The demystification of magnetic resonance imaging?

The interobserver variability in test interpretation is a key parameter to evaluate the diagnostic reliability of a diagnostic examination. It has been evaluated for most clinically relevant cardiac imaging modalities. In many instances the results have been rather sobering. A considerable variability in the visual assessment of coronary artery stenosis severity has been shown between different readers of coronary angiograms. A high reader disagreement has been shown for interpretation of dobutamine stress echocardiograms. The high variability in the interpretation of dobutamine stress echocardiograms has become a matter of debate and has been used as an argument to doubt the diagnostic competence of the method. Low image quality, a large variability in test performance, and insufficient standardization in image interpretation without any objective parameter to define the test result has been referred to as the major limitations of stress echocardiography. Lower observer variability due to more standardized image acquisition, better image quality, and objective parameters of test interpretation has been shown for perfusion scintigraphy and has been used as an argument for its favourable diagnostic performance. Regarding stress echocardiography, multiple shortcomings could be reduced over time. Image quality could be improved. Along with digital image acquisition and more standardized interpretation criteria refinements in the stress echocardiographic techniques have resulted in higher interobserver agreement. Still, interobserver agreement remained far from optimal. Dobutamine stress cardiovascular magnetic resonance imaging (DSMR) incorporates multiple advantages when compared with stress echocardiography. It is performed using standardized acquisition protocols. The acquired imaging views as well as quality of images is less dependent on the individual sonographers performance and the image quality is excellent in most cases. Thus, interobserver agreement is expected to be high considering the most obvious limitations of dobutamine stress echocardiography. However, data on interobserver agreement in the interpretation of DSMR were sparse until recently. In this issue of the Journal, Paesch et al. report on the interobserver variability in the interpretation of DSMR evaluated in a multicenter setting. The study confirms an excellent image quality in the majority of imaging views with the use of DSMR as reported earlier by the investigators as well as other authors. The study confirms also a high diagnostic accuracy for detection of coronary artery disease for all four readers using this technique. However, while the accuracy was almost similar among the four readers, sensitivity for detection of CAD ranged from as low as 71% to as high as 86%, and the specificity had a discordant trend indicating already that readers vary in their interpretation of image data. The surprise of this study is the relatively low interobserver agreement between the four expert observers from different institutions. The disagreement between the four readers was equally distributed and not the effect of one reader with significant deviations from the other readers. How do we explain this result? Excellent images were thought to ensure high diagnostic accuracy but also to facilitate consistent interpretation because of a high confidence in the perception and interpretation of images. Impaired echocardiographic image quality has been a major cause of lower diagnostic accuracy when comparing dobutamine stress echocardiography with dobutamine stress MRI. Poor imaging conditions with resulting insecurity on the interpretation of images have also been shown to be a major cause of disagreement when analysing stress echocardiograms. The rather disappointing level of interobserver agreement confirms other recently published studies which have also indicated that use of MRI is no warranty to reach nearly perfect agreement between different readers on analysis of regional left ventricular function. The interobserver agreement was on a level previously reported for dobutamine echocardiography applied with most advanced echocardiographic techniques. Given these results it appears that reader agreement may be method and imagequality dependent on a low level of agreement. However, once a relatively high image quality is reached this aspect looses importance and other aspects come into play. Thus, we do not reach almost perfect reader agreement based on excellent image quality alone. The difficulty of divergent test results relates to a different issue, involving in particular, the final pathway of image interpretation, which remains a subjective process based on the individual perception. Analysis of regional systolic