Abstract
Background Functional magnetic resonance imaging (fMRI) is a useful method for noninvasive presurgical
functional mapping. However, the scanner environment is inherently unsuitable for
the examination of auditory and language functions, due to the loud acoustic noise
produced by the scanner. Interleaved acquisition methods alleviate this problem by
providing a silent period for stimulus presentation and/or response control (sparse
sampling) but at the expense of a diminished amount of data collected. There are possible
improvements to these sparse acquisition methods that increase the amount of data
by acquiring several images per event (clustered sampling). We tested accelerated
clustered fMRI acquisition in comparison with conventional sparse sampling in a pilot
study.
Methods The clustered and sparse acquisition techniques (7.4 minutes scanning time per protocol)
were directly compared in 15 healthy subjects (8 men; mean age: 24 ± 3 years) using
both a motor (tongue movement) and a language (overt picture-naming) task. Functional
imaging data were analyzed using Statistical Parametric Mapping software (SPM12 Wellcome
Department of Imaging Neuroscience, London, UK). For both tasks, activation levels
were compared and Euclidean distances (EDs) between cluster centers (i.e., local activation
maxima and centers of gravity) were calculated. Overlaps and laterality indices were
computed for the picture-naming task. In addition, the feasibility of the clustered
acquisition protocol in a clinical setting was assessed in one pilot patient.
Results For both tasks, activation levels were higher using the clustered acquisition protocol,
reflected by bigger cluster sizes (p < 0.05). Mean ED between cluster centers ranged between 9.9 ± 5.4 mm (left superior
temporal gyrus; centers of gravity) and 16.6 ± 13.2 mm (left inferior frontal gyrus;
local activation maxima) for the picture-naming task. Overlaps between sparse and
clustered acquisition reached 88% (Simpson overlap coefficient). A similar activation
pattern for both acquisition methods was also confirmed in the clinical case.
Conclusion Despite some drawbacks inherent to the acquisition technique, the clustered sparse
sampling protocol showed increased sensitivity for activation in language-related
cortical regions with short scanning times. Such scanning techniques may be particularly
advantageous for investigating patients with contraindications for long scans (e.g.,
reduced attention span).
Keywords
fMRI - speech - picture naming - sparse sampling - multiband
