Long runtime and incorrect output format for PETPVC rbv correction with 4D images

[ninea-anasovi]

Description:

I am encountering two issues with PETPVC when applying region-based voxel (rbv) correction to 4D PET dynamic images. The PET image consists of 28 frames, and I have a corresponding 4D mask image with the same number of frames.

Long Runtime:

When I attempt to perform the rbv correction using PETPVC with 28 frames, the runtime exceeds 3 hours and the process does not complete. I have left my computer running overnight, but the correction does not finish.
Incorrect Output Format:
As an alternative, I tried applying the rbv correction with only 2 frames. Although the correction completed in a reasonable time frame, the resulting image was in a 3D format instead of the expected 4D output.

Steps to Reproduce:

Prepare a 4D PET dynamic image with 28 frames.
Prepare a 4D mask image with 28 frames.
Apply the rbv correction using PETPVC.
Observe that the correction process takes longer than 3 hours without completing for 28 frames.
Additionally, observe that when using 2 frames, the rbv correction finishes, but the output is in 3D format instead of 4D.

Additional Information:

I have confirmed that both the PET dynamic image and the mask image are in the correct 4D format required by PETPVC.
I have reviewed the PETPVC documentation and did not find any specific instructions regarding the handling of 4D data.
I am using the latest version of PETPVC (please specify the version number if known).

Expected Behavior:

The runtime for the rbv correction should be reasonable, even for 28 frames.
The rbv correction should generate a 4D corrected PET image, preserving the temporal dimension of the input data.
Please let me know if any further information or clarification is needed to address these issues. Thank you!