MR offers the unique possibility to noninvasively investigate cellular energy metabolism via 31P MRS, while blood perfusion, which provides oxygen and substrates to the tissue, is accessible by ...arterial spin labeling (ASL) 1H MRI. Because metabolic and hemodynamic parameters are linked, it would be desirable to study them simultaneously. A 3D-resolved method is presented that allows such measurements with high spatiotemporal resolution and has the potential to discern differences along an exercising muscle.
Multi-voxel localized
P MRS was temporally interleaved with multi-slice pASL 1H MRI. Phosphorus spectra were collected from two adjacent positions in gastrocnemius medialis (GM) during rest, submaximal plantar flexion exercise and recovery, while perfusion and
-weighted axial images were acquired at the same time. Seventeen healthy volunteers (9 f / 8 m) were studied at 7 T.
An increase of postexercise perfusion and
-weighted signal in GM positively correlated with end-exercise PCr depletion and pH drop. At proximal positions functional and metabolic activity was higher than distally, that is, perfusion increase and peak
-weighted signal, end-exercise PCr depletion, end-exercise pH, and PCr recovery time constant were significantly different. An NOE-induced SNR increase of approximately 20 % (P < .001), at rest, was found in interleaved
P spectra, when comparing to
P-only acquisitions.
A technique for fast, simultaneous imaging of muscle functional heterogeneity in ASL,
and acquisition of time-resolved
P MRS data is presented. These single exercise recovery experiments can be used to investigate local variations during disease progression in patients suffering from vascular or muscular diseases.
Purpose
MR offers the unique possibility to noninvasively investigate cellular energy metabolism via 31P MRS, while blood perfusion, which provides oxygen and substrates to the tissue, is accessible ...by arterial spin labeling (ASL) 1H MRI. Because metabolic and hemodynamic parameters are linked, it would be desirable to study them simultaneously. A 3D‐resolved method is presented that allows such measurements with high spatiotemporal resolution and has the potential to discern differences along an exercising muscle.
Methods
Multi‐voxel localized 31P MRS was temporally interleaved with multi‐slice pASL 1H MRI. Phosphorus spectra were collected from two adjacent positions in gastrocnemius medialis (GM) during rest, submaximal plantar flexion exercise and recovery, while perfusion and T2*‐weighted axial images were acquired at the same time. Seventeen healthy volunteers (9 f / 8 m) were studied at 7 T.
Results
An increase of postexercise perfusion and T2*‐weighted signal in GM positively correlated with end‐exercise PCr depletion and pH drop. At proximal positions functional and metabolic activity was higher than distally, that is, perfusion increase and peak T2*‐weighted signal, end‐exercise PCr depletion, end‐exercise pH, and PCr recovery time constant were significantly different. An NOE‐induced SNR increase of approximately 20 % (P < .001), at rest, was found in interleaved 31P spectra, when comparing to 31P‐only acquisitions.
Conclusions
A technique for fast, simultaneous imaging of muscle functional heterogeneity in ASL, T2* and acquisition of time‐resolved 31P MRS data is presented. These single exercise recovery experiments can be used to investigate local variations during disease progression in patients suffering from vascular or muscular diseases.
Purpose
Lactate is a key metabolite in skeletal muscle and whole‐body physiology. Its MR visibility in muscle is affected by overlapping lipid signals and fiber orientation. Double‐quantum filtered ...(DQF) 1H MRS selectively detects lactate at 1.3 ppm, but at ultra‐high field the efficiency of slice‐selective 3D‐localization with conventional RF pulses is limited by bandwidth. This novel 3D‐localized 1H DQF MRS sequence uses adiabatic refocusing pulses to unambiguously detect lactate in skeletal muscle at 7 T.
Methods
Lactate double‐quantum coherences were 3D‐localized using slice‐selective Shinnar–Le Roux optimized excitation and adiabatic refocusing pulses (similar to semi‐LASER). DQF MR spectra were acquired at 7 T from lactate phantoms, meat specimens with injected lactate (exploring multiple TEs and fiber orientations), and human gastrocnemius in vivo during and after exercise (without cuff ischemia).
Results
Lactate was readily detected, achieving the full potential of 50% signal with a DQF, in solution. The effects of fiber orientation and TE on the lactate doublet (peak splitting, amplitude, and phase) were in good agreement with theory and literature. Exercise‐induced lactate accumulation was detected with 30 s time resolution.
Conclusion
This novel 3D‐localized 1H DQF MRS sequence can dynamically detect glycolytically generated lactate in muscle during exercise and recovery at 7 T.
To evaluate the feasibility of motion correction for sodium (
Na) MRI based on interleaved acquired 3D proton (
H) navigator images.
A 3D radial density-adapted sequence for interleaved
Na/
H MRI was ...implemented on a 7 Tesla whole-body MRI system. The
H data obtained during the
Na acquisition were used to reconstruct 140 navigator image volumes with a nominal spatial resolution of (2.5 mm)
and a temporal resolution of 6 s. The motion information received from co-registration was then used to correct the
Na image dataset, which also had a nominal spatial resolution of (2.5 mm)
. The approach was evaluated on six healthy volunteers, whose motion during the scans had different intensities and characteristics.
Interleaved acquisition of two nuclei did not show any relevant influence on image quality (SNR of 13.0 for interleaved versus 13.2 for standard
Na MRI and 176.4 for interleaved versus 178.0 for standard
H MRI). The applied motion correction increased the consistency between two consecutive scans for all examined volunteers and improved the image quality for all kinds of motion. The SD of the differences ranged between 2.30% and 6.96% for the uncorrected and between 2.13% and 2.67% for the corrected images.
The feasibility of interleaved acquired
H navigator images to be used for retrospective motion correction of
Na images was successfully demonstrated. The approach neither affected the
Na image quality nor elongated the scan time and can therefore be an important tool to improve the accuracy of quantitative
Na MRI.
Purpose
To evaluate the feasibility of motion correction for sodium (23Na) MRI based on interleaved acquired 3D proton (1H) navigator images.
Methods
A 3D radial density‐adapted sequence for ...interleaved 23Na/1H MRI was implemented on a 7 Tesla whole‐body MRI system. The 1H data obtained during the 23Na acquisition were used to reconstruct 140 navigator image volumes with a nominal spatial resolution of (2.5 mm)3 and a temporal resolution of 6 s. The motion information received from co‐registration was then used to correct the 23Na image dataset, which also had a nominal spatial resolution of (2.5 mm)3. The approach was evaluated on six healthy volunteers, whose motion during the scans had different intensities and characteristics.
Results
Interleaved acquisition of two nuclei did not show any relevant influence on image quality (SNR of 13.0 for interleaved versus 13.2 for standard 23Na MRI and 176.4 for interleaved versus 178.0 for standard 1H MRI). The applied motion correction increased the consistency between two consecutive scans for all examined volunteers and improved the image quality for all kinds of motion. The SD of the differences ranged between 2.30% and 6.96% for the uncorrected and between 2.13% and 2.67% for the corrected images.
Conclusion
The feasibility of interleaved acquired 1H navigator images to be used for retrospective motion correction of 23Na images was successfully demonstrated. The approach neither affected the 23Na image quality nor elongated the scan time and can therefore be an important tool to improve the accuracy of quantitative 23Na MRI.
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