Method of minimizing dead-periods in magnetic resonance imaging pulse sequences and associated apparatus
First Claim
1. A method of minimizing the duration of dead-periods in magnetic resonance imaging pulse sequences comprisingproviding a specimen disposed within a main magnetic field, a source of pulsed RF signals, receiver means for receiving signals from said specimen responsive to said RF pulses and emitting responsive output signals, computer means for receiving said output signals from said receiver means and establishing image information related thereto and display means for displaying images from said imaging information,determining for said dead-periods for the scan plane gradient pulse for the slice, phase encoding and readout directions determining the starting and ending gradient values and moments of the dead-period waveform,transferring said values and moments to gradient amplifier coordinates,determining minimum dead-periods from said gradient amplifier values, andemploying said minimum dead-periods to establish a hardware optimized waveform based upon said minimum dead-period values.
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Abstract
A method of minimizing dead-periods in magnetic resonance imaging pulse sequences employs a specimen disposed within magnetic field, a source of RF signals, a receiver for receiving signals from the specimen responsive to RF pulses and emitting respective output signals. A computer is provided for receiving the output signals from the receiver and establishing image information which may be displayed. For the dead-period, the minimum and maximum phase encoding step, the scan plane gradient pulse for the slice, phase encoding and readout directions are determined and the moments contained within the dead-period waveform is determined. The values are transformed into gradient amplifier coordinates and the minimum dead-period based on a dead-period waveform is determined. The dead-period is employed in establishing a hardware optimized waveform which may be trapezoidal. The trapezoidal waveform is preferably established by for each phase encoding step determining the starting and ending gradient levels and the moments contained within the dead-period waveform and employing the waveform to design a trapezoidal waveform using the calculated minimum dead-period. The method is particularly advantageous when employed in oblique magnetic resonance imaging. The method may also be employed with velocity-encoded or flow-compensated pulse sequences by employing first gradient moments in the information processing, in addition to the starting and ending gradient levels and the zeroeth moments. For other types of pulse sequences, the zeroeth moment and other higher moments may be employed. Associated apparatus is also disclosed.
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Citations
40 Claims
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1. A method of minimizing the duration of dead-periods in magnetic resonance imaging pulse sequences comprising
providing a specimen disposed within a main magnetic field, a source of pulsed RF signals, receiver means for receiving signals from said specimen responsive to said RF pulses and emitting responsive output signals, computer means for receiving said output signals from said receiver means and establishing image information related thereto and display means for displaying images from said imaging information, determining for said dead-periods for the scan plane gradient pulse for the slice, phase encoding and readout directions determining the starting and ending gradient values and moments of the dead-period waveform, transferring said values and moments to gradient amplifier coordinates, determining minimum dead-periods from said gradient amplifier values, and employing said minimum dead-periods to establish a hardware optimized waveform based upon said minimum dead-period values.
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21. Apparatus for minimizing dead-periods in magnetic resonance imaging pulse sequences comprising
magnetic field generator means for establishing a main magnetic field on a specimen, magnetic field gradient generating means for establishing gradients in said magnetic field, RF signal generating means for emitting pulsed RF signals to at least a portion of said magnetic field passing through said specimen, dead-period determining means for determining phase encoding steps by determining for the slice, phase encoding and readout directions, the pulse starting and ending gradient values and the moments contained within the dead-period waveform, means for transforming these scan plane dead-period values and moments to gradient amplifier coordinates, design waveform creating means for employing a dead-period determined by said dead-period determining means and establishing a hardware optimized waveform based thereon, receiver means for receiving signals emitted from said specimen responsive to said RF pulses and emitting responsive output signals, computer means for receiving said output signals from said receiver means and establishing image information related thereto, and visual display means for displaying images from said image information received from said computer means.
Specification