Ultrasound Imaging Simulation Based On CT Images

Ultrasonic imaging simulation is a kind of technology that is using existing 3d medical image data to simulate the process of ultrasound imaging to get virtual ultrasonic images. This kind of technology can be widely used in ultrasound guided surgery, image processing, ultrasound training, etc.Many researches have been done in the domain of ultrasound imaging simulation. Some algorithms are fast but not considering enough facts. Somes consider enough facts but not very fast. Considering the timeliness and the results of ultrasonic imaging simulation, this thesis uses mathematical modeling method to implement the algorithm of the key technology of virtual ultrasound simulation based on three-dimensional CT reconstruction data.Because the human body is the non-uniform material, when ultrasound is spreading in the body it will be reflected, refracted, and scattered, which is the theory of medical ultrasound imaging. So the main part of the ultrasound imaging simulation is the three-dimensional modeling of virtual human tissue that is the ultrasound transmission medium, the modeling of the ultrasound reflection and the modeling of ultrasound scattering.First of all, this thesis gives the method of reconstructing the virtual human body model based on three-dimensional CT data which is related to ultrasound properties. The first step of this method is to implement the interpolation between CT slices to let the voxel has isotropic resolution. After getting the three-dimensional data of the human body, then deduce the acoustic impedance of the voxel CT value in the human body.Secondly, this thesis gives the steps of building the reflection model and the methods used in the model. The flection model assumes that the ultrasound probe has multiple arrays. The ultrasound beam sent by each array element will be traced in the model. The tracing steps of the spreading of ultrasound in the human body are elaborated in details in the paper. When the ultrasonic reflection and refraction occur, the change rate of acoustic impedance and cosine values of incidence angle are calculated to get the reflectivity coefficient which will be recored. After tracing all the beams sent by the elements, several matrix data connected to the distribution of reflectivity will be gained. Then calculate the average value of each element in these matrixs to get the refleciont image with a small dipalcement because the elements in the probe have a small displacement between each other.Again, as well as the ultrasound reflection model, the ultrasound scattering model is established and the calculation method is are given. The scattering model sums up the develpoing of the scattering image as the convolution of the scatterer distribution equation with the point spread function (PSF). According to the distances between the scatterers follow the gamma distribution, the scatterer distribution matrix can be determined. Combining the corresponding scattering coefficient with the scatterer distribution matrix, scatterer distribution equation is obtained. Then use coordinate transformation and R-Theta interpolation in the convolution image to get the real scattering image.Finally, caculate the weighted sums of the reflection and scattering images to get the ultrasound simulation images. The ultrasound simulation images can display the boundary of the organization correctly, and after combined with scattering signal, the simulation of ultrasonic image is closer to the real ultrasound images. The experiment results of the ultrasound imaging simulation has reached the expected purposes. Using the method of convolution to get scattering image is faster than using Field Ⅱ.