Magnetic Resonance Imaging Evaluation of Cerebral Microbleeds: A Comparative Analysis of Susceptibility Weighted Imaging and T2 Gradient Recalled Echo Sequences

Abstract

Introduction: Cerebral Microbleeds (CMBs) are increasingly recognised as an important predictor of small vessel disease and cannot be detected on routine Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) sequences. Aim: CMBs on MRI and to compare the sensitivity of Susceptibility Weighted Imaging (SWI) and T2* Gradient Recalled Echo (GRE) sequences in detection of these microbleeds. Also, to evaluate association between topography (size, number and location) of CMBs and various risk factors. Materials and Methods: This Prospective Observational analytical study comprised of 67 patients with CMBs who were evaluated with Siemens 1.5 Tesla MRI machine. T2*-weighted GRE sequence and SWI were taken in all the patients in addition to routine MRI sequences. Two observers blinded to clinical information, independently interpreted the T2*GRE and SWI sequences. Both observers recorded the topographical details of CMBs which included presence, number, size and location and their association with various risk factors (hypertension, diabetes, smoking and hyperlipidemia). Inter-rater agreement for the number of CMBs on SWI and T2*GRE was calculated using Cohen’s Kappa (κ) as measure of agreement. Intra-Class Correlation Coefficient (ICC) for reliability index in test-retest, intra-rater and inter-rater reliability was also analysed. The intra-rater reliabilities of each rater were compared. The correlations between CMBs and risk factors was performed with Pearson’s correlation Coefficient (r). The p-value <0.05 was considered statistically significant. Results: The SWI with its Reverse Phase (RP) detected more number of CMBs as compared to T2*GRE. Majority of the subjects (71.6%) had more than five CMBs. CMBs ≥5 mm had a strong correlation with both hypertension and diabetes as compared to CMBs <5 mm. There was a higher frequency of patients with lobar CMBs (89.6%) followed by the deep location (70.1%). An almost perfect agreement was found between both observers for number of CMBs on RP SWI with ‘κ’ value of 0.97a (0.96-0.98) in contrast to a weak agreement on RP T2*GRE with κ=0.52a (0.40-0.64). For SWI, an almost perfect reliability was found (ICC=0.998) as compared to a moderate reliability on T2*GRE (ICC=0.6826). An excellent reliability was seen for size of CMBs <5 mm on RP SWI (ICC 0.998). Conclusion: SWI offered greater reliability and sensitivity for CMB detection as compared to the T2*GRE sequence and is presently the gold standard sequence of MRI for quantifying CMBs. The burden of CMBs may further indicate inappropriately treated hypertension and diabetes.