Physics - Medical Physics Publications (50)


Physics - Medical Physics Publications

Pimple is one of the most common skin diseases for humans. The mechanical modeling of pimple growth is very limited. A finite element model is developed to quantify the deformation field with the expansion of follicle, and then the mechanical stimulus is related to the sensation of pain during the development of pimple. Read More

Background: It is still unknown if physiological complexity and autocorrelations (AC) of long-range stride interval (SI) time series are related to walking direction (WD) and application of galvanic vestibular stimulation (GVS). Methods and results: The SI fluctuations versus time for 34 healthy people walking 15 minutes on an instrumented treadmill is studied in four conditions: forward walking (FW) without GVS (FW_{S0}) and with GVS (FW_{S+}), and backward walking without GVS (BW_{S0}) and with GVS (BW_{S+}). The time series are then analysed from a spatio-temporal point of view and from a long-range AC point of view: particular attention is paid to the Hurst exponent (\alpha) and to the Minkowski fractal dimension, interpreted as indexes expressing predictability and complexity of the time series respectively. Read More

High-dose-rate brachytherapy is a tumor treatment method where a highly radioactive source is brought in close proximity to the tumor. In this paper we develop a simulated annealing algorithm to optimize the dwell times at preselected dwell positions to maximize tumor coverage under dose-volume constraints on the organs at risk. Compared to existing algorithms, our algorithm has advantages in terms of speed and objective value and does not require an expensive general purpose solver. Read More

In electroencephalography (EEG) source imaging, the inverse source estimates are depth biased in such a way that their maxima are often close to the sensors. This depth bias can be quantified by inspecting the statistics (mean and co-variance) of these estimates. In this paper, we find weighting factors within a Bayesian framework for the used L1/L2 sparsity prior that the resulting maximum a posterior (MAP) estimates do not favor any particular source location. Read More

Knowing the correct skull conductivity is crucial for the accuracy of EEG source imaging, but unfortunately, its true value, which is inter- and intra-individually varying, is difficult to determine. In this paper, we propose a statistical method based on the Bayesian approximation error approach to compensate for source imaging errors related to erroneous skull conductivity. We demonstrate the potential of the approach by simulating EEG data of focal source activity and using the dipole scan algorithm and a sparsity promoting prior to reconstruct the underlying sources. Read More

A sperm-driven micromotor is presented as cargo-delivery system for the treatment of gynecological cancers. This particular hybrid micromotor is appealing to treat diseases in the female reproductive tract, the physiological environment that sperm cells are naturally adapted to swim in. Here, the single sperm cell serves as an active drug carrier and as driving force, taking advantage of its swimming capability, while a laser-printed microstructure coated with a nanometric layer of iron is used to guide and release the sperm in the desired area by an external magnet and structurally imposed mechanical actuation, respectively. Read More

In the Alvarez-Macovski[1] method, the line integrals of the x-ray basis set coefficients are computed from measurements with multiple spectra. An important question is whether the data are invertible. This paper presents a proof that measurements with two spectra and a photon counting detector with pileup are invertible. Read More

Object This study proposes a scale space based algorithm for automated segmentation of single-shot tagged images of modest SNR. Furthermore the algorithm was designed for analysis of discontinuous or shearing types of motion, i.e. Read More

The cardiovascular system is composed of the heart, blood and blood vessels. Regarding the heart, cardiac conditions are determined by the electrocardiogram, that is a noninvasive medical procedure. In this work, we propose autoregressive process in a mathematical model based on coupled differential equations in order to model electrocardiogram signals. Read More

By means of a recently-proposed metric or structural derivative, called scale-q-derivative approach, we formulate differential equation that models the cell death by a radiation exposure in tumor treatments. The considered independent variable here is the absorbed radiation dose D instead of usual time. The survival factor, Fs, for radiation damaged cell obtained here is in agreement with the literature on the maximum entropy principle, as it was recently shown and also exhibits an excellent agreement with the experimental data. Read More

Due to its wide field of view, cone-beam computed tomography (CBCT) is plagued by large amounts of scatter, where attenuated photons hit the detector, and corrupt the linear models used for reconstruction. Given that one can generate a good estimate of scatter however, then image accuracy can be retained. In the context of adaptive radiotherapy, one usually has a low-scatter planning CT image of the same patient at an earlier time. Read More

In most of the under developed nations, access to basic health care is scarce. A heater is an indispensable device for many applications, especially for medical purposes. As such a simple and easy to make heater from readily available materials becomes a valuable equipment to help alleviate the human health problems. Read More

Robotics enables a variety of unconventional actuation strategies to be used for endoscopes, resulting in reduced trauma to the GI tract. For transmission of force to distally mounted endoscopic instruments, robotically actuated tendon sheath mechanisms are the current state of the art. Robotics in surgical endoscopy enables an ergonomic mapping of the surgeon movements to remotely controlled slave arms, facilitating tissue manipulation. Read More

Energetic ions lose their energy in tissue mainly by ionising its molecules. This produces secondary electrons which transport this energy radially away from the ion path. The ranges of most of these electrons do not exceed a few nanometres, therefore large energy densities (radial doses) are produced within a narrow region around the ion trajectory. Read More

We demonstrate the determination of the location of the distal-end of a fibre-optic device deep in tissue through the imaging of ballistic and snake photons using a time resolved single-photon detector array. The position was determined to centimetre accuracy, within clinically relevant settings and models. This technique can overcome the limitations imposed by tissue scattering in optically determining the in vivo location of fibre-optic medical instruments. Read More

The patented and proven ABALONE Photosensor Technology (Daniel Ferenc, U.S. Patent 9,064,678, 2010) has the capability of opening new horizons in the fields of fundamental physics, functional medical imaging, and nuclear security. Read More

In numerous applications, Fourier-domain optical coherence tomography (FD-OCT) suffers from a limited imaging depth due to signal roll-off, a limited focal range, and autocorrelation noise. Here, we propose a parallel full-field FD-OCT imaging method that uses a swept laser source and an area camera in combination with an off-axis reference, which is incident on the camera at a small angle. As in digital off-axis holography, this angle separates autocorrelation signals and the complex conjugated mirror image from the actual signal in Fourier space. Read More

3D-Polarized Light Imaging (3D-PLI) reconstructs nerve fibers in histological brain sections by measuring their birefringence. This study investigates another effect caused by the optical anisotropy of brain tissue - diattenuation. Based on numerical and experimental studies and a complete analytical description of the optical system, the diattenuation was determined to be below 4 % in rat brain tissue and to have negligible impact on the fiber orientations derived by 3D-PLI. Read More

The mechanisms by which organs acquire their functional structure and realize its maintenance (or homeostasis) over time are still largely unknown. In this paper, we investigate this question on adipose tissue. Adipose tissue can represent 20 to 50% of the body weight. Read More

The relation between the parameters of the microscopic structure of the myocardium and the spin dephasing is analyzed. The microscopic structure of the myocardium is described in terms of Krogh's capillary model. In this model the myocardium is reduced to a single capillary which is surrounded by a concentric tissue cylinder. Read More

The properties of dephasing and the resulting relaxation of the magnetization are the basic principle on which all magnetic resonance imaging methods are based. The signal obtained from the gyrating spins is essentially determined by the properties of the considered tissue. Especially the susceptibility differences caused by magnetized materials (for example, deoxygenated blood, BOLD-effect) or magnetic nanoparticles are becoming more important for biomedical imaging. Read More

In this work, the time evolution of the free induction decay caused by the local dipole field of a spherical magnetic perturber is analyzed. The complicated treatment of the diffusion process is considered by the strong-collision approximation that allows a determination of the free induction decay in dependence of the underlying microscopic tissue parameters such as diffusion coefficient, sphere radius and susceptibility difference. The interplay between susceptibility- and diffusion-mediated effects yields several dephasing regimes of which, so far, only the classical regimes of motional narrowing and static dephasing for dominant and negligible diffusion, respectively, were extensively examined. Read More

Purpose: Implanted fiducial markers are often used in radiotherapy to facilitate accurate visualization and localization of tumors. Typically, such markers are used to aid daily patient positioning and to verify the target's position during treatment. This work introduces a novel, automated method for identifying fiducial markers in planar x-ray imaging. Read More

Intensity modulated proton therapy (IMPT) provides highly conformal dose distributions through the application of multiple, angularly spaced fields, each applying an ad-hoc pattern of spatially varying particle fluences. In particular, Bragg peaks are simultaneously optimized for all the fields. Once the number and the direction of the fields are set, the dose distribution of the IMPT plan is determined by the dose constraints assigned to specific organs-at-risk (OARs) surrounding the tumour. Read More

In this publication, the interactive planning and reconstruction of cranial 3D Implants under the medical prototyping platform MeVisLab as alternative to commercial planning software is introduced. In doing so, a MeVisLab prototype consisting of a customized data-flow network and an own C++ module was set up. As a result, the Computer-Aided Design (CAD) software prototype guides a user through the whole workflow to generate an implant. Read More

In the orthognathic surgery, dental splints are important and necessary to help the surgeon reposition the maxilla or mandible. However, the traditional methods of manual design of dental splints are difficult and time-consuming. The research on computer-aided design software for dental splints is rarely reported. Read More

We propose the use of a combination of ultrasonic and magnetic fields in conductive media for the creation of RF electrical current via the Lorentz force, in order to achieve current generation with extreme sub-wavelength resolution at large depth. We demonstrate the modeling, generation, and measurement of Lorentz current in conductive solution, and show that this current can be localized at a distance of 13 $cm$ from the ultrasonic source to a region about three orders of magnitude smaller than the corresponding wavelength of electromagnetic waves at the same operation frequency. Our results exhibit greater depth, tighter localization, and closer agreement with prediction than previous work on the measurement of Lorentz current in a solution of homogeneous conductivity. Read More

X-ray fluorescence computed tomography based on sheet-beam can save a huge amount of time to obtain a whole set of projections using synchrotron. However, it is clearly unpractical for most biomedical research laboratories. In this paper, polychromatic X-ray fluorescence computed tomography with sheet-beam geometry is tested by Monte Carlo simulation. Read More

A major open challenge in neuroscience is the ability to measure and perturb neural activity in vivo from well-defined neural sub-populations at cellular resolution anywhere in the brain. However, limitations posed by scattering and absorption prohibit non-invasive (surface) multiphoton approaches for deep (>2mm) structures, while Gradient Refreactive Index (GRIN) endoscopes are thick and cause significant damage upon insertion. Here, we demonstrate a novel microendoscope to image neural activity at arbitrary depths via an ultrathin multimode optical fiber (MMF) probe that is 5-10X thinner than commercially available microendoscopes. Read More

Virtual heart models have been proposed to enhance the safety of implantable cardiac devices through closed loop validation. To communicate with a virtual heart, devices have been driven by cardiac signals at specific sites. As a result, only the action potentials of these sites are sensed. Read More

Image resolvability is the primary concern in imaging. This paper reports an estimation of the full width at half maximum of the point spread function from a Fourier domain plot of real sample images by neither using test objects, nor defining a threshold criterion. We suggest that this method can be applied to any type of image, independently of the imaging modality. Read More

Brain CT has become a standard imaging tool for emergent evaluation of brain condition, and measurement of midline shift (MLS) is one of the most important features to address for brain CT assessment. We present a simple method to estimate MLS and propose a new alternative parameter to MLS: the ratio of MLS over the maximal width of intracranial region (MLS/ICWMAX). Three neurosurgeons and our automated system were asked to measure MLS and MLS/ICWMAX in the same sets of axial CT images obtained from 41 patients admitted to ICU under neurosurgical service. Read More

The problem of variable cell survival probability along the spread-out Bragg peak is one of the long standing problems in planning and optimisation of ion-beam therapy. This problem is considered using the multiscale approach to the physics of ion-beam therapy. The physical reasons for this problem are analysed and understood on a quantitative level. Read More

Purpose: This work analyses relaxation in balanced pseudo steady-state free precession sequences (pSSFP) and provides an optimal control framework to optimize MR-Fingerprinting sequences with respect to noise in the $T_1$- and $T_2$-maps. Method: The Bloch equations were reformulated in spherical coordinates and numerical optimizations of the excitation pattern were performed based on the Cram\'er-Rao bound. The performance of resulting patterns was tested with simulations, as well as in vivo experiments in the human brain. Read More

High-resolution non-invasive 3D study of intact spine and spinal cord morphology on the level of complex vascular and neuronal organization is a crucial issue for the development of treatments for the injuries and pathologies of central nervous system (CNS). X-ray phase contrast tomography enables high quality 3D visualization in ex-vivo mouse model of both vascular and neuronal network of the soft spinal cord tissue at the scale from millimeters to hundreds of nanometers without any contrast agents and sectioning. Until now, 3D high resolution visualization of spinal cord mostly has been limited by imaging of organ extracted from vertebral column because high absorbing boney tissue drastically reduces the morphological details of soft tissue in image. Read More

The secondary neutron fields at the deep tumor therapy terminal at HIRFL (Heavy Ion Research Facility in Lanzhou) were investigated. The distributions of neutron ambient dose equivalent were measured with a FHT762 Wendi-II neutron ambient dose equivalent meter as the 12C ions with energies of 165, 207, 270, and 350 MeV/u bombarded on thick tissue-like targets. The thickness of targets used in experiments is larger than the range of the carbon ions. Read More

A split feasibility formulation for the inverse problem of intensity-modulated radiation therapy (IMRT) treatment planning with dose-volume constraints (DVCs) included in the planning algorithm is presented. It involves a new type of sparsity constraint that enables the inclusion of a percentage-violation constraint in the model problem and its handling by continuous (as opposed to integer) methods. We propose an iterative algorithmic framework for solving such a problem by applying the feasibility-seeking CQ-algorithm of Byrne combined with the automatic relaxation method (ARM) that uses cyclic projections. Read More

Magnetic Particle Imaging (MPI) has been shown to provide remarkable contrast for imaging applications such as angiography, stem cell tracking, and cancer imaging. Recently, there is growing interest in the functional imaging capabilities of MPI, where color MPI techniques have explored separating different nanoparticles, which could potentially be used to distinguish nanoparticles in different states or environments. Viscosity mapping is a promising functional imaging application for MPI, as increased viscosity levels in vivo have been associated with numerous diseases such as hypertension, atherosclerosis, and cancer. Read More

An instability of a liquid droplet traversed by an energetic ion is explored. This instability is brought about by the predicted shock wave induced by the ion. An observation of multifragmentation of small droplets traversed by ions with high linear energy transfer is suggested to demonstrate the existence of shock waves. Read More

Repeated computed tomography (CT) scans are required in some clinical applications such as image-guided radiotherapy and follow-up observations over a time period. To optimize the radiation dose utility, a normal-dose (or full-dose) CT scan is often first performed to set up reference, followed by a series of low-dose scans. Using the previous normal-dose scan to improve follow-up low-dose scans reconstruction has drawn great interests recently, such as the previous normal-dose induced nonlocal means (ndiNLM) regularization method. Read More

Muon Spin Rotation is employed, for the first time, to investigate the spin dynamics of ferritin proteins isolated from the brain of an Alzheimer's disease (AD) patient and of a healthy control, using a reference sample of horse spleen ferritin. A model based on the N\'eel theory of superparamagnetism is developed in order to interpret the spin relaxation rate of the muons stopping in the core of the protein. In light of this model, our preliminary observations show that ferritins from the healthy control are filled with a mineral compatible with ferrihydrite, while ferritins from the AD patient contain a crystalline phase with a larger magnetocrystalline anisotropy, possibly magnetite or maghemite. Read More

Parametric imaging is a compartmental approach that processes nuclear imaging data to estimate the spatial distribution of the kinetic parameters governing tracer flow. The present paper proposes a novel and efficient computational method for parametric imaging which is potentially applicable to several compartmental models of diverse complexity and which is effective in the determination of the parametric maps of all kinetic coefficients. We consider applications to [{18}F]-fluorodeoxyglucose Positron Emission Tomography (FDG--PET) data and analyze the two--compartment catenary model describing the standard FDG metabolization by an homogeneous tissue and the three--compartment non--catenary model representing the renal physiology. Read More

We propose and demonstrate an ultrasonic communication link using spatial degrees of freedom to increase data rates for deeply implantable medical devices. Low attenuation and millimeter wavelengths make ultrasound an ideal communication medium for miniaturized low-power implants. While small spectral bandwidth has drastically limited achievable data rates in conventional ultrasonic implants, large spatial bandwidth can be exploited by using multiple transducers in a multiple-input/multiple-output system to provide spatial multiplexing gain without additional power, larger bandwidth, or complicated packaging. Read More

There is mounting evidence of a link between the properties of electroencephalograms (EEGs) of depressive patients and the outcome of pharmacotherapy. The goal of this study was to develop an EEG biomarker of antidepressant treatment response which would require only a single EEG measurement. We recorded resting, 21-channel EEG in 17 inpatients suffering from bipolar depression in eyes closed and eyes open conditions. Read More

Previous research on unstable footwear has suggested that it may induce plantar mechanical noise during walking. The purpose of this study was to explore whether unstable footwear could be considered as a noise-based training gear to exercise body center of mass (CoM) motion during walking or not. Ground reaction forces were collected among 24 healthy young women walking at speeds between 3 and 6 km h-1 with control running shoes and unstable rocker-bottom shoes. Read More

Real-time fMRI neurofeedback (rtfMRI-nf) with simultaneous EEG allows volitional modulation of BOLD activity of target brain regions and investigation of related electrophysiological activity. We applied this approach to study correlations between thalamic BOLD activity and alpha EEG rhythm. Healthy volunteers in the experimental group (EG, n=15) learned to upregulate BOLD activity of the target region consisting of the mediodorsal (MD) and anterior (AN) thalamic nuclei using the rtfMRI-nf during retrieval of happy autobiographical memories. Read More

A new concept of permanent magnet systems for guiding superparamagnetic particles on arbitrary trajectories is proposed. The basic concept is to use one magnet system with a strong and homogeneous (dipolar) magnetic field to magnetize and orient the particles. A second constantly graded field (quadrupolar) is superimposed to the first to generate a force. Read More

Diffusion MRI measurements using hyperpolarized gases are generally acquired during patient breath hold, which yields a compromise between achievable image resolution, lung coverage and number of b-values. In this work, we propose a novel method that accelerates the acquisition of MR diffusion data by undersampling in both spatial and b-value dimensions, thanks to incorporating knowledge about the signal decay into the reconstruction (SIDER). SIDER is compared to total variation (TV) reconstruction by assessing their effect on both the recovery of ventilation images and estimated mean alveolar dimensions (MAD). Read More