Our goal was to ascertain how fatigue affects performance in reading computed tomography (CT) examinations of patients with multiple injuries. CT images with multiple fractures from a previous study of satisfaction of search (SOS) were read by radiologists after a day of clinical work. Performance in this study with fatigued readers was compared to a previous study in which readers were not fatigued. Detection accuracy for obvious injuries was not affected by fatigue, but accuracy for subtle fractures was reduced (P=0.016). An SOS effect on decision thresholds was evident mirroring recent studies. Without fatigue, readers spent more time interpreting and reporting findings as the number of the injuries increased. When fatigued, readers did not increase reading time as fracture number increased. Without fractures, reading time for not-fatigued and fatigued readers was the same (P=0.493) but was significant (P=0.016) with an added subtle fracture. The difference increased with a major injury (P=0.003) and increased further with both a major injury and subtle fracture (P=0.0007). Fatigue and multiple abnormalities have independent effects on detection performance but do interact in determining search time.
Previous studies have demonstrated that fatigue impacts diagnostic accuracy, especially for those in training. We continued this line of investigation to determine if fatigue has any impact on a common source of errors – satisfaction of search (SOS). SOS requires subjects to participate in 2 sessions (SOS and non-SOS) and so does fatigue (fatigued and not fatigued) so we ran subjets in only the fatigued condition and used a previous non-fatigued study as the comparison. We used 64 chest computed radiographs half demonstrating various ‘‘test’’ abnormalities were read twice by 20 radiologists, once with and once without the addition of a simulated pulmonary nodule. Receiver-operating characteristic detection accuracy and decision thresholds were analyzed to study the effects of adding the nodule on detecting the test abnormalities. Adding nodules did not influence detection accuracy (ROC AUC SOS = 0.667; non-SOS = 0.679), but did induce a reluctance to report them. Adding nodules did not affect inspection time so the reluctance to report was not associated with reduced search. Fatigue did not appear to exacerbate the SOS effect. A second study with fractures revealed the same shift in performance but did reduce viewing times when fatigued. The results of these two studies suggest that the impact of fatigue on SOS is more complicated than expected and thus may require more investigation to fully understand its impact in the clinic.
Satisfaction of search (SOS) occurs when an abnormality is missed because another abnormality has been detected
in radiology examinations. This research includes our study of whether the severity of a detected fracture determines
whether subsequent fractures are overlooked. Each of 70 simulated multitrauma patients presented radiographs of three anatomic areas. Readers evaluated each patient under two experimental conditions: when the images of the first anatomic
area included a severe fracture (the SOS condition), and when it did not (the control condition). The SOS effect was
measured on detection accuracy for subtle test fractures presented on examinations of the second or third anatomic areas.
SOS reduction in ROC area for detecting subtle test fractures with the addition of a major fracture to the first radiograph
was not observed. The same absence of SOS that had been observed when high-morbidity added fractures were
presented on CT was replicated with the high-morbidity added fractures presented on radiographs. This finding rules out
the possibility that there was no SOS in the prior study with CT because SOS effects do not extend from one imaging
modality to another. Taken together, the evidence rejects the hypothesis that the severity of a detected fracture determines the SOS for subsequently viewed fractures.
Collecting clinical cases for medical imaging perception studies is often challenging. We have developed a suite of
software tools for manipulating medical tomographic image sets that overcome these difficulties. In our initial
development, abnormalities were removed or inserted on a slice-by-slice basis. To circumvent the problem with potential
artifacts in orthogonal views, we have redesigned the tools so that they operate in 3 dimensions. An operator controlled
ellipsoid mask region is used to select the removal and the replacement areas. This new approach has been validated on
PET data sets and has also been implemented for CT studies.
The ability to insert abnormalities in clinical tomographic images makes image perception studies with medical images
practical. We describe a new insertion technique and its experimental validation that uses complementary image masks
to select an abnormality from a library and place it at a desired location. The method was validated using a 4-alternative
forced-choice experiment. For each case, four quadrants were simultaneously displayed consisting of 5 consecutive
frames of a chest CT with a pulmonary nodule. One quadrant was unaltered, while the other 3 had the nodule from the
unaltered quadrant artificially inserted. 26 different sets were generated and repeated with order scrambling for a total of
52 cases. The cases were viewed by radiology staff and residents who ranked each quadrant by realistic appearance. On
average, the observers were able to correctly identify the unaltered quadrant in 42% of cases, and identify the unaltered
quadrant both times it appeared in 25% of cases. Consensus, defined by a majority of readers, correctly identified the
unaltered quadrant in only 29% of 52 cases. For repeats, the consensus observer successfully identified the unaltered
quadrant only once. We conclude that the insertion method can be used to reliably place abnormalities in perception
We developed image presentation software that mimics the functionality available in the clinic, but also records time-stamped, observer-display interactions and is readily deployable on diverse workstations making it possible to collect comparable observer data at multiple sites. Commercial image presentation software for clinical use has limited application for research on image perception, ergonomics, computer-aids and informatics because it does not collect observer responses, or other information on observer-display interactions, in real time. It is also very difficult to collect observer data from multiple institutions unless the same commercial software is available at different sites. Our software not only records observer reports of abnormalities and their locations, but also inspection time until report, inspection time for each computed radiograph and for each slice of tomographic studies, window/level, and magnification settings used by the observer. The software is a modified version of the open source ImageJ software available from the National Institutes of Health. Our software involves changes to the base code and extensive new plugin code. Our free software is currently capable of displaying computed tomography and computed radiography images. The software is packaged as Java class files and can be used on Windows, Linux, or Mac systems. By deploying our software together with experiment-specific script files that administer experimental procedures and image file handling, multi-institutional studies can be conducted that increase reader and/or case sample sizes or add experimental conditions.
Image perception studies of medical images provide important information about how radiologists interpret images and insights for reducing reading errors. In the past, perception studies have been difficult to perform using clinical imaging studies because of the problems associated with obtaining images demonstrating proven abnormalities and appropriate normal control images. We developed and evaluated interactive software that allows the seamless removal of abnormal areas from CT lung image sets. We have also developed interactive software for capturing lung lesions in a database where they can be added to lung CT studies. The efficacy of the software to remove abnormal areas of lung CT studies was evaluated psychophysically by having radiologists select the one altered image from a display of four. The software for adding lesions was evaluated by having radiologists classify displayed CT slices with lesions as real or artificial scaled to 3 levels of confidence. The results of these experiments demonstrated that the radiologist had difficulty in distinguishing the raw clinical images from those that had been altered. We conclude that this software can be used to create experimental normal control and "proven" lesion data sets for volumetric CT of the lung fields. We also note that this software can be easily adapted to work with other tissue besides lung and that it can be adapted to other digital imaging modalities.
Clinical signs of radiotherapy failure are often not present until well after treatment has been completed. Methods which could predict the response of tumors either before or early into the radiotherapy schedule would have important implications for patient management. Recent studies performed at our institution suggest that MR perfusion imaging maya be useful in distinguishing between individuals who are likely to benefit from radiation therapy and those who are not. Because MR perfusion imaging reflects tissue vascularity as well as perfusion, quantitative positron emission tomographic (PET) blood flow studies were performed to obtain an independent assessment of tumor perfusion. MR perfusion and PET quantitative blood flow studies were acquired on four women diagnosed with advanced cervical cancer. The MR perfusion studies were acquired on a 1 cm sagittal slice through the epicenter of the tumor mass. Quantitative PET blood flow studies were performed using an autoradiographic technique. The PET and MRI were registered using a manual interactive routine and the mean blood flow in the tumor was compared to the relative signal intensity in a corresponding region on the MR image. The mean blood flow in the cervical tumors ranged form 30-48 ml/min/100 grams. The observed blood flow values are consistent with the assumed relationship between MR contrast enhancement and the distribution of tissue perfusion. The information offered by these studies provides an additional window into the evaluation of the response of cervical tumors to radiation therapy.