"Number needed to read"--how to facilitate clinical trials in MR-angiography.
OBJECTIVE
To evaluate the effect of the number of readers on the statistical results in peripheral MRA.


METHODS
40 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.


RESULTS
Image 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.


CONCLUSIONS
Increasing 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.
Institute of Clinical Radiology and Nuclear Medicine, University Medical Center Mannheim, Medical Faculty Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany.
M
M
Voth
U I
UI
Attenberger
A
A
Luckscheiter
S
S
Haneder
T
T
Henzler
S O
SO
Schoenberg
C
C
Schwenke
H J
HJ
Michaely
D000368:Aged; D002986:Clinical Trials as Topic; D003287:Contrast Media / Q000494:pharmacology; D004867:Equipment Design; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008536:Meglumine / Q000494:pharmacology; D008875:Middle Aged; D009942:Organometallic Compounds / Q000494:pharmacology; D016491:Peripheral Vascular Diseases / Q000473:pathology*; D012107:Research Design; D012189:Retrospective Studies
D003287:Contrast Media; D009942:Organometallic Compounds; C090600:gadobutrol; D008536:Meglumine; C072417:gadoterate meglumine