A practical approach to the spatial-domain calculation of nonprewhitening model observers in computed tomography.

Background: Modern reconstruction algorithms for computed tomography (CT) can exhibit nonlinear properties, including non-stationarity of noise and contrast dependence of both noise and spatial resolution. Model observers have been recommended as a tool for the task-based assessment of image quality (Samei E et al., Med Phys.

Assessment of Photon-Counting Computed Tomography for Quantitative Imaging in Radiation Therapy.

Purpose: To test a first-generation clinical photon-counting computed tomography (PCCT) scanner's capabilities to characterize materials in an anthropomorphic head phantom for radiation therapy purposes.

Methods And Materials: A CIRS 731-HN head-and-neck phantom (CIRS/SunNuclear) was scanned on a NAEOTOM Alpha PCCT and a SOMATOM Definition AS+ with single-energy and dual-energy CT techniques (SECT and DECT, respectively), both scanners manufactured by Siemens (Siemens Healthineers). A method was developed to derive relative electron density (RED) and effective atomic number (EAN) from linear attenuation coefficients (LACs) of virtual mono-energetic images and applied for the PCCT and DECT data.

A compact X-ray source via fast microparticle streams.

The spatiotemporal resolution of diagnostic X-ray images is limited by the erosion and rupture of conventional stationary and rotating anodes of X-ray tubes from extreme density of input power and thermal cycling of the anode material. Conversely, detector technology has developed rapidly. Finer detector pixels demand improved output from brilliant keV-type X-ray sources with smaller X-ray focal spots than today and would be available to improve the efficacy of medical imaging.

Technical note: SpekPy Web-online x-ray spectrum calculations using an interface to the SpekPy toolkit.

Knowledge of the photon spectrum emitted from an x-ray tube is frequently needed in imaging and dosimetry contexts. As the spectrum characteristics are influenced by several parameters and routine measurement of a spectrum is often impractical, a variety of software programs have been developed over the decades for convenient calculations. SpekPy is a state-of-the-art software package containing several spectrum models, and was created to estimate photon spectra originating from x-ray tubes using a small set of input parameters (e.

Ventriculoperitoneal shunt survey in pediatric patients in an emergency setting: a comparison between ultra-low-dose CT using a tin filter and plain radiography.

Objective: The aim of this study was to investigate the diagnostic performance, effective radiation dose, and examination time of ventriculoperitoneal shunt evaluation using full-body ultra-low-dose CT (ULD CT) with a tin filter compared with digital plain radiography in a pediatric population.

Methods: A retrospective cross-sectional study was conducted in an emergency setting. Data from 143 children were collected.

Spatial resolution, noise properties, and detectability index of a deep learning reconstruction algorithm for dual-energy CT of the abdomen.

Background: Iterative reconstruction (IR) has increasingly replaced traditional reconstruction methods in computed tomography (CT). The next paradigm shift in image reconstruction is likely to come from artificial intelligence, with deep learning reconstruction (DLR) solutions already entering the clinic. An enduring disadvantage to IR has been a change in noise texture, which can affect diagnostic confidence.

Stopping-power ratio estimation for proton radiotherapy using dual-energy computed tomography and prior-image constrained denoising.

Background: Dual-energy computed tomography (DECT) is a promising technique for estimating stopping-power ratio (SPR) for proton therapy planning. It is known, however, that deriving electron density (ED) and effective atomic number (EAN) from DECT data can cause noise amplification in the resulting SPR images. This can negate the benefits of DECT.

Performance characterization of a prototype dual-layer cone-beam computed tomography system.

Purpose: Conventional cone-beam computed tomography CT (CBCT) provides limited discrimination between low-contrast tissues. Furthermore, it is limited to full-spectrum energy integration. A dual-energy CBCT system could be used to separate photon energy spectra with the potential to increase the visibility of clinically relevant features and acquire additional information relevant in a multitude of clinical imaging applications.

Estimation of delivered dose to lung tumours considering setup uncertainties and breathing motion in a cohort of patients treated with stereotactic body radiation therapy.

Introduction: Dose-response relationships for local control of lung tumours treated with stereotactic body radiotherapy (SBRT) have proved ambiguous, however, these have been based on the prescribed or planned dose. Delivered dose to the target may be a better predictor for local control. In this study, the probability of the delivered minimum dose to the clinical target volume (CTV) in relation to the prescribed dose was estimated for a cohort of patients, considering geometrical uncertainties.

Technical Note: SpekPy v2.0-a software toolkit for modeling x-ray tube spectra.

Purpose: SpekPy is a free toolkit for modeling x-ray tube spectra with the Python programming language. In this article, the advances in version 2.0 (v2) of the software are described, including additional target materials and more accurate modeling of the heel effect.

Experimental assessment of a phosphor model for estimating the relative extrinsic efficiency in radioluminescent detectors.

Optimising phosphor screens in dose detectors or imaging sensor designs is a cumbersome and time- consuming work normally involving specialised measuring equipment and advanced modelling. It is known that crucial optical parameters of the same phosphor may vary within a wide range of values. The aim of this work was to experimentally assess a simple previously published model where the case specific optical parameters (scattering and absorption) are instead represented by a fixed, single parameter, the light extinction factor, ξ.

A model for the energy and angular distribution of x rays emitted from an x-ray tube. Part I. Bremsstrahlung production.

Purpose: To develop an analytical model for bremsstrahlung production in a thick x-ray target (i.e., the x-ray tube anode) that takes into account the intrinsic bremsstrahlung angular distribution.

A model for the energy and angular distribution of x rays emitted from an x-ray tube. Part II. Validation of x-ray spectra from 20 to 300 kV.

Purpose: To present and validate a complete x-ray emission model (bremsstrahlung and characteristic x-ray emission) for the energy range 20-300 kV.

Methods: An analytical x-ray spectrum model that combines the bremsstrahlung emission model developed in Part I with a previously developed characteristic x-ray emission model is validated by comparison with Monte Carlo calculations, published measured spectra, and models developed by other authors. Furthermore, the assumptions and limitations of previous spectrum models are summarized, and their predictions are compared with results obtained by Monte Carlo simulations of x rays emitted from tungsten and molybdenum targets.

A validation of SpekPy: A software toolkit for modelling X-ray tube spectra.

Purpose: To validate the SpekPy software toolkit that has been developed to estimate the spectra emitted from tungsten anode X-ray tubes. The model underlying the toolkit introduces improvements upon a well-known semi-empirical model of X-ray emission.

Materials And Methods: Using the same theoretical framework as the widely-used SpekCalc software, new electron penetration data was simulated using the Monte Carlo (MC) method, alternative bremsstrahlung cross-sections were applied, L-line characteristic emissions were included, and improvements to numerical methods implemented.

Age-specific and gender-specific radiation risks in paediatric angiography and interventional cardiology: conversion coefficients and risk reference values.

Objectives: To estimate risk for exposure-induced cancer death (REID), organ-specific risks of exposure-induced cancer death (REID) and associated conversion coefficients (CC=REID/kerma-area product (KAP), CC=REID/KAP) in paediatric cardiac catheterizations using data from radiation dose structured reports (RDSR). A novel risk surveillance tool consisting of age-specific and gender-specific risk reference values (RRVs) related to population cancer risk is suggested.

Methods: The PCXMC v.

Comparison of acquisition protocols for ventilation/perfusion SPECT-a Monte Carlo study.

One of the most commonly used imaging techniques for diagnosing pulmonary embolism (PE) is ventilation/perfusion (V/P) scintigraphy. The aim of this study was to evaluate the performance of the currently used imaging protocols for V/P single photon emission computed tomography (V/P SPECT) at two nuclear medicine department sites and to investigate the effect of altering important protocol parameters. The Monte Carlo technique was used to simulate 4D digital phantoms with perfusion defects.

The synthetic localizer radiograph - A new CT scan planning method.

Objective: To investigate if the conventional localizer radiograph (LR) can be replaced by a synthetic LR (SLR), generated from a low-dose spiral CT scan, for CT scan planning with minimal changes to current clinical workflows.

Methods: A dosimetric comparison of SLRs and LRs was made using Monte Carlo methods. Water equivalent diameters (WEDs) of a centered and mis-centered phantom were estimated from low-dose spiral CT scans and LRs acquired at different angles.

Calculating organ and effective doses in paediatric interventional cardiac radiology based on DICOM structured reports - Is detailed examination data critical to dose estimates?

Purpose: To estimate effective dose (E), equivalent organ doses (H) and associated conversion coefficients (CC = E/KAP, CC = H/KAP; KAP = Kerma-area product) in paediatric cardiac interventions, using detailed exposure data from radiation dose structured reports (RDSR). These "RDSR dose estimations" have been compared with estimations performed using the approach currently implemented in the clinic that is based on a simplified assumptions method (SAM).

Methods: The Monte Carlo system PCXMC, incorporated into a previously developed framework, was used to calculate E and H for 202 children.

PRaVDA: The first solid-state system for proton computed tomography.

Purpose: Proton CT is widely recognised as a beneficial alternative to conventional X-ray CT for treatment planning in proton beam radiotherapy. A novel proton CT imaging system, based entirely on solid-state detector technology, is presented. Compared to conventional scintillator-based calorimeters, positional sensitive detectors allow for multiple protons to be tracked per read out cycle, leading to a potential reduction in proton CT scan time.

Organ doses from a proton gantry-mounted cone-beam computed tomography system characterized with MCNP6 and GATE.

Purpose: To determine organ doses from a proton gantry-mounted cone-beam computed tomography (CBCT) system using two Monte Carlo codes and to study the influence on organ doses from different acquisition modes and repeated imaging.

Methods: The CBCT system was characterized with MCNP6 and GATE using measurements of depth doses in water and spatial profiles in air. The beam models were validated against absolute dose measurements and used to simulate organ doses from CBCT imaging with head, thorax and pelvis protocols.

Comparison of CT-number parameterization models for stoichiometric CT calibration in proton therapy.

Purpose: This study compares the predictions of three parameterization models used in previously published works, implementing the stoichiometric CT calibration for proton therapy, and a further two alternative parameterizations suggested here.

Methods: Stoichiometric calibrations of patient CT-number to stopping-power ratio (SPR) were performed for four CT protocols using tissue substitutes supplied by CIRS (CIRS Inc., Norfolk, VA, USA).

The dosimetric impact of including the patient table in CT dose estimates.

The purpose of this study was to evaluate the dosimetric impact of including the patient table in Monte Carlo CT dose estimates for both spiral scans and scan projection radiographs (SPR). CT scan acquisitions were simulated for a Siemens SOMATOM Force scanner (Siemens Healthineers, Forchheim, Germany) with and without a patient table present. An adult male, an adult female and a pediatric female voxelized phantom were simulated.

Accuracy of the dose-shift approximation in estimating the delivered dose in SBRT of lung tumors considering setup errors and breathing motions.

Introduction: Geometrical uncertainties can result in a delivered dose to the tumor different from that estimated in the static treatment plan. The purpose of this project was to investigate the accuracy of the dose calculated to the clinical target volume (CTV) with the dose-shift approximation, in stereotactic body radiation therapy (SBRT) of lung tumors considering setup errors and breathing motion. The dose-shift method was compared with a beam-shift method with dose recalculation.

Practical approaches to approximating MTF and NPS in CT with an example application to task-based observer studies.

Purpose: To investigate two methods of approximating the Modulation Transfer Function (MTF) and Noise Power Spectrum (NPS) in computed tomography (CT) for a range of scan parameters, from limited image acquisitions.

Methods: The two methods consist of 1) using a linear systems approach to approximate the NPS for different filtered backprojection (FBP) kernels with a filter function derived from the kernel ratio of determined MTFs and 2) using an empirical fitted model to approximate the MTF and NPS. In both cases a scaling function accounts for variations in mAs and kV.