Local edge computing for radiological image reconstruction and computer-assisted detection: A feasibility study

Computational requirements for data processing at different stages of the radiology value chain are increasing. Cone beam computed tomography (CBCT) is a diagnostic imaging technique used in dental and extremity imaging, involving a highly demanding image reconstruction task. In turn, artificial intelligence (AI) assisted diagnostics are becoming increasingly popular, thus increasing the use of computation resources. Furthermore, the need for fully independent imaging units outside radiology departments and with remotely performed diagnostics emphasize the need for wireless connectivity between the imaging unit and hospital infrastructure. In this feasibility study, we propose an approach based on a distributed edge-cloud computing platform, consisting of small-scale local edge nodes, edge servers with traditional cloud resources to perform data processing tasks in radiology. We are interested in the use of local computing resources with Graphics Processing Units (GPUs), in our case Jetson Xavier NX, for hosting the algorithms for two use-cases, namely image reconstruction in cone beam computed tomography and AI-assisted cancer detection from mammographic images. Particularly, we wanted to determine the technical requirements for local edge computing platform for these two tasks and whether CBCT image reconstruction and breast cancer detection tasks are possible in a diagnostically acceptable time frame. We validated the use-cases and the proposed edge computing platform in two stages. First, the algorithms were validated use-case-wise by comparing the computing performance of the edge nodes against a reference setup (regular workstation). Second, we performed qualitative evaluation on the edge computing platform by running the algorithms as nanoservices. Our results, obtained through real-life prototyping, indicate that it is possible and technically feasible to run both reconstruction and AI-assisted image analysis functions in a diagnostically acceptable computing time. Furthermore, based on the qualitative evaluation, we confirmed that the local edge computing capacity can be scaled up and down during runtime by adding or removing edge devices without the need for manual reconfigurations. We also found all previously implemented software components to be transferable as such. Overall, the results are promising and help in developing future applications, e.g., in mobile imaging scenarios, where such a platform is beneficial

Resonance laser ionization developments for IGISOL-4

The work presented in this thesis concentrates on the development of the FURIOS laser ion source towards e cient and selective production of low energy radioactive ion beams. This includes design and development of the ion guide and hot cavity catcher systems for laser ion source use, and the development of in-source and in-jet laser spectroscopy techniques. The work has been carried out at the IGISOL facility in the Accelerator laboratory of the University of Jyväskylä. The FURIOS facility was upgraded and developed during the move to the IGISOL-4 facility. The laser transport was greatly improved in order to allow a large fraction of the initial laser intensity to be transported into the gas cell at the IGISOL-4 frontend. The careful design of the IGISOL frontend and the FURIOS facility enable the laser ion source to be utilized e ciently for the production of radioactive ion beams at IGISOL-4. Additionally, in order to overcome the de ciencies of the standard IGISOL ion guide design under on-line conditions, an ion guide based on an original design by the LISOL group in Leuven has been adapted the IGISOL. The shadow gas cell allows e cient resonance laser ionization in a gas cell under on-line conditions. The transport e ciency of the ion guide was determined using recoil source. Additionally, the principal operation of the ion guide was demonstrated under pseudo-on-line conditions utilizing resonance laser ionization. An inductively heated hot cavity catcher laser ion source was developed based on existing electron bombardment heated thermal ionizer design in collaboration with the JYFL ECR group. The motivation behind the development of a new type of recoil catcher at IGISOL is the production of rare isotope of silver, N=Z 94Ag. The evacuation time for the silver atoms from the catcher was measured to be less than 10 ms at a relatively low temperature of 1200 C. Though the hot cavity catcher ion source principle was demonstrated, the commissioning experiment showed the need to further develop the catcher in order to improve the beam quality and ionization e ciency. Lastly, in gas-jet spectroscopy in the form of the LIST approach was studied. Different ion guide nozzles were compared in order to nd a nozzle that would produce long collimated gas jets for the use of the LIST approach. A de Laval type nozzle was found out to be the most promising, being able to produce a well collimated jet spanning a distance of 14 cm. The jet temperature was measured to be very low, which when combined with the low pressure, makes a very attractive environment for laser spectroscopy

Intracavity Frequency Doubling and Difference Frequency Mixing for Pulsed ns Ti:Sapphire Laser Systems at On-Line Radioactive Ion Beam Facilities

Intra-cavity second harmonic generation of a Titanium:sapphire (Ti:sa) laser system has been used to improve the conversion efficiency to the second harmonic. Over the course of several experiments performance data spanning the whole wavelength range of a Ti:sa has been collected, which may be used as a guideline for future experiments. An average output power of up to 3.7 W was achieved, resulting in a conversion efficiency of >75% to the second harmonic. A wavelength coverage from 340–525 nm has been demonstrated. To extend the wavelength range of the solid state laser system, difference frequency mixing has been applied to the intra-cavity doubled light and the fundamental output of a second Ti:sa laser. Up to 30 mW of yellow light at the sodium D2 line at 589 nm was generated. Based on numerical calculations this output power could still be improved by a factor of ten with simple changes in the experimental setup. Laser spectroscopy and measurement of the saturation behaviour has been carried out on an atomic beam of stable sodium

Towards in-jet resonance ionization spectroscopy : An injection-locked Titanium:Sapphire laser system for the PALIS-facility

This article presents a pulsed narrowband injection-locked Titanium:Sapphire laser aimed for high-resolution in-jet resonance ionization spectroscopy at the SLOWRI/PALIS at RIKEN. The laser has been integrated into the PALIS laser laboratory enabling it to be utilized with the existing broadband Titanium:Sapphire and dye lasers. The seed efficiency has been evaluated to be close to unity over the master laser wavelength range ∼ 753 to 791 nm, and the slope efficiency, namely the ratio of the pump power to the output power, was determined to be ∼ 30 % at 780 nm. A two-step ionization scheme with 386.4016 nm first step and 286.731 nm second step into an autoionizing state was developed for resonance ionization spectroscopy of 93Nb. Magnetic hyperfine coupling constants of 1866 ± 8 MHz and 1536 ± 7 MHz were measured for the ground and excited state, respectively, in a good agreement with the literature values. A Gaussian dominated Voigt linewidth of 434.5 ± 7.4 MHz was extracted from the hyperfine spectra measured for niobium. In addition, the resolution of the in-jet resonance ionization in PALIS is estimated through numerical methods.peerReviewe

Photo-enhanced O−, H− and Br− ion production in caesium sputter negative ion source : no evidence for resonant ion pair production

It has been proposed that the negative ion yield of a caesium sputter ion source could be enhanced by promoting neutral caesium atoms to electronically excited 7p states supporting resonant ion pair production. We have tested this hypothesis by illuminating the cathode of a caesium sputter ion source with an adjustable wavelength laser and measuring its effect on the extracted beam currents of O−, H− and Br− anions. The laser exposure causes the beam currents to increase but the effect is independent of the wavelength in the range of 440-460 nm, which leads us to conclude that there is no evidence for resonant ion pair production. The photon-induced beam current enhancement scales with the applied laser power and, depending on the ion source conditions, can more than double the extracted beam current. We present a qualitative explanation for the observed effect. The model, based on photoelectron emission and subsequent increase of the caesium sputtering rate, thus liberating negative ions from the cathode, is supported by the data demonstrating that the caesium sputter ion source can produce Br− beams without thermal surface ionization as a source of Cs+ ions, i.e. in external laser-driven mode without heating the surface ionizer.peerReviewe

High-precision mass measurement of 31S with the double Penning trap JYFLTRAP improves the mass value for 32Cl

peerReviewe

Status and development of the MARA low-energy branch

The MARA Low-Energy Branch is under development at the Accelerator Laboratory of the University of Jyvaskylä. The facility will be employed for laser ionisation and spectroscopy studies and for mass measurements of nuclei close to the proton drip line. This article presents an updated status of the ongoing development of the different parts of this facility, including the buffer gas cell, the ion transport system, the laser system and the detector stations.peerReviewe

Photo-assisted O− and Al− production with a cesium sputter ion source

It has been recently proposed that the production of negative ions with cesium sputter ion sources could be enhanced by laser-assisted resonant ion pair production. We have tested this hypothesis by measuring the effect of pulsed diode lasers at various wavelengths on the O− and Al− beam current produced from Al2O3 cathode of a cesium sputter ion source. The experimental results provide evidence for the existence of a wavelength-dependent photo-assisted enhancement of negative ion currents but cast doubt on its alleged resonant nature as the effect is observed for both O− and Al− ions at laser energies above a certain threshold. The beam current transients observed during the laser pulses suggest that the magnitude and longevity of the beam current enhancement depends on the cesium balance on the cathode surface. It is shown that the ions produced by the laser exposure originate from slightly different potential than the surface produced ions, which allows us to constrain the underlying physical mechanisms. It is concluded that the photo-assisted negative ion production could be of practical importance as it can more than double the extracted beam current under certain operational settings of the cesium sputter ion source. We discuss experiments designed to confirm or dispute the relevance of the ion pair production for negative ion production with cesium sputter ion sources and the possibility of ion pair production explaining the beneficial effect of xenon admixture on the negative ion yield of an RF-driven H− ion source.peerReviewe

The Novels and the Ideas of Madame Marcelle Tinayre

We investigate the decay of 87Br, 88Br and 94Rb using total absorption gamma-ray spectroscopy. These important fission products are beta-delayed neutron emitters. Our data show considerable gamma-intensity, so far unobserved in high-resolution gamma-ray spectroscopy, from states at high excitation energy. We also find significant differences with the beta intensity that can be deduced from existing measurements of the beta spectrum. We evaluate the impact of the present data on reactor decay heat using summation calculations. Although the effect is relatively small it helps to reduce the discrepancy between calculations and integral measurements of the photon component for 235U fission at cooling times in the range 1 to 100 s. We also use summation calculations to evaluate the impact of present data on reactor antineutrino spectra. We find a significant effect at antineutrino energies in the range of 5 to 9 MeV. In addition, we observe an unexpected strong probability for gamma emission from neutron unbound states populated in the daughter nucleus. The gamma branching is compared to Hauser-Feshbach calculations which allow one to explain the large value for bromine isotopes as due to nuclear structure. However the branching for 94Rb, although much smaller, hints of the need to increase the radiative width by one order-of-magnitude. This leads to a similar increase in the calculated (n,gamma) cross section for this very neutron-rich nucleus with a potential impact on r-process abundance calculations