Question about zeroed-out regions in k-space

#1

Hello.

While visualizing the k-space data, I found that many volumes had zeroed-out regions at the edges of k-space.

While this would make the image size larger, this adds no additional information.

I have verified that there are several such cases in the knee data set.

I have not yet checked the brain data set.

Also, all the blanks are in the phase encoding dimension (the last dimension, which has variable length).

Is there a good reason for doing this?

Thank you in advance for helping out.

#2

Hi @veritas9872,

This padding is an artifact of the way the kspace is acquired. I think you can find the exact dimensions that were padded in the ismrmrd_header e.g.:

import ismrmrd
hdr = ismrmrd.xsd.CreateFromDocument(data['ismrmrd_header'][()])
enc = hdr.encoding[0]
enc_size = (enc.encodedSpace.matrixSize.x,
                    enc.encodedSpace.matrixSize.y,
                    enc.encodedSpace.matrixSize.z)
enc_limits_center = enc.encodingLimits.kspace_encoding_step_1.center
enc_limits_max = enc.encodingLimits.kspace_encoding_step_1.maximum + 1
padding_left = enc_size[1] // 2 - enc_limits_center
padding_right = padding_left + enc_limits_max

Thanks,
Tullie