Real-time 3D PET image with pseudoinverse reconstruction

Real-time positron emission tomography (PET) may provide information from first-shot images, enable PET-guided biopsies, and allow awake animal studies. Fully-3D iterative reconstructions yield the best images in PET, but they are too slow for real-time imaging. Analytical methods such as Fourier back projection (FBP) are very fast, but yield images of poor quality with artifacts due to noise or data incompleteness. In this work, an image reconstruction based on the pseudoinverse of the system response matrix (SRM) is presented. w. To implement the pseudoinverse method, the reconstruction problem is separated into two stages. First, the axial part of the SRM is pseudo-inverted (PINV) to rebin the 3D data into 2D datasets. Then, the resulting 2D slices can be reconstructed with analytical methods or by applying the pseudoinverse algorithm again. The proposed two-step PINV reconstruction yielded good-quality images at a rate of several frames per second, compatible with real time applications. Furthermore, extremely fast direct PINV reconstruction of projections of the 3D image collapsed along specific directions can be implemented.Part of the calculations in this work were performed in the “Clúster de Cálculo para Técnicas Físicas” funded in part by UCM and in part by UE Regional Funds. We acknowledge the support from the Spanish Government (FPA2015-65035-P, RTC-2015-3772-2, and RTI2018-095800-A-I00), Comunidad de Madrid (S2013/MIT-3024 TOPUS-CM, B2017/BMD-3888 PRONTO-CM), and European Regional Funds. This work was also supported by the EU’s H2020 under MediNet, a Networking Activity of ENSAR-2 (grant agreement 654002), and by a NIH R01 CA215700-2 grant. The CNIC is supported by the Ministerio de Ciencia, Innovación y Universidades and the Pro CNIC Foundation, and is a Severo Ochoa Center of Excellence (SEV-2015-0505)

The 2018 Martian Global Dust Storm over the South Polar Region studied with MEx/VMC

We study the 2018 Martian global dust storm (GDS 2018) over the Southern Polar Region using images obtained by the Visual Monitoring Camera (VMC) on board Mars Express (MEx) during June and July 2018. Dust penetrated into the polar cap region but never covered the cap completely, and its spatial distribution was nonhomogeneous and rapidly changing. However, we detected long but narrow aerosol curved arcs with a length of ~2,000–3,000 km traversing part of the cap and crossing the terminator into the nightside. Tracking discrete dust clouds allowed measurements of their motions that were toward the terminator with velocities up to 100 m/s. The images of the dust projected into the Martian limb show maximum altitudes of ~70 km but with large spatial and temporal variations. We discuss these results in the context of the predictions of a numerical model for dust storm scenario.This work has been supported by the Spanish project AYA2015-65041-P (MINECO/FEDER, UE) and Grupos Gobierno Vasco IT-1366-19. J. H. B. was supported by ESA Contract 4000118461/16/ES/JD, Scientific Support for Mars Express Visual Monitoring Camera. We acknowledge support from the Faculty of the European Space Astronomy Centre (ESAC). VMC raw images used in this study can be accessed through VMC raw file gallery http://blogs.esa.int/ftp/. VMC raw and calibrated images will be available in ESA PSA in the near future. A list of observations used in this paper is provided in the supporting information. MCD database files are available in http://www-mars.lmd.jussieu.fr/mars.html

Technical note: Measurement of the bunch structure of a clinical proton beam using a SiPM coupled to a plastic scintillator with an optical fiber

This work was funded by Comunidad de Madrid under project B2017/BMD-3888 PRONTO-CM “Protontherapy and nuclear techniques for oncology” and by the Spanish Government and EU Regional Funds (RTI2018-098868-B-I00, RTC-2015-3772-1). A. Espinosa Rodríguez has been funded by a FPU predoctoral fellowship of the Spanish Ministerio de Educación, Cultura y Deporte (FPU18/02551). This is a contribution for the Moncloa Campus of International Excellence, “Grupo de Física Nuclear-UCM”, Ref. 910059. Part of the calculations of this work were performed in the “Clúster de Cálculo para Técnicas Físicas”, funded in part by Universidad Complutense de Madrid and in part by EU Regional Funds.BackgroundRecent proposals of high dose rate plans in protontherapy as well as very short proton bunches may pose problems to current beam monitor systems. There is an increasing demand for real-time proton beam monitoring with high temporal resolution, extended dynamic range and radiation hardness. Plastic scintillators coupled to optical fiber sensors have great potential in this context to become a practical solution towards clinical implementation. PurposeIn this work, we evaluate the capabilities of a very compact fast plastic scintillator with an optical fiber readout by a SiPM and electronics sensor which has been used to provide information on the time structure at the nanosecond level of a clinical proton beam. Materials and methodsA 3 x 3 x 3 mm(3) plastic scintillator (EJ-232Q Eljen Technology) coupled to a 3 x 3 mm(2) SiPM (MicroFJ-SMA-30035, Onsemi) has been characterized with a 70 MeV clinical proton beam accelerated in a Proteus One synchrocyclotron. The signal was read out by a high sampling rate oscilloscope (5 GS/s). By exposing the sensor directly to the proton beam, the time beam profile of individual spots was recorded. ResultsMeasurements of detector signal have been obtained with a time sampling period of 0.8 ns. Proton bunch period (16 ns), spot (10 mu s) and interspot (1 ms) time structures could be observed in the time profile of the detector signal amplitude. From this, the RF frequency of the accelerator has been extracted, which is found to be 64 MHz. ConclusionsThe proposed system was able to measure the fine time structure of a clinical proton accelerator online and with ns time resolution.Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEComunidad de MadridGobierno de EspañaEU Regional FundsMinisterio de Educación, Cultura y Deportepu

Optimization of Monte Carlo code for clinical simulation of electron beams

The aim of this work is to optimize a Monte Carlo (MC) kernel for electron radiation therapy (IOERT) compatible with intraoperative usage and to integrate it within an existing IOERT dedicated treatment planning system (TPS

Iterative determination of clinical beam phase space from dose measurements

Monte Carlo (MC) method can accurately compute the dose produced by medical linear accelerators. However, these calculations require a reliable description of the electron and/or photon beams delivering the dose, the phase space (PHSP), which is not usually available. A method to derive a phase space model from reference measurements that does not heavily rely on a detailed model of the accelerator head is presented. The iterative optimization process extracts the characteristics of the particle beams which best explains the reference dose measurements in water and air, given a set of constrain

Detecting and Characterising atmospheric gravity waves on Mars' atmosphere - Final results using data from OMEGA/Mars Express

We present the final results from the detection and characterisation of mesoscale waves on the lower clouds of Mars [1] using images from the Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (OMEGA) [2] onboard the European Mars Express (MEx) space mission [3]. We used image navigation and processing techniques based on contrast enhancement and geometrical projections to characterise morphological properties of the detected gravity waves (GW), such as horizontal wavelength or packet length. Our study covers 25 months of data spanning from Jan. 2004 to Jan. 2006, and from June to July 2007, corresponding to a one Martian year [MY26- MY27]. Out of 148 detected wave packets, we were able to characterise 61 across more than 4000 images covering a broad region of the Martian globe. Our results reveal that waves exhibit an average horizontal wavelength of 23 km, which is consistent with previous observations [4,5]. We also extend the study by characterising their packet width, length and orientation. Taking advantage of the large dataset available from the OMEGA instrument, we also conducted a spatial and temporal investigation of the waves, namely their occurrence in specific local times and solar longitudes. Our characterisation showed a higher frequency of GW during daytime hours, particularly within the 13-15 LTST range. Concerning the solar longitude that is a measure of the Martian seasons, we noted that GW activity is prevalent during the winter season in both hemispheres, suggesting a relationship between seasonal variations and gravity wave generation, which was previously mentioned in the literature [6–8]. We will also present the preliminary results of GW using the HRSC instrument

An Extremely Elongated Cloud Over Arsia Mons Volcano on Mars: I. Life Cycle

We report a previously unnoticed annually repeating phenomenon consisting of the daily formation of an extremely elongated cloud extending as far as 1,800 km westward from Arsia Mons. It takes place in the solar longitude (Ls) range of ∼220°–320°, around the Southern solstice. We study this Arsia Mons Elongated Cloud (AMEC) using images from different orbiters, including ESA Mars Express, NASA MAVEN, Viking 2, MRO, and ISRO Mars Orbiter Mission (MOM). We study the AMEC in detail in Martian year (MY) 34 in terms of local time and Ls and find that it exhibits a very rapid daily cycle: the cloud growth starts before sunrise on the western slope of the volcano, followed by a westward expansion that lasts 2.5 h with a velocity of around 170 m/s in the mesosphere (∼45 km over the areoid). The cloud formation then ceases, detaches from its formation point, and continues moving westward until it evaporates before the afternoon, when most sun-synchronous orbiters make observations. Moreover, we comparatively study observations from different years (i.e., MYs 29–34) in search of interannual variations and find that in MY33 the cloud exhibits lower activity, while in MY34 the beginning of its formation was delayed compared with other years, most likely due to the Global Dust Storm. This phenomenon takes place in a season known for the general lack of clouds on Mars. In this paper we focus on observations, and a theoretical interpretation will be the subject of a separate paper.This work has been supported by the Spanish project AYA2015-65041-P and PID2019-109467GB-I00 (MINECO/FEDER, UE) and Grupos Gobierno Vasco IT-1366-19. JHB was supported by ESA Contract No. 4000118461/16/ES/JD, Scientific Support for Mars Express Visual Monitoring Camera. The Aula EspaZio Gela is supported by a grant from the Diputación Foral de Bizkaia (BFA). We acknowledge support from the Faculty of the European Space Astronomy Center (ESAC). Special thanks are due to the Mars Express Science Ground Segment and Flight Control Team at ESAC and ESOC. The contributions by K.C and N.M.S were supported by NASA through the MAVEN project

PeneloPET v3.0, an improved multiplatform PET Simulator

PeneloPET is a Monte Carlo simulation tool for positron emission tomography based on PENELOPE. It was developed by the Nuclear Physics Group at University Complutense of Madrid and its initial version was released in 2009. In this work, we present PeneloPET v3.0, which is now available precompiled for Microsoft Windows, MacOS and Linux OS. This new release includes improved simulations of the positron range in different materials and an accurate description of the decay cascades for many radioactive nuclei including the most common non-pure positron emitters used in PET. This enables the simulation of PET acquisitions with positron-gamma emitters. This release also includes many different fully-working examples, of both clinical and preclinical scanners, as well as several numerical phantoms. Due to the simplicity of the input the output files, and the installation process, PeneloPET v3.0 can be perfectly used not only for research, but also as an educational tool in class

Feasibility assessment of the interactive use of a Monte Carlo algorithm in treatment planning for intraoperative electron radiation therapy

This work analysed the feasibility of using a fast, customized Monte Carlo (MC) method to perform accurate computation of dose distributions during pre- and intraplanning of intraoperative electron radiation therapy (IOERT) procedures. The MC method that was implemented, which has been integrated into a specific innovative simulation and planning tool, is able to simulate the fate of thousands of particles per second, and it was the aim of this work to determine the level of interactivity that could be achieved. The planning workflow enabled calibration of the imaging and treatment equipment, as well as manipulation of the surgical frame and insertion of the protection shields around the organs at risk and other beam modifiers. In this way, the multidisciplinary team involved in IOERT has all the tools necessary to perform complex MC dosage simulations adapted to their equipment in an efficient and transparent way. To assess the accuracy and reliability of this MC technique, dose distributions for a monoenergetic source were compared with those obtained using a general-purpose software package used widely in medical physics applications. Once accuracy of the underlying simulator was confirmed, a clinical accelerator was modelled and experimental measurements in water were conducted. A comparison was made with the output from the simulator to identify the conditions under which accurate dose estimations could be obtained in less than 3 min, which is the threshold imposed to allow for interactive use of the tool in treatment planning. Finally, a clinically relevant scenario, namely early-stage breast cancer treatment, was simulated with pre- and intraoperative volumes to verify that it was feasible to use the MC tool intraoperatively and to adjust dose delivery based on the simulation output, without compromising accuracy. The workflow provided a satisfactory model of the treatment head and the imaging system, enabling proper configuration of the treatment planning system and providing good accuracy in the dosage simulation

Detailed spectroscopy of doubly magic Sn-132

The structure of the doubly magic Sn-132(50)82 has been investigated at the ISOLDE facility at CERN, populated both by the beta(-) decay of In-132 and beta(-)-delayed neutron emission of In-133. The level scheme of Sn-13(2) is greatly expanded with the addition of 68 gamma transitions and 17 levels observed for the first time in the beta decay. The information on the excited structure is completed by new gamma transitions and states populated in the beta-n decay of In-133. Improved delayed neutron emission probabilities are obtained both for In-132 and In-133. Level lifetimes are measured via the advanced time-delayed beta gamma gamma(t) fast-timing method. An interpretation of the level structure is given based on the experimental findings and the particle-hole configurations arising from core excitations both from the N = 82 and Z = 50 shells, leading to positive- and negative-parity particle-hole multiplets. The experimental information provides new data to challenge the theoretical description of Sn-132