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Three-dimensional saturation transfer ³¹P-MRI in muscles of the lower leg at 3.0 T.

Parasoglou P, Xia D, Chang G, Regatte RR - Sci Rep (2014)

Bottom Line: However, due to the low MR sensitivity of the (31)P nucleus, most studies on clinically approved magnetic fields (≤3.0 T) have been performed with coarse resolution and limited tissue coverage.We imaged the lower leg muscles of ten healthy volunteers (total experimental time: 40 min, nominal voxel sizes 0.5 mL), and found statistically significant differences between the kinetics of the CK reaction among muscle groups.Our developed technique may allow in the future the early detection of focal metabolic abnormalities in diseases that affect the function of the skeletal muscle.

View Article: PubMed Central - PubMed

Affiliation: Quantitative Multinuclear Musculoskeletal Imaging Group (QMMIG), Department of Radiology, Center for Biomedical Imaging, New York University Langone Medical Center, New York, NY, USA.

ABSTRACT
The creatine kinase (CK) reaction plays a critical role in skeletal muscle function, and can be studied non-invasively using phosphorus ((31)P) saturation transfer (ST) techniques. However, due to the low MR sensitivity of the (31)P nucleus, most studies on clinically approved magnetic fields (≤3.0 T) have been performed with coarse resolution and limited tissue coverage. However, such methods are not able to detect spatially resolved metabolic heterogeneities, which may be important in diseases of the skeletal muscle. In this study, our aim was to develop and implement a (31)P-MRI method for mapping the kinetics of the CK reaction, and the unidirectional phosphocreatine (PCr) to adenosine triphosphate (ATP) metabolic fluxes in muscles of the lower leg on a clinical 3.0 T MR scanner. We imaged the lower leg muscles of ten healthy volunteers (total experimental time: 40 min, nominal voxel sizes 0.5 mL), and found statistically significant differences between the kinetics of the CK reaction among muscle groups. Our developed technique may allow in the future the early detection of focal metabolic abnormalities in diseases that affect the function of the skeletal muscle.

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Unlocalized ST-31P-MRS of the lower leg.A) Fully relaxed 31P spectrum without ST preparation (tsat = 0 s) (left) and 31P-ST Spectrum with complete saturation (arrow) of the γ-ATP resonance (tsat = 6.84 s) (right). B) Series of ST spectra at different tsat. C) PCr signal intensity fitted to Eq.2, (Pearson's product moment correlation = 0.9992).
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f1: Unlocalized ST-31P-MRS of the lower leg.A) Fully relaxed 31P spectrum without ST preparation (tsat = 0 s) (left) and 31P-ST Spectrum with complete saturation (arrow) of the γ-ATP resonance (tsat = 6.84 s) (right). B) Series of ST spectra at different tsat. C) PCr signal intensity fitted to Eq.2, (Pearson's product moment correlation = 0.9992).

Mentions: In order to estimate the pseudo first-order forward rate constant (kf) of the CK reaction, we need to measure the phosphocreatine (PCr) signal while we saturate the γ-adenosine triphosphate (γ-ATP) resonance for different durations (i.e. the progressive ST experiment)13. Assuming a two-pool exchange system between PCr and γ-ATP and complete saturation of γ-ATP, we can estimate the exchange rate between the two metabolites by solving the modified, for chemical exchange, Bloch equation14 (see methods). To confirm the efficiency of our saturation pulses, we acquired unlocalized 31P spectra in the entire volume of the lower leg muscles in all of our volunteers. Typical 31P spectra can be seen in Fig. 1, where the full width at half maximum of the PCr resonance peak was 12.3 ± 4.8 Hz (mean ± SD) across all subjects. As we show in the same figure, the ST module saturates γ-ATP to levels not measurable above the noise.


Three-dimensional saturation transfer ³¹P-MRI in muscles of the lower leg at 3.0 T.

Parasoglou P, Xia D, Chang G, Regatte RR - Sci Rep (2014)

Unlocalized ST-31P-MRS of the lower leg.A) Fully relaxed 31P spectrum without ST preparation (tsat = 0 s) (left) and 31P-ST Spectrum with complete saturation (arrow) of the γ-ATP resonance (tsat = 6.84 s) (right). B) Series of ST spectra at different tsat. C) PCr signal intensity fitted to Eq.2, (Pearson's product moment correlation = 0.9992).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4048915&req=5

f1: Unlocalized ST-31P-MRS of the lower leg.A) Fully relaxed 31P spectrum without ST preparation (tsat = 0 s) (left) and 31P-ST Spectrum with complete saturation (arrow) of the γ-ATP resonance (tsat = 6.84 s) (right). B) Series of ST spectra at different tsat. C) PCr signal intensity fitted to Eq.2, (Pearson's product moment correlation = 0.9992).
Mentions: In order to estimate the pseudo first-order forward rate constant (kf) of the CK reaction, we need to measure the phosphocreatine (PCr) signal while we saturate the γ-adenosine triphosphate (γ-ATP) resonance for different durations (i.e. the progressive ST experiment)13. Assuming a two-pool exchange system between PCr and γ-ATP and complete saturation of γ-ATP, we can estimate the exchange rate between the two metabolites by solving the modified, for chemical exchange, Bloch equation14 (see methods). To confirm the efficiency of our saturation pulses, we acquired unlocalized 31P spectra in the entire volume of the lower leg muscles in all of our volunteers. Typical 31P spectra can be seen in Fig. 1, where the full width at half maximum of the PCr resonance peak was 12.3 ± 4.8 Hz (mean ± SD) across all subjects. As we show in the same figure, the ST module saturates γ-ATP to levels not measurable above the noise.

Bottom Line: However, due to the low MR sensitivity of the (31)P nucleus, most studies on clinically approved magnetic fields (≤3.0 T) have been performed with coarse resolution and limited tissue coverage.We imaged the lower leg muscles of ten healthy volunteers (total experimental time: 40 min, nominal voxel sizes 0.5 mL), and found statistically significant differences between the kinetics of the CK reaction among muscle groups.Our developed technique may allow in the future the early detection of focal metabolic abnormalities in diseases that affect the function of the skeletal muscle.

View Article: PubMed Central - PubMed

Affiliation: Quantitative Multinuclear Musculoskeletal Imaging Group (QMMIG), Department of Radiology, Center for Biomedical Imaging, New York University Langone Medical Center, New York, NY, USA.

ABSTRACT
The creatine kinase (CK) reaction plays a critical role in skeletal muscle function, and can be studied non-invasively using phosphorus ((31)P) saturation transfer (ST) techniques. However, due to the low MR sensitivity of the (31)P nucleus, most studies on clinically approved magnetic fields (≤3.0 T) have been performed with coarse resolution and limited tissue coverage. However, such methods are not able to detect spatially resolved metabolic heterogeneities, which may be important in diseases of the skeletal muscle. In this study, our aim was to develop and implement a (31)P-MRI method for mapping the kinetics of the CK reaction, and the unidirectional phosphocreatine (PCr) to adenosine triphosphate (ATP) metabolic fluxes in muscles of the lower leg on a clinical 3.0 T MR scanner. We imaged the lower leg muscles of ten healthy volunteers (total experimental time: 40 min, nominal voxel sizes 0.5 mL), and found statistically significant differences between the kinetics of the CK reaction among muscle groups. Our developed technique may allow in the future the early detection of focal metabolic abnormalities in diseases that affect the function of the skeletal muscle.

Show MeSH
Related in: MedlinePlus