BACKGROUNDA new lacunar infarction model was recently established in beagle dogs through proximal middle cerebral artery (MCA) occlusion by thrombus. This study aimed to characterize the model by multimodal magnetic resonance imaging (MRI) and to investigate its potential role for the future stroke research.

METHODSThe left proximal MCA was embolized with an autologous thrombus in six beagles. Diffusion-weighted imaging (DWI) and T2-weighted imaging (T2WI) were performed every half hour during the first six hours after occlusion, followed by three time points at 12 hours, 24 hours, and one week. Perfusion-weighted imaging (PWI) and magnetic resonance angiography (MRA) were carried out at six hours, 24 hours and one week. The PWI-DWI mismatch ratio was defined as (PWI-DWI)/DWI ischemic volume.

RESULTSLacunar infarcts induced by MCA occlusion were located in the left caudate nucleus and internal capsule. All the lesions could be detected within two hours by DWI. Lesion volume on DWI increased in a time dependent manner, from (87.19 ± 67.16) mm(3) at one hour up to (368.98 ± 217.05) mm(3) at 24 hours (P = 0.009), while that on PWI gradually decreased from (7315.00 ± 2054.38) mm(3) at six hours to (4900.33 ± 1319.71) mm(3) at 24 hours and (3334.33 ± 1195.11) mm(3) at one week (P = 0.002). The mismatch ratio was 41.93 ± 22.75 at six hours after ischemia, showing "extensive mismatch", and decreased to 18.10 ± 13.74 at 24 hours (P = 0.002). No MCA recanalization was observed within 24 hours after MCA occlusion.

CONCLUSIONSLacunar infarction induced by proximal MCA occlusion could be detected early by DWI and was characterized by extensive PWI-DWI mismatch. Multimodal MRI is useful to demonstrate the natural evolution of PWI-DWI mismatch. This ischemic model could be further used for investigating early thrombolysis in lacunar stroke showing extensive mismatch.