G. James Blaine

Prospects for quantitative computed tomography imaging in the presence of foreign metal bodies using statistical image reconstruction.

X-ray computed tomography (CT) images of patients bearing metal intracavitary applicators or other metal foreign objects exhibit severe artifacts including streaks and aliasing. We have systematically evaluated via computer simulations the impact of scattered radiation, the polyenergetic spectrum, and measurement noise on the performance of three reconstruction algorithms: conventional filtered backprojection (FBP), deterministic iterative deblurring, and a new iterative algorithm, alternating minimization (AM), based on a CT detector model that includes noise, scatter, and polyenergetic spectra. Contrary to the dominant view of the literature, FBP streaking artifacts are due mostly to mismatches between FBPs simplified model of CT detector response and the physical process of signal acquisition. Artifacts on AM images are significantly mitigated as this algorithm substantially reduces detector-model mismatches. However, metal artifacts are reduced to acceptable levels only when prior knowledge of the metal object in the patient, including its pose, shape, and attenuation map, are used to constrain AMs iterations. AM image reconstruction, in combination with object-constrained CT to estimate the pose of metal objects in the patient, is a promising approach for effectively mitigating metal artifacts and making quantitative estimation of tissue attenuation coefficients a clinical possibility.

Perceived Fidelity of Compressed and Reconstructed Radiological Images: A Preliminary Exploration of Compression, Luminance, and Viewing Distance

The authors’ goal was to explore the impact of image compression algorithm and ratio, image luminance, and viewing distance on radiologists’ perception of reconstructed image fidelity. Five radiologists viewed 16 sets of four hard-copy chest radiographs prepared for secondary interpretation. Each set included one uncompressed, and three compressed and reconstruted images prepared using three different algorithms but the same compression ratio. The sets were prepared using two subjects, four compression ratios (10∶1, 20∶1, 30∶1, 40∶1), and two luminance levels (2,400 cd/m2, standard lightbox illumination, and 200 cd/m2, simulating a typical CRT display). Readers ranked image quality and evaluated obviousness and clinical importance of differences. Viewing distances for image screening, inspection, and comparison were recorded. At 10∶1 compression, the compressed and uncompressed images were nearly indistinguishable; the three algorithms were very similar, and differences were rated “not obvious” and “not important.” At higher compression, readers consistently preferred uncompressed images, with notable differences between algorithms. The obviousness and clinical importance of differences were rated higher at lightbox luminance. Viewing distances appeared to be idiosyncratic

Image Quality Assurance in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial Network of the National Lung Screening Trial

The National Lung Screening Trial is evaluating the effectiveness of low-dose spiral CT and conventional chest X-ray as screening tests for persons who are at high risk for developing lung cancer. This multicenter trial requires quality assurance (QA) for the image quality and technical parameters of the scans. The electronic system described here helps manage the QA process. The system includes a workstation at each screening center that de-identifies the data, a DICOM storage service at the QA Coordinating Center, and Web-based systems for presenting images and QA evaluation forms to the QA radiologists. Quality assurance data are collated and analyzed by an independent statistical organization. We describe the design and implementation of this electronic QA system, emphasizing issues relating to data security and privacy, the various obstacles encountered in the installation of a common system at different participating screening centers, and the functional success of the system deployed.

Quality monitoring of soft-copy displays for medical radiography.

As presentation of medical radiographic images on soft-copy displays (cathode ray tubes) becomes increasingly prevalent in electronic radiography, methods of quality assurance must be developed to ensure that radiologists can effectively transfer film-based reading skills. Luminance measurements provide the basis for evaluating the state of soft-copy displays. An integrated approach has been implemented at Mallinckrodt Institute of Radiology (MIR, Washington University, St Louis, MO) that facilitates measurement of geographically distributed soft-copy displays with centralized data logging, performance tracking, and calibration. MIRs central radiology image manager exercises the display station that drives the monitor, harvests the measurement data, stores the results, and submits the resulting data for additional processing. The luminance measurements are collected by a small, portable, photometric instrument designed at MIR that includes a serial port that is accessed via local area terminal service supported by the radiology image manager. The design details of the photometric instrument and example luminance characteristics of several soft-copy displays used at MIR are presented in this report.

Workstation acquisition node for multicenter imaging studies

This site has a contrast as a central data collection and image analysis center for a multilayer study involving four acquisition sites. Magnetic Resonance and Ultrasound studies are to be acquired at the sites and then transmitted via the Internet to the data collection center. This paper will describe the software architecture of a workstation designed to act as a store and forward node at a remote site. The software receives and stores images in DICOM format on the local hard drive. The workstation provides several different mechanisms for removing local identifying patient information and inserting patient and study identifiers which are specific to the multicenter study. After removing or modifying header information, the user may enqueue the data for transmission to the central repository.

A distributed approach to integrated inquiry and display for radiology

Picture archive and communications (PACS) systems should be flexible and modular in design so that new advances in storage, computation, and display technology can be introduced into the system without a significant redesign of existing software. The acquisition, storage, and management of radiologic images must be carefully integrated with a radiology information system. Our architecture is based on a four-level data model: (1) patient information, (2) examination information and reports, (3) image information, and (4) instances of images. The PACS being developed at the Mallinckrodt Institute of Radiology within the Electronic Radiology Laboratory consists of three primary components: application clients, database servers and image servers. One type of application client is an image-capable workstation that supports a radiology image viewing application. The application client queries the database server for information regarding patient and examination data in response to user-level requests. The database server responds to the request by retrieving the appropriate patient demographics and examination information, along with a pointer to the image/instance data from a central database. The client then uses the image data pointer to query the image server for the actual pixel data. The image server responds by transmitting the pixel data to the requesting application client or a designated auxiliary display device. Other clients act as image data acquisition nodes. Queries to the database servers are made via a library of callable subroutines. Software integrity is maintained throughout the system by dynamically loading software from a code-control database. Inquiry and display transactions, supported on a local-area network (Ethernet), have been measured and analyzed. Results and observations are presented.

Filmless digital chest radiography within the radiology department

The technical purposes of this work were to develop improvements in the methodology for assessing the physical performance of CRT monitors and display controller systems and to explore image processing techniques to make soft- and hard-copy image quality visually similar. The clinical purpose was to determine whether, with proper image processing, soft-copy presentations of digital chest radiographs could become equivalent to hard-copy for visualizing normal and pathological features. The luminance characteristic curve, luminance uniformity, modulation transfer function, and noise power spectra of the CRT monitors as well as video waveforms of a display controller were measured. Posteroanterior and lateral chest radiographs were acquired by a dedicated thorax imaging system with a selenium detector and processed using a previously optimized algorithm for printing on film. A Laplacian pyramid filter was employed to compensate for the mid- to high-frequency contrast losses in the soft-copy presentation. Five chest radiologists directly compared the soft- and hard-copy presentations in eighteen patients with CT-proven pathologies. Based on 99 percent confidence intervals, the soft-copy images were preferred for seven of the fourteen anatomic categories and image contrast, and the hard-copy images were preferred for brightness and image granularity. There were no preferences for the depiction of pathologies, spatial resolution, and the remaining anatomic categories. After determining the physical properties of the CRT monitors, image processing operations can be defined to produce soft-copy renditions of soft-copy displays for primary diagnosis to make digital radiography more cost- effective and to encourage additional development of filmless image interpretation and management in a PACS.

Rapid Display of Radiographic Images

The requirements for the rapid display of radiographic images exceed the capabilities of widely available display, computer, and communications technologies. Computed radiography captures data with a resolution of about four megapixels. Large-format displays are available that can present over four megapixels. One megapixel displays are practical for use in combination with large-format displays and in areas where the viewing task does not require primary diagnosis. This paper describes an electronic radiology system that approximates the highest quality systems, but through the use of several interesting techniques allows the possibility of its widespread installation throughout hospitals. The techniques used can be grouped under three major system concepts: a local, high-speed image server, one or more physicians workstations each with one or more high-performance auxiliary displays specialized to the radiology viewing task, and dedicated, high-speed communication links between the server and the displays. This approach is enhanced by the use of a progressive transmission scheme to decrease the latency for viewing four megapixel images. The system includes an image server with storage for over 600 4-megapixel images and a high-speed link. A subsampled megapixel image is fetched from disk and transmitted to the display in about one second followed by the full resolution 4-megapixel image in about 2.5 seconds. Other system components include a megapixel display with a 6-megapixel display memory space and frame-rate update of image roam, zoom, and contrast. Plans for clinical use are presented.

A Dedicated Hardware Architecture for Data Acquisition and Processing in a Time-of-Flight Emission Tomography System (Super-PETT)

We present the architecture, implementation and performance aspects of a dedicated processor for use in Super-PETT, The micro-coded machine accepts event data from the acquisition circuitry and constructs in real time any of three pre-image types, including time-of-flight arrays. Pre-images are later back-loaded to perform high speed reconstructions. One such processor is assigned to each image slice of the Super-PETT. Event rates and processing times are given for various application modalities.

Tools for Managing Image Flow in the Modality to Clinical-Image-Review Chain

Web-based clinical-image viewing is commonplace in large medical centers. As demands for product and performance escalate, physicians, sold on the concept of “any image, anytime, anywhere,” fret when image studies cannot be viewed in a time frame to which they are accustomed. Image delivery pathways in large medical centers are oftentimes complicated by multiple networks, multiple picture archiving and communication systems (PACS), and multiple groups responsible for image acquisition and delivery to multiple destinations. When studies are delayed, it may be difficult to rapidly pinpoint bottlenecks. Described here are the tools used to monitor likely failure points in our modality to clinical-image-viewing chain and tools for reporting volume and throughput trends. Though perhaps unique to our environment, we believe that tools of this type are essential for understanding and monitoring image-study flow, re-configuring resources to achieve better throughput, and planning for anticipated growth. Without such tools, quality clinical-image delivery may not be what it should.