How to understand the time tag in dicom?

The dicom provide many time tags, for example:

0008, 0022: Acquisition Date
0008, 0023: Content Date
0008, 002A: Acquisition DateTime
0008, 0032: Acquisition Time
0008, 0033: Content Time

In my thought, there are nearly the same. I can find the relative explanation in web: Acquisition Time Attribute – DICOM Standard Browser

But, there really make me confuzed. Is there any more details for the explanation?

Additional, which tag record the scan time ?

In my experience AcquistionDateTime is the same as AcquisitionDate, AcquisitionTime - and this is usually the timing of the acquisition of the slice.
ContentTime seem to be used differently by different vendors. Sometimes it equals AcqusitionTime sometimes it is some other time, such as time of reconstruction for example.
Typically AcquisitionTime is the important element and ContentTime less so - with exceptions of course.

The tag that you want will depend on how you plan to use the time.

For example, if a doctor in a hospital wants to know when his or her patient was scanned, they usually want the “Study Time”.

If you want something more precise, the “Content Time” is when the image was generated (kind of a vague definition). In some situations, the “Content Time” will be different from one image to the next image, even within the same scan.

The “Acquisition Time” is a type 3 tag (optional), and it won’t always be present. I think it’s most useful for DERIVED images, since it indicates when the original data was acquired rather than just when the derived data was “created”.

However, if you need to do something like sort a 4D cardiac scan into the correct order, none of the above times will be useful, instead you want to know the “Trigger Time” which says where each image is in the cardiac cycle.

In general, the use of “time” in DICOM is going to be different for X-ray vs. cardiac MRI vs. nuclear medicine etc. Can you explain in more detail what you are using the time for?

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@dgobbi Thank you very much for your detail explanation.

Now, I want to deal with DCE (dynamic contrast enhance) image, which is a 4d image (x/y/z-time). Now, in my calculation, I need to know the time interval for different phase image. Which time should be used to calculate the time interval?

For contrast enhanced time-resolved images, the TriggerTime (0018,1060), if present, will give the time in milliseconds between the injection and the acquisition.

I have checked the dicom image, and I can not find the trigger time (0018, 1060):

For this dicom image, which tag time should be used?

If TriggerTime is missing, then maybe they didn’t use an external trigger when they did the scan?

I suggest comparing the metadata for the 1st phase against the metadata for the 2nd phase to see what tags change. Check any private metadata, too.

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Thank you for your kindly suggestion~~