C.8.14 MR Spectroscopy Modules
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### 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 Table C.8-83 “MR Image and Spectroscopy Instance Macro Attributes” |
Image Type | (0008,0008) | 1 | Spectroscopy data characteristics. See Section C.8.14.5.1.1.
Include Table C.8-107 “MR Spectroscopy Description Macro Attributes” |
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 Section 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 Section 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. See Section C.8.14.1.2 for further explanation on Zero Fills. 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 | Indicates if the images or spectra were created using Water Reference time domain data for phase correction. Enumerated Values: YES NO Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise. See Section C.8.14.1.3 for relation between Water Reference data and other Spectroscopic objects.
Water Referenced Acquisition | (0018,9297) | 3 | Describes the relation to Water Reference data for this instance. Enumerated Values: WATER_REFERENCE USED_DISCARDED REFERENCED NONE See Section C.8.14.1.4 for description of enumerated values.
Referenced Instance Sequence | (0008,114A) | 1C | References to SOP Instances significantly related to the current SOP Instance, including water reference data. Required if Water Reference Acquisition (0018,9297) equals REFERENCED. May be present otherwise. One or more Items shall be present in this Sequence.
>Include Table 10-3 “Image SOP Instance Reference Macro Attributes” |
>Purpose of Reference Code Sequence | (0040,A170) | 1 | Describes the purpose for which the reference is made. Only a single Item shall be included in this Sequence.
>>Include Table 8.8-1 “Code Sequence Macro Attributes”. | Defined CID 7215 “Spectroscopy Purpose of Reference”.

##### 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.8.14.1.2 MR Spectroscopy Zero Fill Explanation

Zero filling is a data processing technique where zero points are appended to the time domain data before Fourier transformation. The effect of zero filling is to increase the digital resolution in the spectrum. Since the zeros contain no new information, there is no new information added to the spectrum. It is artificially increasing the acquisition time after the data collection without adding any new information or true resolution to the spectrum. See Figure C.8.14.1-1, Figure C.8.14.1-2 and Figure C.8.14.1-3.

Figure C.8.14.1-1. Example Result without and with Zero Filling

Figure C.8.14.1-2. Echo Acquisition with Applying Zero Fill

Figure C.8.14.1-3. Free Induction Decay Acquisition with Applying Zero Fill

##### C.8.14.1.3 MR Spectroscopy Water Reference Data Clarification

MR Spectroscopy is using diagnostic data and water reference data. The water reference data is acquired and used to correct the phase of the diagnostic time domain data before the Fourier transformation to the frequency domain. The relation between the different spectroscopy objects is given in Figure C.8.14.1-4.

When Water Reference Acquisition (0018,9297) equals REFERENCED, it means that instances are available that were or can be used for Water Phase Correction. All other values mean that there are no instances available although data might have been used for water phase correction, see Water Referenced Phase Correction (0018,9199).

The water reference data can also be used for quantification of the signal strength of the diagnostic data.

Figure C.8.14.1-4. Relation Between Spectroscopy Instances

##### C.8.14.1.4 Water Reference Acquisition

The value of Water Reference Acquisition (0018,9297) specifies the intent of the spectroscopy data acquired.

Enumerated Values:

WATER_REFERENCE

  This instance is acquired to be used as water reference and can be used by other spectroscopy data in the study for water phase correction.

USED_DISCARDED

  The phase of this spectroscopic instance is corrected with water reference data. The water reference data used is discarded after correction and no longer available.

REFERENCED

  This spectroscopic instance has water reference data available for phase correction or the phase is already corrected with water reference data. The water reference data shall be specified in the Referenced Instance sequence (0008,114A).

NONE

  This spectroscopic instance has not been corrected for the water phase signal and water reference data has not been acquired.

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