1. Field of the Invention
The present invention relates to an apparatus for medical treatment by using the energy of a sound wave, such as an ultrasonic wave generated by a piezoelectric element or an electroacoustic transducer element using electromagnetic induction and, more particularly, to an acoustic medical treatment apparatus such as a stone disintegration apparatus for generating a shock wave (to be referred to as a strong ultrasonic wave) by using, e.g., an electroacoustic transducer element, and disintegrating a stone (calculus) in a body by radiating strong ultrasonic wave on the stone, or a medical treatment apparatus (hyperthermia apparatus) for radiating a continuous ultrasonic wave from an electroacoustic transducer element onto cancer cells in a body so as to perform thermotherapy of the cancer cells.
2. Description of the Related Art
A conventional acoustic medical treatment apparatus, e.g., a stone disintegration apparatus, is designed to radiate a strong ultrasonic wave from the outside of a body onto a stone, in a body, such as a renal calculus or a gallstone, to disintegrate it. In this stone disintegration apparatus, a concave transducer having a diameter of 30 to 40 cm is arranged in an applicator, and a strong ultrasonic wave is emitted from the transducer to a focal point. In this case, the applicator is positioned in relation to the body so as to match the focal position with the stone, and the stone is disintegrated by the energy of the strong ultrasonic wave. This concave transducer is a piezoelectric transducer as an electroacoustic transducer element and radiates an ultrasonic narrow pulse wave from its concave surface. In addition, a tomographic imaging ultrasonic probe can be inserted in a hole formed in the center of the concave transducer. Electronic sector scanning of each transducer of this ultrasonic probe is performed to display a tomographic image on a monitor. The position of the stone can be fixed to a desired position by observing the tomographic image. In this case, a strong ultrasonic wave propagates in the form of a cone. That is, the wave has a relatively large sectional plane near a body surface, and is gradually focused on one point toward the stone.
Owing to sector scanning, the image obtained by the ultrasonic probe has a sectorial shape. That is, the image is substantially observed as a point near the body surface and gradually spreads toward a given position in the body. For this reason, regions near the surface of the body of a patient, other than the above-mentioned point, become blind regions. Therefore, even if the lungs or an intestinal tract or a bone is present in the radiation path of a strong ultrasonic wave near the body surface, it is not displayed on a tomographic image. In addition, since the tomographic image represents a sectional plane, regions other than this sectional plane are not displayed and constitute a large blind region. In order to display a stone as clearly as possible, the ultrasonic probe is preferably located as close to the stone as possible. With such an operation, however, the blind region is increased accordingly. For this reason, image display cannot be performed throughout the propagation path of a strong ultrasonic wave.
Furthermore, a stone is normally located at a position several centimeters away from a body surface. If a bone, an intestinal gas, a portion of a lung, or the like is present in the propagation path of a strong ultrasonic wave, effective ultrasonic energy cannot be radiated on the stone. Moreover, a bone may be damaged, or an ultrasonic wave is reflected by a gas, so that the reflected wave scatters around. This may cause the living body to suffer from a pain or may inflict injury on the body.