Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-02-10
2003-09-23
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C601S002000
Reexamination Certificate
active
06623430
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to a non-invasive therapeutic ultrasonic system, and more particularly, to a system which is capable of acoustically imaging and heating a certain region to be treated (“the treatment region”) in target tissue for therapeutic purposes as well as acoustically monitoring the temperature profile of the treatment region. Further, the present invention relates to a method and apparatus for safely treating a region of body tissue using a single transducer and control unit to monitor and image a temperature profile of the tissue, and using the same transducer and control unit to melt a heat-activated, liposome encapsulated medicant disposed within the tissue.
2. Description of the Related Art
The absorption of energy in tissue, for example, in the human body produces an increase in temperature, which can be exploited for therapeutic purposes. The irradiation of ultrasound to the target tissue such as in the human body, which has been successfully used for decades mainly in increasingly sophisticated diagnostic imaging applications, also allows the target tissue to absorb a certain amount of energy. Thus, ultrasound may be used for therapeutic purposes.
Ultrasound encompasses any sound wave whose frequency is above the human hearing limit which is usually approximated at about 20 KHz. Since frequency and wavelength, and therefore resolution, are inversely related, the lowest sound frequency that is commonly used in imaging the human body is around 1 MHz with a constant trend toward higher frequencies in order to obtain better resolution. Weakening of ultrasonic signals increases with frequency in soft tissues.
In addition, ultrasonic energy at frequencies above 1.5 MHZ has an acoustic wavelength less than 1 mm in the human tissue. This energy is easily controlled in beamwidth and depth of penetration, and has a favorable absorption characteristic in the tissue. These aspects allow the energy to be precisely localized such that regions may be selectively heated while sparing overlying tissue structures.
Therefore, one must consider the exchange in benefits in the depth of penetration that must be achieved for a particular application of diagnostic imaging and the highest frequency that can be used. Applications that require deep penetration, such as cardiology and abdominal applications, typically use frequencies in the 2 to 5 MHz range. Others applications Such as ophthalmology and peripheral vascular applications require shallow penetration but high resolution. Frequencies up to around 20 MHz or higher are used for these types of applications.
Ultrasound has significant advantages for therapeutic applications as compared to micro-wave radio-frequency (RF) energy or optical energy (laser light). In contrast with ultrasound, RF energy is characterized by long wavelengths in tissue, with limited to poor control of energy deposition, and high absorption. These aspects of RF energy constrain its therapeutic usage for large superficial areas. On the other hand, the optical energy which is typically emitted from lasers can be precisely controlled in beamwidth, but the opacity and high absorption in tissue also limits its use to surface treatment or invasive procedures. Furthermore, laser and RF energy are emitted from ionizing radiation sources which are typically associated with some risk, unlike acoustic transducers which are typically used for generating ultrasound.
However, in contrast with the diagnostic uses, the therapeutic uses of ultrasound such as hyperthermia and non-invasive surgery have seen relatively little progress due to several technological barriers. The primary impediment has been a lack of the ability to monitor temperature in the treatment region during the therapeutic treatment process.
Specifically, one objective of the therapeutic application of ultrasound is to create a very well-placed thermal gradient in the target tissue to selectively destroy certain regions. For example, the hyperthermia technique typically requires maintaining tissue temperature near about 43 degrees Celsius, while the goal of non-invasive surgery is typically to elevate tissue temperature above and beyond about 55 degrees Celsius. Moreover, during the therapeutic treatment process, the physiological response of the target tissue is directly related to the spatial extent and temporal duration of the heating pattern. Consequently, in order to appropriately perform feedback and control of the therapeutic treatment process for obtaining successful results, it is absolutely essential to monitor the temperature in the target tissue, for example, so as to know whether or not the temperature in the treatment region has been raised to a level that produces a desired therapeutic effect or destruction in the tissue. In addition, it is preferable to know the temperature distribution in the treatment region and its vicinity for enhancing therapeutic effect.
In the conventional technique, the therapeutic ultrasonic system has typically relied upon thermocouple probes for monitoring the temperature in the treatment region and the vicinity thereof. However, the thermocouple probes are highly invasive because they have to be inserted into the region-of-interest. In addition, use of the thermocouple probes has necessarily led to very poor spatial resolution since only a small number of probes could be safely embedded in the region-of-interest. Furthermore, the embedded thermocouple probes are likely to disturb the acoustic propagation in the tissue and typically cause excessive heating at the probe interface during the therapeutic treatment process. This results in an undesirably modified temperature distribution as well as erroneous measurements.
Another factor which has curtailed progress in the therapeutic uses of ultrasound has been the design of the conventional acoustic transducers.
In general, for the therapeutic treatment process, imaging of the treatment region is necessary to determine the location of the treatment region with respect to the acoustic transducers as well as to evaluate progress of the treatment process. Such essential functions of imaging as well as the aforementioned temperature monitoring may be implemented with the same acoustic transducer to be used for therapeutic purposes, since the acoustic transducers can actually produce an image of the region-of-interest by employing well-established imaging techniques such as B-scan imaging. However, the conventional acoustic transducers which are typically employed for therapeutic purposes are acoustically large, often single-element devices having narrow bandwidth in the frequency domain. Although they are designed to efficiently transmit acoustic energy to the target tissue, the conventional acoustic transducers are typically unsuited for imaging of the treatment region and/or monitoring the temperature profile therein. This precludes development and implementation of these vital functions for performing a desirable precise therapeutic treatment process.
Some prior art references teach the use of ultrasound for therapeutic purposes. For example, U.S. Pat. No. 4,757,820 to Itoh discloses an ultrasound therapy system having functions of imaging and heating the target using ultrasound beams for therapeutic purposes. The system disclosed therein, however, does not include temperature monitoring of the target tissue (treatment region).
U.S. Pat. No. 5,370,121 to Reichenberger et al. discloses a method and apparatus for non-invasive measurement of a temperature change in a subject, in particular a living subject, using ultrasound waveforms. The method and apparatus disclosed therein, however, relies on a differential ultrasound image between two successive ultrasound images of the target. In other words, any temperature change is detected as a temperature-induced change in brightness between the two images, which appears in the differential image. Consequently, an actual real-time monitoring of the temperature may be difficult in the disclosed method and a
Barthe Peter G.
Lishko Valeryi
Slayton Michael H.
Guided Therapy Systems, Inc.
Lateef Marvin M.
Qaderi Runa Shah
Snell & Wilmer
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