Two and three-dimensionally selective RF pulses for magnetic resonance imaging

A method of exciting magnetic resonance in a limited subregion of an examination region, the method comprising:

• creating a static magnetic field through an examination region;
• concurrently transmitting a series of radio frequency pulses and excitation location selection gradient pulses into the examination region, the radio frequency pulses each having a common duration and being immediately temporally contiguous such that the combination of the radio frequency pulses taken together control a magnetic resonance tip angle, the series of excitation location selection pulses including a series of x-gradient pulses including positive and negative x-gradient pulses having a fixed cyclic periodicity, which x-gradient periodicity is an integer multiple of the radio frequency pulses, the x-gradient pulses having amplitudes which diminish linearly over a temporal duration of the radio frequency pulse series, a series of y-gradient pulses including positive and negative y-gradient pulses having a fixed cyclic periodicity, which y-gradient periodicity is an integer multiple of the radio frequency pulses, the y-gradient pulses having amplitudes which diminish linearly over the temporal duration of the radio frequency pulse series, a series of z-gradient pulses including positive and negative z-gradient pulses having a fixed cyclic periodicity, which z-gradient periodicity is an integer multiple of the periodicity of the radio frequency pulses, the z-gradient pulses having amplitudes which diminish linearly over the temporal duration of the radio frequency pulse series, whereby magnetic resonance is excited along a k-space trajectory which spirals symmetrically inward in three dimensions.

An apparatus for exciting magnetic resonance in a limited subregion of an examination region, the apparatus comprising:

• a means for creating a static magnetic field through an examination region;
• means for transmitting a series of radio frequency pulses into the examination region, the radio frequency pulses each having a common duration and being immediately temporally contiguous such that the combination of the radio frequency pulses taken together control a magnetic resonance tip angle;
• a means for applying excitation subregion selection gradient pulses across the examination region, the series of excitation subregion selection pulses including a series of x-gradient pulses including positive and negative x-gradient pulses, a series of y-gradient pulses including positive and negative y-gradient pulses and a series of z-gradient pulses including positive and negative z-gradient pulses;
• a control means for controlling the means for transmitting radio frequency pulses and the gradient applying means such that the x, y, and z-gradient pulse series have a periodicity which is an integer multiple of the radio frequency pulse duration, the x, y, and z-gradient pulses having amplitudes which diminish linearly over the temporal duration of the radio frequency pulse series, whereby magnetic resonance is excited along a k-space trajectory which spirals symmetrically inward in three dimensions.

An apparatus for exciting magnetic resonance in a limited subregion of an examination region, the apparatus comprising:

• a means for creating a static magnetic field through an examination region;
• a means for transmitting a series of temporally contiguous radio frequency pulses each of a common duration into the examination region;
• a means for applying a series of limited subregion selection gradient pulses across the examination region along at least two axes;
• a control means for controlling the radio frequency transmitting means and the gradient applying means such that the series of limited subregion selection gradient pulses have a periodicity which is an integer multiple of the common duration of the radio frequency pulses, the series of contiguous radio frequency pulses and the series of limited subregion selection gradient pulses interacting to cause magnetic resonance to be excited along a k-space trajectory that follows a piecewise linear spiral;
• a means for displacing the limited subregion along a selected one of the axes, the displacing means controlling the gradient applying means and the radio frequency pulse transmitting means to apply an offset gradient pulse concurrently with each limited subregion selection gradient pulse along the selected axis.