Purpose: Rapid imaging is an important requirement for the evaluation of stroke patients, particularly if patients are agitated. The recent availability of multi-channel phased array brain coils and the development of parallel imaging techniques such as SENSE allow an integrated MR stroke imaging protocol to be completed in approximately three minutes. The objective of this study was to evaluate whether the three-minute protocol (TMP) provided images of sufficient diagnostic quality compared to our conventional MR stroke protocol.
Methods and Materials: Twenty-four patients (15 female, age range 48-90 years) referred with a clinical diagnosis of probable acute MCA stroke were prospectively imaged using the TMP and our conventional protocol (duration of approximately 15 minutes) using an 8-channel phased-array brain coil on a 1.5T system (Signa Infinity, GE Medical Systems, Milwaukee WI). Both examinations included a sagittal T1, axial T2, axial DWI, axial FLAIR and an axial 3D time-of-flight MRA. In the three-minute protocol all images are acquired using a SENSE factor of 2, together with a slight reduction in spatial resolution. The TMP images and conventional images were evaluated for image quality and diagnostic yield.
Results: Eighteen patients had an acute MCA stroke, three patients had a posterior fossa stroke, one patient had a left basal ganglia hemorrhage and two patients had negative MR with a final diagnosis of a transient ischemic attack. The DWI was positive using both protocols (sensitivity and specificity 100% respectively). Conventional MRA demonstrated occlusion or reduced MCA flow in 7 cases; the TMP MRA was positive in 6 cases, missing a case of subtle vascular narrowing (sensitivity 86%, specificity 94%, Fishers exact p=0.0001). Two TMP MRAs were of better quality than the conventional MRA, a reflection of the faster imaging sequence. The basal ganglia lesion was correctly identified as a haemorrhage by the TMP protocol.
Conclusion: It is possible to undertake an integrated MR examination of acute stroke patients in three minutes. Including a perfusion sequence will add a further 90 seconds to this protocol; this duration being limited by physiological factors rather than technological advances. Ultra fast imaging has the potential to become a useful triage tool prior to the administration of thrombolytic therapy. It may be of particular benefit in patients unable to tolerate longer sequences.