Synopsis

The tumour grading is of great importance in predicting the biological behaviour of the tumours and offers important guidance for prediction of prognosis and the selection of clinical interventions. For these reasons, with dynamic susceptibility contrast enhanced perfusion weighted imaging (DSC) as reference standards, we retrospectively appraised the diagnostic efficacy of perfusion-related parameters of multiple b values diffusion weighted image (DWI) compared to appraise normalized lesion/normal tissue relative cerebral blood flow (nrCBF)in the prediction of neuroepithelial tumors grading. 62 patients with pathologically proved neuroepithelial tumors underwent conventional magnetic resonance sequences, multiple b values DWI, DSC. The group differences were not significant for these perfusion-related parameters of mono-exponential and biexponential model of multiple b values DWI.

Introduction: The largest by far is tumors of neuroepithelial tissue in 6 major categories of the primary central nervous system neoplasms. The tumour grading is of great importance in predicting the biological behaviour of the tumours and offers important guidance for prediction of prognosis and the selection of clinical interventions, especially in non-resectable tumours^1,2. For these reasons, with dynamic susceptibility contrast enhanced perfusion weighted imaging (DSC) as reference standards, we retrospectively appraised the diagnostic efficacy of perfusion-related parameters of multiple b values diffusion weighted image (DWI) compared to appraise normalized lesion/normal tissue relative cerebral blood flow (nrCBF)in the prediction of neuroepithelial tumors grading.

Methods: 62 patients with pathologically proved neuroepithelial tumors underwent conventional magnetic resonance sequences, multiple b values(b=0,50,100,150,200,300,500,1000,1500,2000,3000,4000s/mm², totally 12 b values) DWI, DSC. With tumor hot-spot area in relative cerebral blood flow (rCBF) map as reference standards, the multiple perfusion-related parameters of tumors were measured postoperatively by using parameter maps progressing from mono-exponential and biexponential model of multiple b values DWI. These parameters were used for statistical evaluation comparing with histopathological tumor grade.

Results：The mean nrCBF ratio(1.778±1.209) of low trade group was significantly lower than that (5.927±3.448) of high grade group (P＜.0001). The mean fast ADC-mono （3.794±2.186）×10-3 mm²/s of low grade tumor was slightly lower than that （4.030±1.597） ×10-3 mm²/s of high grade group（P=0.612）.The mean fast ADC-bi （10.578±14.261）×10-3 mm²/s of low trade group was slightly lower than that （13.141±12.895）×10-3 mm²/s of high grade group（P=0.462）. The group differences were not significant for these perfusion-related parameters of mono-exponential and biexponential model of multiple b values DWI.

Discussion: First of all, the perfusion-related proportion in the mono-exponential and biexponential model of multiple b values DWI in the brain tissue accounts for too small, which is less than 4%³. Secondly, DWI is highly sensitive to motion, such as heartbeat, pulse, breathing, blood flow perfusion and spontaneous or involuntary head movement of patients which can cause the signal intensity of multiple b values DWI weaken⁴. For example, microvascular perfusion with multiple b values DWI in the healthy human brain is significantly different during systole than diastole⁵. In addition, multiple b values DWI is also affected by body temperature, examining room temperature and other non-diffusive factors⁶. Fourthly, it is affected by the signal-to-noise ratio of the image of acquisition sequence in multi-b-value DWI⁷. Above all, the selection and setting of multiple b values accounts most. The combination of under of b values(less than 200s/mm2) is very important for perfusion of fast ADC DWI^7,8. In this study, there are only 4 b values lower than 200s/mm2 in the combination of multiple b values, which demonstrates the span between selected b values is large as well as the number of b values is limited.

Conclusion: There aren’t equal efficacy between those perfusion-related parameters of mono-exponential and biexponential model of multiple b values DWI and DSC. It should be elucidated in the futue research that those perfusion-related parameters of mono-exponential and biexponential model of multiple b values DWI can assess microvascular perfusion of neuroepithelial tumors.

Acknowledgements

References

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