James Anthony Seibert

Determination of imaging performance of a photostimulable phosphor system for digital mammography

Quantitative analysis of a prototype photostimulable phosphor system for digital mammography was performed. The pre-sampled MTF, noise power spectrum (NPS), noise equivalent quanta (NEQ), and detective quantum efficiency (DQE) were measured at 26 and 32 kVp to assess the imaging performance of a commercial computed radiography system dedicated for mammographic imaging. The pre-sampled MTF demonstrated 5 percent modulation at 8 lp/mm with a small dependence on kVp, and noise power estimates indicated x-ray quantum-limited spectral characteristics from 2 mR up to approximately 30 mR incident exposure. Maintenance of x-ray information content up to approximately 500,000 quanta/mm2 based upon NEQ measurements was demonstrated. DQE (0 mm-1) was 30-50 percent, DQE (2.5 mm-1) was 15-25 percent, and DQE (4 mm-1) was 5-15 percent, depending on kVp, incident exposure, and readout direction. A significant increase in DQE compared to previous CR mammography implementations was found. In addition to the quantitative measurements, qualitative experience suggests that CR mammography is essentially equivalent to state-of-the-art mammography screen-film detector systems.

Iterative reconstruction: how it works, how to apply it.

Computed tomography acquires X-ray projection data from multiple angles though an object to generate a tomographic rendition of its attenuation characteristics. Filtered back projection is a fast, closed analytical solution to the reconstruction process, whereby all projections are equally weighted, but is prone to deliver inadequate image quality when the dose levels are reduced. Iterative reconstruction is an algorithmic method that uses statistical and geometric models to variably weight the image data in a process that can be solved iteratively to independently reduce noise and preserve resolution and image quality. Applications of this technology in a clinical setting can result in lower dose on the order of 20–40% compared to a standard filtered back projection reconstruction for most exams. A carefully planned implementation strategy and methodological approach is necessary to achieve the goals of lower dose with uncompromised image quality.

SU‐EE‐A2‐03: Visualization and Identification of Breast Glandular Tissue in Breast CT Volume Data

Purpose: Breast glandular tissue architecture complicates mammographyimage interpretation due to superposition. We have built a dedicated breast CT (BCT) scanner to produce volumetric images of the breast and begun a preliminary clinical trial in volunteers and selected patients. The purpose of this study was to evaluate visualization and identification of breast landular tissue patterns in BCT volume data and its potential to improve lesion detection compared to mammography.Method and Materials: A dedicated BCT scanner was constructed and previously described. Volunteer and patient imaging was performed using 80 kVp at doses comparable to a standard 2‐view mammogram and reconstructed using a modified Feldkamp algorithm. BCT data of 512^3 voxels have an approximately isotropic resolution of 300 μm. Volume data were analyzed and viewed on a specially designed volume workstation and were displayed using blending, maximum‐intensity‐projection (MIP) and summation projection algorithms. Interactive review was possible for the entire volume. Breast glandular structures were identified based on CT number, voxel histograms and structural features. Results: BCT images showed impressive breast parenchyma and glandular structure detail with excellent contrast resolution. Volume rendering, especially summation projection, and thick slices provided optimization of viewing of ductal structures. Multi‐planar slices permitted rapid scrolling through slices. Voxel CT numbers, histograms and architectural features were effective in differentiating glandular from fat, skin and connective tissues. MIP images clearly demonstrated calcifications. Conclusion: BCT provides high‐quality volume data that enhanced visualization of breast glandular tissue and architecture compared to other breast imaging methods. Voxel CT numbers plus direct interactive viewing provided the mammographer clear views of breast architecture and glandular tissues. Workstation display flexibility presented data appearing similar to mammograms plus additional tomographic slices further enhancing conspicuity of breast architecture. A small number of mammographically demonstrated cancers were readily identified in BCT data.

A lesion detectability simulation method for digital x-ray imaging.

A simulation method is described in this work that aids in quantifying the upper limits of lesion detectability as a function of lesion size, lesion contrast, pixel size, and x-ray exposure for digital x-ray imaging systems. The method entails random lesion placement with subsequent simulated imaging on idealized x-ray detectors with no additive noise and 100% quantum detective efficiency. Lesions of different size and thickness were simulated. Mean (expectation) lesion signal-to-noise ratios (LSNRs) were calculated and receiver operating characteristic (ROC) curves were constructed based on LSNR ensembles. Mean (expectation) values of the areas under the ROC curves were calculated for lesions of varying size on pixel arrays of varying size at different exposures. Analyses were performed across several parameters, including lesion size, pixel size, and exposure levels representative of various areas of radiography. As expected, lesion detectability increased with lesion size, contrast, pixel size, and exposure. The model suggests that lesion detectability is strongly dependent on the relative alignment (phase) of the lesion with the pixel matrix for lesions on the order of the pixel size.

Imaging performance of a terbium-doped fiber optic screen for diagnostic imaging

The resolution of a fiberoptical boule was determined experimentally. A boule is a matrix of scintillating glass fibers arranged parallel to each other and compressed into a thick plate. A 51 mm X 51 mm by 3 mm thick terbium-activated boule was optically coupled to a 1 k X 1 k X 16 bit CCD camera. The image of an edge was used to compute the line spread function, and the modulation transfer function was calculated. After correcting for the MTF of the CCD and optics, the MTF of the fiberoptical plate demonstrated 20% modulation at a spatial resolution of 15 line pairs per millimeter. The x-ray absorption of the 3 mm thick plate was 98% at 70 kV (3.3. mm half value layer). It is shown using simple trigonometry that for a very high resolution detector, x-ray beam divergence (angled photons striking the receptor) at the periphery of the field of view may cause substantial resolution losses. The role that fiberoptical plate technology may play in diagnostic medical imaging is discussed.

Legacy system integration using Web technology

As healthcare moves towards a completely digital, multimedia environment there is an opportunity to provide for cost- effective, highly distributed physician access to clinical information including radiology-based imaging. In order to address this opportunity a Universal Clinical Desktop (UCD) system was developed. A UCD provides a single point of entry into an integrated view of all types of clinical data available within a network of disparate healthcare information systems. In order to explore the application of a UCD in a hospital environment, a pilot study was established with the University of California Davis Medical Center using technology from Trilix Information Systems. Within this pilot environment the information systems integrated under the UCD include a radiology information system (RIS), a picture archive and communication system (PACS) and a laboratory information system (LIS).

Error component analysis for PACS: operational sources of data error in real world PACS for DICOM series, study, and patient level identifiers

The gold standard for modern PACS workflow is now considered to be a complete integration of HIS, RIS and PACS datastreams. However, a number of current obstacles exist in regard to achieving this level of integration in real-world practice environments, given the current level of modality support for more advanced DICOM services such as MWL, MPPS, and Storage Commitment. In this paper, many of the more common sources of disparity between HIS/RIS and PACS data are discussed, as well as possible DICOM-based mitigations and possible PACS workflow models not requiring modality upgrades. These are discussed in the context of the IHE model, and compared to the ideal of complete IHE workflow. Various operational sources of modality-based patient demographic data for existing PACS are discussed and analyzed from a DICOM perspective, comparing modality inputs for a typical large PACS to RIS data references. Disparities between PACS and RIS data are emphasized, with the goal of PACS/RIS data reconciliation. The existing obstacles to this integration are discussed, and the application of DICOM Modality Worklist, Storage Commitment, and Performed Procedure Step Services are discussed in reference to these error sources. As the subject site utilizes DICOM Modality Worklist, those operational sources of error that remain after Modality Worklist was implemented are analyzed in the context of the existing modality workflow limitations. The intrinsic disparity between CPT-based billing and reporting structures and existing DICOM modality models for CT, MR, US, R&F, and CR are discussed, and examples given for operational challenges in integrating these elements using existing modality design. Conclusions included that the Modality Worklist, in itself, is inadequate to drive RIS-integrated PACS workflow, and that current modality limitations preclude complete PACS/RIS datastream integration at this time. Several alternative mitigation models are discussed using existing modalities, as well as suggestions for improvements in modality workflow design.

MO-G-19A-01: ABR Exams; A Glimpse Behind the Curtains

While the vast majority of clinical medical physicists either have taken, or will take the ABR certification exams, there appears to be limited understanding about the process of creating, administering, scoring and evaluating the exams. In this course, ABR trustees and volunteers will educate current and future ABR diplomates about the process of question writing, written exam assembly, evaluation of the performance of the exams, and preparation and delivery of the oral board exam. By understanding the process behind creating the written and oral exams, ABR candidates and diplomates will gain a better understanding of the framework of the exams, including the financial resources needed. At the same time, understanding the many hours of volunteer work needed to create a fair and meaningful exam may create a positive incentive to respect the exam confidentiality. LEARNING OBJECTIVES 1. Understand the characteristics of a well-written exam question. 2. Learn about the process of developing and administering an exam. 3. Review the application of psychometric analysis to the ABR exams. 4. Appreciate the effort and expense involved in preparing the certification exams.

WE‐A‐218‐03: Translating X‐Ray Tube Modulation Parameters between Different CT Scanner Models Using Dose Metrics

Purpose: While auto tube current modulation is an effective dose reduction technique, manufacturer‐specific implementation of the technique leads to inconsistencies between scans obtained on different scanners. This research describes efforts to translate comprehensive scan protocols from a reference CTscanner to progeny scanners by matching x‐ray output using a variable diameter phantom. Methods: The phantom consisted of six cylinders of PMMA with increasingly large diameters, much like a wedding cake. The diameters of the cylinders were 10, 13, 16, 20, 25, and 32 cm. The reference CTscanner was a GE LightSpeed 16; the progeny scanners were a GE LightSpeed VCT and Siemens Definition AS+. The phantom was scanned while varying the tube modulation metric (either noise index or reference mAs). Using custom software, the mAs was determined on a slice‐by‐slice basis and then averaged along the length of each phantom. Two conversion metrics were examined as a way to translate x‐ray output between scanners: (1) CTDIw or (2) air exposure. The modulation metric of the progeny CTscanner that produced the output closest to that of the reference CTscanner was then selected as the optimal metric for each phantom size. The metric was then compared to the ad hoc scan protocols currently used for the progeny scanners.Results: The range of appropriate tube modulation metrics is highly dependent on patient diameter. When applied to patients of varying sizes, tube current modulation may be hitting the maximum or minimum limits. Conclusions: Both CTDIw and air exposure are reasonable conversion metrics to match x‐ray output between CTscanners. While matching x‐ray output is the first step towards standardizing scan protocols across different types of scanners, thorough image quality analysis must be done to ensure that clinical tasks can be performed sufficiently

TH‐D‐350‐06: A Web Based Physics Teaching File for Radiology Residents

Purpose: To describe a web‐based digital teaching file of imaging physics for Radiology residents. Method and Materials: The RSNA R&E Foundation supported the development of a web‐based physics teaching file for Radiology residents. This RSNA Physics Teaching File was completed at the end of 2007 and is freely available to any computer with internet access. Modalities that employ x‐rays in the image formation process are described, including radiography,mammography,fluoroscopy,angiography, and computed tomography. There are also sections on general characteristics of digital images and image processing, which has become ubiquitous in digital imaging.Results: The website is hosted at SUNY Upstate Medical University and may be viewed at http://www.upstate.edu/radiology/rsna. Each section contains digital images generated with appropriate phantoms on the various modalities, as well as a selection of clinical images. Illustrated are important technical issues related to image quality (i.e. contrast, resolution, and noise) and how these are affected by parameters associated with image acquisition. Effect of changing tube voltage, tube current, field of view, image matrix size, and scatter reduction techniques are illustrated. Special sections were included to explain dual‐energy imaging and other image processing techniques in radiography.Conclusion: The teaching file web site is a valuable resource for teaching the physics of x‐ray imaging to radiology residents.