DICOM PS3.17 2019c - Explanatory Information

III.4 Diabetic Macular Edema Example (Current)
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## III.4 Diabetic Macular Edema Example

A 48 year old Navajo male with diabetes, decreased visual acuity and fundoscopic stigmata of diabetic retinopathy receives several tests to assess his likelihood of macular edema. Optical coherence tomography (OPT) is performed to assess the thickness of the retina in the macular area. This is performed with retinal thickness depicted by ophthalmic mapping. The results is an Ophthalmic Thickness Map SOP instance with the Ophthalmic Thickness Mapping Type Code Sequence (0022,1436) set to "Absolute Ophthalmic Thickness" and the Measurements Units Code Sequence (0040,08EA) in the Real World Value Mapping Macro, set to "micrometer". The OPT image is also referenced in Attribute Referenced Instance Sequence (0008,114A).

Figure III.4-1. Macula Edema Thickness Map Example

Since the thickness of the macula varies normally based upon a number of dependencies such as age, gender, race, etc. Interpretation of the retinal thickness in any given patient may be done in the context of normative data that accounts for these variables. The thickness data used to generate the thickness map is analyzed using a manufacturer specific algorithm for comparison to normative data relevant to this specific patient. The results of this analysis is depicted on a second thickness "map" (second SOP Instance) showing each pixel's variation from normal in terms of confidence that the variation is real and not due to chance. Specific confidence levels are then depicted by arbitrary color mapping registered to the fundus photograph. This is typically noted as the percent probability that the variation is abnormal e.g., p >5%, p <5%, p <1% etc. The results is an Ophthalmic Thickness Map SOP instance with the Ophthalmic Thickness Mapping Type Code Sequence (0022,1436) set to "Thickness deviation category from normative data". Mapping the "categories" to a code concept is accomplished via Attribute Pixel Value Mapping to Coded Concept Sequence (0022,1450).

Figure III.4-2. Macula Edema Probability Map Example

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DICOM PS3.17 2019c - Explanatory Information