Monte Carlo reference data sets for imaging research: Executive summary of the report of AAPM Research Committee Task Group 195.

The use of Monte Carlo simulations in diagnostic medical imaging research is widespread due to its flexibility and ability to estimate quantities that are challenging to measure empirically. However, any new Monte Carlo simulation code needs to be validated before it can be used reliably. The type and degree of validation required depends on the goals of the research project, but, typically, such validation involves either comparison of simulation results to physical measurements or to previously published results obtained with established Monte Carlo codes.

Evaluation of clinical full field digital mammography with the task specific system-model-based Fourier Hotelling observer (SMFHO) SNR.

Purpose: The purpose of this work is to evaluate the performance of the image acquisition chain of clinical full field digital mammography (FFDM) systems by quantifying their image quality, and how well the desired information is captured by the images.

Methods: The authors present a practical methodology to evaluate FFDM using the task specific system-model-based Fourier Hotelling observer (SMFHO) signal to noise ratio (SNR), which evaluates the signal and noise transfer characteristics of FFDM systems in the presence of a uniform polymethyl methacrylate phantom that models the attenuation of a 6 cm thick 20/80 breast (20% glandular/80% adipose). The authors model the system performance using the generalized modulation transfer function, which accounts for scatter blur and focal spot unsharpness, and the generalized noise power spectrum, both estimated with the phantom placed in the field of view.

Material-specific transfer function model and SNR in CT.

This study presents an analytical model for the edge spread function (ESF) of a clinical CT system that allows reliable fits of noisy ESF data. The model was used for the calculation of the material-specific transfer function TF and an estimation of the signal transfer and the signal-to-noise ratio (SNR) in 2D. Images of the Catphan phantom were acquired with a clinical Siemens Somatom Sensation Cardiac 64 CT scanner combining four different x-ray tube outputs (40, 150, 250 and 350 mAs) with four different reconstruction filters, which covered the range from very smooth (B10s) to very sharp (B70s).

Reducing radiation dose to the female breast during CT coronary angiography: a simulation study comparing breast shielding, angular tube current modulation, reduced kV, and partial angle protocols using an unknown-location signal-detectability metric.

Purpose: The authors compared the performance of five protocols intended to reduce dose to the breast during computed tomography (CT) coronary angiography scans using a model observer unknown-location signal-detectability metric.

Methods: The authors simulated CT images of an anthropomorphic female thorax phantom for a 120 kV reference protocol and five "dose reduction" protocols intended to reduce dose to the breast: 120 kV partial angle (posteriorly centered), 120 kV tube-current modulated (TCM), 120 kV with shielded breasts, 80 kV, and 80 kV partial angle (posteriorly centered). Two image quality tasks were investigated: the detection and localization of 4-mm, 3.

A database for estimating organ dose for coronary angiography and brain perfusion CT scans for arbitrary spectra and angular tube current modulation.

Purpose: The purpose of this study was to develop a database for estimating organ dose in a voxelized patient model for coronary angiography and brain perfusion CT acquisitions with any spectra and angular tube current modulation setting. The database enables organ dose estimation for existing and novel acquisition techniques without requiring Monte Carlo simulations.

Methods: The study simulated transport of monoenergetic photons between 5 and 150 keV for 1000 projections over 360° through anthropomorphic voxelized female chest and head (0° and 30° tilt) phantoms and standard head and body CTDI dosimetry cylinders.

Signal detection and location-dependent noise in cone-beam computed tomography using the spatial definition of the Hotelling SNR.

Purpose: Quality assurance in computed tomography (CT) is commonly performed with the Fourier-based modulation transfer function (MTF) and the noise variance, while more recently the noise power spectrum (NPS) has increased in popularity. The Fourier-based methods make assumptions such as shift-invariance and cyclostationarity. These assumptions are violated in real clinical systems and consequently are expected to result in systematic errors.

Computational high-resolution heart phantoms for medical imaging and dosimetry simulations.

Cardiovascular disease in general and coronary artery disease (CAD) in particular, are the leading cause of death worldwide. They are principally diagnosed using either invasive percutaneous transluminal coronary angiograms or non-invasive computed tomography angiograms (CTA). Minimally invasive therapies for CAD such as angioplasty and stenting are rendered under fluoroscopic guidance.

penMesh--Monte Carlo radiation transport simulation in a triangle mesh geometry.

We have developed a general-purpose Monte Carlo simulation code, called penMesh, that combines the accuracy of the radiation transport physics subroutines from PENELOPE and the flexibility of a geometry based on triangle meshes. While the geometric models implemented in most general-purpose codes--such as PENELOPE's quadric geometry--impose some limitations in the shape of the objects that can be simulated, triangle meshes can be used to describe any free-form (arbitrary) object. Triangle meshes are extensively used in computer-aided design and computer graphics.

Singular value description of a digital radiographic detector: theory and measurements.

The H operator represents the deterministic performance of any imaging system. For a linear, digital imaging system, this system operator can be written in terms of a matrix, H, that describes the deterministic response of the system to a set of point objects. A singular value decomposition of this matrix results in a set of orthogonal functions (singular vectors) that form the system basis.

Anisotropic imaging performance in breast tomosynthesis.

We describe the anisotropy in imaging performance caused by oblique x-ray incidence in indirect detectors for breast tomosynthesis based on columnar scintillator screens. We use MANTIS, a freely available combined x-ray, electron, and optical Monte Carlo transport package which models the indirect detection processes in columnar screens, interaction by interaction. The code has been previously validated against published optical distributions.

Monte Carlo simulation of a realistic anatomical phantom described by triangle meshes: application to prostate brachytherapy imaging.

Purpose: Monte Carlo codes can simulate the transport of radiation within matter with high accuracy and can be used to study medical applications of ionising radiations. The aim of our work was to develop a Monte Carlo code capable of generating projection images of the human body. In order to obtain clinically realistic images a detailed anthropomorphic phantom was prepared.

Anisotropic imaging performance in indirect x-ray imaging detectors.

We report on the variability in imaging system performance due to oblique x-ray incidence, and the associated transport of quanta (both x rays and optical photons) through the phosphor, in columnar indirect digital detectors. The analysis uses MANTIS, a combined x-ray, electron, and optical Monte Carlo transport code freely available. We describe the main features of the simulation method and provide some validation of the phosphor screen models considered in this work.

Generalizing the MTF and DQE to include x-ray scatter and focal spot unsharpness: application to a new microangiographic system.

Detector characterization with modulation transfer function (MTF) and detective quantum efficiency (DQE) inadequately predicts image quality when the imaging system includes focal spot unsharpness and patient scatter. The concepts of MTF, noise power spectrum, noise equivalent quanta and DQE were referenced to the object plane and generalized to include the effect of geometric unsharpness due to the finite size of the focal spot and the effect of the spatial distribution and magnitude of x-ray scatter due to the patient. The generalized quantities provide performance characteristics that consider the complete imaging system, but reduce to a description of the detector properties without magnification or scatter.

Efficiency of the Human Observer Compared to an Ideal Observer Based on a Generalized NEQ Which Incorporates Scatter and Geometric Unsharpness: Evaluation with a 2AFC Experiment.

Under certain assumptions the detectability of the ideal observer can be defined as the integral of the system Noise Equivalent Quanta multiplied by the squared object spatial frequency distribution. Using the detector Noise-Equivalent-Quanta (NEQ(D)) for the calculation of detectability inadequately describes the performance of an x-ray imaging system because it does not take into account the effects of patient scatter and geometric unsharpness. As a result, the ideal detectability index is overestimated, and hence the efficiency of the human observer in detecting objects is underestimated.

Generalized Performance Evaluation of X-ray Image Intensifier compared with a Microangiographic System.

Standard objective parameters such as MTF, NPS, NEQ and DQE do not reflect complete system performance, because they do not account for geometric unsharpness due to finite focal spot size and scatter due to the patient. The inclusion of these factors led to the generalization of the objective quantities, termed GMTF, GNNPS, GNEQ and GDQE defined at the object plane. In this study, a commercial x-ray image intensifier (II) is evaluated under this generalized approach and compared with a high-resolution, ROI microangiographic system previously developed and evaluated by our group.

Study of the Generalized MTF and DQE for a New Microangiographic System.

We study the properties of a new microangiographic system, consisting of a Region of Interest (ROI) microangiographic detector, x-ray source, and patient. The study was performed under conditions intended for clinical procedures such as neurological diagnostic angiograms as well as treatments of intracranial aneurysms, and vessel-stenoses. The study was performed in two steps; first a uniform head equivalent phantom was used as a "filter".

Measurement of flow modification in phantom aneurysm model: comparison of coils and a longitudinally and axially asymmetric stent--initial findings.

Dye-dilution imaging sequences were performed and time-density curves were constructed in elastomer vessel aneurysm models to demonstrate the effectiveness of coils and an asymmetric stent in disrupting standard vortex flow. Compared with the use of coils, the use of stents led to marked flow modification, as seen with imaging sequences, and substantially slower inflow, as indicated by time-density curves, owing to the low-porosity region of the stent that covers the aneurysm orifice. These flow examination results indicate that potentially favorable flow modification features can be created by using the described asymmetric stent design, the use of which may lead to alternative methods of image-guided endovascular cerebral aneurysm therapy.

Micro-angiography for neuro-vascular imaging. I. Experimental evaluation and feasibility.

Minimally invasive image-guided neuro-vascular interventions require very high image-resolution and quality, specifically over regions-of-interest (ROI) crucial to the procedure. ROI imaging or micro-angiography, allows limited patient integral radiation dose while permitting rapid frame transfer of high-resolution images. The design and performance of a charge coupled device (CCD) based x-ray detector or micro-angiographic camera was assessed for neuro-vascular procedures.