bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐E‐T‐6E‐02: Dose‐Volume Modeling & Clinical Radiotherapy: The Art of Systematic Oversimplification
Authors: Bentzen SM
Published: June 2005

Science has been called “the art of systematic oversimplification” (Popper). Using this as a criterion, dose‐volume modeling is a very scientific discipline! A flurry of more or less mechanistic models has been proposed but despite their conceptual appeal these models are obviously oversimplified representations of what we know about the radiation pathogenesis of side‐effects of radiotherapy. From an empirical point of view, most clinical data sets do not provide sufficient structural resolution to allow validation of — or even discrimination between — any of these. Perhaps it is symptomatic that the most widely used, and in some sense most successful, dose‐volume model is the “post‐modern” model proposed by Lyman 20 years ago. Notwithstanding these philosophical concerns, dose‐volume modeling has established itself as an exciting research field and a very useful tool in this age of conformal and intensity‐modulated radiotherapy. Arguably, the use of these oversimplified models has greatly expanded and intensified the systematic collection and analysis of dose‐volume data. It is tempting to draw a parallel to the use of the linear‐quadratic model: originally this was closely linked to the target‐cell hypothesis, a point of view that has all but disappeared now, where most researchers see the model as a pragmatic means of condensing empirical clinical data. Dose‐volume models are currently used at two levels: to obtain a figure of merit for rival radiotherapy plans in daily routine planning and in the development of novel radiotherapy protocols to be tested in clinical trials. While current models have some credibility in the former application, they fail miserably in producing reliable, portable estimates of the absolute incidence of complications when applied in independent data sets or when extrapolated to considerably different dose distributions. This is not entirely the fault of the models: reliable estimates of the incidence of normal‐tissue effects after radiotherapy are generally not available even in case of a uniform dose‐distribution delivered to a critical structure. In the presentation, I will discuss dose‐volume models from the perspective of evidence based medicine. How can these models be used in clinical trials design? And what are the most promising directions for future research? The possible effect of low‐dose hyper‐radiosensitivity and the challenge of incorporating the effect of cytotoxic drugs into dose‐volume models will be discussed.

Educational Objectives:

1. To understand the strengths and weaknesses of current dose‐volume models from the perspective of evidence based medicine.

2. To identify directions for future research on the clinical application of dose‐volume models
TU‐A‐I‐617‐01: Positron Emission Tomography Data Corrections and Calibrations
Authors: Levin CS
Published: June 2005

There are several undesired physical effects inherent to the process of detecting annihilation photons in PET. These factors include photon attenuation, detector response non‐uniformity, detector saturation, random and scatter coincidence background, and isotope decay. Acquired PET data must be corrected for these physical factors either before or during image reconstruction in order to facilitate qualitative and quantitative accuracy. Quantitative accuracy of PET image data further relies upon factors such as proper calibration to true isotope activity and correction for resolution blurring. We will give an overview of undesired physical factors affecting PET data and methods used to reduce or remove their effects through measurements and software algorithms. We will focus only on those techniques implemented in the current state‐of‐the‐art commercial PET systems.

Educational Objectives:

1. To become familiar with physical effects that degrade the accuracy of PET data.

2. To understand common approaches taken to reduce or remove these unwanted effects.
TU‐A‐I‐609‐01: Characteristics and Performance Evaluation of Digital Image Displays
Authors: Roehrig H
Published: June 2005

The diagnostic radiology department is in the middle of a revolutionary change [1, 2]. Digital imaging sensors and displays are replacing the traditional sensor and display, namely, the film‐screen combination. In many institutions the Totally Digital and Film less Radiology Department already exists. Here images are generated using digital detectors, and diagnosis is made using softcopy displays such as Cathode Ray Tube displays (CRT) and Liquid Crystal Displays (LCD). CRTs are analog devices while LCDs are discrete and digital devices. This presentation describes the resulting image quality in terms of spatial resolution or Modulation Transfer Function (MTF) and in terms of spatial and temporal noise or Noise‐Power‐Spectrum (NPS) and Signal‐to‐Noise‐Ratio (SNR). Basic display image quality affects greatly the presentation of clinical images on the specific display. It is the display, which determines if the image quality captured by the image detector is transferred to the observer, i.e. the radiologist. So the display has a special importance amongst all components of the imaging chain. There is a need to test the image quality of the digital displays, called Acceptance Testing, when the displays are acquired from the display companies. In fact, before the acquisition of the displays by the user, there is a need for the display manufacturer to test the image quality of the digital displays in order to get FDA approval (i.e. 410 k). Amongst other performance characteristics the FDA wants to see the MTF and the NPS of the respective displays at several luminance values. There is a need for Image Quality Control in the Reading Room, because many things can go wrong in the Reading Room: (1) The luminance of the digital displays (CRTs as well as LCDs) can change, (2) the spatial resolution of CRTs can change as the luminance changes because the MTF is related to the luminance through the size of the scanning electron beam, (3) the display can be set‐up incorrectly. These problems need to be evaluated in the Reading Room. The AAPM Task Group 18 has prepared a thorough report on “Assessment of Display Performance for Medical Imaging Systems”.

• There are visual or qualitative or basic tests, where a human observer views the display and makes a decision on the presence or absence of a test object.

• There are quantitative or advanced tests, where an instrument like a photometer or a CCD camera is used to make a measurement and provide quantitative data.

Educational Objectives:

1. Understand the operational characteristics of CRTs and LCDs

2. Understand the concept of display Image Quality Evaluation.

3. Understand the need for acceptance testing of display image quality.

4. Understand the need for Image Quality Evaluation in the Reading Room

5. Understand the idea of the AAPM TG18 Assessment of Display Performance for Medical Imaging Systems

6. Understand the idea of quantitative evaluation of display image quality using a hand‐held CCD camera.
TU‐C‐I‐611‐01: Recent Developments in CT Technology
Authors: Kalender W
Published: June 2005

The first lecture in the symposium “The New CT” will cover recent developments in hardware. This relates to the scanner mechanics, the x‐ray source, and the detector system, but also to new designs such as C‐arm and micro‐CT systems. The largest portion will be dedicated to detector concepts and characteristics. With rotation times below 0.5 s, modern clinical CT systems pose increasing demands on the mechanical design of the scanner and of all its components. These are contrasted by the demands of C‐arm systems using flat panel detector where rotation times are typically between 5 and 20 s. Due to the increased rotation speed in clinical CT, x‐ray power levels increase accordingly to allow for unimpaired image quality, in particular unaltered noise levels. The latest developments in x‐ray source technology, which offer power levels of 80 to 100 kW, will be reviewed and explained. CT detector technology has received remarkable interest in the past years. The continuous development from single‐slice to multi‐slice systems, including detectors allowing the simultaneous acquisition of 2, 4, 6, 8, 10, 12, 16, 32, 40, and 64 slices, has even been viewed as the “slice race” or the “slice war” in the media. The technological basis will be reviewed. In particular, the question if this development shall and will continue will be discussed. This also includes the potential role of flat panel detectors which have come into use with C‐arm systems and which are now being used frequently for interventional CT and for CT angiography. The presentation will conclude with a short review of dose management and micro‐CT systems. Conflict of Interest : WAK is a consultant to Siemens Medical Solutions.

Educational Objectives:

1. to understand the detector concepts presently in use in clinical CT

2. to understand the distinction between multi‐row detectors and multi‐slice scanning

3. to understand the concepts and requirements for exposure control systems
TU‐D‐I‐609‐03: Computer‐Aided Detection (CAD) in the Laboratory and the Clinical Environment
Authors: Gur D
Published: June 2005

Computer‐Aided Detection (CAD) is intended to be used in a specific way and several studies have shown that when it is used appropriately improvements in performance can be realized. The effect seems to be much more noticeable in the laboratory than in the clinic. Data ascertained in both environments clearly suggest that the measurement methodology is extremely important as is the actual use of CAD as a part of the clinical workflow. Our observations suggest the following: 1) regardless of the actual improvement (or not) in accuracy, CAD is an important tool; 2) most radiologist do not use it in the clinical environment as originally intended; 3) comparison of sequential viewing “without” followed by “with” CAD may not be the appropriate/optimal way to analyze accuracy improvements; 4) change in detection rates are expected to be low and temporary, while change in average size (or stage) are expected to be small and persistent; 5) performance of the CAD alone does affect observer performance; 6) reliance on CAD in the area of micro‐calcifications may result in an increase in biopsy rates; 7) there is a significant difference in the performance of current CAD systems in regards to the detection of micro‐calcifications and masses, and this difference results in a significant difference in the level of reliance on CAD results with respect to the two abnormalities. These observations and the supporting experimental data will be shown and discussed.

Educational Objectives:

1. Understanding the difficulty in measuring performance changes with the incorporation of CAD technology into the clinical environment.

2. Understanding the importance of study design in measuring the impact of CAD technology.

3. Understanding the magnitude of the “human” factor in observer performance studies.
TU‐E‐P‐618‐01: Maintenance of Certification Update, MOC Educational Opportunities and CARE Update
Authors: Herman M , Hendee W , Morin R , Mills M
Published: June 2005

The official beginning of the ABR Maintenance of Certification program for medical physicists began this year. Many have registered and many more have questions. The purpose of this session is to present a brief review of the ABR MOC program, its current status and to delve into some of the details related to successfully fulfilling the MOC process. The physics trustees of the ABR will first present a review of the MOC program as it is currently being implemented for medical physicists. The driving forces behind MOC as well as the four essential components of the program, Professional Standing, Lifelong Learning/Self Assessment, Cognitive Expertise, Assessment of Practice Performance, will be reviewed. Examples will be provided in each case to help medical physicists understand the details of the process. The web‐based process will be outlined. Specific issues related to individuals who have less than ten years until their certificate expires and to those certified by ABMP will be addressed. The MOC presentation will be followed by presentations from the chair of the ACR Commission on Medical Physics and the Chairman of the American College of Medical Physics, both who will address opportunities and developing programs aimed at providing the essential continuing education credits necessary for each of us to maintain certification. The final portion of this session will be dedicated to an update on the CARE bill. The Alliance for Quality Medical Imaging and Radiation Therapy (of which both the AAPM and ACMP are members) met again in March 2005 to further develop, in anticipation of passage of the Care Bill, statutes designed to specify the training and experience of all medical professions performing or planning medical imaging and radiation therapy. The Bill, as written, is designed to include both Medical Physicists and Medical Dosimetrists in the proposed regulation. The CARE bill was recently reintroduced in the US congress. An opportunity to ask questions of the speakers will be provided at the end of the session.

Educational Objectives:

1. To review the current ABR maintenance of certification program

2. To understand the process for all time limited certificate holders

3. To understand mechanisms offered by ACR and ACMP to obtain MOC credits

4. To review the current status and implications of the CARE Bill
TU‐E‐T‐6E‐04: The Dosimetry Training Tool (DTT) Project
Authors: Boyer A , Kaylor S
Published: June 2005

Goal: A program was funded in 2002 by the NCI to produce and support a web‐based computer‐aided distant learning tool for training medical dosimetrists. Medical physicists, radiation oncologists, and medical dosimetrists have served as volunteer authors of the 24 modules in the tool consistent with the recommendations of the American Association of Medical Dosimetrists (AAMD) for a recognized medical dosimetry training program. The distant learning modules contain assessment instruments for both the summative evaluation of the students as well as the formative evaluation of the learning tools. The intent of this project is for graduates from these programs to apply for the certification examination administered by the Medical Dosimetrist Certification Board when they have accrued the required two years of training and experience. Accomplishments: The authors have developed and refined their individual modules by electronic transmission of course material to developers at Stanford. Over 7000 html pages are currently online. Medical physicists, radiation oncologists, and medical dosimetrists in radiation oncology centers serve as mentors for the students. A test of the tools is being conducted by 73 mentors registered to train approximately 159 students. Resources: Information about the program is available on the web at http: dosimetry.stanford.edu. Upcoming Changes: The html pages are being converted to an xml format using a learning management system being developed at Stanford. The project is now recruiting reviewers to participate in a round of revisions of the existing material that will take place over the next year.

Educational Objectives:

1. To understand the goals and methods of a web‐based training project for Medical Dosimetrists

2. To learn about opportunities to participate in the development of course content in the project.
WE‐A‐I‐611‐01: Cone Beam Reconstruction
Authors: Hsieh J
Published: June 2005

Over the past decade, x‐ray computed tomography has experienced tremendously technological advancements: the introduction of helical/spiral and multi‐slice/volumetric acquisition. These advancements not only allow improved image quality and enable new clinical applications, but also significantly increase the technical challenges associated with image reconstruction. The first part of this lecture will cover the fundamentals of image reconstruction. For the ease of understanding, we start with an explanation of the central slice theorem (Fourier slice theorem) for a 2D parallel beam geometry. Both theoretical and intuitive approaches are used to illustrate the concept. The reconstruction algorithm is then extended to fan beam geometry by mathematical derivation and graphic description. Using the central slice theorem as the foundation, reconstruction algorithms for helical acquisition are discussed in the second part of the lecture. We analyze, for single slice, the major difference between helical and step‐and‐shoot acquisitions. Implications of different reconstruction approaches on image quality and computational complexity are also discussed. Cone beam reconstruction discussion will start with one of the most popular algorithms: FDK algorithm. The derivation of the algorithm from the fan‐beam case is first described and its extension to helical/spiral acquisition is then presented. The lecture ends with a discussion on some of the most recent advances in cone beam reconstruction, including both approximate and exact methods. Jiang Hsieh is an employee of GE Healthcare Technologies.

Educational Objectives:

1. Learn the fundamentals of x‐ray CT reconstruction.

2. Understand recent advancements in reconstruction algorithms.
WE‐A‐T‐6E‐01: Tools for IMRT QA
Authors: Dogan N
Published: June 2005

The intensity Modulated Radiation therapy (IMRT) is an advanced form of three‐dimensional conformal radiation therapy (3‐D CRT) that not only uses 3‐D imaging and treatment delivery, but allows for varying radiation beam intensities to produce much more conformal dose distributions than those possible with conventional 3‐D CRT. The complex nature of IMRT planning and delivery impose new requirements for quality assurance (QA) process. A comprehensive QA for IMRT must address the issues involving the verification of pre‐treatment, patient‐specific, delivery and post‐treatment. A complete set of tools, including detectors and phantoms, and techniques are necessary to accomplish the new QA tasks. Some of the detectors used for IMRT QA include films, TLDs, EPIDs, ion chambers and gel dosimeters. Each of them has distinct characteristics and limitations. Several phantoms are also available to accomplish the verification measurements, including cylindrical or a stack of solid water. Tools also have been developed for the dosimetric analysis of the measurements and calculations. Some of these tools include isodose overlay, dose difference histograms, distance‐to‐agreement and gamma evaluation. This presentation will review the QA tools and techniques that are currently in use for all aspects of IMRT process.

Educational Objectives:

1. To identify the QA tasks involving IMRT

2. To identify the requirements for the QA tools

3. To describe the QA tools for all aspects of IMRT process

4. To explain the limitations of the QA tools

5. To compare the IMRT QA tools and techniques
WE‐B‐I‐618‐01: Testing Flat Panel Imaging Systems‐What the Medical Physicist Needs to Know
Authors: Tomlinson J
Published: June 2005

For many years Medical Physicists have evaluated image quality performance on all medical imaging modalities, except radiographic systems. We have looked at resolution and contrast on MRI, CT, fluoroscopic systems, ultrasound systems, and nuclear medicine cameras; but rarely radiographic equipment, especially those having screen‐film receptors. With the increased presence of flat panel digital radiographic systems, which have dedicated detectors as an integral component, it is appropriate for the Medical Physicist to include an analysis of detail and contrast sensitivity as part of acceptance and routine annual testing. Some vendors provide automated QA hardware and software tools, but these may not give standard results for adequate monitoring. Using commonly available test tools, resolution and contrast sensitivity can be evaluated on each system. Patient radiation dosimetry can also be evaluated for manual and automatic techniques. Test methods and typical results will be presented, which should help the clinical Medical Physicist to monitor and maintain good image quality performance.

Educational Objectives:

1. The participant will learn simple test methods to evaluate image quality performance on flat panel detectors.

2. Typical and expected results will be presented to provide the participant with thresholds of acceptance.
WE‐B‐T‐6E‐01: Source Modelling and Beam Commissioning for Monte Carlo Treatment Planning
Authors: Ma C , Faddegon B , Curran B
Published: June 2005

Source modeling and beam commissioning are important components of a Monte Carlo based treatment planning system. In this presentation, we will review the current status of Monte Carlo simulations of clinical photon and electron beams and the theories and methodologies used in particle phase space representation and reconstruction for Monte Carlo dose calculation. We will discuss the sensitivity of beam characterization to simulation details, such as beam energy, angle, intensity, and details of the treatment head design. We will review different source models for photon and electron beam characterization and discuss the accuracy and efficiency tradeoffs between full phase space and simplified source models. We will describe the methods and software that have been developed for source modeling and beam commissioning for the clinical implementation of the Monte Carlo method for treatment planning and beam delivery verification. We will present different methods for source parameterization based on simulated phase space data and a standard set of measured beam data including in‐air and in‐phantom output factors and in‐phantom dose distributions. We will discuss problems associated with CT scanning and phantoms that can affect Monte Carlo accuracy. We will describe requirements and procedures for commissioning and acceptance testing of Monte Carlo dose calculation software for radiotherapy treatment planning.

Educational Objectives:

1. Introduce the Monte Carlo method for clinical photon and electron beam simulations

2. Review theories and methodologies for phase space representation and reconstruction

3. Present different source models for Monte Carlo dose calculation

4. Describe different methods for source parameterization and beam commissioning

5. Provide requirements and guidelines for the clinical testing of Monte Carlo dose calculation software for radiotherapy treatment planning
WE‐C‐I‐611‐02: Composite Fluorographic System Evaluation
Authors: Bednarek D , Rudin S , Yadava G , Dohatcu A
Published: June 2005

This presentation explores methods for the assessment of total fluorographic system performance as related to typical clinical tasks. Many quantitative imaging system analyses focus on separately evaluating the characteristics of the individual system components. Although there is a place for such individualized characterization in product specification and troubleshooting, image quality depends on the interaction of a number of factors including the focal spot characteristics, the projection geometry of the object of interest, scattered radiation, and the image receptor. To determine how the system will perform requires a composite evaluation that includes the net effect of all components impacting image quality under clinical conditions. This is the intent of the NEMA XR 21–2000 Standard that specifies a procedure and phantom “to benchmark cardiac fluoroscopic and fluorographic performance.” This standard provides a qualitative method of evaluation that is dependent on “trained human observers.” For a quantitative analysis, a generalized systems approach has been developed to determine the GMTF, GNNPS, GNEQ and GDQE. This presentation reviews the mechanics of these methods and explores the advantages as well as limitations of composite system evaluation as opposed to component evaluation.

Educational Objectives:

1. To provide an understanding of those factors that influence the image quality of fluorographic systems

2. To describe methods of total system performance evaluation

3. To explore the usefulness and limitations of the NEMA XR 21 standard

4. To review the steps in the determination of the generalized system parameters of GMTF, GNNPS, GNEQ, and GDQE.

Partially supported by: NIH Grants R01EB002873 and R01NS43924, Toshiba Medical Systems Corp., and the UB Foundation.
WE‐C‐J‐6B‐03: Use of 4D Models for Tracking Motion During Therapy
Authors: Keall P
Published: June 2005

Patient anatomy and physiology, of both normal and tumor tissue, changes with time. These timescales vary from seconds (respiratory, cardiac and skeletal motion, rectal gas) to minutes (bladder filling, stomach emptying, muscle relation) and days (repositioning, tumor growth/shrinkage, radiation‐induced effects on bronchiole obstructions, atelectasis regions, edema, fibrosis, functional reserve capacity). These changes challenge the current paradigm of three‐dimensional radiotherapy methods, and demand the exploration of four‐dimensional (4D) techniques to account for these intra‐and interfractional changes. Several components need to be developed for 4D radiotherapy, including online volumetric imaging, automated planning, deformable model development and associated hardware and software modifications. This presentation will focus on the basis and role of 4D deformable models for tracking motion in radiotherapy. The input to 4D deformable models is volumetric imaging information (either 3D or 4D), and for some algorithms user‐defined landmarks. The output of these models are displacement vector fields (DVFs), in which each anatomy element (imaging voxel) is tracked throughout the imaging data sets. These DVFs allow subsets of the anatomy, such as contours and dose distributions, to be seamlessly transferred from one dataset to another, facilitating reoptimization and accurate dose accumulation. An ideal deformable model would be (a) accurately predict DVFs (and be fail‐safe where this is not possible), (b) be unsupervised and require no human input and (c) be fast to allow online implementation and use of the 4D models. The educational objectives of this course include:

1. Appreciate the importance of 4D deformable models in radiotherapy.

2. Introduce the basis of some models that have been applied to the 4D radiotherapy problem.

3. Describe the clinical process for 4D radiotherapy using deformable models.
WE‐C‐P‐618‐02: NRC Update: Part 35 Training and Experience and Who's ACMUI and Why Should a Medical Physicist Care?
Authors: Lieto R
Published: June 2005

The Nuclear Regulatory Commission (NRC) finalized the training and experience requirements for Authorized Medical Physicists, Authorized Users and Radiation Safety Officers in March 2005. A brief summary of the changes to the regulations will be presented. The Advisory Committee on the Medical Uses of Isotopes (ACMUI) was established in 1958 to advise NRC staff on policy and technical issues that arise in the regulation of the medical uses of radioactive material in diagnosis and therapy. The ACMUI membership includes health care professionals from various disciplines who comment on changes to NRC regulations and guidance; evaluate certain non‐routine uses of radioactive material; provide technical assistance in licensing, inspection, and enforcement cases; and bring key issues to the attention of the Commission for appropriate action. A general description of the ACMUI composition and interactions with NRC will be given. A discussion of the recent activities of the ACMUI and the implication for medical physicists will be presented. Future issues where NRC may have significant impact on the medical physicist will be addressed.

Educational Objective:

1. To understand the make‐up and responsibilities of the ACMUI and the issues being discussed and their implications on medical physicists.
WE‐C‐P‐618‐03: CARE Act Update
Authors: Keys D
Published: June 2005

The Alliance for Quality Medical Imaging and Radiation Therapy (of which both the AAPM and ACMP are members) met again in March 2005 to further develop, in anticipation of passage of the Care Bill, statutes designed to specify the training and experience of all medical professions performing or planning medical imaging and radiation therapy. The Bill, as written, is designed to include both Medical Physicists and Medical Dosimetrists in the proposed regulation. The CARE bill was recently reintroduced in the US congress.

Educational Objective:

1. To review the current status and implications of the CARE Bill
WE‐D‐T‐6C‐02: Role of Imaging in Drug Response: Challenges and Opportunities
Authors: Clarke L
Published: June 2005

Advances in biomedical imaging technology such as anatomical, functional and molecular imaging methods permit new protocols and informatics tools to be developed for measuring drug response. There is, however, an increasing need to harmonize methods for data collection and analysis to provide a greater acceptance of these methods by the clinical community, and in particular, the pharmaceutical industry community. Recently the NCI and the FDA have entered into a broad inter agency agreement, referred to as the Interagency Oncology Task Force (IOTF) to review how to accelerate the use of biomarkers for measurement of drug response. Biomedical imaging is an integral part of this IOTF. NCI is also reviewing its drug trial infrastructure, including web accessible methods to access trial data to enhance the development of informatics tools to measure drug response. http://iotftraining.nci.nih.gov/ NCI Cancer Imaging Program (CIP) therefore has an interest in challenging the cancer center, academic and industry communities to engage in research that may lead to harmonization of imaging protocols, related quality assurance methods and data analysis methods as required to measure drug response across different imaging platforms and clinical sites. NCI is actively engaged, for example, in providing web accessible reference image data sets collected from drug response investigations. These efforts include providing annotated data to permit more standardized methods for measuring the performance of related informatics tools, such as change analysis. They are part of an overall development of a large data archive and web query systems referred to as caBIG. http://imaging.cancer.gov/programsandresources/InformationSystems http://cabig.nci.nih.gov/ This presentation will outline example scientific and NCI programmatic opportunities in this area. The intent of this presentation is to challenge investigators to consider this area of research.

Educational Objectives:

1. Understanding NCI Imaging Initiatives
TU‐C‐T‐617‐01: A Computer Model for Automatic Planning and Optimization for Gamma Knife Radiosurgery Using Auto‐Positioning System
Authors: Changkon V , Jitprapaikulsarn S , Thongphiew D , Wessels B , Wu Q
Published: June 2005

Purpose: This research addresses the automatic‐planning of Gamma Knife radiosurgery using auto‐positioning system (APS). We previously reported a morphology‐guided automatic planning model via optimization of dose conformity and minimization of total number of shots with different collimator sizes. In this work, our goal is to develop an optimization model that is adaptive to APS by using shots with same collimator. Method and Materials: Our three‐step optimization strategy is: (1) configure the initial shot set using a combined process of skeletonization and bin‐covering, (2) optimize the relative weight (exposure time) of each shot to improve target coverage while minimizing normal tissue toxicity, and (3) fine‐tune the shot configuration by adjusting shot locations, and adding or deleting shots to further improve the balance between target coverage and normal tissue toxicity. In the weight optimization phase in step 2, an easy‐to‐solve linear fractional program explicitly models the dual objectives and takes into account of dose‐renormalization (i.e., maximum is always renormalized to 100%). The fine‐tuning step explicitly takes into account of shot overlapping, dose renormalization and target shape thus making the tracking of hot spots and estimating the effects of shot movement, addition and/or deletion possible. Results: We have implemented this optimization model on the Windows‐based platform and have tested it with seven previously treated clinical cases. The target volume ranges from 2.6 to 8.6 cc, while the number of shots used ranges from 13 to 39. Our computer model generates plans in 1‐2 minutes, with compatible quality of physician's plans normally created in 1–4 hours. The target coverage is greater than 95% and PITV ranges from 1.29 to 2.26. Conclusions: Our computer model can be used for real‐time planning, or for generating an initial plan followed by interactive optimization/fine‐tuning, or for creating multiple plans with different trade‐off objectives.
Re-radiation of acoustic waves from the A wave on a submerged elastic shell
Authors: Ahyi A. C. , Cao Hui , Raju P. K. , Überall Herbert
Published: June 2005

We consider evacuated thin semi-infinite shells immersed in a fluid, which may be either of cylindrical shape with a hemispherical shell endcap, or formed two-dimensionally by semi-infinite parallel plates joined together by a semi-cylinder. The connected shell portions are joined in a manner to satisfy continuity but with a discontinuous radius of curvature. Acoustic waves are considered incident along the axis of symmetry (say the z axis) onto the curved portion of the shell, where they, at the critical angle of coincidence, generate Lamb and Stoneley-type waves in the shell. Computations were carried out using a code developed by Cao et al. [Chinese J. Acoust. 14, 317 (1995)] and was used in order to computationally visualize the waves in the fluid that have been re-radiated by the shell waves a the critical angle. The frequency range was below that of the lowest Lamb wave, and only the A0 wave (and partly the S0 wave) was observed to re-radiate into the fluid under our assumptions. The results will be compared to experimental results in which the re-radiated waves are optically visualized by the Schardin–Cranz schlieren method.
Aeroacoustic production of low-frequency unvoiced speech sounds
Authors: Krane Michael H.
Published: June 2005

A theoretical approach to describing unvoiced speech sound production is outlined using the essentials of aerodynamics and aeroacoustics. The focus is on the character and role of nonacoustic air motion in the vocal tract. An idealized picture of speech sound production is presented showing that speech sound production involves the dynamics of a jet flow, characterized by vorticity. A formal expression is developed for the sound production by unsteady airflow in terms of jet vorticity and vocal-tract shape, and a scaling law for the aeroacoustic source power is derived. The generic features of internal jet flows such as those exhibited in speech sound production are discussed, particularly in terms of the vorticity field, and the relevant scales of motion are identified. An approximate description of a jet as a train of vortex rings, useful for sound-field prediction, is described using the scales both of motion and of vocal-tract geometry. It is shown that the aeroacoustic source may be expressed as the convolution of (1) the acoustic source time series due to a single vortex ring with (2) a function describing the arrival of vortex rings in the source region. It is shown that, in general, the characteristics of the aeroacoustic source are determined not only by the strength, spatial distribution, and convection speed of the jet vorticity field, but also the shape of the vocal tract through which the jet flow passes. For turbulent jets, such as those which occur in unvoiced sound production, however, vocal-tract shape is the dominant factor in determining the spectral content of the source.
Coherent reflection in a two-dimensional cochlea: Short-wave versus long-wave scattering in the generation of reflection-source otoacoustic emissions
Authors: Shera Christopher A. , Tubis Arnold , Talmadge Carrick L.
Published: June 2005

The theory of coherent reflection filtering explains the empirical form of the cochlear reflectance by showing how it emerges from the coherent “backscattering” of forward-traveling waves by impedance perturbations in the mechanics of the cochlear partition. Since the theory was developed using the one-dimensional (1-D) transmission-line model of the cochlea, an obvious logical shortcoming is the failure of the long-wavelength approximation near the peak of the traveling wave, where coherent backscattering is purported to occur. Indeed, existing theory suggests that wave reflection may be strongly suppressed in the short-wave regime. To understand how short-wave behavior near the peak modifies the predictions of the long-wave theory, this paper solves the scattering problem in the 2-D cochlear model. The 2-D problem is reduced to a 1-D wave equation and the solution expressed as an infinite series in which successive terms arise via multiple scattering within the cochlea. The cochlear reflectance is computed in response-matched models constructed by solving the inverse problem to control for variations in mechanical tuning among models of different heights and dimensionality. Reflection from the peak region is significantly enhanced by the short-wave hydrodynamics, but other conclusions of the 1-D analysis—such as the predicted relation between emission group delay and the wavelength of the traveling wave—carry over with only minor modifications. The results illustrate the important role of passive hydromechanical effects in shaping otoacoustic emissions and cochlear tuning.
Acoustic power measurements of a damped aeroacoustically driven resonator
Authors: Slaton W. V. , Zeegers J. C. H.
Published: June 2005

Strong self-sustained acoustic oscillations may occur in a gas pipe network under certain gas flow velocities within the network. The pipe network under consideration consists of a main pipe, with a variable mean airflow, with two closed coaxial side branches of variable but equal length joined to the main pipe. Coupling between resonant acoustic standing waves and instabilities of the shear layers separating the flow in the main pipe from the stagnant gas in the closed side branches leads to strong acoustic oscillations at a frequency corresponding to the half-wavelength acoustic mode defined by the total side-branch length. An acoustic damper consisting of a variable acoustic resistance and compliance is used to dissipate power from the resonating mode. The response of the aeroacoustically driven resonator to variable damping will be examined for different fluid flow regimes as well as side-branch geometries.
Acoustic radiation impedance and directional response of rectangular pistons on elliptic cylinders
Authors: Boisvert Jeffrey E. , Van Buren A. L.
Published: June 2005

The self- and mutual radiation impedances and the farfield directional response of rectangular pistons conformal to a rigid elliptic cylindrical baffle are formulated. The pistons are assumed to vibrate with uniform normal velocity and the solution for the acoustic pressure is expressed in terms of a modal series representation in Mathieu functions. The Mathieu functions are obtained using computer programs that have been recently developed to provide accurate values of the functions at high frequencies. Results for the normalized self- and mutual radiation resistance and reactance and the directional response of acoustic radiation are presented over a wide frequency range for different piston sizes and elliptic cylinder cross section shapes.
Measurements of the anisotropy of ultrasonic velocity in freshly excised and formalin-fixed myocardial tissue
Authors: Baldwin Steven L. , Yang Min , Marutyan Karen R. , Wallace Kirk D. , Holland Mark R. , Miller James G.
Published: June 2005

The objective of this study was to quantify the anisotropy of ultrasonic velocity in freshly excised myocardial tissue and to examine the effects of formalin-fixation. Through-transmission radio-frequency-based measurements were performed on ovine and bovine myocardial specimens from 24 different hearts. A total of 81 specimens were obtained from specific locations within each heart to investigate the possibility of regional differences in anisotropy of velocity in the left ventricular wall and septum. No regional differences were observed for either lamb or cow myocardial specimens. In addition, no specific species-dependent differences were observed between ovine and bovine myocardium. Average values of velocity at room temperature for perpendicular and parallel insonification were 1556.9±0.6 and 1565.2±0.7m∕s (mean±standard error), respectively, for bovine myocardium (N=45) and 1556.3±0.6 and 1564.7±0.7m∕s for ovine myocardium (N=36). Immediately after measurements of freshly excised myocardium, ovine specimens were fixed in formalin for at least one month and then measurements were repeated. Formalin-fixation appears to increase the overall velocity at all angles of insonification and to increase the magnitude of anisotropy of velocity.
Three-dimensional electromagnetic articulography: A measurement principle
Authors: Kaburagi Tokihiko , Wakamiya Kohei , Honda Masaaki
Published: June 2005

A measurement principle of the three-dimensional electromagnetic articulographic device is presented. The state of the miniature receiver coil is described by five variables representing the position in the three-dimensional coordinate system and the rotation angles relative to it. When the receiver coil is placed in the magnetic field produced from the distributed transmitter coils, its state can be optimally estimated by minimizing the difference between the measured strength of the received signal and the predicted one using the known spatial pattern of the magnetic field. Therefore, the design and calibration of the field function inherently determine the accuracy in estimating the state of the receiver coil. The field function in our method is expressed in the form of a multivariate B spline as a function of position in the three-dimensional space. Because of the piecewise property of the basis function and the freedom in the selection of the rank and the number of basis functions, the spline field function has a superior ability to flexibly and accurately represent the actual magnetic field. Given a set of calibration data, the spline function is designed to form a smooth curved surface interpolating all of these data samples. Then, an iterative procedure is employed to solve the nonlinear estimation problem of the receiver state variables. Because the spline basis function is a polynomial, it is also shown that the calculation of the Jacobian or Hessian required to obtain updated quantities for the state variables can be efficiently performed. Finally, experimental results reveal that the measurement accuracy is about 0.2 mm for a preliminary condition, indicating that the method can achieve the degree of precision required for observing articulatory movements in a three-dimensional space. It is also experimentally shown that the Marquardt method is a better nonlinear programming technique than the Gauss–Newton or Newton–Raphson method for solving the receiver state problem.
Characterizing noise in nonhuman vocalizations: Acoustic analysis and human perception of barks by coyotes and dogs
Authors: Riede Tobias , Mitchell Brian R. , Tokuda Isao , Owren Michael J.
Published: June 2005

Measuring noise as a component of mammalian vocalizations is of interest because of its potential relevance to the communicative function. However, methods for characterizing and quantifying noise are less well established than methods applicable to harmonically structured aspects of signals. Using barks of coyotes and domestic dogs, we compared six acoustic measures and studied how they are related to human perception of noisiness. Measures of harmonic-to-noise-ratio (HNR), percent voicing, and shimmer were found to be the best predictors of perceptual rating by human listeners. Both acoustics and perception indicated that noisiness was similar across coyote and dog barks, but within each species there was significant variation among the individual vocalizers. The advantages and disadvantages of the various measures are discussed.
Errors in two-point sound reproduction
Authors: Nelson P. A. , Rose J. F. W.
Published: June 2005

This paper deals with the problem of reproducing two signals at two points in space by using two acoustic sources. While much is now known about the techniques available for the design of matrices of inverse filters that enable this objective to be achieved in practice, it is still the basic physics of the sound field produced that controls the effectiveness of such systems and which ultimately dictates their design. The basic physical processes involved in producing the cross-talk cancellation that enables the reproduction of the desired signals is revisited here by using a simple two source/two field point free field model. The singular value decomposition is used to identify those frequencies where the inversion problem becomes ill-conditioned and to explain physically the origin of the ill-conditioning. As observed previously, it is found that cross-talk cancellation becomes problematic when the path length difference between the two sources and one of the field points becomes equal to one half the acoustic wavelength. The ill-conditioned frequencies are also found to be associated with a limited spatial region of cross-talk cancellation and with large source outputs manifested in the time domain by responses of long duration.
Empirical modeling of human face kinematics during speech using motion clustering
Authors: Lucero Jorge C. , Maciel Susanne T. R. , Johns Derek A. , Munhall Kevin G.
Published: June 2005

In this paper we present an algorithm for building an empirical model of facial biomechanics from a set of displacement records of markers located on the face of a subject producing speech. Markers are grouped into clusters, which have a unique primary marker and a number of secondary markers with an associated weight. Motion of the secondary markers is computed as the weighted sum of the primary markers of the clusters to which they belong. This model may be used to produce facial animations, by driving the primary markers with measured kinematic signals.
Comparing F discrimination in sequential and simultaneous conditions
Authors: Micheyl Christophe , Oxenham Andrew J.
Published: June 2005

In an influential study, Carlyon and Shackleton [J. Acoust. Soc. Am. 95, 3541–3554 (1994)] measured listeners’ performance (d′) in fundamental-frequency (F0) discrimination between harmonic complex tones (HCTs) presented simultaneously in different spectral regions and compared their performance with that found in a sequential-comparison task. In this Letter, it is suggested that Carlyon and Shackleton’s analysis of the simultaneous-comparison data did not adequately reflect their assumption that listeners were effectively comparing F0’s across regions. A reanalysis consistent with this assumption is described. The new results suggest that under the assumption that listeners were effectively comparing F0 across regions, their performance in this task was substantially higher than originally estimated by Carlyon and Shackleton, and in some conditions much higher than expected from the performances measured in a traditional F0-discrimination task with sequential HCTs. Possible explanations for this outcome, as well as alternative interpretations, are proposed.