bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐FF‐I‐21: An Empirical Method for Lag Correction in Cone‐Beam CT
Authors: Mail N , Moseley D , Siewerdsen J , Jaffray D 
Published: July 2007

Purpose: Image lag degrades image quality in cone‐beam CT (CBCT), resulting in contrast reduction, lack of CT number accuracy and uniformity, and skin‐line artifacts. This work investigates the magnitude of such degradation and demonstrates a lag correction method based on measured data from a system for CBCT guidance of radiotherapy (Elekta Synergy XVI). Method and Materials: Image lag and its relationship with various parameters including signal strength, photon energy and frame number was investigated for a PerkinElmer (RID1640) flat‐panel imager. An empirical lag correction based on measurements of image lag was developed to manage lag artifacts. The CatPhan phantom within an irregular body annulus was used to demonstrate the magnitude of artifacts before and after correction. Each projection was corrected for lag effects by subtracting previous projections weighted by the magnitude of image lag. The subtraction of previous projections was limited up to 51 frames due to uncorrelated noise. The reconstructed images before and after correction were analyzed for skin‐line and radar type artifacts, CT♯ accuracy, uniformity and contrast of several inserts. Reconstructed images were transformed into polar coordinates for analysis. Results: Experimental results illustrate that the first frame lag of the imager is less than 2.3%, and is independent of the kVp value (70–120 kV) and pixel saturation (20–80%). Lag correction improves the skin‐line artifact and reduces radar artifact by 40%. Contrast enhances by 20% and improves the CT♯ accuracy for water by 2.5%. It improves water uniformity by 5% compared to the nominal images. Conclusion: Lag artifacts can be reduced by correction of the projection images. Lag correction is most important for high contrast and irregularly shaped objects. For a circularly shaped object, lag correction does not improve the skin‐line artifact but can be useful for soft‐tissue visibility adjacent to bony anatomy.This research is sponsored by Elekta.
SU‐FF‐I‐39: Development of Clinical Application Platform Using Digital Tomosynthesis for Target Localization
Authors: Yan H , Ren L , Godfrey D , Yin F 
Published: July 2007

Purpose: To develop a workstation for clinical application of digital tomosynthesis (DTS) for real‐time target localization. Specifically, to accelerate the reconstruction both digitally‐reconstructed radiograph (DRR) and DTS using ultra‐fast interpolation capability of graphics hardware. Method and Materials: The developed workstation for real‐time target localization using DTS technology includes image acquisition, image reconstruction, and image comparison. A critical step to implement this technology is its reconstruction speed, especially real‐time generation of reference DTSs which require DRRs. The new generation graphics hardware provides a fast implementation of image interpolation and allows the bi‐linear/tri‐linear interpolation and the other image operations to be accomplished within second. We implemented classical ray‐casting algorithm for 2D DRR and filtered back‐projection (FBP) algorithm for DTS reconstruction on graphics hardware based on OpenGL programming interface. Specifically, planning CT images and on‐board projection images were loaded into the memory of hardware and saved as textures which were projected onto frame‐buffer according to the given geometry of imaging system. The final images were generated by blending multiple textures projected onto the frame‐buffer. Difference images and correlation coefficients between hardware and software DRRs and DTSs were calculated to assess their similarity. Results: The mean errors and their standard deviations of the differences DRR and DTS images are 1.0% ± 1.5% and 1.2% ± 2.1%. The correlation coefficients are 99.9% for DRRs and 99.5% for DTS. The reconstructed efficiency was improved by a factor of 67 for DRR and 13 for DTS. Conclusions: The hardware method provides fast reconstructions of DRR and DTS with visibility of anatomical structures comparable to those generated using software methods.This allows real‐time target localization for image registration between on‐board and reference DTSs in the application platform.
SU‐FF‐I‐63: Temporal Constrained Registration of Arbitrary Surface Contours for Use in 4D Radiation Therapy
Authors: Jacques R , Glaunès J , Ford E , McNutt T , Taylor R , Wong J 
Published: July 2007

Purpose: To quantify the validity of the temporal interpolation provided by a nonlinear uncorrelated contour based path length minimizing deformable registration algorithm in 4D radiation therapy. Method and Materials: The anatomical surfaces are represented as triangulated meshes. The registration algorithm is implemented by defining a norm between the triangulated meshes, based on the algorithms of Glaunès and Vaillant. This algorithm matches two surfaces as opposed to image intensities or specific points. Additionally, it optimizes the path between them allowing for a temporal interpolation. The registration is defined as the flow of an unlabeled 3D point set to an arbitrary target surface that minimizes both the norm between the target and registered surface and the non‐linear path length between the source and registered surface. Ground truth surfaces were generated from 4D lung datasets using the semi‐automatic mesh segmentation routine from a research version of Pinnacle, with expert manual correction. Results: To test this algorithm we compared its ability to interpolate intermediate shapes with a standard linear interpolation technique. We found that this algorithm performs comparably.The similarity metric used was an Euclidean distance error metric between the ground truth surface and a surface interpolated between a previous and subsequent ground truth surface. It was calculated between the interpolated and truth vertexes and their closest points on the truth and interpolated surfaces, respectively. This metric is independent of the interpolation and surface triangulation used, and thus is applicable to other interpolation algorithms. Conclusion: This work shows that this general, path length minimizing deformable registration algorithm based interpolation performs similarly to linear interpolation in approximately correlated, intrafractional datasets. This algorithm has the advantage of utilizing surfaces with arbitrary triangulations without point correspondences. We further discovered that this specific algorithm exhibited numerical instabilities that require further investigation.
SU‐FF‐I‐72: Reducing PET Scan Duration By Improving SNR Using Super‐Resolution Techniques
Authors: Chang G , Pan T , Qiao F , Clark J , Mawlawi O 
Published: July 2007

Objectives: Super resolution (SR) techniques reconstruct a high resolution image from a series of low resolution images taken from different points of view of the same object. The aim of this abstract is to compare the SNR of images reconstructed with and without SR processing versus total scan duration in an attempt to produce images of similar quality but with shorter scan duration.Methods: A NEMA/IEC phantom containing 6 spheres of varying diameters (1–3.7cm) was filled with F‐18 water and scanned on a DSTE PET/CT scanner. The phantom was scanned in LIST mode for 4 min in 2D and 3D using three different sphere‐to‐background ratios (SBR) (3, 5, and 8). The LIST data was then rebinned into 24 different scan durations in 10 sec increments and reconstructed into 128*128 matrix using OSEM (2 iterations, 21 subsets). In addition, for each scan duration, a 128*128 SR image was generated from 4 64*64 images by offsetting the pixel grid by a 4mm along the X and Y axes. SNR was then determined by drawing ROIs on all spheres and background on all images with and without SR processing for all SBRs and scan durations in both 2D and 3D. Results: For the same scan duration, the noise in images with SR processing is reduced by 19–35% while SNR is improved by 36–40% for all SBRs and scan modes. For the same SNR, scan duration with SR processing can be reduced by 31–41% for different SBRs and scan modes. Conclusion: SR processing produces images with superior SNR and noise content thereby allowing a reduction in PET scan duration while maintaining similar image quality to standard reconstruction. One specific application of SR processing is to improve the quality of gated PET images.
SU‐FF‐I‐94: The Assessment of Structural Variations of Multiple Sclerosis Plaques in Clinically Isolated Syndrome (CIS) Using Magnetization (MTI) Parameters
Authors: Riyahi‐Alam N , Fooladi M , Harirchian M , Firuznia K , Oghabian M , Rafee B , Shakiba M 
Published: July 2007

Purpose: A segmentation method for detection of masses in digitized mammograms has been developed using two parallel approaches: adaptive thresholding method and fuzzy entropy feature as a CAD scheme. Method and Materials: The algorithm consists of the following steps: a) Preprocessing of the digitized mammograms including identification of region of interest (ROI) as candidate for massive lesion through breast region extraction, b) Image enhancement using linear transformation and subtracting enhanced from the original image, c) Characterization of the ROI by extracting the fuzzy entropy feature, d) Local adaptive thresholding for segmentation of mass areas, e)Combine expert of the last two parallel approaches for mass detection. Results: The proposed method was tested on 78 mammograms (30 normal & 48 cancerous) from the BI‐RADS and local databases. The detected regions validated by comparing them with the radiologists' hand‐sketched boundaries of real masses. The current algorithm can achieve a sensitivity of 87% with 1.57 FP/image. Conclusions: This approach showed that the behavior of local adaptive thresholding and fuzzy entropy technique could be a useful method for mass detection on digitized mammograms. Our results suggest that the proposed method could help radiologists as a second reader in mammographic screening of masses.Keywords: Breast Masses, Segmentation, Image Enhancement, local adaptive Thresholding, Fuzzy Entropy.
SU‐FF‐I‐95: Separate Water and Fat Imaging with a Novel Phase‐Correction Algorithm
Authors: Zhou Y , Ma J 
Published: July 2007

Purpose: The purpose of this study is to describe the implementation of an efficient and robust 2‐point Dixon technique with a novel phase‐correction algorithm and a triple‐echo fast spin‐echo (fTED) data acquisition. Methods and Materials: An fTED pulse sequence was developed and used to collect an in vivo raw dataset on 1.5T GE whole body MRI scanner. The pulse sequence was modified from the FSE pulse sequnece by replacing each readout gradient between each 180° refocusing RF pair with three readout gradients of alternating polarity. The separation between the three readout gradients is timed so that the three corresponding raw images have a relative water and fat phase of 180°, 0, 180°, respectively. A novel phase‐correction algorithm was developed to remove phase errors and produce the water‐only and fat‐only images. The algorithm determines the phase vector direction rather than the phase value. Both the pixel intensity and precalculated phase gradients are used to guide the region growth sequence. The advantages of the algorithm include its easy implementation, computational efficiency, and robustness in the presence of pixels with large phase uncertainty. Results: Clean water and fat separation was achieved using the novel phase‐correction algorithm for all the images. Using only phase gradients for determining the growth sequence, small local regions were noted to have reversed water and fat assignment. Such processing errors were corrected when pixel intensity was included in the determination of the growth sequence. Discussion and Conclusion: We showed that both the pixel intensity and phase gradients can be incorporated in the new phase‐correction algorithm. The pulse sequence and the phase‐correction algorithm were demonstrated to be capable of producing water‐only and fat‐only images with excellent scan time efficiency and processing robustness.Acknowledgment: This work was supported by a research grant from the Susan Komen Breast Cancer Research Foundation.
SU‐FF‐I‐115: Cardiac‐Gated Dual‐Energy Imaging of the Chest: Design and Performance Evaluation of a Cardiac Trigger Based On a Fingertip Pulse Oximeter
Authors: Shkumat N , Siewerdsen J , Dhanantwari A , Williams D , Paul N , Yorkston J , Van Metter R 
Published: July 2007

Purpose: A research prototype for high‐performance dual‐energy (DE) imaging of the chest is under development. This paper discusses the development and characterization of a cardiac gating system designed to precisely trigger the imaging system according to cardiac phase and minimize anatomical misregistration due to heart motion. Method and Materials: A fingertip pulse oximeter was employed to measure the peripheral pulse waveform and trigger x‐ray exposures during the quiescent phase of the heart (diastole). Temporal delays accounted in the timing scheme include physiological pulse propagation, waveform processing, and imaging system delays (filter‐wheel, bucky‐grid, and flat‐panel detector). An empirical model of the diastolic period allows calculation of the implemented delay, timp, required to trigger correctly at any patient heart‐rate. Performance was evaluated in terms of accuracy and precision of diastole‐trigger coincidence and expert assessment of cardiac motion artifact in gated and ungated DE images. Results: The model suggests a triggering scheme characterized by two heart‐rate (HR) regimes: below a HR‐threshold, sufficient time exists to expose on the same heartbeat ; above the HR‐threshold, a characteristic timp(HR) delays exposure to the subsequent heartbeat, accounting for all fixed and variable system delays. Initial implementation indicated 83% accuracy in diastole‐trigger coincidence. By modifying the HR estimation method (reduced temporal smoothing of the pulse waveform), trigger accuracy of 100% was achieved. Cardiac‐gated DE patient images demonstrate significantly reduced cardiac motion as assessed by expert radiologists.Conclusion: A pulse oximeter combined with a cardiac model provides accurate x‐ray triggering and significantly reduces heart motion artifacts. A simple fingertip clip presents logistic, cost, and workflow advantages compared to ECG. The system has been implemented in a clinical research trial, with gated and ungated arms allowing characterization of the impact of cardiac motion artifact on diagnostic performance. Conflict of Interest: Research sponsored in part by Eastman Kodak.
SU‐FF‐I‐121: Automated Ultrasound QC Tests: A Method That Does Not Require Perfect Transducer Alignment
Authors: Boote E 
Published: July 2007

Purpose: The purpose of this project is to develop an approach to automatic quality control testing of ultrasound equipment without the requirement to have perfect alignment of the image plane with the test objects in the phantom. Method and Materials: A standard commercial ultrasound phantom is used to acquire images using a typical clinical ultrasound scanner. The phantom used here is one that employs a set of cylindrical voids to evaluate spatial resolution. The ultrasound scanner is configured to acquire a series of images in a clip file and the data is sent via a DICOM connection. A clip is stored as the transducer is swept across the plane of the test objects (An alternative method would be to use a frame‐grabbing system that can acquire a video signal and store data as a multi‐image file.)A program has been written in MATLAB to open the DICOM multi‐image file and store the images. Statistical properties of this set of images are used to create a “composite” image that represents a perfect alignment of the transducer. This image may be used for a series of quantitative evaluations of image quality that have previously been described in the literature. These would include lesion detectability (lesion signal to noise ratio) measures as well as sensitivity measurements (maximum depth of penetration). Results: This approach to image acquisition has the potential to save time and effort (and frustration) for either a technologist or a physicist in the ongoing effort to simplify the manual aspects of computerized quality control for ultrasound. Conclusion: This approach is under evaluation against other computerized ultrasound quality control procedures.
SU‐FF‐I‐126: Effect of Threshold Setting On 3D Visualization and Diameter Measurement Accuracy of Blood Vessels for CT Derived Images
Authors: Szczykutowicz T , Rudin S , Yadava G , Patel V , Ionita C , Hoffmann K , Bednarek D 
Published: July 2007

Purpose: To investigate the effect on vessel sizing of varying the threshold in 3D volume‐rendered CT images and to verify the results with a 2D computer simulation. Method and Materials: 3D‐rendered images of a phantom with a vessel of varying diameter and of a patient with a basilar tip aneurysm were displayed on a Vitrea 2 workstation. Vessel diameters measured from the images were plotted as a function of gray‐scale threshold and actual vessel diameters measured directly from the phantom. A MatLab program was used to simulate different‐size vessel image models by convolving a rect function with a Gaussian point spread function (PSF) and to investigate the effect of threshold on sizing these vessels. Results: Plots of measured vessel diameter vs. threshold setting for varying real‐vessel diameter exhibit a monotonic decrease; with the slope decreasing both for low thresholds because of the extended tail of the PSF and for high thresholds where the vessel rapidly shrinks and then disappears as the threshold exceeds the vessel gray level. For intermediate thresholds there is a greater rate of fall‐off for smaller vessels below the width of the system PSF. Plots of measured diameter vs. real diameter intersect the 45 degree identity line at increasing diameters for increasing intermediate threshold. The crossing‐point indicates the point where the measured diameter equals the real diameter for the given threshold. Below the crossing point, these curves demonstrate reduced measured diameter for smaller vessels and, above the crossing‐point, larger values for larger vessels. The simplified 2D vessel‐model simulation and workstation data follow similar trends. Conclusion: A threshold set to accurately measure one rendered‐vessel diameter will inaccurately render vessels of other diameters. Using this threshold, smaller vessels will be inaccurately small or not be visualized and larger vessels will be too large.(Support: NIH R01‐NS43924, R01‐EB002873, Toshiba Corp.).
SU‐FF‐J‐08: Accuracy of Cranial Co‐Planar Beam Therapy with BrainLab ExacTrac Image Guidance
Authors: Vinci J , Hogstrom K , Rosen I , Chu C , Neck D 
Published: July 2007

Purpose: To evaluate the positional accuracy (displacement between planned and delivered dose distributions) of cranial co‐planar beam treatments for image guided stereotactic radiation therapy with Novalis. Methods and Materials: Positional accuracy was investigated using a CIRS anthropomorphic head phantom loaded with 6.35cm × 6.35cm sections of EDR2 film oriented to measure dose in the three principal planes. BrainScan was used to develop a treatment plan consisting of seven equally spaced coplanar mMLC beams that conformed to irradiate a 2‐cm diameter by 2‐cm long PTV. Prior to delivery phantom misalignments were imposed in combinations of ±8‐mm offsets in one or more of the principal directions. ExacTrac X‐ray corrections were applied 1–3 times until the reported alignment was within 0.4mm/0.4° in all 6 degrees of freedom based on X‐ray to DRR image fusion prior to treatment delivery. Phantom positions were tracked by the Novalis IR system. The delivered dose distribution was measured with a precision of ±0.3mm. Measured and calculated dose distributions were registered using 4 fiducial rods in the phantom. Results: Based on the 70% dose contour, the displacements of the delivered from the planned dose distributions ranged from 0.7 to 1.3mm, −0.4 to 0mm, and −0.6mm to 0.5mm in Posterior‐Anterior, Right‐Left and Inferior‐Superior directions respectively. For the 80% dose contour, the displacements of the delivered from the planned dose distributions ranged from 0.8 to 1.8mm, 0.1 to 0.8mm, and 0.1 to 1.1mm, respectively. Final displacements were independent of initial misalignments. Conclusions: Using recommended Novalis calibration procedures, the ExacTrac X‐ray image‐guidance system used in our clinic can deliver cranial dose distributions within 1.3mm of the planned dose distributions when initial misalignments are within ±8mm in the three principal directions. 80% isodose contours can have up to 1.8‐mm errors.This work is part of a research agreement with BrainLab, Inc.
SU‐FF‐J‐27: Target Localization Verification for Partial Breast Irradiation with An EPID in Cine Mode
Authors: Berbeco R , Ionascu D , Park S , Lyatskaya Y 
Published: July 2007

Purpose: In partial breast irradiation (PBI), even if the target is well defined, and positioned precisely at the beginning of each treatment session, there are no assurances that it will remain so during irradiation. We propose tracking the PBI target using an electronic portal imaging device (EPID) in cine mode. Method and Materials: Phantom studies have been conducted using a breast phantom and diode detector. We quantified the dose enhancement to a point on the surface of the contra‐lateral breast when the EPID is left extended during treatment. Measurements of the dose enhancement were made for multiple field sizes, beam energies and EPID positions. Additional measurements were made of the dose enhancement to the contra‐lateral breast with the medial field included. To preliminarily assess the visibility of targets in the breast, images were taken with a wire fiducial in the field. Additional images were taken with the phantom set in a sinusoidal motion. Results: For a PBI field, the dose enhancement (DE) is 19% for 6 MV and 23% for 10 MV for Source‐to‐Detector Distance (SDD) = 130 cm, compared to 4% and 4.5%, respectively, for SDD = 155 cm. When the dose to the surface of the contra‐lateral breast from the medial field is included in the calculation, the dose enhancement is below 2% for both energies for SDD greater than 142 cm. For a WBI field, DE is below 2% for both energies for SDD greater than 147 cm. In the cine EPID images, visualization of the target can be improved with simple image processing techniques Conclusions: The cine EPID technique may be employed safely to monitor WBI and PBI treatments.This work was funded, in part, by a grant from Varian Medical Systems, Inc.