An ultrasound control apparatus for controlling the generation of an ultrasound, the apparatus comprising: an interface unit configured to receive a medical image comprising anatomical information about a subject, the medical image being a computed tomography image; a characteristics calculation unit configured to calculate at least one characteristic of a tissue (520, 530, 540, 550) in the subject affecting propagation of the ultrasound based on the medical image; a parameter determiner configured to determine at least the relative phase of each element in a phased array of a therapeutic ultrasound irradiation device to create a focal point in the subject using the calculated characteristic; and a control unit configured to produce a control signal for the therapeutic ultrasound irradiation device to generate the ultrasound according to the determined phases wherein the characteristics calculation unit is configured to process the medical image to calculate the characteristic of the tissue on a path along which the ultrasound propagates from an element (510, 1210) of the therapeutic ultrasound irradiation device to the focal point, wherein the characteristics calculation unit comprises a group generator, a first model generator, a second model generator and a calculator, wherein the group generator is arranged to identify a type of one or more tissues on said path, to divide the one or more tissues into a first group and a second group based on the identified types and to transmit information about the tissues in the first group to the first model generator and information about the tissues in the second group to the second model generator, wherein the first model generator is arranged to generate a first model representing characteristics of each of the tissues in the first group using CT numbers, wherein the second model generator is arranged to generate a second model, different from the first model, representing characteristics of each of the tissues in the second group. an interface unit configured to receive a medical image comprising anatomical information about a subject, the medical image being a computed tomography image; a characteristics calculation unit configured to calculate at least one characteristic of a tissue (520, 530, 540, 550) in the subject affecting propagation of the ultrasound based on the medical image; a parameter determiner configured to determine at least the relative phase of each element in a phased array of a therapeutic ultrasound irradiation device to create a focal point in the subject using the calculated characteristic; and a control unit configured to produce a control signal for the therapeutic ultrasound irradiation device to generate the ultrasound according to the determined phases wherein the characteristics calculation unit is configured to process the medical image to calculate the characteristic of the tissue on a path along which the ultrasound propagates from an element (510, 1210) of the therapeutic ultrasound irradiation device to the focal point, wherein the characteristics calculation unit comprises a group generator, a first model generator, a second model generator and a calculator, wherein the group generator is arranged to identify a type of one or more tissues on said path, to divide the one or more tissues into a first group and a second group based on the identified types and to transmit information about the tissues in the first group to the first model generator and information about the tissues in the second group to the second model generator, wherein the first model generator is arranged to generate a first model representing characteristics of each of the tissues in the first group using CT numbers, wherein the second model generator is arranged to generate a second model, different from the first model, representing characteristics of each of the tissues in the second group.