Effect of perfusion on exercised muscle: MR imaging evaluation

Archer, Branch T.; Fleckenstein, James L.; Bertocci, L. A.; Haller, Ronald G.; Barker, Bruce; Parkey, Robert W.; Peshock, Ronald M

doi:10.1002/jmri.1880020409

Cited by 68 publications

(40 citation statements)

References 20 publications

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“…We conclude that changes in extramuscular influences, such as blood flow, are necessary for the decreases in R 1 associated with exercise. This conclusion is consistent with the findings of Archer et al (28) that maximum changes in R 1 require blood flow to the active muscles, and that reactive hyperemia following suprasystolic application of a blood pressure cuff can decrease the R 1 of inactive muscles.…”

Section: The R 2 Decrease During Exercise Occurs Independently Of R 1supporting

confidence: 92%

Intracellular acidification and volume increases explain R₂ decreases in exercising muscle

Damon

Gregory

Hall

et al. 2001

Magnetic Resonance in Med

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Exercise-induced decreases in the 1 H transverse relaxation rate (R 2 ) of muscle have been well documented, but the mechanism remains unclear. In this study, the hypothesis was tested that R 2 decreases could be explained by pH decreases and apparent intracellular volume (V i ) increases. 31 P and 1 H spectroscopy, biexponential R 2 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 R 2 (R 2i ) and pH decreased, while intracellular osmolytes and V i increased. These effects were larger in NaCN-treated and untreated muscles than in IAAtreated muscles. Multiple regression analysis showed that pH and V i changes explain 70% of the R 2i variance. Separate experiments in unexercised muscles demonstrated causal relationships between pH and R 2i and between V i and R 2i . These data indicate that the R 2 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 R 2i change increased as field strength increased, suggesting a role for pH-modulated chemical exchange. Key words: skeletal muscle; exercise; hydrogen-ion concentration; osmolarity; nuclear magnetic resonance Exercise-induced increases in the apparent 1 H transverse relaxation time (T 2 ) of muscle water have been well documented. The amount of T 2 change increases as exercise intensity increases; T 2 plateaus 3-4 min after the onset of exercise (1). Following isometric leg extension to fatigue, T 2 recovery follows an approximately exponential time course and is complete after ϳ35 min. (2). The increase in signal intensity from active muscles in T 2 -weighted images allows muscle activity to be detected reliably and noninvasively, which may aid in the placement of regions of interest or surface coils in spectroscopic studies (2,3). With a full understanding of the mechanism(s) of the T 2 change, this phenomenon may also be useful in functional studies of muscle activation during exercise (e.g., Refs. 4 -6), noninvasive studies of pathologic conditions in which the T 2 response to exercise is altered (e.g., Refs. 7 and 8), and as a means of studying noninvasively those physiological changes that increase T 2 .The most universally offered and best-studied explanation for the T 2 increase during exercise is the concomitant increase in muscle volume. However, the mechanism of the T 2 increase is more complex than total water accumulation. For example, recovery of the muscle's anatomical cross-sectional area is faster than T 2 recovery (2), and enhancement of the extracellular fluid volume increase during exercise is not proportional to the T 2 increase (9). A further complication is that both ex vivo amphibian (10) and in vivo mammalian (11) studies suggest that exchange between the intra-and extracellular spaces in muscle is sl...

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Section: The R 2 Decrease During Exercise Occurs Independently Of R 1supporting

confidence: 92%

Intracellular acidification and volume increases explain R₂ decreases in exercising muscle

Damon

Gregory

Hall

et al. 2001

Magnetic Resonance in Med

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“…Previous studies demonstrated that the increase in T 2 after exercise occurred in the presence of vascular occlusion. 20,21 The increase in extra-cellular fluid was one of the most important factors involved.…”

Section: Discussionmentioning

confidence: 99%

Evaluation ofT₂values and apparent diffusion coefficient of the masseter muscle by clenching

Shiraishi

Chikui

Yoshiura

et al. 2011

Dentomaxillofacial Radiology

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Objective: The aim of this study was to evaluate the changes in T 2 values and apparent diffusion coefficient (ADC) in the masseter muscle by clenching in healthy volunteers. Methods: 37 volunteers were enrolled in the study. We measured bite force using pressuresensitive paper and a T 2 map. The ADC map was obtained at rest, during clenching, immediately after and 5 min after clenching. The spin-echo sequence was used to calculate T 2 , and single-shot spin-echo echo planar imaging was used to calculate the ADC. The motion-probing gradients (MPGs) were applied separately along the posterior-to-anterior (PA), right-to-left (RL) and superior-to-inferior (SI) directions, with b values of 0, 300 and 600 s mm -2 in each direction. ADC-PA, ADC-RL, and ADC-SI values were obtained, and we calculated the ADC-iso for the mean diffusivity. Results: There were no significant differences between the stronger and weaker sides of bite force before, during or 5 min after clenching for T 2 and ADC. The bite force had little effect on these parameters; thus, we used the average of the two sides for the following analyses. Time course analysis of ADC-iso, ADC-PA, ADC-RL and ADC-SI demonstrated a marked increase after clenching and a rapid decrease immediately after clenching, although they did not completely return to the initial values; however, the change in ADC-RL was significantly greater than those in ADC-PA or ADC-SI (P , 0.001 each). The changes in T 2 were similar to those of ADC, although not as marked. Conclusions: ADC (especially ADC-RL) was altered by contraction of the masseter muscle.

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“…1 H-magnetic resonance (MR) imaging can be used to estimate the activity of superˆcial and deep muscles, and MR imaging can document changes produced by exercise in human muscle tissue. [1][2][3][4][5][6][7][8] In contrast to non-exercising tissues, muscles used during exercise appear hyperintense, and this hyperintensity declines during recovery. Exercised-induced changes in signal primarily result from increases in the transverse relaxation time (T 2 ) of tissue caused by changes in water content and are most pronounced on T 2 -weighted images.…”

Section: Introductionmentioning

confidence: 99%

T2 Mapping of Muscle Activity using Ultrafast Imaging

et al. 2011

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Measuring exercise-induced muscle activity is essential in sports medicine. Previous studies proposed measuring transverse relaxation time (T 2 ) using muscle functional magnetic resonance imaging (mfMRI) to map muscle activity. However, mfMRI uses a spin-echo (SE) sequence that requires several minutes for acquisition. We evaluated the feasibility of T 2 mapping of muscle activity using ultrafast imaging, called fast-acquired mfMRI (fastmfMRI), to reduce image acquisition time. The current method uses 2 pulse sequences, spin-echo echo-planar imaging (SE-EPI) and true fast imaging with steady precession (TrueFISP). SE-EPI images are used to calculate T 2 , and TrueFISP images are used to obtain morphological information. The functional image is produced by subtracting the image of muscle activity obtained using T 2 at rest from that produced after exercise. Final fast-mfMRI images are produced by fusing the functional images with the morphologic images. Ten subjects repeated ankle plantar ‰exion 200 times. In the fused images, the areas of activated muscle in the fast-mfMRI and SE-EPI images were identical. The geometric location of the fast-mfMRI did not diŠer between the morphologic and functional images. Morphological and functional information from fast-mfMRI can be applied to the human trunk, which requires limited scan duration. The diŠerence obtained by subtracting T 2 at rest from T 2 after exercise can be used as a functional image of muscle activity.

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Effect of perfusion on exercised muscle: MR imaging evaluation

Cited by 68 publications

References 20 publications

Intracellular acidification and volume increases explain R₂ decreases in exercising muscle

Intracellular acidification and volume increases explain R₂ decreases in exercising muscle

Evaluation ofT₂values and apparent diffusion coefficient of the masseter muscle by clenching

T2 Mapping of Muscle Activity using Ultrafast Imaging

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Effect of perfusion on exercised muscle: MR imaging evaluation

Cited by 68 publications

References 20 publications

Intracellular acidification and volume increases explain R2 decreases in exercising muscle

Intracellular acidification and volume increases explain R2 decreases in exercising muscle

Evaluation ofT2values and apparent diffusion coefficient of the masseter muscle by clenching

T2 Mapping of Muscle Activity using Ultrafast Imaging

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Product

Resources

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Intracellular acidification and volume increases explain R₂ decreases in exercising muscle

Intracellular acidification and volume increases explain R₂ decreases in exercising muscle

Evaluation ofT₂values and apparent diffusion coefficient of the masseter muscle by clenching