What the NIfTI audit checks
The tool recognizes NIfTI-1’s 348-byte and NIfTI-2’s 540-byte headers in either byte order. It checks magic, rank and dimensions, datatype versus bitpix, spatial resolutions, scaling, units, vox_offset, extension framing, and whether the available voxel bytes match the declared array. Both single-file .nii/.nii.gz and paired .hdr plus optional .img storage are supported.
Understanding qform and sform
qform stores a quaternion-derived rigid orientation with voxel scales, while sform stores an explicit affine matrix. Both can be active and can intentionally name different coordinate spaces. This auditor therefore reports numerical displacement and code names separately: a difference is not automatically corruption. Opposite handedness is elevated because it can reverse left/right interpretation between the two active transforms.
How to investigate an orientation warning
Start with the qform and sform codes, their RAS-like direction summaries, determinants, and the sampled corner displacement. Compare the file in the software that produced it and a trusted neuroimaging viewer. Do not “fix” a matrix merely to make both transforms identical: registration, scanner, aligned, and template spaces may legitimately differ, and downstream software can choose transforms differently.
Important clinical and validation boundary
This is a bounded file-structure diagnostic, not a medical device, image viewer, complete NIfTI validator, or clinical interpretation tool. It does not display anatomy, assess acquisition quality, diagnose a person, verify every intent or extension payload, validate external sidecars, infer the scientifically correct coordinate frame, repair headers, or certify safe clinical use. Confirm consequential results with authoritative neuroimaging software and the originating workflow.
Frequently asked questions
Does this upload a patient scan?
No. Parsing, gzip expansion, matrix calculations, and exports happen locally in the current browser tab. Still follow your organization’s rules for handling protected data on the device.
Why is a qform/sform difference only a warning?
The two transforms may deliberately represent scanner and aligned or template spaces. The report provides codes, matrices, handedness, and corner displacement so a knowledgeable user can determine intent.
Does RAS mean the image is clinically oriented correctly?
No. It is a compact description of how positive voxel axes map to world-axis directions. It cannot establish patient identity, correct labeling, acquisition integrity, or clinical correctness.
Authoritative references
The NIfTI-1 reference header and NIfTI-2 reference header define field layouts, datatypes, units, transforms, magic values, and extensions. The NIfTI Data Format Working Group’s qform and sform usage guidance explains the intended coordinate-space roles.
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