arXiv subjects

Johan Alme

Publications and source records attributed to Johan Alme.

4 recordsLinked to original sources

arXiv2022

Exploration of Differentiability in a Proton Computed Tomography Simulation Framework

Objective. Algorithmic differentiation (AD) can be a useful technique to numerically optimize design and algorithmic parameters by, and quantify uncertainties in, computer simulations. However, the effectiveness of AD depends on how "well-linearizable" the software is. In this study, we assess how promising derivative information of a typical proton computed tomography (pCT) scan computer simulation is for the aforementioned applications. Approach. This study is mainly based on numerical experiments, in which we repeatedly evaluate three representative computational steps with perturbed input values. We support our observations with a review of the algorithmic steps and arithmetic operations performed by the software, using debugging techniques. Main results. The model-based iterative reconstruction (MBIR) subprocedure (at the end of the software pipeline) and the Monte Carlo (MC) simulation (at the beginning) were piecewise differentiable. Jumps in the MBIR function arose from the discrete computation of the set of voxels intersected by a proton path. Jumps in the MC function likely arose from changes in the control flow that affect the amount of consumed random numbers. The tracking algorithm solves an inherently non-differentiable problem. Significance. The MC and MBIR codes are ready for the integration of AD, and further research on surrogate models for the tracking subprocedure is necessary.

physics.med-ph↗

arXiv2021

The charge sensitivity calibration of the upgraded ALICE Inner Tracking System

The ALICE detector is undergoing an upgrade for Run 3 at the LHC. A new Inner Tracking System (ITS) is part of this upgrade. The upgraded ALICE ITS features the ALPIDE, a Monolithic Active Pixel Sensor. Due to IC fabrication variations and radiation damages, the threshold values for the ALPIDE chips in ITS need to be measured and adjusted periodically to ensure the quality of data. The calibration is implemented within the ALICE Online-Offline (O$^2$) Computing System, thus it runs in the same framework as the normal operations. This paper describes the concept and first implementation of the charge sensitivity scanning procedures for the upgraded ALICE ITS in the ALICE O$^2$ System, and demonstrates the first results of the scanning of the data taken from the installed ITS.

physics.ins-det↗

arXiv2020

Remote Configuration of the ProASIC3 on the ALICE Inner Tracking System Readout Unit

A Large Ion Collider Experiment (ALICE) is one of the four major experiments conducted at the CERN Large Hadron Collider (LHC). The ALICE detector is currently undergoing an upgrade for the upcoming Run 3 at the LHC. The new Inner Tracking System (ITS) sub-detector is part of this upgrade. The front-end electronics of the ITS is composed by 192 Readout Units, installed in a radiation environment. Single Event Upsets (SEUs) in the SRAM-based Xilinx Kintex Ultrascale FPGAs used in the ITS readout represent a real concern. To clear SEUs affecting the Kintex configuration memory, a secondary Flash-based Microsemi ProASIC3E (PA3) FPGA is used. This device configures and continuously scrubs the Xilinx FPGA while data-taking is ongoing, which avoids accumulation of SEUs. The communication path to the RUs is via the radiation hard Gigabit Transceiver (GBT) system on 100 m long optical links. The PA3 is reachable via the GBT Slow Control Adapter (GBT-SCA) ASIC using a dedicated JTAG bus driving channel. During the course of Run 3, it is foreseeable that the FPGA design of the PA3 will require upgrades to correct possible issues and add new functionality. It is therefore mandatory that the PA3 itself can be configured remotely, for which a dedicated software tool is needed. This paper presents the design and implementation of the distributed tools to re-configure remotely the PA3 FPGAs.

physics.ins-det↗

arXiv2017

Proton tracking in a high-granularity Digital Tracking Calorimeter for proton CT purposes

Radiation therapy with protons as of today utilizes information from x-ray CT in order to estimate the proton stopping power of the traversed tissue in a patient. The conversion from x-ray attenuation to proton stopping power in tissue introduces range uncertainties of the order of 2-3% of the range, uncertainties that are contributing to an increase of the necessary planning margins added to the target volume in a patient. Imaging methods and modalities, such as Dual Energy CT and proton CT, have come into consideration in the pursuit of obtaining an as good as possible estimate of the proton stopping power. In this study, a Digital Tracking Calorimeter is benchmarked for proof-of-concept for proton CT purposes. The Digital Tracking Calorimeteris applied for reconstruction of the tracks and energies of individual high energy protons. The presented prototype forms the basis for a proton CT system using a single technology for tracking and calorimetry. This advantage simplifies the setup and reduces the cost of a proton CT system assembly, and it is a unique feature of the Digital Tracking Calorimeter. Data from the AGORFIRM beamline at KVI-CART in Groningen in the Netherlands and Monte Carlo simulation results are used to in order to develop a tracking algorithm for the estimation of the residual ranges of a high number of concurrent proton tracks. The range of the individual protons can at present be estimated with a resolution of 4%. The readout system for this prototype is able to handle an effective proton frequency of 1 MHz by using 500 concurrent proton tracks in each readout frame, which is at the high end range of present similar prototypes. A future further optimized prototype will enable a high-speed and more accurate determination of the ranges of individual protons in a therapeutic beam.

physics.med-ph↗