9 research outputs found
High spatio-temporal resolution in functional MRI with 3D echo planar imaging using cylindrical excitation and a CAIPIRINHA undersampling pattern
Purpose
The combination of 3D echo planar imaging (3DâEPI) with a 2DâCAIPIRINHA undersampling scheme provides high flexibility in the optimization for spatial or temporal resolution. This flexibility can be increased further with the addition of a cylindrical excitation pulse, which exclusively excites the brain regions of interest. Here, 3DâEPI was combined with a 2D radiofrequency pulse to reduce the brain area from which signal is generated, and hence, allowing either reduction of the field of view or reduction of parallel imaging noise amplification.
Methods
3DâEPI with cylindrical excitation and 4âĂâ3âfold undersampling in a 2DâCAIPIRINHA sampling scheme was used to generate functional MRI (fMRI) data with either 2âmm or 0.9âmm inâplane resolution and 1.1âs temporal resolution over a 5âcm diameter cylinder placed over both temporal lobes for an auditory fMRI experiment.
Results
Significant increases in image signalâtoânoise ratio (SNR) and temporal SNR (tSNR) were found for both 2âmm isotropic data and the highâresolution protocol when using the cylindrical excitation pulse. Both protocols yielded highly significant blood oxygenation levelâdependent responses for the presentation of natural sounds.
Conclusion
The higher tSNR of the cylindrical excitation 3DâEPI data makes this sequence an ideal choice for high spatiotemporal resolution fMRI acquisitions. Magn Reson Med 79:2589â2596, 2018. © 2017 International Society for Magnetic Resonance in Medicine
Superior GRAPPA reconstruction with reduced g-factor noise using 2D CAIPIRINHA for 3D EPI
Efficient GRAPPA or SENSE reconstruction is largely dependent on coil geometry in the direction in which phase encoding steps reduction is performed during partially parallel acquisition. In this study we demonstrate the ability to perform a 2D CAIPIRINHA trajectory in a 3D EPI sequence to reduce the geometry factor (g-factor) noise amplification in the reconstructed images for a predefined total acceleration. 2D CAIPIRINHA style k-space patterns provide improved reconstructions when using very large accelerations on one phase-encode direction, thanks to the ability to use the coil sensitivities along the other phase-encode direction to compensate the reduced coil sensitivity variation
Comparison of an 8-Channel and a 32-Channel Coil for High-Resolution fMRI at 7T
Multi-channel receive array rf-coils have become widely available for fMRI. The improved SNR and possibility of acquisition acceleration through parallel imaging are especially beneficial for high-resolution studies. In this study, an 8-channel and a 32-channel coil were compared in a high-resolution finger tapping fMRI experiment at 7T. 1.3mm3 resolution data acquired with the 32-channel coil provided higher image- and temporal SNR and yielded higher BOLD sensitivity measures, notably higher cluster sizes in MI/SI and increased z-scores, though not an increase in percent signal change. For sub-millimeter resolution fMRI data acquired with the 32-channel coil smaller clusters were found, though percent signal changes were significantly larger, due to reduced partial volume effects. These results demonstrate the utility of the use of an array coil with a large number of receive elements for high-resolution fMRI at ultra-high field
Comparison of an 8-Channel and a 32-Channel Coil for High-Resolution fMRI at 7Â T
Multi-channel receive array rf-coils have become widely available for fMRI. The improved SNR and possibility of acquisition acceleration through parallel imaging are especially beneficial for high-resolution studies. In this study, an 8-channel and a 32-channel coil were compared in a high-resolution finger tapping fMRI experiment at 7 T. 1.3 mm3 resolution data acquired with the 32-channel coil provided higher image- and temporal SNR and yielded higher BOLD sensitivity measures, notably higher cluster sizes in MI/SI and increased z-scores, though not an increase in percent signal change. For sub-millimeter resolution fMRI data acquired with the 32-channel coil smaller clusters were found, though percent signal changes were significantly larger, due to reduced partial volume effects. These results demonstrate the utility of the use of an array coil with a large number of receive elements for high-resolution fMRI at ultra-high field
Microcantilever based biosensors
By combining silicon micromechanical techniques with surface functionalization, it is possible to realize MEMS (Micro-Electro-Mechanical system) systems for biological analysis. In this review, we summarize the working principle of a few selected MEMS bio-sensing devices. We also discuss the fabrication and operational aspects of such sensors and In particular immunosensors which employ the unique principle of antibody-antigen interaction. A complete overview of biological sensing using microcantilevers is presented