bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fast‐MICP for frameless image‐guided surgery
Authors: Lee Jiann‐Der , Huang Chung‐Hsien , Wang Sheng‐Ta , Lin Chung‐Wei , Lee Shin‐Tseng 
Published: August 2010

Purpose:In image‐guided surgery (IGS) systems, image‐to‐physical registration is critical for reliable anatomical information mapping and spatial guidance. Conventional stereotactic frame‐based or fiducial‐based approaches provide accurate registration but are not patient‐friendly. This study proposes a frameless cranial IGS system that uses computer vision techniques to replace the frame or fiducials with the natural features of the patient.Methods:To perform a cranial surgery with the proposed system, the facial surface of the patient is first reconstructed by stereo vision. Accuracy is ensured by capturing parallel‐line patterns projected from a calibrated LCD projector. Meanwhile, another facial surface is reconstructed from preoperative computed tomography (CT) images of the patient. The proposed iterative closest point (ICP)‐based algorithm [fast marker‐added ICP (Fast‐MICP)] is then used to register the two facial data sets, which transfers the anatomical information from the CT images to the physical space.Results:Experimental results reveal that the Fast‐MICP algorithm reduces the computational cost of marker‐added ICP (J.‐D. Lee et al., “A coarse‐to‐fine surface registration algorithm for frameless brain surgery,” in Proceedings of International Conference of the IEEE Engineering in Medicine and Biology Society, 2007, pp. 836–839) to 10% and achieves comparable registration accuracy, which is under 3 mm target registration error (TRE). Moreover, two types of optical‐based spatial digitizing devices can be integrated for further surgical navigation. Anatomical information or image‐guided surgical landmarks can be projected onto the patient to obtain an immersive augmented reality environment.Conclusion:The proposed frameless IGS system with stereo vision obtains TRE of less than 3 mm. The proposed Fast‐MICP registration algorithm reduces registration time by 90% without compromising accuracy.
The accuracy and safety aspects of a novel robotic needle guide manipulator to perform transrectal prostate biopsies
Authors: Schouten Martijn G. , Ansems Janneke , Renema W. Klaas Jan , Bosboom Dennis , Scheenen Tom W. J. , Fütterer Jurgen J. 
Published: August 2010

Purpose:To introduce a new in‐house developed pneumatically controlled magnetic field compatible manipulator as an aid to perform magnetic resonance (MR)‐guided biopsies of the prostate.Methods:A pneumatic controlled manipulator with five degrees of freedom constructed of plastic to achieve magnetic field compatibility was developed to guide biopsies. A risk analysis, mechanical tests, and RF safety tests with respect to needle tip heating were performed to assure future patient safety and to meet standard safety requirements for the use in a medical environment. The accuracy of needle positioning with the needle guide manipulator to sample a predefined target was measured in agar phantoms on a 3 T whole body MR system. The in‐plane error was used to evaluate the accuracy, which is defined as the orthogonal distance between target and biopsy needle. The time for each step in the biopsy procedure was recorded to evaluate the procedure time. The influence of the insertion angle with respect to the static field of the MR scanner on the needle artifact was investigated.Results:The risk analyses met patient safety requirements. No RF induced local heating around the needle tip was observed. The average in‐plane error in 19 measurements was 3.0 mm (range 0–5.6 mm). The average time needed for manipulation to place the needle guide in the desired position was 5 min (range 3–8 min). Total procedure time was 30 min. The needle artifact size increases with the insertion angle with respect to the static field of the MR scanner.Conclusions:The new MR compatible manipulator can be used safely for patient care. It showed a high accuracy and short total procedure time, demonstrating great potential to improve the transrectal prostate biopsy procedure.
Waveguide detuning caused by transverse magnetic fields on a simulated in‐line 6 MV linac
Authors: St. Aubin J. , Steciw S. , Fallone B. G. 
Published: August 2010

Purpose:Due to the close proximity of the linear accelerator (linac) to the magnetic resonance (MR) imager in linac‐MR systems, it will be subjected to magnet fringe fields larger than the Earth's magnetic field of. Even with passive or active shielding designed to reduce these fields, some magnitude of the magnetic field is still expected to intersect the linac, causing electron deflection and beam loss. This beam loss, resulting from magnetic fields that cannot be eliminated with shielding, can cause a detuning of the waveguide due to excessive heating. The detuning, if significant, could lead to an even further decrease in output above what would be expected strictly from electron deflections caused by an external magnetic field. Thus an investigation of detuning was performed through various simulations.Methods:According to the Lorentz force, the electrons will be deflected away from their straight course to the target, depositing energy as they impact the linac copper waveguide. The deposited energy would lead to a heating and deformation of the copper structure resulting in resonant frequency changes.PARMELA was used to determine the mean energy and fraction of total beam lost in each linac cavity. The energy deposited into the copper waveguide from the beam losses caused by transverse magnetic fields was calculated using the Monte Carlo program DOSRZnrc. From the total energy deposited, the rise in temperature and ultimately the deformation of the structure was estimated. The deformed structure was modeled using the finite element method program COMSOL MULTIPHYSICS to determine the change in cavity resonant frequency.Results:The largest changes in resonant frequency were found in the first two accelerating cavities for each field strength investigated. This was caused by a high electron fluence impacting the waveguide inner structures coupled with their low kinetic energies. At each field strength investigated, the total change in accelerator frequency was less than a manufacturing tolerance of 10 kHz and is thus not expected to have a noticeable effect on accelerator performance.Conclusions:The amount of beam loss caused by magnetic fringe fields for a linac in a linac‐MR system depends on the effectiveness of its magnetic shielding. Despite the best efforts to shield the linac from the magnetic fringe fields, some persistent magnetic field is expected which would result in electron beam loss. This investigation showed that the detuning of the waveguide caused by additional electron beam loss in persistent magnetic fields is not a concern.
Magnetic decoupling of the linac in a low field biplanar linac‐MR system
Authors: St. Aubin J. , Steciw S. , Fallone B. G. 
Published: August 2010

Purpose:The integration of a low field biplanar magnetic resonance (MR) imager and linear accelerator (linac) causes magnetic interference at the linac due to the MR fringe fields. In order to eliminate this interference, passive and active magnetic shielding designs are investigated.Methods:The optimized design of passive magnetic shielding was performed using the finite element method. The design was required to achieve no greater than a 20% electron beam loss within the linac waveguide and electron gun, no greater than 0.06 T at the multileaf collimator (MLC) motors, and generate a distortion of the main MR imaging volume of no greater than 300 ppm. Through the superposition of the analytical solution for a single current carrying wire loop, active shielding designs in the form of three and four sets of coil pairs surrounding the linac waveguide and electron gun were also investigated. The optimized current and coil center locations that yielded the best cancellation of the MR fringe fields at the linac were determined using sequential quadratic programming.Results:Optimized passive shielding in the form of two steel cylinders was designed to meet the required constraints. When shielding the MLC motors along with the waveguide and electron gun, the thickness of the cylinders was less than 1 mm. If magnetically insensitive MLC motors are used, no MLC shielding would be required and the waveguide shield (shielding the waveguide and electron gun) became 1.58 mm thick. In addition, the optimized current and coil spacing for active shielding was determined for both three and four coil pair configurations. The results of the active shielding optimization produced no beam loss within the waveguide and electron gun and a maximum MR field distortion of 91 ppm over a 30 cm diameter spherical volume.Conclusions:Very simple passive and active shielding designs have been shown to magnetically decouple the linac from the MR imager in a low field biplanar linac‐MR system. The MLC passive shielding produced the largest distortion of the MR field over the imaging volume. With the use of magnetically insensitive motors, the MR field distortion drops substantially since no MLC shield is required. The active shielding designs yielded no electron beam loss within the linac.
Quiescent period respiratory gating for PET/CT
Authors: Liu Chi , Alessio Adam , Pierce Larry , Thielemans Kris , Wollenweber Scott , Ganin Alexander , Kinahan Paul 
Published: August 2010

Purpose:To minimize respiratory motion artifacts, this work proposes quiescent period gating (QPG) methods that extract PET data from the end‐expiration quiescent period and form a single PET frame with reduced motion and improved signal‐to‐noise properties.Methods:Two QPG methods are proposed and evaluated. Histogram‐based quiescent period gating (H‐QPG) extracts a fraction of PET data determined by a window of the respiratory displacement signal histogram. Cycle‐based quiescent period gating (C‐QPG) extracts data with a respiratory displacement signal below a specified threshold of the maximum amplitude of each individual respiratory cycle. Performances of both QPG methods were compared to ungated and five‐bin phase‐gated images across 21 FDG‐PET/CT patient data sets containing 31 thorax and abdomen lesions as well as with computer simulations driven by 1295 different patient respiratory traces. Image quality was evaluated in terms of the lesion and the fraction of counts included in each gate as a surrogate for image noise.Results:For all the gating methods, image noise artifactually increases when the fraction of counts included in each gate is less than 50%. While simulation data show that H‐QPG is superior to C‐QPG, the H‐QPG and C‐QPG methods lead to similar quantification‐noise tradeoffs in patient data. Compared to ungated images, both QPG methods yield significantly higher lesion . Compared to five‐bin phase gating, the QPG methods yield significantly larger fraction of counts with similar improvement. Both QPG methods result in increased lesion for patients whose lesions have longer quiescent periods.Conclusions:Compared to ungated and phase‐gated images, the QPG methods lead to images with less motion blurring and an improved compromise between and fraction of counts. The QPG methods for respiratory motion compensation could effectively improve tumor quantification with minimal noise increase.
Dosimetric characterization of a multileaf collimator for a new four‐dimensional image‐guided radiotherapy system with a gimbaled x‐ray head, MHI‐TM2000a)
Authors: Nakamura Mitsuhiro , Sawada Akira , Ishihara Yoshitomo , Takayama Kenji , Mizowaki Takashi , Kaneko Shuji , Yamashita Mikiko , Tanabe Hiroaki , Kokubo Masaki , Hiraoka Masahiro 
Published: August 2010

Purpose:To present the dosimetric characterization of a multileaf collimator (MLC) for a new four‐dimensional image‐guided radiotherapy system with a gimbaled x‐ray head, MHI‐TM2000.Methods:MHI‐TM2000 has an x‐ray head composed of an ultrasmall linear accelerator guide and a system‐specific MLC. The x‐ray head can rotate along the two orthogonal gimbals (pan and tilt rotations) up to ±2.5°, which swings the beam up to ±41.9 mm in each direction from the isocenter on the isocenter plane perpendicular to the beam. The MLC design is a single‐focus type, has 30 pairs of 5 mm thick leaves at the isocenter, and produces a maximum field size of. Leaf height and length are 110 and 260 mm, respectively. Each leaf end is circular, with a radius of curvature of 370 mm. The distance that each leaf passes over the isocenter is 77.5 mm. Radiation leakage between adjacent leaves is minimized by an interlocking tongue‐and‐groove (T&G) arrangement with the height of the groove part 55 mm. The dosimetric characterizations including field characteristics, leaf position accuracy, leakage, and T&G effect were evaluated using a well‐commissioned 6 MV photon beam, EDR2 films (Kodak, Rochester, NY), and water‐equivalent phantoms. Furthermore, the field characteristics and leaf position accuracy were evaluated under conditions of pan or tilt rotation.Results:The differences between nominal and measured field sizes were within ±0.5 mm. Although the penumbra widths were greater with wider field size, the maximum width was even for the fully opened field. Compared to the results of field characteristics without pan or tilt rotation, the variation in field size, penumbra width, flatness, and symmetry was within ±1 mm/1% at the maximum pan or tilt rotational angle. The leaf position accuracy was , ranging from −0.3 to 0.2 mm at four gantry angles of 0°, 90°, 180°, and 270° with and without pan or tilt rotation. The interleaf leakage was up to 0.21%, whereas the intraleaf leakage was . T&G decreased the doses by 10.7%, on average.Conclusions:This study demonstrated that MHI‐TM2000 has the capability for high leaf position accuracy and low leakage, leading to highly accurate intensity‐modulated radiotherapy delivery. Furthermore, substantial changes in the dosimetric data on field characteristics and leaf position accuracy were not observed even at the maximum pan or tilt rotation.
A dose distribution evaluation technique using the k‐d tree for nearest neighbor searching
Authors: Yuan Jiankui , Chen Weimin 
Published: August 2010

Purpose:The authors propose an algorithm based on the k‐d tree for nearest neighbor searching to improve the calculation time for 2D and 3D dose distributions.Methods:The calculation method has been widely used for comparisons of dose distributions in clinical treatment plans and quality assurances. By specifying the acceptable dose and distance‐to‐agreement criteria, the method provides quantitative measurement of the agreement between the reference and evaluation dose distributions. The value indicates the acceptability. In regions where , the predefined criterion is satisfied and thus the agreement is acceptable; otherwise, the agreement fails. Although the concept of the method is not complicated and a quick naïve implementation is straightforward, an efficient and robust implementation is not trivial. Recent algorithms based on exhaustive searching within a maximum radius, the geometric Euclidean distance, and the table lookup method have been proposed to improve the computational time for multidimensional dose distributions. Motivated by the fact that the least searching time for finding a nearest neighbor can be an operation with a k‐d tree, where is the total number of the dose points, the authors propose an algorithm based on the k‐d tree for the evaluation in this work.Results:In the experiment, the authors found that the average k‐d tree construction time per reference point is, while the nearest neighbor searching time per evaluation point is proportional to , where is between 2 and 3 for two‐dimensional and three‐dimensional dose distributions, respectively.Conclusions:Comparing with other algorithms such as exhaustive search and sorted list, the k‐d tree algorithm for evaluation is much more efficient.
An investigation of 4D cone‐beam CT algorithms for slowly rotating scanners
Authors: Bergner Frank , Berkus Timo , Oelhafen Markus , Kunz Patrik , Pan Tinsu , Grimmer Rainer , Ritschl Ludwig , Kachelrieß Marc 
Published: August 2010

Purpose:To evaluate several algorithms for 4D cone‐beam computed tomography (4D CBCT) with slow rotating devices. 4D CBCT is used to perform phase‐correlated (PC) reconstructions of moving objects, such as breathing patients, for example. Such motion phase‐dependent reconstructions are especially useful for updating treatment plans in radiation therapy. The treatment plan can be registered more precisely to the motion of the tumor and, in consequence, the irradiation margins for the treatment, the so‐called planning target volume, can be reduced significantly.Methods:In the study, several algorithms were evaluated for kilovoltage cone‐beam CT units attached to linear particle accelerators. The reconstruction algorithms were the conventional PC reconstruction, the McKinnon–Bates (MKB) algorithm, the prior image constrained compressed sensing (PICCS) approach, a total variation minimization (ASD‐POCS) algorithm, and the autoadaptive phase correlation (AAPC) algorithm. For each algorithm, the same motion‐affected raw data were used, i.e., one simulated and one measured data set. The reconstruction results from the authors’ implementation of these algorithms were evaluated regarding their noise and artifact levels, their residual motion blur, and their computational complexity and convergence.Results:In general, it turned out that the residual motion blur was lowest in those algorithms which exclusively use data from a single motion phase. Algorithms using the image from the full data set as initialization or as a reference for the reconstruction were not capable of fully removing the motion blurring. The iterative algorithms, especially approaches based on total variation minimization, showed lower noise and artifact levels but were computationally complex. The conventional methods based on a single filtered backprojection were computationally inexpensive but suffered from higher noise and streak artifacts which limit the usability. In contrast, these methods showed to be less demanding and more predictable in their outcome than the total variation minimization based approaches.Conclusions:The reconstruction algorithms including at least one iterative step can reduce the 4D CBCT specific artifacts. Nevertheless, the algorithms that use the full data set, at least for initialization, such as MKB and PICCS in the authors’ implementation, are only a trade‐off and may not fully achieve the optimal temporal resolution. A predictable image quality as seen in conventional reconstruction methods, i.e., without total variation minimization, is a desirable property for reconstruction algorithms. Fast, iterative approaches such as the MKB can therefore be seen as a suitable tradeoff.
Feasibility of high temporal resolution breast DCE‐MRI using compressed sensing theory
Authors: Wang Haoyu , Miao Yanwei , Zhou Kun , Yu Yanming , Bao Shanglian , He Qiang , Dai Yongming , Xuan Stephanie Y. , Tarabishy Bisher , Ye Yongquan , Hu Jiani 
Published: August 2010

Purpose:To investigate the feasibility of high temporal resolution breast DCE‐MRI using compressed sensing theory.Methods:Two experiments were designed to investigate the feasibility of using reference image based compressed sensing (RICS) technique in DCE‐MRI of the breast. The first experiment examined the capability of RICS to faithfully reconstruct uptake curves using undersampled data sets extracted from fully sampled clinical breast DCE‐MRI data. An average approach and an approach using motion estimation and motion compensation (ME/MC) were implemented to obtain reference images and to evaluate their efficacy in reducing motion related effects. The second experiment, anin vitro phantom study, tested the feasibility of RICS for improving temporal resolution without degrading the spatial resolution.Results:For the uptake‐curve reconstruction experiment, there was a high correlation between uptake curves reconstructed from fully sampled data by Fourier transform and from undersampled data by RICS, indicating high similarity between them. The mean Pearson correlation coefficients for RICS with the ME/MC approach and RICS with the average approach were and , respectively. The comparisons of final reconstruction results between RICS with the average approach and RICS with the ME/MC approach suggested that the latter was superior to the former in reducing motion related effects. For the in vitro experiment, compared to the fully sampled method, RICS improved the temporal resolution by an acceleration factor of 10 without degrading the spatial resolution.Conclusions:The preliminary study demonstrates the feasibility of RICS for faithfully reconstructing uptake curves and improving temporal resolution of breast DCE‐MRI without degrading the spatial resolution.
A solid‐state amorphous selenium avalanche technology for low photon flux imaging applications
Authors: Wronski M. M. , Zhao W. , Reznik A. , Tanioka K. , DeCrescenzo G. , Rowlands J. A. 
Published: August 2010

Purpose:The feasibility of a practical solid‐state technology for low photon flux imaging applications was investigated. The technology is based on an amorphous selenium photoreceptor with a voltage‐controlled avalanche multiplication gain. If this photoreceptor can provide sufficient internal gain, it will be useful for an extensive range of diagnostic imaging systems.Methods:The avalanche photoreceptor under investigation is referred to as HARP‐DRL. This is a novel concept in which a high‐gain avalanche rushing photoconductor (HARP) is integrated with a distributed resistance layer (DRL) and sandwiched between two electrodes. The avalanche gain and leakage current characteristics of this photoreceptor were measured.Results:HARP‐DRL has been found to sustain very high electric field strengths without electrical breakdown. It has shown avalanche multiplication gains as high as and a very low leakage current .Conclusions:This is the first experimental demonstration of a solid‐state amorphous photoreceptor which provides sufficient internal avalanche gain for photon counting and photon starved imaging applications.
In VitroMitochondrial Toxicity of Metacavir, a New Nucleoside Reverse Transcriptase Inhibitor for Treatment of Hepatitis B Virus
Authors: Zhang Pinghu , Zhang Luyong , Jiang Zhenzhou , Wang Tao , Chen Hongkui , Xiong Yating , Li Zhan 
Published: August 2010

ABSTRACTTherapy with nucleoside reverse transcriptase inhibitors (NRTIs) can be associated with mitochondrial toxicity.In vitrostudies have been used to predict the predisposition for and characterize the mechanisms causing mitochondrial toxicity. Metacavir (PNA) is a novel synthetic nucleoside analog for oral administration with potent and specific antiviral activity against hepatitis B virus (HBV). We assessed the potential for mitochondrial toxicity of PNA in long-term cultures of HepG2 hepatoma cells by measuring mitochondrial function (through lactate secretion), levels of mitochondrial DNA (mtDNA), and the activities of respiratory-chain complexes I to IV. Exposure of HepG2 cells to PNA at concentrations up to 50 μM for 15 days resulted in no deleterious effect on cell proliferation, levels of lactate or mtDNA, or enzyme activities of respiratory-chain complexes I to IV. In contrast, dideoxycytosine at 10 μM and zidovudine at 50 μM have significant effects on cell proliferation, levels of lactate and mtDNA, and enzyme activities of respiratory-chain complexes I to IV. However, PNA at a supratherapeutic concentration of 250 μM could result in significant alterations in the levels of mtDNA and the activities of respiratory-chain complex enzymes, revealing evidence of the potential mitochondrial toxicity of PNA. In summary, thesein vitroresults indicate that the potential for PNA to interfere with mitochondrial functions is low.