Know the value range for the image data of a NIFTI image

I’m reading a NIFTI file using Python 3.7 and SimpleITK 1.2.4.

I have used this code to show the header information (you can find the header information here):

import SimpleITK as sitk
flair_file = '/content/gdrive/My Drive/Colab Notebooks/.../FLAIR.nii.gz'

reader = sitk.ImageFileReader()
reader.SetFileName(flair_file)

reader.LoadPrivateTagsOn()
reader.ReadImageInformation()
for k in reader.GetMetaDataKeys():
  v = reader.GetMetaData(k)
  print("({0}) = ="{1}"".format(k,v))

print("Image Size: {0}".format(reader.GetSize()))
print("Image PixelType: {0}".format(sitk.GetPixelIDValueAsString(reader.GetPixelID())))

And this is its output:

(ITK_FileNotes) = =""
(aux_file) = =""
(bitpix) = ="32"
(cal_max) = ="0"
(cal_min) = ="0"
(datatype) = ="16"
(descrip) = =""
(dim[0]) = ="3"
(dim[1]) = ="240"
(dim[2]) = ="240"
(dim[3]) = ="48"
(dim[4]) = ="1"
(dim[5]) = ="1"
(dim[6]) = ="1"
(dim[7]) = ="1"
(dim_info) = ="�"
(intent_code) = ="0"
(intent_name) = =""
(intent_p1) = ="0"
(intent_p2) = ="0"
(intent_p3) = ="0"
(pixdim[0]) = ="1"
(pixdim[1]) = ="0.958333"
(pixdim[2]) = ="0.958333"
(pixdim[3]) = ="3"
(pixdim[4]) = ="0"
(pixdim[5]) = ="0"
(pixdim[6]) = ="0"
(pixdim[7]) = ="0"
(qform_code) = ="2"
(qform_code_name) = ="NIFTI_XFORM_ALIGNED_ANAT"
(qoffset_x) = ="118.611"
(qoffset_y) = ="127.182"
(qoffset_z) = ="13.3168"
(quatern_b) = ="0.0315572"
(quatern_c) = ="-0.216054"
(quatern_d) = ="0.975691"
(scl_inter) = ="0"
(scl_slope) = ="1"
(sform_code) = ="1"
(sform_code_name) = ="NIFTI_XFORM_SCANNER_ANAT"
(slice_code) = ="�"
(slice_duration) = ="0"
(slice_end) = ="0"
(slice_start) = ="0"
(srow_x) = ="-0.955749 -0.048177 0.160403 118.611"
(srow_y) = ="0.0220411 -0.868189 -1.26837 127.182"
(srow_z) = ="0.0667887 -0.402902 2.71395 13.3168"
(toffset) = ="0"
(vox_offset) = ="352"
(xyzt_units) = =""
Image Size: (240, 240, 48)
Image PixelType: 32-bit float

Using the imageJ program, this what I get when I click on Image => Show info…

Title: FLAIR.nii.gz
Width:  230.0000 mm (240)
Height:  230.0000 mm (240)
Depth:  144.0000 mm (48)
Size:  11MB
X Resolution:  1.0435 pixels per mm
Y Resolution:  1.0435 pixels per mm
Voxel size: 0.9583x0.9583x3.0000 mm^3
ID: -2
Bits per pixel: 32 (float)
Display range: 0 - 1980.8942
Image: 1/48
No threshold
ScaleToFit: false
Uncalibrated
Path: /FLAIR.nii.gz
Screen location: 927,131 (1920x1080)
Coordinate origin:  0,0,0
No overlay
No selection

And, when I click on Image => Properties, I get that the image is one channel.

If I want to know the value range for the image data, how can I know it? Because the bits per pixel are 32, and the image has one channel, but I don’t know if their values go from 0.0 to 1.0, or from 0.0 to 255.0.

For image data I mean the value for each pixel.

UPDATE

I have used Numpy to know the max a min values from the image data with this code:

import SimpleITK as sitk
flair_file = '/content/gdrive/My Drive/Colab Notebooks/.../FLAIR.nii.gz'

images = sitk.ReadImage(flair_file)

images_array = sitk.GetArrayFromImage(images)
print("Images Array Shape: ", images_array.shape)
print(np.amin(images_array),np.amax(images_array))

And this is its output:

Images Array Shape:  (48, 240, 240)
0.0 2380.6191

Maybe, the min and max value that I’m looking for are: 0.0 and 2380.6191.

Answer

You can use SimpleITK’s StatisticsImageFilter to compute the minimum, maximum, sum, mean, variance sigma of an image. Add the following lines to your code:

img = reader.Execute()
stats = sitk.StatisticsImageFilter()
stats.Execute(img)
print("Minimum:", stats.GetMinimum())
print("Maximum:", stats.GetMaximum())

Here’s the filter’s documentation: https://itk.org/SimpleITKDoxygen/html/classitk_1_1simple_1_1StatisticsImageFilter.html