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Old May 22nd, 2011, 03:37 PM
jglasermd jglasermd is offline
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First recorded activity by OfficeFrustration: May 2011
Posts: 3
Default manipulating x-axis and calculating derived values from data

Hi all:

I have a couple of things I have been trying to do with Excel, to no avail. I am developing some Excel sheets and charts to use for nuclear medicine imaging test results. Here are my problems:

1. the test in question uses images taken at various time intervals (in minutes): 5, 10, 15, 20, 25, 30, 45, 60, 75, 90, 105, 120. As you can see, the first several intervals are in increments of 5, while the later values are in increments of 15. These tests are graphed with the above times on the x-axis and activity (in imaging count rates) on the y-axis. I have been trying to fix the x-axis so that the spacing of the data points and the slopes between them are accurate even using this irregular interval; until now all the data points look like they are 5 minutes apart and this is not true. If I try to use empty cells to fill dummy points, the curve keeps dipping back to the x-axis assuming the value is zero.

2. Once the above is figured out, I am also trying to take the calculated value of 1/2 of the maximum y-axis value, and automatically generate a value for the corresponding x-axis coordinate. this corresponds to the time where the activity present at the beginning of the test has decreased by half. This has medical significance to us. At the present time, it is measured by hand and is laborious.

Please help!