bluuebunny/crossref_metadata_2025_split huggingface dataset:
A novel respiratory tracking system for smart‐gated PET acquisition
Authors: Nehmeh S. A. , Haj‐Ali A. A. , Qing C. , Stearns C. , Kalaigian H. , Kohlmyer S. , Schoder H. , Ho A. Y. , Larson S. M. , Humm J. L. 
Published: December 2010

Purpose:In this study, the authors validated a novel respiratory tracking device, the multidimensional respiratory tracking (MDRT) system, that was designed to assist in correcting for respiratory motion in PET/CT images. The authors also investigated a novel PET acquisition technique, smart gating (SG), that enables to acquire motion‐free PET data prospectively, with minimum user interference and with no additional postprocessing of the PET data.Methods:MDRT uses visual tracking techniques to track simultaneously the two‐dimensional (in the vertical plane) motion of multiple fiducial markers using a standard video camera. A threshold window is set at the breathing amplitude of interest using the MDRT GUI. A trigger is generated at a rate of 250 Hz as long as the breathing signal is within the threshold window. The triggers are fed into the PET scanner to initialize one single bin of a gated acquisition every 4 ms. No triggers are delivered as the breathing signal drifts outside the threshold window. Consequently, PET data are acquired only whenever the breathing signal is confined within the amplitude threshold window, thus resulting into a motion‐free image set. The accuracy of MDRT in tracking the breathing signal was assessed (1) by comparing the period of an oscillating phantom, as measured by MDRT, to that measured with a photogate timer and (2) by comparing the MDRT output to that of the real‐time position management (RPM) in ten patients. The SG PET/CT acquisition was validated in phantoms and in two stereotactic body radiosurgery (SBRS) lung DIBH‐PET/CT patients.Results:MDRT was in agreement with the photogate timer in determining the period of motion to less than 2%. The percent errors between MDRT and RPM in the positions of the peaks and troughs of the ten patients' breathing signals were within 10%. In phantoms, SG technique enables to correct for motion‐induced artifacts in the PET images and improve the accuracy of PET quantitation. For the SBRS application, in one patient, the patient's CT lesion was not detected in the corresponding clinical PET images, while it exhibited an SUV of 1.8 in the DIBH image set. In the second patient, DIBH‐PET images showed an improved PET‐to‐CT spatial matching and a 52% increase in the lesion SUV.Conclusions:MDRT has been shown to be accurate in tracking breathing motion and assisted in implementing a smart‐gating PET acquisition technique that allowed to acquire prospectively motion‐free PET images.
Spectral optimization for dedicated breast CT
Authors: Weigel Michaela , Vollmar Sabrina V. , Kalender Willi A. 
Published: December 2010

Purpose:The authors investigated the choice of spectra for the optimization of the dose‐weighted contrast‐to‐noise ratio (CNRD) for a dedicated breast CT scanner. The objective is to provide the desired image quality level at minimal dose values. The CNRD was investigated as a function of energy or tube voltage and filtrations for various breast sizes and contrasts.Methods:The authors performed simulations of the pendant female breast as cylinders consisting of a homogeneous mixture of adipose and glandular tissue with diameters from 6 to 18 cm. The contrasts of adipose tissue, calcium hydroxyapatite, and iodine contrast agent relative to glandular tissue were analyzed using inserts of 9 mm in diameter. Simulations were conducted for monochromatic and polychromatic radiation with a 3 mm Al or a 0.3 mm Cu filter. Simulations and measurements on an experimental micro‐CT scanner were performed for validation purposes with a 6 cm water‐equivalent cylinder, with inserts representing a pure density difference of 10%, calcium hydroxyapatite, and iodine contrast agent. A breast tissue sample embedded in paraffin was investigated to confirm the simulation results.Results:Optimal tube voltages were found to be in the range of 30–55 kV for breast CT imaging. For example, with 3 mm Al or 0.3 mm Cu filtration, optimal tube voltages were about 53 and 48 kV, respectively, for the contrast iodine/glandular tissue for all diameters. With 3 mm Al filtration, optimal tube voltages increased from 30 to 37 kV and from 30 to 47 kV for the contrast calcium hydroxyapatite/glandular tissue and adipose/glandular tissue, respectively. Tube power requirements were estimated and the change in tube current relative to 80 kV was found to be between 4 and 14 and between 11 and 214 with 3 mm Al filtration or 0.3 mm Cu filtration, respectively. These numbers show that realizing the low optimal tube voltages may not be feasible in most cases due to power requirements.Conclusions:Depending on the filtration, the authors assume that a compromise solution has to be found between the highest potential dose reduction and a solution working with available x‐ray sources. In view of the tube power constraints, the authors recommend aiming for tube voltages in the range of 50 kV and higher.
Fast intensity‐modulated arc therapy based on 2‐step beam segmentation
Authors: Bratengeier Klaus , Gainey Mark , Sauer Otto A. , Richter Anne , Flentje Michael 
Published: December 2010

Purpose:Single or few arc intensity‐modulated arc therapy (IMAT) is intended to be a time saving irradiation method, potentially replacing classical intensity‐modulated radiotherapy (IMRT). The aim of this work was to evaluate the quality of different IMAT methods with the potential of fast delivery, which also has the possibility of adapting to the daily shape of the target volume.Methods:A planning study was performed. Novel double and triple IMAT techniques based on the geometrical analysis of the target organ at risk geometry (2‐step IMAT) were evaluated. They were compared to step and shoot IMRT reference plans generated using direct machine parameter optimization (DMPO®). Volumetric arc (VMAT) plans from commercial preclinical software (SMARTARC®) were used as an additional benchmark to classify the quality of the novel techniques. Four cases with concave planning target volumes (PTV) with one dominating organ at risk (OAR), viz., the PTV/OAR combination of the ESTRO Quasimodo phantom, breast/lung, spine metastasis/spinal cord, and prostate/rectum, were used for the study. The composite objective value (COV) and other parameters representing the plan quality were studied.Results:The novel 2‐step IMAT techniques with geometry based segment definition were as good as or better than DMPO® and were superior to the SMARTARC® VMAT techniques. For the spine metastasis, the quality measured by the COV differed only by 3%, whereas the COV of the 2‐step IMAT for the other three cases decreased by a factor of 1.4–2.4 with respect to the reference plans.Conclusions:Rotational techniques based on geometrical analysis of the optimization problem (2‐step IMAT) provide similar or better plan quality than DMPO® or the research version of SMARTARC® VMAT variants. The results justify pursuing the goal of fast IMAT adaptation based on 2‐step IMAT techniques.
Monitoring radiation use in cardiac fluoroscopy imaging procedures
Authors: Stevens Nathaniel T. , Steiner Stefan H. , Smith Ian R. , MacKay R. Jock 
Published: December 2010

Purpose:Timely identification of systematic changes in radiation delivery of an imaging system can lead to a reduction in risk for the patients involved. However, existing quality assurance programs involving the routine testing of equipment performance using phantoms are limited in their ability to effectively carry out this task. To address this issue, the authors propose the implementation of an ongoing monitoring process that utilizes procedural data to identify unexpected large or small radiation exposures for individual patients, as well as to detect persistent changes in the radiation output of imaging platforms.Methods:Data used in this study were obtained from records routinely collected during procedures performed in the cardiac catheterization imaging facility at St. Andrew's War Memorial Hospital, Brisbane, Australia, over the period January 2008–March 2010. A two stage monitoring process employing individual and exponentially weighted moving average (EWMA) control charts was developed and used to identify unexpectedly high or low radiation exposure levels for individual patients, as well as detect persistent changes in the radiation output delivered by the imaging systems. To increase sensitivity of the charts, we account for variation in dose area product (DAP) values due to other measured factors (patient weight, fluoroscopy time, and digital acquisition frame count) using multiple linear regression. Control charts are then constructed using the residual values from this linear regression. The proposed monitoring process was evaluated using simulation to model the performance of the process under known conditions.Results:Retrospective application of this technique to actual clinical data identified a number of cases in which the DAP result could be considered unexpected. Most of these, upon review, were attributed to data entry errors. The charts monitoring the overall system radiation output trends demonstrated changes in equipment performance associated with relocation of the equipment to a new department. When tested under simulated conditions, the EWMA chart was capable of detecting a sustained 15% increase in average radiation output within 60 cases ( of operation), while a 33% increase would be signaled within 20 cases.Conclusions:This technique offers a valuable enhancement to existing quality assurance programs in radiology that rely upon the testing of equipment radiation output at discrete time frames to ensure performance security.
Segmentation and quantification of materials with energy discriminating computed tomography: A phantom study
Authors: Le Huy Q. , Molloi Sabee 
Published: December 2010

Purpose:To experimentally investigate whether a computed tomography (CT) system based on CdZnTe (CZT) detectors in conjunction with a least‐squares parameter estimation technique can be used to decompose four different materials.Methods:The material decomposition process was divided into a segmentation task and a quantification task. A least‐squares minimization algorithm was used to decompose materials with five measurements of the energy dependent linear attenuation coefficients. A small field‐of‐view energy discriminating CT system was built. The CT system consisted of an x‐ray tube, a rotational stage, and an array of CZT detectors. The CZT array was composed of 64 pixels, each of which is. Images were acquired at 80 kVp in fluoroscopic mode at 50 ms per frame. The detector resolved the x‐ray spectrum into energy bins of 22–32, 33–39, 40–46, 47–56, and 57–80 keV. Four phantoms were constructed from polymethylmethacrylate (PMMA), polyethylene, polyoxymethylene, hydroxyapatite, and iodine. Three phantoms were composed of three materials with embedded hydroxyapatite (50, 150, 250, and 350 mg/ml) and iodine (4, 8, 12, and 16 mg/ml) contrast elements. One phantom was composed of four materials with embedded hydroxyapatite (150 and 350 mg/ml) and iodine (8 and 16 mg/ml). Calibrations consisted of PMMA phantoms with either hydroxyapatite (100, 200, 300, 400, and 500 mg/ml) or iodine (5, 15, 25, 35, and 45 mg/ml) embedded. Filtered backprojection and a ramp filter were used to reconstruct images from each energy bin. Material segmentation and quantification were performed and compared between different phantoms.Results:All phantoms were decomposed accurately, but some voxels in the base material regions were incorrectly identified. Average quantification errors of hydroxyapatite/iodine were 9.26/7.13%, 7.73/5.58%, and 12.93/8.23% for the three‐material PMMA, polyethylene, and polyoxymethylene phantoms, respectively. The average errors for the four‐material phantom were 15.62% and 2.76% for hydroxyapatite and iodine, respectively.Conclusions:The calibrated least‐squares minimization technique of decomposition performed well in breast imaging tasks with an energy resolving detector. This method can provide material basis images containing concentrations of the relevant materials that can potentially be valuable in the diagnostic process.
Computerized segmentation and measurement of malignant pleural mesothelioma
Authors: Sensakovic William F. , Armato Samuel G. , Straus Christopher , Roberts Rachael Y. , Caligiuri Philip , Starkey Adam , Kindler Hedy L. 
Published: December 2010

Purpose:The current linear method to track tumor progression and evaluate treatment efficacy is insufficient for malignant pleural mesothelioma (MPM). A volumetric method for tumor measurement could improve the evaluation of novel treatments, but a fully manual implementation of volume measurement is too tedious and time‐consuming. This manuscript presents a computerized method for the three‐dimensional segmentation and volumetric analysis of MPM.Methods:The computerized MPM segmentation method segments the lung parenchyma and hemithoracic cavities to define the pleural space. Nonlinear diffusion and a k‐means classifier are then implemented to identify MPM in the pleural space. A database of 31 computed tomography scans from 31 patients with pathologically confirmed MPM was retrospectively collected. Three observers independently outlined five randomly selected sections in each scan. The Jaccard similarity coefficient (J) between each of the observers and between the observer‐defined and computer‐defined segmentations was calculated. The computer‐defined and the observer‐defined segmentation areas (averaged over all observers) were both calculated for each axial section and compared using Bland–Altman plots.Results:The median J value among observers averaged over all sections was 0.517. The median J between the computer‐defined and manual segmentations was 0.484. The difference between these values was not statistically significant. The area delineated by the computerized method demonstrated variability and bias comparable to the tumor area calculated from manual delineations.Conclusions:A computerized method for segmentation and measurement of MPM was developed. This method requires minimal initialization by the user and demonstrated good agreement with manually drawn outlines and area measurements. This method will allow volumetric tracking of tumor progression and may improve the evaluation of novel MPM treatments.
Least squares parameter estimation methods for material decomposition with energy discriminating detectors
Authors: Le Huy Q. , Molloi Sabee 
Published: December 2010

Purpose:Energy resolving detectors provide more than one spectral measurement in one image acquisition. The purpose of this study is to investigate, with simulation, the ability to decompose four materials using energy discriminating detectors and least squares minimization techniques.Methods:Three least squares parameter estimation decomposition techniques were investigated for four‐material breast imaging tasks in the image domain. The first technique treats the voxel as if it consisted of fractions of all the materials. The second method assumes that a voxel primarily contains one material and divides the decomposition process into segmentation and quantification tasks. The third is similar to the second method but a calibration was used. The simulated computed tomography (CT) system consisted of an 80 kVp spectrum and a CdZnTe (CZT) detector that could resolve the x‐ray spectrum into five energy bins. A postmortem breast specimen was imaged with flat panel CT to provide a model for the digital phantoms. Hydroxyapatite (HA) (50, 150, 250, 350, 450, and 550 mg/ml) and iodine (4, 12, 20, 28, 36, and 44 mg/ml) contrast elements were embedded into the glandular region of the phantoms. Calibration phantoms consisted of a 30/70 glandular‐to‐adipose tissue ratio with embedded HA (100, 200, 300, 400, and 500 mg/ml) and iodine (5, 15, 25, 35, and 45 mg/ml). The x‐ray transport process was simulated where the Beer–Lambert law, Poisson process, and CZT absorption efficiency were applied. Qualitative and quantitative evaluations of the decomposition techniques were performed and compared. The effect of breast size was also investigated.Results:The first technique decomposed iodine adequately but failed for other materials. The second method separated the materials but was unable to quantify the materials. With the addition of a calibration, the third technique provided good separation and quantification of hydroxyapatite, iodine, glandular, and adipose tissues. Quantification with this technique was accurate with errors of 9.83% and 6.61% for HA and iodine, respectively. Calibration at one point (one breast size) showed increased errors as the mismatch in breast diameters between calibration and measurement increased. A four‐point calibration successfully decomposed breast diameter spanning the entire range from 8 to 20 cm. For a 14 cm breast, errors were reduced from 5.44% to 1.75% and from 6.17% to 3.27% with the multipoint calibration for HA and iodine, respectively.Conclusions:The results of the simulation study showed that a CT system based on CZT detectors in conjunction with least squares minimization technique can be used to decompose four materials. The calibrated least squares parameter estimation decomposition technique performed the best, separating and accurately quantifying the concentrations of hydroxyapatite and iodine.
Estimation of three‐dimensional intrinsic dosimetric uncertainties resulting from using deformable image registration for dose mapping
Authors: Salguero Francisco J. , Saleh‐Sayah Nahla K. , Yan Chenyu , Siebers Jeffrey V. 
Published: December 2010

Purpose:This article presents a general procedural framework to assess the point‐by‐point precision in mapped dose associated with the intrinsic uncertainty of a deformable image registration (DIR) for any arbitrary patient.Methods:Dose uncertainty is obtained via a three‐step process. In the first step, for each voxel in an imaging pair, a cluster of points is obtained by an iterative DIR procedure. In the second step, the dispersion of the points due to the imprecision of the DIR method is used to compute the spatial uncertainty. Two different ways to quantify the spatial uncertainty are presented in this work. Method A consists of a one‐dimensional analysis of the modules of the position vectors, whereas method B performs a more detailed 3D analysis of the coordinates of the points. In the third step, the resulting spatial uncertainty estimates are used in combination with the mapped dose distribution to compute the point‐by‐point dose standard deviation. The process is demonstrated to estimate the dose uncertainty induced by mapping a 62.6 Gy dose delivered on maximum exhale to maximum inhale of a ten‐phase four‐dimensional lung CT.Results:For the demonstration lung image pair, the standard deviation of inconsistency vectors is found to be up to 9.2 mm with a mean of 1.3 mm. This uncertainty results in a maximum estimated dose uncertainty of 29.65 Gy if method A is used and 21.81 Gy for method B. The calculated volume with dose uncertainty above 10.00 Gy is for method A and for method B.Conclusions:This procedure represents a useful tool to evaluate the precision of a mapped dose distribution due to the intrinsic DIR uncertainty in a patient. The procedure is flexible, allowing incorporation of alternative intrinsic error models.
On the impact of dose rate variation upon RapidArc® implementation of volumetric modulated arc therapy
Authors: Nicolini Giorgia , Clivio Alessandro , Cozzi Luca , Fogliata Antonella , Vanetti Eugenio 
Published: December 2010

Purpose:A study was carried out to evaluate the robustness and mutual interplay of two variables concurring to generate modulation patterns of the RapidArc® (RapidArc) implementation of volumetric modulated arc therapy. Dose rate (DR) and gantry speed (GS) are free parameters optimized alongside field aperture shape by the RapidArc engine; however, they are limited by machine constraints and mutually compensate in order to deliver the proper MU/deg during the gantry rotation.Methods:Four test cases (one geometrical and three clinical) were selected and RapidArc plans were optimized using maximum allowed dose rates from 100 to 600 MU/min. The maximum gantry speed was fixed at 4.8 deg/s. Qualitative analysis of DR and GS patterns from these cases was summarized together with quantitative assessment of delivery parameters. Pretreatment quality assurance measurements and scoring of plan quality aimed to determine whether preferable initial conditions might be identified or the optimization engine might be invariant to those variables and capable of providing adequate plans independently from the limits applied.Results:The results of the study were: (i) High dynamic range in MU/deg is achievable across all dose rates by means of gantry speed modulation; (ii) there is a robust compensation mechanism between the two variables; (iii) from a machine delivery point‐of‐view, slightly improved accuracy is achieved when lower DRs are applied; however, this does not have practical consequences since measurements and plan evaluation showed a lack of clinically relevant deviation; and (iv) reduced total treatment time is a major advantage of high DR.Conclusions:A trend toward improved plan quality for clinical cases was observed with high DR but cannot be generalized, due to the limited amount of cases investigated and the consequent limited significance of the observed differences. As a minimum benefit, the reduced total treatment time should be considered as well.