Surgery – Truss – Pad
Patent
1995-05-30
1998-05-05
Bahr, Jennifer
Surgery
Truss
Pad
A61B 502
Patent
active
057462143
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the invention
This invention concerns investigation of a body. More specifically it is related to tomography and particularly to electrical impedance tomography or so-called EIT.
DESCRIPTION OF THE RELATED ART
EIT as currently developed (see B. H. Brown and D. C. Barber, Electrical ImpedanceTomography, Clin. Phys. and Physiol Meas. 13, Suppl. A., pp.207, 1992) uses an array of electrodes placed around a body, which is normally that of a human patient, to produce an image of changes in tissue resistivity or impedance. It has been shown that both cardiac and respiratory related changes can be imaged. The respiratory related changes arise mainly from the lungs but the cardiac related changes arise from the heart, the lungs and the major blood vessels. The changes from the heart arise from large changes in blood volume. The changes from the blood vessels are due mainly to changes in cross sectional area, and hence blood volume, as the pulse pressure changes. Changes from the lungs are also associated with blood volume changes as the pressure on systole increases the blood content of the pulmonary tree. EIT images of cardiac and respiratory related changes have been made at a single frequency within the range 20-50 kHz. International application W091/19454 describes a real-time EIT system applicable to the investigation of dynamic systems, such as the observation of blood flow in the human body during the cardiac cycle.
Several EIT research groups are now considering making images from measurements made over a range of frequencies, with a view to reducing the effects of body geometry on the images and also in the hope that tissue can be characterized in terms of how its impedance changes with frequency. Such work is described in, among other papers, P. M. Record, R. Gadd and F. Vinther, Multi-frequency EIT, Clin. Phys. and Physiol. Meas. 13, Suppl. A, pp.67-72(1992). H. Griffiths and Z. Zhang, Dual-Frequency Electrical Impedance Tomography in Vitro and in Vivo, Proc. 11th Ann. Conf. of the IEEE Eng. in Med. and Biol. Society, Vol. 11, 12 November 1989, pp. 476-477, similarly describes imaging using dual-frequency EIT.
SUMMARY OF THE INVENTION
The present invention derives from investigations of electrical impedance measurements made on the human trunk over a wide frequency range which have led to results of an unexpected nature. This work was directed towards the study of changes of impedance occurring over a change in the internal state of a body measured at different electrical signal frequencies.
According to the invention there is provided a method of investigation of a body comprising: body; measurements at the different frequencies; impedance measurements at the different frequencies after a change in the internal state of the body; and the first and second signals at the different frequencies.
The work referred to above and described in greater detail below has led to the surprising finding, hitherto not appreciated, that there can be a significant difference in the way in which impedance changes in a dynamic system vary with frequency, depending on which part of the system the impedance or impedance change is associated with.
More specifically, in the case of in vivo investigations of the human or animal body and considering impedances in the trunk of the body, as the frequency increases, the impedance change associated with the cardiac cycle falls considerably more rapidly than that associated with the respiratory cycle. This phenomenon has not anticipated by any studies hitherto made. The temporal change in impedance associated with different dynamic features of the body is found to be a function of frequency, the function depending on which dynamic feature the impedance change is associated with.
In most cases, the change in an internal state of the body is a change in the geometry of at least a part of the body. For example, in the human body, such changes may be changes in the cross sectional area of blood vessels due to a pulsatile blood flow. Alterna
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Barber David Charles
Brown Brian Hilton
Bahr Jennifer
British Technology Group Limited
Gilbert Samuel
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