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US4621235A
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Method of and device for determining a nuclear magnetization distribution in a region of a body
Assignee: US Philips Corp
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Filing: 1984-05-25
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Granted: 1986-11-04
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Expires: 2004-05-25
Abstract
Abstract During measurement cycles for generating and sampling FID signals in NMR imaging devices, a 180° pulse and subsequently a 90° excitation pulse are added to the pulse sequence. The 180° pulse produces an additional echo signal. During (the maximum of) the echo signal, the 90° pulse is generated. The waiting period occurring before the beginning of a next measurement cycle can thus be substantially reduced without giving rise to a significant signal loss in the echo signals to be generated during said cycle. In addition to a reduction of the measurement time, NMR images with different contrasts (other intensity distribution) can be provided.
Inventors
- 👤 Cornelis M. J. van Uijen
- 👤 Johannes H. den Boef
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 01:56
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/44; G01R33/48; G01R33/4818; G01R33/482
Claims Analysis
Total Claims: 18
Claim 1
Independent Claim
138 words
A method of determining a nuclear magnetic distribution in a region of a body comprising the steps of: generating a steady, homogeneous magnetic field in said region, generating a first high-frequency electromagnetic pulse so as to cause a precessional motion of the magnetization of nuclei in the body to thereby generate a resonance signal, extracting a plurality of signal samples from said resonance signal during a measurement period which is divided into a plurality of sampling intervals, generating a high-frequency 180° pulse so as to produce a nuclear spin echo signal, generating a further high-frequency excitation pulse during said echo signal, and thereafter repeating said first pulse generating and said signal sample extracting steps so as to obtain a group of said signal samples from which an image of the distribution of the induced nuclear magnetization is determined.
Claim 2
Independent Claim
138 words
A method of determining a nuclear magnetic distribution in a region of a body comprising the steps of: generating a steady, homogeneous magnetic field in said region, generating a first high-frequency electromagnetic pulse so as to cause a precessional motion of the magnetization of nuclei in the body to thereby generate a resonance signal, extracting a plurality of signal samples from said resonance signal during a measurement period which is divided into a plurality of sampling intervals, generating a high-frequency 180° pulse so as to produce a nuclear spin echo signal, generating a further high-frequency excitation pulse during said echo signal, and thereafter repeating said first pulse generating and said signal sample extracting steps so as to obtain a group of said signal samples from which an image of the distribution of the induced nuclear magnetization is determined.
Claim 3
Dependent Claim
37 words
A method as claimed in claim 1 including the step of producing, in said region, at least one gradient magnetic field during a preparation period which follows said first pulse generating step and precedes said extracting step.
Claim 4
Dependent Claim
64 words
A method as claimed in claim 2 wherein said at least one gradient field produced during said producing step is such that the integral over the intensity during said preparation period has a different value each time said electromagnetic pulse generating and extracting steps are repeated, and deriving a location-dependent nuclear spin resonance spectra from said group of signal samples after Fourier transformation thereof.
Claim 5
Dependent Claim
106 words
A method as claimed in claim 1 including the steps of producing a first gradient magnetic field in said region during a preparation period which follows said first pulse generating step and precedes said extracting step, applying to said region a further gradient field having a gradient direction which extends perpendicularly to the gradient direction of said first gradient field, the integral over the intensity of said first gradient field during said preparation period having a different value each time said electromagnetic pulse generating and extracting steps are repeated, and deriving a nuclear spin density distribution from said group of signal samples after Fourier transformation thereof.
Claim 6
Dependent Claim
42 words
The method as claimed in claim 4 including producing a second gradient magnetic field in said region during said preparation period, said second field having a gradient direction which is perpendicular to the gradient directions of said first and further gradient fields.
Claim 7
Dependent Claim
30 words
A method as claimed in claim 1 or 2 wherein said further high-frequency excitation pulse is generated during the occurrence of the maximum value of the nuclear spin echo signal.
Claim 8
Dependent Claim
31 words
A method as claimed in claim 6, wherein the phase of the further high-frequency excitation pulse leads the resultant phase of the nuclear magnetization by 90° at the instant of echo.
Claim 9
Dependent Claim
31 words
A method as claimed in claim 6, wherein the phase of the further high-frequency excitation pulse lags the resultant phase of the nuclear magnetization by 90° at the instant of echo.
Claim 10
Dependent Claim
19 words
A method as claimed in claim 8, wherein the further high-frequency excitation pulse is a 90° selective excitation pulse.
Claim 11
Dependent Claim
19 words
A method as claimed in claim 7 wherein the further high-frequency excitation pulse is a 90° selective excitation pulse.
Claim 12
Dependent Claim
53 words
A method as claimed in claim 2, wherein after the further high-frequency excitation pulse, after a period of time T, a similar cycle of high-frequency pulses and associated gradient magnetic fields is completed, at least one pulse interval during the first cycle being different from a corresponding pulse interval during the second cycle.
Claim 13
Dependent Claim
51 words
A method as claimed in claim 3, wherein after generating of the first high-frequency electromagnetic pulse and before the gradient magnetic field is applied, a dephasing period is included having a different value during each measuring cycle comprised of said repetition of the first electromagnetic pulse generating and the extracting steps.
Claim 14
Dependent Claim
72 words
A method as claimed in claim 3, wherein the first high-frequency electromagnetic pulse is generated by applying a selective gradient magnetic field and either two or three gradient magnetic fields are applied during the preparation period, the gradient directions thereof being mutually perpendicular and, either by means of a three-dimensional or a four-dimensional Fourier transformation, location-dependent nuclear resonance spectra are obtained either in a slice or in a volume of a body.
Claim 15
Independent Claim
180 words
A device for determining the nuclear magnetization distribution in a region of a body, comprising (a) first means for generating a steady homogeneous magnetic field, (b) second means for generating high-frequency electromagnetic radiation, (c) third means for generating a gradient magnetic field, (c) sampling means for sampling a resonance signal generated by said first and second generating means, (e) processing means for processing the signals provided by the sampling means in order to form a nuclear magnetization distribution, and (f) control means for controlling said first means, second means, third means, sampling means and said processing means, said control means comprising a preprogrammed computer means for generating and supplying control signals to the second means for generating high-frequency electromagnetic radiation so that, in response to said control signals said second means generates an adjustable pulse sequence of 90° and 180° excitation pulses such that the duration of a time interval between two 180° excitation pulses last generated is twice as long as the duration of the time interval between the last 180° pulse and a subsequent further 90° excitation pulse.
Claim 16
Independent Claim
180 words
A device for determining the nuclear magnetization distribution in a region of a body, comprising (a) first means for generating a steady homogeneous magnetic field, (b) second means for generating high-frequency electromagnetic radiation, (c) third means for generating a gradient magnetic field, (c) sampling means for sampling a resonance signal generated by said first and second generating means, (e) processing means for processing the signals provided by the sampling means in order to form a nuclear magnetization distribution, and (f) control means for controlling said first means, second means, third means, sampling means and said processing means, said control means comprising a preprogrammed computer means for generating and supplying control signals to the second means for generating high-frequency electromagnetic radiation so that, in response to said control signals said second means generates an adjustable pulse sequence of 90° and 180° excitation pulses such that the duration of a time interval between two 180° excitation pulses last generated is twice as long as the duration of the time interval between the last 180° pulse and a subsequent further 90° excitation pulse.
Claim 17
Independent Claim
167 words
A method of determining a nuclear magnetic distribution in a region of a body comprising the steps of: generating a steady, homogeneous magnetic field in said region, generating at least one gradient magnetic field in said region, generating a first high-frequency electromagnetic pulse so as to cause a precessional motion of the magnetization of nulcei in the body to thereby generate a resonance signal, extracting a plurality of signal samples from said resonance signal during a measurement period which is divided into a plurality of sampling intervals, generating a high-frequency 180° pulse so as to produce a nuclear spin echo signal and to cancel a phase shift effect exerted on the nuclear magnetization by said gradient field, generating a further high-frequency excitation pulse during said echo signal, and thereafter repeating said gradient generating, said first pulse generating and said signal sample extracting steps so as to obtain a group of said signal samples from which an image of the distribution of the induced nuclear magnetization is determined.
Claim 18
Independent Claim
167 words
A method of determining a nuclear magnetic distribution in a region of a body comprising the steps of: generating a steady, homogeneous magnetic field in said region, generating at least one gradient magnetic field in said region, generating a first high-frequency electromagnetic pulse so as to cause a precessional motion of the magnetization of nulcei in the body to thereby generate a resonance signal, extracting a plurality of signal samples from said resonance signal during a measurement period which is divided into a plurality of sampling intervals, generating a high-frequency 180° pulse so as to produce a nuclear spin echo signal and to cancel a phase shift effect exerted on the nuclear magnetization by said gradient field, generating a further high-frequency excitation pulse during said echo signal, and thereafter repeating said gradient generating, said first pulse generating and said signal sample extracting steps so as to obtain a group of said signal samples from which an image of the distribution of the induced nuclear magnetization is determined.
References Cited (Backward Citations)
US4471306A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1989-11-03 | 1990-05-05 | 1990-11-04 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-11-03 | 1994-05-05 | 1994-11-04 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-11-03 | 1998-05-05 | 1998-11-04 | $7700.00 | Window Closed / Lapsed |