The issue here is that MRI signal has a lot of low frequency drift, due to effects like gradient heating. Unfortunately, your expected frequency is 120s “up”, so a 240s sine-wave. Given the roll-off associated with filters, the standard rule fo thumb would be a 480s high pass filter, which will allow a lot of low frequency noise to leak through. I think you would want to choose your filter carefully. I would anticipate that you will have a null result, the amount of low frequency noise makes it unlikely your signal to noise will survive a statistical threshold. On the other hand, if your effect size is very large, you might find something.