C.8.28.2 Ophthalmic Thickness Map Module
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#### C.8.28.2 Ophthalmic Thickness Map Module

Table C.8.28.2-1 specifies the Attributes that describe an Image produced by ophthalmic thickness mapping devices.

Table C.8.28.2-1. Ophthalmic Thickness Map Module Attributes

Attribute Name | Tag | Type | Attribute Description
--- | --- | --- | ---
Ophthalmic Mapping Device Type | (0022,1415) | 1 | Describes the type of ophthalmic mapping acquisition device. See Section C.8.28.2.1.3 for further explanation. Defined Terms OCT Optical coherence tomography POLARIMETRY Scanning laser polarimetry SLO_TOMO Scanning Laser Ophthalmoscopy Tomography
Acquisition Method Code Sequence | (0022,1420) | 1 | The acquisition method used for obtaining ophthalmic thickness mapping. Only a single Item shall be included in this sequence.
>Include Table 8.8-1 “Code Sequence Macro Attributes” | Defined CID 4261 “Ophthalmic Mapping Acquisition Method”
Acquisition Method Algorithm Sequence | (0022,1423) | 1C | Software algorithm used to provide acquisition method. Required if Acquisition Method Code Sequence (0022,1420) contains an item with the value of (111923, DCM, "Corneal birefringence compensation") May be present otherwise. Only a single Item shall be included in this sequence.
>Include Table 10-19 “Algorithm Identification Macro Attributes” |
Instance Number | (0020,0013) | 1 | A number that identifies this instance.
Content Date | (0008,0023) | 1 | The date the data creation was started.
Content Time | (0008,0033) | 1 | The time the data creation was started.
Acquisition DateTime | (0008,002A) | 1 | The date and time that the acquisition of data that resulted in this image started. ### Note The synchronization of this time with an external clock is specified in the Synchronization Module in Acquisition Time Synchronized (0018,1800).
Image Type | (0008,0008) | 1 | Image identification characteristics. See Section C.8.28.2.1.1 for specialization.
Samples Per Pixel | (0028,0002) | 1 | Number of samples (planes) in this image. See Section C.7.6.3.1.1 for further explanation. Enumerated Values: 1
Photometric Interpretation | (0028,0004) | 1 | Specified the intended interpretation of the pixel data. See Section C.7.6.3.1.2 for further explanation. Enumerated Values: MONOCHROME2
Pixel Representation | (0028,0103) | 1 | Data representation of pixel samples. Enumerated Values: 0000H unsigned integer
Pixel Spacing | (0028,0030) | 1 | Physical distance in the patient between the center of each pixel, specified by a numeric pair - adjacent row spacing (delimiter) adjacent column spacing in mm. ### Note Since a patient's retina is curved, there can be a small error in using Pixel Spacing (0028,0030) for distance measurements in the periphery of the image. See Section 10.7.1.3 for further explanation.
Pixel Aspect Ratio | (0028,0034) | 1 | Ratio of the vertical size and horizontal size of the pixels in the image specified by a pair of integer values where the first value is the vertical pixel size, and the second value is the horizontal pixel size.
Bits Allocated | (0028,0100) | 1 | Number of bits allocated for each pixel sample. Each sample shall have the same number of bits allocated. See PS3.5 for further explanation. Enumerated Values: 8 16
Bits Stored | (0028,0101) | 1 | Number of bits stored for each pixel sample. Enumerated Values: 8 16
High Bit | (0028,0102) | 1 | Most significant bit for pixel sample data. Each sample shall have the same high bit. See PS3.5 for further explanation. Enumerated Values: 7 if Bits Stored (0028,0101) = 8 15 if Bits Stored (0028,0101) = 16
Pixel Presentation | (0008,9205) | 1 | The source of the color information for use during rendering. Enumerated Values: COLOR Use Supplemental Palette Color LUT Module Attributes COLOR_REF Use Referenced Color Palette Instance UID (0028,0304)
Referenced Color Palette Instance UID | (0028,0304) | 1C | The identifier of the color palette (i.e., an instance of the Color Palette Storage SOP Class "1.2.840.10008.5.1.4.39.1") for use during rendering. Required if Pixel Presentation (0008,9205) is COLOR_REF.
Lossy Image Compression | (0028,2110) | 1 | Specifies whether an Image has undergone lossy compression (at a point in its lifetime). Enumerated Values: 00 Image has NOT been subjected to lossy compression. 01 Image has been subjected to lossy compression. Once this value has been set to 01 it shall not be reset. See Section C.7.6.1.1.5.
Lossy Image Compression Ratio | (0028,2112) | 1C | Describes the approximate lossy compression ratio(s) that have been applied to this image. See Section C.7.6.1.1.5 for further explanation. May be multi-valued if successive lossy compression steps have been applied; the value order shall correspond to the values of Lossy Image Compression Method (0028,2114). ### Note For example, a compression ratio of 30:1 would be described in this Attribute with a single value of 30. For historical reasons, the lossy compression ratio may also be described in Derivation Description (0008,2111). Required if Lossy Image Compression (0028,2110) is "01".
Lossy Image Compression Method | (0028,2114) | 1C | A label for the lossy compression method(s) that have been applied to this image. See Section C.7.6.1.1.5 for further explanation. May be multi-valued if successive lossy compression steps have been applied; the value order shall correspond to the values of Lossy Image Compression Ratio (0028,2112). ### Note For historical reasons, the lossy compression method may also be described in Derivation Description (0008,2111). Required if Lossy Image Compression (0028,2110) is "01".
Burned In Annotation | (0028,0301) | 1 | Indicates that the image does not contain burned in annotation to identify the patient and date the image was acquired. Enumerated Values: NO
Recognizable Visual Features | (0028,0302) | 1 | Indicates whether or not the image contains sufficiently recognizable visual features to allow the image or a reconstruction from a set of images to identify the patient. Enumerated Values: NO
Image Laterality | (0020,0062) | 1 | Laterality of object imaged (as described in Anatomic Region Sequence (0008,2218)) examined. Enumerated Values: R right eye L left eye ### Note This Attribute is mandatory, in order to ensure that images may be positioned correctly relative to one another for display. Shall be consistent with any laterality information contained in Primary Anatomic Structure Modifier Sequence (0008,2230), if present. ### Note Laterality (0020,0060) is a Series level Attribute and must be the same for all Images in the Series, hence it must be absent.
Ophthalmic Thickness Map Type Code Sequence | (0022,1436) | 1 | The type of ophthalmic thickness map encoded in this SOP Instance. It specifies the meaning of the pixel values. Only a single Item shall be included in this sequence.
>Include Table 8.8-1 “Code Sequence Macro Attributes” | Defined CID 4263 “Ophthalmic Thickness Map Value Type”
Include Table C.7.6.16-12 “Real World Value Mapping Macro Attributes” if Ophthalmic Thickness Map Type Code Sequence (0022,1436) contains an item with the value (111930, DCM, "Absolute ophthalmic thickness") or (111932, DCM, "Thickness deviation from normative data"). May be present otherwise. | Defined CID for Measurement Units Code Sequence is 4260
Pixel Value Mapping to Coded Concept Sequence | (0022,1450) | 1C | Provides a pixel value and the mapping of that pixel value to an associated Coded Concept. Required if Ophthalmic Thickness Map Type Code Sequence (0022,1436) contains an item with the value (111931, DCM, "Thickness deviation category from normative data"). May be present otherwise. One or more Items shall be present.
>Mapped Pixel Value | (0022,1452) | 1 | Pixel value to be mapped.
>Pixel Value Mapping Code Sequence | (0040,9098) | 1 | The mapping from Mapped Pixel Value (0022,1452) to an associated Coded Concept. Only a single Item shall be included in this sequence.
>>Include Table 8.8-1 “Code Sequence Macro Attributes” | Defined CID 4265 “Ophthalmic Thickness Deviation Categories”.
>Pixel Value Mapping Explanation | (0022,1454) | 3 | Free form text explanation of the Coded Concept.
Ophthalmic Thickness Mapping Normals Sequence | (0022,1443) | 1C | Identifies the data set used for mapping values from a normative data base. Required if Ophthalmic Thickness Map Type Code Sequence (0022,1436) contains an item with the value or (111931, DCM, "Thickness deviation category from normative data") or (111932, DCM, "Thickness deviation from normative data"). May be present otherwise. Only a single Item shall be included in this sequence.
>Include Table 10-22 “Data Set Identification Macro Attributes” |
Relevant OPT Attributes Sequence | (0022,1472) | 1C | Attributes from the OPT image that provide critical context for the interpretation of this ophthalmic map SOP Instance. Required if Ophthalmic Mapping Device Type (0022,1415) is OCT. Only a single Item shall be included in this sequence
>Depth Spatial Resolution | (0022,0035) | 1 | The inherent limiting resolution in microns for depth of the acquisition equipment for high contrast objects for the data gathering and reconstruction technique chosen. If variable, the value at the center of the scanning volume.
>Maximum Depth Distortion | (0022,0036) | 1 | Maximum distortion in depth direction in % of Depth Spatial Resolution.
Source Image Sequence | (0008,2112) | 1C | The Image SOP Class/Instance pair of the Image that was used to generate this Image. Required if Ophthalmic Mapping Device Type (0022,1415) is OCT. May be present otherwise. Only a single Item shall be included 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, (i.e., the role the source image or frame(s) played in the generation of this image). Only a single Item shall be included in this sequence.
>>Include Table 8.8-1 “Code Sequence Macro Attributes” | Defined CID 7202 “Source Image Purposes of Reference”.
Referenced Instance Sequence | (0008,114A) | 1C | A sequence that provides reference to a set of SOP Class/Instance pairs identifying images or other composite SOP Instances to plan the acquisition or significant related information. Required if Ophthalmic Photography Reference Image available. May be present otherwise. See Section C.7.6.16.2.5.1 for further explanation. Zero or more Items may be included in this Sequence.
>Include Table 10-11 “SOP Instance Reference Macro Attributes” |
>Purpose of Reference Code Sequence | (0040,A170) | 1 | Code describing the purpose of the reference to the Instance(s). Only a single Item shall be included in this sequence.
>>Include Table 8.8-1 “Code Sequence Macro Attributes” | Defined CID 4264 “Ophthalmic Map Purposes of Reference”.
Registration to Localizer Sequence | (0022,1465) | 3 | Registration of current instance to a localizer SOP Instance referenced in Attribute Referenced Instance Sequence (0008,114A). See Section C.8.28.2.1.2 for an example.
>Registered Localizer Units | (0022,1466) | 1 | Units of measure for the axes of the registered localizer image. Enumerated Values: PIXEL See Bounding Box Annotation Units (0070,0003) for definition.
>Registered Localizer Top Left Hand Corner | (0022,1467) | 1 | Location of the Top Left Hand Corner (TLHC) of the registered localizer in Registered Localizer Units (0022,1466), given as column\row. Column is the horizontal offset and row is the vertical offset.
>Registered Localizer Bottom Right Hand Corner | (0022,1468) | 1 | Location of the Bottom Right Hand Corner (BRHC) of the registered localizer in which Registered Localizer Units (0022,1466), given as column\row. Column is the horizontal offset and row is the vertical offset.
Include Table 10-5 “General Anatomy Mandatory Macro Attributes” | The concept code for Anatomic Region Sequence (0008,2218) shall be (T-AA000, SRT, "Eye"), and Defined CID 244 “Laterality” shall be used for Anatomic Region Modifier Sequence (0008,2220). Defined CID 4266 “Ophthalmic Anatomic Structure Reference Point” shall be used for Primary Anatomic Structure Sequence (0008,2228). Only a single Item shall be included in this sequence. ### Note Although Primary Anatomic Structure Sequence (0008,2228) is Type 3, it is important to convey this information if able to be determined.
Relative Image Position Code Sequence | (0022,001D) | 3 | The position of this image on the retina (as defined by a specified nomenclature; the nomenclature is implicit in the code used). Only a single Item is permitted in this sequence.
>Include Table 8.8-1 “Code Sequence Macro Attributes”. | Baseline CID 4207 “Ophthalmic Image Position”.
Anatomic Structure Reference Point | (0022,1463) | 1C | Location of a point in the image identified by an anatomic structure. This is used in ophthalmology for a landmark within a patient's eye. Given as column\row. Column is the horizontal offset and row is the vertical offset. Image relative position specified with sub-pixel resolution such that the origin at the Top Left Hand Corner (TLHC) of the TLHC pixel is 0.0\0.0, the Bottom Right Hand Corner (BRHC) of the TLHC pixel is 1.0\1.0, and the BRHC of the BRHC pixel is Columns\Rows (see Figure C.10.5-1). The values must be within the range 0\0 to Columns\Rows. Required if Primary Anatomic Structure Sequence (0008,2228) contains an item with the value (T-AA621, SRT "Fovea centralis") or (T-AA630, SRT, "Optic nerve head") or (M-01000, SRT, "Lesion") or (111934, DCM, "Disc-Fovea"). May be present otherwise.
Retinal Thickness Definition Code Sequence | (0022,1445) | 1C | The definition of the retinal thickness for this image. Required if Attribute Image Type (0008,0008) value 3 is RETINAL_THICK. Only a single Item shall be included in this sequence.
>Include Table 8.8-1 “Code Sequence Macro Attributes” | Defined CID 4262 “Retinal Thickness Definition”

##### C.8.28.2.1 Ophthalmic Thickness Map Module Attribute Descriptions

###### C.8.28.2.1.1 Image Type

For Ophthalmic Thickness Maps, Image Type (0008,0008) is specified to be Type 1 and uses one of the following Defined Terms for Value 3:

Defined Terms:

ONH

  identifies a topographic map of an optic nerve head

RETINAL_THICK

  identifies a Thickness Map for retinal layers or combination of several sub-layers

### Note

1. The images created based upon the source data of the patient examination would be ORIGINAL\PRIMARY.

2. If the value is specified as "RETINAL_THICK", the definition of the retinal thickness is in Retinal Thickness Definition Code Sequence (0022,1445).

###### C.8.28.2.1.2 Referenced Instance Sequence

Equipment generating an ophthalmic map (OPM) image, may also obtain an accompanying "reference/localizer" image. This "reference/localizer" image serves the purpose of orienting and registering the OPM image to the actual retinal location. For example, a fundus photo may be obtained with ophthalmic tomography (OPT). When the retinal thickness map is generated based on OPT data, the OPM is registered with pixel precision to the fundus photo. This "reference/localizer" image is referenced in the OPM SOP Instance using the attribute Referenced Instance Sequence (0008,114A).

An example of a "reference/localizer" image and its relationship to an OPM image is shown in Figure C.8.28.2.1-1. Legend: ( A ) a fundus photo is taken as the "reference/localizer" image. The green box indicates the area the OPT scans are obtained. ( B ) The retinal thickness map (OPM object) is overlaid on the "reference/localizer" fundus photo to show the correspondence. These examples could be referenced from different types of SOP Classes, such as Color Softcopy Presentation State Storage (referencing the OP SOP Instance of a fundus photo), True Color Secondary Capture Image Storage, Encapsulated PDF, etc. The Purpose of Reference Code Sequence (0040,A170) code is set to (DCM, 121311, Localizer) for example A. Registration to Localizer Sequence (0022,1465) would be used for example B.

Figure C.8.28.2.1-1. Reference/Localizer Image Related to OPM Image

###### C.8.28.2.1.3 Ophthalmic Mapping Device Type

For Ophthalmic Mapping Device Type (0022,1415), Scanning Laser Ophthalmoscopy Tomography (SLO_TOMO) produces a topographical representation of the optic nerve head (ONH) rather than a thickness depiction. However, the topographical depiction can be considered as "thickness" measurements of multiple points of the ONH surface relative to an assigned datum plane. For this reason, the topographical image is included in the ophthalmic thickness map module.

Figure C.8.28.2.1-2. Optic Nerve Head Thickness Example

For Ophthalmic Mapping Device Type (0022,1415), Polarimetric Tomography (POLARIMETRY) produces a thickness depiction based on birefringent phase shifts. This is a thickness measure but does not use typical international system of units such as micrometer, etc. Due to this, the unit of measurement is defined by the implementation, such as 'p-um'.

Figure C.8.28.2.1-3. Polarimetry Optic Nerve Head Thickness Example

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