MRA versus digital subtraction angiography in acute subarachnoid haemorrhage:: a blinded multireader study of prospectively recruited patients

We performed a blinded multireader study comparing MR angiography (MRA) with digital subtraction angiography (DSA) in 34 prospectively recruited patients who presented with acute subarachnoid haemorrhage (SAH). Two observers independently reviewed the MRA and DSA studies some months after clinical presentation. Presence of an aneurysm was rated on a LC-point confidence scale. Cases in which the initial interpretation of the observers varied were jointly reviewed to reach a consensus opinion. DSA was deliberately chosen not to represent the reference standard and the clinical course and surgical findings were used to explain significant differences between the consensus readings of MRA and DSA. Diagnostic confidence and interobserver agreement were, overall, higher on DSA than on MRA studies (kappa(DSA)= 0.64 versus kappa(MRA)= 0.52 with 95 % CI for Delta = kappa(DSA)-kappa(MRA) [-0.06, 0.31]). With both methods, discrepancies between observers were due to aneurysms overlooked rather than false-positive readings by one observer. Diagnostic accuracy therefore improved when the readings of the two observers were combined, particularly for MRA. Intermethod agreement was only fair and similar for both readers (kappa (reader 1) = 0.37 versus kappa (reader 2) = 0.32 with 95 % CI for Delta = kappa (reader) (-kappa)(1) (reader 2) [-0.02, 0.11]). Both interobserver and intermethod agreements improved when the data were analysed on a per-study (positive or negative study) rather than on a per-aneurysm basis. Differences in the consensus reading were due to five aneurysms (four single and one multiple) detected only with MRA and five (two single and three multiple) detected only with DSA. MRA and DSA should be regarded as complementary in the investigation of patients with acute SAH. DSA can no longer be regarded as the reference standard.