Quantitative Assessment of the Time Course of Infarct Signal Intensity on Diffusion-Weighted Images
James D. Eastwooda,
Stefan T. Engelterd,
James F. MacFalla,b,
David M. Delongc and
James M. Provenzalea
a Department of Radiology, Duke University Medical Center, Durham, NC
b Department of Neurology, Duke University Medical Center, Durham, NC
c Department of Community and Family Medicine, Division of Biometry, Duke University Medical Center, Durham, NC
d Department of Neurology, University Hospital Basel, Switzerland
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FIG 1. Simultaneous plots of signal intensity on DW images (thick line), signal intensity due to altered ADC (intermediate line), and signal intensity due to T2 effect (thin line). In this logarithmic plot, the effects of T2 and ADC add together to produce the total signal intensity seen on the DW image. The vertical lines separate four periods based on the magnitudes and signs (ie, positive or negative) of the relative contributions of SIb0 and SIRAT to SIDWI.
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FIG 2. Scatterplot of the log of infarct signal intensity on DW images versus the log of hours from symptom onset. The thick line represents the polynomial function of best fit for the study data. The thin lines represent the 95% confidence limits for this fitted curve. The expected signal intensity of lesions was greater than that of control regions during the first 57 days after symptom onset.
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FIG 3. Comparison of infarct diffusibility with time.
A, Scatterplot of relative ADC versus log hours from symptom onset. The line represents the linear regression that fit the data. The line intercepts 1 (ie, infarcts had pseudonormal ADC values) at a time corresponding to 9.8 days.
B, Scatterplot of log of the ratio of lesion signal intensity on the image with b = 1000 s/mm2 to the lesion signal intensity on the image with b = 0 s/mm2. The component of infarct signal intensity due to the ADC effect (SIRAT) is the ratio of SIDWI lesion/SIb0 lesion to SIDWI control/SIb0 control. Decreased ADC contributes in a positive way to infarct signal intensity during the first 10 days after symptom onset. Increased lesion ADC contributes in a negative way to infarct signal intensity thereafter. The thick line represents the best fit for the study data. The thin lines represent the 95% confidence limits for this fitted curve.
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FIG 4. Scatterplot of the log of SIb0 versus the log of hours from symptom onset. The thick line represents the polynomial function of best fit. The thin lines represent the 95% confidence limits for this fitted curve. T2 shine-through was typically substantial and positive throughout the studied time course, and it was maximal at about 2 weeks.
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FIG 5. Images in a 63-year-old woman with an onset of left-sided weakness 26 days before imaging. Regions 1 and 2 indicate the lesion ROI and control ROI, respectively.
A, Ratio DW image was computed as the 1000 times the ratio of the image with b = 1000 s/mm2 image divided by the image with b = 0 s/mm2. Image shows an infarct in the right frontal lobe with signal intensity (-33%) lower than that of the contralateral control tissue. This finding indicates increased tissue water motion in the infarct.
B, Fluid-suppressed image (b = 0 s/mm2, TEeff =101 milliseconds, TI = 2200 milliseconds) shows substantially increased signal intensity (+93%).
C, Standard DW image (b = 1000 s/mm2, TEeff = 101 milliseconds, TI = 2200 milliseconds) with both ADC and T2 effects shows increased signal intensity within the infarct (+30%). This is an example of a patient in period 3 (10–57 days). For patients imaged during this time period, the small negative effect of ADC on infarct signal intensity on DW images more than made up for by larger contribution of the increase of T2 to infarct signal intensity.
D, ADC map shows that infarct ADC is increased 55% over that of the control tissue.
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FIG 6. Images in a 74-year-old man with an onset of left-sided weakness 90 days before imaging.
A, Ratio DW image was computed as the 1000 times the ratio of the image with b = 1000 s/mm2 image divided by the image with b = 0 s/mm2. Image shows that the infarct has a signal intensity 56% less than that of the control tissue.
B, Fluid-suppressed image (b = 0 s/mm2, TEeff = 101 milliseconds, TI = 2200 milliseconds) shows infarct signal intensity 37% greater than that of the control tissue.
C, Standard DW image (b = 1000 s/mm2, TEeff = 101 milliseconds, TI = 2200 ms) with both ADC and T2 effects shows infarct signal intensity 39% less than that of the control tissue. This is an example of a patient in period 4 (later than 57 days). For patients imaged during this time period, the large negative effect of ADC on infarct signal intensity on DW images is greater than the smaller positive contribution of T2 effect.
D, ADC map shows that infarct ADC value is increased 119% compared with that of the contralateral tissue.
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