bluuebunny/crossref_metadata_2025_split huggingface dataset:
Validation of SPAMM tagged MRI based measurement of 3D soft tissue deformation
Authors: Moerman Kevin M. , Sprengers Andre M. J. , Simms Ciaran K. , Lamerichs Rolf M. , Stoker Jaap , Nederveen Aart J. 
Published: March 2011

Purpose:This study presents and validates a novel (non‐ECG‐triggered) MRI sequence based on spatial modulation of the magnetization (SPAMM) to noninvasively measure 3D (quasistatic) soft tissue deformations using only six acquisitions (three static and three indentations). In the current SPAMM tagged MRI approaches, data are typically constructed from many repeated motion cycles. This has so far restricted its application to the measurement of highly repeatable and periodic movements (e.g., cardiac deformation). In biomechanical applications where soft tissue deformation is artificially induced, often by indentation, significant repeatability constraints exist, and for clinical applications, discomfort and health issues generally preclude a large number of repetitions.Methods:A novel (non‐ECG‐triggered) SPAMM tagged MRI sequence is presented, whereby a single 1‐1 (first order) SPAMM set is acquired following a 3D transient field echo acquisition. Full 3D deformation measurement is achieved through the combination of only six acquisitions (three static and three motion cycles). The 3D deformation measurements were validated using quasistatic indentation tests and marker tracking in a silicone gel soft tissue phantom. In addition, the technique's ability to measure 3D soft tissue deformationin vivo was evaluated using indentation of the biceps region of the upper arm in a volunteer.Results:Following comparison to marker tracking in the silicone gel phantom, the SPAMM tagged MRI based displacement measurement demonstrated subvoxel accuracy with a mean displacement difference of and a standard deviation of . In addition, precision of displacement magnitude was evaluated for both the phantom and the volunteer data. The standard deviations of the displacement magnitude with respect to the average displacement magnitude were 75 and for the phantom and volunteer data, respectively.Conclusions:The subvoxel accuracy and precision demonstrated in the phantom in combination with the precision comparison between the phantom and the volunteer data provide confidence in the methods presented for measurement of soft tissue deformationin vivo. To the author's knowledge, since only six acquisitions are required, the presented methodology is the fastest SPAMM tagged MRI method currently available for the noninvasive measurement of quasistatic 3D soft tissue deformation.
Accurate Monte Carlo modeling and performance assessment of the X‐PET™ subsystem of the FLEX Triumph™ preclinical PET/CT scanner
Authors: Zeraatkar N. , Ay M. R. , Kamali‐Asl A. R. , Zaidi H. 
Published: March 2011

Purpose:X‐PET™ is a commercial small animal PET scanner incorporating several innovative designs to achieve improved performance. It is employed as a PET subsystem in the FLEX Triumph™ preclinical PET/CT scanner, the first commercial small animal PET/CT scanner worldwide. The authors report on a novel Monte Carlo (MC) model designed for the evaluation of performance parameters of the X‐PET™.Methods:The Geant4 Application for Tomographic Emission (GATE) MC code was used as a simulation tool. The authors implemented more accurate modeling of the geometry of detector blocks and associated electronic chains, including dead‐time and time‐independent parameters, compared to previously presented MC models of the X‐PET™ scanner. Validation of the MC model involved comparison between simulated and measured performance parameters of the X‐PET™, including spatial resolution, sensitivity, and noise equivalent count rate (NECR). Thereafter, various simulations were performed to assess scanner performance parameters according to NEMA NU 4‐2008 standards with the aim to present a reliable Monte Carlo platform for small animal PET scanner design optimization.Results:The average differences between simulated and measured results were 11.2%, 33.3%, and 9.1% for spatial resolution, sensitivity, and NECR, respectively. The average system absolute sensitivity was 2.7%. Furthermore, the peak true count rate, peak NECR, and scatter fraction were 2050 kcps, 1520 kcps, and 4.7%, respectively, for a mouse phantom and 1017 kcps, 469 kcps, and 18.2%, respectively, for a rat phantom. Spatial resolution was also measured in ten different positions at two axial locations. The radial, tangential, and axial FWHM ranged from 1.31 to 1.96 mm, 1.17 to 2.11 mm, and 1.77 to 2.44 mm, respectively, as the radial position varied from 0 to 25 mm at the centre of the axial field‐of‐view.Conclusions:The developed MC simulation platform provides a reliable tool for performance evaluation of small animal PET scanners and has the potential to be used in other applications such as detector design optimization, correction of image degrading factors such as randoms, scatter, intercrystal scatter, parallax error, and partial volume effect.
Low‐dose 4DCT reconstruction via temporal nonlocal means
Authors: Tian Zhen , Jia Xun , Dong Bin , Lou Yifei , Jiang Steve B. 
Published: March 2011

Purpose:Four‐dimensional computed tomography (4DCT) has been widely used in cancer radiotherapy for accurate target delineation and motion measurement for tumors in the thorax and upper abdomen areas. However, its prolonged scanning duration causes a considerable increase of radiation dose compared to conventional CT, which is a major concern in its clinical application. This work is to develop a new algorithm to reconstruct 4DCT images from undersampled projections acquired at low mA s levels in order to reduce the imaging dose.Methods:Conventionally, each phase of 4DCT is reconstructed independently using the filtered backprojection (FBP) algorithm. The basic idea of the authors' new algorithm is that by utilizing the common information among different phases, the input information required to reconstruct the image of high quality, and thus the imaging dose, can be reduced. The authors proposed a temporal nonlocal means (TNLM) method to explore the interphase similarity. All phases of the 4DCT images are reconstructed simultaneously by minimizing a cost function consisting of a data fidelity term and a TNLM regularization term. The authors utilized a modified forward‐backward splitting algorithm and a Gauss–Jacobi iteration method to efficiently solve the minimization problem. The algorithm was also implemented on a graphics processing unit (GPU) to improve the computational speed. The authors' reconstruction algorithm has been tested on a digital NCAT thorax phantom in three low dose scenarios: All projections with low mA s level, undersampled projections with high mA s level, and undersampled projections with low mA s level.Results:In all three low dose scenarios, the new algorithm generates visually much better CT images containing less image noise and streaking artifacts compared to the standard FBP algorithm. Quantitative analysis shows that by comparing the authors' TNLM algorithm to the standard FBP algorithm, the contrast‐to‐noise ratio has been improved by a factor of 3.9–10.2 and the signal‐to‐noise ratio has been improved by a factor of 2.1–5.9, depending on the cases. In the situation of undersampled projection data, the majority of the streaks in the images reconstructed by FBP can be suppressed using the authors' algorithm. The total reconstruction time for all ten phases of a slice ranges from 40 to 90 s on an NVIDIA Tesla C1060 GPU card.Conclusions:The experimental results indicate that the authors' new algorithm outperforms the conventional FBP algorithm in effectively reducing the image artifacts due to undersampling and suppressing the image noise due to the low mA s level.
Dynamic estimation of three‐dimensional cerebrovascular deformation from rotational angiography
Authors: Zhang Chong , Villa‐Uriol Maria‐Cruz , De Craene Mathieu , Pozo José María , Macho Juan M. , Frangi Alejandro F. 
Published: March 2011

Purpose:The objective of this study is to investigate the feasibility of detecting and quantifying 3D cerebrovascular wall motion from a single 3D rotational x‐ray angiography (3DRA) acquisition within a clinically acceptable time and computing from the estimated motion field for the further biomechanical modeling of the cerebrovascular wall.Methods:The whole motion cycle of the cerebral vasculature is modeled using a 4D‐spline transformation, which is estimated from a 4D to image registration framework. The registration is performed by optimizing a single similarity metric between the entire measured projection sequence and the corresponding forward projections of the deformed volume at their exact time instants. The joint use of two acceleration strategies, together with their implementation on graphics processing units, is also proposed so as to reach computation times close to clinical requirements. For further characterizing vessel wall properties, an approximation of the wall thickness changes is obtained through a strain calculation.Results:Evaluation onin silico and in vitro pulsating phantom aneurysms demonstrated an accurate estimation of wall motion curves. In general, the error was below 10% of the maximum pulsation, even in the situation when substantial inhomogeneous intensity pattern was present. Experiments on in vivo data provided realistic aneurysm and vessel wall motion estimates, whereas in regions where motion was neither visible nor anatomically possible, no motion was detected. The use of the acceleration strategies enabled completing the estimation process for one entire cycle in 5–10 min without degrading the overall performance. The strain map extracted from our motion estimation provided a realistic deformation measure of the vessel wall.Conclusions:The authors' technique has demonstrated that it can provide accurate and robust 4D estimates of cerebrovascular wall motion within a clinically acceptable time, although it has to be applied to a larger patient population prior to possible wide application to routine endovascular procedures. In particular, for the first time, this feasibility study has shown thatin vivo cerebrovascular motion can be obtained intraprocedurally from a 3DRA acquisition. Results have also shown the potential of performing strain analysis using this imaging modality, thus making possible for the future modeling of biomechanical properties of the vascular wall.
Real‐time verification of multileaf collimator‐driven radiotherapy using a novel optical attenuation‐based fluence monitor
Authors: Goulet Mathieu , Gingras Luc , Beaulieu Luc 
Published: March 2011

Purpose:Multileaf collimator (MLC)‐driven conformal radiotherapy modalities [e.g., such as intensity‐modulated radiotherapy (IMRT), intensity‐modulated arc therapy, and stereotactic body radiotherapy] are more subject to delivery errors and dose calculation inaccuracies than standard modalities. Fluence monitoring during treatment delivery could reduce such errors by allowing an independent interface to quantify and assess measured difference between the delivered and planned treatment administration. We developed an optical attenuation‐based detector to monitor fluence for the on‐line quality control of radiotherapy delivery. The purpose of the current study was to develop the theoretical background of the invention and to evaluate the detector's performance both statistically and in clinical situations.Methods:We aligned 60 27‐cm scintillating fibers coupled to a photodetector via clear optical fibers in the direction of motion of each of the 60 leaf pairs of a 120 leaves Millenium MLC on a Varian Clinac iX. We developed a theoretical model to predict the intensity of light collected on each side of the scintillating fibers when placed under radiation fields of varying sizes, intensities, and positions. The model showed that both the central position of the radiation field on the fiber and the integral fluence passing through the fiber could be assessed independently in a single measurement. We evaluated the performance of the prototype by (1) measuring the intrinsic variation of the measured values of and , (2) measuring the impact on the measured values of and of random leaf positioning errors introduced into IMRT fields, and (3) comparing the predicted values of and calculated with the treatment planning software to the measured values of and in order to assess the predictive effectiveness of the developed theoretical model.Results:We observed a very low intrinsic dispersion, dominated by Poisson statistics, for both (standard deviations of less than 1 mm) and (standard deviations of less than 0.20%). When confronted with random leaf positioning errors from IMRT segments, was highly sensitive to single leaf positioning errors as small as 1 mm at isocenter, while was sensitive to leaf pair translation errors of at least 2 mm at isocenter. Owing to the uncertainties in the doses calculated in regions of high perpendicular dose gradients, the measured values of and deviated from the predicted values of and by a mean of 1.3 mm and 2.6%, respectively.Conclusion:Our study showed that an optical attenuation‐based detector can be used to effectively monitor integral fluence during radiotherapy delivery. The performance of such a system would enable real‐time quality control of the incident fluence in current MLC‐driven treatments such as IMRT and future adaptive radiotherapy procedures where new treatment plans will have to be delivered without passing thru the current standard quality control chain.
Experimental validation of a method characterizing bow tie filters in CT scanners using a real‐time dose probe
Authors: McKenney Sarah E. , Nosratieh Anita , Gelskey Dale , Yang Kai , Huang Shin‐ying , Chen Lin , Boone John M. 
Published: March 2011

Purpose:Beam‐shaping or “bow tie” (BT) filters are used to spatially modulate the x‐ray beam in a CT scanner, but the conventional method of step‐and‐shoot measurement to characterize a beam's profile is tedious and time‐consuming. The theory for characterization of bow tie relative attenuation (COBRA) method, which relies on a real‐time dosimeter to address the issues of conventional measurement techniques, was previously demonstrated using computer simulations. In this study, the feasibility of the COBRA theory is further validated experimentally through the employment of a prototype real‐time radiation meter and a known BT filter.Methods:The COBRA method consisted of four basic steps: (1) The probe was placed at the edge of a scanner's field of view; (2) a real‐time signal train was collected as the scanner's gantry rotated with the x‐ray beam on; (3) the signal train, without a BT filter, was modeled using peak values measured in the signal train of step 2; and (4) the relative attenuation of the BT filter was estimated from filtered and unfiltered data sets. The prototype probe was first verified to have an isotropic and linear response to incident x‐rays. The COBRA method was then tested on a dedicated breast CT scanner with a custom‐designed BT filter and compared to the conventional step‐and‐shoot characterization of the BT filter. Using basis decomposition of dual energy signal data, the thickness of the filter was estimated and compared to the BT filter's manufacturing specifications. The COBRA method was also demonstrated with a clinical whole body CT scanner using the body BT filter. The relative attenuation was calculated at four discrete x‐ray tube potentials and used to estimate the thickness of the BT filter.Results:The prototype probe was found to have a linear and isotropic response to x‐rays. The relative attenuation produced from the COBRA method fell within the error of the relative attenuation measured with the step‐and‐shoot method. The BT filter thickness estimates resulting from the dual energy scans on the breast CT system were equivalent to the manufacturing specifications. The clinical CT evaluation produced data conceptually similar to previous computer simulations and plausible relative attenuation profiles were observed.Conclusions:The COBRA method is a fast and accurate method for BT filter characterization, which requires a simple experimental setup in a clinical environment. Because of the ease of data acquisition, multienergy scans can be acquired which allow characterization of the BT filter thickness.
Direct intratumoral infusion of liposome encapsulated rhenium radionuclides for cancer therapy: Effects of nonuniform intratumoral dose distribution
Authors: Hrycushko Brian A. , Li Shihong , Goins Beth , Otto Randal A. , Bao Ande 
Published: March 2011

Purpose:Focused radiation therapy by direct intratumoral infusion of lipid nanoparticle (liposome)‐carried beta‐emitting radionuclides has shown promising results in animal model studies; however, little is known about the impact the intratumoral liposomal radionuclide distribution may have on tumor control. The primary objective of this work was to investigate the effects the intratumoral absorbed dose distributions from this cancer therapy modality have on tumor control and treatment planning by combining dosimetric and radiobiological modeling within vivo imaging data.Methods:‐encapsulated liposomes were intratumorally infused with a single injection location to human head and neck squamous cell carcinoma xenografts in nude rats. High resolution in vivo planar imaging was performed at various time points for quantifying intratumoral retention following infusion. The intratumoral liposomal radioactivity distribution was obtained from 1 mm resolution pinhole collimator SPECT imaging coregistered with CT imaging of excised tumors at 20 h postinfusion. Coregistered images were used for intratumoral dosimetric and radiobiological modeling at a voxel level following extrapolation to the therapeutic analogs, liposomes. Effective uniform dose (EUD) and tumor control probability (TCP) were used to assess therapy effectiveness and possible methods of improving upon tumor control with this radiation therapy modality.Results:Dosimetric analysis showed that average tumor absorbed doses of 8.6 Gy/MBq (318.2 Gy/mCi) and 5.7 Gy/MBq (209.1 Gy/mCi) could be delivered with this protocol of radiation delivery for liposomes, respectively, and 37–92 MBq (1–2.5 mCi)/g tumor administered activity; however, large intratumoral absorbed dose heterogeneity, as seen in dose‐volume histograms, resulted in insignificant values of EUD and TCP for achieving tumor control. It is indicated that the use of liposomes encapsulating radionuclides with higher energy beta emissions, dose escalation through increased specific activity, and increasing the number of direct tumor infusion sites improve tumor control. For larger tumors, the use of multiple infusion locations was modeled to be much more efficient, in terms of activity usage, at improving EUD and TCP to achieve a tumoricidal effect.Conclusions:Direct intratumoral infusion of beta‐emitting radionuclide encapsulated liposomes shows promise for cancer therapy by achieving large focally delivered tumor doses. However, the results of this work also indicate that average tumor dose may underestimate tumoricidal effect due to substantial heterogeneity in intratumoral liposomal radionuclide distributions. The resulting intratumoral distribution of liposomes following infusion should be taken into account in treatment planning and evaluation in a clinical setting for an optimal cancer therapy.
Using an EPID for patient‐specific VMAT quality assurance
Authors: Bakhtiari M. , Kumaraswamy L. , Bailey D. W. , de Boer S. , Malhotra H. K. , Podgorsak M. B. 
Published: March 2011

Purpose:A patient‐specific quality assurance (QA) method was developed to verify gantry‐specific individual multileaf collimator (MLC) apertures (control points) in volumetric modulated arc therapy (VMAT) plans using an electronic portal imaging device (EPID).Methods:VMAT treatment plans were generated in an Eclipse treatment planning system (TPS). DICOM images from a Varian EPID (aS1000) acquired in continuous acquisition mode were used for pretreatment QA. Each cine image file contains the grayscale image of the MLC aperture related to its specific control point and the corresponding gantry angle information. The TPS MLC file of this RapidArc plan contains the leaf positions for all 177 control points (gantry angles). In‐house software was developed that interpolates the measured images based on the gantry angle and overlays them with the MLC pattern for all control points. The 38% isointensity line was used to define the edge of the MLC leaves on the portal images. The software generates graphs and tables that provide analysis for the number of mismatched leaf positions for a chosen distance to agreement at each control point and the frequency in which each particular leaf mismatches for the entire arc.Results:Seven patients plans were analyzed using this method. The leaves with the highest mismatched rate were found to be treatment plan dependent.Conclusions:This in‐house software can be used to automatically verify the MLC leaf positions for all control points of VMAT plans using cine images acquired by an EPID.
Validation for 2D/3D registration I: A new gold standard data set
Authors: Pawiro S. A. , Markelj P. , Pernuš F. , Gendrin C. , Figl M. , Weber C. , Kainberger F. , Nöbauer‐Huhmann I. , Bergmeister H. , Stock M. , Georg D. , Bergmann H. , Birkfellner W. 
Published: March 2011

Purpose:In this article, the authors propose a new gold standard data set for the validation of two‐dimensional/three‐dimensional (2D/3D) and 3D/3D image registration algorithms.Methods:A gold standard data set was produced using a fresh cadaver pig head with attached fiducial markers. The authors used several imaging modalities common in diagnostic imaging or radiotherapy, which include 64‐slice computed tomography (CT), magnetic resonance imaging using Tl, T2, and proton density sequences, and cone beam CT imaging data. Radiographic data were acquired using kilovoltage and megavoltage imaging techniques. The image information reflects both anatomy and reliable fiducial marker information and improves over existing data sets by the level of anatomical detail, image data quality, and soft‐tissue content. The markers on the 3D and 2D image data were segmented usingANALYZE 10.0 (AnalyzeDirect, Inc., Kansas City, KN) and an in‐house software.Results:The projection distance errors and the expected target registration errors over all the image data sets were found to be less than 2.71 and 1.88 mm, respectively.Conclusions:The gold standard data set, obtained with state‐of‐the‐art imaging technology, has the potential to improve the validation of 2D/3D and 3D/3D registration algorithms for image guided therapy.