bluuebunny/crossref_metadata_2025_split huggingface dataset:
External infiltrating lipoma in a two‐week‐old foal: Computed tomographic evaluation for the assessment of the extension and invasiveness of the tumour
Authors: Rebsamen E. , Gygax D. , Dennler M. , Jud R. , Kummer M. 
Published: September 2010

SummaryExternal lipoma is a benign subcutaneous and submucosal tumour and usually is of little clinical concern. Occasionally, the lipoma may invade muscles, the infiltrating lipoma. Complete surgical excision is mandatory because of the infiltrative nature and potentially high incidence of recurrence after inadequate surgery. In order to assess the extension of the tumour accurately, computed tomographic examination is indicated.
Multiple‐stepped Zeeman field offset method applied in acquiring enhanced resolution spin‐echo electron paramagnetic resonance images
Authors: Seifi Payam , Epel Boris , Mailer Colin , Halpern Howard J. 
Published: September 2010

Purpose: Electron paramagnetic resonance (EPR) imaging techniques provide quantitative in vivo oxygen distribution images. Time‐domain techniques including electron spin echo (ESE) imaging have been under study in recent years for their robustness and promising new features. One of the limitations of ESE imaging addressed here is the finite acquisition frequency bandwidth, which imposes limits on applied magnetic field gradients and the resulting image spatial resolution. In order to improve the image spatial resolution, we have extended the effective frequency bandwidth of the imaging system by acquiring projections at multiple Zeeman magnetic field offsets and combining them to restore complete projections obtained with more uniform frequency response, resulting in higher quality images.Methods: In multiple‐stepped magnetic field or multi‐B scheme, every projection of the three dimensional object is acquired at different main or Zeeman magnetic field (B) offset values. The data from field offset steps are combined, normalizing to the imaging system frequency acquisition window function, a sensitivity profile, to restore the complete projection. A multipurpose pulse EPR imager and phantoms containing the same type of spin probe (OX063H) used in routine animal imaging were also used in this study.Results: Using the multi‐B method, we were able to acquire images of our phantoms with enhanced spatial resolution compared to the conventional ESE approach. Compared to standard single‐B ESE images, the resolutions of multi‐B images were superior using a high spatial‐resolution regime. Image artifacts present in high‐gradient single‐B ESE images are also substantially reduced using in the multi‐B scheme.Conclusions: The multi‐B method is less susceptible to instrumental limitations for larger gradient fields and acquiring images with higher spatial resolution better overall quality, without the need to alter the existing pulse ESE image acquisition hardware.
Deformable left‐ventricle mesh model for motion‐compensated filtering in cardiac gated SPECT
Authors: Marin Thibault , Brankov Jovan G. 
Published: September 2010

Purpose:In this article, the authors present a motion‐compensated spatiotemporal processing algorithm to reduce noise in cardiac gated SPECT. Cardiac gated SPECT data are particularly noisy because the acquired photon data are divided among a number of time frames (gates). Classical spatial reconstruction and processing techniques offer noise reduction but they are usually applied on each frame separately and fail to utilize temporal correlation between frames.Methods:In this work, the authors present a motion‐compensated spatiotemporal postreconstruction filter offering noise reduction while minimizing motion‐blur artifacts. The proposed method can be used regardless of the type of image‐reconstruction method (analytical or iterative). The between‐frame volumetric myocardium motion is estimated using a deformable mesh model based on the model of the myocardial surfaces. The estimated motion is then used to perform spatiotemporal filtering along the motion trajectories. Both the motion‐estimation and spatiotemporal filtering methods seek to maintain the wall brightening seen during cardiac contraction. Wall brightening is caused by the partial volume effect, which is usually viewed as an artifact; however, wall brightening is a useful signature in clinical practice because it allows the clinician to visualize wall thickening. Therefore, the authors seek in their method to preserve the brightening effect.Results:The authors find that the proposed method offers better noise reduction than several existing methods as quantitatively evaluated by signal‐to‐noise ratio, bias‐variance plots, and ejection fraction analysis as well as on tested clinical data.Conclusions:The proposed method mitigates for noise in cardiac gated SPECT images using a postreconstruction motion‐compensated filtering approach. Visual as well as quantitative evaluation show considerable improvement in image quality.
Monte Carlo simulation of the effect of miniphantom on in‐air output ratio
Authors: Li Jun , Zhu Timothy C. 
Published: September 2010

Purpose:The aim of the study was to quantify the effect of miniphantoms on in‐air output ratio measurements, i.e., to determine correction factors for in‐air output ratio.Methods:Monte Carlo (MC) simulations were performed to simulate in‐air output ratio measurements by using miniphantoms made of various materials (PMMA, graphite, copper, brass, and lead) and with different longitudinal thicknesses or depths in photon beams of 6 and 15 MV, respectively, and with collimator settings ranging from to . EGSnrc and BEAMnrc (2007) software packages were used. Photon energy spectra corresponding to the collimator settings were obtained from BEAMnrc code simulations on a linear accelerator and were used to quantify the components of in‐air output ratio correction factors, i.e., attenuation, mass energy absorption, and phantom scatter correction factors. In‐air output ratio correction factors as functions of miniphantom material, miniphantom longitudinal thickness, and collimator setting were calculated and compared to a previous experimental study.Results:The in‐air output ratio correction factors increase with collimator opening and miniphantom longitudinal thickness for all the materials and for both energies. At small longitudinal thicknesses, the in‐air output ratio correction factors for PMMA and graphite are close to 1. The maximum magnitudes of the in‐air output ratio correction factors occur at the largest collimator setting and the largest miniphantom longitudinal thickness : for 6 MV and for 15 MV, respectively. The MC simulations of the in‐air output ratio correction factor confirm the previous experimental study.Conclusions:The study has verified that a correction factor for in‐air output ratio can be obtained as a product of attenuation correction factor, mass energy absorption correction factor, and phantom scatter correction factor. The correction factors obtained in the present study can be used in studies involving in‐air output ratio measurements using miniphantoms.
A new fast and fully automated software based algorithm for extracting respiratory signal from raw PET data and its comparison to other methods
Authors: Kesner Adam Leon , Kuntner Claudia 
Published: September 2010

Purpose:Respiratory gating in PET is an approach used to minimize the negative effects of respiratory motion on spatial resolution. It is based on an initial determination of a patient's respiratory movements during a scan, typically using hardware based systems. In recent years, several fully automated databased algorithms have been presented for extracting a respiratory signal directly from PET data, providing a very practical strategy for implementing gating in the clinic. In this work, a new method is presented for extracting a respiratory signal from raw PET sinogram data and compared to previously presented automated techniques.Methods:The acquisition of respiratory signal from PET data in the newly proposed method is based on rebinning the sinogram data into smaller data structures and then analyzing the time activity behavior in the elements of these structures. From this analysis, a 1D respiratory trace is produced, analogous to a hardware derived respiratory trace. To assess the accuracy of this fully automated method, respiratory signal was extracted from a collection of 22 clinical FDG‐PET scans using this method, and compared to signal derived from several other software based methods as well as a signal derived from a hardware system.Results:The method presented required approximately 9 min of processing time for each 10 min scan (using a single 2.67 GHz processor), which in theory can be accomplished while the scan is being acquired and therefore allowing a real‐time respiratory signal acquisition. Using the mean correlation between the software based and hardware based respiratory traces, the optimal parameters were determined for the presented algorithm. The mean/median/range of correlations for the set of scans when using the optimal parameters was found to be 0.58/0.68/0.07–0.86. The speed of this method was within the range of real‐time while the accuracy surpassed the most accurate of the previously presented algorithms.Conclusions:PET data inherently contains information about patient motion; information that is not currently being utilized. We have shown that a respiratory signal can be extracted from raw PET data in potentially real‐time and in a fully automated manner. This signal correlates well with hardware based signal for a large percentage of scans, and avoids the efforts and complications associated with hardware. The proposed method to extract a respiratory signal can be implemented on existing scanners and, if properly integrated, can be applied without changes to routine clinical procedures.
Model‐based calculations of off‐axis ratio of conic beams for a dedicated 6 MV radiosurgery unit
Authors: Yang J. N. , Ding X. , Du W. , Pino R. 
Published: September 2010

Purpose:Because the small‐radius photon beams shaped by cones in stereotactic radiosurgery (SRS) lack lateral electronic equilibrium and a detector's finite cross section, direct experimental measurement of dosimetric data for these beams can be subject to large uncertainties. As the dose calculation accuracy of a treatment planning system largely depends on how well the dosimetric data are measured during the machine's commissioning, there is a critical need for an independent method to validate measured results. Therefore, the authors studied the model‐based calculation as an approach to validate measured off‐axis ratios (OARs).Methods:The authors previously used a two‐component analytical model to calculate central axis dose and associated dosimetric data (e.g., scatter factors and tissue‐maximum ratio) in a water phantom and found excellent agreement between the calculated and the measured central axis doses for small 6 MV SRS conic beams. The model was based on that of Nizin and Mooij [“An approximation of central‐axis absorbed dose in narrow photon beams,” Med. Phys. 24, 1775–1780 (1997)] but was extended to account for apparent attenuation, spectral differences between broad and narrow beams, and the need for stricter scatter dose calculations for clinical beams. In this study, the authors applied Clarkson integration to this model to calculate OARs for conic beams. OARs were calculated for selected cones with radii from 0.2 to 1.0 cm. To allow comparisons, the authors also directly measured OARs using stereotactic diode (SFD), microchamber, and film dosimetry techniques. The calculated results were machine‐specific and independent of direct measurement data for these beams.Results:For these conic beams, the calculated OARs were in excellent agreement with the data measured using an SFD. The discrepancies in radii and in 80%–20% penumbra were within 0.01 cm, respectively. Using SFD‐measured OARs as the reference data, the authors found that the calculated OARs were more accurate than those measured with a microchamber or film dosimetry.Conclusions:The model produces sufficiently accurate conic beam dosimetric data that can be used to validate direct measurement results for such beams.
Dose optimization in pediatric cardiac x‐ray imaging
Authors: Gislason Amber J. , Davies Andrew G. , Cowen Arnold R. 
Published: September 2010

Purpose:The aim of this research was to explore x‐ray beam parameters with intent to optimize pediatric x‐ray settings in the cardiac catheterization laboratory. This study examined the effects of peak x‐ray tube voltage (kVp) and of copper (Cu) x‐ray beam filtration independently on the image quality to dose balance for pediatric patient sizes. The impact of antiscatter grid removal on the image quality to dose balance was also investigated.Methods:Image sequences of polymethyl methacrylate phantoms approximating chest sizes typical of pediatric patients were captured using a modern flat‐panel receptor based x‐ray imaging system. Tin was used to simulate iodine‐based contrast medium used in clinical procedures. Measurements of tin detail contrast and flat field image noise provided the contrast to noise ratio. Entrance surface dose (ESD) and effective dose (E) measurements were obtained to calculate the figure of merit (FOM),, which evaluated the dose efficiency of the x‐ray parameters investigated. The kVp, tube current (mA), and pulse duration were set manually by overriding the system's automatic dose control mechanisms. Images were captured with 0, 0.1, 0.25, 0.4, and 0.9 mm added Cu filtration, for 50, 55, 60, 65, and 70 kVp with the antiscatter grid in place, and then with it removed.Results:For a given phantom thickness, as the Cu filter thickness was increased, lower kVp was favored. Examining kVp alone, lower values were generally favored, more so for thinner phantoms. Considering ESD, the 8.5 cm phantom had the highest FOM at 50 kVp using 0.4 mm of Cu filtration. The 12 cm phantom had the highest FOM at 55 kVp using 0.9 mm Cu, and the 16 cm phantom had highest FOM at 55 kVp using 0.4 mm Cu. With regard to E, the 8.5 and 12 cm phantoms had the highest FOM at 50 kVp using 0.4 mm of Cu filtration, and the 16 cm phantom had the highest FOM at 50 kVp using 0.25 mm Cu. Antiscatter grid removal improved the FOM for a given set of x‐ray conditions. Under aforesaid optimal settings, the 8.5 cm phantom FOM improved by 24% and 33% for ESD and E, respectively. Corresponding improvements were 26% and 24% for the 12 cm phantom and 6% and 15% for the 16 cm phantom.Conclusions:For pediatric patients, using 0.25–0.9 mm Cu filtration in the x‐ray beam while maintaining 50–55 kVp, depending on patient size, provided optimal x‐ray image quality to dose ratios. These settings, adjusted for x‐ray tube loading limits and clinically acceptable image quality, should provide a useful strategy for optimizing iodine contrast agent based cardiac x‐ray imaging. Removing the antiscatter grid improved the FOM for the 8.5 and 12 cm phantoms, therefore grid removal is recommended for younger children. Improvement for the 16 cm phantom declined into the estimated margin of error for the FOM; the need for grid removal for older children would depend on practical feasibility in the clinical environment.
Monte Carlo calculated TG‐60 dosimetry parameters for the emitter brachytherapy source
Authors: Sadeghi Mahdi , Taghdiri Fatemeh , Hamed Hosseini S. , Tenreiro Claudio 
Published: September 2010

Purpose:The formalism recommended by Task Group 60 (TG‐60) of the American Association of Physicists in Medicine (AAPM) is applicable for sources. Radioactive biocompatible and biodegradable glass seed without encapsulation is a emitter radionuclide with a short half‐life and delivers a high dose rate to the tumor in the millimeter range. This study presents the results of Monte Carlo calculations of the dosimetric parameters for the brachytherapy source.Methods:Version 5 of the (MCNP) Monte Carlo radiation transport code was used to calculate two‐dimensional dose distributions around the source. The dosimetric parameters of AAPM TG‐60 recommendations including the reference dose rate, the radial dose function, the anisotropy function, and the one‐dimensional anisotropy function were obtained.Results:The dose rate value at the reference point was estimated to be. Due to the low energy beta emitted from sources, the dose fall‐off profile is sharper than the other beta emitter sources. The calculated dosimetric parameters in this study are compared to several beta and photon emitting seeds.Conclusions:The results show the advantage of the source in comparison with the other sources because of the rapid dose fall‐off of beta ray and high dose rate at the short distances of the seed. The results would be helpful in the development of the radioactive implants using seeds for the brachytherapy treatment.
Monte Carlo evaluation of scatter mitigation strategies in cone‐beam CT
Authors: Lazos Dimitrios , Williamson Jeffrey F. 
Published: September 2010

Purpose:To investigate the efficacy of two widely used scatter mitigation methods: antiscatter grids (ASGs) and beam modulating with bowtie filters (BTFs), in combination with subtractive scatter correction or zeroth order normalization phantom calibration, for improving image noise, contrast, contrast‐to‐noise ratio (CNR), and image uniformity for on‐board cone‐beam CT (CBCT) imaging systems used for image‐guided radiation therapy.Methods:PTRAN Monte Carlo CBCT x‐ray projections of head and pelvic phantoms were calculated for combinations of beam‐modulation and scatter rejection methods and images were reconstructed by in‐house developed software. In addition, a simple one‐dimensional analytic model was developed to predict scatter‐to‐primary ratio (SPR) and CNR as a function of cylindrical phantom thickness, ASG transmission, and beam modulation with bow‐tie filters.Results:ASGs were found to have slightly negative or no effect on head phantom image CNR and to modestly improve CNR (10%–20%) in pelvic phantom images. However, scatter subtraction and norm‐phantom calibration perform better when applied on data acquired with ASGs. Scatter subtraction improves CT number accuracy, but increases noise, and in high SPR/low primary‐photon transmission scenarios can dramatically reduce CNR and introduce streaking artifacts. The BTF is found to reduce SPR and image noise, resulting in a better trade‐off between CNR and imaging dose, but introduces a circular band artifact.Conclusions:Our study shows that ASGs have a modest positive impact in pelvic scans and negative in head scans, scatter subtraction improves the HU accuracy but reduces CNR, while BTF has a clearly positive effect.
Dosimetric variation due to the photon beam energy in the small‐animal irradiation: A Monte Carlo study
Authors: Chow James C. L. , Leung Michael K. K. , Lindsay Patricia E. , Jaffray David A. 
Published: September 2010

Purpose:The impact of photon beam energy and tissue heterogeneities on dose distributions and dosimetric characteristics such as point dose, mean dose, and maximum dose was investigated in the context of small‐animal irradiation using Monte Carlo simulations based on the EGSnrc code.Methods:Three Monte Carlo mouse phantoms, namely, heterogeneous, homogeneous, and bone homogeneous were generated based on the same mouse computed tomography image set. These phantoms were generated by overriding the tissue type of none of the voxels (heterogeneous), all voxels (homogeneous), and only the bone voxels (bone homogeneous) to that of soft tissue. Phase space files of the 100 and 225 kVp photon beams based on a small‐animal irradiator (XRad225Cx, Precision X‐Ray Inc., North Branford, CT) were generated using BEAMnrc. A 360° photon arc was simulated and three‐dimensional (3D) dose calculations were carried out using the DOSXYZnrc code through DOSCTP in the above three phantoms. For comparison, the 3D dose distributions, dose profiles, mean, maximum, and point doses at different locations such as the isocenter, lung, rib, and spine were determined in the three phantoms.Results:The dose gradient resulting from the 225 kVp arc was found to be steeper than for the 100 kVp arc. The mean dose was found to be 1.29 and 1.14 times higher for the heterogeneous phantom when compared to the mean dose in the homogeneous phantom using the 100 and 225 kVp photon arcs, respectively. The bone doses (rib and spine) in the heterogeneous mouse phantom were about five (100 kVp) and three (225 kVp) times higher when compared to the homogeneous phantom. However, the lung dose did not vary significantly between the heterogeneous, homogeneous, and bone homogeneous phantom for the 225 kVp compared to the 100 kVp photon beams.Conclusions:A significant bone dose enhancement was found when the 100 and 225 kVp photon beams were used in small‐animal irradiation. This dosimetric effect, due to the presence of the bone heterogeneity, was more significant than that due to the lung heterogeneity. Hence, for kV photon energies of the range used in small‐animal irradiation, the increase of the mean and bone dose due to the photoelectric effect could be a dosimetric concern.
Monte Carlo characterization of skin doses in 6 MV transverse field MRI‐linac systems: Effect of field size, surface orientation, magnetic field strength, and exit bolus
Authors: Oborn B. M. , Metcalfe P. E. , Butson M. J. , Rosenfeld A. B. 
Published: September 2010

Purpose:The main focus of this work is to continue investigations into the Monte Carlo predicted skin doses seen in MRI‐guided radiotherapy. In particular, the authors aim to characterize the skin doses over a larger range of magnetic field strength and x‐ray field size than in the current literature. The effect of surface orientation on both the entry and exit sides is also studied. Finally, the use of exit bolus is also investigated for minimizing the negative effects of the electron return effect (ERE) on the exit skin dose.Methods:High resolutionGEANT4 Monte Carlo simulations of a water phantom exposed to a 6 MV x‐ray beam (Varian 2100C) have been performed. Transverse magnetic fields of strengths between 0 and 3 T have been applied to a phantom. This phantom is also altered to have variable entry and exit surfaces with respect to the beam central axis and they range from −75° to . The exit bolus simulated is a 1 cm thick (water equivalent) slab located on the beam exit side.Results:On the entry side, significant skin doses at the beam central axis are reported for large positive surface angles and strong magnetic fields. However, over the entry surface angle range of −30° to −60°, the entry skin dose is comparable to or less than the zero magnetic field skin dose, regardless of magnetic field strength and field size. On the exit side, moderate to high central axis skin dose increases are expected except at large positive surface angles. For exit bolus of 1 cm thickness, the central axis exit skin dose becomes an almost consistent value regardless of magnetic field strength or exit surface angle. This is due to the almost complete absorption of the ERE electrons by the bolus.Conclusions:There is an ideal entry angle range of −30° to −60° where entry skin dose is comparable to or less than the zero magnetic field skin dose. Other than this, the entry skin dose increases are significant, especially at higher magnetic fields. On the exit side there is mostly moderate to high skin dose increases for 0.2–3 T with the only exception being large positive angles. Exit bolus of 1 cm thickness will have a significant impact on lowering such exit skin dose increases that occur as a result of the ERE.