1. A method for real-time correction of tissue compression for tracked ultrasound, comprising: acquiring an ultrasound image of tissues of interest with an ultrasound probe having a probe surface, wherein the ultrasound probe is tracked to provide a position and an orientation of the probe surface of the ultrasound probe for the acquired ultrasound image; acquiring intraoperative measurements of the undeformed tissue surface; constructing a generic grid representation of tissues for use with a mathematical model of tissue biomechanics, wherein the generic grid representation is pre-aligned to the acquired ultrasound image by performing a calibration to the ultrasound probe; determining boundary conditions to the mathematical model of tissue biomechanics represented by the generic grid representation; solving the mathematical model of tissue biomechanics for three-dimensional (3D) displacements in the generic grid representation of the tissues; and performing correction of tissue compression by using the reversed and interpolated 3D displacement field on the acquired ultrasound image, wherein the step of acquiring the ultrasound image further comprises calibrating the ultrasound image to a tracked target that is attached to the ultrasound probe, wherein the ultrasound probe is tracked intraoperatively with a tracking device, so that the pose of the ultrasound image is defined in the coordinate system of the tracking device; wherein the step of acquiring the intraoperative measurements of the undeformed tissue surface is performed with a surface acquiring device that is tracked intraoperatively with the tracking device or contains a geometric reference within the field of view of the surface acquiring device; and wherein the step of determining the boundary conditions comprises using the undeformed tissue surface in conjunction with the position and orientation of the ultrasound probe to estimate a depth to which the tissues are compressed, wherein the depth is computed by casting rays down from each point of the cloud obtained by the surface acquiring device in the depth direction, and finding an average length of the ray segments which intersect with the probe surface.