Rofo 2005; 177 - A3
DOI: 10.1055/s-2005-931817

Detection of asymptomatic cerebral microbleeds on T2*-weighted gradient-echo MRI: A comparative study at 1.5 and 3 Tesla

C Stehling 1, C Oelschläger 2, S Orwat 3, S Kloska 1, S Kraemer 1, TU Niederstadt 1, I Nassenstein 1, HS Knecht 2, P Kirchhof 3, WL Heindel 1, R Bachmann 1
  • 1Department of Clinical Radiology, University of Muenster
  • 2Department of Neurology, University of Muenster
  • 3Department of Cardiology and Angiology, University of Muenster, Germany

Purpose: Cerebral microbleeds (CMBs) are frequently associated with small vessel disease, intracerebral haemorrhage, hypertension and lacunar stroke. They are mainly located in the deep and subcortical white matter. Gradient echo T2*-weighted MRI (T2*MRI) has a high sensitivity in detecting CMBs, due to its sensitivity to iron-induced susceptibility changes. On these images hemosiderin deposits in the perivascular space appear as small dot-like hypointense lesions. However, the magnitude of iron-induced susceptibility changes increases with the field strength, which should lead to a higher sensitivity for the detection of CMBs at 3.0 T as compared to 1.5 T. To test these hypotheses, we examined individuals with documented CBMs at 1.5 and 3.0 T.

Methods: 352 elderly individuals, who participated in an interdisciplinary study for healthy aging, were examined at a 3.0 T imaging system (Gyroscan Intera, Philips Medical Systems). T2*MRI sequences (TE/TR/FA=572ms/16/ms/18°) were acquired in the axial plane. Individuals positive for CMBs were asked to undergo an additional examination at 1.5 T (TE/TR/FA=663ms/23/ms/18°).

Images were analysed independently for both field strength by two observers. CMBs were defined as focal areas of low signal intensity on T2*MRI of less than 10mm in diameter and were counted throughout the brain. CMBs were qualitatively analyzed comparing the degree of visible hypointensity on a five-point scale from 1 (complete signal loss) to 5 (normal signal) for both field strengths.

Contrast-to-noise ratio (CNR) of CMBs to the surrounding brain tissue were calculated for both field strengths. Statistical significance was determined by Student's-t- and Wilcoxon-Test.

Results: At 3.0 T CMBs were detected in 25 individuals, 16 agreed to an additional examination at 1.5 T. In these 16 individuals a total of 38 CMBs were detected at 3.0T, whereas at 1.5T only 33 CMBs could be identified. The mean CNR of CMBs was significantly increased at 3.0 T as compared to 1.5 T (27.8±8.1 vs. 17.0±8.0; p<0.001). On qualitative analysis visibility of CMBs was ranked significantly higher at 3.0T (1.2±0.4 vs. 2.9±1.1; p<0.001).

Conclusion: Evidence of past microbleeds may be found even in neurologically normal elderly individuals by MRI. Detection rate and visibility of CMBs clearly benefits from the higher field strength. Diagnosis of certain brain disorders might benefit from the increased sensitivity of T2*-weighted sequences to susceptibility effects at 3.0 T. However, further studies are needed to evaluate these findings.