Search Results (3)

The baseline distortion caused by water and fat signals is a crucial issue in the ¹H MRS(I) study of the human brain. This paper suggests an effective and reliable preprocessing technique to calibrate the baseline distortion caused by the water and fat signals exhibited in the MRS spectral signal. For the preprocessing, we designed a T₂* (or linewidth within the spectral signal) selective filter for the MRS(I) data based on differential filtering within the frequency domain. The number and types for the differential filtering were determined by comparing the T₂* selectivity profile of each differential operator with the T₂* profile of the metabolites to be suppressed within the MRS(I) data. In the performance evaluation of the proposed differential filtering, the simulation data for MRS spectral signals were used. Furthermore, the spectral signal of the human ¹H MRSI data obtained by 2D free induction decay chemical shift imaging with a typical water suppression technique was also used in the performance evaluation. The absolute values of the average of the filtered dataset were quantitatively analyzed using the LCModel software. With the suggested T₂* selective (not frequency selective) filtering technique, in the simulated MRS data, we removed the metabolites from the simulated MRS(I) spectral signal baseline distorted by the water and fat signal observed in the most frequency band. Moreover, in the obtained MRSI data, the quantitative analysis results for the metabolites of interest showed notable improvement in the uncertainty estimation accuracy, the CRLB (Cramer-Rao Lower Bound) levels. Full article

A proton-frequency-transparent (PFT) birdcage RF coil that contains carbon-proton switching circuits (CPSCs) is presented to acquire ¹³C MR signals, which, in turn, enable ¹H imaging with existing ¹H RF coils without being affected by a transparent ¹³C birdcage RF coil. CPSCs were installed in the PFT ¹³C birdcage RF coil to cut the RF coil circuits during ¹H MR imaging. Finite-difference time-domain (FDTD) electromagnetic (EM) simulations were performed to verify the performance of the proposed CPSCs. The performance of the PFT ¹³C birdcage RF coil with CPSCs was verified via phantom and in vivo MR studies. In the phantom MR studies, ¹H MR images and ¹³C MR spectra were acquired and compared with each other using the ¹³C birdcage RF coil with and without the CPSCs. For the in vivo MR studies, hyperpolarized ¹³C cardiac MRS and MRSI of swine were performed. The proposed PFT ¹³C birdcage RF coil with CPSCs led to a percent image uniformity (PIU) reduction of 1.53% in the proton MR images when compared with the case without it. FDTD EM simulations revealed PIU reduction of 0.06% under the same conditions as the phantom MR studies. Furthermore, an SNR reduction of 5.5% was observed at ¹³C MR spectra of corn-oil phantom using the PFT ¹³C birdcage RF coil with CPSCs compared with that of the ¹³C birdcage RF coil without CPSCs. Utilizing the PFT ¹³C birdcage RF coil, ¹³C-enriched compounds were successfully acquired via in vivo hyperpolarized ¹³C MRS/MRSI experiments. In conclusion, the applicability and utility of the proposed 16-leg low-pass PFT ¹³C birdcage RF coil with CPSCs were verified via ¹H MR imaging and hyperpolarized ¹³C MRS/MRSI studies using a 3.0 T MRI system. Full article

The fast Padé transform (FPT) is a method of spectral analysis that can be used to reconstruct nuclear magnetic resonance spectra from truncated free induction decay signals with superior robustness and spectral resolution compared with conventional Fourier analysis. The aim of this study is to show the utility of FPT in reducing of the scan time required for hyperpolarized 13C chemical shift imaging (CSI) without sacrificing the ability to resolve a full spectrum. Simulations, phantom, and in vivo hyperpolarized [1-13C] pyruvate CSI data were processed with FPT and compared with conventional analysis methods. FPT shows improved stability and spectral resolution on truncated data compared with the fast Fourier transform and shows results that are comparable to those of the model-based fitting methods, enabling a reduction in the needed acquisition time in 13C CSI experiments. Using FPT can reduce the readout length in the spectral dimension by 2-6 times in 13C CSI compared with conventional Fourier analysis without sacrificing the spectral resolution. This increased speed is crucial for 13C CSI because T1 relaxation considerably limits the available scan time. In addition, FPT can also yield direct quantification of metabolite concentration without the additional peak analysis required in conventional Fourier analysis. Full article