| Part I Effected Factors on Apparent Diffusion Coefficent Quantitative Measurements of Human BrainPurpose: To evaluate the effect of differences in acquisition technique on apparent diffusion coefficient quantitative measurements of human brain. Materials and Methods: Five different diffusion weighting (b = 500, 1000, 1500, 2000 and 3000s/mm2) were applied in conventional diffusion weighted imaging in 17 health volunteers on 3.0 T MR imager by use of the single shot echo planar diffusion weighted MR sequence in three orthogonal directions. DWI with fluid attenuated inversion recovery (FLAIR) was also performed with b=1000 s/mm2; 10 subjects were imaged using 1.5T MR with b=1000 s/mm2 after 3.0T MR examination. The average ADC value were measured in the centrum semiovale, cingulate gyrus, genu and splenium of corous callosum, thalamus in the left and right hemisphere and the body part of the lateral ventricle. Results: The ADC value of centrum semiovale, cingulate gyrus, genu and splenium of corous callosum, thalamus were significantly different between the five different diffusion weighting, increasing in the b value resulted in a significant decrease in ADC; The ADC of cingulate gyrus (t=3.971, p<0.01) and splenium of corous callosum (t=2.537, p=0.022) were significantly decreased after fluid attenuated inversion recovery was used, no statistic difference was seen between conventional ADC and ADC with FLAIR in centrum semiovale(t = 0.721, p=0.482), genu of corous callosum (t=2.149, p=0.470)and thalamus (t =0.391, p=0.703) ; ADC produced in different part of the brain by different MR systems show no significant difference, except the genu of corous callosum. Conclusion: DWI sequence parameters have a significant effect on ADC quantitative measurements, especial b value; CSF-suppressed ADC measurements at the time of scanning give more accurate measurements in gray matter, which is very important in the atrophy brain; Different magnetic strength MR system manufactured by the same factory has no obvious impact on ADC measurements. Part II Apparent Diffusion Coefficient of Normal Human Brain and it'sChang with Aging.Purpose: To determine whether the average ADC values in various age groups of brain differ with age, sex and hemisphere, and the effect of aging on ADC values, also to establish reference values of the absolute ADC for further studies. Material and Methods: Subjects (60 men and 60 women) were chosen from a healthy population; Six age groups were 20-29, 30-39, 40-49, 50-59, 60-69 years and 70 years or older (n=20 each, 10 man and 10 women for each group). All subjects were examined, including conventional and diffusion weighted imaging with FLAIR in three orthogonal directions with two b values (0 and 1000s/mm2) at 3.0 T MR. Bilateral ADC values were determined in 19 regions of interest encompassing the entire brain, they are: frontal, parietal, occipital, temporal, and cerebellar gray matter and white matter; the caudate nucleus; the putamen; the thalamus; the internal capsule; the pons; centrum semiovale; cingulate gyrus, genu and splenium of corous callosum Results: ADC values of the whole brain was 7.41±0.56×10-4mm2/s. Gray matter has highter ADC (7.60±0.58×10-4mm2/s) than it was in the white matter (7.38±0.55×10-4mm2/s). Thalamus(7.58±0.41×10-4mm2/s) has a higher ADC value than the white matter, and no difference was seen between the cortical gray matter and the thalamus(F=30.92, P<0.01). The average ADC of basal ganglia was 7.09±0.53×10-4mm2/s, the ADC value of thalamus was higher than caudate nucleus, and caudate nucleus higher than putamen(F=136.68, P<0.01). The lowest ADC values were seen in the cerebellum. No differences were observed between hemispheres and sex; The ADC values significantly differed in various age groups in parietal gray and white matter, frontal gray and white matter, occipital gray matter, temporal white matter, cerebellar white matter, putamen, thalamus, internal capsule, centrum semiovale, cingulate gyrus, genu of corpous callosum. The ADC values significantly increased with advanceing age in parietal white matter(r=0.188, P<0.05), frontal white matter(r=0.451, P<0.01), centrum semiovale(r=0.365, P<0.01) and genu of corpous callosum(r=0.248, P<0.01), gray matter of frontal lobe( r=0.193, P<0.05), thalamus (r=0.556, P<0.01). Conclusion: Gray matter has a highter ADC than the white matter, the lowest ADC was seen in the cerebellum. The ADC values of adult human brain show no differences between women and men or between the hemispheres. The ADC values significantly increase with advancing age in the white matter of frontal and parietal; centrum semiovale; genu of corous callosum; thalamus and gray matter of frontal lobe. and this change become obviously after 60 yearsolder. The data we reported about adult human brain also can be used as reference for future studies.Part III Time Course of Apparent Diffusion Coefficient, Diffusion-weighted, and T2-weighted Signal Intensity of Ischemic StrokePurpose: To establish the natural evolution of apparent diffusion coefficient (ADC), ADC with fluid-attenuated inversion recovery (ADCFLAIR), signal intensity of DWI and T2WI in human ischemic stroke, and to assess the potential of using these specific MR parameters to estimate lesion age, and reveal the underline pathophysiological information. Methods: 78 stroke patients (53 male and 25 female; age range, 32-81 years; mean age, 60.56 years) had carried out 139 DWI and FLAIR-DWI examinations at varying time points from the initial ischemic onset. Values of ADCCON, ADCFLAIR, DWI signal intensity (SIDWI), T2-weighted signal intensity (SIT2), and FLAIR signal intensity (SIFLAIR) were measured in the lesions and the normal contralateral region at each time point, and the ratio of lesions to contralateral regions of interest were calculated. Data were expressed as relative ADCCON (rADCCON), relative ADCFLAIR(rADCFLAIR), relative SIDWI(rSIDWI), relative SIT2(rSIT2), and relative SIFLAIR(rSIFLAIR). Results: ADC was markly reduced in the first week after stroke, and ADC pseudonormalization comes during the second week (rADCCON = 0.93±0.25, t = 1.236, P=0.234; rADCFLAIR = 0.99±0.22, t = 0.222, P=0.827 ) , thereafter the ADC came above the normal level. But ADC pseudonormalization could also be early at 72 hours after stroke onset in some few cases. The lesion ADCFLAIR showed the same pattern of evolution of ADCCON. The ADCFLAIR and ADCCON of stroke lesion had no difference during the 14 days, and the ADCFLAIR was markedly low than the ADCCON after 14 days. rSIDWI remained higher than the normal control side during the first month, hence became isointensity, also some of DWI abnormal could be reversed. SIT2 kept high signal intensity all the time; SIFLAIR showed the same initial increase , decreased slightly after 2 weeks, and became isointensity or hypointensity 1 month later. Conclusion: ADC reduced in the first week, pseudonormalized during the second week, and elevated in the later. Time course of ADCFLAIR had the same pattern as ADCCON. FLAIR had no obvious effected on ADC values of infarction lesion within 14 days after stroke onset, ADCCON became higher than ADCFLAIR after 14 days after stroke onset, which suggested the liquationprocess. The application of FLAIR-DWI had a more accurate rADC values by reducing the CST partial volume effect of the normal contralateral side. Initial DWI abnormal can be spontaneously resolved in same few case, and this change occurred after 1 week later since stroke onset, which indicated penumbra also exist in the surround area of DWI high signal intensity, and this can last at least 1 week in human stroke.Part IV Temporal Evolution of Fractional Anisotropy in Human StrokePurpose: We sought to investigate values and temporal evolution of fractional anisotropy (FA) in human stroke from hyperacute to chronic stage. Materials and Methods: we analyzed 149 full diffusion tensor MRI studies from 98 patients(65 male and 33 female ; age range, 42-86 years; mean age, 59.23 years) at varying time points from the initial ischemic onset. 13 case was less than 6 hours, 11 between 7 to 12 hours, 9 between 13 to 24 hours, 19 within the second day, 11 between 3 to 4 days, 21 between 5 to 7 days, 19 between 8 to 14 days, 15 between 15 to 3o days, and 31 case beyond 1 month. 16 diffusion tensor MRI studies were performed at 1.5T MR system, the other 133 were performed at 3.0T MRI system. Fractional anisotropy images were computed offline, values of FA were measured in the lesions and the normal contralateral region at each time point and the ratio of lesions to control regions of interest were calculated. Data were expressed as relative FA. Results: Mean relative FA for studies performed at 6 hours or less was 0.97±0.23; for lesions between 7 to 12 hours was 1.12±0.63, for 13 to 24 hours was 1.00±0.38; for 2days was: 0.77±0.22; for 3 to 4 days was 0.57±0.10; for 5 to 7 days was 0.74±0.32; for 8 to 14 days was 0.58±0.24; for 15 to 30 days was 0.50±0.17; for lesions beyond 1 month was 0.40±0.11. FA values in the ischemic were not significantly different relative to the contralateral side within 24 hours from stroke onset (t = 0.166, p=0.870) , while it was significantly different after 24 hours(t=12.06, p<0.001); FA character is espicially complex within 24 hours after stroke onset, Three patterns of FA characters could be found in this period: elevated, unchanged and decreased. 61.53% of case showed elevated or unchanged FA in this period, while it was only 6.02% of all case after 24 hours(x2 =38.588, P<0.001). Occurrence of elevated or unchanged FA less than 6 hours, between 7 to 12 hours and 13 to 24 hours showed no difference(61.5% vs 60% vs 50%, x2 =1.231, p=0.267). Conclusion: Two phases inthe time course of relative FA changes in human stroke can be found: slightly elevated or unchanged within 24 hours and quickly decreased after 24 hours and further reduced in chronic stage. 24 hour can be a time-point for FA transition; Elevated or unchanged FA after stroke onset mainly distributed in 24 hours, it is rare after 24 hours. Heterogeneity of FA changes in 24 hours may indicate the heterogeneity of stroke evolution between individuals and hence may be useful in selecting an appropriate intervention.Part V Primary Study of MR Fiber Trcatography for Prediction of Clinical Outcome from White Matter InfarctionPurpose: To explore the diagnostic value of 3D fiber trcatography in revealing corticospinal tract (CST) injury after ischemic stroke and it's value in clinical outcome prediction. Materials and Methods: Diffusion tensor imaging were performed in 19 acute ischemic stroke patients involved basal ganglia, inter capsule or corona radiate. All raw DICOM data were transformed to personal computer to rebuilt the white matter tract using Volume-one1.64 and diffusion TENSOR Visualizer (dTV. II .R1), Three seeds were used to reconstruct the corticospinal tract. The spatial relationship between lesion and CST were analyzed. Modified rankin scale (mRS) were used to evaluate the clinical outcome. The degree of CST injury and the lesion volume were compared to the 3-month mRS scores. Results: Three patterns of CST involvement were identified: intact, partial involved and complete involved. Different pattern had totally different clinical outcome (F=0.83, P=0.455), CST intact had a fully recovery, patients with CST completely involved had a lowest mRS scores. 3-month mRS scores was directly related to the degree of CST involvement (r=0.81, p<0.01) , and not related to stroke volume (r=0.383, p= 0.105) . Conclusion: 3D fiber trcatography can show CST injury after stroke, and which can be used to predict stroke outcome at early time.
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