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Biomedical subjects

R G Swensson

Publications and source records attributed to R G Swensson.

13 recordsLinked to original sources
PubMed1992

Practices and attitudes about cathode-ray tube-based and film-based image interpretation.

A questionnaire was mailed to 708 practicing radiologists and 348 members of the Society for Computer applications in Radiology (SCAR) in order to evaluate current practices and attitudes regarding the perceived advantages or disadvantages of film- and CRT-based image interpretation. A total of 27% of the 1,056 questionnaires (137 practicing radiologists; 145 SCAR members were returned. Ninety percent of practicing radiologists used film at least 75% of the time. Advantages of film-based reading listed by more than 75% of the respondents included: film reading is faster, and facilitates viewing multiple images. Advantages of CRT-based reading included: access to the entire dynamic range and potential imaging processing. Desirable attributes of existing displays included: adjustable grey scale, magnification, ability to view multiple images, allow quick review, and viewing by several individuals. Valued potential advances included: multiple higher resolution monitors, image processing and multimodality display. Practicing radiologists and computer applications society members had similar attitudes. Film-based reading is still nearly universal, but radiologists are interested in CRT-based reading if such devices have the proper features and become more available.

Attitude of Health Personnel↗
PubMed1991

Visualization and detection-localization on computed tomographic images.

These studies investigated observers' ability to detect and locate highly visible liver lesions on computed tomographic (CT) images, manipulating both the lesion's location and polarity (brighter or darker than liver background). Visibility of a lesion is not sufficient to guarantee accurate localization. With clinical images, possible confusions between a lesion and coexisting normal structures (like blood vessels) is a serious constraint on observer performance.

Humans↗
PubMed1991

Current use of screening laboratory tests before abdominal interventions: a survey of 603 radiologists.

A survey of 2,153 radiologists was conducted to assess both their current practices of evaluating hemostatic function and their use of blood tests before performing image-guided nonvascular abdominal interventions. Among the 603 (28%) who responded, more radiologists routinely perform prothrombin time (81%) or partial thromboplastin time (78%) tests than platelet counts (59%), and relatively few (7%) obtain bleeding times. The most common practice (51%) is to order all of the first three tests. Use of laboratory tests is quite common (greater than 75%) before biopsy of splenic masses, hemangiomas, or hepatomas and before all catheter insertions. These tests are used less frequently (less than or equal to 70%) before fine-needle procedures, including biopsy and cyst aspiration. Only one-third of the radiologists alter their evaluation in patients who have taken aspirin. Most respondents (64%) believe that there should be written guidelines on how to evaluate patients before interventional procedures. Virtually all (97%) thought such evaluation should be the radiologist's responsibility.

Aspirin↗
PubMed1990

Search and nonsearch protocols for radiographic consultation.

Six radiologists, acting as radiograph reviewers, used two different consultation protocols to differentiate among 292 ambiguous chest radiographic findings: 120 simulated nodules and 172 normal findings (previous readers' false-positive reports of nodules). The nonsearch protocol identified each finding (by film location), and reviewers rated the likelihood of each finding's being a pulmonary nodule. The search protocol asked reviewers to report and rate all locations regarded as possible nodules on each radiograph and assigned a default negative rating to any unreported finding (nodule or normal structure). Receiver operating characteristic analyses demonstrated a significantly higher accuracy for each reviewer's search-protocol discriminations between these nodules and ambiguous normal findings. This superiority-of-search result suggests that radiologists' second opinions about suspected lesions might be more accurate when consultants follow a search protocol, independently reviewing radiographs without prior knowledge of the specific findings that concerned the primary radiograph readers.

False Positive Reactions↗
PubMed1988

Size discrimination in computed tomographic images. Effects of feature contrast and display window.

Studies show that features on computed tomographic (CT) images in clinical formats become less detectable when the images are produced with wider CT display windows. We studied the effects of feature contrast and the display window on observer performance in higher-order tasks that involved discriminating small size differences between features on CT images. The features to be discriminated were pairs of disks (9.0 or 9.5 mm in diameter) superimposed on CT images of water phantoms. Sets of image stimuli for two different types of size-discrimination tasks were generated with various CT contrasts specified for the superimposed features and were produced on film transparencies with display windows ranging from 90 to 2880 Hounsfield units (HU) in width. Observers' performance improved with increasing CT contrast in both size discrimination tasks. Unlike performance in feature-detection tasks, however, size discrimination was unaffected by changing the CT display window over a factor of 16 (from 90 to 1440 HU). Performance fell only at the widest display window (2880 HU), for which CT noise was essentially invisible. These results suggest that the effect of changing the CT display window may depend on the spatial frequency content of image information required for a given task.

Humans↗
PubMed1987

Display thresholding of images and observer detection performance.

In this experiment we studied how thresholding by the gray-scale display transformation altered the observer's ability to detect small, high-contrast lesions in both smooth (lower-noise) and sharp (higher-noise) reconstructions of computed tomographic (CT) images. Different display conditions manipulated the level setting of a narrow CT display window. This varied the fraction of thresholded pixels, set to the maximum or minimum values of brightness in relevant locations of the displayed images. Observers' ability to detect lesions in the smooth CT images was unaffected by moderate asymmetries in the display level but then abruptly declined at both the extremely high- and low-level settings. In sharp CT images, the lesion gradually decreased in detectability as the level setting became more asymmetric. These effects of the display manipulations were modeled by a realizable physical detector, whose decision variable was the cross correlation of the pixel display values with the lesion's expected profile at the specified (lesion and nonlesion) locations in the CT images. This cross-correlator model closely predicted the patterns of changes in lesion detectability that were measured for the human observers. It also predicted how thresholding of the higher or the lower CT numbers differentially altered the shapes of the observers' measured receiver-operating-characteristic curves for the smooth CT images.

Differential Threshold↗
PubMed1978

Improving performance by multiple interpretations of chest radiographs: effectiveness and cost.

The accuracy and cost of four methods of duplicate reading were evaluated. Eight radiologists interpreted 100 random chest radiographs. Using a third independent interpretation to resolve disagreements between pairs of readers ("Pseudoarbitration") was the most effective method overall, reducing errors 37%, increasing correct interpretations 18%, and adding 19% to the cost of an error-free interpretation. Resolving disagreements in facor of positive diagnoses was the best method for reducing omissions, but it almost doubled false-positive diagnoses. The choice between single and multiple interpretations must be evaluated in each clinical setting and should consider expected improvements in accuracy, implications for patient care, and additional costs.

Cost-Benefit Analysis↗
PubMed1977

Omissions in radiology: faulty search or stringent reporting criteria?

Selected difficult chest radiographs were interpreted by 10 radiologists and then reread in a Focused Search condition that directed readers' attention to film regions containing frequently omitted findings. The percentage of true abnormalities reported at any level of confidence increased from 49.3 to 68.3 between the usual and Focused Search conditions. However, the corresponding percentage of significant false positives also increased from 4.6 to 10.6. The separate ROC curves from each condition could be superimposed and the data fit by a single ROC curve. Thus, the reduced omissions in Focused Search were the result of less stringent criteria for reporting the presence of abnormal findings, rather than an enhanced ability to detect abnormalities. There was no evidence that the original omissions were abnormalities simply overlooked in faulty initial searches.

Boston↗
PubMed1976

The value of consultation among radiologists.

The value of group consultation in improving the accuracy of radiologic diagnosis was assessed. Abnormalities on 24 films were pointed out to six groups of three radiologists each. They were asked to reach a specific diagnosis for each case. Accuracy was compared in three settingss: (1) without consultation; (2) with consultation leading to a diagnosis by group consensus; and (3) with consultation followed by independent diagnoses. The accuracy of over 75% of the radiologist improved after consultation in either setting. The extent of improvement was inversely related to the initial accuracy level of the individual. When two or three radiologists agreed initially, they were more frequently correct than not. Group discussion followed by individual diagnosis is a practical approach to radiologic consultation.

Diagnostic Errors↗
PubMedDate not supplied

Improving diagnostic accuracy: a comparison of interactive and Delphi consultations.

Consultation among physicians on difficult diagnostic problems is commonly used to improve the accuracy of medical decisions. Such consultation is most often informal and interactive. Nevertheless, behavioral studies suggest that non-interactive techniques may be more effective problem solving methods. Of these the Delphi approach, involving pooling and feedback of anonymously contributed information, has generated particular interest. To assess the relative effectiveness of independent decision making, interactive group consultation, and Delphi techniques in a clinical setting we compared the diagnostic accuracy of 17 radiologists interpreting radiologic examinations in these settings. Interactive consultation improved performance by 69% compared to radiologists interpreting the studies individually. In addition, two Delphi strategies each produced an additional 20% mean improvement in accuracy over interactive consultation. Whereas interactive consultation improved the accuracy of the best individual readers by only 6%, a Delphi model improved their performance by 25%. Thus, Delphi was an effective, easily applied method of clinical consultation whose usefulness in other clinical setting should be evaluated.

Decision Making↗
PubMedDate not supplied

Evaluation of observer performance in detecting blood vessels on simulated angiographic images.

This paper presents methods for evaluating the effects of technical factors on observers' detection of small blood vessels in angiographic images. A fixed set of physical parameters was used to generate computer-simulated angiographs that contained blood vessels of various diameters. Observers' judgments about each set of images permitted estimation of the receiver operating characteristic (ROC) curves for vessel detection and of the probability of correctly locating the vessels. Both parametric and nonparametric methods were used to characterize the ROC curves. Three different, but theoretically related, measures of vessel detectability varied systematically with changes in the blood vessel's diameter, reflecting changes in observer performance.

Angiography↗
PubMedDate not supplied

Contrast-detail curves for liver CT.

Contrast-detail curves were constructed for liver computed tomographic (CT) images using an objective method. Stimuli were created by superimposing disks at specified locations on sets of 92 normal liver CT images. Bright and dark disks of 9 sizes and 36 possible image contrasts were used. Sets of 92 stimuli were rendered on film at five window widths (64, 128, 256, 512, and 1024 HU). The contrast-detail (CD) curve flattened substantially for disks larger than 7-mm diameter, and its slope (on a log-log plot) was less than predicted from signal-detection theory. Manipulation of display window manipulation had little impact on this disks' visibility. The results indicate that human observers have difficulty visualizing large, low-contrast details on liver CT scans, and suggest that narrowing the display window will have little effect on this limitation.

Contrast Media↗