fMRI studies of sensitivity and habituation effects within the auditory cortex at 1.5 T and 3 T

To assess habituation effects in relation to field strength by fMRI at 1.5 vs. 3.0 T within the auditory cortex of healthy subjects.

fMRI experiments were performed on 19 healthy subjects at 1.5 T (N = 12) and 3 T (N = 12). The auditory cortex was stimulated binaurally by digitally generated pulsed (nu = 5 Hz) 800 Hz sine tones with three alternating on and off periods.

The mean activation after stimulation (4.4% +/- 1.2% (1.5 T) and 5.3% +/- 2.3% (3 T)) and number of activated pixels (96.7 +/- 49.8 (1.5 T) and 139.9 +/- 101 (3 T)) were higher at 3 T compared to 1.5 T; however, that difference did not reach statistical significance. A characteristic signal decay with repeated stimuli was revealed at both 1.5 and 3 T, and the response to the second and third stimulation blocks was significantly lower compared to the first. The habituation pattern was the same, independently of field strength and age.

The mean activation and number of pixels were only modestly higher at 3 T, probably due to higher physiologic noise and higher local macroscopic susceptibility gradients within the temporal lobes at 3 T. Our data reveal that measured auditory habituation is independent of field strength, and data obtained at two different field strengths do not differ fundamentally in this context.