US5079503A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Magnetic resonance imaging apparatus and method for operating same
Assignee: Siemens AG
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Filing: 1990-03-26
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Granted: 1992-01-07
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Expires: 2010-03-26
Abstract
Abstract A magnetic resonance imaging apparatus generates tomograms according to the echo planar imaging method (EPI), with at least one of the gradient coils having a resonant circuit allocated thereto which is excited by an amplifier. A capacitor forms a series resonant circuit with the gradient coil, and a controlled gain amplifier which is operated as a current regulator, such as a switched current regulator, is connected to this series resonant circuit. The read-out gradient G x is switched on at a time t 0 , the gradient G x having a transient region τ 1 beginning at t 0 and ending at a time t 2 . The gradient current I(t) is steady in this transient region τ 1 , and the integral of the gradient current I(t) over t 0 through t 2 is zero.
Inventors
- 👤 Horst Siebold
- 👤 Wolfgang Frie
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 02:17
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/28; G01R33/38; G01R33/385; G01R33/3852
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
223 words
A magnetic resonance imaging tomography apparatus operable according to the echo planar imaging method comprising: means for generating a main magnetic field in which an examination subject is disposed; a plurality of gradient coils for respectively generating gradient magnetic fields; radio frequency means for generating radio frequency signals for inducing nuclear magnetic spins in said examination subject and for acquiring nuclear magnetic resonance signals from said examination subject; means for operating said gradient coils and said radio frequency means according to said echo planar imaging method to obtain a data set of said nuclear magnetic resonance signals corresponding to a selected slice of said examination subject; a capacitance connected to at least one of said gradient coils, said one of said gradient coils having an inductance which, in combination with said capacitance, forms a series resonant circuit; said means for operating said gradient coils including a controlled gain amplifier means operated as a current regulator for regulating current supplied to said one of said gradient coils for generating a read-out gradient magnetic field, having a wave number associated therewith, so that said read-out gradient magnetic field is steady in a transient region immediately preceding a measurement region in which read-out of said nuclear magnetic resonance signals takes place and so that said wave number at the beginning of the measurement region is zero.
Claim 2
Dependent Claim
223 words
A magnetic resonance imaging tomography apparatus operable according to the echo planar imaging method comprising: means for generating a main magnetic field in which an examination subject is disposed; a plurality of gradient coils for respectively generating gradient magnetic fields; radio frequency means for generating radio frequency signals for inducing nuclear magnetic spins in said examination subject and for acquiring nuclear magnetic resonance signals from said examination subject; means for operating said gradient coils and said radio frequency means according to said echo planar imaging method to obtain a data set of said nuclear magnetic resonance signals corresponding to a selected slice of said examination subject; a capacitance connected to at least one of said gradient coils, said one of said gradient coils having an inductance which, in combination with said capacitance, forms a series resonant circuit; said means for operating said gradient coils including a controlled gain amplifier means operated as a current regulator for regulating current supplied to said one of said gradient coils for generating a read-out gradient magnetic field, having a wave number associated therewith, so that said read-out gradient magnetic field is steady in a transient region immediately preceding a measurement region in which read-out of said nuclear magnetic resonance signals takes place and so that said wave number at the beginning of the measurement region is zero.
Claim 3
Dependent Claim
23 words
An apparatus as claimed in claim 1 wherein said capacitance is formed by two capacitors connected symmetrically relative to said one gradient coil.
Claim 4
Dependent Claim
20 words
An apparatus as claimed in claim 2 further comprising two chokes respectively connected in parallel with each of said capacitors.
Claim 5
Dependent Claim
18 words
An apparatus as claimed in claim 1 wherein said controlled gain amplifier is a switched controlled gain amplifier.
Claim 6
Independent Claim
135 words
A method for improved operating of a magnetic resonance imaging apparatus employing the echo planar imaging method comprising the steps of; obtaining an image of an examination subject in a magnetic resonance imaging tomography apparatus according to said echo planar imaging method, including the step of supplying a coil with a gradient current for generating a read-out gradient magnetic field having a cosine-shaped read-out gradient curve in a measurement region in which nuclear magnetic resonance signals are read out from an examination subject; and controlling the gradient current in said coil which generates said read-out gradient magnetic field so that said gradient current is steady in a controlled transient region immediately preceding said measurement region and so that said gradient current has a wave number which is zero at the end of said transient region.
Claim 7
Independent Claim
135 words
A method for improved operating of a magnetic resonance imaging apparatus employing the echo planar imaging method comprising the steps of; obtaining an image of an examination subject in a magnetic resonance imaging tomography apparatus according to said echo planar imaging method, including the step of supplying a coil with a gradient current for generating a read-out gradient magnetic field having a cosine-shaped read-out gradient curve in a measurement region in which nuclear magnetic resonance signals are read out from an examination subject; and controlling the gradient current in said coil which generates said read-out gradient magnetic field so that said gradient current is steady in a controlled transient region immediately preceding said measurement region and so that said gradient current has a wave number which is zero at the end of said transient region.
Claim 8
Dependent Claim
78 words
A method according to claim 5 wherein step of controlling said gradient current is further defined by controlling said gradient current using a controlled gain amplifier connected to a series resonant circuit having a capacitance C and an inductance L and a resonant frequency ω 1 , and wherein said transient region τ 1 occurs between times t 0 and t 2 , and wherein said gradient current in said transient region τ 1 is defined as ##EQU14##
Claim 9
Dependent Claim
33 words
A method as claimed in claim 5, including the step of: generating a slice selection gradient having positive and negative pulses so that the time integral of said slice selection gradient is zero.
Claim 10
Dependent Claim
33 words
A method as claimed in claim 5 including the step generating a phase coding gradient consisting of positive and negative pulses so that the time integral of said phase coding gradient is zero.
Claim 11
Dependent Claim
66 words
A method as claimed in claim 5 wherein the step of generating a read-out gradient magnetic field is further defined by generating a read-out gradient magnetic field having a decay region following said measurement region wherein said read-out gradient curve follows an inverse chronological curve relative to its chronological curve during said transient region, so that the time integral of said read-out gradient curve is zero.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1995-01-06 | 1995-07-08 | 1996-01-07 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1999-01-06 | 1999-07-08 | 2000-01-07 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2003-01-06 | 2003-07-08 | 2004-01-07 | $7700.00 | Window Closed / Lapsed |