Introduction: Magnetic resonance (MR) plaque imaging for carotid arteries is usually performed by using an electrocardiograph (ECG)-gating technique to eliminate pulsation-related artifacts, which can affect the plaque signals because of varied repetition time (TR) among patients. Hence, we investigated whether differences in TR causes signal alterations of the carotid plaque by using a non-gated plaque imaging technique.
Methods: We prospectively examined 19 patients with carotid stenosis by using a T1-weighted self-navigated radial-scan technique with TRs of 500, 700, and 900 ms. The signal intensity of the carotid plaque was measured, and the contrast ratio (CR) relative to the adjacent muscle was calculated.
Results: CRs of the carotid plaques were 1.39 +/- 0.39, 1.29 +/- 0.29, and 1.23 +/- 0.24 with TRs of 500, 700, and 900 ms, respectively, and were significantly different. Among the plaques, those with a hyperintensity signal (CR > 1.5) and moderate-intensity signal (CR 1.2-1.5) at 500 ms showed a TR-dependent signal decrease (hyperintensity plaques, 1.82 +/- 0.26; 1.61 +/- 0.19; and 1.48 +/- 0.17; moderate-intensity plaques, 1.33 +/- 0.08; 1.26 +/- 0.08; and 1.19 +/- 0.07), while those with an isointensity signal (CR < 1.2) remained unchanged regardless of TR (0.96 +/- 0.12, 0.96 +/- 0.11, and 0.97 +/- 0.13).
Conclusion: The signal intensity of the carotid plaque on T1-weighted imaging significantly varies among different TRs and tends to decrease with longer TR. MR plaque imaging with short and constant TR settings that the ECG-gating method cannot realize would be preferable for evaluating plaque characteristics.