The invention concerns a method of magnetic resonance imaging in accordance with the multislice technique with which a single slice (of a measuring object) is initially excited through the application of a radio frequency pulse of low bandwidth in the presence of a slice selection gradient and the transverse magnetization located in the excited slice is subsequently dephased via a time-limited gradient pulse of the so-called read gradient in a direction perpendicular to the plane of the slice, and the dephased magnetization is refocused through the application of an additional radio frequency pulse of low bandwidth in the presence of a slice selection gradient, whereby the bandwidth and the steepness of the gradient are chosen in such a fashion that the refocusing includes precisely those magnetizations which are excited by the first measuring pulse and, through the application of an additional read gradient, a so-called spin echo is subsequently produced which is phase-encoded for imaging by application of a phase-encoding gradient perpendicular to the read and slice gradients in accordance with the two-dimensional Fourier transformation method, whereby the phase encoding gradient can be applied at an arbitrary time between excitation and read out of the transverse magnetization, however, not during application of the radio frequency pulse and the same procedure is subsequently carried out on other slices until, after a predetermined time interval, the same procedure is repeated beginning at the originally chosen slice, whereby the phase encoding of the signal is, however, varied until all individual differing phase-encoded signals required for image reconstruction of all slices are present.
A method of this kind is, for example, known in the art from D. Stark et al., Magnetic Resonance Imaging, Mosby Year Book, St. Louis, 1992, pp. 115ff.
When optimizing the measuring time for recording a large measuring volume with the assistance of the multislice technique, there presently exists the problem that the maximum possible number of slices is limited by the repetition time of the recording of projections of the same slice. In the event that slices in excess of the thereby predetermined number are to be investigated, it is necessary to repeat the acquisition while shifting the slice packet. This causes problems principally when the acquisition is carried out under utilization of a rapid acquisition sequence in a time interval during which the patient is supposed to hold his breath. An acquisition repetition in two breathing cycles causes problems for the investigation of the stomach organs, since breathing displaces same by several centimeters and continuity in the entire volume being investigated cannot therefore be guaranteed.
It is therefore the purpose of the present invention to present a method of the above-mentioned kind with which the measuring volume can be increased in a quasi-continuous fashion through the increase in the number of recorded slices without requiring the acquisition of a completely new slice packet displaced by a length with respect to the original one.
USPTO Backgrounds
USPTO Backgrounds