for therapeutic or other purposes, such as for example location of markers in a geological medium (underground, rocks) or on an in-depth sample in a geological medium (drillcores), for analysing the borrowed preferential trajectory in the flow of the radio element, such as for example for determining the flow sites of rainwater or waste water. Document [1] indicates that such a process can be executed by detecting by a positron emission tomography camera (PET in English) a response line of the radionuclide. According to document [1], the position of the radionuclide is situated at the intersection between the response line and a geometric cone determined from a Compton telescope, the cone having as apex the interaction position of Compton type detected in a detection medium of Compton interactions of the telescope from the photon emitted by the radionuclide, and for semi-opening the angle between the direction of the incident photon of the interaction and the axis of revolution of the cone formed by the direction joining this interaction and the position of another interaction detected by the telescope. Document [1] specifies that measuring the three coordinates and the energy of the two first interactions of the incident photon should be used, but omits describing how to identify these two first interactions via Compton telescope.
The aim of the invention is to provide a process for locating the radionuclide contributing means for resolving this problem. An object of the invention is a process for locating the position of a radionuclide emitting positrons and whereof the child core emits at least one photon by de-excitation, in which a response line of the radionuclide is detected by a positron emission tomography camera, the position of the radionuclide being situated at the intersection between the response line and a determined geometric cone, the cone having as apex the interaction position of Compton type from the photon emitted by the radionuclide, and as semi-opening the angle between the direction of the incident photon of the interaction and the axis of revolution of the cone formed by the direction joining this interaction and the position of another interaction, characterised in that a Compton telescope is used for detecting a plurality, greater than or equal to two, of interactions of Compton type caused in cascade in a detection medium of the Compton telescope from the photon emitted by the radionuclide, the position of each interaction of said plurality is measured by Compton telescope, for each of the multiplicity of arrangements ordered per pair of first and second interactions of Compton type among the plurality of interactions detected, the angle between the direction of the incident photon of the first interaction and the geometric axis joining the position of the first interaction and the position of the second interaction is determined by Compton telescope and the geometric surface of the cone having as apex the position of the first interaction and as semi-opening said angle determined around said geometric axis is reconstructed, said geometric axis forming the axis of revolution of the cone and being oriented in the direction going from the second interaction to the first interaction, those cones arc eliminated whereof the geometric surface has no intersection with the response line, at least one cone whereof the geometric surface has an intersection with the response line is selected, and the position of the radionuclide is selected from said reconstructed intersection of the response line with the geometric surface of the selected cone.
In accordance with embodiments of the invention:                said angle mn for each arrangement per pair is determined by Compton telescope according to the formula:cos θmm=1+mec2(1/E0m−1/(E0m−E1m))where me is the mass of the electron, c represents the speed of light in vacuum, E0m is the measured energy of the incident photon of the first interaction of the pair, E1m is the energy transferred to an electron during the first interaction and measured.        it is determined whether there is only a single selected cone whereof the surface has a point of intersection with the response line, and, in the affirmative, the position of the radionuclide is calculated as being the position of this point of intersection of this single selected cone whereof the surface has a point of intersection with the response line.        it is determined whether there are several selected cones whereof the surface has a point of intersection with the response line, and, in the affirmative, it is determined which of these selected cones whereof the surface has a point of intersection with the response line is the most probable, the position of the radionuclide is calculated as being the position of the point of intersection of the selected cone whereof the surface has a point of intersection with the response line and which is the most probable.        
Other objects of the invention are the following:                Application of the process such as described hereinabove to location imagery of the radionuclide.        Application of the process such as described hereinabove to locating at least one radioactive marker comprising said radionuclide.        This last application can serve to locate at least one radioactive marker, comprising the radionuclide, for locating a radiomarked substance by the marker in a geological medium.        In this last application the radiomarked substance can be water.        Application of the process such as described hereinabove to locating at least one radioactive marker, comprising the radionuclide, to mark a chemical substance in a human or animal body.        Application of the process such as described hereinabove to locating at least one radioactive marker, comprising the radionuclide, to mark a chemical substance in a human or animal body, having been introduced to said body.        Application of the process such as described hereinabove to detection of leaks from a container containing at least the radionuclide.        Application of the process such as described hereinabove to detection of an object containing at least the radionuclide.        
Another object of the invention is a device for carrying out the process such as described hereinabove, comprising a positron emission tomography camera for detecting a response line of the radionuclide, a Compton telescope comprising:                means for detecting a plurality, greater than or equal to two, of interactions of Compton type caused in cascade in a detection medium of the Compton telescope from the photon emitted by the radionuclide,        means for measuring the position of each interaction of said plurality in the detection medium, the device comprising, in addition to the camera and the telescope:        means for determining, for each of the multiplicity of arrangements ordered per pair of first and second interactions of Compton type among the plurality of interactions detected, the angle between the direction of the incident photon of the first interaction and the geometric axis joining the position of the first interaction and the position of the second interaction, to reconstruct the geometric surface of the cone having for apex the position of the first interaction and for semi-opening said angle determined around said geometric axis, said geometric axis forming the axis of revolution of the cone and being oriented in the direction going from the second interaction to the first interaction,        means for eliminating the cones whereof the geometric surface has no intersection with the response line,        means for selecting at least one cone whereof the geometric surface has an intersection with the response line,        means for selecting the position of the radionuclide from said reconstructed intersection of the response line with the geometric surface of the selected cone.