bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐BB‐201B‐02: Effective Use of Web‐Based Resources to Enrich Classroom and Collaborative Learning Activities
Authors: Sprawls P
Published: August 2010

Advances in digital technology, and especially the rapid developments of the internet, the world‐wide web, and associated applications are producing major changes in the process of education. The most significant feature of the web is that it connects learners (students, residents, life‐long learners, etc.) and learning facilitators (teachers, mentors, collaborators, etc.) not only with each other, but with extensive resources that can enrich and enhance their learning experiences.

Learning is a natural human function in which personal experiences produce changes in the brain. Of specific interest to us here are the changes that form knowledge structures of the physical aspects of a variety of medical imaging and therapeutic procedures. There are many variables associated with a learning experience that determine the characteristics of the knowledge structures and especially the outcomes with respect to the ability to perform specific functions.

It is recognized that highly effective learning experiences are ones in which the learner is in direct and interactive contact with the physical reality, the “real thing,” under the guidance of an experienced professional and perhaps working with collaborating learners. This is demonstrated in clinical medical education where there is direct contact with patients or the images used in radiology. Medical physics education is often challenged with the separation or the barrier that exists between a class and conference room learning activity, or small group discussion, and the physical reality that is being studied. This is generally because of issues of efficiency relating to the cost (time, resources, financial, etc.) to provide learners with rich, direct, and interactive experiences.

Vision is generally the most powerful medium for sensing, exploring, and investigating most aspects of the physical universe, and this is especially true for the field of medical physics. Digital technology for the creation, management, and distribution of visual representations and images is one of the major innovations in modern education. It provides the classroom/conference learning facilitators with the opportunity to guide the learners in a highly effective learning experience.

Learning Objectives:

1. Observe and evaluate learning activities with respect to effectiveness in producing desired outcomes and learner capabilities.

2. Experience the value of visuals and images to enrich learning experiences.

3. Use visuals and images to enhance human performance for both teachers and learners in a variety of learning activities.

4. Explore the web as a source of shared resources to enhance medical physics learning activities.

5. Remembering, “Technology is the tool; it is not the teacher.”
SU‐BB‐201B‐04: Effective Use of the RSNA/AAPM Modules
Authors: Hendee W
Published: August 2010

The AAPM has collaborated with the RSNA in producing web‐based educational modules in physics intended principally for radiology residents but also useful as learning tools for graduate students in medical physics. Phase 1 of the module project has been completed and 30 modules, each requiring about an hour of the student's time, are now available on the RSNA website, with an active link from the AAPM website. Another 16 modules comprise Phase 2; these modules are being produced now and will be released by the end of the year. The modules are designed for self‐learning, so that the medical physicist can teach through interactions and Q&A with the residents and students rather than lecturing to them. This approach to teaching is more effective for the residents and students and more rewarding for the physicist.

At the end of this presentation the participant will:

1. Know how to access the RSNA/AAPM web‐based physics modules

2. Know the titles of the modules in Phase 1 and Phase 2 of the RSNA/AAPM project.

3. Appreciate the usefulness of the modules for radiology residents and medical physics graduate students.

4. Understand the importance of questions embedded in the text and in the post‐test.

5. Recognize the opportunity the modules present for a new teaching role for medical physicists.
SU‐DD‐A1‐05: Comparison of Four Different Commercial Devices for Rapid Arc and Sliding Window IMRT QA
Authors: Varatharaj C , Stathakis S , Ravikumar M , Esquivel C , Buckey C , Tynan P , Calvo O , Papanikolaou N
Published: August 2010

Purpose: The aim of the study is to evaluate and compare the four different commercial devices for Rapid Arc and Sliding Window IMRT QA. Materials and methods: Fifteen consecutive RapidArc plans and ten IMRT plans were used for this study. All plans were optimized using Eclipse TPS. For all plans, the corresponding verification dose distributions were calculated using four (n=4) geometries. This include an acrylic phantom with film, the IBA with the MatrixX, the PTW Octavious phantom with the seven29 array, and the Scandidos Delta4 device. All plans and deliveries were calculated and delivered using the actual planned gantry and collimator angles respectively. All measurements were compared against the calculated ones, first by taking into account all points in the measurement planes and second by applying a threshold value where the points that received less than 20% of the normalized dose were excluded from the gamma index calculation. Results:Among these 25 plans, using all available points for the gamma calculation, all of them passed the criteria (3.0% and 3mm DTA) of having gamma values ≤ 1 (more than 90% of points). A few verification plans failed to pass the set gamma criteria when the evaluated points were limited to those only receiving more than 20% of the maximum dose. On average all the QA devices produced very similar results. This was further supported by the Bland‐Altman analysis that was performed and showed that all the calculated gamma values of all detectors were within 5% from those of film. Conclusions: The results showed that there insignificant differences between the detectors. All patient QAs passed the routine clinically criteria of gamma index values of 3% dose difference and 3mm DTA. We conclude that the dosimetric systems under investigation can be used interchangeably for routine patient specific QA. “Research sponsored by PTW‐Freiburg Company.”
SU‐DD‐A2‐01: Mechanistic Model of Radiation Induced Cancer after Fractionated Radiotherapy: Fit to Breast Cancer Risk after Radiation Therapy for Hodgkin's Disease
Authors: Schneider U , Besserer J
Published: August 2010

Purpose: The strongly elevated risk of breast cancer after radiotherapy for Hodgkin's lymphoma has become a major concern for female survivors of this disease. The risk of breast cancer after Hodgkin's lymphoma has been mainly attributed to supradiaphragmatic radiotherapy. Women treated with mantle field radiation experience up to 30‐fold increased risks for breast cancer compared with their peers in the general population. As a consequence radiation volumes and dose prescription for the treatment of Hodgkin's lymphoma have been reduced. The aim of this study is to develop a dose‐response model for breast cancer using risk data from epidemiological studies Hodgkin's disease patients treated with radiation therapy. Materials and Methods: The linear‐quadratic model of cell kill is applied to normal tissues which are unintentionally irradiated during a cancer treatment with radiotherapy. Tumor induction is modeled such that each transformation process results in a tumor cell. The microscopic transformation parameter was chosen such that in the limit of low dose and acute exposure the parameters of the linear‐no‐threshold model for tumor induction were approached. Results: The differential equations describing carcinoma and sarcoma induction were solved analytically. Cancer induction in this model is a function of treatment dose, the cell kill parameters (a, b), the tumor induction variable (μ) and the repopulation parameter (R). The dose‐response relationship for breast cancer was derived based on (i) the cancer risk model described above, (i) the analysis of breast cancer induction after Hodgkin's disease, and (iii) the reconstruction of mantle field treatment plans for Hodgkin's patients treated with radiotherapy. The fitted model parameters for an a/b=3 Gy were a=0.067Gy‐1 and R=0.62. Conclusions: The developed model can be used to further optimize involved field radiotherapy for Hodgkin's lymphoma with regard to second cancer induction.
SU‐DD‐A3‐04: Evaluation of Metal Artifact Reduction Using MVCT and Model Based Image Reconstruction
Authors: Paudel M , Kirvan P , Fallone BG , Rathee S
Published: August 2010

Purpose: To evaluate the performance of a model based image reconstruction in reducing metal artifacts in MVCT system in the image of a phantom representing bilateral hip prostheses, and to compare with traditionally reconstructed image. Method and Materials: A cylindrical plexiglass (19 cm diameter) phantom containing two steel inserts (2 cm diameter) was scanned using bremsstrahlung radiation from 6MeV electron beam passing through 4 cm thick solid water in Varian Clinac 2300C with bench‐top MVCT system. Iterative maximum‐likelihood polychromatic algorithm for CT (IMPACT) modified to include pair and triplet production for the MV spectrum was used with air, plexiglass, bone, and iron as base substances. Detector calibrated signal without beam‐hardening correction was used to get filtered back‐projected (FBP) image and used as an initial image in IMPACT. The final image at 1.25 MeV was obtained after 130 iterations. The second image was reconstructed using FBP with traditional signal and beam‐hardening corrections. The quantitative analysis included calculation of average attenuation coefficient in various regions of interest and their comparisons with theoretical value. Results: Visual inspection of the traditional image shows that the region between two steel inserts is dark with additional white streaks. Attenuation coefficients in ROIs fluctuate largely and deviate from theoretical values. In the iteratively reconstructed image, metal artifacts are remarkably reduced leaving behind only faint shadings in between the inserts. The average attenuation coefficients in ROIs were close to theoretical values. Image profile through the steel inserts shows restored uniform background between them. Conclusion: This experiment emphasizes the importance of model based image reconstruction and MVCT system for the metal artifact reduction. The beam‐hardening correction applied in conventional image reconstruction creates severe darkening and white streaks in the image. The complete removal of the metal artifacts requires further modeling and strategies which will be employed in future studies.
SU‐DD‐A3‐05: On‐Board SPECT: Localization Study Using Scanner‐Acquired Data
Authors: Roper J , Wilson J , Bowsher J , Turkington T , Yin F
Published: August 2010

Purpose: In previous computer‐simulation studies we have shown that on‐board SPECT imaging is a promising approach to localizing biological structure. The purpose of this study is to investigate SPECT localization using scanner‐acquired data. Method and Materials: A torso phantom was filled with 0.75 Ci/ml of 99mTc. Five targets (A–E) of 6:1 activity ratio — diameters of 22 to 34mm — were positioned in phantom. SPECT data were acquired with one Trionix Triad detector. The product of activity and 1.5‐minute count time models a 4.5‐minute clinical scan. Ensembles of 10 images were reconstructed using MLEM for 3 detector trajectories: 360°, 180° left lateral, and 180° right lateral. Localization was assessed across the noisy ensembles using non‐prewhitening observers that were forced to select the most suspicious target location from a 3.6‐cm diameter search region centered on target. True centroids were derived from a 12‐hour SPECT scan that registered with CT to within l/3mm. Localization error was calculated as the distance between true and measured centroids. Significance was assessed with the Wilcoxon rank sum test. Results: Mean localization errors for targets (A–E) are A) 0.80mm, B) 1.2mm, C) 1.9mm, D) 1.2mm, and E) 0.90mm using the 180° trajectory more proximal to each target. With the 360° trajectory, mean errors are A) 1.3mm, B) 1.3mm, C) 2.1mm, D) 2.2mm, and E) 1.5mm. Differences between the above 180° and 360° trajectories are significant (p < 0.05) at A, D, and E. Mean error is typically much worse using the more distal 180° trajectory: A) 4.5mm, B) 3.1mm, C) 2.8mm, D) 4.4mm, and E) 6.9mm. Conclusion: This study, using scanner‐acquired SPECT data, demonstrates mean localizations to within 1 or 2mm with 4.5‐minute scans. The study also shows that detector trajectory can substantially affect target localization and should be optimized for specific target sites.
SU‐EE‐A2‐01: Direct Measurement of Absolute Absorbed Dose in Scanning Proton Beams Based on Water Calorimetry
Authors: Sarfehnia A , Clasie B , Chung E , Lu H , Flanz J , Cascio E , Engelsman M , Paganetti H , Seuntjens J
Published: August 2010

Purpose: To develop a novel primary standard for absorbed dose to water DW measurement in scanning proton beams based on 4°C stagnant water calorimetry. Method and Materials: An in‐house built Domen‐type water calorimeter was used to measure the absolute DW directly in water at isocenter in a relatively flat SOBP region (peak‐to‐trough variation < 0.25%) of a scattered (250 MeV proton) and a scanned (15 layers painted with proton energies between 128–150 MeV) proton beam. The heat loss correction factor, defined as the ratio of the temperature in the calorimeter under ideal conditions to realistic conditions, was numerically calculated using COMSOL MULTIPHYSICS™. The calorimeter was modeled, proton beam scanning was simulated, and a time‐dependent heat‐transport module was used. The calorimetry measurements were compared to dose results from an Exradin T1 Mini Shonka following TRS‐398 protocol. Results: The heat loss correction factor was calculated to be 0.4% in scattered and 4.7% in scanned beams. We calculated the total 1‐sigma uncertainty on dose measurements to be 0.38% (scattered) and 0.64% (scanned). This was in contrast to a 1.86% uncertainty on the dose measured using the ionization chamber. The chamber dose results agreed with the absolute dose to water measurements made using water calorimetry well to within uncertainty: A difference of 0.14% in scattered beams and 0.32% in scanned beams was observed between the two techniques. Conclusions: Feasibility of performing water calorimetry in proton therapy and specifically in scanned beam delivery has been shown both numerically and experimentally. By adopting a water calorimetry‐based primary standard and calibrating user ionization chambers directly in proton beams, national dosimetry laboratories can significantly reduce the uncertainty on dose determination in proton beams from the current 1.5%–2% level down to sub‐percent regime similar to the current standard of practice in high energy photon beams.
SU‐EE‐A3‐03: Audiovisual Biofeedback Significantly Reduces Motion Blurring Artifacts in Four‐Dimensional (4D) PET Images
Authors: Yang J , Yamamoto T , Cho B , Seo Y , Keall P
Published: August 2010

Purpose: To investigate the hypothesis that audiovisual biofeedback reduces motion blurring artifacts in 4D PET images. Method and Materials: 4D PET scans were acquired on a GE PET/CT scanner using audiovisual biofeedback guided and free breathing traces. A static image was used as the reference. The physical phantom consisted of six hollow spheres (NEMA ICE body phantom) with 10, 13, 17, 22, 28 and 37 mm in diameter as targets and a cylinder (Hoffman 3D brain phantom) as background. The sphere targets were filled with 18F‐FDG at a fixed target‐to‐background ratio (8:1) based on 10 mCi/70 kg. The phantom was placed on a 3D programmable motion platform which produced the breathing patterns of four subjects with and without audiovisual biofeedback. 4D PET images with five respiratory bins were reconstructed for each breathing pattern. The segmented volumes, dice coefficients, 1D profiles, and 2D profiles were determined for evaluation and compared for each respiratory bin. The breathing patterns were analyzed for correlation between irregularity of breathing and motion blurring.Results: Audiovisual biofeedback significantly reduced motion blurring by 16.5% (1D profile, p=0.004), 22.6% (2D profile, p=0.003), 34.5% (volume, p=0.009) and 6.5% (dice coefficient, p=0.004) on average for the small spheres (≤17 mm), and by 4.3% (p=0.008), 2.7% (p=0.104), 0.7% (p=0.446) and 5.0% (p=0.014), respectively, for the large spheres (≥20 mm). In general, 4D PET motion blurring was dependent on the magnitude and irregularity of motion. Conclusion: The first investigation of the effect of breathing training on 4D PET images has been performed. The results indicate that audiovisual biofeedback can significantly reduce motion blurring in 4D PET images and may facilitate improved identification and localization of small lung tumors. Conflict of Interest: Supported by NIH/NCI R01 93626
SU‐EE‐A3‐06: Deformations in Tumor Volumes and High Uptake Sub‐Volumes Observed with 4D FDG‐PET
Authors: Aristophanous M , Yap J , Chen A , Killoran J , Berbeco R
Published: August 2010

Purpose: In lung cancer radiotherapy biologically image guided dose painting is a promising new technique. Correct localization of tumor sub‐volumes remains a major challenge. The purpose of this work was to investigate tumor deformations as observed with 4D PET. Method and Materials: A total of 17 lesions were identified on the 4D FDG‐PET/CT scans from 13 patients. The data were binned in five phase bins using the AZ‐733V gating system. On each one of the five phases of the 4D scan a classification algorithm was applied to obtain the region of highest uptake and segment the tumor volume. We looked at the shape deformation of both the high uptake sub‐volumes and the corresponding segmented tumor volumes. We examined the dependence of shape deformation on the amplitude of motion and the variation in the volume estimate. The effect of motion was minimized by registering the volumes of phases 20–80% with the 0% phase (inhale). The Overlap (O) of the volumes was measured and the shape deformation was defined as 1‐O. The variation in the volume estimate between the different phases was measured by the standard deviation of the % difference from the average volume.Results: The shape deformation of the high uptake sub‐volumes was on average 169% larger than that of the full tumor volumes; a statistically significant difference. The shape deformation of the high uptake sub‐volumes was moderately correlated with that of the tumor (0.75) and the amplitude of motion (0.55). The inhale‐to‐exhale phase (20%) resulted in the largest shape deformation.Conclusions: There is a complex relationship between the behavior of tumor volumes and high uptake sub‐volumes. In cases where advanced therapy techniques such as dose painting based on biological sub‐volumes, are being employed, a close examination of a 4D PET scan should be considered.
SU‐GG‐I‐03: Implications for Proton Therapy Treatment Planning of Tissue Characterization Curves from Different CT Scanners
Authors: Cheng C , Zhao L , Wolanski M , Allgower C , Zhao Q , James J , Dikeman K , Mills M , Li M , Frye D , Lu X , Srivastava S , Das I , Johnstone P
Published: August 2010

Purpose: Accuracy in proton beam treatment planning is intimately related to the quality of the treatment planning CT image set characterized by Hounsfield unit (HU). Relative electron density (ED) or relative stopping power (RSP) is associated with HU for inhomogeneity corrections. Variability of these parameters from several scanners is evaluated. Methods: HU‐ED curves were obtained from 15 CT scanners and a TomoTherapy unit operated in a scanner mode from nine different institutions. In all, five different RMI467 CT phantoms were used to obtain the different curves. The ED was converted to RSP using the Bethe‐Bloch formula and ionization energies in ICRU49. The various HU‐RSP curves were then compared. Results: The differences in material composition between the five RMI phantoms were well within the acceptable variation specified by the manufacturer (ranging from 8% for Lung300 to 0.5% for inner bone). The HU‐RSP curve for the TomoTherapy scanner was almost linear. The calibration curves for the 15 CT scanners exhibit similar shapes and can be described by three linear segments. In the HU range −700 to zero, the HU‐RSP curves are almost linear for all scanners, and are within 6% of each other. For the region immediately above water to RSP∼1.1, the RSP changed slowly with HU. Above RSP=1.1, the curves increases approximately linearly with HU. Except for one CT scanner, all other curves have <5% difference. For high Z materials with RSP>1.8, present HU‐RSP variation only allows linear extrapolation. Conclusion: While most CT scanners provide very similar tissue characterization, some exhibit larger variations than others probably because of the x‐ray spectrum. The RMI CT phantom could be modified to accommodate higher density materials covering the range RSP=2.0–7.0 (eg. Al‐Ta) for more accurate inhomogeneity correction for high Z materials. A point at RSP∼0.1–0.2 should also be added for the low density region.
SU‐GG‐I‐04: Effect of CT Scan Parameters on Adult and Pediatric CT Dose When Using Automatic Tube Current Modulation
Authors: Winslow J , Kappadath S
Published: August 2010

Purpose: To develop pediatric CT protocols by characterizing effects of CT parameters on adult and pediatric CT dose using automatic tube‐current modulation (ATCM). Method and Materials: Adult and 10‐year‐old (10yo) ATOM (CIRS) phantoms were scanned on a 16‐channel CT system (Emotion 16, Siemens) using ATCM (CareDose4D) to characterize the relationships between CT scan parameters and patient dose. The scan parameters investigated include scan‐kVp, reference‐mAs, scout‐kVp, patient‐size selection (adult/pediatric), and rotation‐time. Effective‐mAs delivered by ATCM was extracted from the DICOM header of each CT image. Results: Effective‐mAs delivered by ATCM varied with patient‐size selection, relative to reference‐mAs, it decreased for adult but increased for pediatric. Using ATCM the average effective‐mAs for 80, 100, 130 scan‐kVp changed by 81%&124%, 61%&110%, 55%&103% relative to reference‐mAs for the adult&10yo phantoms. However, when the 10yo was selected as adult, the average effective‐mAs decreased to 34%, 29%, and 26% of reference‐mAs. When selected as adult, dose decreased for all anatomical regions but when selected as pediatric, dose increase was observed for abdomen and pelvis (120–155%). ATCM effective‐mAs per slice scaled linearly (1±0.06) with input reference‐mAs. However, the minimum mA limited the modulation of effective‐mAs at low reference‐mAs. For both phantoms, 80 kVp scouts reduced the effective‐mAs by 5–7% on average (up to 20% for thorax) compared to 130 kVp scouts. For identical reference‐mAs, ATCM increased effective‐mAs for lower scan‐kVp; however, patient dose also decreased for lower scan‐kVp. For the adult&10yo phantoms, average dose at 80 and 110 scan‐kVp was 42%&39% and 72%&72% of that at 130 scan‐kVp, respectively. Conclusion: Patient dose with ATCM decreased for adult and increased for pediatric patients. The scout‐kVp affects ATCM schema with lower effective‐mAs for lower scout‐kVp. ATCM effective‐mAs is linear with input reference‐mAs. Net patient dose is reduced despite increased effective‐mAs at lower scan‐kVp using ATCM.
SU‐GG‐I‐05: CT‐Perfusion and FDG‐PET Imaging in Rectal Cancer: New Insights into Tumor Vasculature
Authors: Lammering G , Janssen M , Aerts H , Buijsen J , Öllers M , Lambin P
Published: August 2010

Purpose The purpose of this study was to prospectively investigate tumor perfusion in rectal cancer and to determine early changes after hypofractionated radiotherapy. Furthermore, we correlated FDG uptake and tumor perfusion parameters intratumorally. Method and Materials Thirty patients diagnosed with rectal cancer were prospectively included in this study. All patients underwent FDG‐PET and perfusion‐CT imaging prior to the start of radiotherapy treatment. The perfusion‐CT images were analyzed using the extended Kety‐model, quantifying tumor perfusion with three parameters: Ktrans, ve and vp. On the PET‐images, the tumor was delineated using automated SUV‐thresholding with the threshold (percentage of SUVmax within the tumor) depending on the tumor‐to‐background signal ratio. For each patient and for several tumor subrogions, the mean and maximum FDG uptake (SUV) and tumor perfusion (Ktrans) were quantified and correlated using the Spearman's rank correlation coefficient (ρ).Results The median tumors Ktrans values increased significantly after radiotherapy. Also, histogram analysis showed a shift of tumor voxels from lower Ktrans values towards higher Ktrans values. The median Ktrans values were significantly higher for tumor than for muscle tissue on both the pre‐scan and the post‐scan. In contrast, no differences between tumor and muscle tissues before and after radiotherapy were found for ve and vp. When correlating the tumors mean and maximum Ktrans values to the corresponding SUVs, positive correlations were found. Also when correlating the mean and maximum perfusion and FDG uptake within the created tumor subrogions, positive correlations were found. Conclusion Hypofractionated radiotherapy of rectal cancer leads to an increased tumor perfusion as reflected by an elevated Ktrans. FDG uptake was found to correlate with tumor perfusion assessed from dynamic perfusion‐CT images. Highly perfused rectal tumors presented with higher FDG uptake levels when compared to relatively low perfused tumors.
SU‐GG‐I‐06: Our Experience Reducing CT Radiation Dose to Pediatric Populations
Authors: Mathieu K , Fitzgerald N , Cody D
Published: August 2010

Purpose: To share our experience implementing new strategies (as technology became available) to reduce Computed Tomography (CT) radiation dose to pediatric patients at a high‐volume cancer center housing 13 General Electric (GE) multidetector row CT (MDCT) scanners representing various models. Method and Materials: In October of 2008, tube current modulation (TCM) was implemented and protocols were created based on the display field of view parameter. Approximately 10 months later, the noise index for all protocols was increased by 2. Three months after increasing the noise index, the minimum and maximum tube current (mA) values were both dropped by 20% across all protocols. A chart review was used to identify eight pediatric patients (from 1 – 15 years old) that received chest CT scans before and after implementation of each of the three dose‐reduction strategies; within each patient, all technical parameters other than effective mAs were constant between scans. Results: The average effective mAs (across all eight patients) dropped from 103 mAs (49 – 171 mAs) prior to October 2008 to 75 mAs (42 – 109 mAs) after implementing all of three strategies. TCM alone reduced dose by an average of 19 %, increasing the noise index combined with TCM by 20% on average, and dropping the minimum and maximum mA values combined with the other two strategies by an average of 23%. All of the exams included in this study were of diagnostic quality with respect to the imaging task. Conclusion: To date, the combination of these efforts has led to an average reduction in dose of 23%. Additional approaches (adaptive statistical iterative reconstruction and organ shielding) are currently being evaluated and are expected to provide even greater dose‐savings to our pediatric patients.
SU‐GG‐I‐127: Characterization of Point Spread Functions of Indirect Digital Radiography Detectors
Authors: Sechopoulos I , Schmitz A , Eberhard JW
Published: August 2010

Purpose: To characterize the point spread function (PSF) of indirect digital radiography detectors with varying scintillator thickness. Method and Materials: The Mantis Monte Carlo program was used to simulate x‐ray detection in indirect digital detectors. The simulation was first validated by replicating previously published geometries and comparing the results. Upon validation, the CsI:Tl layer thickness was varied between 0.5 mm to 2.0 mm. Based on previous publications by other groups, the amorphous layer thickness was defined as 20% of the total CsI:Tl layer, and the needles of the structured layer were simulated with a 5° tilt, in varying directions. The incident x‐rays were simulated both normal to the detector and at non‐normal angles, representing incidence at various locations. Methods were developed to estimate the PSF for any needle tilt direction from the results of only four simulated tilt directions. Results: Comparison of the validation results yielded acceptable similarity. The CsI:Tl quantum efficiency (QE) in the simulations agreed with theoretical predictions. It was found that the CsI:Tl needle tilt direction introduces important variations and asymmetries in the PSF, especially for non‐normal x‐ray incidence angles. The interpolation method developed successfully estimates the PSF for any tilt direction from the results of only four simulated tilt directions. As expected, the PSF widens with increasing CsI:Tl, with the presence of the amorphous CsI:Tl layer introducing significant spreading of the PSF. Conclusion: The PSF at various detector locations will be used to develop and test a shift‐variant deconvolution algorithm which will allow for further optimization of the image acquisition process, by allowing for the use of thicker scintillators, to take advantage of potentially increased DQE despite a wider PSF. In addition, the impact of relatively thinner amorphous CsI:Tl layers and smaller needle tilt will be investigated.

Conflict of Interest: Research sponsored by GE Global Research.
SU‐GG‐I‐128: Characterization and Identification of Artifacts for Helical 4D CT Image
Authors: Han D , Bayouth J , Bhatia S , Sonka M , Wu X
Published: August 2010

Purpose: To characterize the artifacts occurring in helical 4D CT imaging and propose a method to identify the artifacts automatically. Method and Material:_Given two adjacent stacks obtained from same respiration phase, we seek to determine if there are artifacts between them. The proposed method uses a “bridge” stack strategy to connect two stacks. Using normalized cross correlation convolution (NCCC), two stacks are mapped to the “bridge” stack and the best matching positions can be located. Using the position information, the method can determine if there is an artifact or not between the two stacks. Furthermore, by combining the matching positions with NCCC values, the performance can be improved. To validate the method, sensitivity and specificity are used as the metrics to evaluate the method with 500 hundred stacks on five patients which are labeled by three physicists independently. Results: Three types of artifact sources are categorized: low frequency respiration, high amplitude period and low amplitude period. Low frequency respiration can cause blurring. Both amplitude period and low amplitude period can cause anatomy gap and overlap occur depend on different anatomy motion directions. The artifacts identification results show that four of the five patients' data are validated using the proposed method. The average sensitivity is about 83% and the average specificity 84%. Furthermore, the results show that the method improves sensitivity to 87.8% and specificity to 89% when combining matching positions with NCCC values. Conclusion: This study shows that the spatial artifacts during 4D CT imaging are characterized and can be located by the proposed method. It is valuable to quantify the quality of 4D CT image and reduce the artifacts directly from the reconstructed images.
SU‐GG‐I‐131: Assessment of Transducer Artifacts Using a Novel, Low Cost Ultrasound Phantom
Authors: King D , Tradup D , Stekel S , Hatz H , Hangiandreou N
Published: August 2010

Purpose: Ultrasound artifacts are often identified by scanning a uniform region of a rigid tissue‐mimicking phantom while moving the transducer across the scan surface, and identifying any deviations from the expected smooth echotexture. Due to the rigid nature of commercial phantoms it is difficult to simultaneously couple the entire face of curved array transducers. We have proposed a novel low cost liquid phantom with a flexible scan surface. The purpose of this work is to demonstrate the proof of concept of this unique phantom. Method and Materials: The phantom consisted of a water/cornstarch solution enclosed in a thin latex balloon (thickness 0.24 mm). When shaken, the cornstarch provides a dynamic speckle pattern. Initial experiments were conducted to establish the basic effectiveness of this innovative phantom to demonstrate artifacts, to assess reproducibility of image acquisition, and inter‐operator variability. The phantom was imaged using an Acuson Sequoia US scanner and 4 transducer models (9L4, 6C2, 4V1 and EC‐10C5), and dynamic clips of the changing speckle field were recorded. Two transducers with independently‐confirmed artifacts were also tested. Results: The flexible scanning surface allowed excellent acoustic coupling of the entire face of all transducer models with the phantom, including tightly curved arrays. Little manual transducer motion was required with the liquid phantom as a result of the dynamic speckle field. Artifacts due to inactive elements were detected, including a single crystal dropout. Using a defined scan protocol, reproducible clips exhibiting low inter‐ and intra‐ operator dependency were obtained by 5 operators with minimal training, for transducers with and without artifacts. Conclusion: Due to its ease of operation, low cost, and sensitivity, this phantom may be superior to current methods of detecting ultrasound artifacts, and has the potential to promote better acceptance and compliance of ultrasound quality control.
SU‐GG‐I‐133: The Analysis of the Transformation Map Construction for Optic Flow Based Image Registrations
Authors: Michalski D , Mutaf Y , Heron D , Bednarz G , Huq M
Published: August 2010

Purpose: A formal analysis and computational examples of the deformation field calculation for optic‐flow‐based image registration algorithms is presented. The addition and composition of the deformation field updates are compared for different types of medium deformation. Method and Materials: A robust family of image registration algorithms is based on the optic flow method. They are iterative and use the conceptual temporal and spatial gradients of the registered images for the determination of the deformation between the objects. This transformation map is obtained iteratively from the current one by: i)the addition and ii)the composition with the update field. These methods are formally different and interplay with image gradients. This effect of the interplay is examined with respect to the type of the deformation. Synthetic and patient images are used in an experiment. Results: The inter‐relation of the deformation field and the gradient forces of the algorithms provides the main gauge of the effectiveness of the iterative process of the determination of the deformation field. The disparity in the alignment of the gradient and the field decreases the efficiency of the iterative process for the additive update. The translational differences between the moving and static image do not affect either methods. The variable deformation is properly addressed by the composition in the iterative process. Conclusion: This analysis can be generalized for any image registration algorithms, which uses the multiple pass approach for the image update in an iterative scheme. The obvious temporal load of the field composition can be mitigated by the use of linear interpolations. For multigrid‐based image registrations, the low resolution steps do can use B‐spline interpolations without sacrificing performance. The improved effectiveness of the deformation field buildup is an important issue for the creation of physically veritable diffeomorphic transformations.
SU‐GG‐I‐139: Synergetic Effect of Docetaxel and MR Guided Focused Ultrasound (MRgFUS) for Prostate Cancer
Authors: Chen L , Mu Z , Wallentine A , Pollack A , Ma C
Published: August 2010

Purpose: Our previous studies showed increased 3H‐docetaxel concentration in prostate tumors in the MRgFUS treated group compared with the control group. The purpose of this study is to determine if MRgFUS increases the efficacy of docetaxel in inhibiting prostate tumor growth. Method and Materials: LNCaP cells (106) were injected into the prostate of male mice. When tumors reached the volume of 47 ± 3 mm3 on MRI, treatment was performed using an InSightec ExAblate 2000 with a 1.5 T GE MR scanner. The animals were randomly divided into 3 groups (n=5/group). For group 1, mice were treated with MRgFUS once a week for two consecutive weeks. Animals were treated with pulsed ultrasound using 1MHz; 5 W acoustic power and the 81 mode setting (5 Hz frequency with 0.1s power on, 01s power off) for 60 seconds for one sonication. Multiple sonications (4–6) were used to cover the whole tumor volume. Immediately after the MRgFUS treatment, docetaxel (10mg/kg) was injected by tail vein. The animal was allowed to survive for 4 weeks after the last treatment. The tumor growth was monitored on MRI. Animals in Group 2 were treated with Docetaxel injection only. Animals in group 3 were used as control. Results: The relative tumor volume in MRgFUS + Docetacel treated group was 0.788 ± 0.07 and 0.75 ±0.11 1 week and 4 weeks after the last MRgFUS treatment, respectively, while for the group received only Docetaxel it was 0.908 ± 0.23 and 1.48 ± 0.54 1 at week and 4 weeks, respectively. Both groups showed smaller tumor volumes compared to the control group. Conclusions: MRgFUS has a potential to increase the efficacy of docetaxel in inhibiting prostate cancer growth. More experiments are under way for optimal ultrasound treatment parameters to improve the synergetic effect.
SU‐GG‐I‐142: Comparison of 3T MRI and 3D Endorectal Ultrasonography for Evaluating Invasion to Muscularis Propria and Perirectal Tissue in Colorectal Cancer
Authors: Feng W , Xuan Y , Hu J
Published: August 2010

Purpose: The purpose of this study is to investigate whether 3T MRI can offer better diagnostic value over 3‐D‐EUS for evaluating the invasion to muscularis propria and perirectal tissue. Method and Materials: 26 patients (age range 45–78, mean age 59.42) with biopsy proven rectal cancer underwent 3T MR Imaging and endorectal sonography. Pathology was the gold standard. Invasion through the muscularis propria and perirectal tissue at histological examination were used as the standard of reference. The sensitivity, specificity, positive predictive value, negative predictive value and overall accuracy in prediction of muscularis propria invasion and perirectal invasion were calculated for both 3T MRI and 3D EUS. Results: In evaluating the muscularis propria invasion in rectal cancer, the overall sensitivity, specificity, positive predictive value, and negative predictive value of 3T MRI 100%, 50%, 91.7%, 100% (P=0.125) respectively, for depiction of the invasion depth to muscularis propria. Sensitivity, specificity, positive predictive value, and negative predictive value using EUS were 90.9%, 100%, 100%, 66.7% (P=0.125) respectively. In evaluating the perirectal tissue invasion in rectal cancer, sensitivity, specificity, positive predictive value, and negative predictive value for 3.0 T MR was 75%, 100%, 100%, 71.4% (P=0.0078) respectively, for depiction of the invasion depth to perirectal tissue. Sensitivity of EUS for the depiction of the invasion depth to perirectal tissue was 25%, specificity was 100%, positive predictive value was 100%, negative predictive value was 45.5%, P=0.0078. 3T is more sensitive and accurate than EUS for evaluating the invasion depth to perirectal tissue. There is no difference between 3T and EUS for evaluating the invasion depth to muscularis propria. Conclusion: 3T MRI derives benefit mainly from the improvement of Single to noise ratio and spatial resolution. 3T MRI is non invasive and offers better diagnostic value over 3‐D‐EUS for evaluating the invasion depth of rectal cancer.
SU‐GG‐I‐144: Accelerating Non‐Contrast‐Enhanced MRA with Inflow Inversion Recovery by Using Skipped Phase Encoding and Edge Deghosting (SPEED)
Authors: Chang Z , Xiang Q , Shen H , Yin F
Published: August 2010

Purpose: Non‐contrast‐enhanced MR angigraphy (MRA) has always been a valuable clinical tool to study vasculatural diseases. The recently arising concerns of constrast agents in contrast‐enhanced MRA encouraged more use of non‐contrast‐enhanced MRA. The aim of this work is to accelerate non‐contrast‐enhanced MRA with inflow inversion recovery (IFIR) with a fast imaging method, Skipped Phase Encoding and Edge Deghosting (SPEED) Method and Materials: IFIR imaging uses a preparatory inversion pulse to reduce signals from static tissue, while leaving inflow arterial blood unaffected, resulting in sparse arterial vasculature on modest tissue background. By taking advantage of vascular sparsity, SPEED can be simplified with a single‐layer‐model to achieve higher efficiency in both scan time reduction and image reconstruction. SPEED can also make use of information available in multiple coils for further acceleration. The techniques are demonstrated with a 3D renal non‐contrast‐enhanced IFIR MRA study performed on a 3.0 T scanner (GE Healthcare,WI) with a Respiratory Triggered IR‐Prepared Fiesta (SSFP) sequence (matrix 256×256, FOV 36cm, TI 200ms, TR 4.2ms, TE 2.1ms, slice thickness 2mm, space between slices 1mm, flip angle 70°, single acquisition, slices 116). Results: Images are reconstructed by SPEED based on a single‐layer model to achieve an undersampling factor of up to 4.2 using one skipped phase encoding direction. By making use of information available in multiple coils, SPEED can achieve an undersampling factor of up to 8.3 with four receiver coils. The reconstructed images generally have comparable quality as that of the reference images reconstructed from full k‐space data. Conclusion: This study demonstrated the successful application of SPEED to accelerate non‐contrast‐enhanced IFIR MRA based on a single‐layer‐model. Although the single‐layer‐model SPEED is demonstrated with only renal IFIR MRA, it may have great potential in other MRI applications, particularly in cases where sparse signals are distributed on a modest tissue background.
SU‐GG‐I‐146: Characterization of Mouse Mammary Glands by Measuring T2*: A Comparison of SV40Tag and FVB/N Mice
Authors: Hipp E , Fan X , Jansen S , Markiewicz E , Vosicky J , Karczmar G
Published: August 2010

Purpose: An improved understanding of T2* in normal breast and intraductal cancer could lead to improvements in diagnostic accuracy. This study characterizes T2* in both a preclinical model of breast/mammary cancer (SV40Tag) and in healthy (FVB/N) mice. At ∼12 weeks, C3(1)SV40Tag mice develop mammary in situ neoplasms (MIN) that resemble ductal carcinoma in situ (DCIS) in women. Method and Materials: Eight SV40Tag and six FVB/N mice were imaged using a 9.4T Bruker magnet. Respiratory gated multi‐gradient echo pulse sequences were used to measure T2* with equivalent TR ∼1000ms, minimum TE of 1.5ms, 9 echoes at 3ms spacing. Generally, T2* was calculated by fitting the MRI signal intensity to a single exponential decay function. However, when fat was present, a modulus of complex double exponential decay function was needed. Results: For SV40Tag mice, T2* of muscle, lymph node, and tumor can be calculated from a single exponential function. T2* of normal mammary gland (NMG) and MIN need to be extracted from the modulus of complex function due to the fatty signal. Conversely, for FVB/N mice, all T2* can be calculated from single exponential function. On average muscle, tumor and NMG water components have slightlysmaller T2* values (∼15ms), but lymph node and NMG water components have slightly smaller T2* values (∼9.5ms). The fat in NMG and MIN have the smallest T2* values (∼3.8ms). In addition, NMG in SV40Tag is fattier than in FVB/N mice (57% vs. 12%, p<0.0001) for the selected ROIs. Conclusion: To accurately determine T2*, it is necessary to separate water/fat in fat‐rich mammary glands. In this pilot study, MIN lesions exhibit a larger separation between the long and short T2* values in comparison to NMG. Additionally, SV40Tag mice exhibit a higher percentage fat in NMG ROIs due to genetic differences.
SU‐GG‐I‐147: Can Compressive Sensing Improve Low‐Contrast Object Detectability in Accelerated MRI Applications?
Authors: Trzasko J , Manduca A , Bao Z , Stiving SO , McGee KP , Bernstein MA
Published: August 2010

Purpose: Compressive Sensing (CS) methods can reduce image artifacts when reconstructing undersampled data sets. Most MRI applications of CS, however, have focused on high contrast objects such as gadolinium‐enhanced vessels, rather than on low‐contrast object detectability (LCOD). Using a novel computational framework, we rigorously examine whether CS reconstruction can improve the LCOD performance of several standard techniques for undersamped MRI reconstruction — across a variety of undersampling rates and strategies. Methods and Materials: The American College of Radiology (ACR) quality control (QC) phantom was imaged on a GE 14.0 1.5T MRI using our routine quality assurance protocol and an 8‐channel head coil. The raw k‐space data corresponding to the 5.1% contrast detectability plane was retrospectively undersampled along the phase‐encoded direction at 10 different rates (10–100%) and, for each, using 3 different distribution strategies: 1) low‐frequency band only; 2) uniform sampling; 3) random sampling (Poisson Disk). For the latter case, 5 sampling instances were generated at each rate. Each undersampled data set was reconstructed using 3 different strategies: 1) zero‐filling with root sum‐of‐squares combination; 2) Tikhonov‐SENSE; and 3) Compressive Sensing (L1‐minimization, finite difference sparsity). Reconstruction results were then analyzed with our in‐house developed QC software to automatically determine the fraction of complete visually detectable spokes which, is a measure of LCOD performance. Results: Across all sampling rates and under all sampling strategies, the LCOD score for CS reconstructions was consistently equal to or higher than that of the other two reconstruction methods. The CS advantage was especially pronounced at very low sampling rates (≤30%). Conclusion: Although most CS work to date has focused on high‐contrast objects, CS reconstructions consistently improved LCOD compared to several standard MRI reconstruction techniques for undersampled data. These results suggest that CS reconstruction is useful not only for undersampled high contrast objects, but can improve LCOD as well.