bluuebunny/crossref_metadata_2025 huggingface dataset:
Local bone enhancement fuzzy clustering for segmentation of MR trabecular bone images
Authors: Folkesson Jenny , Carballido‐Gamio Julio , Eckstein Felix , Link Thomas M. , Majumdar Sharmila
Published: December 2009

Purpose

Segmentation of trabecular bone from magnetic resonance (MR) images is a challenging task due to spatial resolution limitations, signal‐to‐noise ratio constraints, and signal intensity inhomogeneities. This article examines an alternative approach to trabecular bone segmentation using partial membership segmentation termed fuzzy ‐means clustering incorporating local second order features for bone enhancement (BE‐FCM) at multiple scales. This approach is meant to allow for a soft segmentation that accounts for partial volume effects while suppressing the influence of noise.

Methods

A soft segmentation method was developed and evaluated on three different sets of data; interscan reproducibility was evaluated on six test‐retestin vivo MR scans of the proximal femur, correlation between MR and HR‐pQCT measurements was evaluated on 49 in vivo scans from the distal tibia, and the potential for fracture discrimination was evaluated using MR scans of calcaneus specimens from 15 participants with and 15 participants without vertebral fracture. The algorithm was compared to fuzzy clustering using the intensity as the only feature (I‐FCM) and a dual thresholding algorithm. The metric evaluated was bone volume over total volume (BV/TV) within user‐defined regions of interest.

Results

BE‐FCM had a higher interscan reproducibility (rms CV: 2.0%) compared to I‐FCM (5.6%) and thresholding (4.2%), and expressed higher correlation to HR‐pQCT data compared to I‐FCM and thresholding . BE‐FCM was also the method that was best able to differentiate between a control and a vertebral fracture group at a 95% significance level.

Conclusions

The results suggest that trabecular bone segmentation by BE‐FCM can provide a precise BV/TV measurement that is sensitive to pathology. The segmentation method may become useful in MR imaging‐based quantification of bone microarchitecture.
Method for evaluating bow tie filter angle‐dependent attenuation in CT: Theory and simulation results
Authors: Boone John M.
Published: December 2009

Purpose

Dosimetry in computed tomography (CT) is increasingly based on Monte Carlo studies that define the dose in the patient (in mGy) as a function of air kerma (free in air) at isocenter (mGy). The accuracy of Monte Carlo studies depends in part on the accuracy of the characterization of the bow tie filter for a given CT scanner model. A simple method for characterizing the bow tie filter attenuation profile in CT scanners would therefore be very useful. The theory behind such a method is proposed.

Methods

A measurement protocol is discussed mathematically and demonstrated using computer simulation. The proposed method requires the placement of a radiation monitor at the periphery of the CT field, and the time domain signal (kerma rate versus time) is measured with good temporal resolution ( or better) and with all other objects (e.g., patient couch) retracted from the field of view. Knowledge of the source to isocenter distance (or alternately, the isocenter to probe distance) is required. The stationary detector records the kerma rate versus time signal as the gantry rotates through several revolutions. From this temporal data, signal processing techniques are used to extract in‐phase peaks, as well as out‐of‐phase kerma rate levels. From these data, the distance from isocenter to the probe can be determined (or, alternatively, the source to isocenter distance), and the angle‐dependent bow tie filter attenuation can be computed. By measuring the angle‐dependent bow tie filter attenuation at several kVp settings, the bow tie composition versus fan angle can be computed using basis decomposition techniques.

Results

The simulations illustrated that with 2% added noise in the kerma rate versus time signal, the attenuation properties of a hypothetical two component (aluminum and polymethyl methacrylate) bow tie filter could be determined . Although the computed basis material thicknesses were not exactly equal to the actual thicknesses, their combined attenuation factors matched that of the actual filter across kVp's to within an average of 0.057%.

Conclusions

It is concluded that the proposed method may provide a simple noninvasive approach to characterizing the performance of bow tie filters in CT systems; however, experimental validation is necessary.
Photon beam quality variations of a flattening filter free linear accelerator
Authors: Georg Dietmar , Kragl Gabriele , af Wetterstedt Sacha , McCavana Patrick , McClean Brendan , Knöös Tommy
Published: December 2009

Purpose

Recently, there has been an increasing interest in operating conventional linear accelerators without a flattening filter. The aim of this study was to determine beam quality variations as a function of off‐axis ray angle for unflattened beams. In addition, a comparison was made with the off‐axis energy variation in flattened beams.

Methods

Two Elekta Precise linear accelerators were modified in order to enable radiation delivery with and without the flattening filter in the beam line. At the Medical University Vienna (Vienna, Austria), half value layer (HVL) measurements were performed for 6 and 10 MV with an in‐house developed device that can be easily mounted on the gantry. At St. Luke's Hospital (Dublin, Ireland), measurements were performed at 6 MV in narrow beam geometry with the gantry tilted around 270° with pinhole collimators, an attenuator, and the chamber positioned on the table. All attenuation measurements were performed with ionization chambers and a buildup cap (2 mm brass) or a PMMA mini phantom (diameter 3 cm, measurement depth 2.5 cm).

Results

For flattened 6 and 10 MV photon beams from the Elekta linac the relative varies by about 11% for an off‐axis ray angle . These results agree within ±2% with a previously proposed generic off‐axis energy correction. For unflattened beams, the variation was less than 5% in the whole range of off‐axis ray angles up to 10°. The difference in relative HVL data was less than 1% for unflattened beams at 6 and 10 MV.

Conclusions

Off‐axis energy variation is rather small in unflattened beams and less than half the one for flattened beams. Thus, ignoring the effect of off‐axis energy variation for dose calculations in unflattened beams can be clinically justified.
Lung perfusion imaging in small animals using 4D micro‐CT at heartbeat temporal resolution
Authors: Badea Cristian T. , Johnston Samuel M. , Subashi Ergys , Qi Yi , Hedlund Laurence W. , Johnson G. Allan
Published: December 2009

Purpose

Quantitativein vivo imaging of lung perfusion in rodents can provide critical information for preclinical studies. However, the combined challenges of high temporal and spatial resolution have made routine quantitative perfusion imaging difficult in small animals. The purpose of this work is to demonstrate 4D micro‐CT for perfusion imaging in rodents at heartbeat temporal resolution and isotropic spatial resolution.

Methods

We have recently developed a dual tube/detector micro‐CT scanner that is well suited to capture first pass kinetics of a bolus of contrast agent used to compute perfusion information. Our approach is based on the paradigm that similar time density curves can be reproduced in a number of consecutive, small volume injections of iodinated contrast agent at a series of different angles. This reproducibility is ensured by the high‐level integration of the imaging components of our system with a microinjector, a mechanical ventilator, and monitoring applications. Sampling is controlled through a biological pulse sequence implemented inLABVIEW. Image reconstruction is based on a simultaneous algebraic reconstruction technique implemented on a graphic processor unit. The capabilities of 4D micro‐CT imaging are demonstrated in studies on lung perfusion in rats.

Results

We report 4D micro‐CT imaging in the rat lung with a heartbeat temporal resolution (approximately 150 ms) and isotropic 3D reconstruction with a voxel size of based on sampling using 16 injections of each. The total volume of contrast agent injected during the experiments (0.8 mL) was less than 10% of the total blood volume in a rat. This volume was not injected in a single bolus, but in multiple injections separated by at least 2 min interval to allow for clearance and adaptation. We assessed the reproducibility of the time density curves with multiple injections and found that these are very similar. The average time density curves for the first eight and last eight injections are slightly different, i.e., for the last eight injections, both the maximum of the average time density curves and its area under the curve are decreased by 3.8% and 7.2%, respectively, relative to the average time density curves based on the first eight injections. The radiation dose associated with our 4D micro‐CT imaging is 0.16 Gy and is therefore in the range of a typical micro‐CT dose.

Conclusions

4D micro‐CT‐based perfusion imaging demonstrated here has immediate application in a wide range of preclinical studies such as tumor perfusion, angiogenesis, and renal function. Although our imaging system is in many ways unique, we believe that our approach based on the multiple injection paradigm can be used with the newly developed flat‐panel slip‐ring‐based micro‐CT to increase their temporal resolution in dynamic perfusion studies.
Automated estimation of progression of interstitial lung disease in CT images
Authors: Arzhaeva Yulia , Prokop Mathias , Murphy Keelin , van Rikxoort Eva M. , de Jong Pim A. , Gietema Hester A. , Viergever Max A. , van Ginneken Bram
Published: December 2009

Purpose

A system is presented for automated estimation of progression of interstitial lung disease in serial thoracic CT scans.

Methods

The system compares corresponding 2D axial sections from baseline and follow‐up scans and concludes whether this pair of sections represents regression, progression, or unchanged disease status. The correspondence between serial CT scans is achieved by intrapatient volumetric image registration. The system classification function is trained with two different feature sets. Features in the first set represent the intensity distribution of a difference image between the baseline and follow‐up CT sections. Features in the second set represent dissimilarities computed between the baseline and follow‐up images filtered with a bank of general purpose texture filters.

Results

In an experiment on 74 scan pairs, the system classification accuracies were 76.1% and 79.5% for the two feature sets, respectively, while the accuracies of two observer radiologist were 78.5% and 82%, respectively. The agreements of the system with the reference standard, measured by weighted kappa statistics, were 0.611 and 0.683 for the two feature sets, respectively.

Conclusions

The system employing the second feature set showed good agreement with the reference standard, and its accuracy approached that of two radiologists.
Accurate color measurement methods for medical displays
Authors: Saha Anindita , Kelley Edward F. , Badano Aldo
Published: December 2009

Purpose

The necessity for standard instrumentation and measurements of color that are repeatable and reproducible is the major motivation behind this work. Currently, different instrumentation and methods can yield very different results when measuring the same feature such as color uniformity or color difference. As color increasingly comes into play in medical imaging diagnostics, display color will have to be quantified in order to assess whether the display should be used for imaging purposes. The authors report on the characterization of three novel probes for measuring display color with minimal contamination from screen areas outside the measurement spot or from off‐normal emissions. They compare three probe designs: A modified small‐spot luminance probe and two conic probe designs based on black frusta.

Methods

To compare the three color probe designs, spectral and luminance measurements were taken with specialized instrumentation to determine the luminance changes and color separation abilities of the probes. The probes were characterized with a scanning slit method, veiling glare, and a moving laser and LED arrangement. The scanning slit measurement was done using a black slit plate over a white line on an LCD monitor. The luminance was measured in increments from the center of the slit to above and below the slit at different distances between the probe and the slit. The veiling glare setup consisted of measurements of the luminance of a black spot pattern with a white disk of radius of as the black spot increases in radius increments. The moving LED and laser method consisted of a red and green light orthogonal to the probe tip for the light to directly shine into the probe. The green light source was moved away from the red source in increments to measure color stray‐light contamination at different probe distances.

Results

The results of the color testing using the LED and laser methods suggest a better performance of one of the frusta probes at shorter distances between the light sources, which translates to less contamination. The tails of the scans indicate the magnitude of the spread in signal due to light from areas outside the intended measurement spot. The measurements indicate a corresponding glare factor for a large spot of 140, 500, and 2000 for probe A, B1, and B2, respectively. The dual‐laser setup suggests that color purity can be maintained up to a few tens of millimeters outside the measurement spot.

Conclusions

The comparison shows that there are significant differences in the performance of each probe design, and that those differences have an effect on the measured quantity used to quantify display color. Different probe designs show different measurements of the level of light contamination that affects the quantitative color determination.
Computerized lesion segmentation of breast ultrasound based on marker‐controlled watershed transformation
Authors: Gómez W. , Leija L. , Alvarenga A. V. , Infantosi A. F. C. , Pereira W. C. A.
Published: December 2009

Purpose

This paper presents a computerized segmentation method for breast lesions on ultrasound (US) images.

Methods

It consists of first applying a contrast‐enhanced approach, i.e., a contrast‐limited adaptive histogram equalization. Then, aiming at removing speckle and enhancing the lesion boundary, an anisotropic diffusion filter, guided by texture descriptors derived from a set of Gabor filters, is applied. To eliminate the distant pixels that do not belong to the tumor, the resulting filtered image is multiplied by a constraint Gaussian function. By doing so, both the segmentation and the marker functions are generated and could be used in the marker‐controlled watershed transformation algorithm to create potential lesion boundaries. Finally, to determine the lesion contour, the average radial derivative function is evaluated. The proposed method was tested with 50 breast US images and 60 simulated “ultrasound‐like” images. Accuracy and precision of the segmentation method were then assessed. For the accuracy, three parameters were used: Overlap ratio (OR), normalized residual value (nrv), and proportional distance (PD) between contours.

Results

The average results for US images were , , and . For simulated ultrasound‐like images, a better performance (, , and ) was achieved.

Conclusions

The segmentation method proposed was capable of delineating the lesion contours with high accuracy in comparison to both the radiologists’ delineations and the true delineations of simulated images. Moreover, this method was also found to be robust to human‐dependent parameters variations.
Effective point of measurement of thimble ion chambers in megavoltage photon beams
Authors: Tessier Frédéric , Kawrakow Iwan
Published: December 2009

Purpose

Determine the effective point of measurement (EPOM) of 12 thimble ion chambers, including miniature chambers and three models widely used for clinical reference dosimetry. The EPOM is the point at which the measured dose would arise in the measurement medium in the absence of the probe: For cylindrical chambers, it is shifted upstream relative to the central axis of the chamber. Although current dosimetry protocols prescribe a blanket upstream EPOM shift of , with as the chamber cavity radius, it has been shown in recent years that the EPOM does, in fact, depend on every detail of the chamber design and on the beam characteristics. In the wake of this finding, the authors undertake a comprehensive study of the EPOM for a series of chambers in water.

Methods

This work relies on EGSnrc Monte Carlo calculations for the central axis depth dose in a water phantom and in ion chambers. They use a full Elekta Precise linac treatment head simulation to generate realistic photon beams with nominal energies of 6 and and fields sizes of and . The correct EPOM shift for the 12 ion chambers, modeled in realistic detail, is taken as the one minimizing the deviation of the ratio between the dose to water and the dose to the gas of the chamber cavity, according to a method proposed and validated in previous work.

Results

The analysis reveals that the actual EPOM shift is significantly smaller than the recommended value in current dosimetry protocols, by up to 25% for reference‐class chambers and 80% for miniature chambers. The location of the EPOM also depends on the characteristics of the incident beam and varies in a well‐defined way with the cavity length, the central electrode radius, and the thimble wall thickness.

Conclusions

The authors confirm that an upstream EPOM shift of is too large for thimble ion chambers in high energy photon beams. Proper values for the EPOM shift could be tabulated per beam and per chamber, but they envisage that a single shift for all practical beams may prove sufficient. Moreover, the systematic dependence on chamber characteristics provides evidence that a universal parametrization in terms of a few design parameters is conceivable and has implication for the calculation of chamber correction factors.
Monte Carlo based, patient‐specific RapidArc QA using Linac log files
Authors: Teke Tony , Bergman Alanah M. , Kwa William , Gill Bradford , Duzenli Cheryl , Popescu I. Antoniu
Published: December 2009

Purpose

A Monte Carlo (MC) based QA process to validate the dynamic beam delivery accuracy for Varian RapidArc™ (Varian Medical Systems, Palo Alto, CA) using Linac delivery log files (DynaLog) is presented. Using DynaLog file analysis and MC simulations, the goal of this article is to (a) confirm that adequate sampling is used in the RapidArc optimization algorithm (177 static gantry angles) and (b) to assess the physical machine performance [gantry angle and monitor unit (MU) delivery accuracy].

Methods

Ten clinically acceptable RapidArc treatment plans were generated for various tumor sites and delivered to a water‐equivalent cylindrical phantom on the treatment unit. Three Monte Carlo simulations were performed to calculate dose to the CT phantom image set: (a) One using a series of static gantry angles defined by 177 control points with treatment planning system (TPS) MLC control files (planning files), (b) one using continuous gantry rotation with TPS generated MLC control files, and (c) one using continuous gantry rotation with actual Linac delivery log files. Monte Carlo simulated dose distributions are compared to both ionization chamber point measurements and with RapidArc TPS calculated doses. The 3D dose distributions were compared using a 3D gamma‐factor analysis, employing a distance‐to‐agreement criterion.

Results

The dose difference between MC simulations, TPS, and ionization chamber point measurements was less than 2.1%. For all plans, the MC calculated 3D dose distributions agreed well with the TPS calculated doses (gamma‐factor values were less than 1 for more than 95% of the points considered). Machine performance QA was supplemented with an extensive DynaLog file analysis. A DynaLog file analysis showed that leaf position errors were less than for 94% of the time and there were no leaf errors greater than . The mean standard deviation in MU and gantry angle were and 0.355°, respectively, for the ten cases analyzed.

Conclusions

The accuracy and flexibility of the Monte Carlo based RapidArc QA system were demonstrated. Good machine performance and accurate dose distribution delivery of RapidArc plans were observed. The sampling used in the TPS optimization algorithm was found to be adequate.
Low‐ target optimization for spatial resolution improvement in megavoltage imaging
Authors: Connell Tanner , Robar James L.
Published: December 2009

Purpose

Recently, several authors have shown contrast improvements in megavoltage portal imaging and cone‐beam computed tomography using low atomic number targets. This work compliments previous studies by investigating the effects of varying different beam production parameters including target atomic number, target thickness, and incident electron energy on spatial resolution.

Methods

Target materials of beryllium, aluminum, and tungsten were investigated over a range of thicknesses between 10% and 100% of the continuous slowing down approximation range of electrons. Incident electron kinetic energies of 4.5 and were used, in conjunction with custom targets installed above the carousel of a modern radiotherapy linear accelerator. Monte Carlo simulations of the accelerator were constructed and compared to the experimental results.

Results

The results showed that thinner targets, as well higher incident electron energies, generally produce more favorable modulation transfer function (MTF) curves. Due to an MTF dependence of the detector system on the photon energy, the experimental results showed that low‐ targets produced superior MTF curves. Simulations showed 14.5% and 21.5% increases in for the 7.0 and targets (Al; 60% ), respectively, when moved from the carousel to the location of the clinical target. values for the custom targets were compared to the clinical beam and were found to be between 10.4% lower and 15.5% higher .

Conclusions

Integration of low‐ external targets into the treatment head of a medical linear was achieved with only minor modifications. It was shown that reasonably high resolution images on par or better than those acquired with the clinical beam can be achieved using external low‐ targets.
Changes in optically stimulated luminescent dosimeter (OSLD) dosimetric characteristics with accumulated dose
Authors: Jursinic Paul A.
Published: December 2009

Purpose

A new type ofin vivo dosimeter, an optically stimulated luminescent dosimeter (OSLD), has now become commercially available for clinical use. The OSLD is a plastic disk infused with aluminum oxide doped with carbon . Crystals of , when exposed to ionizing radiation, store energy that is released as luminescence (420 nm) when the OSLD is illuminated with stimulation light (540 nm). The intensity of the luminescence depends on the dose absorbed by the OSLD and the intensity of the stimulation light. The effects of accumulated dose on OSLD response were investigated.

Methods

The OSLDs used in this work were nanodot dosimeters, which were read with a MicroStar reader (Landauer, Inc., Glenwood, IL). Dose to the OSLDs was delivered by 6 MV x rays and gamma rays from Co‐60 and Ir‐192. The signal on the OSLDs after irradiation is removed by optical annealing with a 150 W tungsten‐halogen lamp or a 14 W compact fluorescent lamp was investigated.

Results

It was found that OSLD response to dose was supralinear and this response was altered with the amount of accumulated dose to the OSLD. The OSLD response can be modeled by a quadratic and an exponential equation. For accumulated doses up to 60 Gy, the OSLD sensitivity (counts/dose) decreases and the extent of supralinear increases. Above 60 Gy of accumulated dose the sensitivity increases and the extent of supralinearity decreases or reaches a plateau, depending on how the OSLDs were optically annealed. With preirradiation of OSLDs with greater than 1 kGy, it is found that the sensitivity reaches a plateau 2.5 folds greater than that of an OSLD with no accumulated dose and the supralinearity disappears. A regeneration of the luminescence signal in the dark after full optical annealing occurs with a half time of about two days. The extent of this regeneration signal depends on the amount of accumulated dose.

Conclusions

Forin vivo dosimetric measurements, a precision of ±0.5% can be achieved if the sensitivity and extent of supralinearity is established for each OSLD and use. Methods are presented for accomplishing this task.
Noise texture and signal detectability in propagation‐based x‐ray phase‐contrast tomography
Authors: Chou Cheng‐Ying , Anastasio Mark A.
Published: December 2009

Purpose

X‐ray phase‐contrast tomography (PCT) is a rapidly emerging imaging modality for reconstructing estimates of an object's three‐dimensional x‐ray refractive index distribution. Unlike conventional x‐ray computed tomography methods, the statistical properties of the reconstructed images in PCT remain unexplored. The purpose of this work is to quantitatively investigate noise propagation in PCT image reconstruction.

Methods

The authors derived explicit expressions for the autocovariance of the reconstructed absorption and refractive index images to characterize noise texture and understand how the noise properties are influenced by the imaging geometry. Concepts from statistical detection theory were employed to understand how the imaging geometry‐dependent statistical properties affect the signal detection performance in a signal‐known‐exactly/background‐known‐exactly task.

Results

The analytical formulas for the phase and absorption autocovariance functions were implemented numerically and compared to the corresponding empirical values, and excellent agreement was found. They observed that the reconstructed refractive images are highly spatially correlated, while the absorption images are not. The numerical results confirm that the strength of the covariance is scaled by the detector spacing. Signal detection studies were conducted, employing a numerical observer. The detection performance was found to monotonically increase as the detector‐plane spacing was increased.

Conclusions

The authors have conducted the first quantitative investigation of noise propagation in PCT image reconstruction. The reconstructed refractive images were found to be highly spatially correlated, while absorption images were not. This is due to the presence of a Fourier space singularity in the reconstruction formula for the refraction images. The statistical analysis may facilitate the use of task‐based image quality measures to further develop and optimize this emerging modality for specific applications.
Monte Carlo dosimetry for and eye plaque brachytherapy with various seed models
Authors: Thomson R. M. , Rogers D. W. O.
Published: December 2009

Purpose

Dose distributions are calculated for various models of and seeds in the standardized plaques of the Collaborative Ocular Melanoma Study (COMS). The sensitivity to seed model of dose distributions and dose distributions relative to TG‐43 are investigated.

Methods

Monte Carlo simulations are carried out with the EGSnrc user‐code BrachyDose. Brachytherapy seeds and eye plaques are fully modeled. Simulations of one seed in the central slot of a 20 mm Modulay (gold alloy) plaque backing with and without the Silastic (silicone polymer) insert and of a 16 mm fully loaded Modulay/Silastic plaque are performed. Dose distributions are compared to those calculated under TG‐43 assumptions, i.e., ignoring the effects of the plaque backing and insert and interseed attenuation. Three‐dimensional dose distributions for different and seed models are compared via depth‐dose curves, isodose contours, and tabulation of doses at points of interest in the eye. Results are compared to those of our recent BrachyDose study for COMS plaques containing model 6711 or 200 seeds [R. M. Thomson et al., Med. Phys. 35, 5530–5543 (2008)].

Results

Along the central axis of a plaque containing one seed, variations of less than 1% are seen in the effect of the Modulay backing alone for different seed models; for the Modulay/Silastic combination, variations are 2%. For a 16 mm plaque fully loaded with seeds, dose decreases relative to TG‐43 doses are 11%–12% (19%–20%) and 14%–15% (20%) at distances of 0.5 and 1 cm from the inner sclera along the plaque's central axis, respectively. For the same prescription dose, doses at points of interest vary by up to 8% with seed model. Doses to critical normal structures are lower for all seed models than for with the possible exception of the sclera adjacent to the plaque; scleral doses vary with seed model and are not always higher for than for .

Conclusions

Dose decreases relative to doses calculated under TG‐43 assumptions vary slightly with seed model (for each radionuclide). Dose distributions are sensitive to seed model; however, variations are generally no larger than the magnitudes of other systematic uncertainties in eye plaque therapy.
Dosimetric verification of IMAT delivery with a conventional EPID system and a commercial portal dose image prediction tool
Authors: Iori Mauro , Cagni Elisabetta , Paiusco Marta , Munro Peter , Nahum Alan E.
Published: December 2009

Purpose

The electronic portal imaging device (EPID) is a system for checking the patient setup; as a result of its integration with the linear accelerator and software customized for dosimetry, it is increasingly used for verification of the delivery of fixed‐field intensity‐modulated radiation therapy (IMRT). In order to extend such an approach to intensity‐modulated arc therapy (IMAT), the combined use of an EPID system and a portal dose image prediction (PDIP) tool has been investigated.

Methods

The dosimetric behavior of an EPID system, mechanically reinforced to maintain its positional stability during the accelerator gantry rotation, has been studied to assess its ability to measure portal dose distributions for IMAT treatment beams. In addition, the PDIP tool of a commercial treatment planning system, commonly used for static IMRT dosimetry, has been validated for simulating the PDIs of IMAT treatment fields. The method has been applied to the delivery verification of 23 treatment fields that were measured in their dual mode of IMRT and IMAT modalities.

Results

The EPID system has proved to be appropriate for measuring the PDIs of IMAT fields; additionally the PDIP tool was able to simulate these accurately. The results are quite similar to those obtained for static IMRT treatment verification, although it was necessary to investigate the dependence of the EPID signal and of the accelerator monitor chamber response on variable dose rate.

Conclusions

Our initial tests indicate that the EPID system, together with the PDIP tool, is a suitable device for the verification of IMAT plan delivery; however, additional tests are necessary to confirm these results.
Theoretical and empirical investigations of for nearly water‐equivalent radiotherapy dosimetry
Authors: Zheng Yuanshui , Han Zhaohui , Driewer Joseph P. , Low Daniel A. , Li H. Harold
Published: December 2009

Purpose

The low effective atomic number, reusability, and other computed radiography‐related advantages make europium doped potassium chloride a promising dosimetry material. The purpose of this study is to model point dosimeters with a Monte Carlo (MC) method and, using this model, to investigate the dose responses of two‐dimensional (2D) storage phosphor films (SPFs).

Methods

point dosimeters were irradiated using a beam at four depths for each of five square field sizes . The dose measured by was compared to that measured by an ionization chamber to obtain the magnitude of energy dependent dose measurement artifact. The measurements were simulated using DOSXYZnrc with phase space files generated by BEAMnrcMP. Simulations were also performed for films with thicknesses ranging from . The work function of the prototype material was determined by comparing the sensitivity of a thick film to a commercial ‐based SPF with a known work function. The work function was then used to estimate the sensitivity of a thick film.

Results

The simulated dose responses of prototype point dosimeters agree well with measurement data acquired by irradiating the dosimeters in the beam with varying field size and depth. Furthermore, simulations with films demonstrate that an ultrathin film with thickness of the order of would have nearly water‐equivalent dose response. The simulation results can be understood using classic cavity theories. Finally, preliminary experiments and theoretical calculations show that ultrathin film could provide excellent signal in a dose‐to‐water irradiation.

Conclusions

In conclusion, the authors demonstrate that ‐based dosimeters can be accurately modeled by a MC method and that 2D films of the order of thick would have minimal energy dependence. The data support the future research and development of a storage phosphor‐based system for quantitative, high‐resolution multidimensional radiation therapy dosimetry.
Particle size, magnetic field, and blood velocity effects on particle retention in magnetic drug targeting
Authors: Cherry Erica M. , Maxim Peter G. , Eaton John K.
Published: December 2009

Purpose

A physics‐based model of a general magnetic drug targeting (MDT) system was developed with the goal of realizing the practical limitations of MDT when electromagnets are the source of the magnetic field.

Methods

The simulation tracks magnetic particles subject to gravity, drag force, magnetic force, and hydrodynamic lift in specified flow fields and external magnetic field distributions. A model problem was analyzed to determine the effect of drug particle size, blood flow velocity, and magnetic field gradient strength on efficiency in holding particles stationary in a laminar Poiseuille flow modeling blood flow in a medium‐sized artery.

Results

It was found that particle retention rate increased with increasing particle diameter and magnetic field gradient strength and decreased with increasing bulk flow velocity.

Conclusions

The results suggest that MDT systems with electromagnets are unsuitable for use in small arteries because it is difficult to control particles smaller than aboutin diameter.
Quantitative analysis of breast parenchymal patterns using 3D fibroglandular tissues segmented based on MRI
Authors: Nie Ke , Chang Daniel , Chen Jeon‐Hor , Hsu Chieh‐Chih , Nalcioglu Orhan , Su Min‐Ying
Published: December 2009

Purpose

Mammographic density and breast parenchymal patterns (the relative distribution of fatty and fibroglandular tissue) have been shown to be associated with the risk of developing breast cancer. Percent breast density as determined by mammography is a well‐established risk factor, but on the other hand, studies on parenchymal pattern have been scarce, possibly due to the lack of reliable quantitative parameters that can be used to analyze parenchymal tissue distribution. In this study the morphology of fibroglandular tissue distribution was analyzed using three‐dimensional breast MRI, which is not subject to the tissue overlapping problem.

Methods

Four parameters, circularity, convexity, irregularity, and compactness, which are sensitive to the shape and margin of segmented fibroglandular tissue, were analyzed for 230 patients. Cases were assigned to one of two distinct parenchymal breast patterns: Intermingled pattern with intermixed fatty and fibroglandular tissue (Type I,), and central pattern with confined fibroglandular tissue inside surrounded by fatty tissue outside (Type C, ). For each analyzed parameter, the differentiation between these two patterns was analyzed using a two‐tailed ‐test based on transformed parameters to normal distribution, as well as distribution histograms and ROC analysis.

Results

These two groups of patients were well matched both in age ( vs ) and in fibroglandular tissue volume (Type I: vs Type C: ). Between Type I and Type C breasts, all four morphological parameters showed significant differences that could be used to differentiate between the two breast types. In the ROC analysis, among all four parameters, the “compactness” could achieve the highest area under the curve of 0.84, and when all four parameters were combined, the AUC could be further increased to 0.94.

Conclusions

The results suggest that these morphological parameters analyzed from 3D MRI can be used to distinguish between intermingled and central dense tissue distribution patterns, and hence may be used to characterize breast parenchymal pattern quantitatively. The availability of these quantitative morphological parameters may facilitate the investigation of the relationship between parenchymal pattern and breast cancer risk.
Impact of skin removal on quantitative measurement of breast density using MRI
Authors: Nie Ke , Chang Daniel , Chen Jeon‐Hor , Shih Tzu‐Ching , Hsu Chieh‐Chih , Nalcioglu Orhan , Su Min‐Ying
Published: December 2009

Purpose

In breast MRI, skin and fibroglandular tissue commonly possess similar signal intensities, and as such, the inclusion of skin as dense tissue leads to an overestimation in the measured density. This study investigated the impact of skin to the quantitative measurement of breast density using MRI.

Methods

The analysis was performed on the normal breasts of 50 women using nonfat‐saturated (nonfat‐sat) T1 weighted MR images. The skin was segmented by using a dynamic searching algorithm, which was based on the change in signal intensities from the background air (dark), to the skin (moderate), and then to the fatty tissue (bright). Tissue with moderate intensities that fell between the two boundaries determined based on the intensity gradients (from air to skin, and from skin to fat) was categorized as skin. The percent breast density measured with and without skin exclusion was compared. Also the relationship between the skin volume and the breast volume was investigated. Then, this relationship was used to estimate the skin volume from the breast volume for skin correction.

Results

The percentage of the skin volume normalized to the breast volume ranged from 5.0% to 15.2% (median 8.6%, ) among 50 women. The percent breast densities measured with skin and without skin were highly correlated, (, ). The relationship between the skin volume and the breast volume was analyzed based on transformed data (the square root of the skin volume vs the cube root of breast volume) using the linear regression, and yielded , . When this model was used to estimate the skin volume for correction in the density analysis, it provided a better fit to the measured density with skin exclusion (with adjusted , and root mean square ) compared to the correction done by using a fixed cutoff value of 8% (adjusted , root mean square ).

Conclusions

The authors have shown that the skin volume is related to the breast volume, and this relationship may be used to correct for the skin effect in the MRI‐based density measurement. A reliable quantitative density analysis method will aid in clinical investigation to evaluate the role of breast density for cancer risk assessment or for prediction of the efficacy of risk‐modifying drugs using hormonal therapy.
Dynamic multiple thresholding breast boundary detection algorithm for mammograms
Authors: Wu Yi‐Ta , Zhou Chuan , Chan Heang‐Ping , Paramagul Chintana , Hadjiiski Lubomir M. , Daly Caroline Plowden , Douglas Julie A. , Zhang Yiheng , Sahiner Berkman , Shi Jiazheng , Wei Jun
Published: December 2009

Purpose

Automated detection of breast boundary is one of the fundamental steps for computer‐aided analysis of mammograms. In this study, the authors developed a new dynamic multiple thresholding based breast boundary (MTBB) detection method for digitized mammograms.

Methods

A large data set of 716 screen‐film mammograms (442 CC view and 274 MLO view) obtained from consecutive cases of an Institutional Review Board approved project were used. An experienced breast radiologist manually traced the breast boundary on each digitized image using a graphical interface to provide a reference standard. The initial breast boundary (MTBB‐Initial) was obtained by dynamically adapting the threshold to the gray level range in local regions of the breast periphery. The initial breast boundary was then refined by using gradient information from horizontal and vertical Sobel filtering to obtain the final breast boundary (MTBB‐Final). The accuracy of the breast boundary detection algorithm was evaluated by comparison with the reference standard using three performance metrics: The Hausdorff distance (HDist), the average minimum Euclidean distance (AMinDist), and the area overlap measure (AOM).

Results

In comparison with the authors’ previously developed gradient‐based breast boundary (GBB) algorithm, it was found that 68%, 85%, and 94% of images had HDist errors less than 6 pixels (4.8 mm) for GBB, MTBB‐Initial, and MTBB‐Final, respectively. 89%, 90%, and 96% of images had AMinDist errors less than 1.5 pixels (1.2 mm) for GBB, MTBB‐Initial, and MTBB‐Final, respectively. 96%, 98%, and 99% of images had AOM values larger than 0.9 for GBB, MTBB‐Initial, and MTBB‐Final, respectively. The improvement by the MTBB‐Final method was statistically significant for all the evaluation measures by the Wilcoxon signed rank test .

Conclusions

The MTBB approach that combined dynamic multiple thresholding and gradient information provided better performance than the breast boundary detection algorithm that mainly used gradient information.
Simulation of dose reduction in tomosynthesis
Authors: Svalkvist Angelica , Båth Magnus
Published: December 2009

Purpose: Methods for simulating dose reduction are valuable tools in the work of optimizing radiographic examinations. Using such methods, clinical images can be simulated to have been collected at other, lower, dose levels without the need of additional patient exposure. A recent technology introduced to healthcare that needs optimization is tomosynthesis, where a number of low‐dose projection images collected at different angles is used to reconstruct section images of an imaged object. The aim of the present work was to develop a method of simulating dose reduction for digital radiographic systems, suitable for tomosynthesis.

Methods: The developed method uses information about the noise power spectrum (NPS) at the original dose level and the simulated dose level to create a noise image that is added to the original image to produce an image that has the same noise properties as an image actually collected at the simulated dose level. As the detective quantum efficiency (DQE) of digital detectors operating at the low dose levels used for tomosynthesis may show a strong dependency on the dose level, it is important that a method for simulating dose reduction for tomosynthesis takes this dependency into account. By applying an experimentally determined relationship between pixel mean and pixel variance, variations in both dose and DQE in relevant dose ranges are taken into account.

Results: The developed method was tested on a chest tomosynthesis system and was shown to produce NPS of simulated dose‐reduced projection images that agreed well with the NPS of images actually collected at the simulated dose level. The simulated dose reduction method was also applied to tomosynthesis examinations of an anthropomorphic chest phantom, and the obtained noise in the reconstructed section images was very similar to that of an examination actually performed at the simulated dose level.

Conclusions: In conclusion, the present article describes a method for simulating dose reduction suitable for tomosynthesis. However, the method applies equally well to any digital radiographic system, although the benefits of correcting for DQE variations may be smaller.
Topographical and Temporal Diversity of the Human Skin Microbiome
Authors: Grice Elizabeth A. , Kong Heidi H. , Conlan Sean , Deming Clayton B. , Davis Joie , Young Alice C. ,   NISC Comparative Sequencing Program, Bouffard Gerard G. , Blakesley Robert W. , Murray Patrick R. , Green Eric D. , Turner Maria L. , Segre Julia A.
Published: December 2009

The Close and Personal Biome

Fortunately, our skin is readily accessible for ecological studies of the microbial communities that influence health and disease states.

Grice
et al.

(p.
1190
) present a metagenomic survey of body sites from 10 healthy human individuals sampled over time. Although, altogether 18 phyla were discovered, only a few predominated. The most diverse communities were found on the forearm and the least behind the ear, but between people the microorganisms living behind the knees, in the elbow, and behind the ear were most similar. This finding might have some bearing on the common occurrence of atopic dermatitis in these zones, although no similar relationship was discerned between skin microbial flora and psoriasis.
Tearing of Stagnant Slab
Authors: Obayashi Masayuki , Yoshimitsu Junko , Fukao Yoshio
Published: December 2009

Tearing the Plate

Recent seismic data show a widely variable geometry of subduction: Some plates penetrate deep into the mantle; others bend and become horizontal at 670 kilometers near a prominent phase boundary.

Obayashi
et al.

(p.
1173
; see the Perspective by
Nolet
) provide a detailed view of a situation where subduction of juxtaposed plates in the western Pacific, in somewhat different directions, seems to have ripped a gash in the plates starting at a depth of about 300 kilometers. The geometry of the gash provides information on the past evolution of this plate boundary.
What Determines Coral Health?
Authors: Weis Virginia M. , Allemand Denis
Published: December 2009

Genomic and cellular studies are revealing the physiological mechanisms of symbiosis and calcification, which are central to coral health.
Seasonal Influenza Vaccine Provides Priming for A/H1N1 Immunization
Authors: Del Giudice Giuseppe , Stittelaar Koert J. , van Amerongen Geert , Simon James , Osterhaus Albert D. M. E. , Stöhr Klaus , Rappuoli Rino
Published: December 2009

Tests in ferrets show that the vaccine now used for mass inoculation against H1N1 is more effective when coinjected with an oil-in-water adjuvant and after the animals’ exposure to seasonal flu vaccine.
α
2A
-Adrenergic Receptors in the Genetics, Pathogenesis, and Treatment of Type 2 Diabetes
Authors: Liggett Stephen B.
Published: December 2009

Genetic variation of α
2A
-adrenergic receptors on pancreatic β cells provides new avenues for diagnosis and treatment of type 2 diabetes.
Amino Acids to the Rescue
Authors: McDonald Heather B.
Published: December 2009

Consumption of neurotransmitter precursors improves cognitive performance after brain injury in mice.
A Protective Genetic Variant for Lungs
Authors: Kelner Katrina L.
Published: December 2009

Analysis of seven independent groups of subjects uncovers a metalloproteinase variant that protects against lung damage—but only in smokers and people with lung disease.
Dynamic Duo: Cancer Drugs and the Immune System
Authors: LaMarco Kelly
Published: December 2009

In mice with ovarian cancer, treatment with both the drug Doxil and the cytokine interleukin-18 inhibits tumor growth and promotes tumor regression better than either therapy alone.
Secret Entry for Dendritic Cells
Authors: Khidr Lily
Published: December 2009

The basement membrane, thought to be a barrier to cell movement, contains flexible perforations that can serve as cellular gateways.