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Curved Planar Reformat

The Curved Planar Reformat (CPR) tool creates straightened views of curved anatomical structures within volume data. By slicing along a user-defined path and resampling the resulting slices, CPR generates a new volume where the curved structure appears straightened.

Accessing the Tool​

  1. Navigate to the Image tab in the ribbon.
  2. Click Curved Planar Reformat in the Advanced section.

Concepts​

TermDescription
PathA curve defining the centerline of the structure to be straightened
CPRCurved Planar Reformation/Reformat
Straightened CPRThe resulting volume where the curved path becomes straight

Workflow​

1. Create a Path​

Before using CPR, you must define a path along the structure:

  1. Create a curve or spline path.
  2. Place points along the centerline of the curved structure (e.g., vessel, nerve, airway).
  3. Ensure the path follows the structure's course smoothly.

2. Configure CPR Parameters​

Open the CPR tool and configure the following parameters:

ParameterDescription
Curve resolution (mm)Controls path subdivision density; smaller values = smoother result
Slice thickness (mm)Spacing between slices in the output Z-axis
Slice size (pixels)Dimensions of each output slice [X, Y]
Rotation (°)Orientation of output slices around the path (-90° to +90°)
Interpolation modeResampling quality (Nearest, Linear, Cubic)

3. Select Path and Apply​

  1. Select the path from the Paths dropdown.
  2. Choose the Result option (new volume or existing).
  3. Click Apply to generate the straightened volume.

Parameters in Detail​

Curve Resolution​

The curve resolution determines how finely the path is sampled:

  • Smaller values (e.g., 0.5 mm): More slices, smoother result, larger output
  • Larger values (e.g., 2.0 mm): Fewer slices, faster processing, smaller output
tip

Match the curve resolution to your volume's original slice thickness for consistent sampling.

Slice Thickness​

The Z-spacing of the output volume. Controls how the straightened structure is spaced:

  • Typically matches the curve resolution
  • Affects the output volume's physical dimensions

Slice Size​

The X and Y dimensions of each output slice in pixels:

  • Larger values capture more tissue around the path
  • Smaller values focus tightly on the structure
  • Consider the structure's diameter when setting this value

Rotation​

Rotates the slicing plane around the path:

  • 0°: Default orientation
  • ±90°: View from different angles
  • Useful for viewing different aspects of the straightened structure

Interpolation Mode​

ModeQualitySpeed
NearestBlocky, fastFastest
LinearSmooth, balancedMedium
CubicSmoothest, high qualitySlowest

Use Cases​

Vascular Analysis​

Straightening blood vessels for:

  • Stenosis measurement
  • Plaque visualization
  • Diameter assessment along the vessel length

Airway Assessment​

Straightening airways for:

  • Obstruction identification
  • Diameter mapping
  • Surgical planning

Spinal Imaging​

Straightening the spinal canal or column for:

  • Curvature-independent analysis
  • Disc space assessment
  • Stenosis evaluation

Intestinal Analysis​

Straightening the colon or small bowel for:

  • Virtual endoscopy preparation
  • Polyp detection
  • Lesion measurement

Technical Notes​

How CPR Works​

  1. The path is subdivided according to curve resolution.
  2. At each path point, a perpendicular slice plane is computed.
  3. The volume is resampled at that plane to create a 2D slice.
  4. All slices are stacked to form the straightened volume.

Path Requirements​

  • Path should be continuous without sharp turns.
  • More points provide better path definition.
  • Avoid self-intersecting paths.
warning

Very tortuous paths may produce artifacts due to slice overlap or gaps. Adjust parameters or simplify the path if artifacts appear.

Output Volume Properties​

  • X dimension: Slice size X parameter
  • Y dimension: Slice size Y parameter
  • Z dimension: Path length / curve resolution
  • Spacing: Based on slice size and thickness parameters

Best Practices​

  1. Smooth paths: Use enough points for a smooth curve but avoid over-sampling.
  2. Appropriate slice size: Set large enough to capture the structure plus margin.
  3. Preview first: Start with coarser resolution to verify path alignment.
  4. Check for artifacts: Look for dark bands or gaps indicating path issues.

Scripting​

CPR operations are accessible through the Volvicon Python API. Refer to the API documentation for programmatic access to CPR functionality.

info

The straightened volume is a new object that can be saved, exported, or used for further analysis like any other volume in Volvicon.