Useful Papers - fMRI Scanning
Summary: Aguirre et. al experimentally examine the noise profile and power profile of perfusion imaging, demonstrating that perfusion should show increased power relative to BOLD when task-switching frequencies go below blocks of around 60 sec, as well as showing the relative greater across-subject noise for BOLD, and the lack of autocorrelation in perfusion noise.
Summary: Gary describes his trademark spiral in-out sequence, a combination of spiral-in and spiral-out images weighted in a variety of ways, and shows that its use significantly increases SNR over traditional spiral methods and greatly reduces drop-out due to magnetic susceptibility.
Summary: Preston et. al compare a set of tasks known to activate susceptibility-heavy areas using spiral in-out imaging at both 1.5T and 3T, so show that where traditional spiral methods can actually increase dropout at higher field strengths, spiral in-out gets better activation volumes and less dropout at 3T than at 1.5T and confirms spiral in-out is better for a variety of real experimental tasks than traditional spiral.
Summary: Yang et. al describe ways to substantially improve the effective TR of perfusion imaging (although some schemes don't work with all experimental designs), and use event-related paradigms to describe the shape of the impulse response function with perfusion, which is similar to that in BOLD, but precedes it in both rising and falling. The perfusion IRF shows similar nonlinearities to the BOLD IRF.
Summary: Gary discusses various tradeoffs about SNR, such as length of TR and number of interleaves, and walks through the consequences of changing those parameters both in mathematical models and in single-subject data.
Glover handout: Summarizes the above monograph, with a little bit extra about slice thickness. Handout
Philippe handout: A nice primer on k-space and perfusion, and some good page-long summaries on the primary articles. Handout