The Experimental Study On Feedback Control Of Ultrasonic Probe Pressure In Real-time Tissue Elastography(RTE)

Objective To investigate the effects of quantitative feedback control of the value of the pressure and frequency of probe pressure on the reproducibility and diagnostic accuracy of strain ratio(SR)measurements in real-time tissue elastography(RTE).Methods The interactive ultrasound elastography system was achieved by integrating two compression force sensors,a laptop and a clinical ultrasound elastographic system.The force sensors and the ultrasound probe were assembled in a 3D printed mounting bracket for continuous monitoring of compression loads during ultrasound elastography.Both the force measurements and the elastographic maps were obtained and displayed on the laptop in real time.The system was tested on repeatability and accuracy respectively,the method was as follows:(1)Reproducibility test: strain images were obtained by 15 operators under 3 different groups on an ultrasound elasticity QA phantom.Group 1 was the freehand elastography by the conventional method.Group 2 applied interactive elastography with a compression load of 0~80 g and a frequency of 1.5 times/s).Group 3 applied interactive elastography with a compression load of 40~120 g and a frequency of 1.5 times/s.In our examinations,each of 15 physicians tested three groups of compression parameters on a single cylindrical target with the stiffness of 80 k Pa,diameter of 10.4 mm and depth of 3 cm.Each physician obtained 15 strain ratios in each group.(2)Accuracy test: We tested 4 targets of the same diameter(10.4 mm),the same depth(3 cm)and different stiffness levels(8,14,45 and 80 k Pa).Each target was tested 45 times with two different methods(i.e.,freehand elastography and interactive elastography),yielding 180 measured values respectively.The data were divided into the following three groups respectively: group ?(80 k Pa vs 45,14 and 8 k Pa),group ?(80,45 k Pa vs 14,8 k Pa)and group ?(80,45 and 14 k Pa vs 8 k Pa).AUCs were calculated for different stiffness levels.Results(1)Reproducibility test: CV values had significant difference among 3 groups(F=15.853,P<0.001),Group 2 and group 3 yielded the lower CV values than that of group 1(q=4.732,P<0.001;q=5.038,P<0.001),CV values had no significant difference between group 2 and group 3(q=0.625,P=0.685).(2)Accuracy test: In group ?,interactive elastography yielded an AUC level greater than that of freehand elastography(P = 0.0379).In group ? and group ?,two methods yielded the similar AUC levels(P =1.000).However,interactive elastography was able to discern 8 k Pa and 14 k Pa targets(P<0.001),while freehand elastography was hard to differentiate them(P = 0.258).Conclusion The interactive ultrasound elastography can improve the measurement reproducibility and diagnostic accuracy among different operators.