WO2023042108A1

WO2023042108A1 - Scintillation probe with active collimator

Info

Publication number: WO2023042108A1
Application number: PCT/IB2022/058698
Authority: WO
Inventors: Andrea PERGOLA
Original assignee: Ng Detectors S.R.L.
Priority date: 2021-09-17
Filing date: 2022-09-15
Publication date: 2023-03-23
Also published as: IT202100023963A1

Abstract

A scintillation probe with active collimator type comprises a plurality of scintillation crystals arranged to form a tubular geometry structure with a central cavity, wherein said plurality of scintillation crystals has at least three side crystals, at least three front crystals; said side and front crystals being optically insulated with each other at respective side interfaces and at the end opposite to the photo-detecting end.

Description

Scintillation probe with active collimator

Description

The present invention relates to a scintillation probe with active collimator, of the type used to detect the emission of an electromagnetic radiation produced by nuclear radioactive decay or the like , and in case its direction of origin, with the purpose of detecting the respective source of radiations , such as for example high frequency ioni zing radiations during radio-guided surgery interventions or nuclear medicine exams .

The kind of operation of the probe is generally performed by inj ecting a radioactive tracer in the human organism, so that it could accumulate at a speci fic tissue . In particular, this procedure can be used to detect the so- called sentinel lymph node , that is the first lymph node which is reached by possible metastases , which are typical of malignant tumours spreading by lymphatic route , so as to be able to intervene by performing the removal thereof .

Then, overall the detection of the anomalous tumour mass is performed by detecting a source of ioni zing radiation, such as X or gamma rays , emitted by an accumulation of said tracing substance in the tissue submitted to examination . In particular, this type of electromagnetic radiation is emitted, directly or indirectly, during the decay of the speci fic radioisotopes used for marking the radiopharmaceutical .

However, it is meant that the scintillation probe , since it is an instrument to identi fy the origin of an electromagnetic radiation, can be used with any type of radioactive source , even in non-medical fields .

The operation of a scintil lation probe is generally based upon the capability of some types of crystal to generate photons of visible light when hit by the radiation coming from the radioactive source .

These photons are detected by using photo-detecting sensors, in particular photo-multipliers, and transformed into electric pulses.

The number of events, i.e. the single photonic emissions detected in the time unit, is proportional to the concentration of radioisotope inside the measuring cone of the instrument. The detection of high-emission sites take place by comparing the counts performed in real time in the area of interest. The surgeon is informed about the activity of the investigated site both through the direct display of the number of detected gamma rays and through a sound indicator, modulated in frequency proportionally to the amount of the count itself. By moving the probe, then one searches for the area which produces the greatest intensity of emissions.

The known scintillation probes, as those described in European patent application No. EP 1,596,223 Al and in US patent No. 10, 605,932 Bl, detect the incident radiations when they are approached to the source, so that the healthcare professional could identify the lymph node on which one has to intervene.

In its most simplified form, the examination then consists in a scanning performed with the probe on the whole area where the radio-emitting lymph node could be localized.

In this way, however, the time required to identify the lymph node can be long, by increasing the risk of complications for the patient which increase proportionally to the duration of the surgical intervention .

To obviate this drawback, it was thought to obtain a partial image of a patient submitted to this examination, with imaging techniques and instruments designated as gamma camera with reduced sizes.

Even with these expedients, the procedure requires a long time due to the lower efficiency of these detection apparatuses. Therefore, it was proposed to integrate the use of the probe with imaging techniques, to obtain substantially a probe navigation system which could guidp it in a more direct way in the direction of the source.

This combination, however, results to be considerably complex due to instruments and implementation techniques.

Some probes known in the state of art, as described in US patent No. 10, 605, 932 Bl and in "Development of a Novel y Probe for Detecting Radiation Direction", Pani et al., 17^th International Workshop of Radiation Imaging Detectors, detect the radioactive source in two dimensions (2D) , by calculating the azimuth and polar angle of the source with respect to the probe. Disadvantageously, nobody calculates even the distance of the source from the probe, by returning through the software the position in three dimensions (3D) of the source, nor it can identify several sources .

Moreover, several of the existing probes require the acquisition of the radiations by considering different probe positions, before being able to identify the source position. Even this, it is an aspect which slows down the surgical procedures, by increasing the risk for the patient .

In the prior art, there are no probes capable of identifying the presence of more than one source, and in order to do it one makes use of imaging systems, such as the gamma-cameras, or combinations of devices of different nature .

Additionally, the current probes use shields of passive type, mainly made of lead, to shield the detection crystal from all radiations outside the prefixed detection cone.

For example, the most used shape, for which the probe is defined passive collimator, consists in having one or more scintillation crystals on the intra-surgical instrument head, shielded on all sides except on the face, which once aligned, will be proximal to the radioactive source.

In fact, the aim of these probes is only to identify the alignment position, by moving the probe in the space. This type of operation can be defined as binary, wherein the probe does not receive anything, since the radiations hit the shielding, or when it detects a radiation, it means that it is aligned to the source .

Disadvantageously, the shielding of other sources limits the sensitivity of detecting low-intensity sources , eventually it can be compared to the penetration of the shielding by particularly intense external sources .

An additional drawback of the current probes on the market is to require a calibration step, which takes place periodically with a procedure requiring to expose the probe to a calibration source to guarantee that gain variations of electronics do not influence the detection ef fectiveness of the instrument .

The technical problem underlying the present invention is to provide a scintillation probe allowing to obviate the drawbacks mentioned with reference to the known art .

A possible solution idea consists in a scintillation probe of active collimator type , then capable of providing directly to the operator indications related not only to the 2D position (polar and azimuth angle ) , but even at the distance from the radiant source ( 3D) .

Generally, the scintillation probe according to the invention comprises at least one photodetector device and a plurality of scintillation crystals arranged around a central cavity forming a tubular geometry structure wherein a photo-detecting end is defined, thereat said at least one photodetector device is arranged, and an end opposite thereto , which can be manoeuvred by orienting it in direction of the assumed origin of the radioactive emission .

Herein and hereinafter, as tubular geometry structure a structure shaped like a rectilinear tube is meant , with a longitudinal axis extending along the structure , and an internal cavity extending from an end to the other one of the structure , unless , inside the cavity, crystals are provided obstructing it . As segment of the tubular geometry structure , in particular longitudinal segment , a tract of tubular geometry structure is meant , extending for a portion of its overall extension : therefore , the tubular geometry structure can be formed by a sequence of longitudinal segments .

The tubular geometry structure, and the longitudinal segments thereof , can consist o f several crystals with a shape producing, once interconnected, the final geometry of the structure . Then, each scintillation crystal has respective side and end interfaces , in contact with corresponding side and end interfaces of adj acent scintillation crystals . Then, it i s meant that the side interfaces connect crystals belonging to the same segment , whereas the end interfaces connect crystals of adj acent segments .

In a first aspect of the present invention, the technical problems linked to the detection of several sources and to the sel f-calibration are solved by a scintillation probe , of active collimator type , to detect the position di at least a radioactive source .

The probe comprises at least three first side scintillation crystals , shaped to form a f irst longitudinal segment of the tubular geometry structure, and provided with respective first mating side interfaces and in contact with each other .

The probe further comprises at least three second front scintillation crystals , shaped to form a second longitudinal segment of the tubular geometry structure adj acent to said first segment , and provided with respective second mating side interfaces in contact with each other .

Said first and second side and front crystals substantially form the side walls of said tubular geometry structure and, in a preferred embodiment, have the same crosssection, constant along the extension of the tubular geometry structure , to produce continuously smooth wall surfaces , without steps or gaps . In a more preferred embodiment , such sections are circular, with predetermined external and internal diameters .

It can be noted that the crystals designated as lateral are placed in a more approached position at the photodetecting end of the tubular geometry structure , than the crystals designated as frontal , which are provided to face the source of radio-emissions .

In the scintillation probe according to the present invention, said first and second crystals are optically insulated at the side walls thereof , i . e . at the side interfaces as defined above , by insulating optically with each other the crystals of the same longitudinal segment , whereas the other surfaces are transparent to the photons producible inside the crystals , in particular the end interfaces , thus allowing the photons produced in a longitudinal segment to pass in an adj acent segment .

Moreover, in the scintillation probe of the present invention, even the surface of the front crystals , which is at the end opposite to the photo-detecting end, i . e . the onboard terminal surface which is indicatively oriented towards the source of radio-emissions , is optically insulated in the field of the visible light .

In this way, the tubular geometry structure substantially acts as a wave guide wherein the photons generated by scintillation inside thereof are detected at one of the two ends , provided with an adequate photo-detector device .

Moreover, in the scintillation probe of the present invention, the first and second crystals of the first and of the second segment are staggered and in contact with each other, at respective end interfaces , so that each second crystal of the second segment is arranged in contact with at least two first crystals of the first segment .

Thanks to this structure , the possibility of detecting more than one source is given by the fact that all crystals , of which the probe consists , do not limit to detect the incident radiation, but they absorb it and they guide it in direction of the photodetector device , whi ch is capable of identifying the emission direction by comparing, in good substance, the intensity of the emissions of photons at the s ingle crystals of the first segment .

In a preferred embodiment of the present invention, the scintillation crystals are made of materials with high ef fective atomic number, and this allows that each crystal is hit almost exclusively by a primary radiation which is mostly absorbed without transmitting to adj acent crystals , at least in not signi ficant extent , distinguishable by the electronic instruments .

As primary radiation, the radiation coming directly from the source of radio-emissions is meant , which has not crossed any other scintillation crystal before hitting the monitored one .

In this way, with a photo-detecting sensor associated to each crystal , it is possible to identi fy the spectrometry of each crystal , comprising energy windows corresponding to a speci fic directional response . Through the analysis of these data by simple algorithms or by using the so- called arti ficial intelligence , it is possible to identi fy one or more sources .

The detection of several sources is a considerable advantage in all procedures in which there are several sources at the same time .

It is the case of the technique of the sentinel lymph node , wherein the radiation source is inoculated in the peri- areolar area or area proximal to the tumour, to simulate its physiological path towards the lymph node . Typically, the amount of inoculated radioactive is about 100 times higher than the one captured by the lymph node and this represents the maj or source of di sturbance in the surgical procedure . Moreover, frequently, several lymph nodes result to be capturing, which need all to be locali zed and removed . At last , in the laparoscopy surgery, the probe operates in a completely radioactive environment , wherein one has to reach the target by excluding di f ferent sites related to capturing tissues or organs .

Moreover, this feature is what allows to define the probe as an active collimator : each crystal has the double task of revealing the primary radiation, by allowing the identi fication of the direction of origin and to shield the other crystals which are along the same direction of origin of the (not primary) radiation . In the traditional scintillation probes the shielding is always performed with materials such as lead, which allow the shielding against non-primary radiations , but also hinder the probe detection capability .

As said before , the scintillation crystals with great capability of absorbing the radiations have high ef fective atomic number, in particular they can be made o f Cerium- doped Lutetium Orthosilicate ( LSO ( Ce ) Lu2SiOs : Ce ) or Cerium-doped Yttrium-Lutetium Orthosilicate ( LYSO LU₂ ( 1-x) Y₂xSiO₅ : Ce ) .

¹⁷⁶Lu is in turn radioactive , and it decays by emitting /? and y radiations . Despite this could apparently seem a disadvantage , instead is what allows the probe sel fcalibration, since the spectrometric signatures of the radiations due to the decay are known and, through a precise scheme for selecting the crystals , they allow to monitor possible calibration imbalances of the detection system, for example due to temperature variations .

The probe sel f-calibration possibility is one of the maj or advantages of the invention which will be described hereinafter, since it allows to have an always calibrated and reliable device even during the operation thereof under particularly critical conditions , such as the surgical environment .

In a second aspect of the present invention, the solution idea consists in a scintillation probe o f active collimator type , then capable of directly providing to the operator indications about not only the 2D position, but also about the distance from the radiant source . This feature is considerably important in surgery since , apart from providing an important indication about the surgery depth, avoids removing errors in case of overlayed lymph nodes . Such feature results to be particularly relevant in robotic surgery .

Said probe comprises , apart from the side and front crystals , a central oscillation crystal , included in the cavity of the tubular geometry structure .

The main advantage of the probe also comprising the central crystal lies in the fact of allowing a quick detection of the position in the 3D space of the radiant source during the surgical or laparoscopic intervention, by using a simple instrument for the operator, and with a small si ze .

In particular, said probe allows to calculate the relative distance between the probe and the radioactive source with a precision in the order of the millimetre .

In particular, the probe results to be suitable for the intra-surgery use , where rapidity and locali zation precision are fundamental requirements .

The so-constructed probe o f fers a sensitivity and high ef fectiveness for all other intra-surgical or laparoscopic procedures involving the locali zation of tumour tissues or lesions showing a high speci ficity to the radiopharmaceutical , in particular for the applications of radio-guided surgery .

Applications however linked to the in-vi vo locali zation of concentrations of a radiopharmaceutical in a human body are also possible , with the purpose of a quick locali zation thereof , for example aiming at a biopsy or a needle biopsy .

Alternative uses of the probe are obviously possible , to detect any radioactive source , for example with purpose of greater safety in sensitive areas such as the airport areas or in thermonuclear plants or in sites at risk of radioactive contamination, even to detect radioactive waste disposed of incorrectly or unsuitably . The present invention will be described hereinafter according to a preferred embodiment thereof , provided by way of example and not for limitative purpose with reference to the enclosed drawings wherein :

* figure 1 shows a perspective view of an embodiment of the probe according to the invention;

* figure 2 shows a perspective view of another embodiment of the probe according to the invention;

* figure 3 shows a perspective view of a further embodiment of the probe according to the invention;

* figure 4 shows a schematic view of the division into detection areas of the rear crystal and a possible arrangement of the photomultipliers ;

* figure 5 shows a schematic view of the division into detection areas of the rear crystal and another possible arrangement of the photomultipliers ;

* figure 6 shows a schematic view of the division into detection areas of the rear crystal and another possible arrangement of the photomultipliers ;

* figure 7 shows a schematic view of the detection unit ;

* figure 8 shows a schematic view of the probe the invention relates to , with the scintigraphic images obtained in di f ferent points in which the probe is irradiated by a collimated radioactive source ; and

* figure 9 shows a schematic view of the probe the invention relates to , wherein the azimuth and polar angles and an emitting source are shown .

According to a first embodiment of the present invention, with reference to figure 1 , a scintillation probe , of active collimator type , is designated as a whole with 1 .

Said active collimator type scintillation probe 1 allows to detect the 2D position of one or more radioactive sources 2 and comprises a plurality of scintillation crystals arranged to form a tubular geometry structure 4 with a central cavity N, one or more surfaces and one or more interfaces , wherein under surfaces the free portions of a crystal are meant and under interfaces the portion of a crystal in contact with respective portions of another crystal are meant .

Said plurality of scintillation crystals has at least three first side crystals 3 , shaped to form a first longitudinal segment of said tubular geometry structure 4 and with respective first side mating interfaces 7 , in contact with each other ; said first crystals 3 comprise a lower surface , proximal with respect to an operator, which defines a photo-detecting end, thereat a photodetector device of the scintillation probe is arranged .

Said plurality of scintillation crystals further has at least three second front crystals 5 , shaped to form a second longitudinal segment of the tubular geometry structure 4 , and with respective mating side interfaces 7 , in contact with each other, arranged at a distal end 12 of the tubular geometry structure 4 with respect to an operator, opposite to said photo-detecting end; said second crystals 5 comprise an upper surface 46 at said distal end 12 .

In this second segment , each second crystal 5 is arranged in contact with two first side crystals 3 o f the first segment and then adj acent to each other, with the respective mating end interfaces 8 , in contact with each other .

Said first and second side and front crystals 3 , 5 are optically insulated, in the field of the visible light , at the respective side interfaces 7 , of the upper surface 46 of each front crystal 5 , and then transparent at the respective end interfaces 8 and of the lower surface of said first side crystals 3 .

The probe 1 , according to this embodiment ( figure 1 ) , allows to identi fy the azimuth angle and the polar angle of at least a radioactive source . It is to be noted that in the present embodiment example, the first and second side and front crystals 3, 5, substantially form the side walls of said tubular geometry structure and have the same cross section, constant along the extension of the tubular geometry structure, to produce continuously smooth wall surfaces, without steps or gaps. Such sections are circular, with a pre-fixed external diameter and internal diameter.

The scintillation crystals of each segment are four, and they have the same angular span, i.e. 90°; the cross sections 9 of the single crystals have a circular arc geometry. Said crystals extend parallel to the central axis of symmetry X of the tubular geometry structure 4, between the two above-mentioned ends.

In these examples, the second crystals 5 have the same cross section 9 of the first crystals 3, but they have a smaller longitudinal length.

Preferably, in case of four first side crystals 3 and four second front crystals 5, the second crystals have the adjacent side interfaces 7 shifted with respect to the adjacent side interfaces 7 of the first crystals 3 by 45°, so as to symmetrically overlap on two side crystals 3 adjacent to each other.

This symmetrical arrangement of the crystals 3, 5 allows a simpler analysis of data, by speeding up the procedures for identifying at least a source.

According to some embodiments of the invention (figures 2, 3) , the scintillation probe 1, to detect, apart from the 2D position, the distance of a radioactive source 2, also comprises a scintillation central crystal 10 included in the cavity N of the tubular geometry structure 4.

The central crystal 10 occupies the whole cross space addressed thereto, thereby completely obstructing it, and then it has a disc-like shape with cross sizes substantially equal to those of the cavity N receiving it. In this preferred example, its disc-like shape is circular, and its diameter is substantially equal, except mechanical gaps , to the internal diameter of the cavity N of the tubular geometry structure 4 . Then, it comprises a peripheral interface 48 which is in contact with the first crystals of the first segment .

Said central crystal 10 is preferably placed close to the photo-detecting end 6 , inside the first segment , flush with its lower surface .

The central crystal 10 then has a free surface which is facing towards the end opposite to the photo-detecting end 6 , but such a surface is optically insulated like the end surface 46 .

The central crystal 10 has the purpose of detecting the incident radiation parallel to the axis of symmetry X of the probe 1 , and then it activates only when the probe 1 is facing the source 2 , by providing a photopeak of energy, for example , comprised between 30 and 700 keV .

According to other embodiments of the invention ( figure 2 , 3 ) , apart from the above-mentioned central crystal , the scintillation probe 1 comprises at least a third solid transversal crystal 11 , shaped so as to form a third segment of said tubular geometry structure 4 , arranged adj acent to said first segment at the photo-detecting end of the tubular geometry structure 4 , and in contact with respective interfaces of said f irst crystals 3 of the first segment and of the central crystal 10 .

Then, in this embodiment , the third crystal 11 has a shape of a circular disc with a diameter substantially equal to the external diameter of the first segment , and it is in contact with the crystals thereof and with the interface of the central crystal opposite to its optically insulated surface .

Said third cross crystal 11 is optically insulated at its own peripheral surface 44 , and then it is transparent on the interface at the lower surfaces of each first crystal 3 and of the central crystal 10 .

Advantageously, said cross crystal 11 can detect the rear sources 2 with respect to the orientation of the probe 1 , by allowing to remove the scintillation contribution of possible unwished sources 2 . Possible unwished rear sources 2 irradiate the crystals of the probe 1 l i ke all other sources 2 , but the presence of the third crystal 11 allows to quanti fy their contribution in terms of radiations and to filter it , through calculation algorithms , from that of the source of interest 2 .

According to additional embodiments of the invention ( figure 3 ) , the probe 1 further comprises at least even one precision scintillation crystal 14 lying on a portion of central crystal 10 , on the surface facing towards said distal end 12 of the probe 1 , to partially cover it .

Advantageously, the presence of this additional precision crystal 14 allows to optimi ze the alignment of the probe 1 with the source 2 , by detecting with still more precision the position of the source 2 with respect to the cavity N of the tubular geometry structure 4 .

For example , according to an embodiment wherein the probe 1 comprises four precision crystals 14 , it is possible to detect , with each one of them, a certain number of photons , proportional to the incident radiations . Depending upon the di f ference of photons detected on the di f ferent precision crystals 14 and of the mathematical relations used for calculating the angles , it is possible to refine the alignment of the source 2 with the axis of symmetry X of the tubular geometry structure 4 .

The precision crystals 14 are optically insulated on the side interfaces 7 mating to each other, on the cavity interface and on the distal surface, whereas they are transparent on the interface mating with the central crystal 10 .

Preferably, the above crystals 3 , 5 , 10 , 11 , 14 are all made of the same material , but each type of crystal has a respective scintillation feature and this can be obtained by using typologies of crystals with geometries di f ferent from each other . Under typologies:

• typology of side crystals 3;

• typology of front crystal 5;

• typology of central crystal 10;

• typology of cross crystal 11

• typology of precision crystal 14 are meant.

Alternatively, or together with the above-mentioned effect, it is possible that the feature of collecting the light varies from crystal to crystal, prearranging a photodetecting sensor 17 dedicated for each crystal of the type with the higher number of crystals and one at the central crystal 10.

The crystals 3, 5, 10, 11, 14 absorb y rays, with energy comprised between 30 keV and 700 keV, preferably between 30 keV and 200 keV, and the shape and size of the crystals 3, 5, 10, 11, 14 is defined to prevent a transmission of the radiation higher than 8% to other crystals 3, 5, 10, 11, 14 whereon said radiation is not incident directly.

Advantageously, by varying the size of the crystals by reason of the radiation attenuation length, the energy range can be extended until values beyond MeV's, without sensibly modifying the general operation features of the probe 1.

In order to allow a so considerable absorption of y radiations, the crystals 3, 5, 10, 11, 14 are of the type with high effective atomic number, preferably higher than 50. The crystals 3, 5, 10, 11, 14 can be made of Bismuth Germinate (BGO: Bi4Ge30i2 or Bii2GeC>22) or, Cerium-doped Lutetium Orthosilicate (LSO(Ce) Lu2SiOs:Ce) or, Cerium- doped Yttrium-Lutetium Orthosilicate (LYSO LU2 ( 1-x) Y2xSiOs : Ce ) or Cerium-doped Aluminium Gadolinium Gallium Garnet (GAGG:Ce) which have a light yield of about 12 and 30 photons/KeV (scintillation yield) , in case nf absorption of gamma radiation such as from a radio pharmaceutical containing ^99mTc, ¹³¹I , ^11]-In .

Optionally, due to reasons l inked to the required mechanical workability or for technological improvements of the scintillation features , such as the energy resolution, materials with a smaller ef fective atomic number are not excluded .

All these crystals 3 , 5 , 10 , 11 , 14 then have a high light yield .

As it consists of crystals 3 , 5 , 10 , 11 , 14 with a high ef fective atomic number, the structure 4 has the capability of shielding laterally its own interior .

In order that their correct operation is protected, all crystals of the same typology need to be optically insulated from each other .

According to some embodiments , ( figure 1 ) the central crystal 10 needs to be optically insulated on the surface facing towards said distal end 12 and on the peripheral interface 48 , whereas it is transparent on the lower surface .

According to other embodiments ( figure 3 ) the central crystal 10 is transparent even on the surface facing towards said distal end 12 .

According to some embodiments of the invention, the probe 2 also comprises a tubular scintillation crystal 15 , arranged inside said central cavity N, coaxial to the tubular geometry structure 4 so that its external surface mates with the internal surface 16 of said side and front crystals 3 , 5 , by reducing the s i zes of said central cavity N . The interface between the surfaces of the internal crystal 15 and of the side and front crystals 3 , 5 is optically insulated .

The advantage brought to the probe 1 , by the presence of the internal crystal 15, is that it allows to discriminate the radiations in the cavity N from the ones incident on the side crystals 3, allowing to detect at the same time at least a side source 2 and at least a front one.

In order to optically insulate the crystals, coatings are used which guarantee the diffuse reflection, for example with metal base, in particular Al, BaSCh, TiCt or white Teflon tape.

To the proximal end 6 of said tubular geometry structure 4, a photodetector device is coupled.

Said photodetector device can have, or cannot have, features of detecting the position, in reason of the more sophisticated and precise role in localizing multiple sources 2 present in the radiation field.

Given the position of the photodetector device, the first scintillation crystals 3, apart from having the task of detecting the direction of the source 2, also act as optical guide, so that the scintillation light emitted by any scintillation crystal 3, 5 is always guided on the photodetector device, to be able to be detected and to be able to detect the scintillation crystal which emitted it.

Said third scintillation crystal 11 is divided into at least four virtual crystals thereto four detection areas Z correspond and said photodetector device comprises at least a photo-detecting sensor 17 for each one of said detection areas Z. If present, the third scintillation crystal 11 acts as optical guide for all other first scintillation crystals 3, 5, 10, 14, 15.

According to the embodiments of the invention shown in figures 1, 2, 3, five detection areas Z, the four side areas Zl, Z2, Z3, Z4, are detected, they are at each one of the four first scintillation crystals 3, the fifth central area Z0 is at the central scintillation crystal 10, on each area at least a photo-detecting sensor 17 is placed. Each area also corresponds to five imaginary volumes into which the third scintillation crystal 11 is divided. The division of the third scintillation crystal 11 into five imaginary volumes, thereto different photodetecting sensors 17 correspond, allows to identify thp polar and azimuth angle of a possible source detected almost only by this third scintillation crystal 11. Even in this case, the differences between the amounts of detected photons and the used algorithms allow a quick identification of the 2D position of at least a source 2.

The selected number N of detection areas, which is designated as 5 in this example, can vary based upon the structure and the arrangement of the crystals in the probe 1.

According to the embodiment shown in figure 3, there can be eight detection areas Z, four side areas Zl, Z2, Z3, Z4 corresponding to the four first scintillation crystals and four central areas, corresponding to the four precision scintillation crystals 14.

In this embodiment there is a higher discretization of the third scintillation crystal 11 with respect to the embodiment of figure 2, by allowing a still more precise identification of the 2D position.

Alternatively, at the four precision scintillation crystals 14, one single detection area Z0 is defined thereto one single central photo-detecting sensor 17 corresponds, even this configuration guarantees the same precision in identifying the position of the source 2, since each precision scintillation crystal 14 creates a restricted light distribution, adjacent to one of the first scintillation crystals 3, a portion of this light due to the effect of the optical guide of the third scintillation crystal 11 is read by the corresponding photodetection side area Zl, Z2, Z3, Z4. The ratio between the two signals determined univocally the event in the precision crystal 14.

Preferably, to each side detection area Zl, Z2, Z3, Z4 two equal photo-detecting sensors 17 correspond.

Advantageously, the presence of two photo-detecting sensors 17 at the first scintillation crystals 3 allows to identify qualitatively the position of one source 2, placed at a polar angle between 10° and 170° even only bv displaying the scintigraphic images produced by the probe irradiated with a collimated source.

In fact, as illustrated in figure 8 if a collimated source irradiates only a second scintillation crystal 5, two scintigraphic spots are displayed in the image, since the light is channelled through two first scintillation crystals 3 thereto two photo-detecting sensors 17 correspond .

Then, the fact that the scintigraphic spots are two means that the source 2 has a polar angle between 0° and 10°, the possibility of identifying the photo-detecting sensors 17 generating said spots, identifies which one of the four second scintillation crystals 5 is irradiated and then the azimuth angle.

If a collimated source 2 has a polar angle, approximately between 10° and 20°, and then irradiates the contact area between a front crystal 5 and a side crystal 3, there are three scintigraphic spots: two thereof identifying the second scintillation crystal 5 and one thereof identifying the first scintillation crystal 3.

If a collimated source 2 has a polar angle, approximately between 10° and 170°, and then irradiates a first scintillation crystal 3 there will be one only one scintigraphic spot identifying the first scintillation crystal 3.

If a collimated source 2 has a polar angle, approximately between 170° and 180°, and then it irradiates the third scintillation crystal 11, there will be one or more scintigrafic spots, in particular there will be always one scintigraphic spot corresponding to the irradiated central photo-detection area Z0. The azimuth angle is measured with modes analogous to the previous ones.

The discretization of the probe 1 in the ways described in the different embodiments makes faster and easier the identification of the 2D position of the source with respect to the state of art. When the source 2 is aligned with the probe 1 there will be the scintigraphic spots of the second scintillation crystals 5 combined with the scintigraphic spot of the central scintillation crystal 10 or with the scintigraphic spots of the precision scintillation crystals 14 depending upon the embodiments .

Advantageously, the presence of the central scintillation crystal 10 only, or of the central scintillation crystal 10 in combination with the precision scintillation crystals 14 , thereto a photo-detecting sensor 17 or a photo-detecting sensor 17 per precision scintillation crystal 14 correspond, respectively, together with the second scintillation crystals 5 , allow to determine the relative distance between the probe 1 and a radioactive source 2 .

The used photo-detecting sensors 17 are of substantially conventional type , operating on the electronic multiplication or semiconductor principle ( SD Silicon Detectors , SDD Silicon Dri ft Detectors , ADD Avalanche Photodiodes and SiPM, Geiger discharge-based Silicon Photo-Multipliers ) .

The di f ferentiation between the types of scintillation crystals allows the signals obtainable through the emission of light photons to be on bands having di f ferent intensities . Therefore , a suitable detection unit 18 , which will be described hereinafter, can distinguish which one of the scintillation crystals 3 , 5 , 10 , 11 , 14 , 15 emits photons and to what extent , thus by providing a spectrometric indication (peak related to the specific energy of the gamma ray) and a vectorial indication of the direction of origin of the ioni zing radiation .

In case of a free source , emitting on the whole solid angle , each involved scintillation crystal will record a number of detected gamma events proportional to its own solid viewing angle of the source . Each produced scintigraphic spot allows to determine the number of gammas detected by the speci fic scintillation crystal in a determined time interval . The weighed average of the events recorded by all scintillation crystals involved in the reference system of the probe 1 , allows with good precision to determine the polar and azimuth angles . The precision of the measurement will depend upon the number of the involved scintillation crystals and upon the statistics of the detected events .

In this way, the probe 1 has the peculiarity of detecting the direction of origin/emission of the radiation even in absence of defining the direction of detecting the radiation, contrary to many imaging apparatuses such as the scintigraphic cameras .

Once identi fied the direction of origin of the radiations , it is possible to move the probe 1 as far aligning it with the source 2 to calculate the di stance between the probe 1 and the source 2 .

Thanks to the presence of the second scintillation crystals 5 and of the central scintillation crystal 10 or of the precision scintillation crystals 14 , the alignment of the probe 1 is uniquely identi fiable by the balancing of the counts of the second scintillation crystals 5 and/or of the precision scintillation crystals 14 . The precision level of the detected counts is guaranteed by a specific spectrometric signature of each scintillation crystal calibrated in advance to the gamma emission energy of the source 2 .

Once the probe 1 is aligned, one calculates the ratio between : the solid angle between the probe 1 and the central scintillation crystal 10 and the solid angle between the probe 1 and the second scintillation crystals 5 , according to the equation asc D = — sf

Once this ratio is known, the detection unit 18 calculates the distance between probe 1 and the source 2 with an error lower than 1 mm .

What described for the central scintillation crystal 10 is also true for the precision scintillation crystals 14 which however provide four pieces of information which suitably combined define a solid angle allowing to align the source 2 to the axis of symmetry X o f the tubular geometry structure 4 in a still more precise way with respect to what can be obtained with the central scintillation crystal 10 only .

The above-described scintillation probe 1 can belong to an intra-surgery instrument .

Said intra-surgery instrument does not require additional components except a handle of conventional type and the connections between the photodetector device and a detection unit 18 including the detection software .

Then, it could be easily handled, and, thanks to weight and volume , it can be held in one hand .

The above-described probe 1 could have an overall diameter comprised between 10 mm and 50 mm, with a thickness of the tubular geometry structure 4 from 2 to 20 mm and a maximum height of approximately 100 mm .

The thickness of the second scintillation crystals 5 could be for example 3 a 15 mm .

The thickness of the third scintillation crystal 11 could be for example of 3 a 15 mm .

The thickness of the central scintillation crystal 10 could be for example of 3 a 25 mm so that the front free portion of the cavity N has a height of 10 a 75 mm .

The thickness of the precision scintillation crystals 14 could be for example of 0 . 5 a 5 mm and their shape with circumference wedge geometry .

The thickness of the internal scintillation crystal 15 could be for example of 0 . 5 a 5 mm .

The photodetector device comprises a plurality o f photodetecting sensors or photo-multipliers 17 in the solid state of grouped SiPM type , according to the embodiment s of figures 1 , 2 , 3 , in five detection areas Z related to the above-described example . Each detection area Z could consist of one or more photo-multipliers 17 connected to each other parallelly . The photodetector device further includes a temperature sensor 28 used to compensate the bias voltage of the photo-multipliers 17 .

The photo-multipliers 17 convert the light photons emitted by the scintillation crystals 3 , 5 , 10 , 11 , 14 , 15 of the probe 1 into electric charge proportional to the number of incident photons .

With reference to figure 7 , the detection unit 18 implements the detection function and the proces sing of y events thanks to the signals generated by the abovedescribed crystals of the probe 1 . It is described with reference to five detection areas Z , but it could be modi fied upon varying the number N of detection areas .

The detection unit 18 comprises one charge pre-ampli fier 19 for each detection area Z . Each pre-amplifier 19 is connected in direct coupling to an analog-to-digital converter 20 (ADC ) with a sampler of Sampl e & Hold type to keep constant the analog value for the time required to the converter or to other subsequent circuits to perform procedures on the signal , that is in the present case to implement the conversion of the light signal in digital format .

In this way, upon each gamma event , a detector of event 22 that is of pulses , which receives a pulse when a radiation peak y is detected, generates a start signal which is received by a programmable logic device 21 , known as Fi eld Programmabl e Ga te Array or FPGA, which in this regard comprises an analog-digital accelerator device 23 , to synchroni ze the conversion of the signals on the pulse peak and then to acquire the five data from the solid- state detectors 17 , in digital format .

FPGA 21 comprises an area classi fier and an event counter 24 which, by using the f ive digital values , thanks to an algorithm integrated in the hardware , allows to define on which crystal ( s ) of the probe 1 a gamma photon was absorbed . For events absorbed on the third scintillation crystal 11 , the algorithm allows to define five virtual crystals corresponding to the surfaces of the central scintillation crystal 10 and of the first scintillation crystals 3 . The division of the transversal crystal 11 , having planar shape , into five virtual crystals allows to use even the distribution of the events on this scintillation crystal to calculate the pos ition of the source 2 .

FPGA 21 comprises a multi-channel analyser 26 (MCA) , which in the present embodiment example has fourteen channels , that is one for each physical or virtual crystal .

I f the event has been converted into light inside one single (physical or virtual ) crystal , it is increased by the event counter 24 and sent to the multi-channel analyser 26 . I f the event has been absorbed on several physical or virtual crystals , due to an ef fect such as Compton ef fect or the like , or in presence of several coincident events , the event is discarded and no more considered for the purpose of navigation and locali zation of the source 2 . By a user interface , which will be described later, it is possible to set the energy windows of interest for each one of the fourteen channels of the multi-channel analyser 26 . In this case , the event counter 24 , used for the subsequent calculation of the position of the source 2 , is increased only i f the charge is inside the energy window of interest .

FPGA 21 further acquires the reading of a temperature sensor 28 integrated on the photodetector device , and it comprises a module 25 for managing and decoding the commands received by a microcontroller 34 , which will be described later, and a serial analog multiplexer ( SPI ) 27 .

FPGA 21 is also connected to a three-axis accelerometer 29 , to a memory unit 30 , to a speaker 31 and to an aptic actuator 32 .

Through FPGA 21 , the microcontroller 34 adj usts the output voltage of a voltage-controlled power supply (Vbias) 33, to compensate the bias voltage of the photodetectors 17 based upon the temperature detected by the sensor 28.

Moreover, still through FPGA 21, the microcontroller 34 adjusts the offsets of the charge pre-amplifiers 19 through an offset adjustment module 42.

Thanks to the presence of the speaker 31 and of the aptic actuator 32, in turn connected to a driver for speaker and aptic actuator 52, under the guidance of a navigator and suitable tactile and/or sound signals which will indicate up, down, right, left, the operator will move the probe 1 until reaching the position in which it is in front of the source 2.

The above-mentioned microcontroller 34 is connected to said programmable logic device 21 (FPGA) , through a diode digital BUS 54 (Digital Input Output BUS) and a serial peripheral interface (SPI) 55.

The microcontroller 34 comprises in detail an interface module 35 to implement a connection, in particular of wireless (Wi-fi™, Bluetooth™, etc.) type, a first memory module 36 arranged to contain a self-calibration software, a second memory module 38 arranged to include a software for managing the navigation and data processing remotely, a first set of drivers 57 for controlling the integrated circuits (accelerometer, memory, etc.) and a second set of drivers 37 for controlling the diode (Digital Input Output driver) and serial (SPI driver) interfaces, a WEB server 39 to implement a graphic interface on a computer connected to such detection unit 18, a driver for a command line interface 40, for the management and configuration of the device through a USB port, another type of equivalent port or through telnet connection, a Real Time Clock (RTC) 43 for the time keeping and a module for managing the power supply and battery 41, connected to a battery 51, preferably with wireless charging.

During the steps of approaching to the source 2, the relative variation of the counts with the inverse of the square of the distance , by the detection unit 18 , will allow to provide even the remaining distance and the final coordinates of the source 2 itsel f .

The so constructed probe 1 can then provide very high counting accruals , analogously to existing apparatuses which however do not give information about the direction of origin of the radiation, and at least one hundred times higher than imaging systems such as small gamma cameras for scintigraphy; moreover, said probe 1 is capable of sel f-calibrating, in fact , in a second aspect , the present invention relates to a sel f-calibrating method of the scintillation probe 1 .

The sel f-calibrating method of a scintillation probe relates to a category of probes of the previously described type , which are provided with central scintillation crystal 11 in their cavity 4 , and wherein the first and the second scintillation crystals 3 , 5 and the central crystal 11 are made of Cerium-doped Lutetium Orthosilicate ( LSO ( Ce ) Lu2SiOs : Ce ) or Cerium-doped Yttrium-Lutetium Orthosilicate ( LYSO LU2 a-x) Y2xSiOs : Ce ) ; the sel f-calibrating method, which in case can be performed thanks to a sel fcalibration software contained in the first memory module 36 in the microcontroller 34 of the detection unit 18 , provides to position the probe inside a container which shields the background environmental radiations .

The scintillation crystals wi ll self-emit y and |3 radiations , due to ¹⁷⁶Lu decay, which will be detected for each scintillation crystal by the detection unit 18 .

The detection unit 18 acquires the gamma events of the sel f-emission of the scintillation crystals due to ¹⁷⁶Lu decay by identi fying the spectrometric signatures thereof for each scintillation crystal .

The algorithm implemented in the detection unit 18 identi fies the spectrometric peaks of the characteristic energies of ¹⁷⁶Lu decay, and it sel f-calibrates in real time the probe 1 by adj usting gain and of fset , to bring the peaks back to the corresponding channel values . Such method, apart from simpli fying the procedures for checking and calibrating the probe 1 allows to veri fy the correct functionality thereof and the maintaining of the quality of the optical coupling between the scintillation crystals and the detection unit 18 .

An additional advantage of the present invention is that the normal operation, the detection unit 18 processes the counts of the gamma events detected by each scintillation crystal by varying dynamically the integration time based upon the rate of detected gamma events , and by calculating through dedicated algorithms the azimuth and polar angles of at least one source 2 and, for some embodiments , its distance from the probe 1 when locali zed .

The so-processed data are made available in numeric and/or graphic form through the interface module 35 and in case integrated by sound and tactile signals to speed up the locali zation of the source 2 .

To improve the precision of the navigation, centering and depth data it possible to use an option to increase progressively the integration time of gamma events when the probe 1 is kept still , in any position by us ing the data detected by the three-axis accelerometer 29 . When the probe 1 is moved, the integration time is immediately reset to the previous value .

With the suitable use manual skill and a navigation ability, the system can detect radiation sources with a precision up to 1 mm, with so high ef fectiveness as to succeed in locali zing them in a period of time variable between fractions of second and few tens of seconds , in reason of the si zes of the viewing field and of the radioactivity existing in each single source .

A so-constructed probe 1 could also constitute a system for guiding the direction connected to a camera which then can visually make to locali ze even dynamically a radioactive obj ect ( a person, a moving suitcase ) .

A probe 1 comprising said detection unit 18 allows to identi fy multiple radioactive sources 2 , preferably bv availing of artificial intelligence.

In case of fixed apparatuses, a triangulation system based upon three apparatuses positioned in different points can result to be particularly effective. To the above-described scintillation probe and use method thereof, a person skilled in the art, with the purpose of satisfying additional and contingent needs, could introduce several modifications and variants, however all comprised within the protective scope of the present invention, as defined by the enclosed claims.

Claims

1. A scintillation probe (1) , of active collimator type, to detect the position of one or more electromagnetic radiation sources (2) produced by nuclear radioactive decay or the like, comprising at least one photodetector device and a plurality of scintillation crystals arranged around a central cavity (N) forming a tubular geometry structure (4) wherein a photo-detecting end is defined, thereat said at least one photodetector device is arranged, and end (12) opposite thereto, each scintillation crystal of said plurality having respective side and end interfaces, in contact with corresponding side and end interfaces of adjacent scintillation crystals, and other free surfaces, wherein said plurality of scintillation crystals comprises:

• at least three first side scintillation crystals (3) , shaped so as to form a first longitudinal segment of the tubular geometry structure (4) determining a central cavity (N) , and provided with respective first mating side interfaces (7) in contact with each other;

• at least three second front scintillation crystals (5) , shaped so as to form a second longitudinal segment of the tubular geometry structure (4) adjacent to said first segment, and provided with respective second mating side interfaces (7) in contact with each other; wherein the first and the second scintillation crystals (3, 5) of the first and of the second segment are staggered and in contact with each other, at respective end interfaces (8) , so that each second scintillation crystal (5) of the second segment is arranged in contact with at least two first scintillation crystals (3) of the first segment, and wherein said first and second scintillation crystals (3, 5) are optically insulated, in the field of the visible light, with each other, at the respective side interfaces (7) , and at the surface of the second scintillation crystals (5) forming said opposite end (12) .

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2. The scintillation probe (1) according to claim 1, wherein the first and second scintillation crystals (3, 5) are made of the same material.

3. The scintillation probe (1) according to any one of the preceding claims, comprising at least a central scintillation crystal (10) , included in said central cavity (N) so as to completely obstruct it, and optically insulated at a peripheral interface thereof (48) which is in contact with the first scintillation crystals (3) of the first segment, thereby the scintillation probe (1) is arranged to detect a position in a 3D space of a radioactive source (2) , calculating the distance thereof.

4. The scintillation probe (1) according to any one of the preceding claims, wherein, in the first and second scintillation crystals (3, 5) , the absorption of y radiations, with energy comprised between 30 keV and 700 keV, is provided to prevent a transmission of an incident radiation portion higher than 8% of the overall incident radiation in a crystal to other adjacent crystals.

5. The scintillation probe (1) according to any one of claims 1 to 3, wherein first and second scintillation crystals (3, 5) are made of materials absorbing at least 70% of incident radiations y with energy comprised between 30 keV and 200 keV, and not lower than 20% for radiations with higher energies.

6. The scintillation probe (1) according to any one of claims 1 to 3, wherein first and second scintillation crystals (3, 5) are of the type with high effective atomic number, in particular higher than 50, preferably made of a crystalline material selected from a group consisting of: Bismuth Germinate 20 (BGO: Bi4Ge30i2 or Bii2GeC>22) , Cerium-doped Lutetium Orthosilicate (LSO(Ce) Lu2SiOs:Ce) , Cerium-doped Lutetium-Yttrium Orthosilicate (LYSO LU2 (i-x) Y2xSiOs : Ce ) , Cerium-doped Aluminium Gadolinium Gallium Garnet (GAGG:Ce) .

7. The scintillation probe (1) according to any one of the preceding claims, wherein the first side scintillation

30 crystals (3) have a cross section (9) having respective arc of circumference with the same angular extension, extending longitudinally and parallelly to a central axis of symmetry (X) of said tubular geometry structure (4) .

8. The scintillation probe (1) according to claim 3, comprising at least one third solid transversal scintillation crystal (11) , shaped so as to form a third segment of said tubular geometry structure (4) , arranged adjacent to said first segment at the photo-detecting end of the tubular geometry structure (4) , and in contact with respective interfaces of said first crystals (3) of the first segment and of the central crystal (10) , said third scintillation crystal (11) being optically insulated at its own peripheral surface (44) .

9. The scintillation probe (1) according to claim 8, wherein said third scintillation crystal (11) is divided into at least four virtual crystals, thereto four respective detection areas (Z) of the detection end correspond, the photodetector device comprising at least a photo-detecting sensor (17) for each one of said detection areas (Z) .

10. The scintillation probe (1) according to any one of the preceding claims, comprising at least one precision scintillation crystal (14) lying in its surface facing towards said opposite end (12) to cover it partially, to optimize the alignment of the probe (1) with the source (2) .

11. The scintillation probe (1) according to any one of the preceding claims, comprising an additional tubular scintillation crystal (15) , arranged inside the central cavity (N) of the tubular geometry structure (4) , extending coaxially on the whole length thereof, so as to be in contact with the first and the second crystals (3, 5) of the first and of the second segment, by forming a respective interface which is optically insulated.

12. The scintillation probe (1) according to any one of the preceding claims, wherein the scintillation crystals of the tubular geometry structure (4) have a scintillation and/or light diffusion feature different from the scintillation and/or light diffusion feature of other scintillation crystals of the tubular geometry structure (4) .

13. The scintillation probe (1) according to any one of the preceding claims, comprising a detection unit (18) which comprises:

• at least one charge preamplifier (19) for each photodetecting sensor (17) of the photodetector device;

• an analog-to-digital converter (20) for each photodetecting sensor (17) ;

• a FPGA (21) and a microcontroller (34) wherein a detection software for reading the digital data and the processing thereof is implemented;

• a graphic interface and data transmission module (35) ; and

• a feeding system (41) .

14. The scintillation probe (1) according to claim 13, wherein the graphic interface module (35) , through said detection software, is arranged to set the energy windows of interest for each (physical or virtual) crystal thereto a respective MCA (26) corresponds, to identify the spectrometric signature of the crystals irradiated by at least a source (2) .

15. The scintillation probe (1) according to claim 13 or 14, wherein the detection unit (18) , through the detection software, increases progressively the integration time of gamma events in the area classifier and event counter (24) , when the probe is kept still in any position by using the data detected by the three-axis accelerometer (29) whereas, when the probe (1) is moved, the integration time is automatically re-set by the detection software to the previous value.

16. The scintillation probe (1) according to any one of claims 13 to 15, wherein in the microcontroller (34) a self-calibrating software (36) is implemented.

17. The self-calibrating method of a scintillation probe (1) according to claim 3, wherein the first, second and central scintillation crystals (3, 5, 10) are made of Cerium-doped Lutetium Orthosilicate (LSO(Ce) Lu2SiO5:Ce) or Cerium-doped Yttrium-Lutetium Orthosilicate (LYSO Lu2 ( 1— x) Y2xSiO5 : Ge) , comprising the following steps of: a) positioning the probe (1) inside a container shielding the external radiations; b) acquiring the self-emitting radiations of ¹⁷⁶Lu, which will be detected, for each one of the first, second and central scintillation crystals (3, 5, 10) ; c) identifying the energy peaks characteristic of ¹⁷⁶Lu for each one of the first, second and central scintillation crystals (3, 5, 10) ; d) correcting, through a dedicated algorithm, the gains of the charge preamplifiers (19) and the adjustments of the offsets (42) to align the energy peaks of the spectra of the first crystals (3) and of the central crystal (10) to the pre-established channel values; e) verifying the coherence of the energy spectra of the first, second and central scintillation crystals (3, 5, 10) ; and f) identifying, through an analysis of the spectra, possible optical coupling anomalies for each one of the first, second and central scintillation crystals (3, 5, 10) and possible photomultipliers thereof.

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