Periodic Reporting for period 1 - Open-Imaging (Open Geometry PET, with 150ps TOF Resolution, for Real Time Molecular Imaging)
Reporting period: 2022-04-01 to 2023-09-30
Positron Emission Tomography (PET) provides functional information that allows measuring changes in metabolic processes. While PET market is constantly growing, its demand for guiding medical interventions with real-time images, such as radiation and hadron therapy, biopsy guidance in breast and prostate cancer, and assessing myocardium viability inside the operating room in cardio-surgery is still largely unexplored. In these cases, it is essential to design a scanner that enables access to the body of the interventional instruments, while maintaining high sensitivity and resolution to guide the intervention accurately. Nowadays, all commercial scanners use a closed geometry with a ring shape that does not fulfil the desired demands. The solution is an innovative open imaging system that consists of two large panel detectors (26x26 cm2), allowing flexible and adaptable organ exploration in surgical procedures. This design makes it possible to place the detectors closer to the patient body, increasing the sensitivity and reducing the radiation dose compared to commercial scanners.
Moreover, the use of time of flight (TOF) information in the image reconstruction process plays a crucial role in reducing image artifacts due to the gaps in open geometries. When the geometrical configuration of a PET system is open, some angular projections are missing in the data acquisition process. This lack of information means that the reconstructed image is typically stretched in one direction. However, the improvement in TOF resolution reduces the emission probability range, resulting in a strong suppression of these image artefacts.
Open-imaging PET opens new venues in molecular imaging, such as low radiation dose breast cancer diagnosis, therapy guidance and follow-up, real-time imaged-guided surgery and radiation therapy, immune therapy monitoring and in-vivo tracking of a small number of cells throughout the body.
Moreover, the use of time of flight (TOF) information in the image reconstruction process plays a crucial role in reducing image artifacts due to the gaps in open geometries. When the geometrical configuration of a PET system is open, some angular projections are missing in the data acquisition process. This lack of information means that the reconstructed image is typically stretched in one direction. However, the improvement in TOF resolution reduces the emission probability range, resulting in a strong suppression of these image artefacts.
Open-imaging PET opens new venues in molecular imaging, such as low radiation dose breast cancer diagnosis, therapy guidance and follow-up, real-time imaged-guided surgery and radiation therapy, immune therapy monitoring and in-vivo tracking of a small number of cells throughout the body.
We have designed and optimized the PET detector module (WP2) by proving and selecting all its components. In particular, we have tested Silicon PhotoMulitiplier (SiPMs) arrays from various manufacturers (BroadCom, Hamamatsu) and chosen the ones with the best results in terms of timing resolution and quantum efficiency. We have also validated multiple configurations of scintillators from two providers (EPIC and TACrystals), looking at temporal resolution as a critical parameter. We have developed our own Front-End readout electronic boards (WP3) and implemented the Data Acquisition System from PETsys (Portugal). The software for DAQ, Image Reconstruction and User Interface has been developed (WP4). Two modules have been assembled and tested (WP5) in terms of spatial, energy and timing resolution. The full system has been integrated and characterized (WP6). The project has been successfully managed (WP1) and several European companies have shown their interest in the results for exploitation (WP7).
The sensor block, with the aforementioned scintillators and detectors, and appropriately encapsulated in a protective casing, forms a stackable sensor module (5x5 cm2) that allows the capabilities of the technology to be validated through only a pair of modules facing each other, while providing the versatility of forming larger sensor blocks by simply stacking basic units.
Preliminary results were presented at the 2023 IEEE Nuclear Science Symposium, Medical Imaging Conference, 4-11 Nov. 2023, Vancouver, Canada. The abstract, “First steps towards a double-paddle-TOF-PET detector”, was published in the summary of the conference.
Further preliminary results, including simulation of a full two panel system, have been sent for publication to the “European Journal of Nuclear Medicine and Molecular Imaging (EJNMMI)”, Physics section: “Design and Proof of Concept of a double-panel TOF-PET system”, Gonzalez-Montoro, …, J.M. Benlloch.
Laboratory tests have been carried out with two detector modules to validate the exceptional temporal response features. Final experimental results at the laboratory, not yet published, from coincident events of both detector modules show Coincidence Time Resolution (CTR) below 180 picoseconds, which allows us the development of a highly sensitive and real-time PET imaging device.
In summary, during the development of the Open Imaging project, the viability of the proposed technology was demonstrated through a proof of concept. We have reached a new technological milestone enabling an important advance in PET technology, which can be materialized in the improvement of multiple types of equipment.
The sensor block, with the aforementioned scintillators and detectors, and appropriately encapsulated in a protective casing, forms a stackable sensor module (5x5 cm2) that allows the capabilities of the technology to be validated through only a pair of modules facing each other, while providing the versatility of forming larger sensor blocks by simply stacking basic units.
Preliminary results were presented at the 2023 IEEE Nuclear Science Symposium, Medical Imaging Conference, 4-11 Nov. 2023, Vancouver, Canada. The abstract, “First steps towards a double-paddle-TOF-PET detector”, was published in the summary of the conference.
Further preliminary results, including simulation of a full two panel system, have been sent for publication to the “European Journal of Nuclear Medicine and Molecular Imaging (EJNMMI)”, Physics section: “Design and Proof of Concept of a double-panel TOF-PET system”, Gonzalez-Montoro, …, J.M. Benlloch.
Laboratory tests have been carried out with two detector modules to validate the exceptional temporal response features. Final experimental results at the laboratory, not yet published, from coincident events of both detector modules show Coincidence Time Resolution (CTR) below 180 picoseconds, which allows us the development of a highly sensitive and real-time PET imaging device.
In summary, during the development of the Open Imaging project, the viability of the proposed technology was demonstrated through a proof of concept. We have reached a new technological milestone enabling an important advance in PET technology, which can be materialized in the improvement of multiple types of equipment.
Detailed simulation studies performed of the full final system, with PET panel detector dimensions of 256x256 mm, demonstrate higher sensitivities (in the order of 2%) than most whole-body commercial systems (around 1%), allowing real time imaging of the organs for image guided interventions and therapy.
Furthermore, the “Open Imaging” PET system developed has obtained excellent TOF resolution (below 180ps) in the laboratory. The introduction of TOF information increases the effective system’s sensitivity, through Signal to Noise Ratio improvement, and compensates for the limited angle tomography of the two-panel system.
“Open Imaging” PET has several potential clinical impacts:
• Allows performing interventional and clinical procedures such as Radio or Proton therapy, biopsy, ablations, paediatric imaging, personalised therapy, post-therapy assessment, etc. PET imaging can give a very accurate tissue biopsy of the active parts of cancer, avoiding false negatives from standard biopsy procedures.
• Adaptive PET geometry to patient anatomy, optimizing system sensitivity (image quality) and improving patient comfort.
• Compatible with multiple organs, breast, chest wall, axilla, heart, prostate.
• Reduced administered radiotracer dose (20%) and shorter scan time (2-3 min) thanks to higher sensitivity. This translates into patient comfort and faster imaging capability, significantly increasing the number of patients scanned per year, shortening the waiting lists.
• Allows imaging breast in different directions: anteroposterior oblique, craniocaudal, mediolateral, oblique mediolateral, lateromedial, oblique lateromedial, chest wall and axilla, thus covering all breast sites and for most of the world's populations.
• The small size of the system makes it easy to deploy and portable, as it does not require large spaces for installation. A cost reduction will be possible due to silicon photosensors and proprietary signal reduction electronics (Patent ES2939157A1).
• Avoids claustrophobia in patients thanks to its open geometry and reduces patient-size dependence.
• Facilitates new approaches in image reconstruction due to outstanding TOF resolution, such as the combined estimation of emission and attenuation, reducing limited-angle artefacts, in partial-ring and non-cylindrical systems.
• Allows classification of complex lesions and therapeutic follow-up.
• Guides to localize a target: Biopsy of non-visualized lesions or heterogeneous lesions.
• Allows validation of new molecular imaging PET tracers with pathology.
• Provides tissue analysis to confirm a target has been reached.
Furthermore, the “Open Imaging” PET system developed has obtained excellent TOF resolution (below 180ps) in the laboratory. The introduction of TOF information increases the effective system’s sensitivity, through Signal to Noise Ratio improvement, and compensates for the limited angle tomography of the two-panel system.
“Open Imaging” PET has several potential clinical impacts:
• Allows performing interventional and clinical procedures such as Radio or Proton therapy, biopsy, ablations, paediatric imaging, personalised therapy, post-therapy assessment, etc. PET imaging can give a very accurate tissue biopsy of the active parts of cancer, avoiding false negatives from standard biopsy procedures.
• Adaptive PET geometry to patient anatomy, optimizing system sensitivity (image quality) and improving patient comfort.
• Compatible with multiple organs, breast, chest wall, axilla, heart, prostate.
• Reduced administered radiotracer dose (20%) and shorter scan time (2-3 min) thanks to higher sensitivity. This translates into patient comfort and faster imaging capability, significantly increasing the number of patients scanned per year, shortening the waiting lists.
• Allows imaging breast in different directions: anteroposterior oblique, craniocaudal, mediolateral, oblique mediolateral, lateromedial, oblique lateromedial, chest wall and axilla, thus covering all breast sites and for most of the world's populations.
• The small size of the system makes it easy to deploy and portable, as it does not require large spaces for installation. A cost reduction will be possible due to silicon photosensors and proprietary signal reduction electronics (Patent ES2939157A1).
• Avoids claustrophobia in patients thanks to its open geometry and reduces patient-size dependence.
• Facilitates new approaches in image reconstruction due to outstanding TOF resolution, such as the combined estimation of emission and attenuation, reducing limited-angle artefacts, in partial-ring and non-cylindrical systems.
• Allows classification of complex lesions and therapeutic follow-up.
• Guides to localize a target: Biopsy of non-visualized lesions or heterogeneous lesions.
• Allows validation of new molecular imaging PET tracers with pathology.
• Provides tissue analysis to confirm a target has been reached.