Search

Exercise-induced decreases in the ¹H transverse relaxation rate (R2) of muscle have been well documented, but the mechanism remains unclear. In this study, the hypothesis was tested that R2 decreases could be explained by pH decreases and apparent intracellular volume (Vi') increases. ³¹P and ¹H spectroscopy, biexponential R2 analysis, and imaging were performed prior to and following fatiguing exercise in iodoacetate-treated (IAA, to inhibit glycolysis), NaCN-treated (to inhibit oxidative phosphorylation), and untreated frog gastrocnemii. In all exercised muscles, the apparent intracellular R2 (R2i') and pH decreased, while intracellular osmolytes and Vi' increased. These effects were larger in NaCN-treated and untreated muscles than in IAA-treated muscles. Multiple regression analysis showed that pH and Vi' changes explain 70% of the R2i' variance. Separate experiments in unexercised muscles demonstrated causal relationships between pH and R2i' and between Vi' and R2i'. These data indicate that the R2 change of exercise is primarily an intracellular phenomenon caused by the accumulation of the end-products of anaerobic metabolism. In the NaCN-treated and untreated muscles, the R2i' change increased as field strength increased, suggesting a role for pH-modulated chemical exchange. Magn Reson Med 47:14–23, 2002. © 2002 Wiley-Liss, Inc.

Exercise‐induced decreases in the 1H transverse relaxation rate (R2) of muscle have been well documented, but the mechanism remains unclear. In this study, the hypothesis was tested that R2decreases could be explained by pH decreases and apparent intracellular volume (Vi′) increases. 31P and 1H spectroscopy, biexponential R2analysis, and imaging were performed prior to and following fatiguing exercise in iodoacetate‐treated (IAA, to inhibit glycolysis), NaCN‐treated (to inhibit oxidative phosphorylation), and untreated frog gastrocnemii. In all exercised muscles, the apparent intracellular R2(R2i′) and pH decreased, while intracellular osmolytes and Vi′ increased. These effects were larger in NaCN‐treated and untreated muscles than in IAA‐treated muscles. Multiple regression analysis showed that pH and Vi′ changes explain 70% of the R2i′ variance. Separate experiments in unexercised muscles demonstrated causal relationships between pH and R2i′ and between Vi′ and R2i′. These data indicate that the R2change of exercise is primarily an intracellular phenomenon caused by the accumulation of the end‐products of anaerobic metabolism. In the NaCN‐treated and untreated muscles, the R2i′ change increased as field strength increased, suggesting a role for pH‐modulated chemical exchange. Magn Reson Med 47:14–23, 2002. © 2002 Wiley‐Liss, Inc.

As the end product of anaerobic metabolism and a source of H+, lactic acid is important in metabolism and pH regulation. Several methods have been introduced to calculate changes in the lactate anion (Lac–) concentration in exercising skeletal muscle from information derived from the 31P spectrum. Alternatively, Lac–may be observed directly with 1H MRS. Both 1H and 31P spectroscopy have potential problems, which could prevent accurate determination of [Lac–]. It is demonstrated that quantitatively accurate 1H MRS measurements of changes in [Lac–] due to exercise are possible in isolated muscle. In general, calculation by 31P MRS overestimates Lac–production. An analysis is presented of possible sources of errors in the 1H and 31P MRS methods. Magn Reson Med 44:418–426, 2000. © 2000 Wiley‐Liss, Inc.

As the end product of anaerobic metabolism and a source of H⁺, lactic acid is important in metabolism and pH regulation. Several methods have been introduced to calculate changes in the lactate anion (Lac^–) concentration in exercising skeletal muscle from information derived from the ³¹P spectrum. Alternatively, Lac–may be observed directly with ¹H MRS. Both ¹H and ³¹P spectroscopy have potential problems, which could prevent accurate determination of [Lac^–]. It is demonstrated that quantitatively accurate ¹H MRS measurements of changes in [Lac^–] due to exercise are possible in isolated muscle. In general, calculation by ³¹P MRS overestimates Lac–production. An analysis is presented of possible sources of errors in the ¹H and ³¹P MRS methods. Magn Reson Med 44:418–426, 2000. © 2000 Wiley-Liss, Inc.

Quantitative lactate imaging and spectroscopy were performed on phantoms and on electrically stimulated, excised frog skeletal muscle at macroscopic and microscopic resolutions. Lactate selectivity was achieved by use of a zero‐quantum/double‐quantum coherence (ZQC/DQC) lactate filter, which suppressed all signals besides lactate, including water and lipid, to below noise level. Three‐dimensional lactate data sets were acquired in 1–3 h; one of these spatial dimensions was frequency‐encoded and the other two were phase‐encoded. High‐resolution images were reconstructed using the spectral localization by imaging (SLIM) and generalized SLIM (GSLIM) techniques. Lactate quantitation was achieved by employing an external lactate concentration standard and was verified by comparison to quantitative STEAM‐localized and nonlocalized spectra that used total creatine as an internal concentration reference. Additionally, quantitatively accurate behavior of the SLIM and GSLIM techniques as applied to data sets of low signal‐to‐noise ratio and to macroscopically heterogeneous objects was verified using simulations and real muscle lactate data sets with known heterogeneity.

Ultrasound and magnetic resonance imaging show contrast between the inner and outer myometrium, which is useful in the diagnosis of gynecological disorders. To determine whether the image contrast is associated with biochemical differences between these myometrial regions, phosphorus metabolite concentrations in the inner one third of the myometrium (the junctional zone; JZ) were compared with the outermost one third of the myometrium (OM) in hysterectomized uteri using 31P spectral localization by imaging (SLIM). The technique was validated by comparing the results of SLIM with the results of standard Fourier‐encoded spectroscopic imaging (FSI) analysis using phantoms, and by nonlocalized spectroscopy on biopsies taken from the same hysterectomy specimens. As expected theoretically, SLIM yielded better localization than FSI, as judged by spectral intensity and leakage measurements on phantom compartments of known composition. SLIM localization revealed that the JZ has a higher intracellular phosphomonoester (PME) concentration than does the OM, which was confirmed by nonlocalized spectroscopy, and that there is very little NMR‐visible phosphorus in the cervix.