Feeling a little tired from your long image reading session? You're not the only one. But you may be able to reduce fatigue by wearing contact lenses instead of glasses, brightening up the reading room, and viewing images on the right type of LCD monitor, Japanese researchers have concluded.
In a study that evaluated the visual and central nervous system (CNS) fatigue of radiologists after reading sessions, a group from Kyushu University determined that a number of factors contribute to fatigue during soft-copy reading. While many fatigue-inducing factors are out of the control of radiologists, some aren't.
"Our findings suggest that it is necessary for male radiologists to increase the ambient illuminance in a reading room, use an appropriate type of LCD, and improve corrected visual acuity with contact lenses rather than eyeglasses to effectively decrease fatigue in clinical practice," wrote a team led by Yoichiro Ikushima in an article published in the November issue of Academic Radiology (Vol. 20:11, pp. 1448-1456). "Optimizing the slice thickness or scan range without decreasing the diagnostic performance could also be helpful for relieving fatigue."
Reading-induced fatigue
Thanks to ever-increasing demands to read more images in less time, radiologists are increasingly reporting reading-induced fatigue. The researchers sought to analyze the dominant factors causing fatigue to identify effective countermeasures.
They recruited 17 university hospital radiologists, all men with an average age of 39.5. The participants had an average 13.5 years of experience reading images and an average corrected visual acuity of 1.10 ± 0.3 (range, 0.32-1.60). Ten wore glasses, while three wore contact lenses and four had no corrective lenses during image reading.
The radiologists all selected four periods from September 2011 to December 2011 for the reading test sessions, which involved two sessions before noon and two sessions after noon on four different days. The neurologic, thoracic, and abdominal radiologists interpreted plain radiographs, CT, and MRI studies, while the nuclear medicine radiologists read FDG-PET/CT, SPECT/CT, and scintigraphy exams.
Data were excluded from the study if the radiologist was interrupted over a period longer than 10 minutes. Overall, the reading time for a single test session ranged from 1.42 hours to 5 hours, with a mean of 2.99 hours.
All images were transferred from the imaging server with a Synapse PACS workstation (Fujifilm Medical Systems) and read on one of two medical LCD monitors using the Rapideye image viewer software (Toshiba Medical Systems).
One of the displays was a 2-megapixel (MP) color LCD with a nominal maximum luminance of 200 cd/m2, while the second was a 3-MP monochrome LCD with a nominal maximum luminance of 450 cd/m2. While most participants performed the test sessions using the same LCD, some used a different LCD if the first one was being used by another radiologist. A calibrated photometer (ANA-F9 Lux Meter, Tokyo Photo-Electric) was employed to measure the illuminance of the room.
The researchers assessed fatigue in the central nervous system via a critical fusion frequency test and evaluated subjective visual fatigue via a Simulator Sickness Questionnaire administered to the radiologists before and after their soft-copy reading sessions.
As other studies in the literature have found, reading induced both visual fatigue and fatigue in the central nervous system, according to the researchers. Statistically significant differences were seen in both the critical fusion frequency test values and questionnaire scores before and after the reading sessions.
CNS fatigue
Using multiple linear regression analysis, the researchers determined that fatigue in the central nervous system was affected by 10 dominant numerical factors: average number of images/series/case, average number of series/case, average number of images/case, corrected visual acuity, average time to interpret a case, average number of images/series, years of experience in reading, age of radiologist, reading time, and ambient luminance. There were also two dominant categorical factors: subspecialty of reading and type of LCD.
Of the 12 factors, three -- corrected visual acuity, ambient luminance, and type of LCD -- are adjustable, the researchers noted.
"The findings related to the adjustable factors showed that fatigue in the CNS could be relieved by increasing the corrected visual acuity, brightening the reading room, and using a 2-MP color LCD with an [nominal maximum luminance] of 200 cd/m2 rather than a 3-MP monochrome LCD with a [nominal maximum luminance] of 450 cd/m2."
The researchers said they couldn't determine which specific characteristics (i.e., color versus monochrome, resolution, and maximum luminance) of the LCD affected fatigue since only two LCD types were used in the study.
"Nevertheless, soft-copy reading using an appropriate type of LCD could facilitate a decrease in fatigue," they wrote.
The researchers also observed that the factors with the first-, second-, third-, and sixth-largest effects were related to the amount of reading.
"Fatigue in the CNS increased as the number of images per case decreased," they wrote. "In addition, as the average time taken to interpret a case decreased, fatigue in the CNS increased."
Neuroradiologists had the highest CNS fatigue, followed by those reading thoracic and abdominal studies. This may be due to the differences in imaging modality use, and the specific effect of imaging modalities on reading-induced fatigue should be evaluated in a future study, according to the researchers.
Visual fatigue
There were eight dominant factors associated with visual fatigue, two of which were adjustable factors: vision correction and difference in perceived brightness between an LCD and the surfaces surrounding the LCD.
"In terms of vision correction, the radiologists who wore glasses experienced the greatest amount of visual fatigue, followed by those who wore contact lenses and those who did not require any correction," the authors wrote.
As was the case with CNS fatigue, dominant factors for visual fatigue included the average time taken to interpret a case, the average number of series per case, the average number of images per series, the reading time of the reading test session, and the subspecialty of reading. Also, higher ambient illuminance was associated with lower visual fatigue.
However, visual fatigue increased as the time taken to read a case increased, even though CNS fatigue decreased. This could be due to the low frequency of breaks taken by radiologists, the group noted.
Because the average number of series per case and the number of images per series affected both types of fatigue, reasonable adjustments to slice thickness or scan range could also help lower fatigue without impairing diagnostic performance, according to the researchers.
