This year, the LDRR 1.5 Tesla MR unit underwent a significant hardware and software upgrade in order to install new rapidly switching gradients and gradient coils for echo planar imaging (EPI, subsecond imaging). All research pulse sequences developed by LDRR for the older 1.5 Tesla MR units software operating system needed to be rewritten, debugged, and tested which required a significant amount of time. In addition, these research software packages were optimized to take advantage of the new hardware configuration. During the upgrade to LDRR's 1.5 T MR unit, we worked closely with General Electric Medical Systems to correct the hardware problems with the MRI unit. LDRR is cooperating with GE Medical systems on the design of their new gradient amplifier configuration in order to optimize the speed with which one can perform fMRI. Significant improvements and new pulse sequences fast scanning techniques have been developed for functional MR imaging of the brain. A 3D spiral gradient echo imaging sequence when run on LDRR's modified 1.5 Tesla system is able to acquire full brain studies in < 1.7 seconds compared with other commonly used rapid scanning techniques (EPI) which usually require > 3 seconds for a full volumetric study of the brain with isotropic resolution provided by GE on the MRI unit. This technique and its 2D version was specifically developed for fMRI studies in the brain and be sensitive to local changes in the deoxyhemoglobin concentration within the parenchyma or for dynamic contrast studies. The 3D spiral FLASH pulse sequence combines a highly stable gradient echo scheme with a spiral scan technique, which allows the MRI unit to acquire images in a more efficient manner and in shorter periods of time with little trade off in spatial resolution. Two important issues using the 3D spiral FLASH technique in fMRI were addressed. 1) In-flow problem which could artificially enhance vascular structure was substantially suppressed by the true 3D method. 2) High scan-to-scan stability was achieved by spiral waveform and RF phase modulation. FMRI studies using the fast 3D spiral scanning technique were performed at 1.5 T and at 4.0 Tesla MR units to investigate the merit of high field strength for Blood Oxygenation Level Dependent (BOLD) -contrast based functional studies. A simple motor task performed in normal volunteers showed changes in signal intensity associated with activation of primary motor cortex. The BOLD signal changes increased with the echo time (TE) used, however, signal stability over time decreased with the TE at 4 Tesla compared to 1.5 Tesla studies. The overall ability to detect BOLD signal change was actually better at 4 Tesla using shorter echo times. However, the base of the brain susceptibility artifacts at 4.0 Tesla will probably limit the usefulness of the this field strength for whole brain fMRI.
