[Application of diffusion-weighted and perfusion magnetic resonance imaging in definition of the ischemic penumbra in hyperacute cerebral infarction].

OBJECTIVE: To investigate the value of diffusion-weighted imaging (DWI) and perfusion imaging (PI) in definition of the ischemic penumbra in hyperacute cerebral infarction.

METHODS: (1) Animal study: Fifty-five SD rats were randomly divided into 5 groups of 10 rats. Nylon monofilament was inserted into the left middle cerebral artery (MCA) and immediately pulled out in 10 rats as controls (sham operation group or group A). The MCA of 40 rats was occluded by nylon monofilament for 30 minutes (group B), 60 minutes (group C), 180 minutes (group D), and 360 minutes (group E). Then all rats were examined by T(1)WI, T(2)WI, DWI, and PI. Apparent diffusion coefficient (ADC), regional cerebral blood volume (rCBV), relative cerebral blood flow (rCBF) and mean transit time (MTT) topographical maps were archived by the Workstation (GE SUN ADW3.0). The relative values of ADC, rCBV, rCBF, and MTT (ratios between the values of the occluded side and the opposite side) were calculated. The rats were killed and the cerebral infarction areas were stained by TTC (C(19)H(15)N(4)CI) and observed by light microscopy and electron microscopy. The results of microscopic examination were compared with the DWI results. (2) Clinical study: Forty-three patients, 24 males and 19 females,aged 68 years on average with acute stroke symptoms underwent MRI examination within 6 hours of symptom onset. T(1)WI, T(2)WI, DWI and PI were performed on all patients at the first MRI examination and T(2)WI was performed for follow up. The relevant parameters, including ADC, rCBV, rCBF and MTT were computed. The values of ADC, rCBV, rCBF and MTT within the lesions were compared to those at the normal sides and the ratio was calculated. The lesion volumes were measured in ADC map (as vDWI), MTT map (as vPI) and follow-up T(2)WI (as vCI). The differences between vDWI and vPI, and between vDWI and vCI were compared.

RESULTS: (1) Animal study: In the control group DWI and PI showed no change in the signal intensity and no pathological change was found. Hyper-intensity signal was found in the T(2)WI in groups D and E. No abnormal signal was found in the T(1)WI in all groups. Abnormal signals were found in the MCA-supplying region in the DWI and PI of groups B, C, D, and E. The size of hyper-intensity signal in DWI along with the extension of occlusion time. TTC staining showed that the volume of unstained area was similar to that of hyper-intensity signal area in DWI image (t test, P > 0.05). PI showed a decrease of cerebral perfusion in the MCA-supplying region along with the extension of occlusion time. However, the size enlargement of occluded region was not as severe as shown by DWI along with the extension of occlusion time. The size of region with abnormal perfusion shown by PI was larger than that shown by DWI in groups B, C, and D. PI/DWI mismatch region, indicating the existence of ischemic penumbra zone, became gradually smaller along with the extension of occlusion time and almost disappeared 360 minutes after MCA occlusion. No significant change was found in the PI/DWI mismatch region by light microscope but slight swelling of mitochondrion and Golgi apparatus in neurons were observed by electron microscope. (2) Clinical study: The cases of 38 of the 43 patients were diagnosed as cerebral infarction by clinical and MRI follow-up examinations. The first MRI examination of these 38 cases showed no abnormal signal in T(1)WI and hyper-intensity signal in T(2)WI of 4 cases. The vPI was larger than vDWI in 31 cases and the vPI was equal to or smaller than the vDWI in 7 cases. Follow-up examination showed that vCI was larger than vDWI in 28 cases and vCI almost equaled to vDWI in 10 cases. Spearman correlation analysis showed a positive correlation between the volume of ischemic penumbra zone and that of infarction (r = 0.689, P < 0.001) which suggests that the volume change of ischemic penumbra zone influences the size of final infarction directly.

CONCLUSION: Combination of DWI and PI clearly defines the ischemic penumbra in hyperacute stroke patient, thus laying, thus laying a basis for therapeutic intervention plan for stroke patients.