bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐G‐110‐02: Contrast‐Enhanced Dual‐Energy Cone‐Beam CT for Musculoskeletal Radiology
Authors: Zbijewski W , Stayman J , Ding Y , Prakash P , Machado A , Carrino J , Siewerdsen J
Published: November 2011

Purpose: Dual‐energy (DE) imaging has the potential to transcend contrast limitations of conventional CT. We investigate DE imaging in cone‐beam CT (CBCT), including exogenous iodine and gadolinium (the latter relatively novel in CT but with promise in cartilage imaging) and simultaneous imaging of multiple contrast agents. Methods: Experiments used a test‐bench emulating a prototype extremities CBCT scanner. Nominal single‐energy technique was 90 kVp + 0.3 mm Cu (∼0.15 mSv). DE‐CBCT involved a double‐scan at low (60 kVp + 2 mm Al) and high energy (100–120 kVp + 0.5 mm Ag) (∼0.6 mSv total). Projection‐based and reconstruction‐based decomposition were performed. Initial studies included a 16 cm cylindrical phantom (simulated soft tissue, bone, and various concentrations of iodine and Gd) and a cadaveric wrist for DE‐CBCT arthrography. Results: DE‐CBCT improved discrimination of exogenous contrast from bone, facilitating detection of articular abnormalities. Results demonstrate intravascular and/or intraarticular Gd as a viable agent for CBCT and DE‐CBCT, providing significant enhancement over water at low concentrations (down to 0.78 mg/mL) and low radiation dose (∼0.15 mSv). Excellent linearity of DE‐CBCT voxel values was achieved but demonstrated the need for high‐quality scatter correction. Simultaneous DE‐CBCT of iodine and Gd yielded clear discrimination of exogenous contrast in bone‐cancelled images down to 16.7 mg I/mL and 7.8 mg Gd/mL, supporting feasibility in imaging cartilage degeneration and bone marrow edema in rheumatoid applications. Conclusions: Results prove the feasibility of contrast‐enhanced DE‐CBCT, including simultaneous I/Gd discrimination in 3D arthrography. The work supports translation of DE‐CBCT to clinical CT scanners as well as a dedicated CBCT for extremity imaging. Primary limitations include false enhancement from image artifacts and long scan times (20 s) on the current scanner prototype. The work suggests new opportunites for DE‐CBCT in areas conventionally reserved for MRI and ultrasound — e.g., imaging of synovitis and cartilage degeneration.

The research was supported by academic‐industry partnership with Carestream Health Inc. (Rochester NY), and by NIH R01 Grant No. 112163‐04.
TU‐G‐110‐07: Quantitative Measurement of an Iodinated Contrast Agent with Dual Energy and Spectral Breast Computed Tomography
Authors: Ding H , Ducote J , Behroozi F , Molloi S
Published: November 2011

Purpose: To investigate the feasibility of quantifying an iodinated contrast agent with dual energy and spectral breast computed tomography (CT).Methods: A cylindrical Polymethyl methacrylate (PMMA) phantom with a diameter of 4.5 cm was constructed using various iodine concentrations that ranged from 0.4 to 4 mg/ml. Calibrations and measurements were carried out with (1) a flat panel detector using dual kVp technique and (2) a Cadmium‐Zinc‐Telluride (CZT) photon counting detector using a single kVp approach in a spectral CT system. Based on the simulation results, energies of 50 and 120 kVp were chosen for the dual kVp imaging. Energy splitting at 34 keV, which is just above the k‐edge of iodine, was used to bin photons into two images within a single energy acquisition at 50 kVp. Results: Iodinated solutions with different concentrations can be clearly identified in the dedicated iodine image obtained from both dual kVp flat panel imaging and CZT‐based spectral CT. The linear fitting of the experimental data as a function of the known values yielded slopes of 0.998 and 1.021 for the dual kVp and spectral CT techniques, respectively. This suggested that the measured iodine concentrations agreed very well with the known values. Conclusion: The experimental results suggest that both dual kVp and spectral CT can be used for quantitative decomposition of contrast‐enhanced breast imaging. Meanwhile, the CZT‐based spectral CT system may offer a better image quality than the comparable flat panel based dual energy CT system.
TU‐G‐211‐03: Automatic Segmentation of Non‐Small Cell Lung Carcinoma Using 3D Texture Features in Co‐Registered FDG PET/CT Images
Authors: Markel D , Caldwell C , Alasti H , Sun A , Soliman H , Lee J , Ung Y , McGhee P , Webster D
Published: November 2011

Purpose: To evaluate the usage of a combination of FDG‐PET/CT features to improve automated segmentation of the gross tumor volume (GTV) in the thorax in order to reduce target definition uncertainty in radiotherapy. Methods: Features of co‐registered FDG‐PET/CT images of patients with non small cell lung carcinoma (NSCLC) were investigated using spatial gray‐level dependence matrices, neighborhood gray tone difference matrices, Tamura textures, first order statistics and structural characteristics. A training data set of PET and CT scans from 21 patients diagnosed with NSCLC was used. Feature samples were taken from regions of interest that included GTV, positive nodes and healthy structures found in the thorax. A decision tree incorporating KNN classifiers as nodes was trained to segment GTVs using an exhaustive search for the optimal combination of features by area under the curve (AUC) at each node. A validation set of 10 patients deemed difficult to contour was used and a probabilistic ground truth was derived from a combination of three observer contours using simultaneous truth and performance level estimation (STAPLE).Results: The concordance index of the three observers was found to average 0.370. CT skewness and PET coarseness were found to be the most useful discriminators when evaluated independently with AUCs of 0.705 and 0.972 respectively. Evaluation of the segmentation results using Dice coefficients found the resulting DTKNN outperformed a variety of thresholds including signal‐to‐background ratio and an implementation of the 3‐FLAB algorithm. Dice coefficients for the DTKNN averaged 0.65 and reached as high as 0.84. Conclusions: Incorporation of texture features from both modalities offers an improvement in segmentation accuracy over approaches that utilize each modality independently. The largest source of error was found to be the misregistration of PET to CT volumes and blurring of PET due to internal motion.
TU‐G‐211‐04: Evaluation of Image Quality on a Time‐Of‐Flight PET/CT Scanner
Authors: Chang T , Clark J , Mawlawi O
Published: November 2011

Purpose: The aim of this study is to assess the improvement of image quality on a time‐of‐flight (TOF) PET/CT scanner using phantom with varying sphere size and sphere‐to‐background ratio (SBR)Methods: A NEMA IEC phantom containing six spheres (1–3.7cm) was scanned on a GE Discovery‐690 TOF PET/CT scanner. 8 saline bags (250ml each) were attached to the phantom to simulate an obese patient (BMI=32). The scan was repeated for two SBR, 4:1 and 8:1 with background activity concentration of 0.14 and 0.1uCi/cc respectively. PET data was acquired in 3D for 3 minutes for each SBR, and images were reconstructed with and without TOF information, using 16 subsets and varying 1–10 iterations. ROIs were placed in the central slice on each sphere based on CT images, and the mean value in each ROI was calculated. Background mean and standard deviation were measured from 500 randomly selected voxels across 10 slices. Signal‐to‐noise ratio (SNR), contrast recovery coefficient (%CRC), and background variability (%noise) were determined and compared across different sphere size, SBR, and iterations. Results: Contrary to what is expected, SNR w/o TOF is consistently better than with TOF for all sphere sizes, iteration number, and SBR. The CRC for TOF on the other hand is consistently higher than non‐TOF when evaluated at the same noise level for SBR 4:1. This finding however reverses at higher SBRs and iteration number. The CRC gain of TOF vs. non‐TOF increased with decreasing sphere diameter. Conclusions: TOF imaging improves the resulting CRC but not the SNR of PET images when compared using the same number of iteration. The benefit of TOF is highest for small spheres and SBRs.
TU‐G‐211‐06: Partial Volume Correction for Noninvasive PET Image‐Derived Simplified Kinetic Analysis
Authors: Sattarivand M , Caldwell C , Poon I
Published: November 2011

Purpose: To assess a partial volume correction (PVC) method for a non‐invasive PET image based simplified kinetic analysis.Methods and Materials: A phantom was designed with a cylinder tank and six fillable cylinders to simulate vessels with a range of inner diameters from 4.8 to 28.6mm. F‐18 in aqueous solution was injected into the vessels and the tank with an activity concentration ratio of 1.5 to 1. The PET FOV was 576mm and voxel size 4×4×4mm. CT images of this phantom were used to create a digital 3D PET phantom model. The inner and outer vessel cylinders and the tank were automatically contoured and the known true F‐18 activities were assigned to the vessels and tank volume. The CT‐based model was then convolved with a 3D Gaussian PET point spread function to create the simulated phantom. For both simulated and physical phantoms, PVC was applied to recover the F‐18 uptakes using a 3×3 geometric transfer matrix (GTM) method. Recovery coefficients of the vessels were calculated before and after PVC. Results: Severe underestimations in vessel uptake were observed for both simulated and physical phantoms before PVC. After PVC the vessel uptakes recovered closer to the true uptake values. For the simulated phantom, complete PVC recovery was achieved for all vessel sizes with an accuracy <0.2%. For the physical phantom, the PVC recovery was <5% for all vessel sizes except for the smallest vessel (4.8mm) where the vessel uptake was overestimated by 20%. Conclusions: Non‐invasive PET image based simplified kinetic analysis is feasible provided that partial volume corrections are applied to recover vessel tracer uptake. Blood activity may be corrected for partial volume error with better than 5% accuracy using the GTM method for vessels larger than 10mm in diameter. A patient study is needed to confirm these results in clinical settings.
TU‐G‐211‐07: Combined NaF PET and FDG PET Based Assesment of Bone Metastasis Response after Chemotherapy Using Kinetic Analysis
Authors: Simoncic U , Morrison C , Liu G , Jeraj R
Published: November 2011

Purpose: The differentiation between the residual tumor activity and the osseous reaction to the tumor is essential for therapy assessment of bone metastases. The 18‐F‐Sodium Fluoride (NaF) uptake reflects the osteoblastic process, while the FDG uptake reflects the tumor metabolism. The purpose of this study was to evaluate the assessment of treatment response with the kinetic analysis of concurrent NaF/FDG PET/CT images for specific clinical cases. Methods: Three prostate adenocarcinomas were treated with chemotherapy and imaged twice with NaF/FDG PET/CT: a baseline scan and a second scan after four weeks of chemotherapy. The NaF/FDG PET/CT imaging started with NaF injection, followed by 100 min dynamic PET imaging. Next, FDG was injected and followed by an additional 45 min of dynamic PET imaging. Macroparameters K_NaF and K_FDG (defined as K=K1×k3/(k2+k3)) were obtained by compartmental kinetic analysis. The accuracy of the kinetic parameter estimations was evaluated with simulations. Bone metastases were segmented (29 total). The ratio of mid‐therapy to pre‐therapy mean K_FDG and K_NaF parameters, which measured the response to therapy, was calculated for each metastasis. Results: The simulations revealed that the K_NaF and K_FDG estimations are highly correlated to the simulated value (r=0.9) while an estimated error is 50%. The K_FDG response and the K_NaF response are moderately correlated (r=0.7), but the mean K_FDG response over all the metastases is 0.7 while the mean K_NaF response is 0.9. The patterns in K_FDG and K_NaF parametric images are similar, but displaced and slightly distorted. Conclusions: Tumor metabolism and bone repair process can be imaged separately at the same time point using the presented imaging protocol, which was validated with simulations. The addition of FDG PET imaging to the osseous NaF PET imaging provides additional information to treatment response and has the potential to improve the assessment of bone metastasis in therapy.
TU‐G‐211‐09: A Comparison of FLT‐PET and DCE‐CT Kinetic Analysis in a Clinical Trial
Authors: La Fontaine M , Simoncic U , Forrest L , Jeraj R
Published: November 2011

Purpose: Through kinetic modeling, both dynamic FLT‐PET and dynamic contrast‐enhanced CT (DCE‐CT) measure perfusion. However, the set of parameters used by the kinetic models to describe perfusion differs between the two imaging modalities. The purpose of this study was to investigate the correlations between corresponding FLT‐PET and DCE‐CT kinetic ROI and voxel parameters.Methods: Canine patients with sinonasal tumors underwent FLT‐PET and DCE‐CT on the same day. FLT‐PET uptake was modeled with a two‐compartment four‐parameter kinetic model. The DCE‐CT kinetic analysis was done by Kety, deconvolution (Decon) and distributed parameter (DP) models. All models were implemented in‐house using MATLAB. FLT K1 and k2 parameters were correlated with equivalent K1 and k2 DCE‐CT values. FLT vb was correlated with the DCE‐CT parameter blood volume ratio (BVR). ROI analysis was performed over the entire tumor volume, while voxel analysis was calculated on the largest tumor slice. Correlations were done using the population correlation coefficient (p).Results: DCE‐CT and FLT K1 displayed strong ROI correlations (DP: p=0.91, Deconvolution: p=0.87, Kety: p=0.60). The kinetic parameter vb also had high ROI correlations (p=0.82, p=0.89, p=0.89). FLT k2 correlated only marginally with the DCE‐CT models (p ∼ +/−0.50). There were no significant voxel correlations. However, increasing voxel size 128×128 to 32×32 lead to minor improvements in correlation with the most notable being K1, which increased in the distributed parameter and deconvolution models from (p=0.16, p=0.29) to (p=0.52, p=0.42). Conclusions: Significant ROI correlations were found between FLT and DCE‐CT kinetic analysis. The kinetic parameters K1 and vb had relatively high correlations between the DCE‐CT and FLT kinetic models. Even though there were no significant voxel correlations, an increase in K1 correlations with voxel size may indicate kinetic model sensitivity to noise as an important factor in kinetic parameter correlations.
TU‐G‐220‐03: Development of the Basis for Quantitative Ultrasound
Authors: OˈBrien W
Published: November 2011

Our early work to develop a basis for quantitative ultrasound (QUS) imaging started with live animal studies wherein the ultrasonic backscattered coefficient (BSC) was estimated and from the BSC estimate, QUS parameters were estimated. Even earlier (some 5 decades earlier), significant through‐transmission quantitative studies of ultrasonic tissue properties were undertaken (absorption and speed). It was our view, based on the significant early echo‐based work by Lizzi et al., Zagzebski et al., Insana et al. and Hall et al., that QUS imaging technology had the potential to be a new imaging capability that could be used to augment standard B‐mode imaging. QUS imaging utilizes the frequency‐dependent information, and thus the backscattered signals are dependent on the tissue properties (size, shape, number, compressibility, density). Estimating QUS parameters requires a model that incorporates a form factor (FF), that is, a mathematical description/model of the backscattered signal of a single scattering structure as a function of frequency; the better the FF describes anatomical scatterers, the more realistic will be the estimates. We initiated our studies by examining in vivo three solid tumor types (fibroadenoma, mammary carcinoma, soft‐tissue sarcoma). Initially the Gaussian FF was used. Good agreement between processed ultrasound data and pathologic assessments were obtained, but also important questions were being raised. The questions lead to a new approach to identify more accurate FFs as well as new strategies to extract quantitative parameters from the envelop‐detected echo data. The current QUS studies are in collaboration with colleagues at the University of Wisconsin‐Madison, Iowa State University, University of Illinois at Chicago, Brown University and Riverside Research. The presentation will provide the basis for QUS based on our early work as well as our on‐going work.

Research sponsored by NIH CA111289

Learning objectives:

1. Understand backscattered coefficient (BSC) QUS parameters and their relations to tissue properties

2. Understand how to acquire QUS parameters from BSCs

3. Understand the basic concept of QUS and BSC analyses

4. Understand QUS parameters and their relations to tissue properties
TU‐G‐220‐06: Reference Phantom Measurements of Attenuation and Backscatter with Speed of Sound Disparities
Authors: Nam K , Zagzebski J , Rosado‐Mendez I , Hall T , Rubert N
Published: November 2011

Purpose: A quantitative comparison between echo data from a scanned area in a patient to echo data acquired from a well‐characterized reference phantom is an effective means to account for imaging and transducer system dependencies of clinical echo data and to derive back‐scatter and attenuation parameters. An assumption in this “reference phantom method” (RPM) is that the speeds of sound (SOS) in the referencel and in the patient are “close.” This study addresses the impact of disparities between SOSˈs in the sample and reference and possible corrections in the case of errors. Methods: Phantoms with SOSˈs of 1500, 1540, and 1580 m/s and approximately 0.59 dB/cm‐MHz attenuation coefficients were constructed using gels. They were scanned with array transducers on a Siemens S2000 machine equipped with an ultrasound research interface. Data were acquired both with “BF‐sos”, the assumed beam former sound speed set at 1540 m/s and with it set to match the sample SOS. With the 1540 m/s phantom as a reference, echo arrival‐time dependent ratios of intensity from phantom and reference were used to compute attenuation coefficients. Processing was done using a) no adjustments to the signal vs. time data, b) SOS based adjustments so ratios were computed from precisely the same depth, and c) data with BF‐sos matching the SOS of the sample. Results: Variations are seen in attenuation coefficient estimates when the sample and reference phantom have SOS values that differ by the amounts used here. Improvements are noted when data are properly matched depth‐wise. Best results are obtained when this is done AND the BF‐sos matches the sound speed in the sample. Conclusions: Differences between a mediumˈs SOS and that assumed in the beam former result in errors in attenuation measurements. Errors are minimized by matching the sound speed of the beam former with the SOS of medium.

Supported by Grant R01CA111289 from the National Institutes of Health.
WE‐A‐224‐01: Educational Course Therapy: Implanted Target Surrogates for Radiation Treatment Verification
Authors: Wang Z , Kothary N
Published: November 2011

Target surrogates have been extensively used in radiation therapy, especially imaging guided radiation therapy and radiosurgery, for the purposes of target localization and treatment verification. A wide variety of surrogates have been used including gold markers (seeds or coils), surgical clips, long‐lasting contrast agents, brachytherapy seeds, and electro‐magnetic markers. This course will review different types of applications of target surrogates in radiation therapy and discuss the issues related to marker implantation, such as patient complication, marker migration, dropping, deformation, minimum numbers of fiducials, and timing between the implantation and planning imaging acquisition. Application for specific treatment sites, such as prostate, lung, liver, pancreas, and breast will be addressed. Issues related to image guidance techniques with target surrogates will be discussed. Planning target volume (PTV) margin requirements for implanted marker guided setup will be discussed for each individual site. Marker applications in verifying the accuracy of respiratory gated treatments will also be discussed. Quality assurance with respects to marker stability during the whole course of radiation therapy, deformability with specific implantation sites, and geometrical accuracy will be addressed.

Learning objectives:

1. Attendees will learn how to assess the quality of marker placement.

2. Attendees will learn how to set up QA programs for treatment with implanted target surrogates.
WE‐A‐110‐01: Understanding Exposure and Deviation Indices
Authors: Leong D , Shepard S , Butler M
Published: November 2011

As digital radiography systems began to be developed, manufacturers independently developed methods and terminology to express an exposure to their detectors. With each manufacturer having a different scheme, users quickly became confused when moving between equipment. The International Electrotechnical Commission (IEC) and AAPM both realized that there was a problem. Both organization simultaneously produced documents defining terminology and methods for a universal exposure index for general radiology. There was discuss between the groups, but differences between both documents emerged.

This lecture will discuss the terminology and calibration methods in both the AAPM Task Group 116 Report and IEC 62494‐1, explain differences, and what it means in the clinic. Included will be practical issues related to implementation of the Exposure Index (EI) and the Deviation Index (DI), and how they related to the goals outlined in the TG 116 report. Concluding with discussion on experimental results on how the EI and DI index varies with different clinical techniques.

Learning Objectives:

1. Understand AAPM recommendations,

2. Understand the IEC standard,

3. Understand factors that affect Exposure and Deviation Index values.
WE‐A‐211‐01: Biology versus Epidemiology: The Need for an Integrated Model of Radiation Risk
Authors: Vetter Richard
Published: November 2011

The lifetime attributable risk estimates from the National Academy of Sciences BEIR VII report have been used by a number of authors to estimate cancer mortality caused by radiation exposure from medical diagnostic radiology exams. This controversial practice assumes that the dose response relationship between radiation and cancer is linear with no threshold (LNT). For purposes of protecting public health, use of the LNT model is widely accepted. But is it appropriate for estimating risk to individuals exposed to low doses of radiation from medical procedures?

Radiation biology research demonstrates that not all biological processes are linear. It also has provided data that support not only LNT but supra linear and sub linear response models. Results from epidemiology studies can also be used to support the use of any of these models, but the confidence intervals are much larger. Since we canˈt prove which model is correct, for purposes of protecting patients we assume that any exposure has the potential for harm and we use optimization to keep exposures as low as reasonably achievable.

Several areas of research are contributing insight into this dilemma, but they still leave several important questions unanswered:

• How can we accurately extrapolate low‐dose biological effects generated in the laboratory to risk in a human?

• Is extrapolation from high dose, high dose rate, acute exposures appropriate when human exposures are primarily chronic low dose exposures.

Epidemiology alone is unlikely to provide information that will resolve this dilemma. The numbers of individuals required in a sample are too large, and the homogeneity among subjects is lacking. Reliance on radiation biology research alone is problematic because the research is focused primarily on mechanisms and not risk. This paper will present an overview of the issues and suggest areas of research that may contribute to our understanding of the level of risk associated with low doses of medical radiation.

Following this paper, attendees will be able to:

• List the current biological mechanisms that are affected by low doses of ionizing radiation.

• Describe the dilemma of risk extrapolation based on current knowledge of biological effects of radiation.

• Discuss the limitations of extrapolating lifetime attributable risk estimates to cancer mortality for low‐dose medical procedures.
WE‐A‐301‐04: Model‐Based Known Component Reconstruction for Computed Tomography
Authors: Stayman J , Otake Y , Uneri A , Prince J , Siewerdsen J
Published: November 2011

Purpose: We aim to develop model‐based tomographic reconstruction methods that incorporate knowledge about known components (e.g. implants, surgical tools) within the scanning field. Inclusion of such knowledge as part of the reconstruction approach should benefit image quality in situations where there is missing data or where noise levels are particularly high. While the proposed reconstruction framework is general, in this work we focus on metallic implants and elimination of streak artifacts associated with those components. Methods: We have developed a novel model‐based reconstruction technique that parameterizes the image volume as the combination of the underlying background attenuation and an arbitrary number of known components whose attenuation profile is known but whose locations and orientations are unknown. Adopting a tomographic forward model that includes noise allows for derivation of a penalized‐likelihood objective function. Maximization of this objective for the unknown registration and attenuation parameters yields a joint estimate of the object and the position and pose of each known component. We have developed optimization routines to solve this model‐based objective based on an alternating maximization scheme. Results: The proposed reconstruction method has been applied to spine imaging where there are pedicle screws in the imaging field. We compare our novel approach with reconstructions formed from traditional filtered backprojection and ordinary penalized‐likelihood approaches. We find that in the proposed scheme the position and pose of the implants is highly accurate and that streak artifacts associated with the metal implants are greatly reduced. Conclusions: Model‐based reconstruction that utilizes information about known components in the object has the potential to significantly improve image quality. While we have demonstrated this for the case of metallic pedicle screw implants, the technique is general and can apply to other scenarios where the (possibly heterogeneous) structure of components are known.
WE‐A‐301‐05: Over‐Beaming Dose Reduction Using an Axial‐Like Reconstruction Method in Helical Scans
Authors: Cao G , Narayanan S , Thibault J , Hsieh J
Published: November 2011

Purpose: To reduce the over‐beaming dose in conventional helical scans by acquiring and reconstructing the same image volume using a reduced scan range through an axial‐like reconstruction algorithm. Methods: In the proposed framework, the reconstruction volume is split into two types of regions along the z‐direction when the helical scan range is reduced: one central region where conventional reconstruction methods are applied and two boundary regions that have historically not been recoverable. In the boundary regions an axial‐like reconstruction algorithm which combines 3D view‐weighting and modified back‐projection is introduced. The 3D view‐weighting satisfies consistency condition for a ray and its conjugate ray while taking into account the view‐angle, cone‐angle and the distance of the image slice from the center view in a unified framework. The same view range as the edge slice of the middle region is used for reconstructing the boundary region, which makes the reconstruction similar to axial reconstruction.Results: Extensive experiments have been performed using both phantom and clinical scan data on volumetric CT scanners with various detector configurations and helical pitches. Experimental results demonstrated for the same prescribed image volume the xray scan range can be reduced by up to ¼ of the x‐ray beam width in z on each end of the helix compared to conventional scans. This means we may save an additional 8% and 5% dose in routine chest and abdomen scans, respectively, on top of the dose saving achieved with the dynamic collimation method. The proposed method has also been applied to multi‐energy CT scans with similar results. Conclusions: A new axial‐like helical reconstruction method is proposed that reconstructs the prescribed image volume with a reduced xray scan range. Experimental results indicate the new method can reduce the over‐beaming dose significantly. The method can be easily applied to multi‐energy scans.

The authors are with GE Healthcare, Waukesha, WI.
WE‐A‐301‐07: Using Prior Images with Registration in Penalized Likelihood Estimation for CT with Sparse Data
Authors: Stayman J , Zbijewski W , Otake Y , Schafer S , Lee J , Prince J , Siewerdsen J
Published: November 2011

Purpose: We aim to develop tomographic reconstruction methods that utilize prior CT volumes to improve image quality for sparse and undersampled datasets. The ability to handle such data has applications in region‐of‐interest scanning, tomosynthesis, and intraoperative imaging based on few view angles. While compressed sensing techniques like the PICCS algorithm are attractive, there are potential drawbacks. Such approaches often rely on pre‐registered prior images and the forward models for PICCS‐type algorithms tend to be simplified and ignore the noise model. We leverage the ability of likelihood‐based techniques to incorporate both prior images and sophisticated forward models. Methods: We have developed a framework for reconstruction of sparse tomographic data based on penalized‐likelihood estimation. The objective function for this approach is composed of a likelihood term that incorporates the forward model and noise; and a parameterized penalty term that discourages differences from the prior image. The penalty uses a compressed sensing norm and is parameterized to accommodate registration of the prior scan. An iterative algorithm is used to simultaneously solve for the tomographic volume and the registration parameters. The framework is general and can be used with both rigid and deformable registrations. Results: Reconstruction of sparse data using the proposed approach is demonstrated in cases where either rigid or deformable registration is employed in the reconstruction objective. We compare reconstruction results with traditional approaches where prior image data is not utilized. We find a substantial improvement in image quality with significant reduction in artifacts that are associated with the sparse data acquisitions. Conclusions: A new class of penalized‐likelihood estimator has been developed that simultaneously refines attenuation and registration estimates. The framework is general and supports both rigid and non‐rigid transformations of the prior imagery. Image quality and handling of artifacts using the proposed estimator with sparse data is superior to traditional approaches.
WE‐A‐301‐09: Fast, Iterative, Low‐Dose, Cone‐Beam Computed Tomography Reconstruction Using a Gradient Projection Algorithm
Authors: Park J , Song B , Kim J , Park S , Kim H , Suh T , Liu Z , Song W
Published: November 2011

Purpose: Recently introduced compressed sensing theory has enabled accurate, low‐dose CBCT reconstruction of anatomic information with fewer and noisier projections data. However, the reconstruction time remains a significant challenge for practical implementation in a busy clinic. We propose a novel gradient projection algorithm, based on Barzilai and Borwein formulation (GP‐BB), that handles the total variation (TV)‐norm regularization‐based least squares problem for CBCT reconstruction in an extremely efficient manner, with speed acceptable for use in on‐line IGRT. Methods: CBCT is reconstructed by minimizing the energy function consisting of 1) data fidelity term, and 2) TV‐norm regularization term. Both terms are simultaneously minimized by calculating the gradient projection of the energy function with the step size determined using an approximate second‐order Hessian calculation at each iteration, based on Barzilai and Borwein formulation. To speed up the process, a multi‐resolution optimization is used. In addition, the entire algorithm was designed to run with a single GPU card. To evaluate the performance, the CBCT projection data of a clinically‐treated head‐and‐neck patient was acquired from the Varian TrueBeam system. Results: The proposed GP‐BB algorithm was shown to be extremely efficient that a clinically reasonable patient image, using 120 CBCT projections, was reconstructed in 12 iterations for a total time of < 34 seconds. The image quality was visually equivalent to the commercial Feldkamp‐Davis‐Kress (FDK) algorithm using 364 CBCT projections. This represents dose reduction of one‐third (= 120/364) all at while maintaining the speed needed for clinical use. Conclusions: In this work, we developed a novel low‐dose CBCT reconstruction algorithm that is able to generate a clinically reasonable patient image in 12 iterations, using 120 CBCT projections, in total of < 34 seconds, with a single GPU card. This makes our GP‐BB algorithm entirely practical for daily clinical use.
WE‐A‐301‐10: How Much CT Radiation Dose Can Model Based Iterative Reconstruction (Veo) Save? — A Physical Evaluation of the Image Quality Using Standard Phantoms
Authors: Cohen A , Yadava G , Sainath P , Fan J , Madhav P , Budde A , Hsieh J
Published: November 2011

Purpose: This study is a comparative evaluation between Veo, GE Healthcareˈs model based iterative reconstruction engine, and contemporary filtered backprojection (FBP) techniques. The purpose is to estimate Veoˈs ability to produce diagnostic image quality at reduced dose levels. Methods: Standard image quality metrics were measured at different dose levels using physics phantoms commonly found in clinical settings. A GE multi‐slice CT system was used to scan a CATPHAN600® phantom in order to compare the noise and signal properties of FBP and Veo; tungsten wire phantoms were used to characterize high contrast spatial resolution between the two reconstruction algorithms. Three routine clinical protocols were tested: head, adult abdomen, and pediatric. Baseline FBP dose levels for each protocol were determined by the mean noise index from a large international database of scan histories. The metrics used in this study include MTF, noise power, contrast to noise ratio, and statistical low contrast detectability. Results: All of the tested metrics showed improved performance for the Veo at equal dose. Measurement differences between full dose FBP and 1/4th dose Veo were found to be statistically insignificant, indicating similar image quality. Conclusions: Veo reconstruction produces higher image quality than FBP at all measured dose levels and has the ability to greatly reduce the dose of routine CT imaging, as observed from standard physics phantom evaluation.
WE‐A‐301‐11: Low Dose Multi‐Slice Helical CT Reconstruction Using Tight Frame Regularization
Authors: Tian Z , Jia X , Dong B , Lou Y , Jiang S
Published: November 2011

Purpose: Multi‐slice helical CT has been widely used in CT diagnostic imaging due to its large coverage and short acquisition time. However, the associated high x‐ray radiation dose has become a major concern. Two straightforward ways to reduce the dose is to lower the mAs level and use high pitch. Yet, the traditional linear interpolation (LI) based filtered backprojection (FBP) reconstruction method leads to highly degraded images containing obvious image noise and ring artifacts around the edges under these situations. The aim of this work is to propose a novel iterative reconstruction algorithm for low dose helical CT. Methods: In our method, the helical scanning geometry and the cone angle in the multi‐slice CT are accurately modeled by proper computation of the forward projection matrix. CT images are reconstructed by minimizing a cost function consisting of a data fidelity term and a regularization term which requires that the solution has a sparse representation under a piecewise linear Tight‐frame (TF) basis. We tested our algorithm on a digital NCAT phantom at thorax region with two different high pitches (2:1 and 2.5:1) and low mAs level. The conventional LI‐based FBP algorithm was also studied for comparison purposes. Results: The CT images reconstructed by LI‐based FBP method contain obvious noise and ring artifacts around the edges, while the images by our TF‐based method show better quality with less noise and smooth edges. Compared with the LI‐based FBP method, our method enhances the signal‐to‐noise ratio by a factor of about 3.5 and also leads to higher edge cross‐correlation coefficients. Conclusions: The TF‐based iterative reconstruction algorithm outperforms the LI‐based FBP method in effectively removing the image noise due to low mAs level and ring artifacts of edges due to high pitches in the cases studied, demonstrating its promising applications for helical CT reconstruction.
WE‐A‐220‐02: Focused Ultrasound Treatment of Brain‐Review
Authors: Hynynen K
Published: November 2011

MRI‐guided focused ultrasound can concentrate mechanical energy deep in the brain noninvasively. This externally applied pressure wave can be used to thermally coagulate brain tumors or other structure for the treatment of disorders. In addition the focal energy can be used to disrupt Blood‐Brain barrier such that local delivery of therapeutic agents is possible. The basic principles and the current clinical and animal studies of this promising method will be reviewed and the future potential discussed.
WE‐A‐220‐03: Ultrasound Technology for Prostate Thermal Therapies
Authors: Diederich C
Published: November 2011

The objective of this talk is to provide a contemporary review of ultrasound devices and techniques as applied to delivery of thermal therapy to the prostate. This technology allows focal treatment or direct destruction of tissue for treatment of cancer or benign prostatic hyperplasia (BPH), or as an adjunct in the delivery of radiation therapy or chemotherapy, including temperature targeted drug delivery. Two therapeutic regimens are explored ‐ hyperthermia in the 40–45°C range and high temperature (>50°C) at lethal thermal dose exposures for thermal ablation. Commercial and clinical systems in development are reviewed including: transrectal high‐intensity focused ultrasound (HIFU) systems integrated with ultrasound image guidance; transurethral and endorectal high‐intensity ultrasound devices under MR guidance and control; interstitial ultrasound for hyperthermia integrated with HDR brachytherapy; and multi‐sectored endorectal applicators for hyperthermia adjunct to external beam radiation therapy with potential for thermal sensitive drug delivery. These image guided ultrasound therapy systems have the promise to deliver selective and precise thermal therapy or larger volume hyperthermia as required for the specified strategy for treatment of prostate disease. Educational objectives include technical concepts and treatment strategies of ultrasound therapy technology applied to treating prostate disease.
WE‐B‐224‐01: Cranial SRS/SRT
Authors: Yenice K , Solberg T
Published: November 2011

In the 50‐plus years since it was first introduced, stereotactic radiosurgery, high‐dose irradiation of cranial neoplasms delivered in a single fraction, has become a standard of care in the treatment brain tumors, vascular malformations, functional disorders, and pain. Modern radiosurgery can be performed non‐invasively and on an outpatient basis, yet with an extremely high degree of accuracy. Within the past ten years, the field of radiosurgery has seen numerous technological enhancements, including: the development of dedicated devices for stereotactic delivery, the use of relocatable frames to facilitate fractionated delivery, the development of image guided and “frameless” approaches, and the application to extracranial tumor sites. Each of these developments is accompanied by its own challenges in assuring targeting and dosimetric accuracy. In this presentation we review the fundamentals aspects of stereotactic targeting and delivery, the technologies for stereotactic localization and treatment of cranial targets, and the quality assurance aspects associated with establishing and maintaining a clinical radiosurgery program. Specifically, the presentation will:

1. Differentiate how radiation is delivered for Gamma Knife and Linac‐based (conventional and robotic) stereotactic radiosurgery.

2. Define the treatment planning parameters for Gamma Knife and Linac‐based stereotactic radiosurgery.

3. Discuss measures for assuring accuracy in stereotactic localization and dose delivery for Gamma Knife and Linac‐based stereotactic radiosurgery.
WE‐B‐BRA‐02: QA of Helical Tomotherapy TG‐148
Authors: Langen K , Papanikolaou N , Balog J , Crilly R , Followill D , Goddu S , Grant W , Olivera G , Ramsey C , Shi C
Published: November 2011

Helical tomotherapy is a relatively new modality with integrated treatment planning and delivery hardware for radiation therapy treatments. In view of the uniqueness of the hardware design of the helical tomotherapy unit and its implications in routine clinical practice, the Therapy Physics Committee (TPC) of the American Association of Physicists in Medicine (AAPM) commissioned Task Group 148 (TG‐148) to review this modality and make recommendations for quality assurance related methodologies. This report summarizes the findings of the Task Group and aims to provide the practicing clinical medical physicist with the insight into the technology that is necessary to establish an independent and comprehensive quality assurance program for a helical tomotherapy unit. In this task group report an overview of the TomoTherapy system and its unique aspects is provided. Delivery, imaging, and treatment planning quality assurance are discussed in three separate chapters of this report. Lastly quality assurance aspects are summarized according to their recommended frequency.
WE‐B‐214‐02: Radiation Safety for Staff in Fluoroscopy Suites
Authors: Schueler B
Published: November 2011

Radiation protection for staff working with medical x‐ray equipment has long been a concern. Overall, dose to radiation workers has decreased in the past 50 years. However, dose to operators of fluoroscopy equipment is an exception to this trend. In particular, physicians performing fluoroscopically‐guided interventional (FGI) procedures may receive high radiation doses. The nature of FGI procedures causes several conditions that result in unavoidable occupational exposure. The operator generally stands close to the patient to manipulate interventional devices. Close proximity and maintenance of a sterile field make use of lead shielding devices challenging. The clinical condition of the patient and use of anesthesia require that multiple healthcare workers be present in the procedure room. Procedure complexity results in lengthy fluoroscopy times. In addition, the volume of FGI procedures continues to rise resulting in ever‐increasing concern about occupational radiation exposure levels.

Medical physicists have several roles in the management of staff radiation exposure during FGI procedures. They may assist with the design of procedure rooms, including fluoroscopy equipment and control area placement, structural shielding specification and movable shielding device selection. They commonly are involved with fluoroscopic equipment purchase selection and system optimization, which includes evaluation of radiation exposure parameters. They may be asked to investigate instances of higher than expected personnel exposure levels, make specific recommendations for dose reduction and consult with staff about special circumstances such as performing fluoroscopy while pregnant. Most directly, they may be called on to provide radiation safety training to fluoroscopic equipment operators or other staff exposed to stray radiation. This presentation will review information medical physicists need to know in order to competently perform these tasks.

Learning objectives:

1. Summarize studies of occupational radiation exposure reported in the literature for different types of procedures and personnel.

2. Review personnel monitoring processes and procedures.

3. Become familiar with recommendations and resources for radiation safety training of fluoroscopy operators and other staff working with fluoroscopy.

4. Learn about new shielding devices and techniques for personnel protection.
WE‐B‐220‐01: Ultrasound‐Guided Techniques for HIFU Monitoring
Authors: Konofagou E
Published: November 2011

HIFU is the only truly noninvasive and non‐ionizing tumor treatment method. Unlike RF ablation, HIFU does not require interstitial tissue incision or needle insertion, but instead induces heat extracorporeally. Several methods have been developed for efficient HIFU monitoring. In ultrasound‐guided methods, the HIFU lesion can be detected when cavitation or boiling occurs due to the high bubble concentration that causes high echo amplitudes. Tissue coagulation also results in the increase of tissue attenuation, which has also been shown to efficiently map the lesion size when attenuation is estimated. Another technique that combines the resulting well known optical opacity of the resulting lesion and ultrasound is the opto‐acoustic technique that has been shown to determine the lesion formation. Finally, tissue coagulation has been associated with significant changes (2–10 times) in tissue stiffness. Elastography uses a small external compression in the detection of HIFU‐induced lesions after formation ex vivo. Harmonic Motion Imaging (HMI) uses a focused ultrasound (FUS) beam to generate an oscillatory acoustic radiation force for an internal, non‐ contact palpation to simultaneously internally estimate relative tissue stiffness and induce thermal damage. HMI has been shown to be successful in monitoring and assessing the formation of a lesion both ex vivo and in vivo.
WE‐C‐BRA‐01: Optical Imaging Techniques and Applications
Authors: Geng Jason
Published: November 2011

In this presentation, we provide a thorough overview of recent advances in 3D surface imaging technologies. We focus particularly on these non‐ contact 3D surface measurement techniques that require structured illumination. The high speed and high resolution pattern projection capability offered by the digital light projection (DLP) technology, together with the recent advent of imaging sensor technologies, may enable new generation systems for of 3D surface measurement applications that provide much better functionality and performance than existing ones, in terms of speed, accuracy, resolution, size, cost, and ease of use. Performance indexes of 3D imaging system in general are discussed and various 3D surface imaging schemes are categorized, illustrated, and compared. Numerous medical applications of 3D technologies are discussed with several examples.
WE‐C‐BRA‐02: Toward Real‐Time Optical Image‐Guided Radiotherapy
Authors: Li S
Published: November 2011

Looking ahead toward frameless, remote, and real‐time optical image‐guided radiotherapy, we will review the basic principles, mathematics, features, and clinical applications of most advanced optical imaging techniques being applied for live tracking of target motion and real‐time video‐guided repositioning of patients. We will theoretically examine marker‐based and surface‐based registration algorithms, their coordinate calibration and QA programs, measurements and corrections in 6‐degrees of freedom for image‐guided intracranial SRS and IMRT of superficial tumors, monitoring and interpretation of organ motion for gated RT and SBRT of NSCLC, and development in quantification and detection of surface deformation for IMRT of H&N and breast cancer. The advantages of fast imaging and registration, ease of use, and high accuracy and precision, and the drawbacks of correlating surface or markers with the internal target, image shadow artifacts, mismatching problems without robust applications or solutions, are demonstrated through clinical cases accrued in early clinical trials.