# US 2013/0154640 A1 · Magnetic resonance system and method to generate a magnetic resonance image of an examination subject

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- Number: US 2013/0154640 A1
- Document ID: US20130154640A1
- Status: Published application
- Kind: A1
- Application number: 13/714,837
- Filed: 2012-12-14
- Published: 2013-06-20
- Earliest claimed: 2011-12-16
- Assignees: Siemens Aktiengesellschaft
- Inventors: Kai Tobias Block; Matthias Fenchel
- Web page: https://patentgrep.com/patent/US20130154640A1

## CPC

- G01R 33/48: NMR imaging systems
- G01R 33/4838: {using spatially selective suppression or saturation of MR signals}
- G01R 33/56545: {caused by finite or discrete sampling, e.g. Gibbs ringing, truncation artefacts, phase aliasing artefacts}
- G06F 17/40: Data acquisition and logging (for input to computer G06F3/00)
- G01R 33/3415: comprising arrays of sub-coils {, i.e. phased-array coils with flexible receiver channels}
- G01R 33/4816: {NMR imaging of samples with ultrashort relaxation times such as solid samples, e.g. MRI using ultrashort TE [UTE], single point imaging, constant time imaging}
- G01R 33/4824: {using a non-Cartesian trajectory}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)

## Abstract

The invention concerns a method to generate an MR image of an examination subject of MR signals of the examination subject being detected with a receiver coil element of a magnetic resonance system. A spatially related sensitivity is determined for the receiver coil element. A mask is generated for the receiver coil element depending on the sensitivity of the receiver coil element in order to therewith mask a region of the MR image, in which region the receiver coil element has at least one predetermined sensitivity. At least one RF excitation pulse and at least one magnetic field gradient are activated to acquire MR data with the receiver coil element, and a preliminary MR image is generated depending on MR data acquired therewith. The mask of the receiver coil element is applied to the preliminary MR image in order to generate an MR image of the receiver coil element, and an MR image of the examination subject is generated from the MR image for the receiver coil element.

## Claims

### Claim 1

A method to generate a magnetic resonance (MR) image of an examination subject, comprising:
providing a processor with information representing a spatial sensitivity of a receiver coil element of an MR data acquisition unit that will be used to acquire MR data from an examination subject, from which MR data and MR image of the examination subject will be generated;
in said processor, automatically generating a mask for said receiver coil element dependent on said spatial sensitivity of said receiver coil element, in order to mask a region of said MR image using said mask, said region being a region of said MR image in which said receiver coil element has at least one predetermined sensitivity;
from said processor, operating said MR data acquisition apparatus to generate at least one RF excitation pulse and at least one magnetic field gradient in order to acquire said MR data from the examination subject with said receiver coil element;
in said processor, generating a preliminary MR image using the MR data acquired with said receiver coil element;
in said processor, applying said mask to said preliminary MR image in order to generate an MR image of the receiver coil element; and
in said processor, generating said MR image of the examination subject dependent on said MR image generated for said receiver coil element, and making said MR image available as a data file at an output of said processor.

### Claim 2 (depends on 1)

A method as claimed in claim 1 comprising generating said mask by:
in said processor, generating a special MR image from only MR data acquired only by said receiver coil element, said special MR image being comprised of pixels each having a respective pixel value; and
generating said mask dependent on a maximum pixel value in said special MR image.

### Claim 3 (depends on 2)

A method as claimed in claim 2 wherein said preliminary MR image is also comprised of a plurality of pixels, each having a respective pixel value, and wherein said method comprises:
in said processor, generating a threshold pixel value as a predetermined percentage of said maximum pixel value;
in said processor, generating a pixel value curve by interpolating respective pixel values of the pixels of said special MR image; and
in said processor, generating a mask value for each pixel of said preliminary MR image by assigning said mask value for a respective pixel a first value when, according to said pixel value curve, the pixel value of the respective pixel of the preliminary MR image is below said threshold pixel value, and otherwise assigning said mask value for the respective pixel of said preliminary MR image a second value, that is different from said first value.

### Claim 4 (depends on 3)

A method as claimed in claim 3 comprising enlarging said mask with a dilation procedure comprising:
for each respective pixel in said preliminary MR image, determining (a) whether said mask has said second value as a mask value and (b) whether a pixel adjacent to the respective pixel has said second mask value; and
if either (a) or (b) is determined to exist, assigning the mask said second value for the respective pixel.

### Claim 5 (depends on 3)

A method as claimed in claim 3 comprising lowpass filtering said mask to smooth discontinuous transitions between said first and second values.

### Claim 6 (depends on 2)

A method as claimed in claim 2 comprising generating said special MR image by operating said MR data acquisition unit with a gradient echo sequence with Cartesian scanning of k-space.

### Claim 7 (depends on 2)

A method as claimed in claim 2 comprising generating said special MR image with a resolution of a maximum of 64 pixels per 0.5 m of length of the examination subject.

### Claim 8 (depends on 1)

A method as claimed in claim 1 comprising generating said mask by:
in said processor, generating a special MR image from only MR data acquired only by said receiver coil element, said special MR image being comprised of pixels each having a respective pixel value;
determining a frequency distribution that, for all respective pixel values of the special MR image, indicates a frequency at which each pixel value of the special MR image occurs; and
in said processor, generating said mask dependent on said frequency distribution.

### Claim 9 (depends on 8)

A method as claimed in claim 8 wherein said preliminary MR image is also comprised of pixels each having a respective pixel value, and comprising:
in said processor, determining the two highest relative maxima of said frequency distribution;
in said processor, determining a threshold pixel value that is between respective pixel values of the two pixels corresponding to said two highest relative maxima of said frequency distribution; and
in said processor, generating a mask value for each pixel of said preliminary MR image by assigning said mask value for a respective pixel a first value when, according to said pixel value curve, the pixel value of the respective pixel of the preliminary MR image is below said threshold pixel value, and otherwise assigning said mask value for the respective pixel of said preliminary MR image a second value, that is different from said first value.

### Claim 10 (depends on 9)

A method as claimed in claim 9 comprising enlarging said mask with a dilation procedure comprising:
for each respective pixel in said preliminary MR image, determining (a) whether said mask has said second value as a mask value and (b) whether a pixel adjacent to the respective pixel has said second mask value; and
if either (a) or (b) is determined to exist, assigning the mask said second value for the respective pixel.

### Claim 11 (depends on 9)

A method as claimed in claim 9 comprising lowpass filtering said mask to smooth discontinuous transitions between said first and second values.

### Claim 12 (depends on 8)

A method as claimed in claim 8 comprising generating said special MR image by operating said MR data acquisition unit with a gradient echo sequence with Cartesian scanning of k-space.

### Claim 13 (depends on 8)

A method as claimed in claim 8 comprising generating said special MR image with a resolution of a maximum of 64 pixels per 0.5 m of length of the examination subject.

### Claim 14 (depends on 2)

A method as claimed in claim 2 wherein said preliminary MR image is also comprised of a plurality of pixels, each having a respective pixel value, and wherein said method comprises:
in said processor, generating a threshold pixel value as a predetermined percentage of said maximum pixel value;
in said processor, determining a p-quantile of the pixel values of said special MR image wherein p*100 percent of the pixels of the special MR image have a lower pixel value than a pixel value of said p-quantile, wherein p is a shortfall proportion of said p-quantile; and
in said processor, generating said mask dependent on said p-quantile.

### Claim 15 (depends on 14)

A method as claimed in claim 14 wherein said preliminary MR image is also comprised of a plurality of pixels, each having a respective pixel value, and wherein said method comprises:
in said processor, generating a mask value for each pixel of said preliminary MR image by assigning said mask value for a respective pixel a first value when, according to said pixel value curve, the pixel value of the respective pixel of the preliminary MR image is below said pixel value of said p-quantile, and otherwise assigning said mask value for the respective pixel of said preliminary MR image a second value, that is different from said first value.

### Claim 16 (depends on 15)

A method as claimed in claim 15 comprising enlarging said mask with a dilation procedure comprising:
for each respective pixel in said preliminary MR image, determining (a) whether said mask has said second value as a mask value and (b) whether a pixel adjacent to the respective pixel has said second mask value; and
if either (a) or (b) is determined to exist, assigning the mask said second value for the respective pixel.

### Claim 17 (depends on 14)

A method as claimed in claim 14 comprising lowpass filtering said mask to smooth discontinuous transitions between said first and second values.

### Claim 18 (depends on 14)

A method as claimed in claim 14 comprising generating said special MR image by operating said MR data acquisition unit with a gradient echo sequence with Cartesian scanning of k-space.

### Claim 19 (depends on 14)

A method as claimed in claim 14 comprising generating said special MR image with a resolution of a maximum of 64 pixels per 0.5 m of length of the examination subject.

### Claim 20 (depends on 1)

A method as claimed in claim 1 comprising, in said processor, enlarging said mask by implementing a dilation procedure.

### Claim 21 (depends on 1)

A method as claimed in claim 1 wherein said receiver coil element is one receiver coil element among a plurality of receiver coil elements, and comprising:
providing said processor with information representing a respective spatial sensitivity for each of said receiver coil elements;
in said processor, determining a respective mask for each receiver coil element dependent on the respective spatial sensitivity thereof in order to mask respective regions of said MR image with said mask, in which the respective receiver coil element has at least one predetermined sensitivity;
from said processor, operating said MR data acquisition unit to acquire MR data from each of said receiver coil elements;
in said processor, determining a respective preliminary MR image for each of said receiver coil elements;
in said processor, for each receiver coil element, applying the mask generated therefor to the preliminary MR image generated from MR data acquired thereby, in order to create an MR image for the respective receiver coil element; and
in said processor, generating said MR image of the examination subject from all of the MR images from the respective receiver coil elements.

### Claim 22

A magnetic resonance apparatus to generate a magnetic resonance (MR) image of an examination subject, comprising:
an MR data acquisition unit having a receiver coil element;
a processor provided with information representing a spatial sensitivity of the receiver coil element of the MR data acquisition unit that will be used to acquire MR data from an examination subject, from which MR data and MR image of the examination subject will be generated;
said processor being configured to automatically generate a mask for said receiver coil element dependent on said spatial sensitivity of said receiver coil element, in order to mask a region of said MR image using said mask, said region being a region of said MR image in which said receiver coil element has at least one predetermined sensitivity;
said processor being configured to operate said MR data acquisition apparatus to generate at least one RF excitation pulse and at least one magnetic field gradient in order to acquire said MR data from the examination subject with said receiver coil element;
said processor being configured to generate a preliminary MR image using the MR data acquired with said receiver coil element;
said processor being configured to apply said mask to said preliminary MR image in order to generate an MR image of the receiver coil element; and
said processor being configured to generate said MR image of the examination subject dependent on said MR image generated for said receiver coil element, and to make said MR image available as a data file at an output of said processor.

### Claim 23 (depends on 22)

A magnetic resonance apparatus as claimed in claim 22, wherein said receiver coil element is one receiver coil element among a plurality of receiver coil elements of said MR data acquisition unit, and wherein:
said processor is provided with information representing a respective spatial sensitivity for each of said receiver coil elements;
said processor is configured to determine a respective mask for each receiver coil element dependent on the respective spatial sensitivity thereof in order to mask respective regions of said MR image with said mask, in which the respective receiver coil element has at least one predetermined sensitivity;
said processor is configured to operate said MR data acquisition unit to acquire MR data from each of said receiver coil elements;
said processor is configured to determine a respective preliminary MR image for each of said receiver coil elements;
said processor is configured, for each receiver coil element, to apply the mask generated therefor to the preliminary MR image generated from MR data acquired thereby, in order to create an MR image for the respective receiver coil element; and
said processor is configured to generate said MR image of the examination subject from all of the MR images from the respective receiver coil elements.

### Claim 24

A non-transitory, computer-readable data storage medium encoded with programing instructions, said data storage medium being loaded into a computerized processing and control system of a magnetic resonance (MR) apparatus that also comprises an MR data acquisition unit comprising a receiver coil element, said programming instructions causing said computerized control and processing system to:
receive information representing a spatial sensitivity of the receiver coil element of the MR data acquisition unit that will be used to acquire MR data from an examination subject, from which MR data and MR image of the examination subject will be generated;
generate a mask for said receiver coil element dependent on said spatial sensitivity of said receiver coil element, in order to mask a region of said MR image using said mask, said region being a region of said MR image in which said receiver coil element has at least one predetermined sensitivity;
operate said MR data acquisition apparatus to generate at least one RF excitation pulse and at least one magnetic field gradient in order to acquire said MR data from the examination subject with said receiver coil element;
generate a preliminary MR image using the MR data acquired with said receiver coil element;
apply said mask to said preliminary MR image in order to generate an MR image of the receiver coil element; and
generate said MR image of the examination subject dependent on said MR image generated for said receiver coil element, and make said MR image available as a data file at an output of said control and processing system.

### Claim 25 (depends on 24)

A non-transitory, computer-readable data storage medium as claimed in claim 24 wherein said programming instructions cause said control and processing system to:
receive information representing a respective spatial sensitivity for each of said receiver coil elements;
determine a respective mask for each receiver coil element dependent on the respective spatial sensitivity thereof in order to mask respective regions of said MR image with said mask, in which the respective receiver coil element has at least one predetermined sensitivity;
operate said MR data acquisition unit to acquire MR data from each of said receiver coil elements;
determine a respective preliminary MR image for each of said receiver coil elements;
for each receiver coil element, apply the mask generated therefore to the preliminary MR image generated from MR data acquired thereby, in order to create an MR image for the respective receiver coil element; and
generate said MR image of the examination subject from all of the MR images from the respective receiver coil elements.