QRS filter for real time heart imaging with ECG monitoring in the magnetic field of an NMR imaging system and NMR imaging apparatus employing such filter
First Claim
1. A QRS signal filter for use in real time with an NMR imaging system with negligible delay between the image and the filtered signal, said QRS signal having a given frequency range, said filter comprising:
- a low pass filter for attenuating those portions of the QRS signal applied as an input and having a frequency above said given range to produce a first output signal, said low pass filter including means for imposing a first given phase shift on said output signal relative to said input signal; and
a high pass filter responsive to said output signal applied as an input thereto for attenuating those portions of an input signal applied thereto below said given range to produce a second output signal, said high pass filter including means for imposing a second given phase shift relative to the phase shift of the first output signal, said low and high pass filters being arranged so that said first and second phase shifts substantially cancel one another such that there is negligible time delay between said QRS signal applied to the low pass filter and said second output signal.
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Accused Products
Abstract
A pair of Butterworth 4th order filters are cascaded with an absolute value filter to filter the QRS wave of an ECG signal generated in a magnetic field of an NMR imaging system. The NMR system includes a magnet for producing a static BO field and a set of coils for producing RF pulse induced fields in which an ECG monitoring system is located. The ECG monitoring system transmits the resultant QRS waves to a receiver which processes the received signals and applies the received signals to a display via the above filters. The -3 dB point of the high pass filter is at about 10 Hertz to filter the T-wave and Bo field induced breathing artifacts and the -3 dB point of the low pass filter is about 20 Hertz to filte the high frequency components of pulsed static field gradient noise created by the NMR system.
35 Citations
15 Claims
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1. A QRS signal filter for use in real time with an NMR imaging system with negligible delay between the image and the filtered signal, said QRS signal having a given frequency range, said filter comprising:
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a low pass filter for attenuating those portions of the QRS signal applied as an input and having a frequency above said given range to produce a first output signal, said low pass filter including means for imposing a first given phase shift on said output signal relative to said input signal; and a high pass filter responsive to said output signal applied as an input thereto for attenuating those portions of an input signal applied thereto below said given range to produce a second output signal, said high pass filter including means for imposing a second given phase shift relative to the phase shift of the first output signal, said low and high pass filters being arranged so that said first and second phase shifts substantially cancel one another such that there is negligible time delay between said QRS signal applied to the low pass filter and said second output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A QRS signal filter for use in real time with an NMR imaging system with negligible delay between the image and the filtered signal, said QRS signal being produced in the magnetic field of said system and having a given frequency range, said filter comprising:
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a low pass filter responsive to said QRS signal applied as an input thereto and having about a -3 dB response at least about 20 Hertz and a response characteristic of about -24 dB per octave to produce a first output signal, said low pass filter including means for imposing a first given phase shift on said output signal relative to said input signal; a high pass filter responsive to said output signal applied as an input thereto to produce a second output signal, said high pass filter having about a -3 dB response at most about 10 Hertz and a response characteristic of about -24 dB per octave, said high pass filter including means for imposing a second given phase shift relative to the phase shift of the first output signal, said low and high pass filters being arranged so that said first and second phase shifts substantially cancel one another at a given frequency such that there is negligible time delay between said QRS signal applied to the low pass filter and said second output signal; and full wave rectifier means for rectifying said second output signal. - View Dependent Claims (11)
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12. An NMR imaging system comprising:
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magnet means for exposing a patient to a magnetic field, said patient creating signals in response to said magnetic field; imaging means responsive to said patient signals for creating an image of a patient in said field; and transmit and receive means for creating a patient QRS signal of a given frequency range in said magnetic field and for transmitting the QRS signal to said receive means; said receive means including QRS signal filter means such that the image produced by said imaging means and said QRS signal are substantially in phase; said filter means comprising; a low pass filter for attenuating those portions of the QRS signal applied as an input and having a frequency above said given range to produce a first output signal, said low pass filter including means for imposing a first given phase shift on said output signal relative to said input signal; and a high pass filter responsive to said output signal applied as an input thereto for attenuating those portions of an input signal applied thereto below said given range to produce a second output signal, said high pass filter including means for imposing a second given phase shift relative to the phase shift of the first output signal, said low and high pass filters being arranged so that said first and second phase shifts substantially cancel one another such that there is negligible time delay between said QRS signal applied to the low pass filter and said second output signal. - View Dependent Claims (13)
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14. An NMR imaging system comprising:
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magnet means for exposing a patient to a magnetic field, said patient creating signals in response to said magnetic field; imaging means responsive to said patient signals for creating an image of a patient in said field; and transmit and receive means for creating a patient QRS signal of a given frequency range in said magnetic field and for transmitting the QRS signal to said receive means; said receive means including QRS signal filter means for filtering the QRS signal such that the image produced by said imaging means and said QRS signal are substantially in phase wherein there is negligible time delay between said created image and said filtered QRS signal. - View Dependent Claims (15)
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Specification