Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-06-08
2003-03-25
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S437000, C029S025350
Reexamination Certificate
active
06537224
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ultrasonic imaging probes designed for medical applications, and, more particularly, to an improved probe wherein diagnosis and high intensity ultrasound modalities are combined in the same apparatus.
2. Related Art
Ultrasound is used in many different domains for purposes of inspection and medical diagnosis. Transducers capable of sending and receiving ultrasonic energy are commonly made from a piezoelectric material such as a ceramic, crystal or co-polymer which reacts to produce an output in response to electrical or mechanical stress. Until now, imaging modalities are often segregated from Doppler, therapy or treatment modalities because low intensity ultrasound propagating at high frequency is highly attenuated by the tissue being diagnosed and this results in low efficiency Doppler operation. Such low intensity, high frequency ultrasound produces no therapeutic or damaging (non-ionizing) effects on the tissue under test and because of this non-ionizing characteristic, ultrasound is the preferred diagnostic modality for fetus and pediatric applications.
Another factor which governs ultrasonic transducer characteristics is the energy transfer of the ultrasonic transducer device. In this regard, the energy conversion factor of the transducer device is substantially constant and depends on the type of piezoelectric material employed therein. Thus, a balancing exercise must be used by the designer in determining the best compromise between bandwidth and transducer sensitivity. Otherwise, most transducers can be designed to exhibit broad bandwidth operation but only at the expense of low sensitivity in that frequency range.
Typically, an imaging ultrasonic transducer has maximum bandwidth (obtained through the use of low quality factor piezoelectric material) in order to cover the expanded frequency range of the signal being returned through the propagation medium. Moreover, the higher the frequency of transducer, the better the image. When the transducer is used in Doppler operation, the frequency of transducer should be determined based on the velocities of the test object and the depth of the region to be explored. In general, the Doppler frequency is always lower than the associated imaging frequency so as to improve the sensitivity of the received signals.
With regard to high intensity ultrasound, if a therapeutic effect is to be produced in the sonified region, the power of the transmitted ultrasonic energy must be increased in proportion, thereby resulting in heating of the region of tissue of concern. Because conventional imaging transducers are designed with a maximized bandwidth, the application of high power electrical energy to the low quality factor-based transducers used for imaging will rapidly destroy the corresponding transducer because of excessive heating of the transducer core. As a consequence, considering the situation described above, supplying high intensity ultrasonic energy to the tissue under diagnosis dictates the use of a transducer of a particular construction, e.g., a transducer made from high quality factor piezoelectric material, as well as lowering of the frequency used, and, if necessary, cooling of the active transducer material by addition of a heat-sink or an active cooling system.
A further aspect of the application of ultrasound which was not discussed above concerns the new advanced imaging mode referred to as harmonic imaging. In this mode, the transducer must be capable of emitting ultrasound at a fundamental frequency and receiving returned echoes at two, or more, times this frequency. Further, in the case where contrast agents are injected in the blood flow, the transducer must be driven to produce a high power emission in order to collapse micro-bubbles in the contrast agents prior to receiving non-linear responses from the region of interest. It is preferable to control collapsing of the contrast agents by using another transducer operated at a lower frequency specifically tailored for this purpose.
It will be understood from the foregoing that implementing different modalities, such as imaging, Doppler or therapy operations, requires many changes between various probes. This is time consuming and, furthermore, is sometimes impossible, as a practical matter, when scanning of the image is required in guiding the operation to be carried out.
The prior art includes a number of references wherein plural functionalities are combined in the same transducer probe. In U.S. Pat. No. 4,492,120, to Lewis et al., a transducer assembly is provided which comprises separate imaging and Doppler transducers. Each transducer is independently damped according to the performance criteria of the corresponding function. The imaging transducer may be of a linear array type and the Doppler transducer is assembled on the sides of the imaging transducer. Such a construction results in a significant increase in the length of the resultant transducer device and further, the Doppler acoustic pattern is not necessarily included in the image. In general, this concept has now been abandoned and replaced by a technique wherein an array of elements are driven as Doppler transmitter—receivers alternately with an imaging mode of operation.
In U.S. Pat. No. 5,195,519 to Angelsen, a dual function probe is provided, similarly to the Lewis et al. patent. In one of the aspect of the Angelsen patent, the probe is comprised of a steering transducer having double emitting faces. Each face is supplied with a selected frequency so as to be compatible either with an imaging mode or with a Doppler mode. This construction is limited to single element transducers and requires a coupling bath to be operable.
U.S. Pat. No. 4,097,835, to Green, discloses a moving pair or set of focused transducer members which are movable along linear paths. Each transducer member is of a semi-circular shape so the pair taken together forms a circular surface. A first semi circular transducer can be used for B-mode imaging while the second is dedicated to Doppler functions. Because the transducers are completely separated, interference between signals produced during the imaging and Doppler modes can be avoided. However, such a configuration results in a dramatically inferior lateral resolution of the image as well as in substantially inferior Doppler spatial measurements.
U.S. Pat. No. 3,952,216, to Madison et al., discloses a multi-frequency transducer including a first transducer array operating at low frequency and a second transducer array operating at high frequency. The second transducer array is located at the front of device with the first transducer array being disposed there behind. For both transducer arrays, the arrays are formed by a plurality of single elements connected in parallel, and each single transducer element is formed by sandwiching together a plurality of piezoelectric layers. The high frequency transducer array, is used in transmitting high frequency waves in the propagating medium while the low frequency transducer array is dedicated to reception of the low frequency response obtained from the difference of the two consecutive transmitted pulses. Ultrasonic transducers of this type are well adapted for sonar (underwater) applications where the bandwidth is very narrow and sensitivity must be absolutely preserved. However, such transducers are not suitable for high resolution imaging applications and do not employ a multi-element construction.
A further multi-layer transducer construction is disclosed in U.S. Pat. No. 5,957,851, to Hossack, wherein the transducer is comprised of first and second piezoelectric layers, and the second layer is disposed on the first layer. The first and second layers are separately driven and signals from one, or the other, may be isolated each other. The combination of the two layers enables transmission of ultrasonic waves that are controlled in frequency. Echoes returned from the area of examination can be analyzed by either the first or the second piezo
Flesch Aime
Mauchamp Pascal
Jaworski Francis J.
Jung William C.
Larson & Taylor PLC
Vermon
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