Hi Daniel,

I agree, those flip angle differences are quite big and would make a difference to contrast. I suspect gray/white contrast is better for the higher TI and lower flip angles in those scans (and they could benefit from longer TR). So if you have a balanced study/control group it's ok but I wouldn't compare subjects with systematically different protocols like those below.

Cheers,

Andre.

Bruce Fischl wrote:

Hi Daniel

those are pretty big differences in flip angle. I'll cc Andre van der Kouwe on this so he can comment, but I would be hesitant. The increased TE will have a big effect on dura (darkening it), but will also reduce gray/white contrast.

cheers Bruce

On Fri, 17 Aug 2012, Daniel Ferreira wrote:

...

Dear all, We are designing a study based on clinical data. We want to work with a MPRAGE sequence but subjects have been given 4 different sets of parameters:

• TR: 1900; TE: 4,38; TI: 1100; flip angle: 15
• TR: 1900; TE: 3,55; TI: 1100; flip angle: 15
• TR: 1900; TE: 3,39; TI: 900; flip angle: 9
• TR: 1900; TE: 3,39; TI: 900; flip angle: 15

I wonder how these differences could affect the images and thus the results. Can I combine all of them or at least some of them? Are they so different that I should just study them by separate?

thank you very much on advance

Daniel Ferreira