DICOM in Ophthalmology, an Example of a New Enhanced Multiframe Object Herman Oosterwijk Add logo if desired

Enhanced Multiframe Objective: This presentation will answer the following question: What are the major features of the new generation enhanced multiframe DICOM objects, how to understand this new type of object, and how does a typical enhanced multiframe look like, in particular OCT (Optical Coherence Tomography)

Enhanced multiframe: Agenda: Major features of the new generation of DICOM objects, i.e. enhanced multiframe Steps to encode/decode this new type of object OCT object, a sample enhanced multiframe

Traditional Multiframe objects: Vector Single image, multiple frames US, NM, XA, RF, SC, VL Simple structure: # frames Frame rate Frame index pointer Frame increment pointer (NM)

Enhanced multiframe: Why a new generation of objects: CT, MR, ophthalmology, mammography tomo, XA, RF Imaging is moving from pixels in slices (2-D) to voxels (3-D) and beyond (n-D), i.e. time, space, frequency, flow: functional imaging (CTA, etc.) Simple “Study-Series-Image” hierarchy does not suffice anymore for organization, viewing, browsing, sorting using the appropriate hanging protocols Text descriptions for Series leaves room for guessing

Sample application: Cardiac Imaging

Enhanced multiframe: Solution: enhanced multiframe Many Attributes are required (Type 1) Where possible, Attribute contents are encoded Definition of multiple dimensions Header size reduction Protocol efficiency: 1000 slice CT 1000 times C-Store RQ…RS vs 1 time RQ…RS ONE structure serving as a template for all new SOP Classes (CT, MR, XA, RF, OCT, MG…)

Dimension Index Values Dimension example: 3 \ 1 \ 3 Dimension Index Values 5 4 3 2 1 5 Trigger Delay Time ID 1 Stack ID=1 100 ms Dimension Indexes (3): Trigger Delay Time Stack ID Position 5 4 3 2 1 50 ms ID 2 1 Space (2) Time (1) 5 4 3 2 1 0 ms ID 3 Time

Enhanced multiframe encoding: Fixed per frame: Name, ID…. Accession #, Study ID… KV, mAs…. Orientation…. #rows, columns, bits Split header: Fixed information Variable information (keep as minimum as possible) Some information can be in both places (contrast) Header Part 1 Variable for one/more frames: Position Time Scab type Header Part 2 Pixels in frames

Enhanced multiframe: Header part 2 (variable) definition: Implemented as “functional groups”: SQ with zero, one, or more items Documented as “macros” in Multi-Frame Functional Group Module Common functional groups, used for multiple modalities, such as “Frame Content Macro” Structure of dimensions, and concatenations is “generic”: Multi-frame functional group and dimension modules Modality specific functional groups, e.g. for MR, ophthalmology, etc.

Functional groups:

Multiframe Functional Groups: Shared attributes Per-frame attributes Pixel data

OPT multiframe image sample:

IOD: Ophthalmology: IE Module Reference Usage Patient C.7.1.1 M Study General Study C.7.2.1 Patient Study C.7.2.2 U Series General Series C.7.3.1 Ophthalmic Tomography Series C.8.17.X1 Frame of Reference C.7.4.1 C – Required if Reference Image available Synchronization C.7.4.2 Equipment General Equipment C.7.5.1 Enhanced General Equipment C.7.5.2 Image Image Pixel C.7.6.3 Enhanced Contrast/Bolus C 7.6.4b C – Required if contrast was administered Multi-frame Functional Groups C.7.6.16 Multi-frame Dimension C.7.6.17 Acquisition Context C.7.6.14 Cardiac Synchronization C.7.6.18.1 C – Required if cardiac synchronization was used Ophthalmic Tomography Image C.8.17.X2 Ophthalmic Tomography Acquisition Parameters C.8.17.X3 Ophthalmic Tomography Parameters C.8.17.X4 Ocular Region Imaged C.8.17.5 SOP Common C.12.1

MULTI-FRAME FUNCTIONAL GROUPS MODULE ATTRIBUTES Attribute Name Tag Type Attribute Description Shared Functional Groups Sequence (5200,9229) 2 Sequence that contains the Functional Group Macros that are shared for all frames in this SOP Instance. >Include one or more Functional Group Macros that are shared by all frames. Per-frame Functional Groups Sequence (5200,9230) 1 Sequence that contains the Functional Group Macros corresponding to each frame of the Multi-frame Image. >Include one or more Functional Group Macros.

OPHTHALMIC TOMOGRAPHY FUNCTIONAL GROUP MACROS Function Group Macro Usage Pixel Measures M Frame Content M – May not be used as a Shared Functional Group. Plane Position C – Required if no Ophthalmic Photography Reference Image available Plane Orientation C – Required if no Ophthalmic Photography Reference Image available; May be present otherwise Referenced Image C – Required if Ophthalmic Photography Reference Image available. Derivation Image C – Required if the image or frame has been derived from another SOP Instance. Frame Anatomy Cardiac Trigger C – Required if Cardiac Synchronization Technique (0018,9037) equals other than NONE May be present otherwise. Contrast/Bolus Usage C – Required if Contrast/Bolus Agent Sequence (0018,0012) is used. May not be used as a Shared Functional Group Ophthalmic Frame Location U

Implementation issues: Enhanced multiframe: Implementation issues: Support by vendors, especially PACS archives and even more workstations: growing, but slowly Mixed environments: new and old, especially for established modalities (CT, MR, XA, RF) Handling very large files: concatenation (not allowed for OCT) – splitting up into mini-multi frames Retrieval on frame level: to be added to standard

Conclusion: New, enhanced multiframe objects are defined in DICOM, some for existing, some for new modalities These new objects provide better interoperability for n-D (esp. dynamic) objects, allow for more sophisticated display protocols, and give better performance Modalities, and to a lesser degree PACS systems are starting to support it; a mixed environment is inevitable

Herman Oosterwijk: herman@otechimg.com www.otechimg.com Thank you! Herman Oosterwijk: herman@otechimg.com www.otechimg.com