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The equivalence of multi-criteria methods for radiotherapy plan optimization.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Several methods can be used to achieve multi-criteria optimization of radiation therapy treatment planning, which strive for Pareto-optimality. The property of the solution being Pareto optimal is desired, because it guarantees that no criteria can be improved without deteriorating another criteria. The most widely used methods are the weighted-sum method, in which the different treatment objectives are weighted, and constrained optimization methods, in which treatment goals are set and the algorithm has to find the best plan fulfilling these goals. The constrained method used in this paper, the 2pc (2-phase -constrain...
Source: Physics in Medicine and Biology - November 20, 2009 Category: Physics Authors: Breedveld S, Storchi PR, Heijmen BJ Tags: Phys Med Biol Source Type: journals

The correlation between mass-averaged SAR and temperature elevation in the human head model exposed to RF near-fields from 1 to 6 GHz.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In the present study, we investigate the relationship between the mass-averaged specific absorption rate (SAR) and temperature elevation in anatomically based Japanese head models due to the dipole antenna. A homogeneous cubical model is also used as a basis for the investigation. The frequency region considered is from 1 to 6 GHz. We focused on the averaging mass of SAR, which maximizes the correlation with local temperature elevation. An averaged SAR over 10 g was found to reasonably correlate with local temperature elevation even for frequencies from 3 to 6 GHz. The dominant factor influencing the correlation betwee...
Source: Physics in Medicine and Biology - November 20, 2009 Category: Physics Authors: Hirata A, Fujiwara O Tags: Phys Med Biol Source Type: journals

Combined optical and single photon emission imaging: preliminary results.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In vivo optical imaging instruments are generally devoted to the acquisition of light coming from fluorescence or bioluminescence processes. Recently, an instrument was conceived with radioisotopic detection capabilities (Kodak in Vivo Multispectral System F) based on the conversion of x-rays from the phosphorus screen. The goal of this work is to demonstrate that an optical imager (IVIS 200, Xenogen Corp., Alameda, USA), designed for in vivo acquisitions of small animals in bioluminescent and fluorescent modalities, can even be employed to detect signals due to radioactive tracers. Our system is based on scintillator ...
Source: Physics in Medicine and Biology - November 20, 2009 Category: Physics Authors: Boschi F, Spinelli AE, D'Ambrosio D, Calderan L, Marengo M, Sbarbati A Tags: Phys Med Biol Source Type: journals

The effect of electron collimator leaf shape on the build-up dose in narrow electron MLC fields.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Previously, we have found that the build-up dose from abutting narrow electron beams formed with unfocussed electron multi-leaf collimator (eMLC) steal leaves was higher than with the respective open field. To investigate more closely the effect of leaf material and shape on dose in the build-up region, straight, round (radius 1.5 cm) and leaf ends with a different front face angle of alpha (leaf front face pointing towards the beam axis at an angle of 90 - alpha) made of steel, brass and tungsten were modelled using the BEAMnrc code. Based on a treatment head simulation of a Varian 2100 C/D linac, depth-dose curves an...
Source: Physics in Medicine and Biology - November 20, 2009 Category: Physics Authors: Vatanen T, Traneus E, Väänänen A, Lahtinen T Tags: Phys Med Biol Source Type: journals

Comparison of IMRT planning with two-step and one-step optimization: a strategy for improving therapeutic gain and reducing the integral dose.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The aim of this study was to evaluate the effectiveness and efficiency in inverse IMRT planning of one-step optimization with the step-and-shoot (SS) technique as compared to traditional two-step optimization using the sliding windows (SW) technique. The Pinnacle IMRT TPS allows both one-step and two-step approaches. The same beam setup for five head-and-neck tumor patients and dose-volume constraints were applied for all optimization methods. Two-step plans were produced converting the ideal fluence with or without a smoothing filter into the SW sequence. One-step plans, based on direct machine parameter optimization ...
Source: Physics in Medicine and Biology - November 20, 2009 Category: Physics Authors: Abate A, Pressello MC, Benassi M, Strigari L Tags: Phys Med Biol Source Type: journals

Controling the scattering of Intralipid by using optical clearing agents.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Optical clearing agents (OCAs) with high refractive indices and hyperosmolarity can enhance the penetration of light in tissues by reducing scattering in tissues. However, the mechanism of tissue optical clearing is not much clear for the complex interaction between tissues and OCAs. In this work, Intralipid was mixed with different concentrations of OCAs, i.e. dimethyl sulfoxide (DMSO), glycerol, 1,4-butanediol, 1,2-propanediol, poly-ethylene glycol 200 (PEG200) and poly-ethylene glycol 400 (PEG400). Except for PEG200 and PEG400 that make aggregation of particles, the others kept the mixture uniform. The reduced scatt...
Source: Physics in Medicine and Biology - November 7, 2009 Category: Physics Authors: Wen X, Tuchin VV, Luo Q, Zhu D Tags: Phys Med Biol Source Type: journals

Monte Carlo analysis of single fiber reflectance spectroscopy: photon path length and sampling depth.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This study utilizes a Monte Carlo (MC) model to investigate the effect that optical properties have on the propagation of photons that are collected during the single fiber reflectance measurement. MC model estimates of the single fiber photon path length (L(SF)) show excellent agreement with experimental measurements and predictions of a mathematical model over a wide range of optical properties and fiber diameters. Simulation results show that L(SF) is unaffected by changes in anisotropy (g in [0.8, 0.9, 0.95]), but is sensitive to changes in phase function (Henyey-Greenstein versus modified Henyey-Greenstein). A 20% dec...
Source: Physics in Medicine and Biology - November 7, 2009 Category: Physics Authors: Kanick SC, Robinson DJ, Sterenborg HJ, Amelink A Tags: Phys Med Biol Source Type: journals

Monte Carlo simulation of the neutron spectral fluence and dose equivalent for use in shielding a proton therapy vault.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Neutron production is of principal concern when designing proton therapy vault shielding. Conventionally, neutron calculations are based on analytical methods, which do not accurately consider beam shaping components and nozzle shielding. The goal of this study was to calculate, using Monte Carlo modeling, the neutron spectral fluence and neutron dose equivalent generated by a realistic proton therapy nozzle and evaluate how these data could be used in shielding calculations. We modeled a contemporary passive scattering proton therapy nozzle in detail with the MCNPX simulation code. The neutron spectral fluence and dos...
Source: Physics in Medicine and Biology - November 7, 2009 Category: Physics Authors: Zheng Y, Newhauser W, Klein E, Low D Tags: Phys Med Biol Source Type: journals

Quantifying effective magnetic moments of narrow cylindrical objects in MRI.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A new procedure for accurately measuring effective magnetic moments of long cylinders is presented. Partial volume, dephasing and phase aliasing effects are naturally included and overcome in our approach. Images from a typical gradient echo sequence at one single echo time are usually sufficient to quantify the effective magnetic moment of a cylindrical-like object. Only pixels in the neighborhood of the object are needed. Our approach can accurately quantify the magnetic moments and distinguish subpixel changes of cross sections between cylindrical objects. Uncertainties of our procedure are studied through the error...
Source: Physics in Medicine and Biology - November 7, 2009 Category: Physics Authors: N Cheng YC, Hsieh CY, Neelavalli J, Haacke EM Tags: Phys Med Biol Source Type: journals

Rayleigh scatter in kilovoltage x-ray imaging: is the independent atom approximation good enough?Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Monte Carlo simulation is the gold standard method for modelling scattering processes in medical x-ray imaging. General-purpose Monte Carlo codes, however, typically use the independent atom approximation (IAA). This is known to be inaccurate for Rayleigh scattering, for many materials, in the forward direction. This work addresses whether the IAA is sufficient for the typical modelling tasks in medical kilovoltage x-ray imaging. As a means of comparison, we incorporate a more realistic 'interference function' model into a custom-written Monte Carlo code. First, we conduct simulations of scatter from isolated voxels of...
Source: Physics in Medicine and Biology - November 7, 2009 Category: Physics Authors: Poludniowski G, Evans PM, Webb S Tags: Phys Med Biol Source Type: journals

Airway segmentation and analysis for the study of mouse models of lung disease using micro-CT.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Animal models of lung disease are gaining importance in understanding the underlying mechanisms of diseases such as emphysema and lung cancer. Micro-CT allows in vivo imaging of these models, thus permitting the study of the progression of the disease or the effect of therapeutic drugs in longitudinal studies. Automated analysis of micro-CT images can be helpful to understand the physiology of diseased lungs, especially when combined with measurements of respiratory system input impedance. In this work, we present a fast and robust murine airway segmentation and reconstruction algorithm. The algorithm is based on a pro...
Source: Physics in Medicine and Biology - November 7, 2009 Category: Physics Authors: Artaechevarria X, Pérez-Martín D, Ceresa M, de Biurrun G, Blanco D, Montuenga LM, van Ginneken B, Ortiz-de-Solorzano C, Muñoz-Barrutia A Tags: Phys Med Biol Source Type: journals

Scan equalization digital radiography (SEDR) implemented with an amorphous selenium flat-panel detector: initial experience.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
It is well recognized in projection radiography that low-contrast detectability suffers in heavily attenuating regions due to excessively low x-ray fluence to the image receptor and higher noise levels. Exposure equalization can improve image quality by increasing the x-ray exposure to heavily attenuating regions, resulting in a more uniform distribution of exposure to the detector. Image quality is also expected to be improved by using the slot-scan geometry to reject scattered radiation effectively without degrading primary x-rays. This paper describes the design of a prototype scan equalization digital radiography (...
Source: Physics in Medicine and Biology - November 7, 2009 Category: Physics Authors: Liu X, Lai CJ, Chen L, Han T, Zhong Y, Shen Y, Wang T, Shaw CC Tags: Phys Med Biol Source Type: journals

Ultrasound-based transient elastography compared to magnetic resonance elastography in soft tissue-mimicking gels.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This study proposes a comparison between magnetic resonance elastography (MRE) and ultrasound-based transient elastography (TE). Both methods were tested on the same soft tissue-mimicking gels in a common frequency range in order to allow for direct quantitative comparison. For the four gels tested, relatively good agreement was found between the shear moduli measured by both methods, with an averaged relative difference of 23%. This study demonstrates that under the assumption of homogeneous media that are significantly more elastic than viscous, quantitative results obtained by both methods are comparable. PMID: 1988...
Source: Physics in Medicine and Biology - November 7, 2009 Category: Physics Authors: Oudry J, Vappou J, Choquet P, Willinger R, Sandrin L, Constantinesco A Tags: Phys Med Biol Source Type: journals

Reduction in x-ray scatter and radiation dose for volume-of-interest (VOI) cone-beam breast CT-a phantom study.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
With volume-of-interest (VOI) cone-beam computed tomography (CBCT) imaging, one set of projection images are acquired with the VOI collimator at a regular or high exposure level and the second set of projection images are acquired without the collimator at a reduced exposure level. The high exposure VOI scan data inside the VOI and the low exposure full-field scan data outside the VOI are then combined together to generate composite projection images for image reconstruction. To investigate and quantify scatter reduction, dose saving and image quality improvement in VOI CBCT imaging, a flat panel detector-based bench-t...
Source: Physics in Medicine and Biology - October 21, 2009 Category: Physics Authors: Lai CJ, Chen L, Zhang H, Liu X, Zhong Y, Shen Y, Han T, Ge S, Yi Y, Wang T, Yang WT, Whitman GJ, Shaw CC Tags: Phys Med Biol Source Type: journals

Dynamic contrast-enhanced diffuse optical tomography (DCE-DOT): experimental validation with a dynamic phantom.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Dynamic contrast-enhanced diffuse optical tomography (DCE-DOT) can provide spatially resolved enhancement kinetics of an optical contrast agent. We undertook a systematic phantom study to evaluate the effects of the geometrical parameters such as the depth and size of the inclusion as well as the optical parameters of the background on the recovered enhancement kinetics of the most commonly used optical contrast agent, indocyanine green (ICG). For this purpose a computer-controlled dynamic phantom was constructed. An ICG-intralipid-water mixture was circulated through the inclusions while the DCE-DOT measurements were ...
Source: Physics in Medicine and Biology - October 21, 2009 Category: Physics Authors: Unlu MB, Lin Y, Gulsen G Tags: Phys Med Biol Source Type: journals

A generalized inverse planning tool for volumetric-modulated arc therapy.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The recent development in linear accelerator control systems, named volumetric-modulated arc therapy (VMAT), has generated significant interest in arc-based intensity-modulated radiation therapy (IMRT). The VMAT delivery technique features simultaneous changes in dose rate, gantry angle and gantry rotation speed as well as multi-leaf collimator (MLC) leaf positions while radiation is on. In this paper, we describe a generalized VMAT planning tool that is designed to take full advantage of the capabilities of the new linac control systems. The algorithm incorporates all of the MLC delivery constraints such as restrictio...
Source: Physics in Medicine and Biology - October 21, 2009 Category: Physics Authors: Cao D, Afghan MK, Ye J, Chen F, Shepard DM Tags: Phys Med Biol Source Type: journals

Synchrotron microbeam radiation therapy for rat brain tumor palliation-influence of the microbeam width at constant valley dose.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This study shows that microbeam width and peak entrance doses strongly influence tumor responses and normal brain toxicity, even if valley doses are kept constant in all groups. The use of 50 microm wide microbeams combined with moderate peak doses resulted in a higher therapeutic ratio. PMID: 19841517 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - October 21, 2009 Category: Physics Authors: Serduc R, Bouchet A, Bräuer-Krisch E, Laissue JA, Spiga J, Sarun S, Bravin A, Fonta C, Renaud L, Boutonnat J, Siegbahn EA, Estève F, Le Duc G Tags: Phys Med Biol Source Type: journals

Organ dose conversion coefficients on an ICRP-based Chinese adult male voxel model from idealized external photons exposures.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A high-resolution whole-body voxel model called CAM representing the Chinese adult male was constructed in this paper based on a previous individual voxel model. There are more than 80 tissues and organs in CAM, including almost all organs required in the ICRP new recommendation. The mass of individual organs has been adjusted to the Chinese reference data. Special considerations were given to representing the gross spatial distribution of various bone constituents as realistically as possible during the construction of the site-specific skeleton. Organ dose conversion coefficients were calculated for six idealized ext...
Source: Physics in Medicine and Biology - October 21, 2009 Category: Physics Authors: Liu L, Zeng Z, Li J, Qiu R, Zhang B, Ma J, Li R, Li W, Bi L Tags: Phys Med Biol Source Type: journals

An ICRP-based Chinese adult male voxel model and its absorbed dose for idealized photon exposures-the skeleton.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A site-specific skeleton voxel model for a Chinese adult male was constructed in this paper upon a previous Chinese individual voxel model. The whole skeleton was divided into 19 site-specific bones and bone groups; the mass of various skeleton tissues at each bone site, e.g. red bone marrow, was specified according to Asian reference data and the distribution data from ICRP Publication 70. The resultant voxel model (called CAM) has a resolution of 1.741 mm x 1.741 mm in plane, and the total bone mass is 8397.8 g which is almost equal to the Asian reference value. Dose coefficients for the red bone marrow and bone surf...
Source: Physics in Medicine and Biology - October 21, 2009 Category: Physics Authors: Liu L, Zeng Z, Li J, Zhang B, Qiu R, Ma J Tags: Phys Med Biol Source Type: journals

Statistical LOR estimation for a high-resolution dMiCE PET detector.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We develop a statistical line of response (LOR) estimator of the three-dimensional interaction positions of a pair of annihilation photons in a PET detector module with depth of interaction capability. The three-dimensional points of interaction of a coincidence pair of photons within the detector module are estimated by calculation of an expectation of the points of interaction conditioned on the signals measured by the photosensors. This conditional expectation is computed from estimates of the probability density function of the light collection process and a model of the kinetics of photon interactions in the detec...
Source: Physics in Medicine and Biology - October 8, 2009 Category: Physics Authors: Champley KM, Lewellen TK, Macdonald LR, Miyaoka RS, Kinahan PE Tags: Phys Med Biol Source Type: journals

The dynamics of a non-equilibrium bubble near bio-materials.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In many medical treatments oscillating (non-equilibrium) bubbles appear. They can be the result of high-intensity-focused ultrasound, laser treatments or shock wave lithotripsy for example. The physics of such oscillating bubbles is often not very well understood. This is especially so if the bubbles are oscillating near (soft) bio-materials. It is well known that bubbles oscillating near (hard) materials have a tendency to form a high speed jet directed towards the material during the collapse phase of the bubble. It is equally well studied that bubbles near a free interface (air) tend to collapse with a jet directed ...
Source: Physics in Medicine and Biology - October 8, 2009 Category: Physics Authors: Ohl SW, Klaseboer E, Khoo BC Tags: Phys Med Biol Source Type: journals

Trade-off bounds for the Pareto surface approximation in multi-criteria IMRT planning.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
One approach to multi-criteria IMRT planning is to automatically calculate a data set of Pareto-optimal plans for a given planning problem in a first phase, and then interactively explore the solution space and decide on the clinically best treatment plan in a second phase. The challenge of computing the plan data set is to ensure that all clinically meaningful plans are covered and that as many clinically irrelevant plans as possible are excluded to keep computation times within reasonable limits. In this work, we focus on the approximation of the clinically relevant part of the Pareto surface, the process that consti...
Source: Physics in Medicine and Biology - October 8, 2009 Category: Physics Authors: Serna JI, Monz M, Küfer KH, Thieke C Tags: Phys Med Biol Source Type: journals

Thermal ablation produced using a surgical toroidal high-intensity focused ultrasound device is independent from hepatic inflow occlusion.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In the liver, the efficacy of radiofrequency or high-intensity focused ultrasound (HIFU) ablation is impaired by blood perfusion. This can be overcome by hepatic inflow occlusion. Here we report the in vivo evaluation of ablations performed in the liver using a surgical toroidal HIFU device used during an open procedure with and without hepatic inflow occlusion. The HIFU device was composed of 256 toroidal-shaped emitters working at 3 MHz and an integrated ultrasound imaging probe working at 7.5 MHz. Using an intermittent Pringle maneuver (IPM), thermal ablations were created in three pigs with hepatic inflow occlusion...
Source: Physics in Medicine and Biology - October 8, 2009 Category: Physics Authors: Melodelima D, N'djin WA, Favre-Cabrera J, Parmentier H, Rivoire M, Chapelon JY Tags: Phys Med Biol Source Type: journals

An extended convection diffusion model for red blood cell-enhanced transport of thrombocytes and leukocytes.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Transport phenomena of platelets and white blood cells (WBCs) are fundamental to the processes of vascular disease and thrombosis. Unfortunately, the dilute volume occupied by these cells is not amenable to fluid-continuum modeling, and yet the cell count is large enough that modeling each individual cell is impractical for most applications. The most feasible option is to treat them as dilute species governed by convection and diffusion; however, this is further complicated by the role of the red blood cell (RBC) phase on the transport of these cells. We therefore propose an extended convection-diffusion (ECD) model b...
Source: Physics in Medicine and Biology - October 8, 2009 Category: Physics Authors: Hund SJ, Antaki JF Tags: Phys Med Biol Source Type: journals

Topographic localization of brain activation in diffuse optical imaging using spherical wavelets.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Diffuse optical imaging is a non-invasive technique that uses near-infrared light to measure changes in brain activity through an array of sensors placed on the surface of the head. Compared to functional MRI, optical imaging has the advantage of being portable while offering the ability to record functional changes in both oxy- and deoxy-hemoglobin within the brain at a high temporal resolution. However, the reconstruction of accurate spatial images of brain activity from optical measurements represents an ill-posed and underdetermined problem that requires regularization. These reconstructions benefit from incorporat...
Source: Physics in Medicine and Biology - October 8, 2009 Category: Physics Authors: Abdelnour F, Schmidt B, Huppert TJ Tags: Phys Med Biol Source Type: journals

An optically stimulated luminescence system to measure dose profiles in x-ray computed tomography.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This paper describes an LED-based optically stimulated luminescence (OSL) system for dose profile measurements using OSL detector strips and investigates its performance in x-ray computed tomography (CT) dosimetry. To compensate for the energy response of the Al(2)O(3):C OSL detectors, which have an effective atomic number of 11.28, field-specific energy correction factors were determined using two methods: (a) comparing the OSL profiles with ionization chamber point measurements (0.3 cm(3) ionization chamber) and (b) comparing the OSL profiles integrated over a 100 mm length with 100 mm long pencil ionization chamber ...
Source: Physics in Medicine and Biology - October 8, 2009 Category: Physics Authors: Yukihara EG, Ruan C, Gasparian PB, Clouse WJ, Kalavagunta C, Ahmad S Tags: Phys Med Biol Source Type: journals

Four-dimensional targeting error analysis in image-guided radiotherapy.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The objective comparison of different motion mitigation strategies can be achieved by quantifying the residual uncertainties in tumor targeting, to be detected by means of IGRT technologies. Such quantification requires an extension of targeting error theory to a 4D space, where the 3D tumor trajectory as a function of time measured (4D Targeting Error, 4DTE). Accurate 4DTE analysis can be represented by a motion probability density function, describing the statistical fluctuations of tumor trajectory. We illustrate the application of 4DTE analysis through examples, including weekly variations in tumor trajectory as detect...
Source: Physics in Medicine and Biology - September 25, 2009 Category: Physics Authors: Riboldi M, Sharp GC, Baroni G, Chen GT Tags: Phys Med Biol Source Type: journals

A quantitative evaluation study of four-dimensional gated cardiac SPECT reconstruction.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In practice, gated cardiac SPECT images suffer from a number of degrading factors, including distance-dependent blur, attenuation, scatter and increased noise due to gating. Recently, we proposed a motion-compensated approach for four-dimensional (4D) reconstruction for gated cardiac SPECT and demonstrated that use of motion-compensated temporal smoothing could be effective for suppressing the increased noise due to lowered counts in individual gates. In this work, we further develop this motion-compensated 4D approach by also taking into account attenuation and scatter in the reconstruction process, which are two majo...
Source: Physics in Medicine and Biology - September 3, 2009 Category: Physics Authors: Jin M, Yang Y, Niu X, Marin T, Brankov JG, Feng B, Pretorius PH, King MA, Wernick MN Tags: Phys Med Biol Source Type: journals

The correspondence between coronary arterial wall strain and histology in a porcine model of atherosclerosis.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this study, we further evaluate the method by assessing the correspondence of the calculated strain distribution and the histological composition of atherosclerotic coronary arteries from Sinclair miniature pigs following 12 months of a high fat diet. The images were acquired in situ using a clinical IVUS system and under computer-controlled pressurization. After image acquisition, the artery segments were fixed for histology to identify plaque components. The strain distributions were aligned with the corresponding histological sections. The stiffness of various components of the lesion, inferred from the wall strain d...
Source: Physics in Medicine and Biology - September 3, 2009 Category: Physics Authors: Liang Y, Zhu H, Friedman MH Tags: Phys Med Biol Source Type: journals

A feasibility study of using conventional jaws to deliver complex IMRT plans for head and neck cancer.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In conclusion, conventional jaws can be used solely to deliver complex IMRT plans for patients with nasopharyngeal cancer yet still within a practical delivery time. PMID: 19724096 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - September 3, 2009 Category: Physics Authors: Mu G, Xia P Tags: Phys Med Biol Source Type: journals

A scheme for PET data normalization in event-based motion correction.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Line of response (LOR) rebinning is an event-based motion-correction technique for positron emission tomography (PET) imaging that has been shown to compensate effectively for rigid motion. It involves the spatial transformation of LORs to compensate for motion during the scan, as measured by a motion tracking system. Each motion-corrected event is then recorded in the sinogram bin corresponding to the transformed LOR. It has been shown previously that the corrected event must be normalized using a normalization factor derived from the original LOR, that is, based on the pair of detectors involved in the original coinc...
Source: Physics in Medicine and Biology - August 19, 2009 Category: Physics Authors: W Zhou V, Kyme AZ, Meikle SR, Fulton R Tags: Phys Med Biol Source Type: journals

A comprehensive system for dosimetric commissioning and Monte Carlo validation for the small animal radiation research platform.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Our group has constructed the small animal radiation research platform (SARRP) for delivering focal, kilo-voltage radiation to targets in small animals under robotic control using cone-beam CT guidance. The present work was undertaken to support the SARRP's treatment planning capabilities. We have devised a comprehensive system for characterizing the radiation dosimetry in water for the SARRP and have developed a Monte Carlo dose engine with the intent of reproducing these measured results. We find that the SARRP provides sufficient therapeutic dose rates ranging from 102 to 228 cGy min(-1) at 1 cm depth for the availa...
Source: Physics in Medicine and Biology - August 19, 2009 Category: Physics Authors: Tryggestad E, Armour M, Iordachita I, Verhaegen F, Wong JW Tags: Phys Med Biol Source Type: journals

A wearable diffuse reflectance sensor for continuous monitoring of cutaneous blood content.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
An optical diffuse reflectance sensor for characterization of cutaneous blood content and optimized for continuous monitoring has been developed as part of a non-invasive multisensor system for glucose monitoring. A Monte Carlo simulation of the light propagation in the multilayered skin model has been performed in order to estimate the optimal geometrical separation of the light source and detector for skin and underlying tissue. We have observed that the pathlength within the upper vascular plexus of the skin which defines the sensor sensitivity initially grows with increasing source-detector distance (SDD) before re...
Source: Physics in Medicine and Biology - August 19, 2009 Category: Physics Authors: Zakharov P, Talary MS, Caduff A Tags: Phys Med Biol Source Type: journals

The low-energy ion range in DNA.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In fundamental studies of low-energy ion irradiation effects on DNA, calculation of the low-energy ion range, an important basic physical parameter, is often necessary. However, up to now a unified model and approach for range calculation is still lacking, and reported data are quite divergent and thus unreliable. Here we describe an approach for calculation of the ion range, using a simplified mean-pseudoatom model of the DNA target. Based on ion stopping theory, for the case of low-energy (</= a few keV) ion implantation into DNA, the stopping falls in the low reduced energy regime, which gives a cube-root energy ...
Source: Physics in Medicine and Biology - August 6, 2009 Category: Physics Authors: Yu LD, Kamwanna T, Brown IG Tags: Phys Med Biol Source Type: journals

Echocardiography to magnetic resonance image registration for use in image-guided cardiac catheterization procedures.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We present a robust method to register three-dimensional echocardiography (echo) images to magnetic resonance images (MRI) based on anatomical features, which is designed to be used in the registration pipeline for overlaying MRI-derived roadmaps onto two-dimensional live x-ray images during cardiac catheterization procedures. The features used in image registration are the endocardial surface of the left ventricle and the centre line of the descending aorta. The MR-derived left ventricle surface is generated using a fully automated algorithm, and the echo-derived left ventricle surface is produced using a semi-automatic s...
Source: Physics in Medicine and Biology - August 6, 2009 Category: Physics Authors: Ma YL, Penney GP, Rinaldi CA, Cooklin M, Razavi R, Rhode KS Tags: Phys Med Biol Source Type: journals

A Monte Carlo study of cellular S-factors for 1 keV to 1 MeV electrons.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A systematic study of cellular S-factors and absorbed fractions for monoenergetic electrons of initial energy from 1 keV to 1 MeV is presented. The calculations are based on our in-house Monte Carlo codes which have been developed to simulate electron transport up to a few MeV using both event-by-event and condensed-history techniques. An extensive comparison with the MIRD tabulations is presented for spherical volumes of 1-10 microm radius and various source-to-target combinations relevant to the intracellular localization of the emitted electrons. When the primary electron range is comparable to the sphere radius, we...
Source: Physics in Medicine and Biology - August 6, 2009 Category: Physics Authors: Bousis C, Emfietzoglou D, Hadjidoukas P, Nikjoo H Tags: Phys Med Biol Source Type: journals

Estimation of the absorption coefficients of two-layered media by a simple method using spatially and time-resolved reflectances.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Our newly developed method using spatially and time-resolved reflectances can easily estimate the absorption coefficients of each layer in a two-layered medium if the thickness of the upper layer and the reduced scattering coefficients of the two layers are known a priori. We experimentally validated this method using phantoms and examined its possibility of estimating the absorption coefficients of the tissues in human heads. In the case of a homogeneous plastic phantom (polyacetal block), the absorption coefficient estimated by our method agreed well with that obtained by a conventional method. Also, in the case of t...
Source: Physics in Medicine and Biology - August 6, 2009 Category: Physics Authors: Shimada M, Sato C, Hoshi Y, Yamada Y Tags: Phys Med Biol Source Type: journals

Uncertainty reduction in intensity modulated proton therapy by inverse Monte Carlo treatment planning.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We present the inverse Monte Carlo treatment planning system IKO for protons (IKO-P), which tries to minimize the errors described above to a large extent. Additionally, robust planning is introduced by beam angle optimization according to an objective function penalizing paths representing strongly longitudinal and transversal tissue heterogeneities. The same score function is applied to optimize spot planning by the selection of a robust choice of spots. As spots can be positioned on different energy grids or on geometric grids with different space filling factors, a variety of grids were used to investigate the influenc...
Source: Physics in Medicine and Biology - July 25, 2009 Category: Physics Authors: Morávek Z, Rickhey M, Hartmann M, Bogner L Tags: Phys Med Biol Source Type: journals

Quantitative evaluation of signal integrity for magnetocardiography.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Magnetocardiography (MCG) is a non-invasive diagnostic tool used to investigate the activity of the heart. For applications in an unshielded environment, in order to extract the very weak signal of interest from the much higher background noise, dedicated hardware configuration and sophisticated signal processing techniques have been developed during the last decades. Being powerful in noise rejection, the signal processing may introduce signal distortions, if not properly designed and applied. However, there is a lack of an effective tool to quantitatively evaluate the signal integrity for MCG at present. In this pape...
Source: Physics in Medicine and Biology - July 25, 2009 Category: Physics Authors: Zhang S, Wang Y, Wang H, Jiang S, Xie X Tags: Phys Med Biol Source Type: journals

Influence of the surface averaging procedure of the current density in assessing compliance with the ICNIRP low-frequency basic restrictions by means of numerical techniques.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Although the calculation of the surface average of the low-frequency current density distribution over a cross-section of 1 cm(2) is required by ICNIRP guidelines, no reference averaging algorithm is indicated, neither in the ICNIRP guidelines nor in the Directive 2004/40/EC that is based on them. The lack of a general standard algorithm that fulfils the ICNIRP guidelines' requirements is particularly critical in the prospective of the 2004/40/EC Directive endorsement, since the compliance to normative limits refers to well-defined procedures. In this paper, two case studies are considered, in which the calculation of ...
Source: Physics in Medicine and Biology - July 25, 2009 Category: Physics Authors: Zoppetti N, Andreuccetti D Tags: Phys Med Biol Source Type: journals

Characteristics of time-domain optical coherence tomography profiles generated from blood-saline mixtures.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Time-domain optical coherence tomography (OCT) employing a 1300 nm broadband source is used to study flowing blood-saline mixtures with blood concentration ranging from 20% to 100%. The study emphasizes the characteristics of the recorded OCT signal and its connection with the properties of the corresponding fluids. There are three regions with distinct properties along the compounded OCT profiles showing the signal dependence on depth. The recorded OCT signal increases for the first 80 microm into the fluid. The flow characteristics of the solution and the average spatial orientation of the blood cells can be extracte...
Source: Physics in Medicine and Biology - July 25, 2009 Category: Physics Authors: Popescu DP, Sowa MG Tags: Phys Med Biol Source Type: journals

Real-time profiling of respiratory motion: baseline drift, frequency variation and fundamental pattern change.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this study, we try to decompose the above-mentioned components from discrete observations in real time. Baseline drift, frequency (equivalently phase) variation and fundamental pattern change characterize different aspects of respiratory motion and have distinctive clinical indications. Furthermore, smoothness is a valid assumption for each one of these components in their own spaces, and facilitates effective extrapolation for the purpose of estimation and prediction. We call this process 'profiling' to reflect the integration of information extraction, decomposition, processing and recovery. The proposed method has th...
Source: Physics in Medicine and Biology - July 25, 2009 Category: Physics Authors: Ruan D, Fessler JA, Balter JM, Keall PJ Tags: Phys Med Biol Source Type: journals

The determination of beam quality correction factors: Monte Carlo simulations and measurements.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Modern dosimetry protocols are based on the use of ionization chambers provided with a calibration factor in terms of absorbed dose to water. The basic formula to determine the absorbed dose at a user's beam contains the well-known beam quality correction factor that is required whenever the quality of radiation used at calibration differs from that of the user's radiation. The dosimetry protocols describe the whole ionization chamber calibration procedure and include tabulated beam quality correction factors which refer to (60)Co gamma radiation used as calibration quality. They have been calculated for a series of io...
Source: Physics in Medicine and Biology - July 25, 2009 Category: Physics Authors: González-Castaño DM, Hartmann GH, Sánchez-Doblado F, Gómez F, Kapsch RP, Pena J, Capote R Tags: Phys Med Biol Source Type: journals

Contralateral breast doses measured by film dosimetry: tangential techniques and an optimized IMRT technique.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The contralateral breast (CLB) doses for three tangential techniques were characterized by using a female thorax phantom and GafChromic EBT film. Dose calculations by the pencil beam and collapsed cone algorithms were included for comparison. The film dosimetry reveals a highly inhomogeneous dose distribution within the CLB, and skin doses due to the medial fields that are several times higher than the interior dose. These phenomena are not correctly reproduced by the calculation algorithms. All tangential techniques were found to give a mean CLB dose of approximately 0.5 Gy. All wedged fields resulted in higher CLB do...
Source: Physics in Medicine and Biology - July 25, 2009 Category: Physics Authors: Saur S, Fjellsboe LM, Lindmo T, Frengen J Tags: Phys Med Biol Source Type: journals

4D CT sorting based on patient internal anatomy.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Respiratory motion during free-breathing computed tomography (CT) scan may cause significant errors in target definition for tumors in the thorax and upper abdomen. A four-dimensional (4D) CT technique has been widely used for treatment simulation of thoracic and abdominal cancer radiotherapy. The current 4D CT techniques require retrospective sorting of the reconstructed CT slices oversampled at the same couch position. Most sorting methods depend on external surrogates of respiratory motion recorded by extra instruments. However, respiratory signals obtained from these external surrogates may not always accurately re...
Source: Physics in Medicine and Biology - July 25, 2009 Category: Physics Authors: Li R, Lewis JH, Cerviño LI, Jiang SB Tags: Phys Med Biol Source Type: journals

Simulation of dose deposition in stereotactic synchrotron radiation therapy: a fast approach combining Monte Carlo and deterministic algorithms.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A hybrid approach, combining deterministic and Monte Carlo (MC) calculations, is proposed to compute the distribution of dose deposited during stereotactic synchrotron radiation therapy treatment. The proposed approach divides the computation into two parts: (i) the dose deposited by primary radiation (coming directly from the incident x-ray beam) is calculated in a deterministic way using ray casting techniques and energy-absorption coefficient tables and (ii) the dose deposited by secondary radiation (Rayleigh and Compton scattering, fluorescence) is computed using a hybrid algorithm combining MC and deterministic ca...
Source: Physics in Medicine and Biology - July 9, 2009 Category: Physics Authors: Smekens F, Freud N, Létang JM, Adam JF, Ferrero C, Elleaume H, Bravin A, Estève F, Babot D Tags: Phys Med Biol Source Type: journals

An examination of automatic exposure control regimes for two digital radiography systems.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The influence of two methods of an automatic exposure control (AEC) setup using a simple measure of detectability is examined as a function of x-ray beam quality for a computed radiography (CR) system and for an indirect conversion digital radiography (DR) system. The regimes assessed were constant air kerma at the detector and the constant contrast noise ratio (CNR). A low scatter geometry was employed with x-ray spectra varying from 60 kV and 1 mm Cu to 125 kV and 2 mm Cu. The CNR was measured using a 2 mm thick Al square of dimension 1 cm by 1 cm. Detectability was quantified via a nominal contrast for a fixed beam ...
Source: Physics in Medicine and Biology - July 9, 2009 Category: Physics Authors: Marshall NW Tags: Phys Med Biol Source Type: journals

Cone beam computerized tomography: the effect of calibration of the Hounsfield unit number to electron density on dose calculation accuracy for adaptive radiation therapy.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The availability of cone beam computerized tomography (CBCT) images at the time of treatment has opened possibilities for dose calculations representing the delivered dose for adaptive radiation therapy. A significant component in the accuracy of dose calculation is the calibration of the Hounsfield unit (HU) number to electron density (ED). The aim of this work is to assess the impact of HU to ED calibration phantom insert composition and phantom volume on dose calculation accuracy for CBCT. CBCT HU to ED calibration curves for different commercial phantoms were measured and compared. The effect of the scattering volu...
Source: Physics in Medicine and Biology - July 9, 2009 Category: Physics Authors: Hatton J, McCurdy B, Greer PB Tags: Phys Med Biol Source Type: journals

Deconvolution of x-ray phase contrast images as a way to retrieve phase information lost due to insufficient resolution.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
When free-space propagation x-ray phase contrast imaging is implemented outside synchrotron radiation facilities, the combined effect of detector resolution and source size swamps the fine phase contrast fringes, often making them almost undetectable. In an attempt to mitigate this effect, a simple deconvolution procedure based on division in the Fourier space plus multiplication by an appropriate filter was applied to experimental x-ray phase contrast images of a simple geometric phantom. The filter parameter was varied in order to assess its impact on the level of retrieved phase signal. The deconvolved images were c...
Source: Physics in Medicine and Biology - July 9, 2009 Category: Physics Authors: Olivo A, Speller RD Tags: Phys Med Biol Source Type: journals

Excitation spectroscopy in multispectral optical fluorescence tomography: methodology, feasibility and computer simulation studies.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This study is carried out in a realistic inhomogeneous mouse atlas using singular value decomposition and analysis of reconstructed spatial resolution versus noise. For simplicity, quantitative results have been shown for one representative fluorescent probe (Alexa 700(R)) and effects due to tissue autofluorescence have not been taken into account. We also demonstrate the performance of our method for 3D reconstruction of tumors in a simulated mouse model of metastatic human hepatocellular carcinoma. PMID: 19590118 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - July 9, 2009 Category: Physics Authors: Chaudhari AJ, Ahn S, Levenson R, Badawi RD, Cherry SR, Leahy RM Tags: Phys Med Biol Source Type: journals