Study On Measurement Of Cerebral Blood Flow By Ultrasound Based On Vector Velocity

Background:Abnormal cerebral blood flow is the main cause of secondary brain injury in patients with severe craniocerebral injury.Previous studies have recommended monitoring cerebral perfusion pressure(CPP)to regulate cerebral blood flow.The fourth version of the U.S.Guidelines for Severe Head Injuries indicates that CPP should be targeted at 50-70mmHg,while other monitoring is needed to further assess cerebral blood flow status.According to the research on the automatic regulation function of the brain conducted by the Brain Center of the University of Cambridge in the UK,for some patients with craniocerebral injury,the maintenance of CPP within the range of 50-70mmHg would still lead to ischemic or congestive brain injury.Therefore,the cerebral perfusion pressure alone can not fully meet our goal of monitoring cerebral blood flow.Clinical monitoring methods of cerebral blood flow mainly include bedside transcranial Doppler ultrasound(TCD)monitoring,PET-CT,SPPET,cranial magnetic resonance(MR)perfusion imaging,CT perfusion scanning,etc.However,monitoring methods such as PET-CT and cranial MR perfusion imaging cannot achieve realtime bedside evaluation,so their value in the treatment and evaluation of severe craniocerebral injury patients in the acute phase is limited.Although TCD can be evaluated at the bedside in real time,it can only reflect the change of cerebral blood flow velocity rather than directly reflect the change of cerebral blood flow,which also limits its clinical application.Intrusive cerebral blood flow monitoring can reflect the changes of cerebral blood flow,but because it may increase the risk of intracranial infection and can only reflect the changes of cerebral blood flow in the local area of the probe,it is rarely used in clinical practice.Therefore,there is still a lack of accurate bedside non-invasive cerebral blood flow monitoring technology.Some studies have shown that parameters such as vessel diameter and flow velocity can be obtained through clear display of vascular diameter by ultrasound and pulse Doppler spectrum analysis of arterial blood flow,and arterial blood flow can be calculated according to the measurement results.However,whether this method can be applied to bedside monitoring in intensive care remains to be determined.Objective:To explore a robust bedside non-invasive cerebral blood flow assessment technique based on ultrasound in intensive care unit.Methods:A total of 15 healthy volunteers and 40 patients with brain injury/cerebral hemorrhage are selected.Five intensivists in the department of intensive care are used to evaluate the common carotid artery using the longitudinal section method,the transverse fixed Angle method,the trigonometric double section method,the trigonometric single section method,and the trigonometric single section method.And the maximum velocity approximation method,the mean velocity approximation method and the improved ring approximation method are used to analyze the robustness of the measurement results of each method.To explore a better robust blood flow assessment method,and use this method to evaluate internal carotid blood flow,and robustness analysis.Results:Robustness analysis is performed based on the coefficient of variation and percentage measurement method.The common carotid artery is used as the measuring vessel to evaluate the robustness of blood flow velocity.The results showed that the robustness of the trigonometric double section evaluation method is significantly better than that of the longitudinal section evaluation method,and the difference is statistically significant(coefficient of variation:0.232vs0.408,P=0.000;Percentage measurement:0.629vs1.134,P=0.000).The robustness of the trigonometric double section evaluation method is significantly better than that of the cross-section fixed Angle evaluation method,and the difference is statistically significant(coefficient of variation:0.232vs0.256,P=0.000;Perc entage measurement:0.629vs0.739,P=0.000).The robustness of trigonometric single sectional assessment method is significantly better than that of trigonometric double sectional assessment method,and the difference is statistically significant(coefficient of variation:0.211vs0.232,P=0.000;Percentage measurement:0.586vs0.629,P=0.003).There is no significant difference between the robustness of trigonometric single section color Doppler ultrasound and that of trigonometric single section color Doppler ultrasound(coefficient of variation:0.201vs0.211,P=0.248;Percentage measurement:0.567vs0.586,P=0.174).However,in the subgroup analysis,the robustness of trigonometric single-section color ultrasound evaluation method is significantly better than that of trigonometric single-section evaluation method,with statistical difference(obese group:coefficient of variation:0.171vs0.306,P=0.000;Percentage measurement:0.560vs0.927,P=0.000).To evaluate the robustness of the flow velocity-flow conversion method,there is no significant difference between the robustness of the maximum flow velocity assessment method and the mean velocity approximation method(coefficient of variation:0.201vs0.201,P=l;Percentage measurement:0.568vs0.568,P=1).There is no significant difference between the robustness of the improved ring approximation method and the maximum flow velocity approximation method(coefficient of variation:0.193vs0.201,P=0.756;Percentage measure:0.541vs0.568,P=0.327).However,in the subgroup analysis,the robustness of the modified ring approximation method is significantly better than that of the maximum flow velocity approximation method,with statistical difference(In the plaque group:coefficient of variation:0.140vs0.248,P=0.015;Percentage measurement:0.389vs0.672,P=0.000).Using the modified ring approximation method,the common carotid artery was used as the measurement vessel.The proportion of variation coefficient less than 0.2 was 59.1%,and the proportion of variation coefficient less than 0.3 was 71.8%.With the internal carotid artery as the measurement vessel,the proportion of coefficient of variation less than 0.2 was 52.7%,and the proportion of coefficient of variation less than 0.3 was 76.4%.Conclusion:In this study,through the processing and analysis of the blood flow data of the common carotid artery of volunteers and patients,it was found that the trigonometric function single section assessment method could measure a relatively stable blood flow velocity index.Color ultrasound can be used to measure the angle between ultrasound and blood vessels when the detection depth is deep and the boundary of blood vessels is not clear.For patients with arterial plaques,ring approximation is recommended for blood flow assessment.In conclusion,the trigonometric function single-section color ultrasound based on the ring approximation method can obtain relatively stable blood flow data of internal carotid artery.