Investigation of the three-dimensional spiral technique for functional magnetic resonance imaging

Blood Oxygenation Level Dependent (BOLD) contrast has been widely used in functional Magnetic Resonance Imaging (fMRI). The typical voxel size of traditional BOLD fMRI studies is ∼4mmx4mmx5mm. The coarse resolution typically employed is enough for many applications in clinical or cognitive neuroscience. However, in the study of fine cortical structures, high resolution fMRI is necessary. For high resolution fMRI studies, low Signal to Noise Ratio (SNR) and limited spatial coverage are the major challenges. My research is mainly focused on developing acquisition methods to address those issues.;When thermal noise dominates physiological noise in the experiment, which is true for high resolution fMRI studies, the 3D acquisition method in general can provide a higher SNR compared to the 2D method. Although the 3D method suffers from reduced steady-state signal due to the shorter repetition time (TR), it also benefits from the reduced noise due to the averaging in the slice-select direction inherent in the inverse Fourier transform. The effect of noise reduction will overcompensate that of signal loss. As a result, a better SNR performance can be achieved by using the 3D method.;For fMRI studies, a volume scan time which is below 3 seconds is preferred to track the temporal signal change caused by the BOLD effect. Since high resolution scans require the acquisition of a very large k-space, a substantial increase in scan time per slice is necessary. As a result, the number of slices which could fit into a given temporal resolution decreases. A new method which combines the 3D acquisition method with the UNFOLD technique is proposed here. By doing so, a much larger spatial coverage could be achieved without sacrificing the total scan time and the quality of activation maps. Theoretically, there will be a decrease in temporal resolution and an increase in SNR performance, which are associated with the UNFOLD technique. However, those effects are negligible when a small reduction factor is used.;In summary, the 3D spiral acquisition method provides a better alternative to the traditional 2D multi-slice method for high resolution fMRI studies.