Number needed to read-—How to facilitate clinical trials in MR-angiographyReport as inadecuate

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European Radiology

, Volume 21, Issue 5, pp 1034–1042

First Online: 23 October 2010Received: 11 July 2010Revised: 30 August 2010Accepted: 29 September 2010


PurposeTo evaluate the effect of the number of readers on the statistical results in peripheral MRA.

Materials and methods40 patients with peripheral arterial occlusive disease were included as a sample dataset in this study, randomly separated into two matched groups with n = 20 patients group 1—gadobutrol, group 2—gadoterate meglumine who underwent a continuous table movement MRA of the peripheral vessels at 3 T. Image quality IQ of 17 vessel segments was evaluated by 5 independent readers. The effect of the number of readers on significance and statistical power was statistically analyzed.

ResultsImage quality in group 1 gadobutrol ranks significantly higher compared to group 2 gadoterade meglumine with a diagnostic IQ in 97% vs. 78% p < 0.0001. For the diagnostic-non-diagnostic IQ assessment significance was reached with one reader 1-5 times 20%, with two readers in 4-10 40%, with three readers in 6-10 60%, with four readers in 4-5 80%, with five readers in 1-1 100%. Power considerations showed considerable gain when increasing the number of readers.

ConclusionIncreasing the number of readers in a diagnostic MRA-study can be used to achieve a higher power or to decrease the number of subjects included with maintained statistical validity.

KeywordsMRA Comparison study Power analysis Vessel segments Statistical significance  Download fulltext PDF

Author: M. Voth - U. I. Attenberger - A. Luckscheiter - S. Haneder - T. Henzler - S. O. Schoenberg - C. Schwenke - H. J. Michae


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