1K versus 2K monitor: a clinical alternative free-response receiver operating characteristic study of observer performance using pulmonary nodules

Consistency of response and image recognition, pulmonary nodules

OBJECTIVE

To investigate the effect of recognition of a previously encountered radiograph on consistency of response in localized pulmonary nodules.

METHODS

13 radiologists interpreted 40 radiographs each to locate pulmonary nodules. A few days later, they again interpreted 40 radiographs. Half of the images in the second set were new. We asked the radiologists whether each image had been in the first set. We used Fisher's exact test and Kruskal-Wallis test to evaluate the correlation between recognition of an image and consistency in its interpretation. We evaluated the data using all possible recognition levels-definitely, probably or possibly included vs definitely, probably or possibly not included by collapsing the recognition levels into two and by eliminating the "possibly included" and "possibly not included" scores.

RESULTS

With all but one of six methods of looking at the data, there was no significant correlation between consistency in interpretation and recognition of the image. When the possibly included and possibly not included scores were eliminated, there was a borderline statistical significance (p = 0.04) with slightly greater consistency in interpretation of recognized than that of non-recognized images.

CONCLUSION

We found no convincing evidence that radiologists' recognition of images in an observer performance study affects their interpretation on a second encounter.

ADVANCES IN KNOWLEDGE

Conscious recognition of chest radiographs did not result in a greater degree of consistency in the tested interpretation than that in the interpretation of images that were not recognized.

Memory for previously viewed radiographs and the effect of prior knowledge of memory task

RATIONALE AND OBJECTIVES

To investigate the effect of being forewarned that they would be asked to identify repeated images on radiologists' recognition of previously interpreted versus new chest radiographs.

MATERIALS AND METHODS

Thirteen radiologists viewed 60 posterior-anterior chest radiographs, 31 with and 29 without nodules, in two sets of 40 images each. Eight radiologists were forewarned and five radiologists were not forewarned of the memory task. Twenty images in each of the two sets were unique to each set and 20 images occurred in both sets. The readers indicated the presence or absence of any nodules during both readings, and in the second reading session they also indicated whether they thought each image had also occurred in the first reading.

RESULTS

There was no significant difference in recognition memory performance between forewarned and not-forewarned readers. Overall accuracy in distinguishing previously-viewed from new images was 60.7%.

CONCLUSIONS

Being forewarned of the memory task did not improve recognition memory.

Effect of greyscale liquid crystal displays of different resolutions on observer performance during detection of small solitary pulmonary nodules

OBJECTIVE

The aim of this study was to evaluate the effect of monochrome liquid crystal displays (LCDs) with different resolutions on observer performance during detection of small solitary pulmonary nodules.

METHODS

Chest images of digital radiography were selected online from the hospital's picture archiving and communication system. Of the 164 images selected, small solitary non-calcified pulmonary nodules were present in 63 images and absent in 101 images. Observer performance was assessed among 3 extremely experienced, 3 very experienced and 3 moderately experienced radiologists, who independently interpreted these images on 2, 3 and 5 megapixel greyscale LCDs. A five-point confidence level rating scale was used to represent the presence of nodules: definite absence, probable absence, indetermination, probable presence and definite presence. The observers were requested to rank each image on the given display according to the presence of the pulmonary nodule. Observer performance was analysed in terms of receiver operating characteristics (ROCs).

RESULTS

The areas under the ROC curves which represented the observer performance for the 2, 3 and 5 megapixel LCDs were found to be 0.705, 0.722 and 0.764, respectively, for the extremely experienced radiologists; 0.687, 0.712 and 0.721, respectively, for the very experienced radiologists; and 0.689, 0.696 and 0.711, respectively, for the moderately experienced radiologists. These differences were not statistically significant.

CONCLUSION

The observer performances for detection of small solitary non-calcified pulmonary nodules by radiologists with varying degrees of experience were comparable between the 2, 3 and 5 megapixel monochrome LCDs.

Influence of liquid crystal displays (LCDs) with different resolutions on the detection of pulmonary nodules: an observer performance study

PURPOSE

To evaluate the influence of monochrome LCDs with different resolutions on the detection performance of pulmonary nodules.

MATERIALS AND METHODS

187 chest DR images were selected from our hospital's picture archiving and communication system (PACS), including 111 normal cases and 76 cases with solitary pulmonary nodules. Those positive images were divided into two groups, A and B, according to the diameter of nodules. Three high-, three mid-, and three low-experienced radiologists interpreted those images with a 2 megapixel (MP), a 3 MP and a 5 MP monochrome LCD independently. Regarding the presence of the nodule, five-point confidence level rating scale was used: definite absence, probable absence, indetermination, probable presence and definite presence. The observers were requested to rank each image on the given display according to the presence of pulmonary nodule. Receiver operation characteristic (ROC) analysis was used to interpret the data.

RESULTS

When detecting the pulmonary nodules of Group A on 2 MP-, 3 MP- and 5 MP-LCD, the areas under ROC curves (AUCs) were 0.641, 0.683 and 0.732 for high-experienced radiologists, 0.633, 0.679 and 0.716 for mid-experienced radiologists, 0.620, 0.652 and 0.719 for low-experienced radiologists, respectively; when detecting the pulmonary nodules of Group B, the AUCs were 0.811, 0.830 and 0.842 for high-experienced radiologists, 0.771, 0.821 and 0.837 for mid-experienced radiologists, 0.759, 0.770 and 0.829 for low-experienced radiologists, respectively. However, there were no significant differences among different reading modalities.

CONCLUSION

For detecting pulmonary nodules, it is equivalent of observer performance among 2 MP-, 3 MP- and 5 MP-LCD.

A comparative contrast perception phantom image of brain CT study between high-grade and low-grade liquid crystal displays (LCDs) in electronic medical charts

The purpose of this study was to clarify whether non-medical-grade liquid crystal displays (LCDs) are acceptable for the soft-copy reading of brain CTs. Four kinds of color LCDs with different image quality levels were used: medical-grade LCD, low-grade general LCD calibrated with the grayscale display function (GSDF), low-grade general LCD calibrated with gamma 2.2 and a notebook personal computer display panel. In Osirix's standard window setting for brain CTs, the average CT values of brain parenchyma in 100 cases were correlated with a grayscale level ranging from 71 to 91 in a 256-step grayscale. At these gray levels, the image contrast on the two low-grade LCDs calibrated with gamma 2.2 was higher than that on the medical-grade LCD. Eleven healthy volunteers participated in the contrast perception study, which used electronically generated target phantom images that simulated subtle abnormalities with a low or high attenuation difference in brain parenchyma. The three low-grade LCDs showed correct response rates and reaction times that were superior to those of the medical-grade display. The grayscale calibrations, GSDF or gamma 2.2, are likely to be more critical than the display grade, suggesting that the use of a low-grade LCD may be acceptable in the image contrast of brain CT.

Should 3K zoom function be used for detection of pneumothorax in cesium iodide/amorphous silicon flat-panel detector radiographs presented on 1K-matrix soft copies?

The purpose of the study was to evaluate observer performance in the detection of pneumothorax with cesium iodide and amorphous silicon flat-panel detector radiography (CsI/a-Si FDR) presented as 1K and 3K soft-copy images. Forty patients with and 40 patients without pneumothorax diagnosed on previous and subsequent digital storage phosphor radiography (SPR, gold standard) had follow-up chest radiographs with CsI/a-Si FDR. Four observers confirmed or excluded the diagnosis of pneumothorax according to a five-point scale first on the 1K soft-copy image and then with help of 3K zoom function (1K monitor). Receiver operating characteristic (ROC) analysis was performed for each modality (1K and 3K). The area under the curve (AUC) values for each observer were 0.7815, 0.7779, 0.7946 and 0.7066 with 1K-matrix soft copies and 0.8123, 0.7997, 0.8078 and 0.7522 with 3K zoom. Overall detection of pneumothorax was better with 3K zoom. Differences between the two display methods were not statistically significant in 3 of 4 observers (p-values between 0.13 and 0.44; observer 4: p = 0.02). The detection of pneumothorax with 3K zoom is better than with 1K soft copy but not at a statistically significant level. Differences between both display methods may be subtle. Still, our results indicate that 3K zoom should be employed in clinical practice.

Pulmonary nodule detection with digital projection radiography: an ex-vivo study on increased latitude post-processing

To evaluate increased image latitude post-processing of digital projection radiograms for the detection of pulmonary nodules. 20 porcine lungs were inflated inside a chest phantom, prepared with 280 solid nodules of 4-8 mm in diameter and examined with direct radiography (3.0x2.5 k detector, 125 kVp, 4 mAs). Nodule position and size were documented by CT controls and dissection. Four intact lungs served as negative controls. Image post-processing included standard tone scales and increased latitude with detail contrast enhancement (log-factors 1.0, 1.5 and 2.0). 1280 sub-images (512x512 pixel) were centred on nodules or controls, behind the diaphragm and over free parenchyma, randomized and presented to six readers. Confidence in the decision was recorded with a scale of 0-100%. Sensitivity and specificity for nodules behind the diaphragm were 0.87/0.97 at standard tone scale and 0.92/0.92 with increased latitude (log factor 2.0). The fraction of "not diagnostic" readings was reduced (from 208/1920 to 52/1920). As an indicator of increased detection confidence, the median of the ratings behind the diaphragm approached 100 and 0, respectively, and the inter-quartile width decreased (controls: p<0.001, nodules: p=0.239) at higher image latitude. Above the diaphragm, accuracy and detection confidence remained unchanged. Here, the sensitivity for nodules was 0.94 with a specificity from 0.96 to 0.97 (all p>0.05). Increased latitude post-processing has minimal effects on the overall accuracy, but improves the detection confidence for sub-centimeter nodules in the posterior recesses of the lung.

Flat-panel display (LCD) versus high-resolution gray-scale display (CRT) for chest radiography: an observer preference study

OBJECTIVE

Our objective was to compare cathode ray tube (CRT) display with liquid crystal display (LCD) for soft-copy viewing of chest radiographs in a clinical setting.

MATERIALS AND METHODS

We displayed 80 posteroanterior digital chest radiographs side by side on a 5-megapixel CRT display and a 3-megapixel LCD. Gradation characteristics of both monitors were adjusted to DICOM display standards. Using a 4-point scale, seven radiologists ranked overall image quality and visibility of anatomic landmarks. Data analysis included Wilcoxon's rank sum test to assess the significance of preference for the different display modes and calculation of the percentage of images ranked equally by at least five of the seven radiologists.

RESULTS

Wilcoxon's rank sum test found significant preferences (p < 0.001) for the CRT display for visualization of structures in low-attenuation areas of the thorax and for the LCD for visualization of structures in high-attenuation areas of the thorax. Overall image quality was ranked equal by at least five radiologists in 70% of cases, whereas for the remaining images a significant preference was found for the CRT display.

CONCLUSION

We conclude that, under subdued ambient lighting conditions and without use of windowing, for most images the overall quality is equal with high-resolution CRT display and LCD. In images judged preferentially, we found a significant superiority for LCD for delineating mediastinal structures and for CRT display for delineating structures in the lung.

Soft-Copy Reading of Digital Chest Radiographs

OBJECTIVE

We sought to evaluate whether soft-copy reading of simulated pulmonary chest lesions is influenced by ambient light and automatic optimization of cathode ray tube (CRT) monitor luminance.

MATERIALS AND METHODS

Four types of simulated lesions (nodules, lines, micronodules, and patchy opacities) were superimposed over an anthropomorphic chest phantom. Lesion detection with soft-copy reading was assessed using a high-contrast grayscale 2K CRT monitor under the following conditions: (1) subdued lighting (<50 lux); (2) normal lighting conditions (450 lux) without, and (3) with a sensitivity modulation to automatically adjust the CRT luminance to the increased amount of ambient light. Reading data were analyzed according to receiver operating curve. Significance of differences was tested using an analysis of variance for repeated measures.

RESULTS

Ambient room light of 450 lux did not significantly influence the detection of nodules and patchy opacities. However, bright ambient light significantly decreased detection of micronodules (0.60 vs. 0.74) and lines (0.52 vs. 0.66) relative to subdued lighting conditions. Automatic luminance adjustment could compensate the effect of ambient light for the micronodules (0.77) but not for the lines (0.53).

CONCLUSION

Bright ambient light significantly decreases detection of small low-contrast structures. This may be partially but not completely compensated by an automatic luminance adaptation.