Cache DICOM SEG referenced series UIDs to eliminate 30s delay on volume selection

[Copilot]

Selecting a volume triggers getAssociatedSegmentationFileNumber(), which calls pydicom.dcmread() once per SEG series in the study to check if it references the selected volume. With many SEG files, this causes ~30 second delays.

Changes

Added simple cache for referenced series lookups:

• _referencedSeriesCache dict maps SEG series UID → referenced CT series UID
• Modified getReferencedCtSeries() to check cache before reading DICOM files
• Cache None for missing files/failures to avoid repeated errors
• Added clearReferencedSeriesCache() for manual invalidation if needed

Result:

• First call per SEG series: unchanged (reads DICOM)
• Subsequent calls: O(1) dict lookup
• Benefits getAssociatedSegmentationFileNumber() (line 773) and loadDicomSeries() (line 1826)

def getReferencedCtSeries(self, segmentation_uid):
    # Check cache first
    if segmentation_uid in self._referencedSeriesCache:
        return self._referencedSeriesCache[segmentation_uid]
    
    # Read DICOM file only if not cached
    ds = pydicom.dcmread(series_files[0], stop_before_pixels=True, specific_tags=["ReferencedSeriesSequence"])
    referenced_series = ds.ReferencedSeriesSequence[0].SeriesInstanceUID
    self._referencedSeriesCache[segmentation_uid] = referenced_series
    return referenced_series

Cache is safe since DICOM Series Instance UIDs are immutable identifiers.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Long delay/reaction time after selecting input volume</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Long delay/reaction time after selecting input volume #4

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