Rationale and objectives: The magnitude of iron-induced susceptibility changes in gradient echo T2*-weighted magnet resonance imaging (T2* MRI) increases with the field strength and should increase the sensitivity for detection of cerebral microbleeds (CMBs) at 3.0 T. To test these hypotheses, we prospectively examined individuals with documented CMBs at 1.5 and 3.0 T.
Materials and methods: Five hundred fifty elderly individuals, who participated in an interdisciplinary study of healthy aging, were examined at 3.0 T using T2* MRI sequences (repetition time [TR]/echo time [TE]/flip angle [FA] = 573 ms/16 ms/18 degrees ). Individuals positive for CMBs were asked to undergo an additional examination at 1.5 T (TR/TE/FA = 663 ms/23 ms/18 degrees ). Images were analyzed independently by two observers. CMBs were counted throughout the brain and were qualitatively analyzed comparing the degree of visible hypointensity on a 5-point scale from 1 (complete signal loss) to 5 (no detection) for both field strengths. Contrast-to-noise ratio of CMBs to surrounding brain tissue was calculated.
Results: At 3.0 T, CMBs were detected in 45 of 550 individuals; 25 agreed to an additional examination at 1.5 T. In this group (n = 25), a total of 53 CMBs were detected at 3.0 T, compared to 41 CMBs at 1.5 T. The mean contrast-to-noise ratio of CMBs was significantly increased at 3.0 T compared to 1.5 T (27.4 +/- 8.2 vs. 17.4 +/- 8.0; p < .001). On qualitative analysis, visibility of CMBs was ranked significantly higher at 3.0 T (1.3 +/- 0.4 vs. 2.9 +/- 1.1; p < .001).
Conclusion: Evidence of past microbleeds may even be found in neurologically normal elderly individuals by MRI. Detection rate and visibility of CMBs benefit from the higher field strength, resulting in a significantly improved depiction of iron-containing brain structures (CMBs) at 3.0 T with potential clinical relevance.