Fix a CT Scan with Stacked Phases

OsiriX and Horos Course · Database

I'm Dr. Alexandre Amato, and in this lesson I show a very common problem when we receive exams from labs that don't save in the standard format: a study that looks normal in the axial view but, in 3D MPR, triggers an irregular-slices warning and distortion — because the lab placed two datasets “one on top of the other” within the same series. In the example, when scrolling through the aorta exam, it looks normal. However, when opened in 3D MPR, a warning appears saying the slices are irregular, varying from ~1 mm to almost 500 mm, which can cause measurement errors and distortions. The cause becomes clear: there is an arterial phase (more contrast-enhanced) and, right below it, another less enhanced phase (probably venous/delayed) stacked in the same dataset. How to fix it (step by step, as shown in the video) 1) Exit 3D MPR and go back to the axial dataset Close the 3D MPR window and return to the exam's axial series (in the example, “Angio Aorta”). 2) Make a backup before changing anything Before deleting anything: I export the exam to the Desktop (DICOM), so there is no risk of losing the original study. The idea is to edit the files safely, keeping an intact copy. 3) Find the “cut line” between the phases In the axial image preview, I look for the last image that still has contrast (arterial phase). In the video, you can spot the turning point because: contrast is still visible up to a certain slice suddenly more inferior images appear (e.g., hip/femur) and the next image “goes back” to a superior region (e.g., lung) This clearly indicates that the series “restarted” and contains two blocks (two datasets). 4) Delete the part you want to discard I select all images from the cut point downward (the duplicated/unwanted block). I press Delete and confirm the deletion. In the example: the dataset had 700-something images after cleanup, it was left with 398 images 5) Reopen in 3D MPR and check the warning When reconstructing again, the irregularity drops considerably (in the video, it now varies from 1 mm to 2 mm). Result: you now have a single dataset, suitable for evaluating the patient without the distortions caused by the duplication. 6) How to recover the original exam (if needed) I re-import the backup I exported to the Desktop. This way, OsiriX has all the original images again, keeping your copy intact. In the video, I also mention that there is another option (such as renaming the exam), but the main focus is the simple and safe method: backup → locate the cut → delete the duplicated block → reconstruct → re-import if needed.