KEYWORDS: Lung, Monte Carlo methods, Image quality, Image resolution, Phase modulation, Computed tomography, Tissues, 3D modeling, Natural surfaces, Breast
Using numerical simulations, the influence of various imaging parameters on the resulting image can be determined for various imaging technologies. To achieve this, visualization of fine tissue structures needed to evaluate the image quality with different radiation quality and dose is essential. The present work examines a method that employs simulations of the imaging process using Monte Carlo methods and a combination of a standard and higher resolution voxel models. A hybrid model, based on nonlinear uniform rational B-spline and polygon mesh surfaces, was constructed from an existing voxel model of a female patient of a resolution in the range of millimeters. The resolution of the hybrid model was 500 μm, i.e., substantially finer than that of the original model. Furthermore, a high resolution lung voxel model [(0.11 mm)3 voxel volume, slice thickness: 114 μm] was developed from the specimen of a left lung lobe. This has been inserted into the hybrid model, substituting its left lung lobe and resulting in a dual-lattice geometry model. “Dual lattice” means, in this context, the combination of voxel models with different resolutions. Monte Carlo simulations of radiographic imaging were performed and the fine structure of the lung was easily recognizable.
In radiography there is generally a conflict between the best image quality and the lowest possible patient dose. A proven
method of dosimetry is the simulation of radiation transport in virtual human models (i.e. phantoms). However, while the
resolution of these voxel models is adequate for most dosimetric purposes, they cannot provide the required organ fine
structures necessary for the assessment of the imaging quality.
The aim of this work is to develop hybrid/dual-lattice voxel models (called also phantoms) as well as simulation methods
by which patient dose and image quality for typical radiographic procedures can be determined. The results will provide
a basis to investigate by means of simulations the relationships between patient dose and image quality for various
imaging parameters and develop methods for their optimization.
A hybrid model, based on NURBS (Non Linear Uniform Rational B-Spline) and PM (Polygon Mesh) surfaces, was
constructed from an existing voxel model of a female patient. The organs of the hybrid model can be then scaled and
deformed in a non-uniform way i.e. organ by organ; they can be, thus, adapted to patient characteristics without losing
their anatomical realism. Furthermore, the left lobe of the lung was substituted by a high resolution lung voxel model,
resulting in a dual-lattice geometry model. “Dual lattice” means in this context the combination of voxel models with
different resolution.
Monte Carlo simulations of radiographic imaging were performed with the code EGS4nrc, modified such as to perform
dual lattice transport. Results are presented for a thorax examination.
Gold nanoparticles (GNPs) were demonstrated as X-ray imaging contrast agents and radiosensitizers in mice. However, the translational medical applications of GNPs in to the clinical practice need further detailed information on the biological effects related to the enhanced doses in malignant and healthy cells. The idea of improving radiotherapy with high atomic number materials, especially gold foils, was initiated in our research unit in the 1980s. Recently, experimental and theoretical efforts were made to investigate the potential improvement of imaging and radiotherapy with GNPs. Initially, the present work attempts to validate the dose enhancement effects of GNPs to cancer cells; secondly, it intends to examine the possible side effects on healthy cells when using GNPs as X-ray contrast agent. In this study, three Monte Carlo simulation programs, namely PENELOPE-2011, GEANT4 and EGSnrc were used to simulate the local energy deposition and the resulting dose enhancement of GNPs. Diameters of the GNPs were assumed to be 2 nm, 15 nm, 50 nm, 100 nm and 200 nm. The X-ray energy spectra for irradiation were 60 kVp, 80 kVp, 100 kVp, 150 kVp with a filtering of 2.7 mm Al for projectional radiography, and 8 mm Al for 100 kVp and 150 kVp for computed tomography. Additional peak energy of 200 kVp was simulated for radiotherapy purpose. The information of energy deposition and dose enhancement can help understanding the physical processes of medical imaging and the implication of nanoparticles in radiotherapy.
The international standard IEC 62220-1-2 defines the measurement procedure for determination of the detective quantum
efficiency (DQE) of digital x-ray imaging devices used in mammography. A mobile setup complying to this standard and
adaptable to most current systems was constructed in the Helmholtz Zentrum München to allow for an objective
technical comparison of current full field digital mammography units employed in mammography screening in Germany.
This article demonstrates the setup's capabilities with a focus on the measurement uncertainties of all quantities
contributing to DQE measurements. Evaluation of uncertainties encompasses results from measurements on a Sectra
Microdose Mammography in clinical use, as well as on a prototype of a Fujifilm Amulet system at various radiation
qualities. Both systems have a high spatial resolution of 50 μm × 50 μm. The modulation transfer function (MTF), noise
power spectrum (NPS) and DQE of the Sectra MDM are presented in comparison to results previously published by
other authors.
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