Small Animal Imaging Resource Program @ Johns Hopkins
A time-activity curve (TAC) is the activity concentration measured over the course of a dynamic study, and may correspond to a region-of-interest (ROI) or even a single voxel.
- To load the PET data, click File->Load as.” Enter the .img file of interest, which is probably the full-frames, dynamic version of the PET file. Click on “Single Multivolume” at the prompt.
- With the image highlighted in red, click on the “ROI tool” button.
- Click on File->Load Object map, and load the ROI’s.
- To set the data at the correct time for sampling, click on Generate->Slice. Using the toolbars, set Volume to 1, Increment to 1, and Number to the largest value (sliding the toolbar farthest to the right). Primary Increment set to Volume
- Click on the “Sample Opts” button on the top toolbar, which stands for sample options.
- Click on “Select Object,” and select all.
- Keep all options on, except for “Sequence Display” which can be turned off to increase the speed of sampling time (if Sequence Display is on, the image will be shown as it is sampled).
- Turn Log Stats ON to produce a log of the data. Configure Log Stats to include desired options such as file, object number, mean, number of voxels, etc.
- Click OK to leave Sample Options.
- On the left toolbar, click on “Sample Images.” The log is produced, showing the sampled data.
- Select all the data in the log, right click, and turn on “Editable.” This allows you to copy and paste the data into Excel.
- When you copy and paste the data into Excel, it is entered into one column. To extract the time-activity curves (TAC’s), select the column, and click on Data->Text to Columns”, and extract the data (probably using the Delimited, then Space options).
- At this point, one can manipulate the TAC’s as desired. To quickly obtain the TAC’s for each region, select the topmost row and click on Data->Filter->AutoFilter. Then, when one clicks on the cell at the top of the “Object” column, one can quickly isolate the data for the object/ROI.
- When you click on “Object1,” the data for that region alone appears in the data column. This data can then be copied and pasted into it’s own column in a separate sheet. There, it can be given it’s proper heading of region name, eg Thalamus.
- Once all the TAC’s are in separate columns, the time data can be imported into the leftmost column in that sheet, allowing plotting of X-Y scatter plots