Cell and extracellular matrix growth theory and its implications for tumorigenesis.

Cells associated with an abnormal (cancerous) growth exchange flows, morph freely and grow hand-in-glove with their immediate environment, the extracellular matrix (ECM). The cell structure experiences two mass flows in counterflow. Flowing into the structure are nutrients and flowing out is refuse from the metabolically active biomass within. The physical effect of the evolution of the cell and extracellular structure is more flow and mixing in that space, that is, more mixing than in the absence of a biological growth in that space. The objective of the present theory is to predict the increase in the size of the cell cluster as a function of its structure, and also to predict the critical cluster sizes that mark the transitions from one distinct cluster configuration to the next. This amounts to predicting the timing and the main features of the transitions from single cell to clusters with two, four, eight and more cells, including larger clusters with cells organized on its outer surface. The predicted evolution of the size and configuration of the cell cluster is validated successfully by comparison with measurements from several independent studies of cancerous and non-cancerous growth patterns.

Awareness of medical radiation exposure among patients: A patient survey as a first step for effective communication of ionizing radiation risks.

INTRODUCTION: The European Directive 2013/59/EURATOM requires patient radiation dose information to be included in the medical report of radiological procedures. To provide effective communication to the patient, it is necessary to first assess the patient's level of knowledge regarding medical exposure. The goal of this work is to survey patients' current knowledge level of both medical exposure to ionizing radiation and professional disciplines and communication means used by patients to garner information. MATERIAL AND METHODS: A questionnaire was designed comprised of thirteen questions: 737 patients participated in the survey. The data were analysed based on population age, education, and number of radiological procedures received in the three years prior to survey. RESULTS: A majority of respondents (56.4%) did not know which modality uses ionizing radiation. 74.7% had never discussed with healthcare professionals the risk concerning their medical radiological procedures. 70.1% were not aware of the professionals that have expertise to discuss the use of ionizing radiation for medical purposes, and 84.7% believe it is important to have the radiation dose information stated in the medical report. CONCLUSION: Patients agree with new regulations that it is important to know the radiation level related to the medical exposure, but there is little awareness in terms of which modalities use X-Rays and the professionals and channels that can help them to better understand the exposure information. To plan effective communication, it is essential to devise methods and adequate resources for key professionals (medical physicists, radiologists, referring physicians) to convey correct and effective information.

Finite-element modeling of compression and gravity on a population of breast phantoms for multimodality imaging simulation.

PURPOSE: The authors are developing a series of computational breast phantoms based on breast CT data for imaging research. In this work, the authors develop a program that will allow a user to alter the phantoms to simulate the effect of gravity and compression of the breast (craniocaudal or mediolateral oblique) making the phantoms applicable to multimodality imaging. METHODS: This application utilizes a template finite-element (FE) breast model that can be applied to their presegmented voxelized breast phantoms. The FE model is automatically fit to the geometry of a given breast phantom, and the material properties of each element are set based on the segmented voxels contained within the element. The loading and boundary conditions, which include gravity, are then assigned based on a user-defined position and compression. The effect of applying these loads to the breast is computed using a multistage contact analysis in FEBio, a freely available and well-validated FE software package specifically designed for biomedical applications. The resulting deformation of the breast is then applied to a boundary mesh representation of the phantom that can be used for simulating medical images. An efficient script performs the above actions seamlessly. The user only needs to specify which voxelized breast phantom to use, the compressed thickness, and orientation of the breast. RESULTS: The authors utilized their FE application to simulate compressed states of the breast indicative of mammography and tomosynthesis. Gravity and compression were simulated on example phantoms and used to generate mammograms in the craniocaudal or mediolateral oblique views. The simulated mammograms show a high degree of realism illustrating the utility of the FE method in simulating imaging data of repositioned and compressed breasts. CONCLUSIONS: The breast phantoms and the compression software can become a useful resource to the breast imaging research community. These phantoms can then be used to evaluate and compare imaging modalities that involve different positioning and compression of the breast.

The development of a population of 4D pediatric XCAT phantoms for imaging research and optimization.

PURPOSE: We previously developed a set of highly detailed 4D reference pediatric extended cardiac-torso (XCAT) phantoms at ages of newborn, 1, 5, 10, and 15 yr with organ and tissue masses matched to ICRP Publication 89 values. In this work, we extended this reference set to a series of 64 pediatric phantoms of varying age and height and body mass percentiles representative of the public at large. The models will provide a library of pediatric phantoms for optimizing pediatric imaging protocols. METHODS: High resolution positron emission tomography-computed tomography data obtained from the Duke University database were reviewed by a practicing experienced radiologist for anatomic regularity. The CT portion of the data was then segmented with manual and semiautomatic methods to form a target model defined using nonuniform rational B-spline surfaces. A multichannel large deformation diffeomorphic metric mapping algorithm was used to calculate the transform from the best age matching pediatric XCAT reference phantom to the patient target. The transform was used to complete the target, filling in the nonsegmented structures and defining models for the cardiac and respiratory motions. The complete phantoms, consisting of thousands of structures, were then manually inspected for anatomical accuracy. The mass for each major tissue was calculated and compared to linearly interpolated ICRP values for different ages. RESULTS: Sixty four new pediatric phantoms were created in this manner. Each model contains the same level of detail as the original XCAT reference phantoms and also includes parameterized models for the cardiac and respiratory motions. For the phantoms that were 10 yr old and younger, we included both sets of reproductive organs. This gave them the capability to simulate both male and female anatomy. With this, the population can be expanded to 92. Wide anatomical variation was clearly seen amongst the phantom models, both in organ shape and size, even for models of the same age and sex. The phantoms can be combined with existing simulation packages to generate realistic pediatric imaging data from different modalities. CONCLUSIONS: This work provides a large cohort of highly detailed pediatric phantoms with 4D capabilities of varying age, height, and body mass. The population of phantoms will provide a vital tool with which to optimize 3D and 4D pediatric imaging devices and techniques in terms of image quality and radiation-absorbed dose.

Organ localization: toward prospective patient-specific organ dosimetry in computed tomography.

PURPOSE: With increased focus on radiation dose from medical imaging, prospective radiation dose estimates are becoming increasingly desired. Using available populations of adult and pediatric patient phantoms, radiation dose calculations can be catalogued and prospectively applied to individual patients that best match certain anatomical characteristics. In doing so, the knowledge of organ size and location is a required element. Here, the authors develop a predictive model of organ locations and volumes based on an analysis of adult and pediatric computed tomography (CT) data. METHODS: Fifty eight adult and 69 pediatric CT datasets were segmented and utilized in the study. The maximum and minimum points of the organs were recorded with respect to the axial distance from the tip of the sacrum. The axial width, midpoint, and volume of each organ were calculated. Linear correlations between these three organ parameters and patient age, BMI, weight, and height were determined. RESULTS: No statistically significant correlations were found in adult patients between the axial width, midpoint, and volume of the organs versus the patient age or BMI. Slight, positive linear trends were found for organ midpoint versus patient weight (max r(2) = 0.382, mean r(2) = 0.236). Similar trends were found for organ midpoint versus height (max r(2) = 0.439, mean r(2) = 0.200) and for organ volume versus height (max r(2) = 0.410, mean r(2) = 0.153). Gaussian fits performed on probability density functions of the adult organs resulted in r(2)-values ranging from 0.96 to 0.996. The pediatric patients showed much stronger correlations overall. Strong correlations were observed between organ axial midpoint versus age, height, and weight (max r(2) = 0.842, mean r(2) = 0.790; max r(2) = 0.949, mean r(2) = 0.894; and max r(2) = 0.870, mean r(2) = 0.847, respectively). Moderate linear correlations were also observed for organ axial width versus height (max r(2) = 0.772, mean r(2) = 0.562) and for organ volume versus height (max r(2) = 0.781, mean r(2) = 0.601). CONCLUSIONS: Adult patients exhibited small variations in organ volume and location with respect to height and weight, but no meaningful correlation existed between these parameters and age or BMI. Once adulthood is reached, organ morphology and positioning seem to remain static. However, clear trends are evident between pediatric organ locations versus age, height, and weight. Such information can be incorporated into a matching methodology that may provide the highest probability of representing the anatomy of a patient undergoing a clinical exam to prospectively estimate the radiation dose.

A set of 4D pediatric XCAT reference phantoms for multimodality research.

PURPOSE: The authors previously developed an adult population of 4D extended cardiac-torso (XCAT) phantoms for multimodality imaging research. In this work, the authors develop a reference set of 4D pediatric XCAT phantoms consisting of male and female anatomies at ages of newborn, 1, 5, 10, and 15 years. These models will serve as the foundation from which the authors will create a vast population of pediatric phantoms for optimizing pediatric CT imaging protocols. METHODS: Each phantom was based on a unique set of CT data from a normal patient obtained from the Duke University database. The datasets were selected to best match the reference values for height and weight for the different ages and genders according to ICRP Publication 89. The major organs and structures were segmented from the CT data and used to create an initial pediatric model defined using nonuniform rational B-spline surfaces. The CT data covered the entire torso and part of the head. To complete the body, the authors manually added on the top of the head and the arms and legs using scaled versions of the XCAT adult models or additional models created from cadaver data. A multichannel large deformation diffeomorphic metric mapping algorithm was then used to calculate the transform from a template XCAT phantom (male or female 50th percentile adult) to the target pediatric model. The transform was applied to the template XCAT to fill in any unsegmented structures within the target phantom and to implement the 4D cardiac and respiratory models in the new anatomy. The masses of the organs in each phantom were matched to the reference values given in ICRP Publication 89. The new reference models were checked for anatomical accuracy via visual inspection. RESULTS: The authors created a set of ten pediatric reference phantoms that have the same level of detail and functionality as the original XCAT phantom adults. Each consists of thousands of anatomical structures and includes parameterized models for the cardiac and respiratory motions. Based on patient data, the phantoms capture the anatomic variations of childhood, such as the development of bone in the skull, pelvis, and long bones, and the growth of the vertebrae and organs. The phantoms can be combined with existing simulation packages to generate realistic pediatric imaging data from different modalities. CONCLUSIONS: The development of patient-derived pediatric computational phantoms is useful in providing variable anatomies for simulation. Future work will expand this ten-phantom base to a host of pediatric phantoms representative of the public at large. This can provide a means to evaluate and improve pediatric imaging devices and to optimize CT protocols in terms of image quality and radiation dose.

Population of anatomically variable 4D XCAT adult phantoms for imaging research and optimization.

PURPOSE: The authors previously developed the 4D extended cardiac-torso (XCAT) phantom for multimodality imaging research. The XCAT consisted of highly detailed whole-body models for the standard male and female adult, including the cardiac and respiratory motions. In this work, the authors extend the XCAT beyond these reference anatomies by developing a series of anatomically variable 4D XCAT adult phantoms for imaging research, the first library of 4D computational phantoms. METHODS: The initial anatomy of each phantom was based on chest-abdomen-pelvis computed tomography data from normal patients obtained from the Duke University database. The major organs and structures for each phantom were segmented from the corresponding data and defined using nonuniform rational B-spline surfaces. To complete the body, the authors manually added on the head, arms, and legs using the original XCAT adult male and female anatomies. The structures were scaled to best match the age and anatomy of the patient. A multichannel large deformation diffeomorphic metric mapping algorithm was then used to calculate the transform from the template XCAT phantom (male or female) to the target patient model. The transform was applied to the template XCAT to fill in any unsegmented structures within the target phantom and to implement the 4D cardiac and respiratory models in the new anatomy. Each new phantom was refined by checking for anatomical accuracy via inspection of the models. RESULTS: Using these methods, the authors created a series of computerized phantoms with thousands of anatomical structures and modeling cardiac and respiratory motions. The database consists of 58 (35 male and 23 female) anatomically variable phantoms in total. Like the original XCAT, these phantoms can be combined with existing simulation packages to simulate realistic imaging data. Each new phantom contains parameterized models for the anatomy and the cardiac and respiratory motions and can, therefore, serve as a jumping point from which to create an unlimited number of 3D and 4D variations for imaging research. CONCLUSIONS: A population of phantoms that includes a range of anatomical variations representative of the public at large is needed to more closely mimic a clinical study or trial. The series of anatomically variable phantoms developed in this work provide a valuable resource for investigating 3D and 4D imaging devices and the effects of anatomy and motion in imaging. Combined with Monte Carlo simulation programs, the phantoms also provide a valuable tool to investigate patient-specific dose and image quality, and optimization for adults undergoing imaging procedures.

Assessment of multi-directional MTF for breast tomosynthesis.

A method was developed to assess the multi-directional modulation transfer function (MTF) of breast tomosynthesis imaging systems using a sphere phantom. The method was initially developed based on a simulation dataset. Projections were simulated for a uniform voxelized breast phantom with sphere inserts using a fluence modeled from a 28 kVp beam incident upon an indirect flat-panel detector. Based on cascaded systems modeling, characteristic noise and blurring were added to each projection. The projections were reconstructed using a standard filtered backprojection technique, producing a 3D volume with an isotropic voxel size of 200 µm. ROIs that completely encompassed single spheres were extracted and conical regions were prescribed along the three major axes extending from the centroids. Pixels within the cones were used to form edge spread functions (ESFs), from which the directional MTFs were calculated. Binning size and conical range were adjusted to maximize the accuracy and to minimize the noise of the MTF. A method was further devised to remove out-of-plane artifacts from the ESF in the x-y plane. Finally, the method was applied to experimentally assess the directional MTF of a prototype tomosynthesis system. Comparisons of the sphere-based MTF along the different axes and the theoretical MTF yielded good agreement. A 30° angular cone and a 20 µm sampling were found to provide an ideal trade-off between the noise and accuracy of the measurement. The removal of artifacts in ESF yielded 'modified' MTFs that enabled a resolution-only characterization of the in-slice resolution of tomosynthesis. Drop-off frequencies in the x- and y-directional MTFs were 1.6 cycles mm(-1) and 1.5 cycles mm(-1), respectively. The presented method of separating the effective resolution and artifacts from the measured ESF was found experimentally implementable and is expected to facilitate the interpretation of MTF measurements in tomosynthesis.

TU-F-217A-01: Informatics 2: Dose Monitoring.

Public concern over radiation from medical imaging is now higher than ever before and hospitals are being placed under increased scrutiny to ensure that their patients do not receive radiation overdoses. California already requires that there is a record of a dose estimate for every CT examination. In response, there has been a renewed interest in research and commercial ventures for the best method to monitor radiation dose for medical imaging procedures. The goal of this session is to highlight some tools that are currently available for dose monitoring, to illustrate how using these tools can improve the quality of care at an institution, and to provide a sample of the future developments in radiation dose monitoring. LEARNING OBJECTIVES: 1. To provide an understanding of the basic science behind dose monitoring 2. To demonstrate few clinical implementation of dose monitoring systems 3. To discuss the advanced concepts currently under investigation (eg, patient size tracking) 4. To demonstrate how dose monitoring systems can be used for improved quality initiatives.

SU-E-I-47: Comparison of Risks for Two Medical Imaging Procedures.

PURPOSE: Radiologists may need to decide which type of image procedure is most appropriate for a particular patient. One factor relevant in making this decision is the relative risk of secondary cancers due to each relevant procedure. Differences in the risk posed by each method are not just due to the total radiation dose imparted by each procedure, but also the distribution of absorbed dose across various organs in the imaging procedure. Two imaging procedures with the same total radiation dose may pose different risks of differential sensitivity to radiation across organs. METHODS: New methods of radiation dosimetry enable us to estimate the dose distribution across organs in individual patients. We propose a measure of the relative risk of two medical imaging procedures derived from the hazard function of cancer incidence. The relative risk measure is shown to approximately equal to a weighted sum of the dose difference in each organ. The weights are proportional to organ specific incidence rates. The measure is also sensitive to factors such as the patient's age at exposure to radiation, the attained age and gender, as well as the incidence characteristics of the population to which the patient belongs. We propose to quantify the effects of these factors using information from publically available SEER database for US based patients as well as the LSS study of atomic bomb survivors. The method is illustrated by application to a study comparing chest and abdominal CT scans for a group of pediatric patients. RESULTS: Fig. 1 shows higher absolute relative risk for those exposed at younger ages, with chest scans being riskier for females while abdominal scans were riskier for males. At higher ages, the relative risk is approximately equal. CONCLUSIONS: Relative risks can quantify risks comparisons between imaging procedures.

SU-D-217A-03: Nuclear Medicine Uniformity Assessment Using 2D Noise Power Spectrum.

PURPOSE: Nuclear medicine quality control programs require daily evaluation for the presence of potential non-uniformities by commonly utilizing a traditional pixel value-based assessment (Integral CFOVUniformity). While this method effectively captures regional non- uniformities in the image, it does not adequately reflect subtle periodic structures that are visually apparent and clinically unacceptable, therefore requiring the need for additional visual inspection of the image. The goal of this project was to develop a new uniformity assessment metric by targetingstructural patterns and more closely correlating with visual inspection. METHODS: The new quantitative uniformity assessment metric is based on the 2D Noise Power Spectrum (NPS). A full 2D NPS was performed on each image. The NPS was thresholded to remove quantum noise and further filtered by the visual response function. A score, the Structure Noise Index (SNI), was then applied to each based on the average magnitude of the structured noise in the processed image. To verify the validity of the new metric, 50 daily uniformity images with varying degrees of visual structured and non-structured non-uniformity were scored by 5 expert nuclear medicine physicists. The correlation between the visual score and SNI were assessed. The Integral CFOV was also compared against the visual score. RESULTS: Our new SNI assessment metric compared to the Integral CFOV showed in increase in sensitivity from 67% to 100% in correctly identifying structured non-uniformities. The overall positive predictive value also increased from 55% to 72%. CONCLUSIONS: Our new uniformity metric correlates much more closely with visual assessment of structured non- uniform NM images than the traditional pixel-based method. Using this new metric in conjunction with the traditional pixel value-based assessment will allow a more accurate quantitative assessment of nuclear medicineuniformity.

SU-E-I-77: X-Ray Coherent Scatter Diffraction Pattern Modeling in GEANT4.

PURPOSE: To model X-ray coherent scatter diffraction patterns in GEANT4 for simulating experiments involving material detection through diffraction pattern measurement. Although coherent scatter cross-sections are modeled accurately in GEANT4, diffraction patterns for crystalline materials are not yet included. Here we describe our modeling of crystalline diffraction patterns in GEANT4 for specific materials and the validation of the results against experimentally measured data. METHODS: Coherent scatter in GEANT4 is currently based on Hubbell's non-relativistic form factor tabulations from EPDL97. We modified the form-factors by introducing an interference function that accounts for the angular dependence between the Rayleigh-scattered photons and the photon wavelength. The modified form factors were used to replace the inherent form-factors in GEANT4. The simulation was tested using monochromatic and polychromatic x-ray beams (separately) incident on objects containing one or more elements with modified form-factors. The simulation results were compared against the experimentally measured diffraction images of corresponding objects using an in-house x-ray diffraction imager for validation. The comparison was made using the following metrics: number of diffraction rings, radial distance, absolute intensity, and relative intensity. RESULTS: Sharp diffraction pattern rings were observed in the monochromatic simulations at locations consistent with the angular dependence of the photon wavelength. In the polychromatic simulations, the diffraction patterns exhibited a radial blur consistent with the energy spread of the polychromatic spectrum. The simulated and experimentally measured patterns showed identical numbers of rings with close agreement in radial distance, absolute and relative intensities (barring statistical fluctuations). No significant change was observed in the execution time of the simulations. CONCLUSIONS: This work demonstrates the ability to model coherent scatter diffraction in GEANT4 in an accurate and efficient manner without compromising the accuracy or runtime of the simulation. This work was supported by the Department of Homeland Security under grant DHS (BAA 10-01 F075), and by the Department of Defense under award W81XWH-09-1-0066.

MO-D-BRA-01: Limits of Dose Reduction in CT: Where are They and How Will We Know When We Get There?

Radiation Dose continues to be a concern with respect to all diagnostic imaging using ionizing radiation, but especially so with CT imaging. We have always known how to reduce radiation dose in CT - for example, simply turning down the system output (e.g. reduce mAs). What we have not been able to do is to simultaneously reduce dose and maintain "diagnostic image quality". Many recent technical developments have appeared, and will continue to appear, that will allow users to reduce radiation dose in CT while "maintaining image quality". However, this last term is ill-defined and current metrics of image quality are not very applicable to actual clinical practice. The purpose of this symposium is to: (a) describe several current and possible future radiation dose reduction methods and the magnitude of their potential for dose reduction, (b) some description of what "diagnostic image quality" means, the effects that dose reductions methods have on this property, description of some metrics that may help us assess this property quantitatively and this information can be used to guide how low radiation doses can be reduced. LEARNING OBJECTIVES: 1. Understand both conventional and emerging radiation dose reduction methods in CT. 2. Understand the implications on diagnostic image quality for each radiation dose reduction method. 3. Understand some of the issues in evaluating how much radiation dose can be reduced and still accomplish a diagnostic imaging task.

Mass detection on mammograms: influence of signal shape uncertainty on human and model observers.

We studied the influence of signal variability on human and model observers for detection tasks with realistic simulated masses superimposed on real patient mammographic backgrounds and synthesized mammographic backgrounds (clustered lumpy backgrounds, CLB). Results under the signal-known-exactly (SKE) paradigm were compared with signal-known-statistically (SKS) tasks for which the observers did not have prior knowledge of the shape or size of the signal. Human observers' performance did not vary significantly when benign masses were superimposed on real images or on CLB. Uncertainty and variability in signal shape did not degrade human performance significantly compared with the SKE task, while variability in signal size did. Implementation of appropriate internal noise components allowed the fit of model observers to human performance.

Three-dimensional simulation of lung nodules for paediatric multidetector array CT.

The purpose of this study was to develop and validate a technique for three-dimensional (3D) modelling of small lung nodules on paediatric multidetector array computed tomography (MDCT) images. Clinical images were selected from 21 patients (<18 years old) who underwent MDCT examinations. Sixteen of the patients had one or more real lung nodules with diameters between 2.5 and 6 mm. A mathematical simulation technique was developed to emulate the 3D characteristics of the real nodules. To validate this technique, MDCT images of 34 real nodules and 55 simulated nodules were randomised and rated independently by four experienced paediatric radiologists on a continuous scale of appearance between 0 (definitely not real) and 100 (definitely real). Receiver operating characteristic (ROC) analysis, t-test, and equivalence test were performed to assess the radiologists' ability to distinguish between simulated and real nodules. The two types of nodules were also compared in terms of measured shape and contrast profile irregularities. The areas under the ROC curves were 0.59, 0.60, 0.40, and 0.63 for the four observers. Mean score differences between simulated and real nodules were -8, -11, 13, and -4 for the four observers with p-values of 0.17, 0.06, 0.17, and 0.26, respectively. The simulated and real nodules were perceptually equivalent and had comparable shape and contrast profile irregularities. In conclusion, mathematical simulation is a feasible technique for creating realistic small lung nodules on paediatric MDCT images.

Improving mammographic decision accuracy by incorporating observer ratings with interpretation time.

Mammography is currently the most established technique for the early detection of breast cancer. However, mammography would benefit from further improvements as it does produce some errors, such as not finding all early-stage cancers. The objectives of this study were first, to measure the timing of correct and incorrect reading decisions in mammography and second, to exploit those dependencies to improve accuracy in mammographic interpretation. To address these objectives, an experiment was conducted where experienced breast imaging radiologists reviewed 400 mammographic regions equally divided among images that contained simulated benign masses, malignant masses, malignant microcalcifications and no lesions. The experiment recorded the radiologists' decision as well as the length of time the mammogram was interpreted in. The experiment results showed that incorrect detection as well as incorrect classification decisions were associated with longer interpretation times (p<0.0001). The timing results were used to create a model that would flag cases for review that had a higher probability of error. The flagged cases had a median accuracy drop of 13% for detection decisions and 16% for classification decisions compared with unflagged cases. This suggests that interpretation time can be incorporated into mammographic decision-making in order to identify cases with higher probabilities of perceptual error that require further review.

Luminance and contrast performance of liquid crystal displays for mammographic applications.

Liquid crystal displays (LCDs) are gradually replacing cathode-ray tubes (CRTs) as the primary means of electronic display of digital radiographs. The transition from CRT to LCD is fueled by advantages of the LCD technology such as enhanced maximum luminance and smaller form factor. This transition is expected to extend to digital mammography as well. The purpose of this study was to report the on-axis luminance and contrast performance of five medical-grade LCDs in terms of compliance with the DICOM grayscale display function (GSDF) and AAPM TG18 guidelines. The display devices included two 3 Mpx monochrome LCDs (Planar Dome C3, and NDS 20.8" Nova), two 5 Mpx monochrome LCDs (NDS 21.3" Nova, and Totoku ME511L), and one 9 Mpx color LCD (IBM T221). The on-axis luminance values were measured at all 8-bit driving levels using the TG18-LN test patterns and a baffled luminance meter and the results averaged. The luminance data were analyzed according to the AAPM TG18 methodology. The measured L(min), L(max), mean DeltaJND/Deltap, and maximum local deviation in DeltaJND/Deltap from GSDF, kappa(256), ranged within 0.43-0.87 cd/m(2), 263-715 cd/m(2), 2.15-2.72, and 0.79-1.46 intervals, respectively. While the values varied notably between different devices, all devices conformed to the TG18 criteria for primary class displays in terms of on-axis luminance response, and thus judged suitable for mammographic applications from on-axis luminance standpoint. Notwithstanding the findings, other factors such as matrix size, angular response, and color functionality should further be taken into consideration.

Evaluation of a quality control phantom for digital chest radiography.

RATIONALE AND OBJECTIVES: To examine the effectiveness and suitability of a quality control (QC) phantom for a routine QC program in digital radiography. MATERIALS AND METHODS: The chest phantom consists of copper and aluminum cutouts arranged to resemble the appearance of a chest. Performance of the digital radiography (DR) system is evaluated using high and low contrast resolution objects placed in the "heart," "lung," and "subdiaphragm" areas of the phantom. In addition, the signal levels from these areas were compared to similar areas from clinical chest radiographs. RESULTS: The test objects included within the phantom were effective in assessing image quality except within the subdiaphragm area, where most of the low contrast disks were visible. Spatial resolution for the DR systems evaluated with the phantom ranged from 2.6 lp/mm to 4 lp/mm, falling within the middle of the line pair range provided. The signal levels of the heart and diaphragm regions relative to the lung region of the phantom were significantly higher than in clinical chest radiographs (0.67 versus 0.21 and 0.28 versus 0.10 for the heart and diaphragm regions, respectively). The heart-to-diaphragm signal level ratio, however, was comparable to those in clinical radiographs. CONCLUSION: The findings suggest that the attenuation characteristics of the phantom are somewhat different from actual chests, but this did not appear to affect the post-processing used by the imaging systems and usefulness for QC of these systems. The qualitative and quantitative measurements on the phantom for different systems were similar, suggesting that a single phantom can be used to evaluate system performance in a routine QC program for a wide range of digital radiography systems. This makes the implementation of a uniform QC program easier for institutions with a mixture of different digital radiography systems.

Performance evaluation of computed radiography systems.

Recommended methods to test the performance of computed radiography (CR) digital radiographic systems have been recently developed by the AAPM Task Group No. 10. Included are tests for dark noise, uniformity, exposure response, laser beam function, spatial resolution, low-contrast resolution, spatial accuracy, erasure thoroughness, and throughput. The recommendations may be used for acceptance testing of new CR devices as well as routine performance evaluation checks of devices in clinical use. The purpose of this short communication is to provide a tabular summary of the tests recommended by the AAPM Task Group, delineate the technical aspects of the tests, suggest quantitative measures of the performance results, and recommend uniform quantitative criteria for the satisfactory performance of CR devices. The applicability of the acceptance criteria is verified by tests performed on CR systems in clinical use at five different institutions. This paper further clarifies the recommendations with respect to the beam filtration to be used for exposure calibration of the system, and the calibration of automatic exposure control systems.

Health physics consequences of out-patient treatment of non-Hodgkin's lymphoma with 131I-radiolabeled anti-B1 antibody.

The Medical University of South Carolina is currently participating in clinical trials of 131I radiolabeled Anti-B1 antibody for treatment of Non-Hodgkin's lymphoma. Under current South Carolina Department of Health and Environmental Control regulatory guidelines,; these patients are required to be admitted to the hospital and to remain as inpatients until the whole body burden is <30 mCi or the exposure rate measured 1 m from the patient is <5 mR h(-1). We demonstrate that these patients can be released in accordance with the new recommended guidelines of the Nuclear Regulatory Commission for the release of patients containing radioactive materials in compliance with all radioactive material and public dose standards. This benefits these patients by reducing their risk of infection and other hospital insults and by reducing the length of hospitalizations. Further, unnecessary hospital admissions are decreased, and the overall cost of healthcare delivery for these patients is significantly reduced.