A proof-of-concept of cross-luminescent metascintillators: testing results on a BGO:BaF2metapixel.

Objective: Time-of-flight positron emission tomography (PET) is the next frontier in improving the effective sensitivity. To achieve superior timing for time-of-flight PET, combined with high detection efficiency and cost-effectiveness, we have studied the applicability of BaF2 in metascintillators driven by the timing of cross-luminescence photon production.Approach: Based on previous simulation studies of energy sharing and analytic multi-exponential scintillation pulse, as well as sensitivity characteristics, we have experimentally tested a pixel of 3 × 3 × 15 mm3 based on 300µm BGO and 300µm BaF2 layers. To harness the deep ultraviolet cross-luminescent light component, which carries improved timing, we use the FBK VUV SiPM. Metascintillator energy sharing is addressed through a double integration approach.Main results: We reach an energy resolution of 22%, comparable to an 18% resolution of simple BGO pixels using the same readout, through the optimized use of the integrals of the metascintillator pulse in energy sharing calculation. We measure the energy sharing extent of each pulse with a resolution of 25% and demonstrate that experimental and simulation results agree well. Based on the energy sharing, a timewalk correction is applied, exhibiting significant improvements for both the coincidence time resolution (CTR) and the shape of the timing histogram. We reach 242 ps CTR for the entire photopeak, while for a subset of 13% of the most shared events, the CTR value improves to 108 ps, comparable to the 3 × 3 × 5 mm3 LYSO:Ce:Ca reference crystal.Significance: While we are considering different ways to improve further these results, this proof-of-concept demonstrates the applicability of cross-luminescence for metascintillator designs through the application of VUV compatible SiPM coupling, and easily implementable digital algorithms. This is the first test of BaF2-based metascintillators of sufficient stoppng power to be included in a PET scanner, demonstrating the industrial applicability of such cross-luminescent metascintillators.

On the way to the 10 ps time-of-flight PET challenge.

There is a consensus for gathering the multidisciplinary academic and industrial medical imaging community around the ambitious challenge to develop a 10 ps Time-of-Flight PET scanner (TOFPET). The goal is to reduce the radiation dose (currently 5-25 mSv for whole-body PET/CT) and/or scan time (currently > 10 min) by an order of magnitude, with a significant gain in the patient comfort and cost per exam (currently in the range of 1000 € per scan). To achieve this very ambitious goal it is essential to significantly improve the performance of each component of the detection chain: light production, light transport, photodetection, readout electronics. Speeding up progress in this direction is the goal of the challenge and will have an important impact on the development of a new generation of ionization radiation detectors. The possibility to reach 10 ps time-of-flight resolution at small energies (511 keV), as required in finely granulated calorimeters and PET scanners, although extremely challenging, is not limited by physical barriers and a number of disruptive technologies, such as multifunctional heterostructures, combining the high stopping power of well-known scintillators with the ultrafast photon emission resulting from the 1D, 2D or 3D quantum confinement of the excitons in nanocrystals, photonic crystals, photonic fibers, as well as new concepts of 3D digital SiPM structures, open the way to new radiation detector concepts with unprecedented performance.

Time-of-flight computed tomography - proof of principle.

Computed tomography has greatly improved over the last decade, especially through x-ray dose exposure reduction while maintaining image quality. Herein, a new concept is proposed to improve the contrast-to-noise ratio (CNR) by including the time-of-flight (TOF) information of individual photons to obtain further insight on the photon's trajectory and to reject scatter contribution. The proof of the concept relies on both simulation and experimental measurements in a cone-beam computed tomography arrangement. Results show a statistical difference between the TOF of scattered and primary photons exploitable in TOF computed tomography. For a large volume of the size of a human abdomen, a scatter reduction from 296% to 4% is achieved in our simulation setup with perfect timing measurements which yields a 110% better CNR, or a dose reduction by a factor of four. Cup artifacts are also reduced from 24.7% to 0.8%, and attenuation inaccuracies are improved from -26.3% to -0.8%. With 100 ps and 10 ps FWHM timing jitters, respectively 75% and 95% of the scatter contribution can be removed with marginal gains below 10 ps. Experimental measurements confirm the feasibility of measuring statistical differences between the TOF of scattered and primary photons.

On light sharing TOF-PET modules with depth of interaction and 157 ps FWHM coincidence time resolution.

The performance of a light sharing and recirculation mechanism that allows the extraction of depth of interaction (DOI) are investigated in this paper, with a particular focus on timing. In parallel, a method to optimize the coincidence time resolution (CTR) of PET detectors by use of the DOI information is proposed and tested. For these purposes, a dedicated 64-channels readout setup has been developed with intrinsic timing resolution of 16 ps FWHM. Several PET modules have been produced, based on LYSO:Ce scintillators and commercial silicon photomultiplier (SiPM) arrays, with [Formula: see text] mm2 individual SiPM size. The results show the possibility to achieve a timing resolution of 157 ps FWHM, combined with the already demonstrated spatial resolution of 1.5 mm FWHM, DOI resolution of 3 mm FWHM, and energy resolution of 9% FWHM at 511 keV, with 15 mm long crystals of section [Formula: see text] mm2 and [Formula: see text] mm2. At the same time, the extraction of the DOI coordinate has been demonstrated not to deteriorate the timing performance of the PET module.

Towards a metamaterial approach for fast timing in PET: experimental proof-of-concept.

Achieving fast timing in positron emission tomography (PET) at the level of few tens of picoseconds of picoseconds is limited by the photon emission rate of existent materials with standard scintillation mechanisms. This has led to consider quantum confined excitonic sub-1 ns emission in semiconductors as a viable solution to enhance the amount of fast-emitted photons produced per gamma event. However the introduction of nanocrystals and nanostructures into the domain of radiation detectors is a challenging problem. In order to move forward along this line, the standard bulk detector geometry and readout should be updated to allow for the implementation of new materials and within others, compensate for some of their intrinsic limitations. In this paper we will cover two study cases in which a fast emitter is combined with state-of-the-art scintillators in a sampling geometry designed to provide better timing for a fraction of the 511 keV events. For this test, we use a fast plastic scintillator BC-422 able to deliver a detector time resolution (DTR) of 25 ps FWHM (equivalent coincidence time resolution CTR of 35 ps) and we combined it with LYSO or BGO 200 [Formula: see text]m thick plates building a sampling pixel composed by two active scintillating materials. We develop a new proof of concept readout that allows for the identification of different types of events, carrying standard or improved timing information. Results are showing a DTR of 67 ps FWHM (equivalent to a CTR of 95 ps) for one third of the events depositing 511 keV in the BGO + BC-422 [Formula: see text] mm3 sampling pixel. The other two third of the 511 keV events perform like standard bulk 3 mm long BGO crystals with a time resolution of around 117 ps (equivalent to a CTR of 165 ps). For the case of LYSO + BC-422 sampling pixel, shared 511 keV events reach a DTR of 39 ps (CTR of 55 ps) in comparison to 57 ps (CTR of 83 ps) for 511 keV events fully contained in LYSO of the same size. This work is a step forward in the integration of fast semiconductor nanocrystals and nanostructures with present detector technologies.

A new method for depth of interaction determination in PET detectors.

A new method for obtaining depth of interaction (DOI) information in PET detectors is presented in this study, based on sharing and redirection of scintillation light among multiple detectors, together with attenuation of light over the length of the crystals. The aim is to obtain continuous DOI encoding with single side readout, and at the same time without the need for one-to-one coupling between scintillators and detectors, allowing the development of a PET scanner with good spatial, energy and timing resolutions while keeping the complexity of the system low. A prototype module has been produced and characterized to test the proposed method, coupling a LYSO scintillator matrix to a commercial SiPMs array. Excellent crystal separation is obtained for all the scintillators in the array, light loss due to depolishing is found to be negligible, energy resolution is shown to be on average 12.7% FWHM. The mean DOI resolution achieved is 4.1 mm FWHM on a 15 mm long crystal and preliminary coincidence time resolution was estimated in 353 ps FWHM.

[Retinal vascular occlusion and primary antiphospholipid syndrome. Report of 2 cases]. / Occlusion vasculaire rétinienne et syndrome primaire des antiphospholipides. A propos de 2 cas.

INTRODUCTION: The antiphospholipid syndrome is characterized by the association of antiphospholipid antibodies and occlusive vascular events. The ocular vascular damage is described in the literature and may reveal the syndrome. It's diagnosis is important because this disease, which generally affects young people, may endanger ocular and vital prognosis. Two cases are reported. PATIENTS: Two young people aged 22 and 32 presented with a sudden unilateral loss of vision. In both cases, fundus examination and fluorescein angiography revealed a severe retinal vascular occlusion. For one patient, an antiphospholipid syndrome was discovered during etiological check-up. for the second one, it was associated with a heterozygote state mutation of Leiden V factor. In both cases the visual function of the affected eye was lost. DISCUSSION: In most cases central artery or vein occlusion means atherosclerosis. However, other etiologies must be studied in young patients. According to several studies: antiphospholipid syndrome has been detected in 5% to 33% of the patients showing a major vascular retinal obstruction. The association of thrombophilia must be considered because it increases the risk of thrombotic recurrence. CONCLUSION: The antiphospholipid syndrome must be studied in cases of numerous and severe retinal vascular obstruction occurring in young patients, even if vascular risks exist. This diagnosis is important because it may imply a long-lasting anticoagulative or an antiaggregative treatment to significantly reduce the risk of recurrent thrombotic events.

[Comparative study between topical anesthesia and sub-Tenon's capsule anesthesia for cataract surgery]. / Etude comparative entre anesthésie topique et anesthésie sous-ténonienne pour la chirurgie de la cataracte.

AIM OF THE STUDY: We performed a prospective study to compare two techniques of local anesthesia: topical and subtenon anesthesia. Twenty-five patients underwent cataract surgery on both eyes by phakoemulsification and insertion of foldable lenses in the capsular bag. The second eye was operated 24 hours after the first one. We evaluated patient confort, surgeon confort, surgical complications and pupillary diameter evolution during the procedure. RESULTS: 64% of patients preferred subtenon anesthesia procedure. Surgeon confort was better with subtenon anesthesia. No surgical complications occurred in either group. The pupillar diameter evolution was different, decreasing for about 25% for topical anesthesia and 15% for subtenon anesthesia. CONCLUSION: Subtenon anesthesia is more comfortable for the patient: deeper anesthesia, reliable, longer lasting; light tolerance is better. It is also more comfortable for the surgeon: better pupillar dilatation during the procedure. Topical anesthesia has inconstant efficiency.

[In vitro changes induced by phenylmercury nitrate on fungi causing keratitis. Scanning electron microscopy study]. / Modifications induites in vitro par le nitrate de phénylmercure sur des champignons responsables de kératites. Examen en microscopie électronique à balayage.

Antifungal activity of phenylmercury nitrate was studied on fungi from keratitis. Important deterioration and bursting were observed with 2 mg/100 ml phenylmercury nitrate concentration on Aspergillus flavus, Scedosporium and Candida albicans spores.

[Failure of trabeculectomies. 15 years' evaluation]. / A propos des échecs des trabéculectomies. Bilan sur 15 ans.

Several means should allow to go for a surgical treatment more often in glaucoma.

[Modification of the intraocular pressure during induction and intubation with propofol]. / Modifications de la pression intra-oculaire lors de l'induction et de l'intubation sous propofol.

The authors have compared intraocular pressure in during induction and intubation mode. All measures were made with an aplanation tonometer (Schiotz), before induction, after induction, and immediately after intubation. Both NNLA and propofol induced an important decrease of the IOP, more with propofol (45.6%) than with NLA (28.1%). It increased again during intubation, but less with propofol (-26.8%) than with NLA (+9%).

Treatment of bilateral spontaneous dural carotid-cavernous fistulas by coils and sclerotherapy. Case report.

A case of bilateral spontaneous carotid-cavernous fistulas producing increased intraocular pressure is reported. The fistulas lay between the meningeal branches of the internal carotid artery (ICA) and the cavernous sinus, but the ICA itself was not involved. Successful treatment was accomplished by the introduction of steel coils and a sclerotic liquid into the cavernous sinus via the distal superior ophthalmic vein.