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".
Table C.8-102 specifies the Attributes of the MR Spectroscopy Module.
Table C.8-102. MR Spectroscopy Module Attributes
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Include Table C.8-83 “MR Image and Spectroscopy Instance Macro Attributes” |
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Spectroscopy data characteristics. See Section C.8.14.5.1.1. |
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Include Table C.8-107 “MR Spectroscopy Description Macro Attributes” |
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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. |
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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. |
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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. |
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Name of volume localization technique used. Shall be "NONE" if no spatial localization was performed. Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise. |
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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. |
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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. |
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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. |
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Indicates whether de-coupling was active. Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise. |
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See Section C.8.14.1.1 for further explanation of the ordering. |
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The center frequency (Hz) for the de-coupling. See Section C.8.14.1.1 for further explanation of the ordering. |
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The chemical shift in ppm at the de-coupling frequency. See Section C.8.14.1.1 for further explanation of the ordering. |
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Describes time domain filtering or apodization applied. Shall be NONE if no filtering operations were applied to the time domain data. Defined Terms: 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. |
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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. |
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Describes baseline correction techniques. Shall be NONE if no baseline correction was performed. Defined Terms: Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise. |
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Specifies whether operations were performed to correct resonant frequency of metabolite peaks due to B0 field inhomogeneities. Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise. |
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Describes whether a first order (frequency dependent) phase correction was applied to the spectral data. Required if Image Type (0008,0008) Value 1 is ORIGINAL or MIXED. May be present otherwise. |
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Indicates if the images or spectra were created using Water Reference time domain data for phase correction. 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. |
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Describes the relation to Water Reference data for this Instance. See Section C.8.14.1.4 for description of enumerated values. |
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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. |
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>Include Table 10-3 “Image SOP Instance Reference Macro Attributes” |
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>>Include Table 8.8-1 “Code Sequence Macro Attributes”. |
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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):
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).
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.
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.
The value of Water Reference Acquisition (0018,9297) specifies the intent of the spectroscopy data acquired.
Enumerated Values:
- WATER_REFERENCE
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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
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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
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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
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This spectroscopic Instance has not been corrected for the water phase signal and water reference data has not been acquired.