NRRD File Compatibility

NRRD header requirements for 3D medical assets in Ango Hub

Ango Hub supports NRRD files in the 3D Medical labeling editor when they describe a single 3D medical volume with enough spatial information to build the Axial, Coronal, and Sagittal views.

The .nrrd file extension alone does not guarantee that the file can be opened. The NRRD header must also describe a supported volume.

Supported NRRD files

A supported NRRD asset must meet all of the following requirements:

Header field	Required value
dimension	Must be 3.
sizes	Must contain exactly 3 values, one for each axis.
space	Must be one of left-posterior-superior, LPS, right-anterior-superior, RAS, left-anterior-superior, or LAS.
space directions	Must be a 3x3 matrix. Each of the 3 rows must contain exactly 3 values.
space origin	Must contain exactly 3 values.
space units	Optional. If omitted, Ango Hub uses mm.

Ango Hub supports NRRD files using raw, ascii, txt, text, gzip, or gz encoding.

The voxel data must use a scalar numeric NRRD type, such as signed or unsigned 8-bit, 16-bit, or 32-bit integers, float, or double.

Unsupported NRRD files

Ango Hub does not support NRRD assets with any of the following properties:

• 2D, 4D, time-series, vector, or multi-component volumes where dimension is not 3.

• 4D medical volumes with a leading list/vector/time axis, even if only 3 of the axes are spatial.

• Scanner-based coordinate systems, including scanner-xyz and 3D-* spaces.

• Coordinate systems other than LPS, RAS, or LAS.

• Files with missing or malformed sizes, space directions, or space origin values.

• Detached-header NRRD files that use data file or datafile.

• NRRD files using hex, bzip2, or other encodings outside the supported encodings listed above.

• NRRD files using block or 64-bit integer data types.

If an unsupported NRRD file is opened in Ango Hub, the asset may fail to load and the editor may show warnings such as Only 3D volumes are supported, Space information is missing in the NRRD file, or Space directions matrix is of incorrect shape.

Example supported header

NRRD0005
type: short
dimension: 3
space: left-posterior-superior
sizes: 512 512 128
space directions: (0.7,0,0) (0,0.7,0) (0,0,1.5)
space origin: (0,0,0)
space units: "mm" "mm" "mm"
encoding: gzip

What to do if a file is not supported

Convert the volume before importing it into Ango Hub. The converted file should be a single 3D scalar volume with an LPS, RAS, or LAS coordinate system, 3 values in sizes, a 3x3 space directions matrix, and a 3-value space origin.