Method for medical imaging in TOF-PET tomography

Abstract

The invention relates to a method for reconstruction of an image of a morphometric parameter being a ratio of the frequency of annihilation of an electron with a positron to three and two quanta. The device for imaging the interior of the studied object comprises a series of TOF-PET detection modules (110), a data acquisition subsystem (111), a data selection subsystem (113) configured so as to record and identify all types of quanta emitted from the studied object after administration of an isotopic marker, the data processing system being characterised in that it allows for reconstructing (121, 123, 131, 133, 141) and visualising (143) of a δ.sub.3γ(x,y,z) image of the ration of two-quantum and three-quantum annihilations without the necessity to measure the deexcitation quanta.

Claims

1. A method for medical imaging in TOF-PET tomography, comprising the following steps: introducing an object containing a positron-emitting radioisotope into a diagnostic chamber of a tomograph, recording gamma quanta emitted from the object in an imaged volume, attributing recorded events to 2γ and 3γ annihilation subgroups, reconstructing a 2γ image of the imaged volume, reconstructing a 3γ image of the imaged volume, normalising the 2γ image to obtain a normalised 2γ image so that the integral of values over all voxels of the normalized 2γ image is equal to the total number of 2γ annihilations which have occurred in the imaged volume, normalising the 3γ image to obtain a normalised 3γ image so that the integral of values over all voxels of the normalised 3γ image is equal to the total number of 3γ annihilations which have occurred in the imaged volume, determining a value of a morphometric indicator δ.sub.3γ for every voxel of the imaged volume based on the following dependence: ${\delta }_{3\gamma }=\frac{{\left(f_{3\mathrm{\gamma 2\gamma }}\right)}_t-{\left(f_{3\mathrm{\gamma 2\gamma }}\right)}_r}{{\left(f_{3\mathrm{\gamma 2\gamma }}\right)}_r}\times 1000\%$ where: (f.sub.3γ2γ).sub.t is a ratio of count number of annihilations with 3γ emission to a count number of annihilations with 2γ emission, calculated for every voxel of the imaged volume basing on the normalized 2γ image and the normalized 3γ image, and (f.sub.3γ2γ).sub.t is a ratio of count number of annihilations with 3γ emission to a count number of annihilations with 2γ emission in a reference material, visualising the morphometric image of the imaged volume, having voxels of values basing on the determined values of the morphometric indicators δ.sub.3γ.

2. The method according to claim 1, comprising, in a defined time interval, recording two gamma quanta originating from a two-quantum positron-electron annihilation and recording one gamma quantum or no quantum from a deexcitation.

3. The method according to claim 1, comprising, in a defined time interval, recording three gamma quanta originating from a three-quantum positron-electron annihilation and recording one gamma quantum or no quantum from a deexcitation.

4. The method according to claim 1, comprising creating at least one of: an anatomical image and a morphological image of the object, and overlaying the δ.sub.3γ image onto the at least one of the anatomical image and the morphological image of the object.

5. The method according to claim 1, wherein the object comprises more than one positron-emitting radioisotope, and the method comprises recording the gamma quanta for each radioisotope.

Description

BRIEF DESCRIPTION OF FIGURES

(1) The invention is show by means of example embodiment in a drawing, wherein FIG. 1 shows a flow chart of a process for reconstruction of the 3γ/2γ fractions of annihilating positrons in an exemplary TOF-PET detector.

EXAMPLE

(2) For recording of gamma quanta, PET tomographs known in prior art may be used, consisting of both organic and inorganic scintillators, after using the method described in the present invention, which allows for recording both two-quantum and three-quantum annihilations.

(3) In FIG. 1, a flow chart of a procedure for obtaining a 3D image of the 3γ/2γ ratio originating from positron-electron annihilation vs. the location of the studied object is illustrated. Tomograph 110 comprises detectors which allow for determining the position and time of the reaction in the tomograph of gamma quanta emitted from the studied object. Electric signals from the detectors 110 are read and processed into digital form by a data acquisition system (DAQ) 111, and then they are transmitted in step 112 to a recording device, which processes them in step 113 or stores on a disc. Data acquisition may be performed using method known in prior art. A processor 113 identifies detectors which have recorded the quanta from 3γ and 2γ annihilations, using conventional methods known to persons skilled in the art.

(4) The event is identified as recording of two or more quanta in the defined time interval (e.g. of several nanoseconds).

(5) The events classified as 2γ annihilation are used for reconstruction of a metabolic image 124 by TOF-PET methods 121, 122, 123 known in prior art.

(6) The events classified as 3γ annihilation are used for reconstruction of (x,y,z) coordinates of the point, in which the annihilation has occurred, and the plane of response (POR) 132. The identification is carried out using a processor 131, by methods known in prior art (e.g. those described in Patent Application No. WO2015/028604). The plane of response is defined as a plane containing point, in which 3γ interacted with the detectors. In the next step 133, based on the data of 132, a 3γ annihilation density image, 133, is reconstructed.

(7) The conventional 2γ image obtained in the TOF-PET 124 and the 3γ image 134 are used by a processor 141 for reconstruction of a 3γ/2γ morphometric image 142. The reconstructed images 124, 134, and 142 are visualised in step 143. The morphometric image is defined by calculating the value of the γ.sub.3γ parameter for every voxel, according to the dependence (4), where the f.sub.3γ2γ ratio is determined based on the corresponding normalised 2γ and 3γ images. The image is normalised so as to the integral of the values over all voxels of the normalised 2γ image is equal to the total number of 2γ annihilations which have occurred in the imaged part of the studied object. Analogically, the integral of the events in the whole normalised 3γ image is equal to the total number of 3γ annihilations in the imaged part of the studied object.

(8) To enhance the diagnostic options, prior to the morphometric reconstruction 141, the 2γ image 124 and 3γ image 134 may be improved (i.e. corrected for attenuation of gamma quanta in the studied object) using anatomical or morphological images. The latter may be obtained simultaneously or sequentially by the KT or MR tomographic imaging techniques known in prior art. To improve the diagnostic quality, the obtained 3γ/2γ morphometric images may be overlaid onto anatomical or morphological images.

(9) The described method may be used also in imaging using several isotopes. In such a case, the processor 113 identifies also the signals originating from deexcitation quanta (if recorded) emitted by a certain class of isotopic markers discussed earlier. Energy of these quanta has a value characteristic for each isotope. Thus, in the case of multiisotopic imaging, the two-quantum and three-quantum annihilations events may be classified correspondingly for every isotope, enabling simultaneous imaging using radiopharmaceuticals labelled with radioisotopes from various isotope classes discussed in the present description. It is particularly important e.g. of the case of monitoring of production of various β.sup.+-radioactive isotopes during hadron therapy.

(10) The presented method of 3γ/2γ imaging and the morphometric indicator δ.sub.3γ have the following advantages: the δ.sub.3γ indicator is a measure of porosity of tissues of the studied organism and serves as a measure of advancement of structural changes in cell on the molecular level; δ.sub.3γ is an additional indicator for SUV—standardised indicator of cell metabolism being defined in PET, and it provides additional information useful in diagnosing; the 3γ/2γ image does not depend on the time of examination, so it does not need to be corrected for the decrease of the radioisotope activity in the studied object in time, which is of high significance in examinations requiring moving the patient along the scanner to record images of various body parts; also the δ.sub.3γ indicator value does not depend on time elapsed from the administration of the radiopharmaceutical to the patient. Thus, the knowledge of the physical or biological half-life of the radiopharmaceutical, or its initial activity is not necessary to determine the δ.sub.3γ value; the morphometric indicator δ.sub.3γ and the SUV indicator may be determined simultaneously during the same examination; the δ.sub.3γ morphometric image may be determined using all radiopharmaceuticals utilised in the PET techniques, thus, as opposite to other morphometric indicator known in prior art, it is not limited only to the class of radioisotopes emitting a deexcitation quantum; determining the δ.sub.3γ value does not require recording of a deexcitation quantum, which leads to an increase in the imaging efficiency while compared to other currently known indicators for morphometric imaging; the presented system allows for dividing images originating from various radioisotopes in the case of multiisotopic imaging, provided that these isotopes emit deexcitation quanta with various energies.

(11) The technical solutions presented herein are outlined, described and defined in relation to specific preferred applications. However, the discussed various versions of imaging are only examples and they do not exhaust the full scope of the technical solution presented herein. The scope of protection is not limited to the described examples, but only to the following claims.