bluuebunny/crossref_metadata_2025 huggingface dataset:
Physical effects of mechanical design parameters on photon sensitivity and spatial resolution performance of a breast‐dedicated PET system
Authors: Spanoudaki V. C. , Lau F. W. Y. , Vandenbroucke A. , Levin C. S.
Published: November 2010

Purpose:

This study aims to address design considerations of a high resolution, high sensitivity positron emission tomography scanner dedicated to breast imaging.

Methods:

The methodology uses a detailed Monte Carlo model of the system structures to obtain a quantitative evaluation of several performance parameters. Special focus was given to the effect of dense mechanical structures designed to provide mechanical robustness and thermal regulation to the minuscule and temperature sensitive detectors.

Results:

For the energies of interest around the photopeak (450–700 keV energy window), the simulation results predict a 6.5% reduction in the single photon detection efficiency and a 12.5% reduction in the coincidence photon detection efficiency in the case that the mechanical structures are interspersed between the detectors. However for lower energies, a substantial increase in the number of detected events (approximately 14% and 7% for singles at a 100–200 keV energy window and coincidences at a lower energy threshold of 100 keV, respectively) was observed with the presence of these structures due to backscatter. The number of photon events that involve multiple interactions in various crystal elements is also affected by the presence of the structures. For photon events involving multiple interactions among various crystal elements, the coincidence photon sensitivity is reduced by as much as 20% for a point source at the center of the field of view. There is no observable effect on the intrinsic and the reconstructed spatial resolution and spatial resolution uniformity.

Conclusions:

Mechanical structures can have a considerable effect on system sensitivity, especially for systems processing multi‐interaction photon events. This effect, however, does not impact the spatial resolution. Various mechanical structure designs are currently under evaluation in order to achieve optimum trade‐off between temperature stability, accurate detector positioning, and minimum influence on system performance.
Feature selection using factor analysis for Alzheimer's diagnosis using PET images
Authors: Salas‐Gonzalez D. , Górriz J. M. , Ramírez J. , Illán I. A. , López M. , Segovia F. , Chaves R. , Padilla P. , Puntonet C. G. ,   The Alzheimer's Disease Neuroimage Initiative
Published: November 2010

Purpose:

This article presents a computer‐aided diagnosis technique for improving the accuracy of the early diagnosis of Alzheimer's disease (AD). Two hundred and ten PET images from the ADNI initiative [52 normal controls (NC), 114 mild cognitive impairment (MCI), and 53 AD subjects] are studied.

Methods:

The proposed methodology is based on the selection of voxels of interest using the t‐test and a posterior reduction of the feature dimension using factor analysis. Factor loadings are used as features for three different classifiers: Two multivariate Gaussian mixture model, with linear and quadratic discriminant function, and a support vector machine with linear kernel.

Results:

An accuracy rate up to 95% when NC and AD are considered and an accuracy rate up to 88% and 86% for NC‐MCI and NC‐MCI, AD, respectively, are obtained using SVM with linear kernel.

Conclusions:

Results are compared to the voxel‐as‐features and a PCA‐ based approach and the proposed methodology achieves better classification performance.
High frame rate ultrasound monitoring of high intensity focused ultrasound‐induced temperature changes: A novel asynchronous approach
Authors: Liu Hao‐Li , Huang Sheng‐Min , Li Meng‐Lin
Published: November 2010

Purpose: When applying diagnostic ultrasound to guide focused ultrasound (FUS) thermal therapy, high frame rate ultrasonic temperature monitoring is valuable in better treatment control and dose monitoring. However, one of the potential problems encountered when performing ultrasonic temperature monitoring of a FUS procedure is interference between the FUS and imaging systems. Potential means of overcoming this problem include the switch between the FUS system and the imaging system (limited by a reduced frame rate of thermal imaging) or the development of complex synchronization protocols between the FUS therapeutic system and the ultrasonic imaging apparatus (limited by implementation efforts both for software and hardware designs, and low potential for widespread diffusion). In this paper, we apply an asynchronous idea to retrieving high frame rate and FUS‐interference‐free thermal imaging during FUS thermal therapy.

Methods: Tone‐burst delivery mode of the FUS energy is employed in our method, and the imaging and FUS systems are purposely operated in an asynchronous manner. Such asynchronous operation causes FUS interference to saturate sequential image frames at different A‐lines; thus clean A‐lines from several image frames can be extracted by a total energy‐thresholding technique and then combined to reconstruct interference‐free B‐mode images at a high frame rate for temperature estimation. The performance of the proposed method is demonstrated by phantom experiments. Relationships of the FUS duty‐cycle with the maximum reconstructed frame rate of thermal imaging and the corresponding maximum temperature increase are also studied. Its performance was also evaluated and compared with the existing manually synchronous and synchronous approaches.

Results: By proper selection of the FUS duty‐cycle, using our method, the frame rate of thermal imaging can be increased up to tenfold compared with that provided by the manually synchronous approach. Our method is capable of pushing the frame rate of thermal images to the same order as that of the synchronous approach while avoiding sacrificing the observable field of view (FOV) of temperature mapping.

Conclusions: The asynchronous method can be easily implemented and allows thermal imaging at an improved frame rate, without the need for complex synchronization protocols between the FUS therapeutic system and the ultrasonic imaging apparatus and without sacrifice of observable FOV. This technology may provide an effective alternative for real‐time temperature measuring during thermal ablation procedures and can be easily integrated into current high intensity focused ultrasound systems.
Intensity inhomogeneity correction for the breast sonogram: Constrained fuzzy cell‐based bipartitioning and polynomial surface modeling
Authors: Lee Chia‐Yen , Chou Yi‐Hong , Huang Chiun‐Sheng , Chang Yeun‐Chung , Tiu Chui‐Mei , Chen Chung‐Ming
Published: November 2010

Purpose:

To develop an intensity inhomogeneity algorithm for breast sonograms in order to assist visual identification and automatic delineation of lesion boundaries.

Methods:

The proposed algorithm was composed of two essential ideas. One was decomposing the region of interest (ROI) into foreground and background regions by a cell‐based segmentation algorithm, called constrained fuzzy cell‐based bipartition‐EM (CFCB‐EM) algorithm. The CFCB‐EM algorithm deformed the contour in a fuzzy cell‐based deformation fashion with the cell structures derived by the fuzzy cell competition (FCC) algorithm as the deformation unit and the boundary estimated by the normalized cut (NC) algorithm as the reference contour. The other was modeling the intensity inhomogeneity in an ROI as a spatially variant normal distribution with a constant variance and spatially variant means, which formed a polynomial surface of order. The proposed algorithm was formulated as a nested EM algorithm comprising the outer‐layer EM algorithm, i.e., the intensity inhomogeneity correction‐EM (IIC‐EM) algorithm, and the inner‐layer EM algorithm, i.e., the CFCB‐EM algorithm. The E step of the IIC‐EM algorithm was to provide a reasonably good bipartition separating the ROI into foreground and background regions, which included three major component algorithms, namely, the FCC, the NC, and the CFCB‐EM. The M step of the IIC‐EM algorithm was to estimate and correct the intensity inhomogeneity field by least‐squared fitting the intensity inhomogeneity to an order polynomial surface. Forty‐nine breast sonograms with intensity inhomogeneity, each from a different subject, were randomly selected for performance analysis. Three assessments were carried out to evaluate the effectiveness of the proposed algorithm.

Results:

Based on the visual evaluation of two experienced radiologists, in the first assessment, 46 out of 49 breast lesions were considered to have better contrasts on the inhomogeneity‐corrected images by both radiologists. The interrater reliability for the radiologists was found to be . In the second assessment, the mean gradients of the low‐gradient boundary points before and after correction of the intensity inhomogeneity were compared by the paired t‐test, yielding a ‐value of 0.000, which suggested the proposed intensity inhomogeneity algorithm may enhance the mean gradient of the low‐gradient boundary points. By using the paired t‐test, the third assessment further showed that the Chan and Vese level set method could derive a much better lesion boundary on the inhomogeneity‐corrected image than on the original image .

Conclusions:

The proposed intensity inhomogeneity correction algorithm could not only augment the visibility of lesion boundary but also improve the segmentation result on a breast sonogram.
Optimization of a dual‐energy contrast‐enhanced technique for a photon‐counting digital breast tomosynthesis system: I. A theoretical model
Authors: Carton Ann‐Katherine , Ullberg Christer , Lindman Karin , Acciavatti Raymond , Francke Tom , Maidment Andrew D. A.
Published: November 2010

Purpose:

Dual‐energy (DE) iodine contrast‐enhanced x‐ray imaging of the breast has been shown to identify cancers that would otherwise be mammographically occult. In this article, theoretical modeling was performed to obtain optimally enhanced iodine images for a photon‐counting digital breast tomosynthesis (DBT) system using a DE acquisition technique.

Methods:

In the system examined, the breast is scanned with a multislit prepatient collimator aligned with a multidetector camera. Each detector collects a projection image at a unique angle during the scan. Low‐energy (LE) and high‐energy (HE) projection images are acquired simultaneously in a single scan by covering alternate collimator slits with Sn and Cu filters, respectively. Sn filters ranging from 0.08 to 0.22 mm thickness and Cu filters from 0.11 to 0.27 mm thickness were investigated. A tube voltage of 49 kV was selected. Tomographic images, hereafter referred to as DBT images, were reconstructed using a shift‐and‐add algorithm. Iodine‐enhanced DBT images were acquired by performing a weighted logarithmic subtraction of the HE and LE DBT images. The DE technique was evaluated for 20–80 mm thick breasts. Weighting factors,, that optimally cancel breast tissue were computed. Signal‐difference‐to‐noise ratios (SDNRs) between iodine‐enhanced and nonenhanced breast tissue normalized to the square root of the mean glandular dose (MGD) were computed as a function of the fraction of the MGD allocated to the HE images. Peak and optimal dose allocations were identified. and dose allocations were computed for several practical feasible system configurations (i.e., determined by the number of collimator slits covered by Sn and Cu). A practical system configuration and Sn–Cu filter pair that accounts for the trade‐off between SDNR, tube‐output, and MGD were selected.

Results:

depends on the Sn–Cu filter combination used, as well as on the breast thickness; to optimally cancel 0% with 50% glandular breast tissue, values were found to range from 0.46 to 0.72 for all breast thicknesses and Sn–Cu filter pairs studied. The optimal values needed to cancel all possible breast tissue glandularites vary by less than 1% for 20 mm thick breasts and 18% for 80 mm breasts. The system configuration where one collimator slit covered by Sn is alternated with two collimator slits covered by Cu delivers nearest to the peak value. A reasonable compromise is a 0.16 mm Sn–0.23 mm Cu filter pair, resulting in SDNR values between 1.64 and 0.61 and MGD between 0.70 and 0.53 mGy for 20–80 mm thick breasts at the maximum tube current.

Conclusions:

A DE acquisition technique for a photon‐counting DBT imaging system has been developed and optimized.
Level‐set segmentation of pulmonary nodules in megavolt electronic portal images using a CT prior
Authors: Schildkraut J. S. , Prosser N. , Savakis A. , Gomez J. , Nazareth D. , Singh A. K. , Malhotra H. K.
Published: November 2010

Purpose:

Pulmonary nodules present unique problems during radiation treatment due to nodule position uncertainty that is caused by respiration. The radiation field has to be enlarged to account for nodule motion during treatment. The purpose of this work is to provide a method of locating a pulmonary nodule in a megavolt portal image that can be used to reduce the internal target volume (ITV) during radiation therapy. A reduction in the ITV would result in a decrease in radiation toxicity to healthy tissue.

Methods:

Eight patients with nonsmall cell lung cancer were used in this study. CT scans that include the pulmonary nodule were captured with a GE Healthcare LightSpeed RT 16 scanner. Megavolt portal images were acquired with a Varian Trilogy unit equipped with an AS1000 electronic portal imaging device. The nodule localization method uses grayscale morphological filtering and level‐set segmentation with a prior. The treatment‐time portion of the algorithm is implemented on a graphical processing unit.

Results:

The method was retrospectively tested on eight cases that include a total of 151 megavolt portal image frames. The method reduced the nodule position uncertainty by an average of 40% for seven out of the eight cases. The treatment phase portion of the method has a subsecond execution time that makes it suitable for near‐real‐time nodule localization.

Conclusions:

A method was developed to localize a pulmonary nodule in a megavolt portal image. The method uses the characteristics of the nodule in a prior CT scan to enhance the nodule in the portal image and to identify the nodule region by level‐set segmentation. In a retrospective study, the method reduced the nodule position uncertainty by an average of 40% for seven out of the eight cases studied.
Evaluation of tear evaporation from ocular surface by functional infrared thermography
Authors: Tan Jen‐Hong , Ng E. Y. K. , Acharya U. Rajendra
Published: November 2010

Purpose:

A novel technique was developed to measure tear evaporation and monitor its variation with respect to time, for the studying of ocular physiology based on dynamic functional infrared thermography and the first law of thermodynamics using the measured ocular surface temperatures (OSTs). This is a noninvasive, noncontact temperature measuring method that is widely applied in the field of biomedicine.

Methods:

A simple method based on the ocular thermal data was proposed to measure the rate of tear evaporation. The OST of 60 normal subjects were recorded in the form of sequential thermal images. For each thermal sequence, the ocular region was selected and warped to a standard form. Thermal data within the regions were processed, on the basis of the first law of thermodynamics to derive the evaporation rate.

Results:

For elder subjects (aged above 35), the rate was determined to be and for younger subjects, the rate was . The corneal rate of evaporation in elder subjects was found statistically larger than their younger counterparts. The rate of blinking was observed to be related to the variation of evaporation rate.

Conclusions:

The authors have measured the evaporation rate on a sequence of thermographic images. A region of interest was selected at first and the same region on all the images were warped into a standard form. Calculations were performed based on the thermal data in those regions to obtain the values of interest. The authors found that the tear evaporation rate for subjects of all age groups was and the corneal tear evaporation was higher in elder subjects. The corneal rate of evaporation fluctuated in a larger magnitude in subjects who blinked more than average.
A feasibility study of photosensor charge signal transmission to preamplifier using long cable for development of hybrid PET‐MRI
Authors: Kang Jihoon , Choi Yong , Hong Key Jo , Jung Jin Ho , Hu Wei , Huh Yoon Suk , Lim Hyunkeong , Kim Byung‐Tae
Published: November 2010

Purpose:

A new positron emission tomography (PET) detector signal processing method, the charge signal transmission approach, is proposed for the development of a hybrid PET‐magnetic resonance imaging (MRI). A number of experiments were performed to demonstrate that the Geiger‐mode avalanche photodiode (GAPD) charge output could be transmitted to a preamplifier using a long cable without degrading the PET signal performance.

Methods:

A PET module consisted of LYSO and a GAPD with a array. The GAPD output was transmitted to the preamplifier through flexible flat cables. The effect of the cable length on the PET performance was examined using seven different lengths ranging from 10 to 300 cm outside and inside the 7 T animal MRI. Four parameters (rise time, fall time, amplitude, and area of the preamplifier output) were measured as a function of the cable length using a 10 GS/s oscilloscope and three parameters (photopeak position, energy resolution, and time resolution) were measured using a 100 MS/s DAQ unit. The effect of the cable length on the MR phantom images was investigated. In addition, the effect of the PET module configuration on its temperature stability was assessed by acquiring the energy and time spectra.

Results:

There were no significant changes in the PET module performance as a function of the cable length, both outside and inside MRI. The performance changes in energy information, such as the amplitude, area, photopeak position, and energy resolution, were with cable lengths ranging from 10 to 300 cm and the change in the time resolution was . There were no obvious artifacts or changes in the line profile in the MR phantom images. Moreover, no manifest changes in the photopeak position and coincidence counting rate were observed in the PET modules employing the charge signal transmission approach, whereas considerable degradation of the PET module performance was observed in the voltage signal transmission approach.

Conclusions:

This study demonstrated that it is feasible to design a hybrid PET‐MRI using the charge signal transmission approach, which is expected to have more advantages than other approaches.
Computerized method for evaluating diagnostic image quality of calcified plaque images in cardiac CT: Validation on a physical dynamic cardiac phantom
Authors: King Martin , Rodgers Zachary , Giger Maryellen L. , Bardo Dianna M. E. , Patel Amit R.
Published: November 2010

Purpose:

In cardiac computed tomography (CT), important clinical indices, such as the coronary calcium score and the percentage of coronary artery stenosis, are often adversely affected by motion artifacts. As a result, the expert observer must decide whether or not to use these indices during image interpretation. Computerized methods potentially can be used to assist in these decisions. In a previous study, an artificial neural network (ANN) regression model provided assessability (image quality) indices of calcified plaque images from the softwareNCAT phantom that were highly agreeable with those provided by expert observers. The method predicted assessability indices based on computer‐extracted features of the plaque. In the current study, the ANN‐predicted assessability indices were used to identify calcified plaque images with diagnostic calcium scores (based on mass) from a physical dynamic cardiac phantom. The basic assumption was that better quality images were associated with more accurate calcium scores.

Methods:

A 64‐channel CT scanner was used to obtain 500 calcified plaque images from a physical dynamic cardiac phantom at different heart rates, cardiac phases, and plaque locations. Two expert observers independently provided separate sets of assessability indices for each of these images. Separate sets of ANN‐predicted assessability indices tailored to each observer were then generated within the framework of a bootstrap resampling scheme. For each resampling iteration, the absolute calcium score error between the calcium scores of the motion‐contaminated plaque image and its corresponding stationary image served as the ground truth in terms of indicating images with diagnostic calcium scores. The performances of the ANN‐predicted and observer‐assigned indices in identifying images with diagnostic calcium scores were then evaluated using ROC analysis.

Results:

Assessability indices provided by the first observer and the corresponding ANN performed similarly ( vs ) as that of the second observer and the corresponding ANN ( vs ). Moreover, the ANN‐predicted indices were generated in a fraction of the time required to obtain the observer‐assigned indices.

Conclusions:

ANN‐predicted assessability indices performed similar to observer‐assigned assessability indices in identifying images with diagnostic calcium scores from the physical dynamic cardiac phantom. The results of this study demonstrate the potential of using computerized methods for identifying images with diagnostic clinical indices in cardiac CT images.
Statistical analysis of dose heterogeneity in circulating blood: Implications for sequential methods of total body irradiation
Authors: Molloy Janelle A.
Published: November 2010

Purpose:

Improvements in delivery techniques for total body irradiation (TBI) using Tomotherapy® and intensity modulated radiation therapy have been proven feasible. Despite the promise of improved dose conformality, the application of these “sequential” techniques has been hampered by concerns over dose heterogeneity to circulating blood. The present study was conducted to provide quantitative evidence regarding the potential clinical impact of this heterogeneity.

Methods:

Blood perfusion was modeled analytically as possessing linear, sinusoidal motion in the craniocaudal dimension. The average perfusion period for human circulation was estimated to be approximately 78 s. Sequential treatment delivery was modeled as a Gaussian‐shaped dose cloud with a 10 cm length that traversed a 183 cm patient length at a uniform speed. Total dose to circulating blood voxels was calculated via numerical integration and normalized to 2 Gy per fraction. Dose statistics and equivalent uniform dose (EUD) were calculated for relevant treatment times, radiobiological parameters, blood perfusion rates, and fractionation schemes. The model was then refined to account for random dispersion superimposed onto the underlying periodic blood flow. Finally, a fully stochastic model was developed using binomial and trinomial probability distributions. These models allowed for the analysis of nonlinear sequential treatment modalities and treatment designs that incorporate deliberate organ sparing.

Results:

The dose received by individual blood voxels exhibited asymmetric behavior that depended on the coherence among the blood velocity, circulation phase, and the spatiotemporal characteristics of the irradiation beam. Heterogeneity increased with the perfusion period and decreased with the treatment time. Notwithstanding, heterogeneity was less than for perfusion periods less than 150 s. The EUD was compromised for radiosensitive cells, long perfusion periods, and short treatment times. However, the EUD was unaffected (within 10%) for perfusion periods of less than 150 s or treatment times of 20 min or greater. Treatment over six fractions improved the EUD per fraction such that all parametric combinations resulted in unaffected EUD. The stochastic models confirmed these results.

Conclusions:

Dose heterogeneity in circulating blood cells is clinically acceptable for typical treatment times, perfusion rates, and cell types. Development of conformal, sequential TBI treatment techniques should not be withheld based on concerns over circulating blood dose heterogeneity.
Estimation of the minimum detectable activity of preclinical PET imaging systems with an analytical method
Authors: Bao Qinan , Chatziioannou Arion F.
Published: November 2010

Purpose:

The traditional figures of merit used in the evaluation of positron emission tomography (PET) systems, including system sensitivity and spatial resolution, do not directly reflect the minimum detectable activity (MDA) performance, despite the fact that it is one of the most important tasks for a PET system. MDA, as a combination of the more traditional PET system parameters, is directly related to lesion detection. However, MDA evaluation is task specific and cannot be done by a single measurement. Therefore, a simple method to evaluate system detectability needs to be developed.

Methods:

In this work, an analytical method of MDA estimation was developed, taking into account system sensitivity, spatial resolution, source properties, and noise propagation in image reconstruction by using the Rose criterion and/or the Curie equation as the detection standard. In the implementation, the source background, as well as the intrinsic activity background from the scintillation material of the system, was also taken into consideration. The accuracy of this method was evaluated in two commercially available preclinical PET systems, with phantom experiments that were designed to closely mimicin vivo tumor uptake without introducing finite boundaries between the source and the background.

Results:

The lesion contrast‐to‐noise ratio calculated by the analytical evaluation showed good agreement with that obtained from the experiments. Visual assessment of the reconstructed images at the detection limit (based on analytical evaluation) also was in agreement with the Rose criterion. The MDA performance was quantitatively compared between the two preclinical PET systems and showed different detection limits under different imaging conditions, suggesting that the detection limit of a PET system strongly depends on the lesion properties and acquisition settings.

Conclusions:

An analytical method of evaluating the PET system detectability was developed and validated by experiments. Overall, the analytical MDA calculation provides a simple way to evaluate the signal detectability of a PET system and can be used for comparing different systems. It also provides guidelines for designing new PET tomographs as well as optimizing data acquisition protocols.
Scatter correction for cone‐beam computed tomography using moving blocker strips: A preliminary study
Authors: Wang Jing , Mao Weihua , Solberg Timothy
Published: November 2010

Purpose:

One well‐recognized challenge of cone‐beam computed tomography (CBCT) is the presence of scatter contamination within the projection images. Scatter degrades the CBCT image quality by decreasing the contrast, introducing shading artifacts, and leading to inaccuracies in the reconstructed CT number. The authors propose a blocker‐based approach to simultaneously estimate scatter signal and reconstruct the complete volume within the field of view (FOV) from a single CBCT scan.

Methods:

A physical strip attenuator (i.e., “blocker”), consisting of lead strips, is inserted between the x‐ray source and the patient. The blocker moves back and forth along the‐axis during the gantry rotation. With such a design, the data required for the filtering step of the Feldkamp–Davis–Kress (FDK) algorithm are complete in the unblocked region and the entire volume within the FOV has the measurements at different projection views. The two‐dimensional scatter fluence is estimated by interpolating the signal from the blocked regions. A modified FDK algorithm and an iterative reconstruction based on the constraint optimization are used to reconstruct CBCT images from unblocked projection data after the scatter signal is subtracted. A simulation study and an experimental study are performed to evaluate the performance of the proposed scatter correction scheme.

Results:

The scatter‐induced shading/cupping artifacts are substantially reduced in CBCT using the proposed strategy. In the simulation study, the mean relative error is reduced from 25% to 3% and 2% in the images reconstructed by the modified FDK and constraint optimization, respectively. In the experimental study using a CatPhan® 600 phantom, CT number errors in the selected regions of interest are reduced from 256 to less than 20.

Conclusions:

An effective scatter correction scheme is proposed for CBCT. A moving blocker consisting of lead strips is inserted between the x‐ray source and the patient during CBCT acquisition. The proposed method allows the authors to simultaneously estimate the scatter signal in projection data, reduce the imaging dose, and obtain complete volumetric information within the FOV.
A spatio‐temporal detective quantum efficiency and its application to fluoroscopic systems
Authors: Friedman S. N. , Cunningham I. A.
Published: November 2010

Purpose:

Fluoroscopic x‐ray imaging systems are used extensively in spatio‐temporal detection tasks and require a spatio‐temporal description of system performance. No accepted metric exists that describes spatio‐temporal fluoroscopic performance. The detective quantum efficiency (DQE) is a metric widely used in radiography to quantify system performance and as a surrogate measure of patient “dose efficiency.” It has been applied previously to fluoroscopic systems with the introduction of a temporal correction factor. However, the use of a temporally‐corrected DQE does not provide system temporal information and it is only valid under specific conditions, many of which are not likely to be satisfied by suboptimal systems. The authors propose a spatio‐temporal DQE that describes performance in both spaceand time and is applicable to all spatio‐temporal quantum‐based imaging systems.

Methods:

The authors define a spatio‐temporal DQE (two spatial‐frequency axes and one temporal‐frequency axis) in terms of a small‐signal spatio‐temporal modulation transfer function (MTF) and spatio‐temporal noise power spectrum (NPS). Measurements were made on an x‐ray image intensifier‐based bench‐top system using continuous fluoroscopy with an RQA‐5 beam at/frame and hardened 50 kVp beam (0.8 mm Cu filtration added) at /frame.

Results:

A zero‐frequency DQE value of 0.64 was measured under both conditions. Nonideal performance was noted at both larger spatialand temporal frequencies; DQE values decreased by at the cutoff temporal frequency of 15 Hz.

Conclusions:

The spatio‐temporal DQE enables measurements of decreased temporal system performance at larger temporal frequencies analogous to previous measurements of decreased (spatial) performance. This marks the first time that system performance and dose efficiency in both space and time have been measured on a fluoroscopic system using DQE and is the first step toward the generalized use of DQE on clinical fluoroscopic systems.
Use of a realistic breathing lung phantom to evaluate dose delivery errorsa)
Authors: Court Laurence E. , Seco Joao , Lu Xing‐Qi , Ebe Kazuyu , Mayo Charles , Ionascu Dan , Winey Brian , Giakoumakis Nikos , Aristophanous Michalis , Berbeco Ross , Rottman Joerg , Bogdanov Madeleine , Schofield Deborah , Lingos Tania
Published: November 2010

Purpose:

To compare the effect of respiration‐induced motion on delivered dose (the interplay effect) for different treatment techniques under realistic clinical conditions.

Methods:

A flexible resin tumor model was created using rapid prototyping techniques based on a computed tomography (CT) image of an actual tumor. Twenty micro‐MOSFETs were inserted into the tumor model and the tumor model was inserted into an anthropomorphic breathing phantom. Phantom motion was programed using the motion trajectory of an actual patient. A four‐dimensional CT image was obtained and several treatment plans were created using different treatment techniques and planning systems: Conformal (Eclipse), step‐and‐shoot intensity‐modulated radiation therapy (IMRT) (Pinnacle), step‐and‐shoot IMRT (XiO), dynamic IMRT (Eclipse), complex dynamic IMRT (Eclipse), hybrid IMRT [60% conformal, 40% dynamic IMRT (Eclipse)], volume‐modulated arc therapy (VMAT) [single‐arc (Eclipse)], VMAT [double‐arc (Eclipse)], and complex VMAT (Eclipse). The complex plans were created by artificially pushing the optimizer to give complex multileaf collimator sequences. Each IMRT field was irradiated five times and each VMAT field was irradiated ten times, with each irradiation starting at a random point in the respiratory cycle. The effect of fractionation was calculated by randomly summing the measured doses. The maximum deviation for each measurement point per fraction and the probability that 95% of the model tumor had dose deviations less than 2% and 5% were calculated as a function of the number of fractions. Tumor control probabilities for each treatment plan were calculated and compared.

Results:

After five fractions, measured dose deviations were less than 2% for more than 95% of measurement points within the tumor model for all plans, except the complex dynamic IMRT, step‐and‐shoot IMRT (XiO), complex VMAT, and single‐arc VMAT plans. Reducing the dose rate of the complex IMRT plans from 600 to 200 MU/min reduced the dose deviations to less than 2%. Dose deviations were less than 5% after five fractions for all plans, except the complex single‐arc VMAT plan.

Conclusions:

Rapid prototyping techniques can be used to create realistic tumor models. For most treatment techniques, the dose deviations averaged out after several fractions. Treatments with unusually complicated multileaf collimator sequences had larger dose deviations. For IMRT treat‐ments, dose deviations can be reduced by reducing the dose rate. For VMAT treatments, using two arcs instead of one is effective for reducing dose deviations.
A grating‐based single‐shot x‐ray phase contrast and diffraction method for in vivo imaging
Authors: Bennett Eric E. , Kopace Rael , Stein Ashley F. , Wen Han
Published: November 2010

Purpose:

The purpose of this study is to develop a single‐shot version of the grating‐based phase contrast x‐ray imaging method and demonstrate its capability ofin vivo animal imaging. Here, the authors describe the principle and experimental results. They show the source of artifacts in the phase contrast signal and optimal designs that minimize them. They also discuss its current limitations and ways to overcome them.

Methods:

A single lead grid was inserted midway between an x‐ray tube and an x‐ray camera in the planar radiography setting. The grid acted as a transmission grating and cast periodic dark fringes on the camera. The camera had sufficient spatial resolution to resolve the fringes. Refraction and diffraction in the imaged object manifested as position shifts and amplitude attenuation of the fringes, respectively. In order to quantify these changes precisely without imposing a fixed geometric relationship between the camera pixel array and the fringes, a spatial harmonic method in the Fourier domain was developed. The level of the differential phase (refraction) contrast as a function of hardware specifications and device geometry was derived and used to guide the optimal placement of the grid and object. Bothex vivo and in vivo images of rodent extremities were collected to demonstrate the capability of the method. The exposure time using a 50 W tube was 28 s.

Results:

Differential phase contrast images of glass beads acquired at various grid and object positions confirmed theoretical predictions of how phase contrast and extraneous artifacts vary with the device geometry. In anesthetized rats, a single exposure yielded artifact‐free images of absorption, differential phase contrast, and diffraction. Differential phase contrast was strongest at bone‐soft tissue interfaces, while diffraction was strongest in bone.

Conclusions:

The spatial harmonic method allowed us to obtain absorption, differential phase contrast, and diffraction images, all from a single raw image and is feasible in live animals. Because the sensitivity of the method scales with the density of the gratings, custom microfabricated gratings should be superior to off‐the‐shelf lead grids.
Spectral perturbations from silicon diode detector encapsulation and shielding in photon fields
Authors: Eklund Karin , Ahnesjö Anders
Published: November 2010

Purpose:

Silicon diodes are widely used as detectors for relative dose measurements in radiotherapy. The common manufacturing practice is to encapsulate the diodes in plastic for protection and to facilitate mounting in scanning devices. Diodes intended for use in photon fields commonly also have a shield of a high atomic number material (usually tungsten) integrated into the encapsulation to selectively absorb low‐energy photons to which silicon diodes would otherwise over‐response. However, new response models based on cavity theories and spectra calculations have been proposed for direct correction of the readout from unshielded (e.g., “electron”) diodes used in photon fields. This raises the question whether it is correct to assume that the spectrum in a water phantom at the location of the detector cavity is not perturbed by the detector encapsulation materials. The aim of this work is to investigate the spectral effects of typical encapsulations, including shielding, used for clinical diodes.

Methods:

The effects of detector encapsulation of an unshielded and a shielded commercial diode on the spectra at the detector cavity location are studied through Monte Carlo simulations withPENELOPE‐2005. Variance reduction based on correlated sampling is applied to reduce the CPU time needed for the simulations.

Results:

The use of correlated sampling is found to be efficient and to not introduce any significant bias to the results. Compared to reference spectra calculated in water, the encapsulation for an unshielded diode is demonstrated to not perturb the spectrum, while a tungsten shielded diode caused not only the desired decrease in low‐energy scattered photons but also a large increase of the primary electron fluence. Measurements with a shielded diode in a 6 MV photon beam proved that the shielding does not completely remove the field‐size dependence of the detector response caused by the over‐response from low‐energy photons. Response factors of a properly corrected unshielded diode were shown to give comparable, or better, results than the traditionally used shielded diode.

Conclusions:

Spectra calculated for photon fields in water can be directly used for modeling the response of unshielded silicon diodes with plastic encapsulations. Unshielded diodes used together with appropriate corrections can replace shielded diodes in photon dose measurements.
A neural network based 3D/3D image registration quality evaluator for the head‐and‐neck patient setup in the absence of a ground truth
Authors: Wu Jian , Murphy Martin J.
Published: November 2010

Purpose:

To develop a neural network based registration quality evaluator (RQE) that can identify unsuccessful 3D/3D image registrations for the head‐and‐neck patient setup in radiotherapy.

Methods:

A two‐layer feed‐forward neural network was used as a RQE to classify 3D/3D rigid registration solutions as successful or unsuccessful based on the features of the similarity surface near the point‐of‐solution. The supervised training and test data sets were generated by rigidly registering daily cone‐beam CTs to the treatment planning fan‐beam CTs of six patients with head‐and‐neck tumors. Two different similarity metrics (mutual information and mean‐squared intensity difference) and two different types of image content (entire image versus bony landmarks) were used. The best solution for each registration pair was selected from 50 optimizing attempts that differed only by the initial transformation parameters. The distance from each individual solution to the best solution in the normalized parametrical space was compared to a user‐defined error threshold to determine whether that solution was successful or not. The supervised training was then used to train the RQE. The performance of the RQE was evaluated using the test data set that consisted of registration results that were not used in training.

Results:

The RQE constructed using the mutual information had very good performance when tested using the test data sets, yielding the sensitivity, the specificity, the positive predictive value, and the negative predictive value in the ranges of 0.960–1.000, 0.993–1.000, 0.983–1.000, and 0.909–1.000, respectively. Adding a RQE into a conventional 3D/3D image registration system incurs only about 10%–20% increase of the overall processing time.

Conclusions:

The authors' patient study has demonstrated very good performance of the proposed RQE when used with the mutual information in identifying unsuccessful 3D/3D registrations for daily patient setup. The classifier had very good generality and required only to be trained once for each implementation. When the RQE is incorporated with an automated 3D/3D image registration system, it can improve the robustness of the system.
Verification of patient‐specific dose distributions in proton therapy using a commercial two‐dimensional ion chamber array
Authors: Arjomandy Bijan , Sahoo Narayan , Ciangaru George , Zhu Ronald , Song Xiaofei , Gillin Michael
Published: November 2010

Purpose:

The purpose of this study was to determine whether a two‐dimensional (2D) ion chamber array detector quickly and accurately measures patient‐specific dose distributions in treatment with passively scattered and spot scanning proton beams.

Methods:

The 2D ion chamber array detector MatriXX was used to measure the dose distributions in plastic water phantom from passively scattered and spot scanning proton beam fields planned for patient treatment. Planar dose distributions were measured using MatriXX, and the distributions were compared to those calculated using a treatment‐planning system. The dose distributions generated by the treatment‐planning system and a film dosimetry system were similarly compared.

Results:

For passively scattered proton beams, the gamma index for the dose‐distribution comparison for treatment fields for three patients with prostate cancer and for one patient with lung cancer was less than 1.0 for 99% and 100% of pixels for a 3% dose tolerance and 3 mm distance‐to‐dose agreement, respectively. For spot scanning beams, the mean (± standard deviation) percentages of pixels with gamma indices meeting the passing criteria were and for MatriXX and film dosimetry, respectively, for 20 fields used to treat patients with prostate cancer.

Conclusions:

Unlike film dosimetry, MatriXX provides not only 2D dose‐distribution information but also absolute dosimetry in fractions of minutes with acceptable accuracy. The results of this study indicate that MatriXX can be used to verify patient‐field specific dose distributions in proton therapy.
Selective‐diffusion regularization for enhancement of microcalcifications in digital breast tomosynthesis reconstruction
Authors: Lu Yao , Chan Heang‐Ping , Wei Jun , Hadjiiski Lubomir M.
Published: November 2010

Purpose:

Digital breast tomosynthesis (DBT) has been shown to improve mass detection. Detection of microcalcifications is more challenging because of the large breast volume to be searched for subtle signals. The simultaneous algebraic reconstruction technique (SART) was found to provide good image quality for DBT, but the image noise is amplified with an increasing number of iterations. In this study, the authors developed a selective‐diffusion (SD) method for noise regularization with SART to improve the contrast‐to‐noise ratio (CNR) of microcalcifications in the DBT slices for human or machine detection.

Methods:

The SD method regularizes SART reconstruction during updating with each projection view. Potential microcalcifications are differentiated from the noisy background by estimating the local gradient information. Different degrees of regularization are applied to the signal or noise classes, such that the microcalcifications will be enhanced while the noise is suppressed. The new SD method was compared to several current methods, including the quadratic Laplacian (QL) method, the total variation (TV) method, and the nonconvex total‐variation (TpV) method for noise regularization with SART. A GE GEN2 prototype DBT system with a stationary digital detector was used for the acquisition of DBT scans at 21 angles in 3° increments over a ±30° range. The reconstruction image quality without regularization and that with the different regularization methods were compared using the DBT scans of an American College of Radiology phantom and a human subject. The CNR and the full width at half maximum (FWHM) of the line profiles of microcalcifications within the in‐focus DBT slices were used as image quality measures.

Results:

For the comparison of large microcalcifications in the DBT data of the subject, the SD method resulted in comparable CNR to the nonconvex TpV method. Both of them performed better than the other two methods. For subtle microcalcifications, the SD method was superior to other methods in terms of CNR. In both the subject and phantom DBT data, for large microcalcifications, the FWHM of the SD method was comparable to that without regularization, which was wider than that of the TV type methods. For subtle microcalcifications, the SD method had comparable FWHM values to the TV type methods. All three regularization methods were superior to the QL method in terms of FWHM.

Conclusions:

The SART regularized by the selective‐diffusion method enhanced the CNR and preserved the sharpness of microcalcifications. In comparison with three existing regularization methods, the selective‐diffusion regularization was superior to the other methods for subtle microcalcifications.
A Fas2 Track down the Axon
Authors: Adler Elizabeth M.
Published: November 2010

Glial migration in the fly peripheral nervous system depends on an axonal gradient of Fasciclin2.
The Inside Scoop on Toll
Authors: Ray L. Bryan
Published: November 2010

The early endosome, rather than the cell membrane, appears to be the critical location of signaling by the developmental morphogen receptor Toll in
Drosophila
.
Controlling Chloride Channels
Authors: Vinson Valda
Published: November 2010

The structure of a chloride transporter and its regulatory domain provides insight into the ion-exchange mechanism.
Innate Innit?
Authors: Mueller Kristen L.
Published: November 2010

Immune cells develop to preempt intestinal colonization by microbial symbionts.
Fibroblast Growth Factor Receptor Signaling Crosstalk in Skeletogenesis
Authors: Miraoui Hichem , Marie Pierre J.
Published: November 2010

Crosstalk of fibroblast growth factor signaling with other pathways may offer therapeutic strategies for skeletal dysplasias.
Activities of NXL104 Combinations with Ceftazidime and Aztreonam against Carbapenemase-Producing
Enterobacteriaceae
Authors: Livermore David M. , Mushtaq Shazad , Warner Marina , Zhang Jiancheng , Maharjan Sunil , Doumith Michel , Woodford Neil
Published: November 2010

Combinations of NXL104 with ceftazidime and aztreonam were tested against carbapenem-resistant members of the
Enterobacteriaceae
. Ceftazidime-NXL104 was active against strains with the OXA-48 enzyme or with combinations of impermeability and an extended-spectrum β-lactamase (ESBL) or AmpC enzyme and also against most
Klebsiella
spp. with the KPC enzyme, but metallo-β-lactamase producers were resistant. Aztreonam-NXL104 was active against all carbapenemase producers at 4 and 4 μg/ml, including those with metallo-β-lactamases.