Surgery – Diagnostic testing – Measuring electrical impedance or conductance of body portion
Reexamination Certificate
2000-09-19
2004-04-20
Shaw, Shawna J (Department: 3737)
Surgery
Diagnostic testing
Measuring electrical impedance or conductance of body portion
C128S920000, C705S003000
Reexamination Certificate
active
06725087
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to a method and apparatus for imaging the internal structure of biological tissue through the technique of electrical impedance tomography (“EIT”), and this invention specifically relates to a method and apparatus for remotely imaging the internal structure of biological tissue by acquiring raw data, transmitting same to a remote computer through a communications network, processing the raw EIT data at the remote computer and displaying an image of the internal structure of the biological tissue at said remote computer, at the location of data acquisition or at any other location.
BACKGROUND OF THE INVENTION
In the fields of medical diagnosis and research it is often necessary to visualize the internal tissue structures of biological subjects or patients which cannot be otherwise observed without invasive procedures. An example of an area where such visualization is helpful is in the detection, monitoring and analysis of tumors and other malignancies hidden inside the soft tissue of a subject or patient. When dealing with live subjects or patients it is usually not medically advisable or preferable to conduct an invasive procedure for diagnostic purposes unless there exists some prior indication that a particular feature, such as a tumor, is present in the tissue to be examined. In addition, even where there is knowledge or suspicion that a target feature exists, such a feature is sometimes located in an area which either cannot be reached through invasive procedures or would expose the subject or patient to undue medical risk should an invasive procedure be attempted. Moreover, invasive procedures expose subjects and patients to more generalized risks such as infection, bleeding, and other complications, which are not present with non-invasive visualization techniques. Finally, invasive procedures are almost invariably significantly more expensive and time-consuming than non invasive procedures.
Several non-invasive procedures have been developed to aid in the monitoring and visualization of internal structures found in biological tissue. Examples of such techniques are x-rays, ultrasound imaging, magnetic resonance imaging (“MRI”), computerized tomography (“CT”), and positron emission tomography (“PET.”) Another such imaging technique, the technique to which the subject invention is directed to, is electrical impedance tomography (“EIT.”) EIT relies on differences in bio-electrical properties within the target tissue to characterize different regions within it and subsequently output an image correlating to such characterization. Generally, an EIT scan is performed by placing a series of electrodes in a predetermined configuration in electrical contact with the tissue to be imaged. A low level electrical sinusoidal current is injected through one or more of the electrodes and a resulting voltage is measured at the remaining electrodes. This process may be repeated using different input electrodes, and electrical currents of different frequencies. By comparing the various input currents with their corresponding resulting voltages, a map of the electrical impedance characteristics of the interior regions of the tissue being studied can be imaged. It is also possible to map the impedance characteristics of the tissue by imposing a voltage and measuring a resulting current or by injecting and measuring combinations of voltages and currents. By correlating the impedance map obtained through an EIT scan with known impedance values for different types of tissues and structures, discrete regions in the resulting image can be identified as particular types of tissue (i.e., malignant tumors, muscle, fat, etc.)
Each of the above-mentioned imaging techniques has relative advantages and disadvantages, including varying abilities to image different types of tissue and structures at differing resolutions and different speeds. All modem imaging implementations, however, share one basic characteristic: they require equipment which is large, expensive and largely non-mobile, making it necessary for the subject or patient to be transported to a facility which houses the imaging equipment in order to have access to it.
For many reasons, some of which are herein detailed, it is desirable to be able to perform an EIT scan of a patient at a remote location, generate an image at a different location, and transmit the image back to the patient's location or to a physician or technician who may be located at yet a third site. In almost all situations, it is impractical from both an economic and logistical standpoint to transport current imaging equipment to a remote site where it is more convenient for the subject or patient for the imaging to be performed. Also, on occasion, it is impossible, due to health of the patient or subject and for other reasons, to transport the subject or patient to the facility housing the imaging equipment making it altogether impossible to perform imaging using currently available equipment and techniques. In addition, in some regions of the world there is very limited access, if any, to advanced imaging equipment, such as EIT, and to qualified physicians and/or technicians who can interpret the results of a diagnostic scan. For patients located in such regions it is impossible to receive the benefits of this type of diagnostic tool using existing equipment. Finally, the ability to perform EIT scans remotely, process images locally, and transmit resulting images to patients, technicians and/or physicians, carries the additional benefit of permitting a single server to operate as a central processing location for multiple scanning locations scattered anywhere within range of the communications network used to transmit data and images between the server and remote locations. Because the scanning equipment used for EIT imaging is relatively inexpensive in comparison with the image processing and generation equipment, the ability to service multiple scanners using one server has the potential to generate tremendous cost savings and efficiency gains.
Previous attempts have been made to provide remote capabilities to equipment used for imaging of biological tissue and structures such as described in U.S. Pat. No. 6,044,131 to McEvoy et al. ('131 patent); U.S. Pat. No. 6,006,191 to DiRienzo ('191 patent) and U.S. Pat. No. 5,851,186 to Wood et al. ('186 patent); all of which are incorporated herein by reference.
The '131 patent describes a security system for capture of x-ray images to a digital cassette which can download the images to a computer and assign them electronic signatures. The computer, in turn, can be directly connected to other computers via a modem or to a digital network of computers via a private communications link. Images on this system are accessible from remote locations by those who have proper authentication codes and have computers which have access to the private communications link. Although this system allows for electronic distribution of images to remote locations, x-ray systems such as this one inherently rely on large, expensive and non-mobile equipment to scan the subject or patient and to process the scanned data once it is digitized. As a result, this invention does not solve the problems associated with requiring a subject or patient to travel to a fixed location to be scanned. Moreover, because this system does not separate the data acquisition and processing functions, it is not possible to achieve the economic benefits of using a centralized data processing component to service multiple data acquisition components. Finally, the invention described by the '131 patent is limited to x-ray imaging which is not as effective as EIT in visualizing muscle and other soft tissues. Accordingly, the invention described in the '131 patent does not address or overcome the above-listed problems with existing imaging techniques.
The '191 patent describes a system for transmitting, storing, retransmitting and receiving electronic medical images and permits more
Otten David
Rubinsky Boris
Lott & Friedland, P.A.
Shaw Shawna J
Telectroscan, Inc.
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