C.8.14 MR Spectroscopy Modules

This section describes the MR Spectroscopy Modules.

Note: Many attributes have names and descriptions that include the terms “pixel” and “image”. Although MR spectroscopy is not pixel based, some of these “pixel” and “image” attributes encode concepts that are still relevant for this technique. Where such attributes appear in the MR Spectroscopy IOD, it may be helpful to consider the term “pixel” to be equivalent to a spectroscopy “voxel”, and the term “image” to be equivalent to “MR Spectroscopy SOP Instance”.

C.8.14.1 MR Spectroscopy Module

Table C.8-102 specifies the attributes of the MR Spectroscopy Module.

Table C.8-102 MR SPECTROSCOPY MODULE ATTRIBUTES

Attribute Name Tag Type Attribute Description
Include ' MR Image and Spectroscopy Instance Macro' Table C.8-81
Image Type (0008,0008) 1 Spectroscopy data characteristics. See C.8.14.5.1.1.
Include 'MR Spectroscopy Description Macro' Table C.8-107
Transmitter Frequency (0018,9098) 1C Precession frequency in MHz of the nucleus being addressed for each spectral axis. See section C.8.14.1.1 for further explanation of the ordering. Required if Image Type (0008,0008) Value 1 is ORIGINAL. May be present otherwise.
Spectral Width (0018,9052) 1C Spectral width in Hz. See section C.8.14.1.1 for further explanation of the ordering. Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Chemical Shift Reference (0018,9053) 1C The chemical shift at the transmitter frequency in ppm. See section C.8.14.1.1 for further explanation of the ordering. Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Volume Localization Technique (0018,9054) 1C Name of volume localization technique used. Shall be “NONE” if no spatial localization was performed. Defined Terms: ILOPS ISIS PRIME PRESS SLIM SLOOP STEAM NONE Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Volume Localization Sequence (0018,9126) 1C A sequence of Items that provide the position of RF excitations used to select a volume of tissue. The selected volume is described by the intersection of the sequence Items. One or more Items shall be included in this sequence. Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED and Volume Localization Technique (0018,9054) is other than NONE. May be present if Volume Localization Technique (0018,9054) is other than NONE.
>Slab Thickness (0018,9104) 1 Thickness of slab in mm.
>Slab Orientation (0018,9105) 1 The direction cosines of a normal vector perpendicular to the selection plane with respect to the patient. See C.7.6.2.1.1 for further explanation.
>Mid Slab Position (0018,9106) 1 The x, y, and z coordinates of the mid-point of the slab in mm. See C.7.6.2.1.1 for further explanation.
De-coupling (0018,9059) 1C Indicates whether de-coupling was active. Enumerated Values: YES NO Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
De-coupled Nucleus (0018,9060) 1C Nucleus being de-coupled. Defined Terms: 1H 3HE 7LI 13C 19F 23NA 31P 129XE See section C.8.14.1.1 for further explanation of the ordering. Required if De-coupling (0018,9059) equals YES.
De-coupling Frequency (0018,9061) 1C The center frequency (Hz) for the de-coupling. See section C.8.14.1.1 for further explanation of the ordering. Required if De-coupling (0018,9059) equals YES.
De-coupling Method (0018,9062) 1C The de-coupling modulation scheme used. Defined Terms: MLEV WALTZ NARROWBAND Required if De-coupling (0018,9059) equals YES.
De-coupling Chemical Shift Reference (0018,9063) 1C The chemical shift in ppm at the de-coupling frequency. See section C.8.14.1.1 for further explanation of the ordering. Required if De-coupling (0018,9059) equals YES.
Time Domain Filtering (0018,9065) 1C Describes time domain filtering or apodization applied. Shall be NONE if no filtering operations were applied to the time domain data. Defined Terms: COSINE COSINE_SQUARED EXPONENTIAL GAUSSIAN HAMMING HANNING LORENTZIAN LRNTZ_GSS_TRNSFM NONE See section C.8.14.1.1 for further explanation of the ordering. Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Number of Zero Fills (0018,9066) 1C Number of zero fills added to the time domain data before FT. Shall be 0 (zero) if no zero filling performed. See section C.8.14.1.1 for further explanation of the ordering. Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Baseline Correction (0018,9067) 1C Describes baseline correction techniques. Shall be NONE if no baseline correction was performed. Defined Terms: LINEAR_TILT LOCAL_LINEAR_FIT POLYNOMIAL_FIT SINC_DECONVOLUTN TIME_DOMAIN_FIT SPLINE NONE Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Frequency Correction (0018,9101) 1C Specifies whether operations were performed to correct resonant frequency of metabolite peaks due to B0 field inhomogeneities. Enumerated Values: YES NO Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
First Order Phase Correction (0018,9198) 1C Describes whether a first order (frequency dependent) phase correction was applied to the spectral data. Enumerated Values: YES NO Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Water Referenced Phase Correction (0018,9199) 1C Enumerated Values: YES NO Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.

C.8.14.1.1 MR Spectroscopy Attribute Multiplicity Ordering

The following attributes may have a Value Multiplicity of one or two depending whether one or two frequency axes are used as specified by the value of Data Point Rows (0028,9001):

Transmitter Frequency (0018,9098)

Resonant Nucleus (0018,9100)

Spectral Width (0018,9052)

Chemical Shift Reference (0018,9053)

De-coupled Nucleus (0018,9060)

De-coupling Frequency (0018,9061)

De-coupling Chemical Shift Reference (0018,9063)

Time Domain Filtering (0018,9065)

Number of Zero Fills (0018,9066)

Value 1 shall contain the value corresponding to the sampling time axis (the axis along a data point row).

Value 2, if present, shall contain the value corresponding to the evolution time axis (the axis along a data point column).

C.8.14.2 MR Spectroscopy Pulse Sequence Module

The primary purpose of this module is to identify the pulse sequence and variations which were used in creation of the spectroscopic data. Terminology is intended to be neutral, and allow equivalent sequences provided by different vendors to be classified together.

Table C.8-103 specifies the attributes of the MR Spectroscopy Pulse Sequence Module.

Table C.8-103MR SPECTROSCOPY PULSE SEQUENCE MODULE ATTRIBUTES

Attribute Name Tag Type Attribute Description
Pulse Sequence Name (0018,9005) 1C Name of the pulse sequence for annotation purposes. Potentially vendor-specific name. Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
MR Spectroscopy Acquisition Type (0018,9200) 1C Identification of data encoding scheme. Defined Terms: SINGLE_VOXEL ROW PLANE VOLUME Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Echo Pulse Sequence (0018,9008) 1C Echo category of pulse sequences. Enumerated Values: SPIN GRADIENT BOTH Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Multiple Spin Echo (0018,9011) 1C Multiple Spin Echo category of pulse sequence used to collect different lines in k-space for a single frame. Enumerated Values: YES NO Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED and Echo Pulse Sequence (0018,9008) equals SPIN or BOTH. Otherwise may be present if Image Type (0008,0008) Value 1 is DERIVED and Echo Pulse Sequence (0018,9008) equals SPIN or BOTH.
Multi-planar Excitation (0018,9012) 1C Technique that simultaneously excites several volumes. Enumerated Values: YES NO Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Steady State Pulse Sequence (0018,9017) 1C Steady State Sequence. Defined Terms: FREE_PRECESSION TRANSVERSE TIME_REVERSED LONGITUDINAL NONE Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Echo Planar Pulse Sequence (0018,9018) 1C Echo Planar category of pulse-sequences. Enumerated Values: YES NO Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Spectrally Selected Suppression (0018,9025) 1C Spectrally Selected Suppression. Defined Terms: WATER FAT FAT_AND_WATER SILICON_GEL NONE Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Geometry of k-Space Traversal (0018,9032) 1C Geometry category of k-Space traversal. Defined Terms: RECTILINEAR RADIAL SPIRAL Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Rectilinear Phase Encode Reordering (0018,9034) 1C Rectilinear phase encode reordering. Defined Terms: LINEAR CENTRIC SEGMENTED REVERSE_LINEAR REVERSE_CENTRIC Required if Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED and Geometry of k-Space Traversal (0018,9032) equals RECTILINEAR. Otherwise may be present if Image Type (0008,0008) Value 1 is DERIVED and Geometry of k-Space Traversal (0018,9032) equals RECTILINEAR.
Segmented k-Space Traversal (0018,9033) 1C Segmented k-Space traversal. If Geometry of k-Space Traversal is rectilinear, multiple lines can be acquired at one time. If Geometry of k-Space Traversal is spiral or radial, paths can be interleaved and acquired at one time. Enumerated Values: SINGLE = successive single echo coverage PARTIAL = segmented coverage FULL = single shot full coverage Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.
Coverage of k-Space (0018,9094) 1C Coverage of k-Space. Defined Terms: FULL CYLINDRICAL ELLIPSOIDAL WEIGHTED Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED and MR Spectroscopy Acquisition Type (0018,9200) equals VOLUME. Otherwise may be present if Image Type (0008,0008) Value 1 is DERIVED and MR Spectroscopy Acquisition Type (0018,9200) equals VOLUME.
Number of k-Space Trajectories (0018,9093) 1C Number of interleaves or shots. Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise.

C.8.14.3 MR Spectroscopy Functional Group Macros

The following sections contain Functional Group Macro's specific to the MR Spectroscopy IOD.

Note: The attribute descriptions in the Functional Group Macros are written as if they were applicable to a single frame (i.e., the macro is part of the Per-frame Functional Groups Sequence). If an attribute is applicable to all frames (i.e. the macro is part of the Shared Functional Groups Sequence) the phrase "this frame" in the attribute description shall be interpreted to mean " for all frames".".

C.8.14.3.1 MR Spectroscopy Frame Type Macro

Table C.8-104 specifies the attributes of the MR Spectroscopy Frame Type Functional Group macro.

Table C.8-104MR SPECTROSCOPY FRAME TYPE MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
MR Spectroscopy Frame Type Sequence (0018,9227) 1 Identifies sequence containing Frame Type Attributes. Only a single Item shall be included in this sequence.
>Frame Type (0008,9007) 1 Spectroscopy data characteristics. See C.8.14.5.1.1.
>Include 'MR Spectroscopy Description Macro' Table C.8-107

C.8.14.3.2 MR Spectroscopy FOV/Geometry Macro

Table C.8-105 specifies the attributes of the MR Spectroscopy FOV/Geometry Functional Group Macro.

Table C.8-105MR SPECTROSCOPY FOV/GEOMETRY MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
MR Spectroscopy FOV/Geometry Sequence (0018,9103) 1 Identifies the geometry parameters of this frame. Only a single Item shall be included in this sequence.
>Spectroscopy Acquisition Data Columns (0018,9127) 1C Number of data points in the columns direction. Required if Frame Type (0008,9007) Value 1 is ORIGINAL. May be present otherwise.
>Spectroscopy Acquisition Phase Rows (0018,9095) 1C Number of Phase Encoding Rows. Required if Frame Type (0008,9007) Value 1 is ORIGINAL. May be present otherwise.
>Spectroscopy Acquisition Phase Columns (0018,9234) 1C Number of Phase Encoding Columns. Required if Frame Type (0008,9007) Value 1 is ORIGINAL. May be present otherwise.
>Spectroscopy Acquisition Out-of-plane Phase Steps (0018,9159) 1C Number of out-of-plane Phase Encoding steps. Required if MR Spectroscopy Acquisition Type (0018,9200) equals PLANE and Frame Type (0008,9007) Value 1 is ORIGINAL. May be present otherwise.
>Percent Sampling (0018,0093) 1C Fraction of acquisition matrix lines acquired, expressed as a percent. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Percent Phase Field of View (0018,0094) 1C Ratio of field of view dimension in phase direction to field of view dimension in frequency direction, expressed as a percent. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.

C.8.14.4 MR Spectroscopy Data Module

Table C.8-106 specifies the attributes that describe the Spectroscopy Data.

Table C.8-106MR SPECTROSCOPY DATA MODULE ATTRIBUTES

Attribute Name Tag Type Attribute Description
Rows (0028,0010) 1 Number of voxels in the vertical direction in the frame.
Columns (0028,0011) 1 Number of voxels in the horizontal direction in the frame.
Data Point Rows (0028,9001) 1 Number of rows of data points in spectroscopic data.
Data Point Columns (0028,9002) 1 Number of columns of data points in spectroscopic data.
Data Representation (0028,9108) 1 Data representation of the data points. Each data point shall have the same representation. Enumerated Values: COMPLEX = Data is complex pair REAL = Data contains only real component IMAGINARY = Data contains only imaginary component MAGNITUDE = Magnitude data
Signal Domain Columns (0028,9003) 1 Domain of represented signal in column direction. Enumerated Values: FREQUENCY TIME
Signal Domain Rows (0028,9235) 1C Domain of represented signal in row direction. Enumerated Values: FREQUENCY TIME Required if Data Point Rows (0028,9001) has a value of more than 1.
First Order Phase Correction Angle (5600,0010) 1C First Order Phase Correction Angle. Number of values is determined by Row ( Column ( Number of Frames. Required if First Order Phase Correction (0018,9198) equals YES
Spectroscopy Data (5600,0020) 1 A data stream of the signal intensities that comprise the spectroscopic data. See C.8.14.4.1 for further explanation.

C.8.14.4.1 Spectroscopy Data

The Spectroscopy Data attribute (5600,0020) contains the Signal intensities for the spectra. The order of voxels sent for each spectral plane is left to right, top to bottom, i.e., the upper left voxel (labeled 1,1) is sent first followed by the remainder of row 1, followed by the first voxel of row 2 (labeled 2,1) then the remainder of row 2 and so on. Each "voxel" represents an entire spectrum. The complete spectral data from each voxel is sent, followed by the spectral data from the next voxel position.

The number of voxels on each frame are described by Rows (0028,0010) and Columns (0028,0011). The number of frames is described by Number of Frames (0028,0008). The frames may represent different locations in a 3D acquisition, or the same position at a different point of time, or a difference of some other combination of attributes.

Note: Either Rows or Columns or both may have a value of 1 (e.g., for single voxel spectroscopy). A value of zero for the corresponding value of Pixel Spacing in the Pixel Measures Macro is permitted under these circumstances. See 10.7.1.3.

The spectral data points are ordered from high frequencies to low frequencies for a fixed static magnetic field strength, in the case that the Signal Domain Columns (0028,9003) or Signal Domain Rows (0028,9235) attributes contain the value FREQUENCY.

The spectral data points are ordered in sequence of increasing time in the case that the Signal Domain Columns (0028,9003) or Signal Domain Rows (0028,9235) attributes contain the value TIME.

The apparent rotation of magnetization in a quadrature representation shall be counterclockwise (from the (positive) real part to the (positive) imaginary part) for positive relative frequencies.

Note: When Complex time data points are transformed by a straightforward Fourier transformation to complex spectral data points, these are ordered from low frequency to high frequency.

For two-dimensional spectral acquisitions, the ordering is such that all data points from a row (corresponding to all data points acquired in an individual sampling period), are followed by all data points from the successive sampling period. Following all data of the rows from a given voxel position, the data from the subsequent voxel position are sent. The axis parallel to the row direction corresponds to the sampling time axis. The axis parallel to the column direction corresponds to the evolution time axis.

The dimensions of each spectrum that make up a voxel are described by Data Point Rows (0028,9001) and Data Point Columns (0028,9002). In the case of 1D spectra, the number of Data Point Rows shall be 1.

For a Data Representation (0028,9108) value of COMPLEX, the order of data points is real channel followed by imaginary channel for each spectral data point. For the other Data Representation values (REAL, IMAGINARY and MAGNITUDE), each spectral data point contains only a single value.

The Figure C.8-18 depicts 6 frames each made up of 4 rows and 4 columns of voxels. Specific values for Data Point Rows (0028,9001) and Data Point Columns (0028,9002) of these voxels are not depicted.

[pic]

Figure C.8-18Dimensions of spectroscopy data.

C.8.14.5 MR Spectroscopy Description Macro

Table C.8-107 specifies the attributes that describe the Spectroscopy.

Table C.8-107MR SPECTROSCOPY DESCRIPTION MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Volumetric Properties (0008,9206) 1 Indication if geometric manipulations are possible with frames in the SOP Instance. See C.8.14.5.1.2 for a description and Enumerated Values.
Volume Based Calculation Technique (0008,9207) 1 Method used for volume calculations with frames in the SOP Instance. See C.8.14.5.1.3 for a description and Defined Terms.
Complex Image Component (0008,9208) 1 Representation of complex data of frames in the SOP Instance. See C.8.14.5.1.4 for a description and Defined Terms.
Acquisition Contrast (0008,9209) 1 Indication of acquisition contrast used with frames in the SOP Instance. See C.8.14.5.1.5 for a description and Defined Terms.

C.8.14.5.1 MR Spectroscopy Description Attribute Description

C.8.14.5.1.1 Image Type and Frame Type

The Image Type (0008,0008) and Frame Type (0008,9007) are not included in this Macro but one or the other is always included in the Module or Macro that invokes this Macro, and they are therefore described here.

In addition to the requirements specified in C.8.16.1 Image Type and Frame Type, the following additional requirements and Defined Terms are specified.

C.8.14.5.1.1.1 Pixel Data Characteristics

See C.8.16.1.1. No additional requirements or Defined Terms.

C.8.14.5.1.1.2 Patient Examination Characteristics

See C.8.16.1.2. No additional requirements or Defined Terms.

C.8.14.5.1.1.3 Image Flavor

See C.8.16.1.3 for requirements, but not Defined Terms.

Table C.8-108 specifies the Defined Terms for MR Spectroscopy for Value 3 for Image Type (0008,0008) and Frame Type (0008,9007).

Table C.8-108MR SPECTROSCOPY IMAGE TYPE AND FRAME TYPE VALUE 3

Defined Term Name Defined Term Description
SPECTROSCOPY Spectroscopy

C.8.14.5.1.1.4 Derived Pixel Contrast

See C.8.16.1.4 for requirements, but not Defined Terms.

Table C.8-109 specifies the Defined Terms for Value 4 for Image Type (0008,0008) and Frame Type (0008,9007).

Table C.8-109MR SPECTROSCOPY IMAGE TYPE AND FRAME TYPE VALUE 4

Defined Term Name Defined Term Description
ADDITION Created through point by point addition operation
DIVISION Created through point by point division operation
MAXIMUM Created through point by point maximum operation
MEAN Created through point by point mean operation
MINIMUM Created through point by point minimum operation
MULTIPLICATION Created through point by point multiplication operation
STD_DEVIATION Standard Deviation
SUBTRACTION Created through point by point subtraction operation
NONE Not calculated
MIXED Used only as value in Image Type (0008,0008) if frames within the spectroscopy SOP Instance contain different values for value 4 in their Frame Type (0008,9007) attribute.

C.8.14.5.1.2 Volumetric Properties

See C.8.16.2.1.2. No additional requirements or Defined Terms.

C.8.14.5.1.3 Volume Based Calculation Technique Attribute

See C.8.16.2.1.3 for requirements, but not Defined Terms.

Table C.8-110 specifies the Defined Terms for the Volume Based Calculation Technique (0008,9207) attribute.

Table C.8-110VOLUME BASED CALCULATION TECHNIQUE ATTRIBUTE VALUES

Defined Term Name Defined Term Description
MAX_IP Maximum Intensity Projection
MIN_IP Minimum Intensity Projection
NONE Pixels not derived geometrically
MIXED Used only as a value in Volume Based Calculation Technique (0008,9207) attribute in the MR Spectroscopy Module if frames within the image SOP Instance contain different terms for the Volume Based Calculation Technique attribute in MR Spectroscopy Frame Type Functional Group.

C.8.14.5.1.4 Complex Image Component

The value of the Complex Image Component attribute (0008,9208) shall be used to indicate which component of the complex representation of the signal is represented in the spectroscopy data.

Table C.8-111 specifies the Defined Terms for Complex Image Component attribute (0008,9208).

Table C.8-111COMPLEX IMAGE COMPONENT ATTRIBUTE VALUES

Defined Term Name Defined Term Description
MAGNITUDE The magnitude component of the complex spectroscopy data.
PHASE The phase component of the complex spectroscopy data.
REAL The real component of the complex spectroscopy data.
IMAGINARY The imaginary component of the complex spectroscopy data.
COMPLEX The real and imaginary components of the complex spectroscopy data
MIXED Used only as a value in Complex Image Component (0008,9208) in the MR Spectroscopy Module if frames within the image SOP Instance contain different values for the Complex Image Component attribute in the MR Spectroscopy Frame Type Functional Group.

C.8.14.5.1.5 Acquisition Contrast

Table C.8-112 specifies the Defined Terms for Acquisition Contrast attribute (0008,9209).

Table C.8-112ACQUISITION CONTRAST VALUES

Defined Term Name Defined Term Description
PROTON_DENSITY Proton Density weighted contrast
T1 T1 weighted contrast
T2 T2 weighted contrast
UNKNOWN Value should be UNKNOWN if acquisition contrasts were combined resulting in an unknown contrast. Also this value should be used when the contrast is not known.
MIXED Used only as a value in Acquisition Contrast (0008,9209) attribute in the MR Spectroscopy Module if frames within the SOP Instance contain different values for the Acquisition Contrast attribute in the MR Spectroscopy Frame Type Functional Group.