nibabel

name	nibabel
description	Read and write neuroimaging file formats: NIfTI, GIFTI, CIFTI, MGH, Minc, Analyze, SPM. Core I/O for fMRI, diffusion MRI, structural MRI pipelines. Use when handling brain imaging data.
tags	["neuroimaging","nifti","fmri","mri","medical-imaging","python","zorai"]

Overview

NiBabel is the core Python library for neuroimaging file I/O. Use it to read and write NIfTI, GIFTI, CIFTI, MGH, MINC, and Analyze files, inspect affine metadata, and move data between imaging tools and NumPy.

Installation

uv pip install nibabel

Load a NIfTI volume

import nibabel as nib

img = nib.load('brain_t1.nii.gz')
data = img.get_fdata()
affine = img.affine
header = img.header

print(data.shape)
print(header.get_zooms())
print(affine)

Save a modified image

import numpy as np

masked = (data > data.mean()).astype(np.float32)
out = nib.Nifti1Image(masked, affine, header)
nib.save(out, 'brain_mask.nii.gz')

4D fMRI example

fmri = nib.load('rest_bold.nii.gz')
arr = fmri.get_fdata()   # shape like (x, y, z, t)
tr = fmri.header.get_zooms()[-1]
print(arr.shape, tr)

Coordinate handling

NiBabel stores the affine transform from voxel coordinates to world coordinates. Do not ignore it if you are mixing tools, resampling data, or comparing scans across sessions.

Workflow

1. Load with nib.load().
2. Inspect shape, affine, voxel spacing, and orientation assumptions.
3. Use .get_fdata() when you want floating-point arrays.
4. When saving derived outputs, preserve affine/header unless intentionally changing them.
5. For resampling/reorientation, combine with Nilearn, DIPY, or ANTs/SimpleITK workflows rather than hacking the array blindly.