Magnetic resonance tomography apparatus and method employing a true FISP sequence with improved off-resonant behavior of two spin ensembles

Claim 1

A magnetic resonance tomography apparatus comprising: a basic magnetic field system which generates a static basic magnetic field having a volume adapted to receive a subject containing different nuclei which, when excited to produce precessing nuclear spins, respectively represent a first spin ensemble and a second spin ensemble having respective steady state signals associated therewith; a gradient coil system which emits gradient pulse trains respectively for a slice selection gradient, a phase coding gradient having a phase coding direction, and a readout gradient; a radio-frequency system which emits RF excitation pulses to excite said nuclear spins and which, under said readout gradient, receives said respective steady state signals; and a sequence controller which operates said radio-frequency system and said gradient coil system to generate a FISP pulse sequence in said volume, said FISP pulse sequence including a plurality of RF excitation pulses separated by respective repetition times, with each repetition time being incremented relative to an immediately preceding repetition time by a phase angle increment, and with respective flip angles ≦90° that alternate in sign from excitation pulse-to-excitation pulse, so that said steady state signals have respective signal polarities with a relationship selected from the group consisting of identical signal polarities and opposite signal polarities, and wherein said FISP pulse sequence further includes respective phase coding gradients that alternate as to said phase coding direction from repetition time-to-repetition time, and completely balanced gradient pulse trains within each repetition time.

Claim 9

A method for operating a magnetic resonance tomography apparatus comprising the steps of: generating a static basic magnetic field having a volume adapted to receive a subject containing different nuclei which, when excited to produce precessing nuclear spins, respectively represent a first spin ensemble and a second spin ensemble having respective steady state signals associated therewith; providing a gradient coil system which emits gradient pulse trains respectively for a slice selection gradient, a phase coding gradient having a phase coding direction, and a readout gradient; providing a radio-frequency system which emits RF excitation pulses to excite said nuclear spins and which, under said readout gradient, receives said respective steady state signals; and operating said radio-frequency system and said gradient coil system to generate a FISP pulse sequence in said volume, said FISP pulse sequence including a plurality of RF excitation pulses separated by respective repetition times, with each repetition time being incremented relative to an immediately preceding repetition time by a phase angle increment, and with respective flip angles ≦90° that alternate in sign from excitation pulse-to-excitation pulse, so that said steady state signals have respective signal polarities with a relationship selected from the group consisting of identical signal polarities and opposite signal polarities, and wherein said FISP pulse sequence further includes respective phase coding gradients that alternate as to said phase coding direction from repetition time-to-repetition time, and completely balanced gradient pulse trains within each repetition time.

Claim 10

A method for operating a magnetic resonance tomography apparatus comprising the steps of: generating a static basic magnetic field having a volume adapted to receive a subject containing different nuclei which, when excited to produce precessing nuclear spins, respectively represent a first spin ensemble and a second spin ensemble having respective steady state signals associated therewith; providing a gradient coil system which emits gradient pulse trains respectively for a slice selection gradient, a phase coding gradient having a phase coding direction, and a readout gradient; providing a radio-frequency system which emits RF excitation pulses to excite said nuclear spins and which, under said readout gradient, receives said respective steady state signals; and operating said radio-frequency system and said gradient coil system to generate a FISP pulse sequence in said volume, said FISP pulse sequence including a plurality of RF excitation pulses separated by respective repetition times, with each repetition time being incremented relative to an immediately preceding repetition time by a phase angle increment, and with respective flip angles ≦90° that alternate in sign from excitation pulse-to-excitation pulse, so that said steady state signals have respective signal polarities with a relationship selected from the group consisting of identical signal polarities and opposite signal polarities, and wherein said FISP pulse sequence further includes respective phase coding gradients that alternate as to said phase coding direction from repetition time-to-repetition time, and completely balanced gradient pulse trains within each repetition time.