fix(ultrasound): guard inline region decode against malformed values

decodeUltrasoundRegion throws on truncated FD/US bytes. Mirror the
file path's try/catch in DicomMetaLoader so a malformed sequence
can't abort the metadata stream.

Also align the unit-code comment to decimal (matches the spec test)
and note that applyUltrasoundSpacing reads only chunks[0].

Author: PaulHax

src/core/streaming/dicom/dicomMetaLoader.ts

@@ -78,7 +78,13 @@ export class DicomMetaLoader implements MetaLoader {
           el.element === SEQUENCE_OF_ULTRASOUND_REGIONS[1] &&
           !ultrasoundRegions
         ) {
-          ultrasoundRegions = decodeUltrasoundRegion(el.data);
+          // Decoding can throw if a malformed FD/US value has an unexpected
+          // length; swallow rather than abort the whole metadata load.
+          try {
+            ultrasoundRegions = decodeUltrasoundRegion(el.data);
+          } catch (err) {
+            console.warn('Failed to decode SequenceOfUltrasoundRegions:', err);
+          }
         }
       },
     });

src/core/streaming/dicom/ultrasoundRegion.ts

@@ -7,8 +7,8 @@ import { Tags, tagToGroupElement } from '@/src/core/dicomTags';
 // DICOM unit codes for PhysicalUnitsXDirection / YDirection.
 // See DICOM PS3.3 C.8.5.5.1.15. The only spatial spacing code defined for
 // this field is 3 (cm). Other codes (0=none, 1=percent, 2=dB, 4=seconds,
-// 5=hertz, 6=dB/seconds, 7=cm/sec, 8=cm², 9=cm²/sec, A=cm³, B=cm³/sec,
-// C=degrees) are time, frequency, velocity, area, volume, or angle, so
+// 5=hertz, 6=dB/sec, 7=cm/sec, 8=cm², 9=cm²/sec, 10=cm³, 11=cm³/sec,
+// 12=degrees) are time, frequency, velocity, area, volume, or angle, so
 // they are not converted to a VTK image spacing.
 export const US_UNIT_CENTIMETERS = 3;
 

src/core/streaming/dicomChunkImage.ts

@@ -286,6 +286,10 @@ export default class DicomChunkImage
   private applyUltrasoundSpacing() {
     if (this.getModality() !== 'US') return;
 
+    // Ultrasound DICOMs are typically a single multi-frame chunk, so the
+    // region table on chunk[0] applies to the whole image. If a US series
+    // ever spanned multiple chunks with differing regions, this would
+    // silently use the first chunk's spacing for all of them.
     const regions = this.chunks[0]?.ultrasoundRegions;
     if (!regions?.region) return;