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Question Posted 02/26/14:
I am encountering the following issue while trying to download longitudinal (or entire sets) of image collections.

For example, if I want to download the entire PET image dataset from a subject, I have been setting the following parameters:

- PET data
- ADNI 1 / ADNI Go
- Subjects with Baseline & 6 Month & 12 Month & 24 Month images. I specifically choose the AND option

However despite using these option, I occasionally get subjects with only one or less than 4 longitudinal PET data series.

Is there a bug in the search tool so that the \'AND\' does not search for only subjects with all 4 images from those dates?
Response posted 02/26/14 by Jessie, IDA:
On the search function, the Study/Visit parameter is not dependent on the Image (Modality) parameter. Therefore, when you select ADNI 1 Baseline, and ADNI1/GO Months 6, 12, and 24, you are technically not searching for subjects with PET images on all 4 of those visit dates. You are rather searching for images of subjects who were present on all four of those visits. With the subjects that you have identified (with less than all 4 scans), the subjects were present at all 4 of those specified visits, but they did not necessarily have PET images taken.

If you download the Early Discontinuation and Withdrawal table from the Enrollment category, you can see why some of these subjects might not have all four PET scans. For example, a subject with only one baseline PET scan may have been discontinued from further PET scans for some reason or another (ex. neck pain), but completed all other ADNI scans and assessments on the 4 study visits specified.
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