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arXiv2014

Heart-induced movements in the thorax as detected by MRI

In order to provide information for the use of radar in diagnostics a qualitative map of movements in the thorax has been obtained. This map was based on magnetic resonance image sequences of a human thorax during suspended respiration. The movements were measured using two distinct techniques. Segmentation provided measures of aorta dilatation and displacements, and image edge detection indicated other movements. The largest heart movements were found in the anterior and left regions of the heart with in-plane displacements on the order of 1 cm and which caused lung vessels displacements on the order of 2-3mm especially on the left side due to the heart ventricular. Mechanical coupling between the heart and aorta caused aorta displacements and shape distortions. Despite this coupling, aorta dilatations most likely reflected blood pressure variations.

physics.med-ph↗

arXiv2014

Generalized coordinate transformations for Monte Carlo (DOSXYZnrc and VMC++) verifications of DICOM compatible radiotherapy treatment plans

The International Electrotechnical Commission (IEC) has previously defined standard rotation operators for positive gantry, collimator and couch rotations for the radiotherapy DICOM coordinate system that is commonly used by treatment planning systems. Coordinate transformations to the coordinate systems of commonly used Monte Carlo (MC) codes (BEAMnrc/DOSXYZnrc and VMC++) have been derived and published in the literature. However, these coordinate transformations disregard patient orientation during the computed tomography (CT) scan, and assume the most commonly used 'head first, supine' orientation. While less common, other patient orientations are used in clinics - Monte Carlo verification of such treatments can be problematic due to the lack of appropriate coordinate transformations. In this work, a solution has been obtained by correcting the CT-derived phantom orientation and deriving generalized coordinate transformations for field angles in the DOSXYZnrc and VMC++ codes. The rotation operator that includes any possible patient treatment orientation was determined using the DICOM Image Orientation tag (0020,0037). The derived transformations of the patient image and beam direction angles were verified by comparison of MC dose distributions with the Eclipse treatment planning system, calculated for each of the eight possible patient orientations.

physics.med-ph↗

arXiv2014

The Surface Laplacian Technique in EEG: Theory and Methods

This paper reviews the method of surface Laplacian differentiation to study EEG. We focus on topics that are helpful for a clear understanding of the underlying concepts and its efficient implementation, which is especially important for EEG researchers unfamiliar with the technique. The popular methods of finite difference and splines are reviewed in detail. The former has the advantage of simplicity and low computational cost, but its estimates are prone to a variety of errors due to discretization. The latter eliminates all issues related to discretization and incorporates a regularization mechanism to reduce spatial noise, but at the cost of increasing mathematical and computational complexity. These and several others issues deserving further development are highlighted, some of which we address to the extent possible. Here we develop a set of discrete approximations for Laplacian estimates at peripheral electrodes and a possible solution to the problem of multiple-frame regularization. We also provide the mathematical details of finite difference approximations that are missing in the literature, and discuss the problem of computational performance, which is particularly important in the context of EEG splines where data sets can be very large. Along this line, the matrix representation of the surface Laplacian operator is carefully discussed and some figures are given illustrating the advantages of this approach. In the final remarks, we briefly sketch a possible way to incorporate finite-size electrodes into Laplacian estimates that could guide further developments.

physics.bio-ph↗

arXiv2014

Real time evaluation of overranging in helical computed tomography

Overranging or overscanning increases the dose delivered to patients undergoing helical Computed Tomography examinations. In order to reduce it, nowadays most of the multidetector tomographs close the X-ray beam aperture at the scan extremes. This technical innovation, usually referred to as dynamic or adaptive collimation, also influences the overranging assessment methods. In particular, the film free approach proposed in previous studies is not suitable for these modern tomographs. The present study aims to introduce a new method of estimating overranging with real time dosimetry, even suitable for tomographs equipped with adaptive collimation. The approach proposed is very easy to implement and time saving because only a pencil chamber is required. It is also equivalent in precision and in accuracy to the film based one, considered an absolute benchmark.

physics.med-ph↗

arXiv2014

A Novel Light Source Design for Spectral Tuning in Biomedical Imaging

We propose a novel architecture with a remote phosphor based modular and compact light source in a non-contact dermoscope prototype for skin cancer screening. The spectrum and color temperature of the output light can easily and significantly be changed depending on spectral absorption characteristics of the tissues being imaged. The new system has several advantages compared to state-of-the-art phosphor converted ultra-bright white LEDs, used in a wide range of medical imaging devices, which have a fixed spectrum and color temperature at a given operating point. In particular, the system can more easily be adapted to the requirements originating from different tissues in the human body which have wavelength dependent absorption and reflectivity. This leads to improved contrast for different kinds of imaged tissue components. The concept of such a lighting architecture can be vastly utilized in many other medical imaging devices including endoscopic systems.

physics.med-ph↗

arXiv2014

Trace element distribution in human teeth by x-ray fluorescence spectrometry and multivariate statistical analysis

X-ray fluorescence spectrometry (XRFS) was used as a multielement method of evaluation of individual whole human tooth or tooth tissues for their amounts of trace elements. Measurements were carried out on human enamel, dentine, and dental cementum, and some differences in tooth matrix composition were noted. In addition, the elemental concentrations determined in teeth from subjects of different ages, nutritional states, professions and gender, living under various environmental conditions and dietary habits, were included in a comparison by multivariate statistical analysis (MVSA) methods. By factor analysis it was established that inorganic components of human teeth varied consistently with their source in the tissue, with more in such tissue from females than in that from males, and more in tooth incisor than in tooth molar.

physics.med-ph↗

arXiv2014

Predictive Modelling of Bone Age through Classification and Regression of Bone Shapes

Bone age assessment is a task performed daily in hospitals worldwide. This involves a clinician estimating the age of a patient from a radiograph of the non-dominant hand. Our approach to automated bone age assessment is to modularise the algorithm into the following three stages: segment and verify hand outline; segment and verify bones; use the bone outlines to construct models of age. In this paper we address the final question: given outlines of bones, can we learn how to predict the bone age of the patient? We examine two alternative approaches. Firstly, we attempt to train classifiers on individual bones to predict the bone stage categories commonly used in bone ageing. Secondly, we construct regression models to directly predict patient age. We demonstrate that models built on summary features of the bone outline perform better than those built using the one dimensional representation of the outline, and also do at least as well as other automated systems. We show that models constructed on just three bones are as accurate at predicting age as expert human assessors using the standard technique. We also demonstrate the utility of the model by quantifying the importance of ethnicity and sex on age development. Our conclusion is that the feature based system of separating the image processing from the age modelling is the best approach for automated bone ageing, since it offers flexibility and transparency and produces accurate estimates.

cs.LG↗

arXiv2014

Monte Carlo simulation of MLC-shaped TrueBeam electron fields benchmarked against measurement

Modulated electron radiotherapy (MERT) and combined, modulated photon/electron radiotherapy (MPERT) have received increased research attention, having shown capacity for reduced low dose exposure to healthy tissue and comparable, if not improved, target coverage for a number of treatment sites. Accurate dose calculation tools are necessary for clinical treatment planning, and Monte Carlo (MC) is the gold standard for electron field simulation. With many clinics replacing older accelerators, MC source models of the new machines are needed for continued development, however, Varian has kept internal schematics of the TrueBeam confidential and electron phase-space sources have not been made available. TrueBeam electron fields are not substantially different from those generated by the Clinac 21EX, so we have modified the internal schematics of the Clinac 21EX to simulate TrueBeam electrons. BEAMnrc/DOSXYZnrc were used to simulate 5x5 and 20x20 cm$^2$ electron fields with MLC-shaped apertures. Secondary collimating jaws were set 0.5 cm beyond the MLC periphery and to 40x40 cm$^2$. Complete accelerator models agreed with diode measurement within 2%/2 mm at 12 and 20 MeV, and within 3%/3 mm at 6 MeV. Comparisons of measured depth and profile data showed dose-dependencies on jaw position; simulated energy fluences scored just above the phantom showed that, for small apertures, dose dependencies on jaw position are dominated by changes in the in-field energy fluence (not scattered by jaws or MLC) at 6 MeV, while at 20 MeV dose dependencies are dominated by the scattered component. Our models reproduce these jaw position dependencies, which is an asset as there is no consensus on the optimal position for jaws in modulated electron field delivery. Good agreement between simulation and measurement and flexibility in jaw position make our models appropriate for use in MERT and MPERT planning.

physics.med-ph↗

arXiv2014

Mathematical modeling applied to the left ventricle of heart

Background: How can mathematics help us to understand the mechanism of the cardiac motion? The best known approach is to take a mathematical model of the fibered structure, insert it into a more-or-less complex model of cardiac architecture, and then study the resulting fibers of activation that propagate through the myocardium. In our paper, we have attempted to create a novel software capable of demonstrate left ventricular (LV) model in normal hearts. Method: Echocardiography was performed on 70 healthy volunteers. Data evaluated included: velocity (radial, longitudinal, rotational and vector point), displacement (longitudinal and rotational), strain rate (longitudinal and circumferential) and strain (radial, longitudinal and circumferential) of all 16 LV myocardial segments. Using these data, force vectors of myocardial samples were estimated by MATLAB software, interfaced in the echocardiograph system. Dynamic orientation contraction (through the cardiac cycle) of every individual myocardial fiber could be created by adding together the sequential steps of the multiple fragmented sectors of that fiber. This way we attempted to mechanically illustrate the global LV model. Result: Our study shows that in normal cases myocardial fibers initiate from the posterior basal region of the heart, continues through the LV free wall, reaches the septum, loops around the apex, ascends, and ends at the superior-anterior edge of LV. Conclusion: We were able to define the whole LV myocardial model mathematically, by MATLAB software in normal subjects. This will enable physicians to diagnose and follow up many cardiac diseases when this software is interfaced within echocardiographic machines.

physics.med-ph↗

arXiv2014

Support vector machine classification of dimensionally reduced structural MRI images for dementia

We classify very-mild to moderate dementia in patients (CDR ranging from 0 to 2) using a support vector machine classifier acting on dimensionally reduced feature set derived from MRI brain scans of the 416 subjects available in the OASIS-Brains dataset. We use image segmentation and principal component analysis to reduce the dimensionality of the data. Our resulting feature set contains 11 features for each subject. Performance of the classifiers is evaluated using 10-fold cross-validation. Using linear and (gaussian) kernels, we obtain a training classification accuracy of 86.4% (90.1%), test accuracy of 85.0% (85.7%), test precision of 68.7% (68.5%), test recall of 68.0% (74.0%), and test Matthews correlation coefficient of 0.594 (0.616).

cs.CV↗

arXiv2014

Current Density Imaging through Acoustically Encoded Magnetometry: A Theoretical Exploration

The problem of determining a current density confined to a volume from measurements of the magnetic field it produces exterior to that volume is known to have non-unique solutions. To uniquely determine the current density, or the non-silent components of it, additional spatial encoding of the electric current is needed. In biological systems such as the brain and heart, which generate electric current associated with normal function, a reliable means of generating such additional encoding, on a spatial and temporal scale meaningful to the study of such systems, would be a boon for research. This paper explores a speculative method by which the required additional encoding might be accomplished, on the time scale associated with the propagation of sound across the volume of interest, by means of the application of a radially encoding pulsed acoustic spherical wave.

physics.med-ph↗

arXiv2014

Quantitative read-out of Al2O3:C,Mg-based fluorescent nuclear track detectors using a commercial confocal microscope

Fluorescent nuclear track detectors (FNTD) show great potential for applications in ion-beam therapy research, such as dosimetry, advanced beam characterization, in-vivo use or as radiobiological assay. A essential feature of FNTDs is their ability to assess the energy loss of single ions yielding for example LET estimations. This article describes the basic characterisations of FNTDs and our read-out system (a Zeiss LSM710 confocal laser scanning microscope) to enable quantative measurements of energy loss.

physics.ins-det↗

arXiv2014

Skewness and kurtosis as measures of range mixing in time resolved diode dosimetry

Technical Note describing studies, in 2011, of time resolved diode dosimetry in an anthropomorphic phantom at the Francis H. Burr Proton Therapy Center, Massachusetts General Hospital, Boston, MA. This technique measures the water equivalent path length (WEPL) to a diode dosimeter with sub-millimeter precision, using very little dose. It may allow one to use the proton stopping point (otherwise too uncertain) to cut between tissue to be treated and tissue to be spared, in cases (such as the prostate) where a diode can be placed in a cavity (the rectum) distal to the target. A potential problem is range mixing, where (because of scattering) protons may arrive at a diode with different energy-loss histories. The WEPL reported by such a diode is meaningless and must be ignored. We therefore use an array of diodes, of which some are likely to be at more favorable locations. In addition to the overall analysis of time resolved data, this Note describes in detail how range mixed diodes can be identified by looking at the skewness and kurtosis of the time dependent signal.

physics.med-ph↗

arXiv2014

Transient and secular radioactive equilibrium revisited

The two definitions of radioactive equilibrium are revisited in this paper. The terms activity equilibrium and effective life equilibrium are proposed to take the place of currently used terms transient equilibrium and secular equilibrium. The proposed new definitions have the advantage of providing a clearer physics meaning. Besides the well known instant activity equilibrium, another class of exact effective life-time equilibrium is also discussed in this letter.

physics.med-ph↗

arXiv2014

Development of a highly pixelated direct charge sensor, Topmetal-I, for ionizing radiation imaging

Using industrial standard 0.35μm CMOS Integrated Circuit process, we realized a highly pixelated sensor that directly collects charge via metal nodes placed on the top of each pixel and forms two dimensional images of charge cloud distribution. The first version, Topmetal-I, features a 64x64 pixel array of 80μm pitch size. Direct charge calibration reveals an average capacitance of 210fF per pixel. The charge collection noise is near the thermal noise limit. With the readout, individual pixel channels exhibit a most probable equivalent noise charge of 330e-.

physics.ins-det↗

arXiv2014

Mini-review on the temporal resolution of fluorescence imaging systems

Imaging of rapidly occurring events in biology requires high temporal resolution. In this review article, I have tried to investigate an approximate estimate to quantify temporal resolution limit of a fluorescence imaging system. It was realised that, the temporal resolution is essentially determined by the fact that, once excited, almost all ($99.9\%$) excited molecules relax to ground state. We determined the time required for $99.9\%$ of molecules to relax is about $3τ_p = 3/{(k_f +k_{nr})\log_{10}e}$, where $k_f +k_{nr}$ is the total emission rate. To arrive at this expression we assumed that, the quantum efficiency of the detector is unity, no scattering and there are no other loses. We further discuss few microscopy technique that are capable of high temporal resolution. These technique includes, multifocal multiphoton microscopy (MMM), multiple excitation spot optical microscopy (MESO) and multiple light-sheet microscopy (MLSM).

physics.med-ph↗

arXiv2014

Evaluation of Spatial Resolution and Noise Sensitivity of sLORETA Method for EEG Source Localization Using Low-Density Headsets

Electroencephalography (EEG) has enjoyed considerable attention over the past century and has been applied for diagnosis of epilepsy, stroke, traumatic brain injury and other disorders where 3D localization of electrical activity in the brain is potentially of great diagnostic value. In this study we evaluate the precision and accuracy of spatial localization of electrical activity in the brain delivered by a popular reconstruction technique sLORETA applied to EEG data collected by two commonly used low-density headsets with 14 and 19 measurement channels, respectively. Numerical experiments were performed for a realistic head model obtained by segmentation of MRI images. The EEG source localization study was conducted with a simulated single active dipole, as well as with two spatially separated simultaneously active dipoles, as a function of dipole positions across the neocortex, with several different noise levels in the EEG signals registered on the scalp. The results indicate that while the reconstruction accuracy and precision of the sLORETA method are consistently high in the case of a single active dipole, even with the low-resolution EEG configurations considered in the present study, successful localization is much more problematic in the case of two simultaneously active dipoles. The quantitative analysis of the width of the reconstructed distributions of the electrical activity allows us to specify the lower bound for the spatial resolution of the sLORETA-based 3D source localization in the considered cases.

physics.med-ph↗

arXiv2014

Artificial Left Ventricle

This Artificial left ventricle is based on a simple conic assumption shape for left ventricle where its motion is made by attached compressed elastic tubes to its walls which are regarded to electrical points at each nodal .This compressed tubes are playing the role of myofibers in the myocardium of the left ventricle. These elastic tubes have helical shapes and are transacting on these helical bands dynamically. At this invention we give an algorithm of this artificial left ventricle construction that of course the effect of the blood flow in LV is observed with making beneficiary used of sensors to obtain this effecting, something like to lifegates problem. The main problem is to evaluate powers that are interacted between elastic body (left ventricle) and fluid (blood). The main goal of this invention is to show that artificial heart is not just a pump, but mechanical modeling of LV wall and its interaction with blood in it (blood movement modeling) can introduce an artificial heart closed to natural heart.

physics.med-ph↗