To evaluate the diagnostic efficacy of a simple quantitative measurement method based on magnetic resonance imaging (MRI) for predicting the vulnerability of atherosclerotic plaques by focusing on the associated cerebral infarcts. Forty-five patients with cervical carotid stenosis were prospectively enrolled for analyzing the contrast ratio on MR plaque imaging and cerebral infarcts. Compared with plaques without the associated acute infarcts, the mean contrast ratios of plaques with acute infarcts were significantly higher on T1-weighted imaging (T1WI; P < 0.001) and lower on T2-weighted imaging (T2WI; P = 0.028), respectively. A receiver operating characteristic (ROC) analysis of the contrast ratio on T1WI yielded an optimal cutoff of 1.192. By focusing on the associated acute infarcts, the contrast ratio based on T1WI reliably predicted plaque vulnerability.