fix(RTStruct): RTSTRUCT contours rendered on first slice for multi-frame images without IPP

[arul-trenser]

Context

• Fixes [Bug] RTSTRUCT contours rendered on first slice for multi-frame images without IPP #5802
• This PR has been incorporated by FlyWheel.io.

Changes & Results

When a multi-frame DICOM dataset does not contain ImagePositionPatient (IPP) in any of the expected locations (PerFrameFunctionalGroupsSequence, SharedFunctionalGroupsSequence, or DetectorInformationSequence), the RTSTRUCT contour mapping logic is unable to resolve the correct referenced image per contour. As a result, all contours are rendered on the first slice.

This PR reintroduces and applies a fallback mechanism that assigns a synthetic IPP based on frame index ([0, 0, frameNumber]) when no valid IPP is available anywhere in the dataset. This allows contour-to-frame resolution to behave deterministically and prevents all contours from collapsing onto the first slice.

Before:
https://github.com/user-attachments/assets/c9a26b76-d9bf-46cd-8afd-9a50b7fd23ea

After:
https://github.com/user-attachments/assets/266ccc80-628f-4298-be90-10fa9425995e

Testing

Load a multi-frame
Drag and drop RTSTRUCT.
Scroll through slices.

Checklist

PR

• My Pull Request title is descriptive, accurate and follows the
  semantic-release format and guidelines.

Code

• My code has been well-documented (function documentation, inline comments,
  etc.)

Public Documentation Updates

• [] The documentation page has been updated as necessary for any public API
  additions or removals.

Tested Environment

• OS: Windows 11
• Node version: v22.19.0
• Browser: Version 144.0.7559.133

Greptile Overview

Greptile Summary

This PR fixes RTSTRUCT contour rendering for multi-frame DICOM images that lack ImagePositionPatient (IPP) metadata. Previously, when IPP was absent from PerFrameFunctionalGroupsSequence, SharedFunctionalGroupsSequence, and DetectorInformationSequence, contours would collapse onto the first slice.

The fix adds || NumberOfFrames > 1 to the condition at combineFrameInstance.ts:35, ensuring all multi-frame datasets enter the code block that provides the synthetic IPP fallback [0, 0, frameNumber] at line 100. This guarantees deterministic contour-to-frame mapping based on frame index when no real IPP is available.

The change is minimal, well-targeted, and directly addresses the reported issue without affecting single-frame images or multi-frame images with proper IPP metadata.

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• The change is a one-line addition that extends an existing conditional to ensure multi-frame images without IPP metadata receive synthetic position values. The logic is sound, well-documented, and addresses a specific rendering bug. The fallback mechanism already exists (line 100); this PR just ensures it's reached for all multi-frame cases. No breaking changes or new dependencies introduced.
• No files require special attention

Important Files Changed

Filename	Overview
platform/core/src/utils/combineFrameInstance.ts	Added condition to ensure all multi-frame images enter the IPP fallback logic, fixing RTSTRUCT contour mapping for images without IPP metadata

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[arul-trenser]

Sample data: US multi-frame data download from https://nbia.cancerimagingarchive.net/ and removed the PerFrameFunctionalGroupsSequence and SharedFunctionalGroupsSequence

https://drive.google.com/file/d/1yBfsNprgm50lKony_Ytcbf_haruTUdEP/view?usp=sharing