Physiological and Perceptual Responses of Human Volunteers during Whole-Body RF Exposure at 450 MHz

We have used a 3-h primed continuous infusion of [1,2-13C]acetate in five fasted (24 h) volunteers to quantify splanchnic and leg acetate metabolism ( protocol 1). Fractional extraction of acetate by both tissues was high (∼70%), and simultaneous uptake and release of acetate were observed. Labeled carbon recovery in CO2 was 37.9 ± 2.3% at the whole body level, 37.7 ± 1.5% across the splanchnic bed, and 37.3 ± 2.9% across the leg. Furthermore, we calculated whole body labeled carbon recovery during 15 h of [1,2-13C]acetate infusion in three volunteers ( protocol 2). Whole body acetate carbon recovery in CO2 was significantly higher (66.7 ± 4.5%) after 15 h of tracer infusion than after 3 h. We conclude that acetate is rapidly taken up by the leg and splanchnic tissues and that the percent recovery of CO2from the oxidation of acetate is heavily dependent on the length of acetate tracer infusion. In the postabsorptive state, labeled carbon recovery from acetate across the leg and the splanchnic region is similar to the whole body CO2 recovery.

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Statistical Evaluation of Radiofrequency Exposure during Magnetic Resonant Imaging: Application of Whole-Body Individual Human Model and Body Motion in the Coil

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph16061069 ◽

2019 ◽

Vol 16 (6) ◽

pp. 1069 ◽

Cited By ~ 3

Author(s):

Wenli Liu ◽

Hongkai Wang ◽

Pu Zhang ◽

Chengwei Li ◽

Jie Sun ◽

...

Keyword(s):

Body Motion ◽

Human Model ◽

Whole Body ◽

Patient Specific ◽

Accurate Estimation ◽

Modelling Method ◽

Rf Exposure ◽

Imaging Application ◽

Magnetic Resonance Imaging Mri ◽

The Individual

The accurate estimation of patient’s exposure to the radiofrequency (RF) electromagnetic field of magnetic resonance imaging (MRI) significantly depends on a precise individual anatomical model. In the study, we investigated the applicability of an efficient whole-body individual modelling method for the assessment of MRI RF exposure. The individual modelling method included a deformable human model and tissue simplification techniques. Besides its remarkable efficiency, this approach utilized only a low specific absorption rate (SAR) sequence or even no MRI scan to generate the whole-body individual model. Therefore, it substantially reduced the risk of RF exposure. The dosimetric difference of the individual modelling method was evaluated using the manually segmented human models. In addition, stochastic dosimetry using a surrogate model by polynomial chaos presented SAR variability due to body misalignment and tilt in the coil, which were frequently occurred in the practical scan. In conclusion, the dosimetric equivalence of the individual models was validated by both deterministic and stochastic dosimetry. The proposed individual modelling method allowed the physicians to quantify the patient-specific SAR while the statistical results enabled them to comprehensively weigh over the exposure risk and get the benefit of imaging enhancement by using the high-intensity scanners or the high-SAR sequences.

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Effects of epinephrine on human muscle glucose and protein metabolism

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1995.268.1.e55 ◽

1995 ◽

Vol 268 (1) ◽

pp. E55-E59 ◽

Cited By ~ 8

Author(s):

D. A. Fryburg ◽

R. A. Gelfand ◽

L. A. Jahn ◽

D. Oliveras ◽

R. S. Sherwin ◽

...

Keyword(s):

Plasma Insulin ◽

Forearm Blood Flow ◽

Muscle Protein ◽

Human Muscle ◽

Whole Body ◽

Epinephrine Infusion ◽

Healthy Human ◽

Human Volunteers ◽

Human Forearm ◽

Forearm Muscle

Systemic epinephrine infusion causes hypoaminoacidemia and inhibits whole body leucine flux (proteolysis) in humans. Its specific action on muscle protein is not known and is difficult to assess during systemic epinephrine infusions, which affect plasma insulin, amino acid, and free fatty acid concentrations. During a steady-state infusion of L-[ring-2,6-3H]phenylalanine, we examined the effect of locally infused epinephrine on the metabolism of protein and glucose in forearm muscle of 10 healthy human volunteers. During local epinephrine infusion, systemic concentrations of glucose, phenylalanine, insulin, and epinephrine were unchanged and lactate declined (P < 0.02). Compared with baseline, epinephrine induced significant increases in forearm blood flow (P < 0.01) and net lactate release (P < 0.001) and a decrease in glucose uptake (P < 0.01) at both 2 and 4 h. At 2 and 4 h phenylalanine release from muscle proteolysis was suppressed (P < 0.01), and at 4 h the net phenylalanine balance was less negative than baseline (P < 0.02), indicating an anticatabolic effect on muscle protein. We conclude that in human forearm muscle epinephrine, at physiological concentrations, has a catabolic effect on muscle glycogen but an anticatabolic action on muscle protein. The mechanism of this latter effect is not known.

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