Research On Automatic Fetal Head Position Measurement Method Based On Freehand Three-Dimensional Ultrasound Imaging Technology

The fetal head position is an important parameter in the labor process,and abnormal fetal head position is a major cause of dystocia.Abnormal fetal head position affects the health of maternal and neonatal.It is of great significance for reducing the complications of maternal and neonatal and unnecessary cesarean section to pay close attention to the progress of labor and clearly understand the fetal head position during labor.The most common method for examining the fetal head position in clinical practice is vaginal finger examination,however when the fetal head is edema and the bony mark is not clear,it is difficult for the doctor to assess the correct fetal head position.Two-dimensional ultrasound can visualize the anatomy of the fetus and pelvis in a two-dimensional image,but two-dimensional ultrasound shows the anatomical information of a section,requiring the doctor to distinguish the anatomical features of the fetal head and pelvis.Then,construct the spatial positional relationship between the fetal head and the pelvis in the mind in order to determine the fetal head position which is still a time-consuming and laborious task.Both methods of examination rely heavily on the doctor’s clinical experience and are subjective.Therefore,it is still difficult to determine the fetal head position early in the labor process to determine the abnormal fetal head position.With the aim to solve the problems above,this paper proposed a method for measuring the fetal head position based on freehand 3D ultrasound technique.The key techniques of freehand 3D ultrasound imaging technology and the measurement method of fetal head position were studied.Firstly,a freehand 3D ultrasound system combining two-dimensional ultrasound and electromagnetic positioning was built,and the software system was designed.Based on this system,the calibration method of the freehand 3D ultrasonic probe was studied.A calibration phantom with multiple marking points and an automatic calibration algorithm were designed,the accuracy and precision of the calibration were evaluated.It is shown that the calibration method only needed to collect a small number of ultrasound images(1-3 images)to obtain accurate calibration results,and the calibration results were reliable.Then,based on the freehand 3D ultrasound technique,the pelvis was located by point coordinate mapping and feature points reconstruct based on singular value decomposition.The feature point vector was used to locate the fetal head,then the fetal head position was calculated.The quantitative experimental results based on the standard device for fetal head position indicated that the average angle of the fetal head position measurement method based on freehand 3D ultrasound is higher,but within the acceptable range.The Bland-Altman consistency analysis showed that the fetal head position measurement based on the freehand 3D ultrasound technique was highly consistent with the gold standard,and all the points fell within the consistency range,indicating that the method had high accuracy.The qualitative experimental results of the brain-midline mode showed that our method effectively measured the fetal head position parameter and met various measurement modes.The experimental analysis showed that the new method proposed in this paper provided accurate and reliable measurement methods for quantitative description of fetal head position,and had practical value for safe navigation of labor and scientific decision-making during labor.