Radio frequency receiver for a NMR instrument
First Claim
1. A receiver for processing an electrical signal in a medical imaging apparatus which receives an input signal containing frequency modulated image information in a range of frequencies contained within a frequency band having a bandwidth BW, the receiver comprising:
- means for demodulating the input signal to produce a resultant signal in which the image information from the input signal lies within a band of frequencies centered at a frequency which is substantially 1.5 times the bandwidth BW; and
an analog to digital converter for sampling the resultant signal at ar ate substantially equal to twice the bandwidth BW and converting the samples into a digital signal.
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Accused Products
Abstract
A receiver processes an NMR signal to produce a baseband image information signal from which two quadrature component signals are derived. An intermediate frequency section mixes the received NMR signal with two reference signals to shift the image information into a frequency band having a bandwidth BW and centered at a frequency that is 1.5 times the bandwidth BW. The resultant signal is filtered to remove extraneous signals outside the image information band. An analog to digital converter samples the filtered signal at a rate that is twice the bandwidth BW and digitizes the samples into a digital signal. A quadrature detector derives I and Q output signals from the digital signal by alternately selecting digital samples and negating every other sample selected for each of the I and Q output signals. The quadature detector also digitally filters the I and Q signals which are then used to construct an NMR image.
72 Citations
16 Claims
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1. A receiver for processing an electrical signal in a medical imaging apparatus which receives an input signal containing frequency modulated image information in a range of frequencies contained within a frequency band having a bandwidth BW, the receiver comprising:
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means for demodulating the input signal to produce a resultant signal in which the image information from the input signal lies within a band of frequencies centered at a frequency which is substantially 1.5 times the bandwidth BW; and an analog to digital converter for sampling the resultant signal at ar ate substantially equal to twice the bandwidth BW and converting the samples into a digital signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A radio frequency receiver for a medical imaging apparatus which processes an input signal containing image information in a band of frequencies having a bandwidth BW comprising:
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an analog to digital converter for sampling the input signal at a frequency f and converting the signal samples into digital form, the resulting digital signal samples being ordinally numbered; means for generating first and second secondary signals from the digital signal samples wherein one of the secondary signals is a component of the input signal which is in phase with a reference signal having a frequency f/4 and the other secondary signal is a component of the input signal which is ninety degrees out of phase with the reference signal, said means for generating the two secondary signals including; (a) means for selecting even numbered digital signal samples to produce the first secondary signal and for selecting odd numbered digital signal samples to produce the second secondary signal; and (b) means for negating every other digital signal sample selected for each of the first and second secondary signals. - View Dependent Claims (9, 10, 11, 12)
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13. A magnetic resonance imaging system receiver, which processes an input signal containing image information in a band of frequencies having a bandwidth BW, comprising:
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a first filter which rejects frequencies in the input signal that are above the frequency of a first reference signal; a first means for heterodyning a signal from the first filter with the first reference signal to shift the image information into a band of frequencies centered at a first intermediate frequency, thereby producing a first intermediate signal; a second filter which the rejects the frequencies in the first intermediate signal that are outside a band of frequencies which contain the image information; a second means for heterodyning a signal from said second filter with a second reference signal to produce a second intermediate signal in which the image information is shifted into a band of frequencies centered at a frequency that is substantially 1.5 times the bandwidth BW; a third filter which rejects the frequencies in the second intermediate signal that are outside a band of frequencies which contain the image information; and an analog to digital converter means for sampling a signal from said third filter at a rate substantially equal to twice the bandwidth BW and converting the samples into a digital signal. - View Dependent Claims (14, 15, 16)
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Specification