Author: Sulaiman D. Aldoohan, Gerardo Garcia 👨🔬
Affiliation: University of Toledo Medical Center 🌍
Purpose: To evaluate the noise power spectra (NPS) of images acquired using parallel imaging with varying acceleration factors in 1-D and 3-D spaces and to compare the level of the power of the noise for these images to those obtained with reference spin echo pulse sequence images.
Methods: A 3T MRI scanner equipped with a 32-channel head coil was used with a vendor QC head phantom to obtain five different sets of images using three different pulse sequences: spin echo, fast spin echo, and gradient echo. Parallel imaging with acceleration factors of R = 2 and R = 4 were used with both fast spin echo and gradient echo pulse sequences. Images of noise were generated for each image acquisition through image subtraction. The 2-D NPS was plotted in a 3-D space for visualization purposes. The 1-D NPS was calculated using pixel intensity profile data through the central frequency- and phase-encoding directions of the images of noise and was plotted against the NPS of the reference spin echo pulse sequence for comparison.
Results: In both the 2- and 1-D NPS plots, frequencies from DC to medium-range exhibit the highest noise power, while frequencies above the medium-range exhibit the lowest noise power. The power of the noise in parallel imaging using fast spin echo and gradient echo pulse sequences are higher when compared to the power of the noise for the reference pulse sequence. Increasing the acceleration factor from R = 2 to R = 4 also increases the level of noise power in parallel imaging.
Conclusion: Image acquisition using parallel imaging with fast spin echo and gradient echo pulse sequences and increasing the acceleration factor enhances the level of noise and the power of the noise as computed using the NPS.