Magnetic resonance and ultrasound parametric image is fused or combined. MRI and ultrasound imaging are used to acquire the same type of parametric images. Fused data is created by combining ultrasound and MRI parametric data at times for which both types of data are available. Rather than sacrificing rate, fused data is created for times for which MRI data is not acquired. A curve representing the values of the parameter over time is fit to the available MRI and ultrasound data of each location, resulting in fused data at times for which MRI data is not available.