APPARATUS FOR ULTRASONIC THERAPEUTIC TREATMENT

Abstract: The apparatus comprises a piezoelectric vibrator (2) adapted to generate ultrasonic energy which is transmitted through an output section (4) to a plastics head (6). The shape of the head (6) may be varied to suit whichever part of a body (8) on which it is to be used. The material and shape of the head (6) is chosen to allow accurate control of frequency and amplitude of the ultrasonic energy. The preferred ultrasonic frequency is in the range of 20-120 kHz.

Description: APPARATUS FOR ULTRASONIC THERAPEUTIC TREATMENT The present invention relates to an ultrasonic therapeutic treatment device. The application of ultrasound in diagnostic scanning techniques and therapeutic treatment of specific medical conditions has been widely reported in the technical literature over the last 20-30 years. However, we have found no relevant reference to the use of frequencies in the range 30-100 kHz. The reported applications of therapeutic ultrasound relate almost exclusively to use of frequencies in the MHz band. This stems from the concept that therapeutic treatment using ultrasonic energy should be directed accurately to a well defined region of tissue and that this is best achieved with a finely focussed beam which in turn dictates the use of high frequencies. Similar arguments apply to the selection of frequencies for ultrasonic imaging applications. For example the characteristic wavelength corresponding to a 3MHz transmission through soft tissue is about 0.5mm; but at 40kHz the wavelength would be approximately 37.5mm. Furthermore, it is known that the attenuation of ultrasonic waves increases with increasing frequency. The general effect of high frequency transmission is to produce relatively high energy absorption rates close to the entry surface and for the effect to fall off with increasing depth. It might therefore be concluded that for a given power input there is a greater likelihood of potentially harmful side effects in tissue near the surface than for a corresponding low frequency input. When treating deep tissue injuries this consideration becomes very important since in order to transmit enough energy to the required region, the risk of excessive absorption in surface layers may become unreasonably high when applying therapeutic ultrasound in the MHz band. For this reason energy levels are limited by the requirement that power input should not exceed 3 watts/cm 2 . By selecting an operating frequency band in the range 30-130 kHz a good wave penetration through deep muscle tissue is ensured and frequencies which are known to result in high attenuation in bone tissue are avoided. Experience of this form of therapy reveals a need to effect treatment in regions of the body which naturally inhibit access, particularly the hands and feet. In such cases the use of a specially shaped therapy head may greatly facilitate the treatment of an injured joint. It is recognised that under such circumstances repetitive cyclic movement of the treatment head over the skin surface may be difficult and that the need to avoid the establishment of standing waves must therefore be satisfied by an alternative technique. It is an object of the present invention to address the problem of probe access whilst at the same time choosing an operating frequency which optimises the relationship between wave penetration, treatment intensity and minimum risk of tissue damage. According to one aspect of the present invention there is provided an apparatus to treat muscular injuries below a body surface or to diagnose bone fractures characterised in that it comprises piezo electric means to generate ultrasonic energy at a frequency in the range 20 - 120 kHz, a head means adapted to be applied closely to the body surface, and means to transfer said ultrasonic energy to the head means and thereby into the body. The frequency range employed permits significantly higher energy dosage to deep seated injuries without causing damage to surface tissue as might be the case using more conventional high frequency radiation. According to another aspect of the invention, there are provided methods by which low frequency vibrations are introduced through a moulded plastic head permitting effective coupling to irregularly shaped surfaces and ensuring even energy distribution throughout the targeted volume of tissue. The head may be machined or moulded from a range of dense polymers including acetal, polypropylene and polycarbonate. These and similar materials all permit the transmission of low amplitude ultrasound in the frequency range 30-100 kHz with very low energy absorption. The head is machined from plastics material which is chosen because its. specific impedance closely matches that of human soft tissue. As an example, acetal may be used, in which case figures are: w ace+ - a l = 1-86 x 10 kg m- 2 sec ; t.i•s-.s--,u-e-., = 1.65 x 10 kg m- 2 sec- . This allows good coupling using virtually any fluid which excludes air from the head/tissue interface. It must be noted that this approach could not be used for radiation in the MHz band since absorption in the head material would be very high at these frequencies. Clinical trials using this technique have so far proved that the treatment is effective in rapidly reducing pain levels related to conditions such as; ankle sprains, anterior knee pain, lower back pain, neck and wrist sprains, and muscle spasm such as may be related t spasticity. According to another aspect of the invention there is provided a method for the application of low frequenc vibrations to an injured limb in order to provide a simpl screening test for suspected fractures. The presence of a hairline fracture would normally b detected by radiography but if a high proportion of X-ray examinations prove negative there is a strong argument fo conducting a simple preliminary examination to identif those cases presenting definable symptons. Whe ultrasound is transmitted through bone tissue containing fine crack the wave is partially reflected at th interface between the two sections of bone, due to th mechanical discontinuity in the transmission medium. Som energy is however absorbed at the site of the injur causing a local transient sensation of pain which provide an initial indication of a fracture. It should b emphasised that this preliminary indication may resul from a routine therapeutic treatment of an injury and no a specific intention to test for a fracture. Embodiments of the invention will now be described mor particularly, by way of example, and with reference to th accompanying drawings, in which: FIGURE 1 is a graphical representation of th velocity and stress distributed across the transducer an head indicating the travelling wave amplitude in the head FIGURE 2 shows a schematic view of a piezo electri transducer and head assembly; FIGURES 3 to 7 show alternative head members fo use in an apparatus embodying the present invention; FIGURE 8 shows the electrical drive system for said transducer and head; FIGURE 9 shows an apparatus embodying the invention and which incorporates an accelerometer; and FIGURES 10 and . 11 show an apparatus adapted for use on an injured hand. Referring now to the drawings; Figure 1 shows a vibrator in the form of a PZT sandwich transducer incorporating a backplate 5, PZT ceramic rings 2 (piezo electric transducer means), electrode 3 and stepped output section 4. This vibrator transmits waves at a predetermined frequency through a shaped plastic head 6 into tissue 8 via coupling medium 7. Figure 1 shows the waveform in the system. A standing wave is established in the transducer with output amplitude, and this is transmitted through a shaped therapy head 6 emerging as a travelling wave of amplitude E LM . The velocity and pressure wave amplitudes in the plastic head are seen to be relatively constant under loaded conditions; they therefore represent the travelling wave amplitude for energy transmitted into the patient. This condition is established due to reflection at the transducer/head interface and almost complete transmission at the head/tissue interface. The shape of the head may be varied at least according to the examples given in Figues 3 to 7. This characteristic reflects the particular properties of the plastics chosen for the head construction which allow accurate control of frequency and amplitude. For given transducer dimensions the shape and size of the head can be varied between wide limits whilst maintaining a controlled output power. In operation the energy transmitted to the subject tissue must not result in standing waves since this might cause excessive local absorption. This would normally be avoided by moving the head over the tissue surface during treatment; however when treating the hand or other inaccessible area such movement may be inhibited by the head shape and an alternative method must be used. The broad band transmission characteristic of the head permits the use of frequency modulation derived from the system shown in the drawings. A further advantage which derives from the- use of a plastics, mouldable head is the ability to employ a shaped head designed to give maximum contact in locations with difficult access e.g. hand and feet. For example in severe cases of rheumatoid arthritis the head could be moulded to form a hand grip which when held by the patient would permit general treatment of the hand joints simultaneously. This is shown in Figures 10 and 11. When the power input is supplied by battery means or some other transportable source, the transducer may be located within the stem of a walking stick or cane, the grip of which comprises the head. This invention offers an improved method and means for the therapeutic treatment of deep seated soft tissue injuries by ensuring that adequate power is safely transmitted to the affected region. It offers a novel means of treating irregularly shaped areas using moulding or machined heads that allow good transmission of energy without the need to traverse the surface. According to the invention, there is provided an apparatus which offers a major benefit in the technique available to monitor the treatment power delivered to a patient. It is known that the intensity of transmitted ultrasound, I, is related to displacement amplitude, ^ , by the expression; Λ ό cc~τvr- ζCx.O ~ ,, wwhneerree />> is the head material density, c the phase velocity and-ur, the angular frequency defined as 2τrf . Sincere is the wave impedance of the head material which by design matches that of the treated tissue, then I ^ - . If we monitor the displacement amplitude within the treatment head it is a relatively simple matter to obtain a linear signal, proportional to displacement amplitude and intensity, using a differentiating amplifier. This method offers much greater reliability that the current technique which depends on monitoring the electrical signal to the transducer. Any variation in the transducer performance would therefore cause a power measuring error. Figure 9 shows a head with a displacement sensor or accelerometer incorporated. This enables the displacement amplitude of vibrations transmitted to the patient to be determined. The measurements may be . transmitted to indicating means for the user to control the power input. The output of the displacement sensor may alternatively be used to control directly the power input.

Claims: CLAIMS 1. An apparatus to treat muscular injuries below a body surface or to diagnose bone fractures characterised in that it comprises piezo electric means to generate ultrasonic energy at a frequency in the range 20 - 120 kHz, a head means adapted to be applied closely to the body surface, and means to transfer said ultrasonic energy to the head means and thereby into the body. 2. An apparatus as claimed in claim 1, characterised in that the frequency is in the range of 30 -100 kHz. 3. An apparatus as claimed in either claim 1 or claim 2, characterised in that the frequency is in the region of 40 kHz. 4. An apparatus as claimed in any one of the preceding claims, characterised in that the material of the head means is adapted to transmit ultrasonic vibrations at frequencies in the region of 20 - 120 kHz and is adapted to be shaped appropriately for the treatment being given. 5. An apparatus as claimed in claim 4, characterised in that said head means comprises a shaped plastics material, such as acetal, polypropylene or polycarbonate. 6. An apparatus as claimed in claim 4 or claim 5, characterised in that means are provided in said head means to determine displacement amplitude at a treatment surface of the head. 7. An apparatus as claimed in any one of claims 4 to 6, characterised in that said head means is shaped to be manually grippable and to be accommodated within a hand. 8. An apparatus as claimed in claim 7, characterised in that the head means forms a hand grip of a cane or walking stick, and in that the piezo electric means are accommodated within a stem of the cane. 9. A method of treating muscular injuries below a body surface comprising applying to said surface a means of transmitting ultrasonic energy at a frequency in the range 20 - 120 kHz. 10. A method of diagnosing bone fractures comprising applying to a surface of a body containing said bone a means of transmitting ultrasonic energy at a frequency in the range 20 - 120 kHz.

Inventors: BRADNOCK BRIAN R D P, YOUNG MICHAEL JOHN RADLEY, BRADNOCK, BRIAN, ROBERT, DENIS, PETER, YOUNG, MICHAEL, JOHN, RADLEY
Applicants: BRADNOCK BRIAN R D P, YOUNG MICHAEL JOHN R, BRADNOCK, BRIAN, ROBERT, DENIS, PETER, YOUNG, MICHAEL, JOHN, RADLEY
Application year: 1993
Main classification: A61B19
IPC codes: A61B8, A61B17, A61F7, A61N7