Understanding the LC Indicator

Synapse appends (LC) to a measurement made on an image when there is low confidence in the accuracy of the result.

LC indicates Low Confidence because measurement results are based on a paucity of data. This means the values used for the calculation are inconsistent some expected data is missing from the DICOM file, or DICOM compliance is not being followed.

Caution:

If the measurement has an (LC) indicator, verify the measurement with another source or calibrate the image.

Conditions When LC Indicator Displays

The following conditions cause the LC indicator to display:

  • Spacing obtained from Imager Pixel Spacing, regardless of whether Estimated Radiographic Magnification Factoring (ERMF) was applied for non-projection-based images.
  • Spacing obtained from Nominal Scanned Pixel Spacing.
  • Spacing obtained from Pixel Spacing when Imager Pixel Spacing, Pixel Spacing Calibration Type, and ERMF/Distance Source to Detector (SID)/Distance Source to Patient (SOD) attributes are absent. This only applies to projection radiography images. This does not apply to Fujifilm projection or Fujifilm BT images.
  • Spacing obtained from Pixel Spacing when the value matches the Nominal Scanned Pixel Spacing attribute.
  • Spacing obtained from Pixel Spacing when the value matches the Imager Pixel Spacing attribute.
    • This does not apply to MG Projection. MG projection only uses Imager pixel spacing and should not have pixel spacing compared to imager pixel spacing.
    • This does not apply to MG synthetics, specifically for Hologic, GE, and Fujifilm .
    • This does not apply to Fujifilm projection images or Fujifilm BT images.

SOP Classes When LC Indicator Displays

For the following Service Object Pair (SOP) classes, Synapse appends LC when any spacing type is used or when the image is manually calibrated.

Note:

Synapse appends LC when Photographic SOP Classes are used in an image that might contain content whose distance from the camera varies. Because Synapse cannot determine the accuracy of the distance of these SOP Classes from the camera, Synapse cannot accurately measure the object.

  • A measured object might be farther away from the camera lens than another measured object.
  • Parts of a measured object might be farther from the camera lens than other parts of that same object.
  • VL Endoscopic Image Storage
  • VL Microscopic Image Storage (might not be essentially flat as is VL Slide-Coordinates Microscopic Image Storage)
  • VL Photographic Image Storage

Applying Manual Calibration

Applying Manual Calibration on the above images behaves in the following ways:

  • Non VL image cases: Synapse removes the LC and displays the asterisk * since the manually-calibrated value still has improved accuracy
  • VL images: Synapse continues to display the LC label after manual calibration and appends the label with an asterisk *, indicating that while the image is still impacted by the varied camera distance, a user has attempted to manually calibrate it.

When LC is appended for annotations, it is also reflected in the Scale Marker.

Related Topics

Using the Ruler

Calibrating the Ruler

Using Ratios