"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.
Voth
M
M
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.
Attenberger
U I
UI
Luckscheiter
A
A
Haneder
S
S
Henzler
T
T
Schoenberg
S O
SO
Schwenke
C
C
Michaely
H J
HJ
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