Method for generating multi-ray spin-excitation sequences and application thereof to magnetic resonance imaging

A method for implementing a control computer configured and/or operable for designing a multi-spoke spin-excitation pulse sequence in magnetic resonance imaging for implementation with a magnetic resonance imaging appliance, with said pulse sequence being suitable for selectively exciting nuclear spins in a respective slice (CP) of a volume of interest (ROI) of a body (C) immersed in a static magnetic field (B0) and comprising a same predetermined number of radiofrequency pulses (IRF1, IRF2, IRF3) at a Larmor frequency of said nuclear spins alternated with magnetic gradient pulses (IG1, IG2, IG3), with the slice being identified by values of a position coordinate (ζ) and of a pair of angular orientation coordinates (ϕ, θ), the method comprising the steps of:

• a) providing with a control computer a global parameterization for a family of such excitation sequences, with said global parameterization being made up of a first and a second plurality of sets of coefficients of respective truncated series of functions of said position and orientation coordinates of one of said slices, with each set of the first plurality of sets being made up of the coefficients of a truncated series of functions defining a parameter of a radiofrequency pulse and each set of the second plurality of sets being made up of the coefficients of a truncated series of functions defining a parameter of a magnetic gradient pulse;
• and
• b) computing with the control computer the values of said gradient pulse and radiofrequency pulse parameters from said global parameterization, said truncated series of functions and the values of said position coordinate of said pair of angular orientation coordinates of the slice, wherein said gradient pulse and radiofrequency pulse parameters are configured and/or operable to control gradient coils and control at least one radiofrequency emission and reception antenna.

A control computer (OC) configured and/or operable for implementation with a magnetic resonance imaging appliance and the control computer programmed for:

• receiving with the control computer as input at least one intensity map of radiofrequency radiation in a volume of interest (ROI) of a body (C) immersed in a static magnetic field (B0) generated by at least one magnet, with said radiofrequency radiation being at a Larmor frequency of nuclear spins of said body;
• defining with the control computer a global parameterization for a family of multi-spoke spin-excitation pulse sequences in magnetic resonance imaging, with each pulse sequence of said family being suitable for selectively exciting nuclear spins in a slice of said volume of interest and comprising radiofrequency pulses (IRF1, IRF2, IRF3) at a Larmor frequency of said nuclear spins alternated with magnetic gradient pulses (IG1, IG2, IG3), with said global parameterization comprising a first set of parameters characterizing said radiofrequency pulses and a second set of parameters characterizing said magnetic gradient pulses, with a value of each parameter of each of said sets being expressed by a truncated series of functions of a position coordinate (ζ) and of a pair of angular orientation coordinates (ϕ, θ) of one of said slices with each series being determined by its coefficients, and said radiofrequency pulses and said magnetic gradient pulses are configured and/or operable to control gradient coils and control at least one radiofrequency emission and reception antenna;
• and
• computing with the control computer, from said one or more intensity maps, the values of the coefficients of said truncated series of functions that minimize a function representing a mean deviation from a setpoint of the excitation of the nuclear spins, with the mean being computed for said volume of interest and for all possible orientations and positions of said slices.