Korean J Radiol.  2013 Apr;14(2):307-315. 10.3348/kjr.2013.14.2.307.

Serial MR Analysis of Early Permanent and Transient Ischemia in Rats: Diffusion Tensor Imaging and High b Value Diffusion Weighted Imaging

• Kim JH
• Na DG
• Chang KH
• Song IC
• Choi SH
• Son KR
• Kim KW
• Sohn CH

• KMID: 1482792
• DOI: http://doi.org/10.3348/kjr.2013.14.2.307

Abstract

OBJECTIVE
To evaluate the temporal evolution and diagnostic values of the diffusion tensor imaging (DTI) and the high b value diffusion weighted imaging (DWI) in the early permanent and transient cerebral ischemia.
MATERIALS AND METHODS
For permanent or 30-minute transient-ischemia induced 30 rats, DTI and DWIs at both high b (b = 3000 s/mm2) and standard b value (b = 1000 s/mm2) were obtained at the following conditions: at 15, 30, 45, 60 minutes after the occlusion of what for hyperacute permanent ischemia; at 1, 3, 5, 7, 9 hours after the occlusion for acute permanent ischemia; and at 15 minutes before reperfusion, 0.5, 2.5, and 24 hours after reperfusion for transient ischemia. The diffusion parameters and their ratios were obtained and compared between different b values, and among different time points and groups, respectively.
RESULTS
For both b values, the apparent diffusion coefficient (ADC) ratio decreased for first three hours, and then slightly increased until 9 hours after the occlusion during a gradual continuous increase of DWI signal intensity (SI) ratio, with excellent correlation between ADC ratios and DWI SI ratios. The DWI showed a higher contrast ratio, but the ADC map showed a lower contrast ratio for permanent ischemia at high b value than at standard b value. Fractional anisotropy (FA) increased for 1 hour, then gradually decreased until 9 hours after the occlusion in permanent ischemia and showed transient normalization and secondary decay along with change in ADC in transient ischemia.
CONCLUSION
This study presents characteristic initial elevation and secondary decay of FA, higher contrast ratio of DWI, and lower contrast ratio of ADC map at high b value, in addition to the time evolutions of diffusion parameters in early permanent and transient ischemia.

Keyword

Ischemia; Diffusion weighted imaging; Diffusion tensor imaging; Apparent diffusion coefficient; Fractional anisotropy

MeSH Terms

Animals
Contrast Media/diagnostic use
Diffusion Magnetic Resonance Imaging/*methods
Gadolinium DTPA/diagnostic use
Ischemic Attack, Transient/*diagnosis
Male
Rats
Rats, Sprague-Dawley
Contrast Media
Gadolinium DTPA

Figure

• 

  Fig. 1 Serial MRI patterns of hyperacute (A) and acute (B) ischemia on DWIs and ADC maps, at b = 1000 s/mm2 and b = 3000 s/mm2; and FA map in two representative rats, with rat brain (C) stained with triphenyltetrazolium chloride 9 hours after occlusion. DWI hyperintensity and ADC hypointensity at both b values are seen in left cerebral hemisphere from 15 minutes to 9 hours. Compared with lesion contrast at b = 1000 s/mm2, that at b = 3000 s/mm2 is higher on DWI but lower on ADC map. FA in left cerebral hemisphere is higher than normal tissue for 1 hour. It decreases to value lower than that of normal tissue at 9 hours. Rat brain stained with triphenyltetrazolium chloride shows pale brain area, suggesting adequate infarct of middle cerebral artery. ADC = apparent diffusion coefficient, DWI = diffusion weighted imaging, FA = fractional anisotropy

• 

  Fig. 2 Time curves of ratios of DWI signal intensity, ADC, and FA in hyperacute and acute permanent ischemia groups. Values of 1 hour parameters are mean of both hyperacute and acute permanent ischemia groups (arrows). Values at ipsilateral ischemia were normalized by contralateral normal values to produce ratios of all parameters. Error bars reflect standard error of mean. ADC = apparent diffusion coefficient, DWI = diffusion weighted imaging, FA = fractional anisotropy, SI = signal intensity

• 

  Fig. 3 Scatterplots of correlation in ADC ratios and DWI SI ratios between b = 3000 s/mm2 and b = 1000 s/mm2. Strong correlation in ADC ratios (A) and DWI SI ratios (B) between both b values is seen. ADC = apparent diffusion coefficient, DWI = diffusion weighted imaging, SI = signal intensity

• 

  Fig. 4 Serial MRI patterns of transient ischemia on DWI and ADC maps at b = 1000 s/mm2 and b = 3000 s/mm2, and FA map. After 30 minute transient ischemia, normalizations of DWI hyperintensity and ADC hypointensity at both b values, as well as normalization of FA hyperintensity at left caudoputamen area are seen during first 2.5 hours, with the exception of some peripheral portions. ADC = apparent diffusion coefficient, DWI = diffusion weighted imaging, FA = fractional anisotropy

• 

  Fig. 5 Time curves in transient ischemia group and Comparison of ADC and FA in permanent and transient groups. (A) Time curves of DWI signal intensity, ADC, and FA ratios in transient ischemia group. After 30 minute transient cerebral ischemia, initial high DWI SI and FA ratios reach plateau of near 1 during first 2.5 hours after reperfusion, followed by reincrease of DWI SI ratio and decrease of FA ratio at 24 hours. Initial low ADC ratio reaches plateau of near 1 during first 2.5 hours after reperfusion, followed by redecrease of ADC ratio at 24 hours. (B) Comparison of ADC and FA in permanent and transient groups. At 30 minutes after 30 minute occlusion in transient ischemia group, which is comparable to 1 hour after occlusion in permanent ischemia group, FA decreased and ADC increased significantly, resulting in normalized values. ADC = apparent diffusion coefficient, DWI = diffusion weighted imaging, FA = fractional anisotropy, SI = signal intensity

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