1. Field
The invention pertains to a sonic resonator system for use in biomedical applications. The invention also pertains to a method of calibrating the sonic resonator system and to methods of using the sonic resonator system in various biomedical applications.
2. Description of the Background Art
This section describes background subject matter related to the disclosed embodiments of the present invention. There is no intention, either express or implied, that the background art discussed in this section legally constitutes prior art.
There are numerous non-invasive biomedical procedures which can benefit from the use of high intensity, wide bandwidth ultrasonic impulses. Conventional technology is capable of delivering high sonic intensities as a sonic shock wave or as a continuous sonic wave (CW), where conventional devices deliver high intensities of sonic energy focused to a point in space. There exist several methods of achieving this spatial focus, including the shaping of piezoelectric elements.
One example of such a piezoelectric element is a high-intensity focused ultrasound (HIFU) transducer, which is shaped to form a spherical lens to focus the sonic energy. FIG. 1 shows this concept, where the diagram 100 shows a transducer 102 shaped to form a spherical lens 104, to produce focused energy at a point in space 106. In another embodiment (not shown), a plurality of sonic elements having a desired shape can be arranged in a mosaic in order to achieve mechanical focus. An array of elements could have any shape (e.g., flat); the elements are then “fired” with the appropriate delay in order to create a focus and/or steer the beam. This is known as a “phased array”.
In an even older example, lithotripters utilize a concave mirror to focus the energy from a “spark plug” sonic source. In all of these earlier examples, focus is achieved by an array of elements and/or the physical construct of the sonic device; for example, by forming the piezoelectric element to have a particular shape, using a lens assembly or by electronic delay of the excitation pulses (e.g., a phase array) to focus the sonic energy to a specific point in space.
When piezoelectric elements are used to achieve spatial focus, high intensity sonic impulses are typically achieved by applying a high voltage impulse across the piezoelectric element. There are limits to the voltage that can be applied and, hence, to the resulting sonic amplitude. If the voltage is too high, it can “de-pole” the ceramic of the piezoelectric element, arc across the piezoelectric element, or produce a strain so high that it fractures the piezoelectric element. These and other effects limit the maximum amplitude sonic pulse that can be generated using conventional methods.
Another practical limitation of the current technology is that higher sonic intensities are generated using narrow bandwidth transducers operating over a narrow frequency range in a resonant continuous wave (CW) mode. However, wide bandwidth impulses of high sonic intensity cannot be generated using narrow bandwidth devices. In medical applications, there are several advantages in having the ability to generate an impulse having a wide bandwidth. Conventional continuous wave (CW), fixed-focus sonic devices cannot deliver a high intensity impulse that can create very high sonic pressures with short duration particle velocities.
In general, broadband sonic performance has been achieved at the expense of efficiency. This broadband performance might be achieved by absorbing a portion of the generated sonic energy in the transducer to damp the resonance. Or, the broadband performance might be accomplished by operating the transducer far from its natural resonance, where its ability to generate large amplitude sonic signals is poor.
The following are descriptions of various biomedical methods and apparatus known in the art:
U.S. Pat. No. 5,143,063, to Fellner, discloses electromedical apparatus which is employed to non-invasively remove adipose tissue from the body by causing necrosis of the tissue, by localizing (e.g., focusing) radiant energy. The radiant energy may be of any suitable kind, for example, localized radiofrequency, microwave, or ultrasound energy, which is impinged upon the cells to be eliminated. Cell destruction occurs through a mechanism such as heating or mechanical disruption beyond a level which the adipose tissue can survive. (Abstract)
U.S. Pat. No. 5,827,204, to Grandia et al., discloses medical noninvasive operations using focused modulated high power ultrasound, which generally includes a transmitter for exciting a multifrequency ultrasound wave for causing vaporous cavitation bubbles in a small focal zone of a medical target region. A low frequency signal is induced at a level slightly below that required for causing cavitation and a high frequency signal is superimposed on the low frequency signal to exceed the cavitation threshold. Focused ultrasound is said to be used for both dissolving tissues, as well as causing clots in order to destroy cancerous growths. In addition, an imaging system is provided for enabling viewing of the medical target area during the therapy. (Abstract and Col. 2 lines 26-32)
U.S. Pat. No. 6,071,239, to Cribbs et al., discloses non-invasive destruction of fat cells in a living patient, without separating the skin from the body, by applying to the fat layer high intensity focused ultrasound simultaneously in a multiplicity of discrete focal zones produced by a single transducer array. A phasing apparatus for producing a widely variable set of focal zone patterns for lipolytic therapy and other purposes is disclosed. (Abstract)
U.S. Pat. No. 6,607,498, to Eshel, discloses a method and apparatus for producing lysis of adipose tissue underlying the skin of a subject by applying an ultrasonic transducer to the subject's skin to transmit therethrough ultrasonic waves focused on the adipose tissue, and electrically actuating the ultrasonic transducer to transmit ultrasonic waves to produce cavitational lysis of the adipose tissue without damaging non-adipose tissue. (Abstract)
U.S. Pat. No. 6,716,184, to Vaezy et al., discloses a method and apparatus for the simultaneous use of ultrasound on a probe for imaging and therapeutic purposes. The probe limits the effects of undesirable interference noise in a display by synchronizing HIFU waves with an imaging transducer to cause the noise to be displayed in an area of the image that does not overlap the treatment site. In one embodiment, the HIFU is first energized at a low power level that does not cause tissue damage, so that the focal point of the HIFU can be identified by a change in the echogenicity of the tissue caused by the HIFU. Once the focal point is properly targeted on a desired treatment site, the power level is increased to a therapeutic level. The location of each treatment site is stored and displayed to the user to enable a plurality of spaced-apart treatment sites to be achieved. A preferred application of the HIFU waves is to cause lesions in blood vessels, so that the supply of nutrients and oxygen to a region, such as a tumor, is interrupted. The tumor will thus eventually be destroyed. (Abstract)
U.S. Pat. No. 7,258,674, to Cribbs et al., discloses a system for the destruction of adipose tissue utilizing HIFU within a patient's body. The system comprises a controller for data storage and the operation and control of a plurality of elements. One element is a means for mapping a human body to establish three-dimensional coordinate position data for existing adipose tissue. The controller is able to identify the plurality of adipose tissue locations on the human body and establish a protocol for the destruction of the adipose tissue. A HIFU transducer assembly having one or more piezoelectric element(s) is used along with at least one sensor, wherein the sensor provides feedback information to the controller for the safe operation of the piezoelectric element(s). The sensor is electronically coupled to the controller, and the controller provides essential treatment command information to one or more piezoelectric element(s) based on positioning information obtained from the three-dimensional coordinate position data. (Abstract)
U.S. Pat. No. 7,347,855, to Eshel et al., discloses a methodology and system for lysing adipose tissue including directing ultrasonic energy at a multiplicity of target volumes within the region, which target volumes contain adipose tissue, in order to selectively lyse the adipose tissue in the target volumes and generally not lyse non-adipose tissue in the target volumes, and computerized tracking of the multiplicity of target volumes notwithstanding movement of the body. (Abstract)
U.S. Pat. No. 7,510,536, to Foley et al., discloses a method for using HIFU to treat neurological structures to achieve a desired therapeutic effect. Depending on the dosage of HIFU applied, it can have a reversible or irreversible effect on neural structures. For example, a relatively high dose of HIFU can be used to permanently block nerve function, to provide a non-invasive alternative to severing a nerve to treat severe spasticity. Relatively lower doses of HIFU can be used to reversibly block nerve function, to alleviate pain, to achieve an anaesthetic effect, or to achieve a cosmetic effect. Where sensory nerves are not necessary for voluntary function, but are involved in pain associate with tumors or bone cancer, HIFU can be used to non-invasively destroy such sensory nerves to alleviate pain without drugs. (Abstract)
The disclosures of the above-cited references are hereby incorporated by reference herein in their entireties.