A perceptually tempered display for digital mammograms.

The cathode ray tube of a workstation for use with digital mammograms was calibrated with a photometer to produce an input-output characteristic curve similar to the perceptually linear curve defined by a current display standard. Then, a test pattern consisting of bars of increasing intensity containing disks of decreasing contrast was used by an observer to estimate the minimal detectable contrast (MDC) at different levels of display luminance. The MDC was modeled by a parabola. The shape of the parabola was determined by the observer's perceptual responses, and the range was determined by the maximum and minimum pixel values of the breast parenchyma. As each mammogram was displayed, the contour of the breast was automatically found and pixels within the breast image were sampled to determine the pixel values that were used to compute the maximum and minimum pixel values. The parabola was integrated to determine the look-up table for the initial MDC-tempered display of the mammogram. Preliminary observer performance tests showed no significant differences in the accuracy and speed of three radiologists who read a set of mammograms when the MDC-tempered display was compared with the perceptually linear display.

Nature of expertise in searching mammograms for breast masses.

RATIONALE AND OBJECTIVES: The authors investigated how training and experience affect the performance of observers searching mammograms for breast masses. METHODS: Eye positions of mammographers, mammography technologists, mammography residents, and laypersons were compared to scan paths generated by a simulated scanner as each searched nine two-view digital mammogram pairs for breast masses. RESULTS: Analysis of time-to-hit data revealed that mammographers and mammography technologists with the most extensive training and experience had the fastest search times in the detection and confirmation of a breast mass on two views. Scanning patterns of less-experienced mammography residents were less efficient due to wider dispersion of visual attention between potential breast masses and perturbations in breast parenchyma. Because laypersons lacked both training and experience in mammography, bright blobs in the breast image were considered to be intuitively valid target candidates and these features distracted the search by capturing visual attention. CONCLUSION: Experience reading normal and abnormal mammograms plays a critical role in training radiologists. Experience combined with training provides the basis for generating efficient visual search strategies and developing distinctive conceptual criteria for perceptual differentiation and interpretation of true breast masses from image artifacts and structured noise that mimics breast abnormalities.

Mechanism of satisfaction of search: eye position recordings in the reading of chest radiographs.

PURPOSE: To use the eye position recordings of observers as they read chest images to advance understanding of the mechanism of "satisfaction of search," a phenomenon in which the detection of one abnormality interferes with the detection of other abnormalities. MATERIALS AND METHODS: Eight radiologists examined chest images that contained simulated pulmonary nodules and native abnormalities. Accuracy in detecting nodules and native abnormalities and eye position, gaze duration, and total search time were recorded. RESULTS: Nodule detectability was lower on native abnormality-containing images than it was on normal images (P < .005). Native-abnormality detectability was not negatively affected by the nodules. Most missed nodules were fixated; only those on images without native abnormalities, however, received prolonged visual attention. CONCLUSION: The satisfaction of search phenomenon is an important source of error in the detection of subtle abnormalities but not of obvious abnormalities. Obvious abnormalities capture visual attention and decrease vigilance for more subtle abnormalities.

Searching for bone fractures: a comparison with pulmonary nodule search.

RATIONALE AND OBJECTIVES: We aimed to determine if the characteristics and principles of visual search described for the detection of pulmonary nodules apply to extremity fractures. METHODS: The eye positions of staff orthopedic radiologists, radiology residents, and medical students were monitored as they searched hand and wrist X-ray images for fractures and a chest image for nodules. RESULTS: More systematic scanning patterns were observed for experienced observers than inexperienced observers. Positive decisions for bone images were associated with prolonged gaze durations; prolonged gaze durations were significantly longer for false-negative versus true-negative decisions. Intercluster jump distances were found to be greater for chest images than bone images. CONCLUSIONS: A search for bone fractures can be qualitatively characterized by classifying observer scan paths, dwell times, and jump distances. Gaze duration can be a useful predictor of bone image locations containing potential missed fractures. Perceptual feedback could aid observers in the detection of inconspicuous fractures.

Comparison scans while reading chest images. Taught, but not practiced.

Radiology instructors and residents were surveyed for their methods of instruction concerning viewing techniques. A similar group of radiologists had their eye activity measured as they viewed chest images. Image reading techniques are taught to be systematic and directive with comparisons of bilateral features. Yet, most images are read by a free search method; bilateral comparisons comprise less than 4% of the visual activity. Instructors and residents show this discrepancy between instructional techniques and reading practice.

Densitometric measurements of lung nodules on chest radiographs.

A technique is described whereby embedded nodular densities appearing on chest radiographs can be densitometrically measured without the obscurring effects of anatomic structures. The technique consists of rear-projecting a light beam into a chest radiograph and an observe adjusting this beam until the lucency matches that of the nodule's appearance. The radiography is then removed, and the lucency is scanned and analyzed with a microcomputer. Calibration data using simulated nodules show a good accuracy in measuring size, contrast, and edge gradient.