bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aperture modulated, translating bed total body irradiation
Authors: Hussain Amjad , Villarreal‐Barajas Jose Eduardo , Dunscombe Peter , Brown Derek W. 
Published: February 2011

Purpose:Total body irradiation (TBI) techniques aim to deliver a uniform radiation dose to a patient with an irregular body contour and a heterogeneous density distribution to within ±10% of the prescribed dose. In the current article, the authors present a novel, aperture modulated, translating bed TBI (AMTBI) technique that produces a high degree of dose uniformity throughout the entire patient.Methods:The radiation beam is dynamically shaped in two dimensions using a multileaf collimator (MLC). The irregular surface compensation algorithm in the Eclipse™ treatment planning system is used for fluence optimization, which is performed based on penetration depth and internal inhomogeneities. Two optimal fluence maps (AP and PA) are generated and beam apertures are created to deliver these optimal fluences. During treatment, the patient/phantom is translated on a motorized bed close to the floor (source to bed distance: 204.5 cm) under a stationary radiation beam with 0° gantry angle. The bed motion and dynamic beam apertures are synchronized.Results:The AMTBI technique produces a more homogeneous dose distribution than fixed open beam translating bed TBI. In phantom studies, the dose deviation along the midline is reduced from 10% to less than 5% of the prescribed dose in the longitudinal direction. Dose to the lung is reduced by more than 15% compared to the unshielded fixed open beam technique. At the lateral body edges, the dose received from the open beam technique was 20% higher than that prescribed at umbilicus midplane. With AMTBI the dose deviation in this same region is reduced to less than 3% of the prescribed dose. Validation of the technique was performed using thermoluminescent dosimeters in a Rando® phantom. Agreement between calculation and measurement was better than 3% in all cases.Conclusions:A novel, translating bed, aperture modulated TBI technique that employs dynamically shaped MLC defined beams is shown to improve dose uniformity in three dimensions. In comparison with the fixed open beam TBI technique, homogeneity of dose distribution is greatly improved.
Is Weisskoff model valid for the correction of contrast agent extravasation with combined and effects in dynamic susceptibility contrast MRI?
Authors: Liu Ho‐Ling , Wu Yi‐Ying , Yang Wei‐Shan , Chen Chih‐Feng , Lim Kun‐Eng , Hsu Yuan‐Yu 
Published: February 2011

Purpose:The Weisskoff model has been widely applied for correcting the effect of the contrast agent leakage in the measured dynamic susceptibility contrast (DSC)‐MRI signals. This study aimed to modify the Weisskoff model for the inclusion of both and effects of the contrast agent extravasation.Methods:A two‐compartment model was proposed and implemented into the original Weisskoff model to describe the combined and effects from the contrast agent leakage in the measured DSC‐MRI signals. A computer simulation was performed to evaluate the dependence of versus dominance on imaging parameter, field strength, baseline , and severity of the leakage. The modified Weisskoff model was employed to correct the relative cerebral blood volume (rCBV) maps in three patients with brain tumors to demonstrate its use.Results:The resultant equation had the same mathematical form as the original model, but with a different expression for the fitting constant. This new parameter can be of either a positive or a negative value. Results of the computer simulation showed more probable dominance with longer TE, higher field strength, shorter baseline , and greater extraction of the contrast agent. Clinical data were well fitted by the model, with a positive indicating dominance and underestimated rCBV and a negative indicating dominance and overestimated rCBV. The values of normal‐appearing brain tissues were distributed in a much smaller range than the values of enhancing tumors. The ratios of corrected over uncorrected normalized CBV (nCBV) for gray matter (GM) were in the range between 1.04 and 1.05, meaning that the nCBV remained rather stable before and after correction. The ratios for the tumors were 0.65, 0.42, and 2.81, either much smaller or greater than the ratios for GM.Conclusions:This study proposed a modified Weisskoff model that was able to explain both and dominant effects of the contrast agent extravasation in DSC‐MRI. Further development is needed to make the parameter a quantitative indicator of the vessel permeability.
Experimentally determined spectral optimization for dedicated breast computed tomography
Authors: Prionas Nicolas D. , Huang Shih‐Ying , Boone John M. 
Published: February 2011

Purpose:The current study aimed to experimentally identify the optimal technique factors (x‐ray tube potential and added filtration material/thickness) to maximize soft‐tissue contrast, microcalcification contrast, and iodine contrast enhancement using cadaveric breast specimens imaged with dedicated breast computed tomography (bCT). Secondarily, the study aimed to evaluate the accuracy of phantom materials as tissue surrogates and to characterize the change in accuracy with varying bCT technique factors.Methods:A cadaveric breast specimen was acquired under appropriate approval and scanned using a prototype bCT scanner. Inserted into the specimen were cylindrical inserts of polyethylene, water, iodine contrast medium (iodixanol, 2.5 mg/ml), and calcium hydroxyapatite (100 mg/ml). Six x‐ray tube potentials (50, 60, 70, 80, 90, and 100 kVp) and three different filters (0.2 mm Cu, 1.5 mm Al, and 0.2 mm Sn) were tested. For each set of technique factors, the intensity (linear attenuation coefficient) and noise were measured within six regions of interest (ROIs): Glandular tissue, adipose tissue, polyethylene, water, iodine contrast medium, and calcium hydroxyapatite. Dose‐normalized contrast to noise ratio (CNRD) was measured for pairwise comparisons among the six ROIs. Regression models were used to estimate the effect of tube potential and added filtration on intensity, noise, and CNRD.Results:Iodine contrast enhancement was maximized using 60 kVp and 0.2 mm Cu. Microcalcification contrast and soft‐tissue contrast were maximized at 60 kVp. The 0.2 mm Cu filter achieved significantly higher CNRD for iodine contrast enhancement than the other two filters, but microcalcification contrast and soft‐tissue contrast were similar using the copper and aluminum filters. The average percent difference in linear attenuation coefficient, across all tube potentials, for polyethylene versus adipose tissue was 1.8%, 1.7%, and 1.3% for 0.2 mm Cu, 1.5 mm Al, and 0.2 mm Sn, respectively. For water versus glandular tissue, the average percent difference was 2.7%, 3.9%, and 4.2% for the three filter types.Conclusions:Contrast‐enhanced bCT, using injected iodine contrast medium, may be optimized for maximum contrast of enhancing lesions at 60 kVp with 0.2 mm Cu filtration. Soft‐tissue contrast and microcalcification contrast may also benefit from lower tube potentials (60 kVp). The linear attenuation coefficients of water and polyethylene slightly overestimate the values of their corresponding tissues, but the reported differences may serve as guidance for dosimetry and quality assurance using tissue equivalent phantoms.
Frame‐to‐frame image realignment assessment tool for dynamic brain positron emission tomography
Authors: Dinelle Katherine , Ngo Henry , Blinder Stephan , Vafai Nasim , Topping Geoff , Sossi Vesna 
Published: February 2011

Purpose:Subject motion during positron emission tomography (PET) brain scans can reduce image quality and may lead to incorrect biological outcome measures, especially for data acquired with high resolution tomographs. A semiautomatic method for assessing the quality of frame‐to‐frame image realignments to compensate for subject motion in dynamic brain PET is proposed and evaluated.Methods:A test set of 256‐raclopride (a dopamine D2‐type receptor antagonist) brain PET image frames was used to develop and evaluate the proposed method. The transformation matrix to be applied to each image to achieve a frame‐to‐frame realignment was calculated with two independent methods: Using motion data measured with the Polaris Vicra optical tracking device and using the image‐based realignment algorithm AIR (automated image registration). The quality assessment method is based on the observation that there is a very low probability that two independent approaches to motion detection will produce equal, but incorrect results. Agreement between transformation matrices was taken to be a signature of an accurate motion determination and thus realignment. Each pair of realignment matrices was compared and used to calculate a metric describing the frame‐to‐frame image realignment accuracy. In order to determine the range of values of the metric that correspond to a successful realignment, a comparison was made to a detailed visual inspection of the frame‐to‐frame realigned images for each image in the test set. The threshold on the metric for realignment acceptance was then selected to optimize the numbers of true‐positives (realignments accepted by both the protocol and the operator) and minimize the number of false‐positives (accepted by the protocol but not the operator).Results:The proposed method categorized 53% of the image realignments in the test dataset as successful, of which 11% were incorrectly categorized (6% of the total dataset). Implementation of the proposed assessment tool resulted in a 45% time savings compared to the same visual inspection applied to all image realignments.Conclusions:The frame‐to‐frame image realignment assessment tool presented here required less operator time to evaluate realignment success compared to a method requiring visual inspection of all realigned images, while maintaining the same level of accuracy in the realigned dataset. This practical method can be easily implemented at any center with motion monitoring capabilities or, for centers lacking this technology, methods of estimating image realignment parameters that use independent information. In addition, the procedure is flexible, allowing modifications to be made for different tracer types and/or downstream analysis goals.
Characterization of mesothelioma and tissues present in contrast‐enhanced thoracic CT scans
Authors: Corson Neal , Sensakovic William F. , Straus Christopher , Starkey Adam , Armato Samuel G. 
Published: February 2011

Purpose:The purpose of this study was to characterize the Hounsfield unit (HU) distributions of mesothelioma and other tissues present in contrast‐enhanced thoracic CT scans, to compare the HU distributions of mesothelioma, muscle, and liver by scanner and reconstruction filter/kernel combination, and to assess interpatient HU distribution variability.Methods:The database consisted of 28 contrast‐enhanced thoracic CT scans from different patients. For each scan, regions of interest were manually outlined within each of 13 tissues, including mesothelioma. For each tissue, the empirical percentiles in HU values were calculated along with the interpatient variability. The HU distributions of select tissues were compared across three different scanner and reconstruction filter/kernel combinations.Results:The HU distributions of blood‐containing tissues demonstrated substantial overlap, as did the HU distributions of pleural effusion, mesothelioma, muscle, and liver. The HU distribution of fat had the least overlap with the other tissues. Fat and muscle had the lowest interpatient HU variability and the narrowest HU distributions, while blood‐containing tissues had the highest interpatient HU variability. A soft‐tissue reconstruction filter/kernel yielded the narrowest HU distribution, and fat with artifact had the widest HU distribution.Conclusions:Characterization of tissues in CT scans enhances the understanding of those tissues' HU distributions. Due to their overlapping HU distributions and close spatial proximity to one another, separating pleural effusion, mesothelioma, muscle, and liver from one another is a difficult task based on HU value thresholding alone. The results illustrate the wide distributions and large variability that exist for tissues present in clinical thoracic CT scans.
Comparison of three image comparison methods for the visual assessment of the image fidelity of compressed computed tomography images
Authors: Kim Bohyoung , Lee Hyunna , Kim Kil Joong , Seo Jinwook , Park Seongjin , Shin Yeong‐Gil , Kim Soo Hong , Lee Kyoung Ho 
Published: February 2011

Purpose:This study aimed to comparatively evaluate three different image comparison methods: alternate displaywithout an intervening blank image (AWOB), alternate display with an intervening blank image (AWB), and side‐by‐side display (SSD), in terms of the perceptual sensitivity to image differences between Joint Photographic Experts Group 2000 (JPEG2000) compressed body CT images and their originals.Methods:A total of 50 body CT images obtained with five different scan protocols (5‐mm‐thick abdomen, 0.67‐mm‐thick abdomen, 5‐mm‐thick lung, 0.67‐mm‐thick lung, and 5‐mm‐thick low‐dose lung) were compressed to one of five compression ratios (reversible, 6:1, 8:1, 10:1, and 15:1) using JPEG2000 algorithm. The fidelity of the compressed images was visually assessed on a four‐grade scale independently by five radiologists using each of the three image comparison methods of AWOB, AWB, and SSD. The fidelity grading results for the 40 irreversibly compressed images were compared between the three image comparison methods using the Friedman tests withpost hoc Tukey tests. The number of image pairs with no perceptible difference was compared using the exact tests for paired proportions. The time required for the fidelity assessment for all of the 50 compressed images was also compared using the Friedman tests with post hoc Tukey tests.Results:For the 40 irreversibly compressed images, the fidelity grade was significantly lower for AWOB than for AWB or SSD ( for all readers); however, there was no significant difference between AWB and SSD (‐value range, 0.06–0.92). The percentage of image pairs with no perceptible difference tended to be smaller for AWOB than for AWB ( for all readers) or SSD ( for readers 1–3, for reader 4, and for reader 5). However, there was no significant difference between AWB and SSD (‐value range, ). For all of the 50 compressed images, the fidelity grading time significantly increased in the order of AWOB, SSD, and AWB.Conclusions:In assessing the image fidelity of JPEG2000 compressed body CT images, AWOB yields lower fidelity grade and requires less fidelity grading time than AWB or SSD, indicating that AWOB is most sensitive to image differences among of them.
A compensative model for the angle‐dependence of motion estimates in noninvasive vascular elastography
Authors: Mercure Elizabeth , Deprez Jean‐François , Fromageau Jérémie , Basset Olivier , Soulez Gilles , Cloutier Guy , Maurice Roch L. 
Published: February 2011

Purpose:Atherosclerosis of peripheral cerebral arteries can lead to stroke either by stenosis formation or plaque rupture. This pathology is initiated by the alteration of arterial wall mechanical properties shown to be assessable by ultrasound elastography. Recently, noninvasive vascular elastography (NIVE) was introduced for noninvasive imaging of the mechanical properties of superficial arteries as markers of vulnerable plaques. However, NIVE motion estimates are angle‐dependent, with optimal scanning angle being represented by the alignment of tissue motion with ultrasound beam orientation. The objective of this study was to introduce a model that compensates for such angle‐dependence in order to reduce the bias on strain estimates, namely, when investigating longitudinal vessel segments.Methods:The model is based on the Lagrangian speckle model estimator (LSME) because the LSME assesses the 2D‐deformation matrix required to compute the scanning angle.Results:Experiments on vessel‐mimicking phantoms indicated that such a model enables the estimation of scanning angle with less than 3‐degrees error. The method was also validatedin vivo in human carotid arteries where less than 4‐degrees error was observed. In both cases, the compensative model estimated the inclination angles with low variability.Conclusion:Angle‐dependence may be an important factor to consider in avoiding potentially distort clinical diagnoses. Results, reported in this article, suggest that the LSME‐based compensative model might be considered as a very interesting and promising clinical tool for NIVE applications.
Sensitivity of postplanning target and OAR coverage estimates to dosimetric margin distribution sampling parameters
Authors: Xu Huijun , Gordon J. James , Siebers Jeffrey V. 
Published: February 2011

Purpose:A dosimetric margin (DM) is the margin in a specified direction between a structure and a specified isodose surface, corresponding to a prescription or tolerance dose. The dosimetric margin distribution (DMD) is the distribution of DMs over all directions. Given a geometric uncertainty model, representing inter‐ or intrafraction setup uncertainties or internal organ motion, the DMD can be used to calculate coverage, which is the probability that a realized target or organ‐at‐risk (OAR) dose metric exceeds the corresponding prescription or tolerance dose. Postplanning coverage evaluation quantifies the percentage of uncertainties for which target and OAR structures meet their intended dose constraints. The goal of the present work is to evaluate coverage probabilities for 28 prostate treatment plans to determine DMD sampling parameters that ensure adequate accuracy for postplanning coverage estimates.Methods:Normally distributed interfraction setup uncertainties were applied to 28 plans for localized prostate cancer, with prescribed dose of 79.2 Gy and 10 mm clinical target volume to planning target volume (CTV‐to‐PTV) margins. Using angular or isotropic sampling techniques, dosimetric margins were determined for the CTV, bladder and rectum, assuming shift invariance of the dose distribution. For angular sampling, DMDs were sampled at fixed angular intervals (e.g., ). Isotropic samples were uniformly distributed on the unit sphere resulting in variable angular increments, but were calculated for the same number of sampling directions as angular DMDs, and accordingly characterized by the effective angular increment . In each direction, the DM was calculated by moving the structure in radial steps of size until the specified isodose was crossed. Coverage estimation accuracy was quantified as a function of the sampling parameters or and .Results:The accuracy of coverage estimates depends on angular and radial DMD sampling parameters or and , as well as the employed sampling technique. Target and OAR can be achieved with sampling parameters or , . Better accuracy (target and OAR ) can be achieved with or , . As the number of sampling points decreases, the isotropic sampling method maintains better accuracy than fixed angular sampling.Conclusions:Coverage estimates for post‐planning evaluation are essential since coverage values of targets and OARs often differ from the values implied by the static margin‐based plans. Finer sampling of the DMD enables more accurate assessment of the effect of geometric uncertainties on coverage estimates prior to treatment. DMD sampling with or and should be adequate for planning purposes.
Per‐beam, planar IMRT QA passing rates do not predict clinically relevant patient dose errors
Authors: Nelms Benjamin E. , Zhen Heming , Tomé Wolfgang A. 
Published: February 2011

Purpose:The purpose of this work is to determine the statistical correlation between per‐beam, planar IMRT QA passing rates and several clinically relevant, anatomy‐based dose errors for per‐patient IMRT QA. The intent is to assess the predictive power of a common conventional IMRT QA performance metric, the Gamma passing rate per beam.Methods:Ninety‐six unique data sets were created by inducing four types of dose errors in 24 clinical head and neck IMRT plans, each planned with 6 MV Varian 120‐leaf MLC linear accelerators using a commercial treatment planning system and step‐and‐shoot delivery. The error‐free beams/plans were used as “simulated measurements” (for generating the IMRT QA dose planes and the anatomy dose metrics) to compare to the corresponding data calculated by the error‐induced plans. The degree of the induced errors was tuned to mimic IMRT QA passing rates that are commonly achieved using conventional methods.Results:Analysis of clinical metrics (parotid mean doses, spinal cord max and, CTV , and larynx mean) vs IMRT QA Gamma analysis (3%/3 mm, 2/2, 1/1) showed that in all cases, there were only weak to moderate correlations (range of Pearson's ‐values: −0.295 to 0.653). Moreover, the moderate correlations actually had positive Pearson's ‐values (i.e., clinically relevant metric differences increased with increasing IMRT QA passing rate), indicating that some of the largest anatomy‐based dose differences occurred in the cases of high IMRT QA passing rates, which may be called “false negatives.” The results also show numerous instances of false positives or cases where low IMRT QA passing rates do not imply large errors in anatomy dose metrics. In none of the cases was there correlation consistent with high predictive power of planar IMRT passing rates, i.e., in none of the cases did high IMRT QA Gamma passing rates predict low errors in anatomy dose metrics or vice versa.Conclusions:There is a lack of correlation between conventional IMRT QA performance metrics (Gamma passing rates) and dose errors in anatomic regions‐of‐interest. The most common acceptance criteria and published actions levels therefore have insufficient, or at least unproven, predictive power for per‐patient IMRT QA.
A variable echo‐number method for estimating in MRI‐based polymer gel dosimetry
Authors: Watanabe Yoichi , Kubo Hitoshi 
Published: February 2011

Purpose:Spin‐spin relaxation rate is commonly used to quantify absorbed dose for magnetic resonance imaging (MRI)‐based polymer gel dosimetry. is estimated by applying a parameter fitting algorithm to a train of spin‐echo signals. However, a careless application of a large number of echoes can result in anomalous values because the echo signal intensity decreases to the background signal offset level for a long echo time. In this article, the authors proposed and evaluated a variable echo‐number (VAREC) method to remedy the problem.Methods:The VAREC algorithm uses only echo signals, whose intensities are greater than a preset threshold. Here, the threshold is defined as the standard deviation of Gaussian noise times a multiplier. The authors implemented three estimation methods in an in‐house program: The nonlinear least‐squares algorithm (NLLS), the VAREC method, and the maximum likelihood estimator with the Rician signal intensity distribution (MLE_R). Those methods were used to estimate the values of test phantoms with known values and BANG3‐type polymer gels, which were irradiated to 12 different doses ranging from 0 to 50 Gy. The values were measured by using a 32‐echo CPMG pulse sequence on 3 T MRI scanners. The values of the VAREC method were compared with those of NLLS and MLE_R.Results:The values of the NLLS method incorrectly decreased to the zero‐dose level for doses greater than 10 Gy. The values of the VAREC method with agreed with those of MLE_R within the measurement uncertainty. The uncertainties of the values were the smallest for or 3 among various values.Conclusions:The VAREC algorithm is simple, fast, and robust for the estimation. The authors recommend this method with or 3 for estimation using multispin echo MRI protocols.