A Comparison of Mean Displacement Values Using High b-Value Q-Space Diffusion-weighted MRI with Conventional Apparent Diffusion Coefficients in Patients with Stroke

Rationale and Objectives

Q-space analysis using high b-value diffusion-weighted magnetic resonance (MR) data provides information on tissue microstructure in contrast to conventional MR imaging (MRI) based on low b-value diffusion-weighted imaging (DWI). The purpose of this study was to evaluate the use of mean displacement (MDP) map in stroke patients using q-space diffusion-weighted MRI (QSI).

Materials and Methods

Twenty-one patients presenting with a total of 22 acute or subacute cerebral infarctions were included. MR protocol consisted of conventional MR sequences, DWI (b-value; 1000 s/mm 2 ) and QSI (b-value; maximum 12,000 s/mm 2 ). Apparent diffusion coefficient (ADC) maps of conventional DWI and MDP maps of QSI data were obtained and compared in the ischemic lesions and corresponding normal tissues.

Results

Decreased ADC values were present in all lesions. There was no correlation between ADC and MDP values in the lesions ( r = 0.21). MDP values of the lesions were 8.60 ± 1.26 μm (mean ± SD). Most of the lesions (16/22) had higher MDP values than normal brain tissue. Three lesions showed lower MDP values and three showed mixed MDP values.

Conclusions

The MDP maps using QSI data provides additional information for stroke patients compared to conventional DWI.

Diffusion-weighted imaging (DWI) is widely applied as a noninvasive magnetic resonance (MR) technique for assessing brain development and pathological conditions. Clinically, single-shot echo-planar imaging (EPI) with low b-values (800–1000 s/mm 2 ) is the most common technique because of its short acquisition time (<1 minute) to complete whole brain imaging, relatively high signal-to-noise ratio (SNR), and high sensitivity and specificity for detecting acute stroke lesions . Apparent diffusion coefficient (ADC) is a DWI-derived parameter used to estimate stroke lesions.

However, ADC is not a reliable predictor of brain tissue damage because even severely decreased ADC values may normalize in human stroke . Moreover, brain tissue with initially decreased ADC values may include “tissue at risk” for stroke . For the reasons ADC values derived from conventional DWI of limited use in the evaluation of brain tissue damage in stroke patients.

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Materials and methods

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Table 1

Summary of Stroke Patients Clinical Information

Patient Age (y) Time After Stroke Onset Previous History of Cerebral Infarction Leukoaraiosis 1 61 120 + − 2 63 72 + + 3 80 3 + + 4 64 3 + + 5 57 21 + + 6 48 28 − − 7 76 6 − + 8 80 268 + − 9 58 24 + − 10 57 312 − − 11 53 48 − + 12 93 192 + + 13 52 16 − + 14 72 3 + + 15 67 168 + + 16 37 18 − − 17 78 312 + + 18 63 48 + + 19 63 216 + + 20 69 96 + + 21 74 48 + +

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Ps(R,tdif)=FT{Etdif(q)} P

(

dif

)

{

tdif

(

)

}

Where t dif = Δ –δ/3, the effective diffusion time.

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MDPvalue=0.425×FWHM MDP

value

0.425

FWHM

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Results

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Table 2

Mean Values for ADCs and MDP

Ischemic Lesion Contralateral Region ADC, 10 −3 mm 2 /s 0.53 ± 0.15 0.84 ± 0.14 MDP, μm 7.31 ± 1.07 5.15 ± 2.78

ADC, apparent diffusion coefficient; MDP, mean displacement.

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Discussion

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Conclusion

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References

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A Comparison of Mean Displacement Values Using High b-Value Q-Space Diffusion-weighted MRI with Conventional Apparent Diffusion Coefficients in Patients with Stroke

Rationale and Objectives

Materials and Methods

Results

Conclusions

Materials and methods

Results

Discussion

Conclusion

References

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