C.8.12.5 Optical Path Module
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#### C.8.12.5 Optical Path Module

Table C.8.12.5-1 specifies the attributes of the optical paths used in the VL imaging. Each optical path is a combination of illumination, filters, lenses, and sensors, and each combination is identified for possible reference by attributes in other modules. Additional optical path parameters may be specified in the Acquisition Context Module.

Table C.8.12.5-1. Optical Path Module Attributes

Attribute Name | Tag | Type | Attribute Description
--- | --- | --- | ---
Optical Path Sequence | (0048,0105) | 1 | Describes the optical paths used during the acquisition of this image. One or more Items shall be included in this sequence. See Section C.8.12.5.1.1
>Optical Path Identifier | (0048,0106) | 1 | Identifier for the optical path specified in the Sequence Item. The identifier shall be unique for each Item within the Optical Path Sequence.
>Optical Path Description | (0048,0107) | 3 | Description of the optical path specified in the Sequence Item.
>Illuminator Type Code Sequence | (0048,0100) | 3 | Type of illuminator. Only a single Item is permitted in this sequence.
>>Include Table 8.8-1 “Code Sequence Macro Attributes” | Context ID may be defined in the IOD constraints.
>Illumination Wave Length | (0022,0055) | 1C | Nominal wavelength of the illuminator in nm. Required if Illumination Color Code Sequence (0048,ee08) is not present. May be present otherwise.
>Illumination Color Code Sequence | (0048,0108) | 1C | Color of the illuminator. Only a single Item shall be included in this sequence. Required if Illumination Wave Length (0022,0055) is not present. May be present otherwise.
>>Include Table 8.8-1 “Code Sequence Macro Attributes” | Context ID may be defined in the IOD constraints.
>Illumination Type Code Sequence | (0022,0016) | 1 | Coded value for illumination method. See Section C.8.12.5.1.2. One or more Items shall be included in this sequence.
>>Include Table 8.8-1 “Code Sequence Macro Attributes” | Context ID may be defined in the IOD constraints.
>Light Path Filter Type Stack Code Sequence | (0022,0017) | 3 | Filters used in the light source (excitation) path. One or more Items are permitted in this sequence. See Section C.8.12.5.1.3.
>>Include Table 8.8-1 “Code Sequence Macro Attributes” | Context ID may be defined in the IOD constraints.
>Light Path Filter Pass-Through Wavelength | (0022,0001) | 3 | Nominal pass-through wavelength of light path filter(s) in nm
>Light Path Filter Pass Band | (0022,0002) | 3 | Pass band of light path filter(s) in nm. This Attribute has two Values. The first is the shorter and the second the longer wavelength relative to the peak. The values are for the - 3dB nominal (1/2 of peak) pass through intensity. One of the two Values may be zero length, in which case it is a cutoff filter.
>Image Path Filter Type Stack Code Sequence | (0022,0018) | 3 | Describes stack of filters used in image (emission) path between the imaging target and the optical sensor. One or more items are permitted in this sequence. See Section C.8.12.5.1.3.
>>Include Table 8.8-1 “Code Sequence Macro Attributes” | Context ID may be defined in the IOD constraints.
>Image Path Filter Pass-Through Wavelength | (0022,0003) | 3 | Nominal pass-through wavelength of image path filter(s) in nm
>Image Path Filter Pass Band | (0022,0004) | 3 | Pass band of image path filter(s) in nm. This Attribute has two Values. The first is the shorter and the second the longer wavelength relative to the peak. The values are for the - 3dB nominal (1/2 of peak) pass through intensity. One of the two Values may be zero length, in which case it is a cutoff filter
>Lenses Code Sequence | (0022,0019) | 3 | Lenses that were used in this optical path. One or more items are permitted in this sequence.
>>Include Table 8.8-1 “Code Sequence Macro Attributes” | Context ID may be defined in the IOD constraints.
>Condenser Lens Power | (0048,0111) | 3 | Nominal power of the condenser lens
>Objective Lens Power | (0048,0112) | 3 | Nominal power of the objective lens. If a single lens is used as both condenser and objective, its power is specified in this attribute.
>Objective Lens Numerical Aperture | (0048,0113) | 3 | Nominal numerical aperture of the objective lens.
>Channel Description Code Sequence | (0022,001A) | 1C | Describes the light color sensed for each channel to generate the image. Required if this differs from the natural interpretation. ### Note For MONOCHROME2, the natural interpretation is the full visible light spectrum. A full spectrum sensor may be presented with light of only a single color based on illumination and filters. Equipment may use a color Photometric Interpretation (RGB, YBR) as a container representing up to 3 channels of any detected wavelength. Shall have the same number of Items as the value of Samples per Pixel Used (0028,0003) if present, or otherwise the value of Samples per Pixel (0028,0002). The channels shall be described in the order in which the channels are encoded.
>>Include Table 8.8-1 “Code Sequence Macro Attributes” | Context ID may be defined in the IOD constraints.
>Palette Color Lookup Table Sequence | (0048,0120) | 3 | For MONOCHROME2 images, provides a transform of the pixel values with this optical path into an RGB color representation. The LUT provides a mapping to an appropriate color or pseudo-color for display purposes. Only a single Item is permitted in this sequence.
>>Include Table C.7-22a “Palette Color Lookup Table Macro Attributes” |
>ICC Profile | (0028,2000) | 1C | An ICC Profile encoding the transformation of device-dependent stored pixel values into PCS-Values. See Section C.8.12.5.1.4 Required if Photometric Interpretation (0028,0004) is not MONOCHROME2, or if Palette Color Lookup Table Sequence (0048,0120) is present.

##### C.8.12.5.1 Optical Path Attribute Descriptions

###### C.8.12.5.1.1 Optical Path Sequence and Optical Path Identifier

The Optical Path Sequence (0048,0105) shall include an Item for every optical path used in the acquisition of the current image.

For single frame images that do not include the Multi-frame Functional Groups Module, this Sequence shall include only one Item.

For images that use the Multi-frame Functional Groups Module, the optical path associated with each frame is identified by reference to the Optical Path Identifier (0048,0106) of this Sequence (see Optical Path Identification Sequence (0048,0207) in Section C.8.12.6.2). The Optical Path Sequence may include Items for defined optical paths that are not referenced by any frame.

For Whole Slide Microscopy Image LOCALIZER images (see Section C.8.12.4.1.1 and Section C.8.12.7), all the optical paths associated with referenced images shall be described in Items of this Optical Path Sequence. The optical path associated with each referenced frame is identified in the Referenced Image Navigation Sequence (0048,0200) by reference to an Optical Path Identifier (0048,0106) of this Sequence. The Optical Path Identifiers used in the LOCALIZER image do not have to be identical to those used in the referenced images.

### Note

1. For example, each of four referenced images may use a different optical path (color), and within each of those image SOP Instances the single Optical Path Sequence Item is identified as "1", although the meaning of optical path "1" is different for each image. The LOCALIZER, however, must include all four optical paths with distinct identifiers "1", "2", "3", and "4".

2. The Optical Path Identifier is not necessarily numeric; it is a string of up to 16 characters (VR SH).

###### C.8.12.5.1.2 Illumination Type Code Sequence

Illumination Type Code Sequence (0022,0016) specifies the type of illumination of the imaging target. This attribute may include multiple Items, as some techniques may involve multiple methods, or some method identifiers may not be completely descriptive.

### Note

For example, this attribute might include two items, (111741, DCM, "Transmission illumination") and (111748, DCM, "Differential interference contrast") to indicate "Transmission DIC".

The type of illumination often prescribes the set of optical path components such as filters and prisms, and their arrangement in the optical path.

### Note

For instance, phase contrast illumination will utilize a condenser annulus and a phase contrast plate; this may be indicated by an item (111747, DCM, "Phase contrast illumination") in this attribute, but with no further specification in the filters and lenses identification attributes.

###### C.8.12.5.1.3 Light Path and Image Path Filter Type Stack Code Sequences

In some optical imaging methods, e.g., epifluorescence, there may be a single light path with its associated imaging components that is used in both illumination/excitation of the imaging target and in the transmitted/emitted path to the imaging sensor. In this case, the optical components are to be specified in the Image Path Filter Type Stack Code Sequence (0022,0018).

###### C.8.12.5.1.4 ICC Profile

ICC Profile (0028,2000) provides the transform for mapping stored color pixel values into ICC standard color Profile Connection Space (PCS). For MONOCHROME2 pixels that have a preferred color rendering through the Palette Color Lookup Table Sequence (0048,0120), this attribute provides a mapping of that preferred RGB color rendering into PCS. The ICC Profile shall follow the requirements specified in Section C.11.15.1.1.

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