The present invention relates to an improved medical appliance for ultrasonic therapeutic treatment and/or other operation upon living body tissue.

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 to 30 years. However, prior to our application GB 2274996A, which does disclose treatment apparatus operating in the kHz band, we found no relevant reference to the use of frequencies in the range 30 to 100 kHz.

It is known that ultrasound therapeutic radiation in the MHz band has beneficial effects when treating soft tissue injuries, and that such emissions are absorbed to differing degrees in different types of living tissue.

This characteristic limits to some extent the scope for treating certain types of injury since in order to transmit adequate intensities of radiation to a deep injury, potentially harmful levels would have to be introduced into the outer tissue layers. In order to overcome this problem of natural attenuation at greater depth of injury, we have previously proposed to use long wave radiation in the 45 to 50 kHz band, which gives correspondingly improved transmission characteristics. This is described in our application GB 2274996A.

The use of frequencies in the MHz band 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 focused beam. However, it is often necessary to apply a broader range of treatment, and in this case, a mixture of comparatively higher and lower frequency vibrations is to be desired. For example, the characteristic wavelength corresponding to a 3 MHz transmission through soft tissue is about 0 5 mm; but at 40 kHz, the wavelength would be approximately 37 5mm.

The combination of wavelengths, however achieved, will give a more even distribution of energy within the tissue being treated. Also, in cases where only local treatment, or treatment of an area close to the surface, is required, there is still a need for a treatment device which can selectively treat chosen areas

However, since 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 may therefore be concluded that, tor a given power input, it is preferred to use a 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 Tor this reason, energy levels are limited by the requirement that intensity should not exceed 3 watts/cm ² .

Furthermore, conventional high frequency systems produce columnar energy beams which can lead to a danger of standing waves, internal reflection and consequent hot spots in irradiated tissue. In contrast to this, long wave length transmissions give a spherical wave front with diverse propagation characteristics and little or no risk of standing waves

It is an object of the present invention to combine the benefits associated with long wave length treatment with those associated with shorter wave length treatment

According to a first aspect of the present invention there is provided an apparatus to treat

muscular injuries within or below a body surface or to diagnose bone fractures, wherein the device comprises piezo electric means to generate ultrasonic energy, said piezo electric means comprising at least two generator means each adapted to deliver energy at a different frequency between 10 kHz and 4 MHz, at least one application head adapted to be applied closely to the body surface and to deliver thereto energy from either one or more of said generator means, said at least one application head being adapted to transfer said ultrasonic energy into the body of the patient

Preferably, a first generator means provides energy at a frequency of between, 10-l lOkHz, advantageously 20 to 100 kHz, optionally in the region of 45 kHz.

Advantageously, a second generator means generates energy at a frequency in the region ot, 0 5 to 4 MHz, advantageously, 0 5 to 3 MHz, optionally in the region of 1 MHz

In one preferred embodiment of this aspect of the invention, the second generator means is located adjacent a treatment surface of the apparatus.

In another preferred embodiment each generator means is located adjacent a treatment surface of the apparatus

According to a second aspect of the present invention, there is provided an apparatus to treat muscular injuries below a body surface or to diagnose bone fractures, wherein the device comprises piezoelectric means to generate ultrasonic energy, said ultrasonic energy being delivered in the form of a relatively low frequency carrier wave onto which carrier wave is superimposed ultrasonic energy at a higher frequency, an application head 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.

Preferably the carrier wave has a frequency between 10 kHz and 1 10 kHz onto which carrier wave is superimposed ultrasonic energy at a higher frequency in the range of 0.5 to 4 MHz

Advantageously, the frequency of the carrier wave is 20 - 100 kHz.

The frequency of the superimposed wave is preferably 0.5 - 3 MHz.

The low frequency carrier wave may be a square wave.

Alternatively, the low frequency carrier wave may be a sinusoidal wave.

Other wave forms are possible for the carrier wave.

The superimposed high frequency wave form is preferably sinusoidal, but again other forms can be used.

The application 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 to 100 kHz, with relatively low energy absorption. The head is machined from plastics material which is chosen because its specific impedance (W) closely matches that of human soft tissue.

As an example, acetal may be used, in which case applicable figures are:

W _acelal = 1.86 x 10 ⁶ kg m sec ^l ; _{soft tlssue} = 1.65 x 10 ⁶ kg m sec ' .

According to a third aspect of the present invention, there is provided a method of treating muscular injuries or of diagnosing bone fractures comprising applying to an external surface of the tissue a two component source of energy, each component having a different frequency in the range between 10 kHz and 4 MHz.

According to a fourth aspect of the present invention, there is provided a method of treating muscular injuries or of diagnosing bone fractures comprising the steps of applying to an external surface of overlying tissue an application head and transmitting there through an ultrasonic wave comprising a low frequency carrier wave onto which is superimposed a high frequency transmission.

According to a fifth aspect of the present invention, there is provided a method of treating deep seated muscular injuries or of diagnosing bone fractures comprising the steps of applying to an external surface of the tissue an application head which comprises a first member capable of emitting energy at a comparatively low frequency, optionally in the region of between 10 and 1 10 kHz and applying also energy generated by a second piezo electric source at a frequency in the region of 0.5 to 3 MHz.

Embodiments of the invention will now be described more particularly by way of example and with reference to the accompanying drawings, in which :

Figure 1 is a graphical representation of the velocity and stress distributed along the axis of a transducer and head of the invention, wuh indication of the travelling wave amplitude in the head:

Figure 2 is a schematic view of an appliance comprising a piezoelectric transducer and head assembly, to the same scale of overall length as the dimension x of Figure 1 ;

Figure 3A shows schematically means for driving an ultrasonic transducer;

Figure 3B shows schematically a combined wave form where the carrier wave is a square wave and the superimposed wave is a sinusoidal high frequency wave;

Figure 4A shows schematically in cross section treatment head means to generate coaxially combined wave form;

Figure 4B shows schematically an end view of the apparatus of Figure 4A;

Figure 5 A shows a more detailed view in cross section of the embodiment of Figure 4:

Figure 5B shows an end view corresponding to Figure 5 A;

Figure 6 is a cross sectional view of an apparatus embodying the invention;

Figure 7 shows a test apparatus utilising the invention;

Figure 8 A shows a beam profile generated by apparatus of the present invention, whilst

Figure 8B shows an unacceptable beam profile with an intense central peak;

Figures 9 to 13 show the results of tests determining heat and therefore energy distribution within porcine muscle tissue for higher and lower frequency ultrasonic emissions together with the results of comparative examples; and

Figure 14 shows the high frequency element beam profile.

Referring now to the drawings, Figure 2, shows a vibrator in the form of a PZT sandwich transducer incorporating a backplate 5, PZT ceramic rings 2 (piezoelectric transducer means), an electrode 3 and a stepped output section 4. This vibrator transmits waves at a

RECTIFIED SHEET (RULE 91) IS

predetermined frequency through a shaped plastics head 6 into tissue 8 via a coupling medium 7. This is known from our previous patent application no. GB 22 74996A.

Figure 1 shows a waveform in the system. A standing pressure wave is established in the transducer with output amplitude at 9, and this is transmitted through a shaped therapy head 6, emerging as a travelling wave of amplitude _LM . The velocity and pressure-wave amplitudes (stress) in the plastics 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, but an overall rounded shape is preferred.

In operation, the energy transmitted to the subject tissue must not result in standing waves since this might cause excessive local absorption.

Referring now to Figures 4 to 6, separate piezoelectric means are provided to generate the low frequency and the high frequency energy supplied by the head. In this embodiment, piezoelectric means 2 generate a comparatively low frequency which is transmitted via the standard head 6 to the tissue to be treated.

Embedded within the head 6, and possibly but not generally conforming to its general frontal curvature is a second piezoelectric means 10 adapted to generate energy at a comparatively higher frequency. This is powered by electric leads passing through the centre of the head 6 and through an aperture in the handle. This second piezoelectric generator is separated from the head by means of an air gap 1 1 and by means of 0-rings 20. In this embodiment, the frequency applied to the tissue surface by the main surface of the head 6 is in the region of 45 kHz, whilst the energy supplied by the insert piezoelectric transducer 10 is in the region of 1 MHz. As can be seen from Figure 6, a separate head 12, within the overall head 6, is provided. This may be of titanium or aluminium or an alloy thereof, and is preferably of diameter 10mm +. 0.5mm. The radius of curvature is most usually smaller than the radius of curvature of the main head 6. As discussed below, it is believed that such an arrangement will give a more advantageous beam profile.

Indeed, as may be seen from Figures 8A and 8B, the beam profile is particularly important and the relative radii and sizes of the two heads 6 and 12 do have an effect on such profile, as well of course as the frequency transmitted by each of them.

An ideal beam profile is near rectangular in order to avoid or minimise unwanted and potentially dangerous wave reinforcement in the near field zone.

The beam profile may be controlled by containing the piezo ceramic driver in a metal holder, the geometry of which is chosen carefully to avoid vibrational antinodes which could possibly generate local high amplitude movement.

Switch means may be provided to activate one or other or both of the piezoelectric transducers When both are utilised concurrently, treatment of a wide range of subcutaneous conditions is possible given the potential for more even deposition of energy throughout the tissue to be treated.

As an alternative, it would be possible to interleave the signals so that, for example a short period, say one millisecond of long wavelength input, is interspersed by a short period, say one millisecond, of short wavelength radiation

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.

The effect of this technique is to enhance the absorption rate in an area of tissue penetrated by the long wavelength transmissions. The carrier wave is not focused and the amplitude of the superimposed high frequency wave form is relatively low and persists through a greater tissue depth than it would in its pure form. Due to the naturally greater rate of absorption at high frequencies, it is possible to enhance the energy delivered to an area of deep tissue

It is of course possible to vary both the frequency and amplitude of the carrier wave form and the superimposed wave form to provide an optimum delivery characteristic.

It is also possible to control the ultrasonic transmission so that the high frequency element can be switched in or out of the treatment program as required.

Examples

Performance testing was carried out on a prototype Ultrasound Diathermy Device which addressed the heating ability at depth in a phantom.

Low-Frequency Characteristics

Frequency 45 kHz ± 5 %

ERA 13.5 cm ²

BNR 6.5

Beam Type Diverging

Power Settings 0.4 W, 0.6 W, 1 W

Mode Continuous

High-Frequency Characteristics

Frequency 1 MHz ± 5 %

ERA 0.9 cm ²

BNR { 5.0

Beam Type Diverging

Power Settings 0.5 W, 1W, 2W

Mode Continuous and Pulsed (20% duty cycle)

General

The timer has an accuracy for different settings of:

Less than 5 minutes ± 1.7%

5 - 10 minutes ± 0.7%

Greater than 10 minutes ± 0.5 %

The maximum timer setting is 30 minutes.

NOTE: The Beam Non-Uniformity Ratio (BNR) is a measure of the variation in power density across the effective radiating area of the applicator. The unique coaxial design of the device was evolved by independent measurement of each transmitting source.

Diathermy Effects

Referring to the apparatus shown in Figure 7 which was used to examine experimentally the effects in porcine muscle of ultrasonic vibration at frequencies of 45 kHz and 1 MHz, a container is 25 is held to an ultrasound handset by an adaptor 26. Within the container 25 is a transmission medium 27 comprising de-gassed water, caster oil and porcine muscle tissue, sealed by membrane 28 at a remote end of the container. A temperature recorder 30 keeps a record of the temperatures measured by a thermocouple 29 at various distances from the head.

Referring now to Figures 9 to 13, tests on heating ability on phantoms were carried out for the device and for a comparative device, with a 1 cm applicator. All the graphs are plotted according to an average of three runs to show the temperature rise at depths in pig muscle. These tests demonstrate that the device embodying the invention operating at a maximum output provides equal or better heating characteristics than the Mettler 720 at maximum output at all depths measured. The statement that the device has equal or better heating characteristics does not mean that more heat is deposited at all depths than the Mettler, because the Mettler definitely causes more surface heating than the device. However, surface heating is an unwanted side effect in diathermy as it tends to limit the amount of heating at depth that can be achieved because of the limits of patient tolerance of surface heating.

First, the device was evaluated under three conditions in a phantom containing pig muscle:

(1) 45 kHz alone @ 1W

(2) 1 MHz alone @ 2W

(3) 45 kHz @ 1W plus 1 MHz @ 2W (simultaneously)

The results, shown in Figure 9, demonstrate the advantages of dual frequency treatments. Note that while the treatment at 1 MHz alone deposits six times the energy of the 45 kHz treatment at 2 cm depth (three times, on a per watt basis), deeper in the phantom at 5 cm depth, the 45 kHz treatment actually deposits twice the

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energy of the 1 MHz treatment, in spite of having only half the output power As can be readily seen from the graphs, the energy deposited at depth by the 45 kHz component is obtained at a small cost in surface heating This results in much better heating performance for the dual frequency treatment beyond 4 cm depth than can be obtained with the 1 MHz component alone.

The device with only the 1 MHz channel activated (at 2 W) provides heating profiles that are similar to those of a conventional device (one operating at 1 MHz operating at 2 W, which can be compared with the device at 1 MHz alone (also at 2 W) in Figure 10 Note that the heating pattern at depth is qualitatively similar for the two devices, though because ot differences in beam divergence characteristics, they are not identical

The dual-frequency treatment heating performance ot the device at maximum output may be compared directly with a conventional 1 MHz device operating at 2 W (its maximum) in Figure 1 1 While the heating caused by the two devices is similar at 3 cm depth, the device embodying the invention produces three times the heating at 5 cm depth than does the conventional device Note that the increased penetration ot energy is obtained at less "cost" in surface heating.

These data demonstrate that the device has heating characteristics that are equal to or better than those ot a conventional device with I cm applicator