Magnetic resonance method and system to automatically generate a selective MR image

摘要

In a magnetic resonance method and system for automatic generation of a selective MR image from a first MR image (corresponding to raw data acquired at a first echo time after excitation pulses) and a second MR image (corresponding to raw data acquired at a second echo time after the same excitation pulses), wherein at least one raw data measurement point was measured in the absence of gradient fields, a time constant prevailing in the depicted imaging space is calculated from the measurement data measured during readout of the raw data measurement point measured in the absence of gradient fields. Weighting factors for the first and/or the second MR image are determined depending on this time constant. The selective MR image is generated by weighting the first and/or second MR image with the calculated weighting factors and subtraction of the weighted MR images from one another.

主权项

1. A method for generating a selective magnetic resonance (MR) image, comprising:
operating an MR data acquisition unit, comprising a radio-frequency (RF) transmission/reception system and a gradient coil system, with a subject situated in said MR data acquisition unit, to radiate an RF excitation pulse, via said RF transmission/reception system, that places nuclear spins in tissue in the examination subject in an excited state and thereby causes the nuclear spins in said excited state to emit an MR signal as said nuclear spins relax from said excited state, thereby causing said MR signal to exhibit an amplitude decay; operating said MR data acquisition unit with said subject therein, after a first echo time of said MR signal, to acquire a first set of raw data, in a first detection window, representing said MR signal at a plurality of points in time in said first detection window, during selected activation of gradient fields with said gradient coil system, and entering said first set of raw data at respective data entry points in a memory organized as first k-space matrix, having matrix axes defined by said gradient fields, said respective points in said matrix having coordinates defined by said axes of said first k-space matrix, said first set of raw data acquired during said first detection window representing a first MR image with said tissue being represented therein as intensity values associated with a time constant that prevails globally in said first MR image due to the amplitude decay of said MR signal during said first detection window; operating said MR data acquisition unit, with said subject therein, after a second echo time of said MR signal that extends beyond an end of said first detection window, to acquire a second set of raw data in a second detection window representing said MR signal at a plurality of points in time during said second detection window, with selected activation of gradient fields with said gradient coil system, and entering said second set of raw data at respective data entry points in a memory organized as second k-space matrix, having matrix axes defined by said gradient fields, said respective points in said matrix having coordinates defined by said axes of said second k-space matrix, said raw data acquired during said second detection window representing a second MR image with said tissue represented therein as intensity values associated with a time constant that prevails globally in said second MR image due to the amplitude decay of said MR signal during said second detection window; operating said MR data acquisition unit to implement said selected activation of said gradient fields during said first and second detection windows to cause at least one of (a) data in said first data set to be entered in said first k-space matrix at a data entry point that is a center of said first k-space matrix by virtue of having coordinate values of zero on all of said axes of said first k-space matrix, and (b) data in said second data set to be entered in said second k-space matrix at a data entry point that is a center of said second k-space matrix by virtue of having coordinate values of zero on all of said axes of said second k-space matrix; supplying said raw data representing each of said first MR image and said second MR image to a processor and, in said processor, calculating, for at least one image selected from first and second MR images, the time constant that prevails globally in said at least one image, dependent only on the raw data at said center of said at least one of said first or second k-space matrices; in said processor, using the calculated time constant to generate a weighting factor; in said processor, generating a selective image as a combination of intensity values in said first MR image and in said second MR image, with the intensity values in at least one of said first MR image and said second MR image being weighted, in said combination, by said weighting factor; and making the selective image available at an output of the processor in electronic form.