Challenges in Acquiring Clinical Simultaneous SPECT-MRI on a PET-MRI Scanner

The INSERT is the world’s first clinical SPECTMRI brain imaging system based on scintillation detectors with a SiPM readout. Here we demonstrate its use within a clinical MRI environment for the first time. Using a standard transmit-receive head coil, and with an appropriate selection of a custom MRI sequence (GRE), we overcome mutual interference. The INSERT and its bulky 50 kg tungsten collimator introduce magnetic field inhomogeneity. Due to the specific MRI-compatible collimator design, inhomogeneity is compensated by shimming, leading to simultaneous acquisition. We process the SPECT data acquired alongside the MRI sequence to evaluate the SPECT system performance and the impact of the MRI. Finally, we present a set of simultaneous SPECT-MRI acquisitions, demonstrating multimodal imaging capabilities, albeit with a limited MRI sequence

Handheld Magnetic-Compliant Gamma-Ray Spectrometer for Environmental Monitoring and Scrap Metal Screening

Spotting radioactive material in waste is of paramount importance for environment protection. This is particularly challenging when orphan sources are hidden in scrap metal that shields their activity from the traditional detectors in the portals scanning incoming trucks. In order to address this issue, we present a wireless and compact SiPM-based gamma spectrometer compatible with strong magnetic fields (0.1 T) to be installed in the bore of the lifting electromagnets to scan reduced volumes of metal and thus achieve higher sensitivity. The microcontroller-based instrument provides 11% energy resolution (at 662 keV), an energy range from 60 keV to 1.5 MeV, a max. count rate of 30 kcps, a weight <1 kg, and a power consumption <1 W. The results of its extensive characterization in the laboratory and its validation in the field, including operation in a scrap yard as well as on a drone, are reported

SITH: a 16-channel ASIC for SiPMs Readout in Hadrontherapy Applications

In hadrontherapy treatments, charged particles deposit a high and localized dose in the tumor volume. Detection of secondary radiations like Prompt Gammas (PG) can be used to monitor the dose profile falloff position, increasing the precision of this technique. In this work we present the design of SITH: an ASIC developed for the readout of Silicon Photomultipliers (SiPMs) coupled with scintillators used in this application. PG characteristics set specific requirements for the front-end electronics such as the capability to process up to 5nC input charge (energy up to 8MeV), timing resolution better than 1ns (e.g. for scattering correction), multiple triggering logic and potential for neutron/photon discrimination. We report an overview of the principal electronic stages and simulation results

Challenges in Acquiring Clinical Simultaneous SPECT-MRI on a PET-MRI Scanner

The INSERT is the world's first clinical SPECT-MRI brain imaging system based on scintillation detectors with a silicon photomultiplier readout. Here, we demonstrate its use within a clinical MRI environment for the first time. Using a standard transmit-receive head coil, and with an appropriate selection of a custom MRI sequence (GRE), we overcome mutual interference. The INSERT and its bulky 50kg tungsten collimator introduce magnetic field inhomogeneity. Due to the specific MRI-compatible collimator design, inhomogeneity is compensated by shimming, leading to simultaneous acquisition. We process the SPECT data acquired alongside the MRI sequence to evaluate the SPECT system performance and the impact of the MRI. Finally, we present a set of simultaneous SPECT-MRI acquisitions, demonstrating multimodal imaging capabilities, albeit with a limited MRI sequence

First Simultaneous Acquisition of a Clinical SPECT-MRI Brain INSERT

The INSERT (INtegrated SPECT/MRI for Enhanced stratification of brain tumours in Radio-chemoTherapy) is currently the only MRI-compatible SPECT stationary system for clinical application, in particular for brain multimodal imaging with an inner bore of 28 cm and a field of view of 20 cm (transaxial) × 10 cm (axial). The intrinsic spatial resolution is 1 mm and the extrinsic one is 10 mm. This modular scanner fits in an unmodified MRI scanner and is a scale-up of a smaller preclinical version, whose mutual compatibility with MRI was extensively characterized. It is composed of 20 detection modules (with 8-mm thick CsI:Tl scintillators of 5 cm 10 cm area read by an array of SiPM) and a massive multi-mini×slit-slat collimator, realized in tungsten. Here we report the first demonstration of successful simultaneous SPECT/MRI acquisition of phantoms (hot rods) using a commercial transceiver coil in a Siemens Biograph mMR scanner

Detection and discrimination of neutron capture events for NCEPT dose quantification

Neutron Capture Enhanced Particle Therapy (NCEPT) boosts the effectiveness of particle therapy by capturing thermal neutrons produced by beam-target nuclear interactions in and around the treatment site, using tumour-specific 10B or 157Gd-based neutron capture agents. Neutron captures release high-LET secondary particles together with gamma photons with energies of 478 keV or one of several energies up to 7.94 MeV, for 10B and 157Gd, respectively. A key requirement for NCEPT’s translation is the development of in vivo dosimetry techniques which can measure both the direct ion dose and the dose due to neutron capture. In this work, we report signatures which can be used to discriminate between photons resulting from neutron capture and those originating from other processes. A Geant4 Monte Carlo simulation study into timing and energy thresholds for discrimination of prompt gamma photons resulting from thermal neutron capture during NCEPT was conducted. Three simulated 300 × 300 × 300 mm3 cubic PMMA targets were irradiated by 4He or 12C ion beams with a spread out Bragg peak (SOBP) depth range of 60 mm; one target is homogeneous while the others include 10 × 10 × 10 mm3 neutron capture inserts (NCIs) of pure 10B or 157Gd located at the distal edge of the SOBP. The arrival times of photons and neutrons entering a simulated 50 × 50 × 50 mm3 ideal detector were recorded. A temporal mask of 50–60 ns was found to be optimal for maximising the discrimination of the photons resulting from the neutron capture by boron and gadolinium. A range of candidate detector and thermal neutron shielding materials were simulated, and detections meeting the proposed acceptance criteria (i.e. falling within the target energy window and arriving 60 ns post beam-off) were classified as true or false positives, depending on their origin. The ratio of true/false positives (RTF) was calculated; for targets with 10B and 157Gd NCIs, the detector materials which resulted in the highest RTF were cadmium-shielded CdTe and boron-shielded LSO, respectively. The optimal irradiation period for both carbon and helium ions was 1 µs for the 10B NCI and 1 ms for the 157Gd NCI