Question
Question Posted 03/07/25:
Dear ADNI experts, I have downloaded ADNI1 pre-processed (Co-registered and averaged) FDG PET studies. Image values are in the order of magnitude of 1e-4 (with RescaleSlope already applied, as it is done automatically when reading the DICOM series on 3D Slicer or with ITK). What are the units of the data? How can the data be scaled to activity concentration?
Thank you in advance.
Best regards
Dear ADNI experts, I have downloaded ADNI1 pre-processed (Co-registered and averaged) FDG PET studies. Image values are in the order of magnitude of 1e-4 (with RescaleSlope already applied, as it is done automatically when reading the DICOM series on 3D Slicer or with ITK). What are the units of the data? How can the data be scaled to activity concentration?
Thank you in advance.
Best regards
Response posted 03/07/25 by Robert Koeppe:
Co-registered and averaged FDG scans should have several different scales depending on the scanner model. Siemens ECAT HR+ and HRRT scanners will have these low values. They should be treated as being completed UNscaled. Even though the processed images are dicom files, the original images were not. For newer scanners, the units will be in Bq/cc, and have peaks on the average of 30K +/- a far amount. The 3rd pre-processed image set is the one your are asking about, but reoriented to a standard grid size and orientation, plus normalized so the global brain value is about 1. Even if you started with this image set, you would want to intensity normalize these scans but the method of your choice.
