The effect of image display size on observer performance an assessment of variance components

Focal lung pathology detection in radiology: Is there an effect of experience on visual search behavior?

In radiology, 60% to 80% of diagnostic errors are perceptual. The use of more efficient visual search behaviors is expected to reduce these errors. We collected eye-tracking data from participants with different levels of experience when interpreting chest X-rays during the completion of a pathology-detection task. Eye-tracking measures were assessed in the context of three existing visual search theories from the literature to understand the association between visual search behavior and underlying processes: the long-term working memory theory, the information-reduction hypothesis, and the holistic model of image perception. The most experienced participants (radiology residents) showed the highest level of performance, albeit their visual search behaviors did not differ from the intermediate group. This suggests that radiology residents better processed the represented information on the X-ray, using a visual search strategy similar to the intermediate group. Since similar visual search resulted in more information extraction in the radiology residents compared with the intermediates, we suggest that this result might support the long-term working memory theory. Furthermore, compared with novices, intermediates and radiology residents fixated longer on areas that were more important to avoid missing any pathology, which possibly confirms the information-reduction hypothesis. Finally, the larger distances between fixations observed in more experienced participants could support the holistic model of image perception. In addition, measures of generic skills were related to a lower time cost for switching between global and local information processing. Our findings suggest that the three theories may be complementary in chest X-ray interpretation. Therefore, a unified theory explaining perceptual-cognitive superiority in radiology is considered.

Image Size Influences Visual Search and Perception of Hemorrhages When Reading Cranial CT: An Eye-Tracking Study

OBJECTIVE

The aim of this study was to explore reader gaze, performance, and preference during interpretation of cranial computed tomography (cCT) in stack mode at two different sizes.

BACKGROUND

Digital display of medical images allows for the manipulation of many imaging factors, like image size, by the radiologists, yet it is often not known what display parameters better suit human perception.

METHOD

Twenty-one radiologists provided informed consent to be eye tracked while reading 20 cCT cases. Half of these cases were presented at a size of 14 × 14 cm (512 × 512 pixels), half at 28 × 28 cm (1,024 × 1,024 pixels). Visual search, performance, and preference for the two image sizes were assessed.

RESULTS

When reading small images, significantly fewer, but longer, fixations were observed, and these fixations covered significantly more slices. Time to first fixation of true positive findings was faster in small images, but dwell time on true findings was longer. Readers made more false positive decisions in small images, but no overall difference in either jackknife alternative free-response receiver operating characteristic or reading time was found.

CONCLUSION

Overall performance is not affected by image size. However, small-stack-mode cCT images may better support the use of motion perception and acquiring an overview, whereas large-stack-mode cCT images seem better suited for detailed analyses.

APPLICATION

Subjective and eye-tracking data suggest that image size influences how images are searched and that different search strategies might be beneficial under different circumstances.

Investigation of optimal display size for viewing T1-weighted MR images of the brain using a digital contrast-detail phantom

We clarified the relationship between the display size of MRI images and observer performance using a digital contrast-detail (d-CD) phantom. The d-CD phantom was developed using Microsoft Visual Basic 2010 Express. It had a 512 × 512 matrix in size and a total of 100 holes, whose diameter increased stepwise from 4 to 40 pixels with a 4-pixel interval in the vertical direction; the contrast varied stepwise in the horizontal direction. The digital driving level (DDL) of the back-ground, the width of the DDL, and the contrast were adjustable. These parameters were determined on the basis of the actual T1-weighted magnetic resonance (MR) images of the brain. In this study, the DDL, width, and contrast were set to 85, 20, and 1, respectively. The observer performance study was performed for three different display sizes (30 cm × 30 cm as the enlarged size, 16 cm × 16 cm as the original size, and 10 cm × 10 cm as the reduced size) using a 2-megapixel color liquid crystal display monitor, and it was analyzed using Friedman and Wilcoxon statistical tests. The observer performances for the original display (p < 0.01) and the reduced display sizes (p < 0.01) were superior to that observed for the enlarged size, whereas there was no significant difference between the original display and reduced display sizes (p = 0.31). Evaluation with the digital phantom simulating MR imaging also revealed that the original and reduced display sizes were superior to the enlarged display size in observer performance. The d-CD phantom enables a short-term evaluation of observer performance and is useful in analyzing relation-ship between display size and observer performance.

Effect of display resolution on time to diagnosis with virtual pathology slides in a systematic search task

Performing diagnoses using virtual slides can take pathologists significantly longer than with glass slides, presenting a significant barrier to the use of virtual slides in routine practice. Given the benefits in pathology workflow efficiency and safety that virtual slides promise, it is important to understand reasons for this difference and identify opportunities for improvement. The effect of display resolution on time to diagnosis with virtual slides has not previously been explored. The aim of this study was to assess the effect of display resolution on time to diagnosis with virtual slides. Nine pathologists participated in a counterbalanced crossover study, viewing axillary lymph node slides on a microscope, a 23-in 2.3-megapixel single-screen display and a three-screen 11-megapixel display consisting of three 27-in displays. Time to diagnosis and time to first target were faster on the microscope than on the single and three-screen displays. There was no significant difference between the microscope and the three-screen display in time to first target, while the time taken on the single-screen display was significantly higher than that on the microscope. The results suggest that a digital pathology workstation with an increased number of pixels may make it easier to identify where cancer is located in the initial slide overview, enabling quick location of diagnostically relevant regions of interest. However, when a comprehensive, detailed search of a slide has to be made, increased resolution may not offer any additional benefit.

Does preference influence performance when reading different sizes of cranial computed tomography?

Radiology practice is based on the implicit assumption that the preference for a particular presentation mode goes hand in hand with superior performance. The present experiment tests this assumption in what pertains to image size. Forty-three radiologists were asked to identify intracranial hemorrhages on 20 cranial computed tomography scans in two image sizes, [Formula: see text] and [Formula: see text]. They were asked to indicate which size they preferred and subsequently rated each size on a continuous scale in terms of how much they liked them. The results show no correlation between the jackknife free-response receiver operating characteristic figure of merit and preference rated on a continuous scale (large image: [Formula: see text], [Formula: see text]; small images: [Formula: see text], [Formula: see text]). Similarly, there was no significant correlation between the time a radiologist took to read a case and preference rated on the continuous scale (large image: [Formula: see text], [Formula: see text]; small images: [Formula: see text], [Formula: see text]). When dividing radiologists into two groups according to their size preference, there was no significant difference in performance between groups with regard to either large or small images. The results suggest that the preference for an image size and performance with regard to it are not related.

Is the iPad suitable for image display at American Board of Radiology examinations?

OBJECTIVE

The study aimed to determine the acceptability of the iPad 3 as a display option for American Board of Radiology (ABR) examinations.

SUBJECTS AND METHODS

A set of 20 cases for each of nine specialties examined by the ABR was prepared. Each comprised between one and seven images and case information and had been used in previous ABR Initial Certification examinations. Examining radiologists (n = 119) at the ABR oral Initial Certification examinations reviewed sets from one or more specialties on both a 2 MP LED monitor and on the iPad 3 and rated the visibility of the salient image features for each case. The Wilcoxon signed rank test was performed to compare ratings. In addition, a thematic analysis of participants' opinions was undertaken.

RESULTS

When all specialties were pooled, the iPad 3 ratings were significantly higher than the monitor ratings (p = 0.0217). The breast, gastrointestinal, genitourinary, and nuclear medicine specialties also returned significantly higher ratings for the visibility of relevant image features for the iPad 3. Monitor ratings were significantly higher for the vascular and interventional specialty, although no images were rated unacceptably poor on the iPad in this specialty.

CONCLUSION

The relevant image features were rated more visible on the iPad 3 than on the monitors overall. The iPad 3 was well accepted by a large majority of examiners and can be considered adequate for image display for examination in most or all specialties.

Remote CT reading using an ultramobile PC and web-based remote viewing over a wireless network

We developed a new type of mobile teleradiology system using an ultramobile PC (UMPC) for web-based remote viewing over a wireless network. We assessed the diagnostic performance of this system for abdominal CT interpretation. Performance was compared with an emergency department clinical monitor using a DICOM viewer. A total of 100 abdominal CT examinations were presented to four observers. There were 56 examinations showing appendicitis and 44 which were normal. The observers viewed the images using a UMPC display and an LCD monitor and rated each examination on a five-point scale. Receiver operating characteristics (ROC) analysis was used to test for differences. The sensitivity and specificities of all observers were similarly high. The average area under the ROC curve for readings performed on the UMPC and the LCD monitor was 0.959 and 0.976, respectively. There were no significant differences between the two display systems for interpreting abdominal CTs. The web-based mobile teleradiology system appears to be feasible for reading abdominal CTs for diagnosing appendicitis and may be valuable in emergency teleconsultation.

Effect of display magnification on perceived growth of liver lesions on computed tomography

Our goal was to investigate the effect of displayed image magnification on perception of the size of hepatic lesions on abdominal computed tomography (CT) scans. Institutional review board approval and informed observer consent were obtained. Three experienced radiologists reviewed 90 CT image pairs in one session. Each image pair demonstrated a solitary, well-defined hypodense hepatic lesion measuring greater than 1 cm obtained at two points in time. The image pairs were presented three times in random order, once with the left image magnified, once with the right image magnified, and once with neither image magnified. The radiologists were asked to determine on which image the lesion was smaller or if there was no difference. The responses were analyzed statistically. The proportion of correct responses increased significantly as the difference in lesion size increased (p < 0.001). The percent of correct responses was higher when neither CT image was magnified. Magnification of one image decreased the accuracy of the readers' performance, especially at smaller differences, both of which were statistically significant (p < 0.001). Thus, accuracy of detecting lesion size differences was degraded when the images were presented at differing magnification. This should be kept in mind when evaluating serial CT scans for growth or regression of tumors and other lesions.

Diagnostic efficacy of handheld devices for emergency radiologic consultation

OBJECTIVE

Orthopedic injury and intracranial hemorrhage are commonly encountered in emergency radiology, and accurate and timely diagnosis is important. The purpose of this study was to determine whether the diagnostic accuracy of handheld computing devices is comparable to that of monitors that might be used in emergency teleconsultation.

SUBJECTS AND METHODS

Two handheld devices, a Dell Axim personal digital assistant (PDA) and an Apple iPod Touch device, were studied. The diagnostic efficacy of each device was tested against that of secondary-class monitors (primary class being clinical workstation display) for each of two image types-posteroanterior wrist radiographs and slices from CT of the brain-yielding four separate observer performance studies. Participants read a bank of 30 wrist or brain images searching for a specific abnormality (distal radial fracture, fresh intracranial bleed) and rated their confidence in their decisions. A total of 168 readings by examining radiologists of the American Board of Radiology were gathered, and the results were subjected to receiver operating characteristics analysis.

RESULTS

In the PDA brain CT study, the scores of PDA readings were significantly higher than those of monitor readings for all observers (p < or = 0.01) and for radiologists who were not neuroradiology specialists (p < or = 0.05). No statistically significant differences between handheld device and monitor findings were found for the PDA wrist images or in the iPod Touch device studies, although some comparisons approached significance.

CONCLUSION

Handheld devices show promise in the field of emergency teleconsultation for detection of basic orthopedic injuries and intracranial hemorrhage. Further investigation is warranted.