Pure parahydrogen (pH(2) ) is the prerequisite for optimal pH(2) -based hyperpolarization experiments, promising approaches to access the hidden orders of magnitude of MR signals. pH(2) production on-site in medical research centers is vital for the proliferation of these technologies in the life sciences. However, previously suggested designs do not meet our requirements for safety or production performance (flow rate, pressure or enrichment). In this article, we present the safety concept, design and installation of a pH(2) converter, operated in a clinical setting. The apparatus produces a continuous flow of four standard liters per minute of ≈98% enriched pH(2) at a pressure maximum of 50 bar. The entire production cycle, including cleaning and cooling to 25 K, takes less than 5 h, only ≈45 min of which are required for actual pH(2) conversion. A fast and simple quantification procedure is described. The lifetimes of pH(2) in a glass vial and aluminum storage cylinder are measured to be T(1C) (glass vial) =822 ± 29 min and T(1C) (Al cylinder) =129 ± 36 days, thus providing sufficiently long storage intervals and allowing the application of pH(2) on demand. A dependence of line width on pH(2) enrichment is observed. As examples, (1) H hyperpolarization of pyridine and (13) C hyperpolarization of hydroxyethylpropionate are presented.
A novel balanced SSFP technique for the separation or suppression of different resonance frequencies (e.g., fat suppression) is presented. The method is based on applying two alternating and different repetition times, TR 1 and TR 2 . This RF scheme manipulates the sensitivity of balanced SSFP to offresonance effects by a modification of the frequency response profile. Starting from a general approach, an optimally broadened stopband within the frequency response function is designed. This is achieved with a TR 2 being one third of TR 1 and an RF-pulse phase increment of 90°. With this approach TR 2 is too short (ϳ1 ms) to switch imaging gradients and is only used to change the frequency sensitivity. Without a significant change of the spectral position of the stopband, TR 1 can be varied over a range of values (ϳ2.5-4.5 ms) while TR 2 and phase cycling is kept constant. On-resonance spins show a magnetization behavior similar to balanced SSFP, but with maximal magnetization at flip angles about 10°lower than in balanced SSFP. The total scan time is increased by about 30% compared to conventional balanced SSFP. Balanced SSFP (TrueFISP, FIESTA, b-FFE, bSSFP) shows high SNR at short repetition times (1,2) and is frequently used in applications that require high temporal resolution, such as in cardiac imaging or perfusion studies. The T 2 / T 1 -weighted contrast of bSSFP generates a bright fat signal (T 2 /T 1 ϳ0.3) comparable to the signal intensity of liquids or fluids. A separation or suppression of fat signals is thus essential for, e.g., coronary artery imaging (3) or cartilage imaging (4), or in general, to separate different resonances or metabolites.Several methods have been proposed to generate frequency selective bSSFP images. A simple and robust approach is FS-SSFP (spectral or fat saturated SSFP) (5), where magnetization is longitudinally stored after an ␣/2 flipback pulse, thereby offering an interruption of the steady state and making the insertion of a spectral selective saturation pulse possible. A different method is FEMR (fluctuating equilibrium MR) (6), which is based on a modification of the frequency response function of bSSFP generated by modified phase cycling schemes. Two resonances, such as fat and water images, can be acquired simultaneously in an interleaved manner. In LC-SSFP (linear combination SSFP) (7,8), several images with different frequency responses are combined to generate a shaped frequency sensitivity. A similar approach is based on binominal excitation patterns (9) or on the direct synthesis of shaped frequency response function (10). A further possibility is to use the phase difference of the fat and water spins for separation, either by direct phase detection (11) or Dixon-type post processing (12-15).An intrinsic drawback of FEMR, LC-SSFP, binominal excitation patterns (9), and similar variants (16) is the large increase (ϳ100%) in total acquisition time to generate the required frequency response function, as well as a restriction of possible repetition times TR. FS-SSFP...
Fast metabolite mapping based on multiecho balanced SSFP in combination with an iterative reconstruction approach could successfully separate several (1)H resonances and hyperpolarized (13)C metabolites.
A high-level, flexible and hardware-independent approach to sequence programming is ideal for the rapid development of new sequences. The framework is currently not suitable for large patient studies or routine scanning although this would be possible with deeper integration into existing workflows. Magn Reson Med 77:1544-1552, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.