Theoretical and experimental investigation of the VASO contrast mechanism.

TitleTheoretical and experimental investigation of the VASO contrast mechanism.
Publication TypeJournal Article
Year of Publication2006
AuthorsDonahue MJ, Lu H, Jones CK, Edden RAE, Pekar JJ, van Zijl PCM
JournalMagnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine
Date Published2006 Dec

Vascular space occupancy (VASO)-dependent functional MRI (fMRI) is a blood-nulling technique capable of generating microvascular cerebral blood volume (CBV)-weighted images. It is shown that at high magnetic field (3.0T) and high spatial resolution (1.89 x 1.89 x 3 mm(3)), the VASO signal changes are too large (6-7%) to originate from CBV effects alone. Additional contributions are investigated theoretically and experimentally as a function of MRI parameters (TR and TE), as well as the signal-to-noise ratio, (SNR) and spatial resolution. First, it is found that an arterial spin labeling (ASL) contribution causes large negative VASO signal changes at short TR. Second, even at high fMRI spatial resolution, CSF volume contributions (7-13%) cause VASO signal changes to become more negative, most noticeably at long TR and TE. Third, white matter (WM) effects reduce signal changes at lower spatial resolution. The VASO technique has been tested using different stimulus paradigms and field strengths (1-3), giving results consistent with comparable tasks investigated using BOLD and cerebral blood flow (CBF)-based techniques. Finally, simulations show that a mixture of fresh and steady-state blood may significantly alter signal changes at short TR (< or =3 s), permitting larger VASO signal changes than expected under pure steady-state conditions. Thus, many competing effects contribute to VASO contrast and care should be taken during interpretation.

Alternate JournalMagn Reson Med