Student T-Test on Area Sizes and P-Value significance

Hello. I am running a t-test. 2 groups, group 1 is a area size of a vein before intervention and the second is a vein after intervention. Some decrease and some increase in area. I need to determine if these increase/decrease changes are significant. I tried student t-test type 2, tail 3. Question 1: Am I using the correct tail #? Question 2: How can I determine if the changes are significant? Thank you for your time.


Omega Contributor
So for clarification:

You have a sample with a continuous measure then perform intervention and have a post-intervention value for the same vein?

What is your sample size? What does the distribution of your differences look like, shape-wise?

You will likely use paired t-test and compare your differences to the value "0", which represents no change. Or if the sample is small and differences skewed or distribution is bimodal, etc., you will likely use Wilcoxon signed rank test.