“…We recorded a PCr/ATP of 1.90 ± 0.92 using the AW FT‐MRS method, which is in good agreement with the previous literature values at 1.5, 3, and 7 T 8–10,33 . The AW FT‐MRS method had a CoR of 1.79 and a CoV of 0.48.…”
Section: Discussionsupporting
confidence: 89%
“…Reconstructions that use the AW phase‐encoding scheme are highlighted by the surrounding black box. PCr/ATP values are in the expected range 8–10,33 . ATP, adenosine triphosphate; AW, acquisition‐weighted; fSLAM, fractional SLAM; FT‐MRS, Fourier transform‐based magnetic resonance spectroscopic imaging; PCr, phosphocreatine; SLAM, magnetic resonance spectroscopy with linear algebraic modelling; SLIM, spectral localization by imaging; SNR, signal‐to‐noise ratio.…”
Even at 7 T, cardiac 31P magnetic resonance spectroscopic imaging (MRSI) is fundamentally limited by low signal‐to‐noise ratio (SNR), leading to long scan times and poor temporal and spatial resolutions. Compartment‐based reconstruction algorithms such as magnetic resonance spectroscopy with linear algebraic modeling (SLAM) and spectral localization by imaging (SLIM) may improve SNR or reduce scan time without changes to acquisition. Here, we compare the repeatability and SNR performance of these compartment‐based methods, applied to three different acquisition schemes at 7 T. Twelve healthy volunteers were scanned twice. Each scan session consisted of a 6.5‐min 3D acquisition‐weighted (AW) cardiac 31P phase encode‐based MRSI acquisition and two 6.5‐min truncated k‐space acquisitions with increased averaging (4 × 4 × 4 central k‐space phase encodes and fractional SLAM [fSLAM] optimized k‐space phase encodes). Spectra were reconstructed using (i) AW Fourier reconstruction; (ii) AW SLAM; (iii) AW SLIM; (iv) 4 × 4 × 4 SLAM; (v) 4 × 4 × 4 SLIM; and (vi) fSLAM acquisition–reconstruction combinations. The phosphocreatine‐to‐adenosine triphosphate (PCr/ATP) ratio, the PCr SNR, and spatial response functions were computed, in addition to coefficients of reproducibility and variability. Using the compartment‐based reconstruction algorithms with the AW 31P acquisition resulted in a significant increase in SNR compared with previously published Fourier‐based MRSI reconstruction methods while maintaining the measured PCr/ATP ratio and improving interscan reproducibility. The alternative acquisition strategies with truncated k‐space performed no better than the common AW approach. Compartment‐based spectroscopy approaches provide an attractive reconstruction method for cardiac 31P spectroscopy at 7 T, improving reproducibility and SNR without the need for a dedicated k‐space sampling strategy.
“…We recorded a PCr/ATP of 1.90 ± 0.92 using the AW FT‐MRS method, which is in good agreement with the previous literature values at 1.5, 3, and 7 T 8–10,33 . The AW FT‐MRS method had a CoR of 1.79 and a CoV of 0.48.…”
Section: Discussionsupporting
confidence: 89%
“…Reconstructions that use the AW phase‐encoding scheme are highlighted by the surrounding black box. PCr/ATP values are in the expected range 8–10,33 . ATP, adenosine triphosphate; AW, acquisition‐weighted; fSLAM, fractional SLAM; FT‐MRS, Fourier transform‐based magnetic resonance spectroscopic imaging; PCr, phosphocreatine; SLAM, magnetic resonance spectroscopy with linear algebraic modelling; SLIM, spectral localization by imaging; SNR, signal‐to‐noise ratio.…”
Even at 7 T, cardiac 31P magnetic resonance spectroscopic imaging (MRSI) is fundamentally limited by low signal‐to‐noise ratio (SNR), leading to long scan times and poor temporal and spatial resolutions. Compartment‐based reconstruction algorithms such as magnetic resonance spectroscopy with linear algebraic modeling (SLAM) and spectral localization by imaging (SLIM) may improve SNR or reduce scan time without changes to acquisition. Here, we compare the repeatability and SNR performance of these compartment‐based methods, applied to three different acquisition schemes at 7 T. Twelve healthy volunteers were scanned twice. Each scan session consisted of a 6.5‐min 3D acquisition‐weighted (AW) cardiac 31P phase encode‐based MRSI acquisition and two 6.5‐min truncated k‐space acquisitions with increased averaging (4 × 4 × 4 central k‐space phase encodes and fractional SLAM [fSLAM] optimized k‐space phase encodes). Spectra were reconstructed using (i) AW Fourier reconstruction; (ii) AW SLAM; (iii) AW SLIM; (iv) 4 × 4 × 4 SLAM; (v) 4 × 4 × 4 SLIM; and (vi) fSLAM acquisition–reconstruction combinations. The phosphocreatine‐to‐adenosine triphosphate (PCr/ATP) ratio, the PCr SNR, and spatial response functions were computed, in addition to coefficients of reproducibility and variability. Using the compartment‐based reconstruction algorithms with the AW 31P acquisition resulted in a significant increase in SNR compared with previously published Fourier‐based MRSI reconstruction methods while maintaining the measured PCr/ATP ratio and improving interscan reproducibility. The alternative acquisition strategies with truncated k‐space performed no better than the common AW approach. Compartment‐based spectroscopy approaches provide an attractive reconstruction method for cardiac 31P spectroscopy at 7 T, improving reproducibility and SNR without the need for a dedicated k‐space sampling strategy.
“…Single voxel cardiac 31 P-MRS spectra were obtained from the left ventricle with subjects in the supine position as reported previously [9]. A 10 cm coil was fixed on the chest, at the level of the myocardium.…”
Cardiac lipid accumulation is associated with decreased cardiac function and energy status (PCr/ATP). It has been suggested that elevated plasma fatty acid (FA) concentrations are responsible for the cardiac lipid accumulation. Therefore, the aim of the present study was to investigate if elevating plasma FA concentrations by exercise results in an increased cardiac lipid content, and if this influences cardiac function and energy status. Eleven male subjects (age 25.4 ± 1.1 years, BMI 23.6 ± 0.8 kg/m2) performed a 2-h cycling protocol, once while staying fasted and once while ingesting glucose, to create a state of high versus low plasma FA concentrations, respectively. Cardiac lipid content was measured by proton magnetic resonance spectroscopy (1H-MRS) at baseline, directly after exercise and again 4 h post-exercise, together with systolic function (by multi-slice cine-MRI) and cardiac energy status (by 31P-MRS). Plasma FA concentrations were increased threefold during exercise and ninefold during recovery in the fasted state compared with the glucose-fed state (p < 0.01). Cardiac lipid content was elevated at the end of the fasted test day (from 0.26 ± 0.04 to 0.44 ± 0.04%, p = 0.003), while it did not change with glucose supplementation (from 0.32 ± 0.03 to 0.26 ± 0.05%, p = 0.272). Furthermore, PCr/ATP was decreased by 32% in the high plasma FA state compared with the low FA state (n = 6, p = 0.014). However, in the high FA state, the ejection fraction 4 h post-exercise was higher compared with the low FA state (63 ± 2 vs. 59 ± 2%, p = 0.018). Elevated plasma FA concentrations, induced by exercise in the fasted state, lead to increased cardiac lipid content, but do not acutely hamper systolic function. Although the lower cardiac energy status is in line with a lipotoxic action of cardiac lipid content, a causal relationship cannot be proven.
“…Although the variability of MRS is often cited as a limitation, modern techniques typically yield a variability of 13% for PCr/ATP ratios, which is in the same range as LV volumes and functional assessment on CMR imaging and echocardiography. 67 , 68 , 69 Future developments and technical advances of MRS at higher field strengths aim to deliver substantial further improvements to make the method valuable for clinical practice. Figure 5 Pyruvate Metabolism Hyperpolarization imaging helps in investigating the metabolic fate of the first carbon atom (blue) when pyruvate is metabolized to alanine via alanine transaminase (ALT), to lactate via lactate dehydrogenase (LDH), and to bicarbonate via pyruvate dehydrogenase (PDH).…”
Section: Metabolic Alterations In As and Their Assessment With The Us...mentioning
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