A 2D-GRAPPA Algorithm with a Boomerang Kernel for 3D MRI Data Accelerated along Two Phase-Encoding Directions.

For the reconstruction of 3D MRI data that are accelerated along the two phase-encoding directions, the 2D-generalized autocalibrating partially parallel acquisitions (GRAPPA) algorithm can be used to estimate the missing data in the k-space. We propose a new boomerang-shaped kernel based on theoretic and systemic analyses of the shape and dimensions of the kernel. The reconstruction efficiency of the 2D-GRAPPA algorithm with the proposed boomerang-shaped kernel (i.e., boomerang kernel (BK)-2D-GRAPPA) was compared with other 2D-GRAPPA algorithms that utilize different types of kernels (i.e., EX-2D-GRAPPA and SK-2D-GRAPPA) based on computer simulation, phantom and in vivo experiments. The proposed method was validated for different sets of ACS lines with acceleration factors from four to eight and various sizes of the kernels. A quantitative analysis was also performed by comparing the normalized root mean squared error (nRMSE) in the images and the undersampled edges. Computer simulation, in vivo and phantom experiments, and the quantitative analysis, showed that the proposed method could reduce aliasing artifacts without reducing the SNRs of the reconstructed images.

T2* quantification using multi-echo gradient echo sequences: a comparative study of different readout gradients.

To quantify T2*, multiple echoes are typically acquired with a multi-echo gradient echo sequence using either monopolar or bipolar readout gradients. The use of bipolar readout gradients achieves a shorter echo spacing time, enabling the acquisition of a larger number of echoes in the same scan time. However, despite their relative time efficiency and the potential for more accurate quantification, a comparative investigation of these readout gradients has not yet been addressed. This work aims to compare the performance of monopolar and bipolar readout gradients for T2* quantification. The differences in readout gradients were theoretically investigated with a Cramér-Rao lower bound and validated with computer simulations with respect to the various imaging parameters (e.g., flip angle, TR, TE, TE range, and BW). The readout gradients were then compared at 3 T using phantom and in vivo experiments. The bipolar readout gradients provided higher precision than monopolar readout gradients in both computer simulations and experimental results. The difference between the two readout gradients increased for a lower SNR and smaller TE range, consistent with the prediction made using Cramér-Rao lower bound. The use of bipolar readout gradients is advantageous for regions or situations where a lower SNR is expected or a shorter acquisition time is required.

Setting Criterion for Adolescent Circuit Exercise Program.

The purpose of this study was to develop criteria for an adolescent circuit exercise program. The subjects of this study were 5268 middle- and high-school students. It consisted of three types of circuit exercise programs which were conducted in the physical education class. In the result of this study, we have found two significant finding. First, there were statistically significant differences by grade level and gender in three types of circuit exercise programs. Second, in order to improve the utilization rate and convenience of various adolescents' physical activity environments and the field of school physical education, the gender of each circuit exercise program was classified and the five-grade evaluation criteria were presented. The criteria for circuit exercise program developed in this study will be utilized for various youth physical activities to contribute to improving health and physical fitness. In addition, physical education teachers are expected to use this criteria as a standard for evaluating the physical fitness level of adolescents.

Comparison of Male Adolescents' Physical Fitness Using Physical Activity Promotion System and Circuit Exercise Program.

The purpose of this study is to compare the physical fitness level of adolescents through a physical fitness assessment and a circuit exercise program. A total of 142 middle school students participated. Physical education class consists of a physical fitness assessment, namely, physical activity promotion system (PAPS), and a circuit exercise program. The PAPS measurements include endurance, flexibility, strength, power, body mass index, and total score. The circuit exercise program consists of twist spine, hand walking, rolling squat, cross knee up, jumping and squat, and level-up pacer. First, there were significant differences in PAPS and circuit exercise program according to grade. Second, there was a significant difference in the results of the circuit exercise program according to the level of each physical fitness variable of PAPS. Third, significant correlations were found in the results of the PAPS and circuit exercise program. The use of a circuit exercise program to measure fitness for adolescents can offer convenience for school physical education and be of value as a measure of physical fitness for adolescents. In addition, the circulatory exercise programs used in this study are thought to be applicable to exercise prescriptions to improve endurance, strength, and BMI.

Multi-Exponential Relaxometry Using l1 -Regularized Iterative NNLS (MERLIN) With Application to Myelin Water Fraction Imaging.

A new parameter estimation algorithm, MERLIN, is presented for accurate and robust multi-exponential relaxometry using magnetic resonance imaging, a tool that can provide valuable insight into the tissue microstructure of the brain. Multi-exponential relaxometry is used to analyze the myelin water fraction and can help to detect related diseases. However, the underlying problem is ill-conditioned, and as such, is extremely sensitive to noise and measurement imperfections, which can lead to less precise and more biased parameter estimates. MERLIN is a fully automated, multi-voxel approach that incorporates state-of-the-art l1 -regularization to enforce sparsity and spatial consistency of the estimated distributions. The proposed method is validated in simulations and in vivo experiments, using a multi-echo gradient-echo (MEGE) sequence at 3 T. MERLIN is compared to the conventional single-voxel l2 -regularized NNLS (rNNLS) and a multi-voxel extension with spatial priors (rNNLS + SP), where it consistently showed lower root mean squared errors of up to 70 percent for all parameters of interest in these simulations.