Study On Key Problems Of In Vivo Measurement Of Lens Mechanical Properties Based On Acoustic Radiation Force

The crystalline lens of the aged population is extremely susceptible to physiological and pathological changes,causing changes in its optical and mechanical properties,resulting in Presbyopia and Cataract.To explore in vivo measurement methods of lens mechanical properties is helpful to study the pathogenesis of old vision and cataract,and to find effective means to prevent and delay the occurrence of old vision and cataract.In this study,high frequency ultrasound method used L22-14 v ultrasound linear array probe(128 array elements,Center frequency: 15.625 MHz,Bandwidth: 14-22MHz)was developed and used to measure the rabbits' lens mechanical properties in vivo.The principle of high frequency ultrasound measurement method is as follows: Based on the programmable VerasonicsTM Vantage256 platform,the lens is excited by the continuous excitation produced by L22-14 v probe at three points of different depth in the same axial position.Then the same probe detected the tissue vibration in the direction of shear wave propagation and calculated the shear wave group velocity by linear regression method to be used as an evaluation index of lens mechanical properties.In this experiment,the moving velocity of excitation points is 50m/s,and the number of Maher cone is about 22.Compared with the previous low frequency ultrasound method,the high frequency ultrasound measurement method improves the imaging resolution and reduces the sound power on the lens of in vivo measurement.In the experiment,month-age animal model of 4 month old,5 month old,6 month old and 7 month old were established,and the low frequency ultrasound measurement method based on L11-4v probe developed by our team was also used.The results showed that there was no significant differences between the lens' group velocities of 4 month old,5 month old,6 month old and 7 month old of rabbit groups at high frequency and low frequency(p>0.05),indicating that the different excitation frequency had no significant influence on the group velocity results of lens.The experimental results also showed that the group velocities of rabbit lens in different month-age increased with the increase of month,and the group velocity of single rabbit also increased with the increase of month,which showed that the stiffness of rabbit lens in different month-age and the stiffness of single rabbit's lens increased with the increase of month.The correlation analysis showed that the correlation coefficient R1 and R2 of day-age and group velocities of 4 to 7 month old rabbits under the low frequency and high frequency ultrasound measurements in this experiment were 0.57(p<10E-4)and 0.44(p<0.01).The correlation coefficient R0 of day-age and group velocities of 2 to 5 month old lenses of rabbits in the previous experiment was 0.84(p<10E-7).Combining 4 to 7 month old rabbits in this experiment with the previous experimental data,the correlation coefficient R3 and R4 of dayage and group velocities of 2 to 7 month old under low frequency and high frequency ultrasound measurement is 0.69(p<10E-11)and 0.63(p<10E-8),respectively.Adding low month old data from previous experiment increased the correlation coefficient of day-age and group velocity of low frequency ultrasound measurement and high frequency ultrasound measurement method.It shows that the stiffness' s of rabbit lens in low month-age groups increase rapidly with day-age,and the stiffness' s of rabbit lens in high month-age groups grow slowly with dayage and enters the platform period.The rules of lens' stiffness growth with day-age are consistent with the growth and development rule of rabbits.The mean values of group velocities obtained by in vitro high frequency ultrasound measurement method,in vivo high frequency ultrasound measurement method,in vitro low frequency ultrasound measurement method,and in vivo high frequency ultrasound measurement method of 4 rabbits in 4 to7 month old rabbits groups were 2.37 ± 0.24m/s,2.52 ± 0.19m/s,2.36 ± 0.12m/s and 2.44 ± 0.26m/s,respectively.There is no significant differences between the group velocity of various methods above(p<0.05),which is in agreement with the results of compression test in our experiment.It proves the reliability and accuracy of high frequency ultrasound measurement method developed in this experiment.It also indicates that group velocity can be used as a characteristic parameter for evaluating the mechanical properties of lens.This experiment can be used to study the law of rabbit growth and development by the group velocity distribution of the lens measured by high frequency ultrasound measurement technology in this experiment.This technique is expected to be applied to the research of change rules of lens mechanical properties associated with the physiological and pathological changes of human eye lens.The high frequency ultrasound measurement technology is also expected to be a powerful clinical diagnostic tool for the study of presbyopia and cataract caused by pathology and physiology changes of the lens.