Voxel-based analysis of diffusion MRI data is increasingly popular. However, most white matter voxels contain contributions from multiple fibre populations (often referred to as crossing fibres), and therefore voxel-averaged quantitative measures (e.g. fractional anisotropy) are not fibre-specific and have poor interpretability. Using higher-order diffusion models, parameters related to fibre d...

INTRODUCTION The presence of calcium deposits in the breast can be an indicator of malignancy, so the ability to detect such abnormalities by MRI would be significant. Calcium deposits have a different magnetic susceptibility from surrounding tissues that can in principle be observed using susceptibility weighted imaging (SWI) [1]. Here we perform simulations and phantom experiments to determin...

PURPOSE To develop a phantom for validating MRI pulse sequences and data processing methods to quantify microscopic diffusion anisotropy in the human brain. METHODS Using a liquid crystal consisting of water, detergent, and hydrocarbon, we designed a 0.5-L spherical phantom showing the theoretically highest possible degree of microscopic anisotropy. Data were acquired on the Connectome scanne...

Accurate knowledge of ionizing radiation dose from cone-beam CT (CBCT) imaging in radiotherapy is important to allow concomitant risks to be estimated and for justification of imaging exposures. This study uses a Monte Carlo CBCT model to calculate imaging dose for a wide range of imaging protocols for male and female patients. The Elekta XVI CBCT system was modeled using GATE and simulated dos...

Introduction It was shown recently in an isotropic water phantom that ADC values are not equal in each measured diffusion direction due to gradient mis-calibrations [1]. MR resonance frequency is also dependent on the orientation of anisotropic structures in the magnetic field [2], which possibly contributes to deviations in the diffusion measurement. We investigated the effect of orientation o...

Brain activation studies based on PET or fMRI seek to explore neuroscience questions by statistically analyzing the acquired images to produce statistical parametric images (SPIs). An increasingly wide range of univariate and multivariate analysis techniques are used to generate SPIs in order to detect mean-signal activations and/or long-range spatial interactions. However, little is known abou...

The primary aim of the present work was to analyze the effects of varying scatter-to-primary ratios on the appearance of simulated nodules in chest tomosynthesis section images. Monte Carlo simulations of the chest tomosynthesis system GE Definium 8000 VolumeRAD (GE Healthcare, Chalfont St. Giles, UK) were used to investigate the variation of scatter-to-primary ratios between different angular ...

This paper reports the implementation of the SIMIND Monte Carlo code on an IBM SP2 distributed memory parallel computer. Basic aspects of running Monte Carlo particle transport calculations on parallel architectures are described. Our parallelization is based on equally partitioning photons among the processors and uses the Message Passing Interface (MPI) library for interprocessor communicatio...

PURPOSE To analyze the effect of B0 field drift on multivoxel MR spectroscopic imaging and to propose an approach for its correction. THEORY AND METHODS It is shown, both theoretically and in a phantom, that for ∼30 min acquisitions a linear B0 drift (∼0.1 ppm/h) will cause localization errors that can reach several voxels (centimeters) in the slower varying phase encoding directions. An effi...

PURPOSE To present a technique for simultaneous mapping of T1 , T2 , and relative spin density (M0 ) in human lung using inversion recovery ultra-fast steady-state free precession (IR-ufSSFP) imaging. METHODS Pulmonary relaxometry with IR-ufSSFP is based on an interleaved time series acquisition of 2D images acquired at 1.5T. The technique was tested in a phantom and in four healthy volunteer...