Computing the beamforming phase delays applied to individual elements of high intensity focused ultasound transducer array based on MR images

High Intensity Focused Ultrasound (HIFU) is becoming increasingly available for ablation of unwanted tissue, for coagulation of blood and for crushing kidney stones. One of the important problems associated with HIFU is the smearing and spatial shift of the focal spot due to phase errors. For a homogeneous medium the phase delays associated with each ultrasonic array element to form a beam is known exactly. However, when the medium is inhomogeneous like human body, the variations in the speed of sound cause phase errors. Knowing the speed of sound in tissue between the transducer array and target greatly remedies this problem. The information obtained from MR images can be used to correct the phase of each transducer element. In this way, treatment duration for MRgFUS reduces. In this study we used water supressed and fat supressed MR images for determining the speed of sound in tissue then we used this information and some methods, like backprojection, to compute the phase delays associated with each aray element of the HIFU transducer.