Observer variability of absolute and relative thrombus density measurements in patients with acute ischemic stroke.
BACKGROUND
Thrombus density may be a predictor for acute ischemic stroke treatment success. However, only limited data on observer variability for thrombus density measurements exist. This study assesses the variability and bias of four common thrombus density measurement methods by expert and non-expert observers.


METHODS
For 132 consecutive patients with acute ischemic stroke, three experts and two trained observers determined thrombus density by placing three standardized regions of interest (ROIs) in the thrombus and corresponding contralateral arterial segment. Subsequently, absolute and relative thrombus densities were determined using either one or three ROIs. Intraclass correlation coefficient (ICC) was determined, and Bland-Altman analysis was performed to evaluate interobserver and intermethod agreement. Accuracy of the trained observer was evaluated with a reference expert observer using the same statistical analysis.


RESULTS
The highest interobserver agreement was obtained for absolute thrombus measurements using three ROIs (ICCs ranging from 0.54 to 0.91). In general, interobserver agreement was lower for relative measurements, and for using one instead of three ROIs. Interobserver agreement of trained non-experts and experts was similar. Accuracy of the trained observer measurements was comparable to the expert interobserver agreement and was better for absolute measurements and with three ROIs. The agreement between the one ROI and three ROI methods was good.


CONCLUSIONS
Absolute thrombus density measurement has superior interobserver agreement compared to relative density measurement. Interobserver variation is smaller when multiple ROIs are used. Trained non-expert observers can accurately and reproducibly assess absolute thrombus densities using three ROIs.
Department of Radiology, Erasmus MC - University Medical Center Rotterdam, P.O. Box 2040, 3000 CA, Rotterdam, The Netherlands. e.santos@erasmusmc.nl.|Department of Radiology, AMC, Amsterdam, The Netherlands. e.santos@erasmusmc.nl.
Emilie M M
EM
Santos
Texas Stroke Institute, Plano, TX, USA.
Albert J
AJ
Yoo
Department of Radiology, AMC, Amsterdam, The Netherlands.
Ludo F
LF
Beenen
Department of Radiology, AMC, Amsterdam, The Netherlands.|Department of Neurology, Erasmus MC, Rotterdam, The Netherlands.
Olvert A
OA
Berkhemer
Department of Biomedical Engineering and Physics, AMC, Amsterdam, The Netherlands.
Mark D
MD
den Blanken
Department of Biomedical Engineering and Physics, AMC, Amsterdam, The Netherlands.
Carrie
C
Wismans
Department of Radiology, Erasmus MC - University Medical Center Rotterdam, P.O. Box 2040, 3000 CA, Rotterdam, The Netherlands.|Faculty of Applied Sciences, Delft University of Technology, Delft, The Netherlands.
Wiro J
WJ
Niessen
Department of Radiology, AMC, Amsterdam, The Netherlands.
Charles B
CB
Majoie
Department of Radiology, AMC, Amsterdam, The Netherlands.|Department of Biomedical Engineering and Physics, AMC, Amsterdam, The Netherlands.
Henk A
HA
Marquering
D015502:Absorptiometry, Photon / Q000379:methods*; D000208:Acute Disease; D000368:Aged; D000465:Algorithms; D002533:Cerebral Angiography / Q000379:methods*; D000072226:Computed Tomography Angiography / Q000379:methods; D005260:Female; D006801:Humans; D020767:Intracranial Thrombosis / Q000000981:diagnostic imaging*; D008297:Male; D009426:Netherlands; D015588:Observer Variation; D011856:Radiographic Image Enhancement / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D020521:Stroke / Q000000981:diagnostic imaging*; D013927:Thrombosis / Q000000981:diagnostic imaging*
Brain ischemia; Computed tomography; Observer agreements; Thromboembolism; X-ray