Monitoring apparatus for resonant circuit intracranial pressure implants
First Claim
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1. Apparatus for monitoring an implanted circuit means whose resonant frequency provides indication of a selected physiological activity, comprising:
- an RF sweep frequency generator means for generating an output RF signal whose frequency varies in a predetermined manner throughout an operating frequency range encompassing the resonant frequency of said implanted circuit means,a transmission line having one input end connected to receive the RF signal from said sweep frequency generator means, said transmission line having a predetermined characteristic impedance,a resistance means connected across the opposite output end of said transmission line and having a resistance value matching the characteristic impedance of said transmission line to minimize the standing wave ration of said transmission line,a parallel resonant inductor-capacitor circuit connected across the output end of said transmission line in parallel with said resistance means and adapted to be brought into coupling relationship to said implanted circuit means,said parallel connected resistance means and resonant circuit producing a constant broadband response throughout the operating range of said RF sweep frequency generator and a constant value RF voltage across said parallel resonant circuit when not coupled to said implanted circuit means,a maximum energy transfer occurring between said parallel resonant circuit and said implanted circuit means, when coupled, when the output signal generated by said RF sweep frequency generator corresponds to the resonant frequency of said implanted circuit means, said maximum energy transfer resulting in a minimum value RF voltage being produced across said parallel resonant circuit denoting the resonant frequency of said implanted circuit means,detector means for converting the RF voltage appearing across said parallel resonant circuit to a corresponding DC voltage, andindicator means responsive to the value of said DC voltage.
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Abstract
The invention relates to interrogation, detection, and monitoring apparatus useful for monitoring changes in the resonant frequency of a passive L-C circuit implanted in the cranium, the resonant frequency of the implanted circuit varying in a predetermined fashion with changes in the intracranial pressure. The present invention is disposed externally of the skull and provides apparatus for imposing electro-magnetic radiation on the implanted circuit, the frequency at which the radiation is absorbed being then detected and converted into an indication of intracranial pressure.
121 Citations
6 Claims
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1. Apparatus for monitoring an implanted circuit means whose resonant frequency provides indication of a selected physiological activity, comprising:
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an RF sweep frequency generator means for generating an output RF signal whose frequency varies in a predetermined manner throughout an operating frequency range encompassing the resonant frequency of said implanted circuit means, a transmission line having one input end connected to receive the RF signal from said sweep frequency generator means, said transmission line having a predetermined characteristic impedance, a resistance means connected across the opposite output end of said transmission line and having a resistance value matching the characteristic impedance of said transmission line to minimize the standing wave ration of said transmission line, a parallel resonant inductor-capacitor circuit connected across the output end of said transmission line in parallel with said resistance means and adapted to be brought into coupling relationship to said implanted circuit means, said parallel connected resistance means and resonant circuit producing a constant broadband response throughout the operating range of said RF sweep frequency generator and a constant value RF voltage across said parallel resonant circuit when not coupled to said implanted circuit means, a maximum energy transfer occurring between said parallel resonant circuit and said implanted circuit means, when coupled, when the output signal generated by said RF sweep frequency generator corresponds to the resonant frequency of said implanted circuit means, said maximum energy transfer resulting in a minimum value RF voltage being produced across said parallel resonant circuit denoting the resonant frequency of said implanted circuit means, detector means for converting the RF voltage appearing across said parallel resonant circuit to a corresponding DC voltage, and indicator means responsive to the value of said DC voltage. - View Dependent Claims (2, 3, 4, 5, 6)
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Current AssigneeJohns Hopkins University
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Original AssigneeJohns Hopkins University
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InventorsSeylar, George R.
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Primary Examiner(s)Kamm, William E.
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Assistant Examiner(s)Jaworski, Francis J.
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Application NumberUS05/741,231Time in Patent Office676 DaysField of Search128/2 P, 128/2.0 SE, 128/2.1 A, 128/1.5, 128/419 R, 73/410, 73/67.4, 73/4, 73/304 C, 73/718, 73/724, 73/728, 324/57 SS, 324/57 Q, 324/58.5 B, 324/61 QS, 324/61 QL, 324/58.5 C, 324/58.5 DUS Class Current600/409CPC Class CodesA61B 5/0031 Implanted circuitryA61B 5/031 Intracranial pressureY10S 165/401 including tube support or s...
