Unexpected BOLD behavior at 11.7 Tesla: A Comparison of Experimental Data with the Integrative BOLD Signal Model

Introduction: It is generally accepted that the contrast of BOLD response increases with higher magnetic field strength [1]. However, in experimental and clinical studies it was shown that the intravascular component (IV) of the BOLD effect disappears for magnetic fields higher 4.0 Tesla, which is due to very short blood T2 at higher fields. Extravascular components (EV) are still expected to increase linearly to super-linearly with field strength [2]. Data up to 7.0 Tesla support this argument, but no data comparing higher field strengths has been published so far. Latest results in our group pointed out that this increase might diminish at higher field strengths [3]. Recently, theoretical predictions by the Integrative BOLD Signal Model [4] support this finding for spin-echo (SE) EPI whereas for gradient-echo (GE) EPI an increase with magnetic field strength is still expected. Here, experimental data are compared to theoretical predictions, an explanation for SE-EPI BOLD behavior is given and GE-EPI data are discussed.