A medical apparatus (400) comprising an ultrasound transmitter (444, 602) and receiver (446, 604) system (600) for acquiring ultrasound data (476) descriptive of the speed of ultrasound (304, 306) along at least two paths (606, 1114). The medical apparatus further comprises a medical imaging system (402) for acquiring medical image data (468) and a memory (464) containing instructions (490, 492, 494, 496, 498, 500, 502, 504) that causes the processor to acquire (100, 200) the medical image data. The instructions further cause the processor to acquire (102, 202) the ultrasound data. The instructions further cause the processor to segment (104, 204) the medical image data into at least two tissue types (434, 436, 610, 612, 708, 710). The instructions further causes the processor to determine (106, 206) at least two distances corresponding to the at least two paths in the subject. The instructions further cause the processor to calculate (108, 208) the speed of ultrasound in the at least two tissue types.
