Method and magnetic resonance apparatus for slice-selective magnetic resonance imaging

Patent metadata

Field	Value
Publication number	US-2015309139-A1
Application number	US-201514699366-A
Country	US
Kind code	A1
Filing date	Apr 29, 2015
Priority date	Apr 29, 2014
Publication date	Oct 29, 2015
Grant date	—

Abstract

In a method and magnetic resonance apparatus for slice-selective magnetic resonance imaging, read partitions in a cyclical sequence of slices are read out. At least two slices have a different number of read partitions. The same predefined number of read partitions for the slices is read out in all cycles of the sequence. SEMAC techniques are used.

First claim

We claim as our invention:

1 . A method for slice-selective magnetic resonance (MR) imaging of a plurality of slices of an examination subject, comprising:
from a control computer, operating an MR scanner, while an examination subject is situated in the MR scanner, to slice-selectively acquire MR data from each of a plurality of slices of the examination subject, wherein slices in said plurality of slices are respective adjacent to each other along a first direction and extend perpendicularly to said first direction; from said control computer, operating said MR scanner to acquire said MR data from said plurality of slices in a plurality of read partitions in each slice, the read partitions of each slice being adjacent to each other along said first direction, and at least two slices in said plurality of slices having a different number of said read partitions; from said control computer, operating said MR scanner to read out MR data in said read partitions in a cyclical sequence of the slices in said plurality of slices with successive read-out read partitions respective being in different slices, and maintaining a minimum repetition time between sequential readout of respective read partitions of a same slice and wherein a same predetermined number of read partitions is read out in each cycle of said cyclical sequence, and with said cyclical sequence comprising at least two sub-sequences that differ from each other with respect to one of said slices in said plurality of slices; and providing said MR data to an image reconstruction computer and, in said image reconstruction computer, reconstructing an MR image for each slice from the MR data of the read partitions of that respective slice and MR data of read partitions of other slices in said plurality of slices.

2 . A method as claimed in claim 1 comprising, in said control computer, selecting said predetermined number of read partitions in each cycle in said cyclical sequence to be lower than a total number of slices in said plurality of slices.

3 . A method as claimed in claim 1 comprising, from said control computer, operating said MR scanner to execute a total number of cycles in said cyclical sequence that is greater than a maximum number of said read partitions in each slice in said plurality of slices.

4 . A method as claimed in claim 1 comprising operating said MR scanner to execute said at least two sub-sequences successively or in an interleaved manner.

5 . A method as claimed in claim 1 comprising, from said control computer, operating said MR scanner with a first of said sub-sequences comprising a same number of read-out read partitions as cycles in said cyclical sequence and wherein a second of said sub-sequences comprises a lower number of read-out read partitions than cycles of said cyclical sequence.

6 . A method as claimed in claim 5 comprising, from said control computer, operating said MR scanner with a repetition time of said first of said sub-sequences being longer than a repetition time of a second of said sub-sequences.

7 . A method as claimed in claim 1 comprising, from said control computer, operating said MR scanner with cycles of said at least two sub-sequences having a same predetermined number of read-out read partitions as cycles of said cyclical sequence.

8 . A method as claimed in claim 1 comprising, from said control computer, operating said MR scanner with a first group of slices, among said plurality of slices, having read partitions that are read out in a first of said sub-sequences being different from a second group of slices, in said plurality of slices having read partitions that are read out in a second of said sub-sequences.

9 . A method as claimed in claim 8 wherein said first and second groups are disjunct from each other, or partially overlap.

10 . A method as claimed in claim 1 comprising, from said control computer, operating said MR scanner with a total number of cycles in said cyclical sequence equal to a total number of said read partitions of all slices in said plurality of slices, divided by a maximum number of read partitions per slice.

11 . A method as claimed in claim 1 comprising, from said control computer, operating said MR scanner with each cycle of said cyclical sequence comprising a predetermined dead time having a predetermined duration, without application of any gradients or radio-frequency pulses.

12 . A method as claimed in claim 1 comprising, from said control computer, operating said MR scanner to select a number of read partitions per slice dependent on a distance of a respective slice from a predetermined location, said location being selected from the group consisting of a source of magnetic field inhomogeneities of a basic magnetic field generated in said MR scanner, and a location determined dependent on a measured off-resonance of the respective slice.

13 . A method as claimed in claim 1 comprising, from said control computer, operating said MR scanner to read out said MR data from each read partition by:
slice-selective excitation of nuclear spins in the respective slice by applying at least one slice selection gradient in said first direction correlated in time with radiation of at least one excitation pulse;
slice-selective refocusing of the excited nuclear spins in the respective slice by sequential application of a plurality of further slice selection gradients in said first direction correlated in time with radiation of a plurality of refocusing pulses; and
for each further slice selection gradient with a correlated refocusing pulse, applying at least one phase encoding gradient in said first direction that defines a read partition, and applying at least one phase encoding gradient in a second direction for acquiring the MR data, wherein said first direction and said second direction are perpendicular to each other.

14 . A method as claimed in claim 1 comprising, from said control computer, operating said MR scanner to acquire said MR data in an interleaved SEMAC MR data acquisition sequence.

15 . A magnetic resonance (MR) apparatus comprising:
an MR scanner; a control computer configured to operate said MR scanner, while an examination subject is situated in the MR scanner, to slice-selectively acquire MR data from each of a plurality of slices of the examination subject, wherein slices in said plurality of slices are respective adjacent to each other along a first direction and extend perpendicularly to said first direction; said control computer being configured to operate said MR scanner to acquire said MR data from said plurality of slices in a plurality of read partitions in each slice, the read partitions of each slice being adjacent to each other along said first direction, and at least two slices in said plurality of slices having a different number of said read partitions; said control computer being configured to operate said MR scanner to read out MR data in said read partitions in a cyclical sequence of the slices in said plurality of slices with successive read-out read partitions respective being in different slices, and to maintain a minimum repetition time between sequential readout of respective read partitions of a same slice, and to read out a same predetermined number of read partitions in each cycle of said cyclical sequence, and with said cyclical sequence comprising at least two sub-sequences that differ from each other with respect to one of said slices in said plurality of slices; and a reconstruction computer provided with said MR data, said image reconstruction computer being configured to reconstruct an MR image for each

Assignees

• Siemens Ag

Inventors

• Bachschmidt Theresa
• Paul Dominik

Classifications

• G01R33/288

  Provisions within MR facilities for enhancing safety during MR, e.g. reduction of the specific absorption rate [SAR], detection of ferromagnetic objects in the scanner room · CPC title

• G01R33/4835 Primary

  of multiple slices · CPC title

• G01R33/56536

  due to magnetic susceptibility variations · CPC title

• G01R33/385

  using gradient magnetic field coils · CPC title

• G01R33/341

  comprising surface coils · CPC title