bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐I‐14: Avoiding a Common Pitfall in Performing MTF Measurements with High Resolution Kernels
Authors: Rubert N , Szczykutowicz T , Ranallo F 
Published: June 2015

Purpose:The modulation transfer function (MTF) is frequently used to assess high contrast spatial resolution for routine quality assurance in CT imaging. High resolution reconstruction kernels provide new challenges for MTF estimation. The purpose of this work is to demonstrate the effect of CT number saturation on MTF estimation.Methods:A small bead contained in a CATPHAN 600 phantom was imaged at two different slice thicknesses, 2.5 mm and 5.0 mm, on a GE CT 750 HD scanner using an HD Bone Plus reconstruction algorithm in a high resolution scan mode. The resulting images were 2‐D point spread functions (PSF's), which were integrated to create line spread functions, and Fourier transformed to yield MTF's.Results:Using a high resolution reconstruction algorithm and the 2.5 mm slice thickness, it was found that the CT number for several pixels in the PSF reached 3071, the maximum value allowed for this system. Using the same algorithm with the 5.0 mm slice, no pixel values reached the CT number limit. Comparing the two MTF's it was found that the MTF affected by CT number saturation had a 10% cut‐off that was shifted downwards, from 15.6 lp/cm to 14.9 lp/cm. Additionally, the MTF affected by CT number saturation exhibited a spurious lobe beyond the true limiting resolution of the CT scanner.Conclusion:The downwards shift in MTF cut‐off is a subtle but important effect to consider when attempting to measure MTF for routine quality assurance. While a downwards shift in MTF cut‐off is not easily identified, CT number saturation is readily identified in by examining the entire MTF curve and identifying the spurious lobe produced. CT number saturation is an important consideration when examining test objects to be used for MTF estimation when the algorithm being used is high resolution.This work was supported by the AAPM grant for Diagnostic Imaging Residencies
SU‐E‐I‐17: Evaluation of Commercially Available Extension Plates for the ACR CT Accreditation Phantom
Authors: Greene‐Donnelly K , Ogden K 
Published: June 2015

Purpose:To evaluate the impact of commercially available extension plates on Hounsfield Unit (HU) values in the ACR CT accreditation phantom (Model 464, Gammex Inc., Middleton, Wi). The extension plates are intended to improve water HU values in scanners where the traditional solution involves scanning the phantom with an adjacent water or CTDI phantom.Methods:The Model 464 phantom was scanned on 9 different CT scanners at 8 separate sites representing 16 and 64 slice MDCT technology from four CT manufacturers. The phantom was scanned with and without the extension plates (Gammex 464 EXTPLT‐KIT) in helical and axial modes. A water phantom was also scanned to verify water HU calibration. Technique was 120 kV tube potential, 350 mAs, and 210 mm display field of view. Slice thickness and reconstruction algorithm were based on site clinical protocols. The widest available beam collimation was used. Regions of interest were drawn on the HU test objects in Module 1 of the phantom and mean values recorded.Results:For all axial mode scans, water HU values were within limits with or without the extension plates. For two scanners (both Lightspeed VCT, GE Medical Systems, Waukesha WI), axial mode bone HU values were above the specified range both with and without the extension plates though they were closer to the specified range with the plates installed. In helical scan mode, two scanners (both GE Lightspeed VCT) had water HU values above the specified range without the plates installed. With the plates installed, the water HU values were within range for all scanners in all scan modes.Conclusion:Using the plates, the Lightspeed VCT scanners passed the water HU test when scanning in helical mode. The benefit of the extension plates was evident in helical mode scanning with GE scanners using a nominal 4 cm beam.Disclosure: The extension plates evaluated in this work were provided free of charge to the authors. The authors have no other financial interest in Gammex Inc.
SU‐E‐I‐23: A General KV Constrained Optimization of CNR for CT Abdominal Imaging
Authors: Weir V , Zhang J 
Published: June 2015

Purpose:While Tube current modulation has been well accepted for CT dose reduction, kV adjusting in clinical settings is still at its early stage. This is mainly due to the limited kV options of most current CT scanners. kV adjusting can potentially reduce radiation dose and optimize image quality. This study is to optimize CT abdomen imaging acquisition based on the assumption of a continuous kV, with the goal to provide the best contrast to noise ratio (CNR).Methods:For a given dose (CTDIvol) level, the CNRs at different kV and pitches were measured with an ACR GAMMEX phantom. The phantom was scanned in a Siemens Sensation 64 scanner and a GE VCT 64 scanner. A constrained mathematical optimization was used to find the kV which led to the highest CNR for the anatomy and pitch setting. Parametric equations were obtained from polynomial fitting of plots of kVs vs CNRs. A suitable constraint region for optimization was chosen. Subsequent optimization yielded a peak CNR at a particular kV for different collimations and pitch setting.Results:The constrained mathematical optimization approach yields kV of 114.83 and 113.46, with CNRs of 1.27 and 1.11 at the pitch of 1.2 and 1.4, respectively, for the Siemens Sensation 64 scanner with the collimation of 32 × 0.625mm. An optimized kV of 134.25 and 1.51 CNR is obtained for a GE VCT 64 slice scanner with a collimation of 32 × 0.625mm and a pitch of 0.969. At 0.516 pitch and 32 × 0.625 mm an optimized kV of 133.75 and a CNR of 1.14 was found for the GE VCT 64 slice scanner.Conclusion:CNR in CT image acquisition can be further optimized with a continuous kV option instead of current discrete or fixed kV settings. A continuous kV option is a key for individualized CT protocols.
SU‐E‐I‐87: Calibrating Cherenkov Emission to Match Superficial Dose in Tissue
Authors: Zhang R , Glaser A , Gladstone D , Pogue B 
Published: June 2015

Purpose:Through Monte Carlo simulations and phantom studies, the dominant factors affecting the calibration of superficial Cherenkov intensity to absolute surface dose was investigated, including tissue optical properties, curvatures, beam properties and imaging angle.Methods:The phasespace files for the TrueBeam system from Varian were used in GAMOS (a GEANT4 based Monte Carlo simulation toolkit) to simulate surface emission Cherenkov signals and the correlated deposited dose. The parameters examined were: i) different tissue optical properties (skin color from light to dark), ii) beam types (X‐ray and electron beam), iii) beam energies, iv) thickness of tissues (2.5 cm to 20 cm), v) SSD (80 cm to 120 cm), vi) field sizes (0.5×0.5 cm2 to 20×20 cm2), vii) entrance/exit sides, viii) curvatures (cylinders with diameters from 2.5 cm to 20cm) and ix) imaging angles (0 to 90 degrees). In a specific case, for any Cherenkov photon emitted from the surface, the original position and direction, final position and direction and energy were recorded. Similar experimental measurements were taken in a range of the most pertinent parameters using tissue phantoms.Results:Combining the dose distribution and sampling sensitivity of Cherenkov emission, quantitatively accurate calibration factors (the amount of radiation dose represented by a single Cherenkov photon) were calculated. The data showed relatively large dependence upon different optical properties, curvature, entrance/exit and beam types. For a diffusive surface, the calibration factor was insensitive to imaging angles smaller than 60 degrees. Normalization with the reflectance image was experimentally validated as a simple and accurate method for calibrations of different optical properties.Conclusion:This study sheds light on how and to what extent different conditions affect the calibration from Cherenkov intensity to absolute superficial dose and provides practical solutions to allow quantitative Cherenkov imaging to be used as a dose surrogate for imaging.
SU‐E‐I‐88: The Effect of System Dead Time On Real‐Time Plastic and GOS Based Fiber‐Optic Dosimetry Systems
Authors: Hoerner M , Hintenlang D 
Published: June 2015

Purpose:A methodology is presented to correct for measurement inaccuracies at high detector count rates using a plastic and GOS scintillation fibers coupled to a photomultiplier tube with digital readout. This system allows temporal acquisition and manipulation of measured data.Methods:The detection system used was a plastic scintillator and a separate gadolinium scintillator, both (0.5 diameter) coupled to an optical fiber with a Hamamatsu photon counter with a built‐in microcontroller and digital interface. Count rate performance of the system was evaluated using the nonparalzable detector model. Detector response was investigated across multiple radiation sources including: orthovoltage x‐ray system, colbat‐60 gamma rays, proton therapy beam, and a diagnostic radiography x‐ray tube. The dead time parameter was calculated by measuring the count rate of the system at different exposure rates using a reference detector.Results:The system dead time was evaluated for the following sources of radiation used clinically: diagnostic energy x‐rays, cobalt‐60 gamma rays, orthovoltage xrays, particle proton accelerator, and megavoltage x‐rays. It was found that dead time increased significantly when exposing the detector to sources capable of generating Cerenkov radiation, all of the sources sans the diagnostic x‐rays, with increasing prominence at higher photon energies. Percent depth dose curves generated by a dedicated ionization chamber and compared to the detection system demonstrated that correcting for dead time improves accuracy. On most sources, nonparalzable model fit provided an improved system response.Conclusion:Overall, the system dead time was variable across the investigated radiation particles and energies. It was demonstrated that the system response accuracy was greatly improved by correcting for dead time effects. Cerenkov radiation plays a significant role in the increase in the system dead time through transient absorption effects attributed to electron hole‐pair creations within the optical waveguide.
SU‐E‐J‐02: Towards Real‐Time PRFS Thermometry Using Simultaneous MultiSlice Acquisitions
Authors: Borman P , Crijns S , Bos C , Moonen C , Raaymakers B 
Published: June 2015

Purpose:To speed up PRFS thermometry using Simultaneous MultiSlice acquisitions (SMS) with a focus on HIFU treatments, where temperatures at multiple locations such as near field, far field and focus need to be monitored in real‐time.Methods:The phantom is a 2% agar 2% silica gel. The gel was heated using an ultrasound transducer operating at 1.2MHz with a focus of 8mm, delivering 60W for 60 seconds. The temperature is measured with two optical probes; one at the focus and one 4cm above that. The probes are used to compare the PRFS thermometry results with. The images are made on a 1.5T Philips Achieva scanner with a SMS GRE acquisition using CAIPIRINHA: two slices are excited simultaneously with a Multi‐Band pulse and one slice is shifted one half FOV, resulting in minimal overlap and optimal sensitivity.The images are reconstructed offline in MATLAB using ReconFrame (GyroTools). The temperature is calculated from the PRFS and averaged over an ROI at the focus. The SMS acquisition has acceleration factor 2 and can be combined with SENSE. Results are compared to M2D acquisitions with SENSE factors 1 and 2. Results: The SMS temperature curves are in good qualitative agreement with the temperature curves of the probes. The difference is probably caused by the probes not being exactly at the focus. There is good agreement between the M2D and SMS curves, even though SMS scans have acceleration factor 2. We also showed that SMS can be combined with SENSE to achieve acceleration factor 3.Results:The SMS temperature curves are in good qualitative agreement with the temperature curves of the probes. The difference is probably caused by the probes not being exactly at the focus. There is good agreement between the M2D and SMS curves, even though SMS scans have acceleration factor 2. We also showed that SMS can be combined withSENSE to achieve acceleration factor 3. Conclusion: This work showsthatPRFSthermometry inmultiple slices can be accelerated by SMS techniques. We demonstrated that the temperature measured using SMS scans is in agreement with the M2D scans, while the dynamic scan time of the former is almost half of that of the latter.Conclusion:This work shows that PRFS thermometry in multiple slices can be accelerated by SMS techniques. We demonstrated that the temperature measured using SMS scans is in agreement with the M2D scans, while the dynamic scan time of the former is almost half of that of the latter.This work was funded by the SoRTS consortium
SU‐E‐J‐03: Characterization of the Precision and Accuracy of a New, Preclinical, MRI‐Guided Focused Ultrasound System for Image‐Guided Interventions in Small‐Bore, High‐Field Magnets
Authors: Ellens N , Farahani K 
Published: June 2015

Purpose:MRI‐guided focused ultrasound (MRgFUS) has many potential and realized applications including controlled heating and localized drug delivery. The development of many of these applications requires extensive preclinical work, much of it in small animal models. The goal of this study is to characterize the spatial targeting accuracy and reproducibility of a preclinical high field MRgFUS system for thermal ablation and drug delivery applications.Methods:The RK300 (FUS Instruments, Toronto, Canada) is a motorized, 2‐axis FUS positioning system suitable for small bore (72 mm), high‐field MRI systems. The accuracy of the system was assessed in three ways. First, the precision of the system was assessed by sonicating regular grids of 5 mm squares on polystyrene plates and comparing the resulting focal dimples to the intended pattern, thereby assessing the reproducibility and precision of the motion control alone. Second, the targeting accuracy was assessed by imaging a polystyrene plate with randomly drilled holes and replicating the hole pattern by sonicating the observed hole locations on intact polystyrene plates and comparing the results. Third, the practicallyrealizable accuracy and precision were assessed by comparing the locations of transcranial, FUS‐induced blood‐brain‐barrier disruption (BBBD) (observed through Gadolinium enhancement) to the intended targets in a retrospective analysis of animals sonicated for other experiments.Results:The evenly‐spaced grids indicated that the precision was 0.11 +/− 0.05 mm. When image‐guidance was included by targeting random locations, the accuracy was 0.5 +/− 0.2 mm. The effective accuracy in the four rodent brains assessed was 0.8 +/− 0.6 mm. In all cases, the error appeared normally distributed (p<0.05) in both orthogonal axes, though the left/right error was systematically greater than the superior/inferior error. Conclusions: The targeting accuracy of this device is sub‐millimeter, suitable for many preclinical applications including focused drug delivery and thermal therapy.Funding support provided by Philips Healthcare
SU‐E‐J‐24: Can Fiducial Marker‐Based Setup Using ExacTrac Be An Alternative to Soft Tissue‐Based Setup Using Cone‐Beam CT for Prostate IMRT?
Authors: Tanabe S , Utsunomiya S , Abe E , Satou H , Sakai H , Yamada T , Aoyama H 
Published: June 2015

Purpose:To assess an accuracy of fiducial maker‐based setup using ExacTrac (ExT‐based setup) as compared with soft tissue‐based setup using Cone‐beam CT (CBCT‐based setup) for patients with prostate cancer receiving intensity‐modulated radiation therapy (IMRT) for the purpose of investigating whether ExT‐based setup can be an alternative to CBCT‐based setup.Methods:The setup accuracy was analyzed prospectively for 7 prostate cancer patients with implanted three fiducial markers received IMRT. All patients were treated after CBCT‐based setup was performed and corresponding shifts were recorded. ExacTrac images were obtained before and after CBCT‐based setup. The fiducial marker‐based shifts were calculated based on those two images and recorded on the assumption that the setup correction was carried out by fiducial marker‐based auto correction. Mean and standard deviation of absolute differences and the correlation between CBCT and ExT shifts were estimated.Results:A total of 178 image dataset were analyzed. On the differences between CBCT and ExT shifts, 133 (75%) of 178 image dataset resulted in smaller differences than 3 mm in all dimensions. Mean differences in the anterior‐posterior (AP), superior‐inferior (SI), and left‐right (LR) dimensions were 1.8 ± 1.9 mm, 0.7 ± 1.9 mm, and 0.6 ± 0.8 mm, respectively. The percentages of shift agreements within ±3 mm were 76% for AP, 90% for SI, and 100% for LR. The Pearson coefficient of correlation for CBCT and ExT shifts were 0.80 for AP, 0.80 for SI, and 0.65 for LR.Conclusion:This work showed that the accuracy of ExT‐based setup was correlated with that of CBCT‐based setup, implying that ExT‐based setup has a potential ability to be an alternative to CBCT‐based setup. The further work is to specify the conditions that ExT‐based setup can provide the accuracy comparable to CBCT‐based setup.
SU‐E‐J‐26: A Novel Technique for Markerless Self‐Sorted 4D‐CBCT Using Patient Motion Modeling: A Feasibility Study
Authors: Zhang L , Zhang Y , Harris W , Yin F , Ren L 
Published: June 2015

Purpose:To develop an automatic markerless 4D‐CBCT projection sorting technique by using a patient respiratory motion model extracted from the planning 4D‐CT images.Methods:Each phase of onboard 4D‐CBCT is considered as a deformation of one phase of the prior planning 4D‐CT. The deformation field map (DFM) is represented as a linear combination of three major deformation patterns extracted from the planning 4D‐CT using principle component analysis (PCA). The coefficients of the PCA deformation patterns are solved by matching the digitally reconstructed radiograph (DRR) of the deformed volume to the onboard projection acquired. The PCA coefficients are solved for each single projection, and are used for phase sorting. Projections at the peaks of the Z direction coefficient are sorted as phase 1 and other projections are assigned into 10 phase bins by dividing phases equally between peaks. The 4D digital extended‐cardiac‐torso (XCAT) phantom was used to evaluate the proposed technique. Three scenarios were simulated, with different tumor motion amplitude (3cm to 2cm), tumor spatial shift (8mm SI), and tumor body motion phase shift (2 phases) from prior to on‐board images. Projections were simulated over 180 degree scan‐angle for the 4D‐XCAT. The percentage of accurately binned projections across entire dataset was calculated to represent the phase sorting accuracy.Results:With a changed tumor motion amplitude from 3cm to 2cm, markerless phase sorting accuracy was 100%. With a tumor phase shift of 2 phases w.r.t. body motion, the phase sorting accuracy was 100%. With a tumor spatial shift of 8mm in SI direction, phase sorting accuracy was 86.1%.Conclusion:The XCAT phantom simulation results demonstrated that it is feasible to use prior knowledge and motion modeling technique to achieve markerless 4D‐CBCT phase sorting.National Institutes of Health Grant No. R01‐CA184173 Varian Medical System
SU‐E‐J‐27: Shifting Multiple EPID Imager Layers to Improve Image Quality and Resolution in MV CBCT
Authors: Chen H , Rottmann J , Yip S , Morf D , Fueglistaller R , Star‐Lack J , Zentai G , Berbeco R 
Published: June 2015

Purpose:Vertical stacking of four conventional EPID layers can improve DQE for MV‐CBCT applications. We hypothesize that shifting each layer laterally by half a pixel relative to the layer above, will improve the contrast‐to‐noise ratio (CNR) and image resolution.Methods:For CNR assessment, a 20 cm diameter digital phantom with 8 inserts is created. The attenuation coefficient of the phantom is similar to lung at the average energy of a 6 MV photon beam. The inserts have attenuations 1, 2…8 times of lung. One of the inserts is close to soft tissue, resembling the case of a tumor in lung. For resolution assessment, a digital phantom featuring a bar pattern is created. The phantom has an attenuation coefficient similar to soft tissue and the bars have an attenuation coefficient of calcium sulfate. A 2 MeV photon beam is attenuated through these phantoms and hits each of the four stacked detector layers. Each successive layer is shifted by half a pixel in the × only, y only, and × and y (combined) directions, respectively. Blurring and statistical noise are added to the projections. Projections from one, two, three and four layers are used for reconstruction. CNR and image resolution are evaluated and compared.Results:When projections from multiple layers are combined for reconstruction, CNR increases with the number of layers involved. CNR in reconstructions from two, three and four layers are 1.4, 1.7 and 1.99 times that from one layer. The resolution from the shifted four layer detector is also improved from a single layer. In a comparison between one layer versus four layers in this preliminary study, the resolution from four shifted layers is at least 20% better.Conclusion:Layer‐shifting in a stacked EPID imager design enhances resolution as well as CNR for half scan MV‐CBCT.The project described was supported, in part, by a grant from Varian Medical Systems, Inc., and Award No. R01CA188446‐01 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health
SU‐E‐J‐32: Dosimetric Evaluation Based On Pre‐Treatment Cone Beam CT for Spine Stereotactic Body Radiotherapy: Does Region of Interest Focus Matter?
Authors: Magnelli A , Xia P 
Published: June 2015

Purpose:Spine stereotactic body radiotherapy requires very conformal dose distributions and precise delivery. Prior to treatment, a KV cone‐beam CT (KV‐CBCT) is registered to the planning CT to provide image‐guided positional corrections, which depend on selection of the region of interest (ROI) because of imperfect patient positioning and anatomical deformation. Our objective is to determine the dosimetric impact of ROI selections.Methods:Twelve patients were selected for this study with the treatment regions varied from C‐spine to T‐spine. For each patient, the KV‐CBCT was registered to the planning CT three times using distinct ROIs: one encompassing the entire patient, a large ROI containing large bony anatomy, and a small target‐focused ROI. Each registered CBCT volume, saved as an aligned dataset, was then sent to the planning system. The treated plan was applied to each dataset and dose was recalculated. The tumor dose coverage (percentage of target volume receiving prescription dose), maximum point dose to 0.03 cc of the spinal cord, and dose to 10% of the spinal cord volume (V10) for each alignment were compared to the original plan.Results:The average magnitude of tumor coverage deviation was 3.9%±5.8% with external contour, 1.5%±1.1% with large ROI, 1.3%±1.1% with small ROI. Spinal cord V10 deviation from plan was 6.6%±6.6% with external contour, 3.5%±3.1% with large ROI, and 1.2%±1.0% with small ROI. Spinal cord max point dose deviation from plan was: 12.2%±13.3% with external contour, 8.5%±8.4% with large ROI, and 3.7%±2.8% with small ROI.Conclusion:A small ROI focused on the target results in the smallest deviation from planned dose to target and cord although rotations at large distances from the targets were observed. It is recommended that image fusion during CBCT focus narrowly on the target volume to minimize dosimetric error. Improvement in patient setups may further reduce residual errors.