Imaging of skeletal muscle function using (18)FDG PET: force production, activation, and metabolism

Muscle Function, Muscle Disease, and Positron Emission Tomography-Computed Tomography: A Narrative Review

18F-fluorodeoxyglucose (18F-FDG) is a radiopharmaceutical that exhibits glucose-like kinetics and is used in positron emission tomography (PET). 18F-FDG is used for cancer diagnosis in clinical practice. However, 18F-FDG uptake is also observed in normal organs, such as the brain, liver, and heart, with high glucose consumption. Moreover, 18F-FDG uptake is also observed in muscles, where its accumulation and radioactivity reflect muscle activity. Dystonia is characterized by excessive muscle movement. Recently, 18F-FDG and technetium-99m-methoxyisobutyl isocyanide ([99mTc]MIBI) have been used for the diagnosis and botulinum toxin therapy evaluation of dystonia. This review aimed to summarize the utility of 18F-FDG-PET for the evaluation of muscle activity and diagnosis of muscle diseases such as dystonia, polymyositis, dermatomyositis, and polymyalgia rheumatica.

Validation and comparison of trunk muscle activities in male participants during exercise using an innovative device and abdominal bracing maneuvers

BACKGROUND

Abdominal bracing is effective in strengthening the trunk muscles; however, assessing performance can be challenging. We created a device for performing abdominal trunk muscle exercises. The effectiveness of this device has not yet been evaluated or comparedOBJECTIVE: We aimed to quantify muscle activity levels during exercise using our innovative device and to compare them with muscle activation during abdominal bracing maneuvers.

METHODS

This study included 10 men who performed abdominal bracing exercises and exercises using our device. We measured surface electromyogram (EMG) activities of the rectus abdominis (RA), external oblique, internal oblique (IO), and erector spinae (ES) muscles in each of the exercises. The EMG data were normalized to those recorded during maximal voluntary contraction (%EMGmax).

RESULTS

During the bracing exercise, the %EMGmax of IO was significantly higher than that of RA and ES (p< 0.05), whereas during the exercises using the device, the %EMGmax of IO was significantly higher than that of ES (p< 0.05). No significant difference was observed in the %EMGmax of any muscle between bracing exercises and the exercises using the device (p= 0.13-0.95).

CONCLUSIONS

The use of our innovative device results in comparable activation to that observed during abdominal bracing.

Evaluation of skeletal muscle activity during foot training exercises using positron emission tomography

The foot exercises “rock-paper-scissors” and “towel gathering” are widely used in patients with lower limb disorders; however, there are no detailed reports on muscle activity during such training. We quantitatively evaluated the difference in skeletal muscle activity between the two exercises using positron emission tomography. Eight university student athletes were included. Four participants each were assigned to the foot rock-paper-scissors and towel gathering groups. Participants in each group underwent continuous training for 15 min, and received an intravenous injection of 18F-fluorodeoxyglucose. After retraining for 15 min, participants rested for 45 min. Regions of interest were defined in 25 muscles. The standardized uptake value (SUV) in the trained limb was compared with that in the non-trained control limb. SUVs increased in four skeletal muscles (tibialis anterior, peroneus brevis, extensor hallucis brevis, and abductor hallucis) in the rock-paper-scissors group, and in four muscles (flexor digitorum longus, extensor hallucis brevis, extensor digitorum brevis, and quadratus plantae) in the towel gathering group. Thus, foot rock-paper-scissors and towel gathering involved skeletal muscles related to the medial longitudinal arch and toe grip strength, respectively. Given that the two exercises target different skeletal muscles, they should be taught and implemented according to their respective purposes.

Pitfalls in Interpretation of PET/CT in the Chest

Whole body positron emission tomography (PET)/computed tomography (CT) imaging with [18F]-fluoro-2-deoxy-D-glucose (FDG) is widely used in oncologic imaging. In the chest, common PET/CT applications include the evaluation of solitary pulmonary nodules, cancer staging, assessment of response to therapy, and detection of residual or recurrent disease. Knowledge of the technical artifacts and potential pitfalls that radiologists may encounter in the interpretation of PET/CT in the thorax is important to avoid misinterpretation and optimize patient management. This article will review pitfalls in the interpretation of PET/CT in the chest related to technical factors, physiologic uptake, false positive findings, false negative findings, and iatrogenic conditions.

Physiological 2-deoxy-2-[fluorine-18] fluoro-D-glucose accumulation in the thenar eminence in adults: a single-center retrospective study

OBJECTIVE

This study evaluated the frequency, and effect of physiological 2-deoxy-2-[fluorine-18] fluoro-D-glucose (FDG) tracer injection and its association with the penetration rates of mobile devices.

METHODS

This retrospective analysis included 213 patients (mean age ± standard deviation, 66.2 ± 14.1 years; range 23-93 years; 125 men) who underwent FDG-positron emission tomography examination. Elevated FDG activity in the thenar eminence with maximum standardized uptake value (SUVmax) ≥ 2.5 was considered positive. Differences according to age, sex, laterality, and tracer injection side were evaluated using Fisher's exact test. Associations were assessed using Pearson's correlation coefficient.

RESULTS

Twenty-three percent (49/213) of the patients had elevated FDG activity in the thenar eminence (mean SUVmax, 3.50 ± 1.04; range 2.5-6.3), including 18 with bilateral findings. No significant difference existed according to age (< 50 years vs. 50-69 years vs. ≥ 70 years), sex, laterality, or tracer injection side. No significant correlation existed between penetration rates of mobile devices and the findings (p = 0.08).

CONCLUSION

Elevated FDG activity in the thenar eminence occurs in adults, regardless of age, sex, laterality, or tracer injection side. This should be considered a common physiological change that does not warrant any further investigation.

Symmetry and spatial distribution of muscle glucose uptake in the lower limbs during walking measured using FDG-PET

Purpose

This study aimed to elucidate whether muscle activity (in terms of glucose uptake) between the legs can be considered symmetrical during walking. Furthermore, we aimed to determine whether the [¹⁸F]-fluorodeoxyglucose was distributed heterogeneously throughout each muscle, and if so, whether areas of high uptake would be clustered.

Methods

Ten healthy participants walked on a treadmill at self-selected comfortable walking speed for a total of 90 minutes, 60 minutes before and 30 minutes after intravenous injection of 50 MBq [¹⁸F]-fluorodeoxyglucose. Thereafter, a positron emission tomography/computed tomography scan of the lower limb was acquired. Three-dimensional muscle contours of 78 (= 39x2) muscles of the left and right lower limb were semi-automatically determined from magnetic resonance imaging scans. After non-rigid registration, those muscle contours were used to extract [¹⁸F]-fluorodeoxyglucose uptake from the positron emission tomography scans.

Results

Large asymmetries were observed in the lower leg muscles (e.g. median absolute asymmetry index of 42% in the gastrocnemius medialis) and in the gluteus minimus (30% asymmetry) and gluteus medius (15% asymmetry), whereas the uptake in the thighs was relatively symmetrical between the limbs (<6% asymmetry). These were not related to limb-dominance nor to inter-limb differences in muscle volume. The [¹⁸F]-fluorodeoxyglucose distribution was not distributed normally; most voxels had a relatively low standardized uptake value, and a minority of voxels had a relatively high standardized uptake value. The voxels with higher [¹⁸F]-fluorodeoxyglucose uptake were distributed heterogeneously; they were clustered in virtually all muscles.

Conclusion

The findings in this study challenge the common assumption of symmetry in muscle activity between the limbs in healthy subjects. The clustering of voxels with high uptake suggests that even in this prolonged repetitive task, different spatial regions of muscles contribute differently to walking than others.

Imaging skeletal muscle volume, density, and FDG uptake before and after induction therapy for non-small cell lung cancer

AIM

To assess whether changes in body composition could be assessed serially using conventional thoracic computed tomography (CT) and positron-emission tomography (PET)/CT imaging in patients receiving induction chemotherapy for non-small cell lung cancer (NSCLC).

MATERIALS AND METHODS

CT-based skeletal muscle volume and density were measured retrospectively from thoracic and lumbar segment CT images from 88 patients with newly diagnosed and untreated NSCLC before and after induction chemotherapy. Skeletal muscle 2-[¹⁸F]-fluoro-2-deoxy-d-glucose (FDG) uptake was measured from PET/CT images from a subset of patients (n=42). Comparisons of each metric before and after induction chemotherapy were conducted using the non-parametric Wilcoxon signed-rank test for paired data. The association between clinical factors and percentage change in muscle volume was examined using univariate linear regression models, with adjustment for baseline muscle volume.

RESULTS

Following induction chemotherapy, thoracic (-3.3%, p=0.0005) and lumbar (-2.6%, p=0.0101) skeletal muscle volume were reduced (adiposity remained unchanged). The proportion of skeletal muscle with a density <0 HU increased (7.9%, p<0.0001), reflecting a decrease in skeletal muscle density and skeletal muscle FDG uptake increased (10.4-31%, p<0.05). No imaging biomarkers were correlated with overall survival.

CONCLUSION

Changes in body composition can be measured from routine thoracic imaging. During chemotherapy skeletal muscle volume and metabolism are altered; however, there was no impact on survival in this retrospective series, and further validation in prospective, well-controlled studies are required.

Shivering and nonshivering thermogenesis in skeletal muscles

Humans have inherited complex neural circuits which drive behavioral, somatic, and autonomic thermoregulatory responses to defend their body temperature. While they are well adapted to dissipate heat in warm climates, they have a reduced capacity to preserve it in cold environments. Consequently, heat production is critical to defending their core temperature. As in other large mammals, skeletal muscles are the primary source of heat production recruited in cold-exposed humans. This is achieved voluntarily in the form of contractions from exercising muscles or involuntarily in the form of contractions from shivering muscles and the recruitment of nonshivering mechanisms. This review describes our current understanding of shivering and nonshivering thermogenesis in skeletal muscles, from the neural circuitry driving their recruitment to the metabolic substrates that fuel them. The presence of these heat-producing mechanisms can be measured in vivo by combining indirect respiratory calorimetry with electromyography or biomedical imaging modalities. Indeed, much of what is known regarding shivering in humans and other animal models stems from studies performed using these methods combined with in situ and in vivo neurologic techniques. More recent investigations have focused on understanding the metabolic processes that produce the heat from both contracting and noncontracting mechanisms. With the growing interest in the potential therapeutic benefits of shivering and nonshivering skeletal muscle to counter the effects of neuromuscular, cardiovascular, and metabolic diseases, we expect this field to continue its growth in the coming years.

Regional Variation in Skeletal Muscle and Adipose Tissue FDG Uptake Using PET/CT and Their Relation to BMI

RATIONALE AND OBJECTIVES

Skeletal muscle metabolism is a primary contributor to whole-body energy expenditure. Currently, methods to measure changes in skeletal muscle metabolism in vivo are limited. Our objectives were to characterize the regional variation in skeletal muscle and adipose tissue (AT) FDG uptake as a surrogate for glycolytic metabolism using ¹⁸F-2-fluorodeoxyglucose (FDG)-positron emission tomography (PET)/computed tomography (CT) in healthy men and to correlate these findings to body mass index (BMI).

MATERIALS AND METHODS

Eighteen healthy men were enrolled and underwent FDG-PET/CT. The mean standardized uptake value of 14 skeletal muscles and two AT regions was measured and linear regression analysis was performed to identify metabolic predictors of BMI.

RESULTS

FDG-PET/CT reliably detected changes in skeletal muscle and AT depot metabolic activity based on location. The most metabolically active muscles were those used for posture and breathing, which have the highest percentage of reported type I muscle myofiber content. Visceral AT tended to have a higher FDG uptake than subcutaneous AT. The mean standardized uptake value of VAT, pectoralis major, and gluteus maximus muscles accounted for 64% of the variance in BMI.

CONCLUSIONS

FDG-PET/CT can be used to quantify the regional variation in glucose metabolism of multiple skeletal muscle groups and AT depots.

Innovative exercise device for the abdominal trunk muscles: An early validation study

BACKGROUND

Exercise is one of the few treatments that provide significant improvements in chronic low back pain (CLBP). We developed an innovative exercise device for abdominal trunk muscles. This device can be used in a sitting or standing position and contains a built-in system to measure abdominal trunk muscle strength. We examined whether subjects can adequately use the device to perform the exercises and measure their abdominal trunk muscle strength.

METHODS

We collected data on the body height, body weight, body mass index, and girth of 30 healthy male volunteers, and measured their grip power and trunk extensor muscle strength using a dynamometer. The volunteers performed a sit-up test as an indicator of trunk flexor muscle strength, and we measured their abdominal muscle strength using the device. We then evaluated the correlations between abdominal trunk muscle strength and anthropometric parameters as well as the strength of other muscles. In subsequent tests, 5 of the 30 subjects participated in two positron emission tomography (PET) series consisting of examinations after a resting period (control study) and during exercise (exercise study). For the exercise study, the subjects performed 2 sets of exercises for 20 minutes using the device before and after an injection of 18F-fluorodeoxyglucose (FDG). PET-computed tomography images were obtained 60 minutes after FDG injection in each study. We compared the skeletal muscle metabolism of the participants in both studies using the standardized uptake value.

RESULTS

The muscle strength measured by the device and the 30-second sit-up frequency were correlated. FDG accumulation within the diaphragm and abdominal rectus muscles was significantly higher in the exercise study.

CONCLUSION

Our innovative exercise device facilitates a coordinated contraction of the abdominal trunk muscles at the anterior aspect and the roof of the core, and enables subjects to measure the strength of these muscles.

Metabolic imaging in exercise physiology

This minireview focuses on selected, noninvasive imaging techniques that have been used in the study of exercise physiology. These imaging modalities can be roughly divided into two categories: tracer based and nontracer based. Tracer-based methods use radiolabeled substrates whose location and quantity can subsequently be imaged once they are incorporated into metabolic processes. Nontracer-based imaging modalities rely on specific properties of substrates to identify metabolites and determine their concentrations. Identification and quantification of metabolites is usually based on magnetic properties or on differences in light absorption. In this review, we will highlight two tracer-based imaging modalities, positron emission tomography and single-photon-emission computed tomography, as well as two nontracer-based methods, magnetic resonance spectroscopy and near-infrared spectroscopy. Some of the recent findings that each technique has provided on cerebral and skeletal muscle metabolism during exercise, as well as the strengths and limitations of each technique, will be discussed.

Overall Activity of All Masticatory Muscles during Lateral Excursion

Quantification of the overall activity of every masticatory muscle is requisite for the analysis of stomatognathic function, which has not been accomplished by conventional electromyography. We used positron emission tomography and 18F-fluoro-deoxy-glucose to quantify the overall activity of every masticatory muscle during lateral excursion, and to evaluate the relative contribution of each masticatory muscle to lateral excursion. The present study suggested that lateral and medial pterygoid muscles are more responsible for lateral excursion than are masseter and temporal muscles. In particular, the contralateral lateral pterygoid muscle plays a major role, followed by the contralateral medial pterygoid muscle.

Assessment of muscle function using hybrid PET/MRI: comparison of 18F-FDG PET and T2-weighted MRI for quantifying muscle activation in human subjects

Purpose

The aim of this study was to determine the relationship between relative glucose uptake and MRI T₂ changes in skeletal muscles following resistance exercise using simultaneous PET/MRI scans.

Methods

Ten young healthy recreationally active men (age 21 – 28 years) were injected with ¹⁸F-FDG while activating the quadriceps of one leg with repeated knee extension exercises followed by hand-grip exercises for one arm. Immediately following the exercises, the subjects were scanned simultaneously with ¹⁸F-FDG PET/MRI and muscle groups were evaluated for increases in ¹⁸F-FDG uptake and MRI T₂ values.

Results

A significant linear correlation between ¹⁸F-FDG uptake and changes in muscle T₂ (R² = 0.71) was found. for both small and large muscles and in voxel to voxel comparisons. Despite large intersubject differences in muscle recruitment, the linear correlation between ¹⁸F-FDG uptake and changes in muscle T₂ did not vary among subjects.

Conclusion

This is the first assessment of skeletal muscle activation using hybrid PET/MRI and the first study to demonstrate a high correlation between ¹⁸F-FDG uptake and changes in muscle T₂ with physical exercise. Accordingly, it seems that changes in muscle T₂ may be used as a surrogate marker for glucose uptake and lead to an improved insight into the metabolic changes that occur with muscle activation. Such knowledge may lead to improved treatment strategies in patients with neuromuscular pathologies such as stroke, spinal cord injuries and muscular dystrophies.

Prognostic value of preoperative total psoas muscle area on long-term outcome in surgically treated oesophageal cancer patients

OBJECTIVES

Although a decrease in psoas muscle area (PMA) has been reported as a risk factor for survival in several malignancies, there have been few studies regarding its prognostic value in oesophageal cancer. We investigated the prognostic role of PMA and its F-18 fluorodeoxyglucose uptake in patients who had surgically treated oesophageal cancer.

METHODS

From 2004 to 2013, 131 patients who underwent surgical resection and complete lymph node dissection for oesophageal cancer were retrospectively reviewed. The PMA and mean standardized uptake value (SUVmean) of the psoas muscle were measured at the L3 spine level on preoperative positron emission tomography/computed tomography images.

RESULTS

The mean age was 63.38 ± 8.47 years and male patients were 125 (95.4%). The pathological stage I, II and III were 38 (29.0%), 41 (31.3%) and 52 (39.7%), respectively. The mean body mass index (BMI), PMA and SUVmean of the psoas muscle were 59.50 ± 10.14, 14.42 ± 4.30 and 1.51 ± 0.27, respectively. Operative mortality occurred in 7 (5.3%) patients. The BMI and PMA were lower in patients with operative mortality than in patients who survived. The median follow-up time was 32.52 months. A multivariate analysis revealed that PMA was an adverse risk factor for overall survival (OS) (hazard ratio, HR = 0.930; P= 0.004), whereas BMI was related to OS. The 3-year OS rates were 64.9% in high-PMA (≥15.8) patients; however, it was only 37.1% in low-PMA (less than 15.8) patients (P= 0.002). Akaike information criterion was the lowest by including PMA in the multivariate model.

CONCLUSIONS

Decreased PMA was an adverse significant prognostic factor for OS in patients with oesophageal cancer.

Core muscle characteristics during walking of patients with multiple sclerosis

The purpose of this study was to investigate core muscle characteristics during walking in patients with multiple sclerosis (MS). Eight patients (4 men) with relapsing-remitting MS (aged 44.9 +/- 8.6 yr) and sex-matched controls (37.9 +/- 8.4 yr) walked on a treadmill for 15 min at a self-selected speed. Positron emission tomography/computed tomography imaging was used to measure core muscle activity immediately after walking based on glucose uptake. Activity was not different between the MS and control group for any of the identified muscles (p > 0.28). Within the MS group, side differences in activity were identified in the lateral flexor group, the external and internal obliques, and the rectus abdominis (p < 0.05), with the less-affected side being activated more. Furthermore, greater muscle volume was found on the more-affected side of the transversus abdominis, quadratus lumborum, and the low-back extensor group (p < 0.03). These muscle characteristics suggest patients with MS utilize compensatory mechanisms during walking to maintain balance and posture. These strategies likely result in increased muscle energy cost and early fatigability.

FDG-PET detects nonuniform muscle activity in the lower body during human gait

INTRODUCTION

Nonuniform muscle activity has been partially explained by anatomically defined neuromuscular compartments. The purpose of this study was to investigate the uniformity of skeletal muscle activity during walking.

METHODS

Eight participants walked at a self-selected speed, and muscle activity was quantified using [¹⁸ F]-fluorodeoxyglucose positron emission tomography imaging. Seventeen muscles were divided into 10 equal length sections, and within muscle activity was compared.

RESULTS

Nonuniform activity was detected in 12 of 17 muscles (ƒ > 4.074; P < 0.046), which included both uni- and multi-articular muscles. Greater proximal activity was detected in 6 muscles (P < 0.049), and greater distal versus medial activity was found in the iliopsoas (P < 0.042).

CONCLUSIONS

Nonuniform muscle activity is likely related to recruitment of motor units located within separate neuromuscular compartments. These findings indicate that neuromuscular compartments are recruited selectively to allow for efficient energy transfer, and these patterns may be task-dependent. Muscle Nerve 54: 959-966, 2016.

Changes in muscle activity after performing the FIFA 11+ programme part 2 for 4 weeks

Changes in muscle activity were evaluated by positron emission tomography-computed tomography (PET-CT) after performing part 2 of the Fédération Internationale de Football Association's 11+ programme (11+) for 4 weeks. Eleven males performed part 2 of the 11+ for 20 min before and after 37 MBq of (18)F-fluorodeoxyglucose (FDG) was injected intravenously. PET-CT images were obtained 50 min after FDG injection. The participants were then instructed to perform part 2 of the 11+ 3 times per week for 4 consecutive weeks, after which another set of PET-CT images was obtained following the same procedure. Regions of interest were defined within 30 muscles. The standardised uptake value (SUV) of FDG by muscle tissue per unit volume was calculated, and FDG accumulation was compared between pre- and post-training PET-CT results. Performing part 2 of the 11+ for 4 weeks increased mean SUV in the sartorius, semimembranosus, biceps femoris, abductor hallucis, and flexor hallucis brevis muscles (P < 0.05). In conclusion, routinely performing part 2 of the 11+ for 4 weeks increased glucose uptake related to muscle activity in the hamstrings and hallux muscles. We speculate that there is some possibility of this change of muscle activity contributing to a decrease in sports-related injuries.

Effects of the belt electrode skeletal muscle electrical stimulation system on lower extremity skeletal muscle activity: Evaluation using positron emission tomography

BACKGROUND

Lower-extremity muscle weakness in athletes after lower limb trauma or surgery can hinder their return to sports, and the associated muscle atrophy may lead to deterioration in performance after returning to sports. Recently, belt electrode skeletal muscle electrical stimulation (B-SES) which can contract all the lower limb skeletal muscles simultaneously was developed. However, no study has evaluated skeletal muscle activity with B-SES. Since only superficial muscles as well as a limited number of muscles can be investigated using electromyography, we investigated whether positron emission tomography (PET) can evaluate the activity of all the skeletal muscles in the body simultaneously. The purpose of this study was to evaluate the effectiveness of the B-SES system using PET.

METHODS

Twelve healthy males (mean age, 24.3 years) were divided into two groups. The subjects in the control group remained in a sitting position for 10 min, and [(18)F] fluorodeoxyglucose (FDG) was intravenously injected. In the exercise group, subjects exercised using the B-SES system for 20 min daily for three consecutive days as a pre-test exercise. On the measurement day, they exercised for 10 min, received an injection of FDG, and exercised for another 10 min. PET-computed tomography images were obtained in each group 60 min after the FDG injection. Regions of interest were drawn in each lower-extremity muscle. We compared each skeletal muscle metabolism using the standardized uptake value.

RESULTS

In the exercise group, FDG accumulation in the gluteus maximus, gluteus medius, gluteus minimus, quadriceps femoris, sartorius, and hamstrings was significantly higher than the muscles in the control (P < 0.05).

CONCLUSION

Exercise with B-SES increased the skeletal muscle activity of the gluteal muscles as well as the most lower-extremity muscles simultaneously.

[18F]-FDG positron emission tomography--an established clinical tool opening a new window into exercise physiology

Positron emission tomography (PET) with [(18)F]-fluorodeoxyglucose (FDG) is an established clinical tool primarily used to diagnose and evaluate disease status in patients with cancer. PET imaging using FDG can be a highly valuable tool to investigate normal human physiology by providing a noninvasive, quantitative measure of glucose uptake into various cell types. Over the past years it has also been increasingly used in exercise physiology studies to identify changes in glucose uptake, metabolism, and muscle activity during different exercise modalities. Metabolically active cells transport FDG, an (18)fluorine-labeled glucose analog tracer, from the blood into the cells where it is then phosphorylated but not further metabolized. This metabolic trapping process forms the basis of this method's use during exercise. The tracer is given to a participant during an exercise task, and the actual PET imaging is performed immediately after the exercise. Provided the uptake period is of sufficient duration, and the imaging is performed shortly after the exercise; the captured image strongly reflects the metabolic activity of the cells used during the task. When combined with repeated blood sampling to determine tracer blood concentration over time, also known as the input function, glucose uptake rate of the tissues can be quantitatively calculated. This synthesis provides an accounting of studies using FDG-PET to measure acute exercise-induced skeletal muscle activity, describes the advantages and limitations of this imaging technique, and discusses its applications to the field of exercise physiology.

Glucose uptake heterogeneity of the leg muscles is similar between patients with multiple sclerosis and healthy controls during walking

BACKGROUND

Difficulties in ambulation are one of the main problems reported by patients with multiple sclerosis. A previous study by our research group showed increased recruitment of muscle groups during walking, but the influence of skeletal muscle properties, such as muscle fiber activity, has not been fully elucidated. The purpose of this investigation was to use the novel method of calculating glucose uptake heterogeneity in the leg muscles of patients with multiple sclerosis and compare these results to healthy controls.

METHODS

Eight patients with multiple sclerosis (4 men) and 8 healthy controls (4 men) performed 15 min of treadmill walking at a comfortable self-selected speed following muscle strength tests. Participants were injected with ≈ 8 mCi of [(18)F]-fluorodeoxyglucose during walking after which positron emission tomography/computed tomography imaging was performed.

FINDINGS

No differences in muscle strength were detected between multiple sclerosis and control groups (P>0.27). Within the multiple sclerosis, group differences in muscle volume existed between the stronger and weaker legs in the vastus lateralis, semitendinosus, and semimembranosus (P<0.03). Glucose uptake heterogeneity between the groups was not different for any muscle group or individual muscle of the legs (P>0.16, P≥0.05).

INTERPRETATIONS

Patients with multiple sclerosis and healthy controls showed similar muscle fiber activity during walking. Interpretations of these results, with respect to our previous study, suggest that walking difficulties in patients with multiple sclerosis may be more associated with altered central nervous system motor patterns rather than alterations in skeletal muscle properties.

Comparison of muscle activity in the empty-can and full-can testing positions using 18 F-FDG PET/CT

Background

There has been much controversy over specific tests for diagnosis of supraspinatus tendon tear. The aim of this study was to evaluate the metabolic activity of the deltoid and rotator cuff muscles while maintaining the full-can and empty-can testing positions using 2-deoxy-2-[¹⁸ F]fluoro-D-glucose (¹⁸ F-FDG) positron emission tomography (PET)/computed tomography (CT).

Methods

Ten healthy volunteers without shoulder pain or diabetes mellitus participated in this study. Following FDG injection, both arms were maintained in either the empty-can or full-can position for 10 min. PET/CT was performed 40 min after injection. Maximum standardized uptake values (SUVs) were measured in the deltoid and rotator cuff muscles on axial PET images.

Results

The middle deltoid exhibited the most significant increase in muscle activity at both testing positions. Additionally, a significant increase in muscle activity was observed in the middle deltoid compared with the supraspinatus (P < 0.05) in the empty-can testing position. SUVs of the middle deltoid, supraspinatus, and subscapularis showed a significant increase in the empty-can testing position compared with the full-can testing position (P < 0.05).

Conclusions

Significantly increased activity of the supraspinatus in conjunction with the middle deltoid and subscapularis after empty-can testing may result in decreased specificity of the empty-can test in detecting isolated supraspinatus activity. The full-can test, however, may be used to test the function of the supraspinatus with the least amount of surrounding middle deltoid and subscapularis activity.

Unilateral isometric muscle fatigue decreases force production and activation of contralateral knee extensors but not elbow flexors

Nonlocal muscle fatigue occurs when fatiguing 1 muscle alters performance of another rested muscle. The purpose of the study was to investigate if fatiguing 2 separate muscles would affect the same rested muscle, and if fatiguing the same muscle would affect 2 separate muscles. Twenty-one trained males participated in 2 studies (n = 11; n = 10). Subjects performed 2 pre-test maximum voluntary contractions (MVCs) with the nondominant knee extensors. Thereafter they performed two 100-s MVCs with their dominant knee extensors, elbow flexors, or rested. Between and after the sets, a single MVC with the nondominant rested knee extensors was performed. Subsequently, 12 nondominant knee extensors repeated MVCs were completed. Force, quadriceps voluntary activation (VA), and electromyography (EMG) were measured. The same protocol was employed in study 2 except the nondominant elbow-flexors were tested. Study 1: Compared with control conditions, a significant decrease in nondominant knee extensors force, EMG, and VA was found under both fatiguing conditions (P ≤ 0.05; effect size (ES) = 0.91-1.15; 2%-8%). Additionally, decrements in all variables were found from the first post-intervention MVC to the last (P ≤ 0.05; ES = 0.82-2.40; 9%-20%). Study 2: No differences were found between conditions for all variables (P ≥ 0.33; ES ≤ 0.2; ≤3.0%). However, all variables decreased from the first post-intervention MVC to the last (P ≤ 0.05; ES = 0.4-3.0; 7.2%-19.7%). Whereas the rested knee extensors demonstrated nonlocal effects regardless of the muscle being fatigued, the elbow-flexors remained unaffected. This suggests that nonlocal effects are muscle specific, which may hold functional implications for training and performance.

Greater glucose uptake heterogeneity in knee muscles of old compared to young men during isometric contractions detected by [(18)F]-FDG PET/CT

We used positron emission tomography/computed tomography (PET/CT) and [¹⁸F]-FDG to test the hypothesis that glucose uptake (GU) heterogeneity in skeletal muscles as a measure of heterogeneity in muscle activity is greater in old than young men when they perform isometric contractions. Six young (26 ± 6 years) and six old (77 ± 6 years) men performed two types of submaximal isometric contractions that required either force or position control. [¹⁸F]-FDG was injected during the task and PET/CT scans were performed immediately after the task. Within-muscle heterogeneity of knee muscles was determined by calculating the coefficient of variation (CV) of GU in PET image voxels within the muscles of interest. The average GU heterogeneity (mean ± SD) for knee extensors and flexors was greater for the old (35.3 ± 3.3%) than the young (28.6 ± 2.4%) (P = 0.006). Muscle volume of the knee extensors were greater for the young compared to the old men (1016 ± 163 vs. 598 ± 70 cm³, P = 0.004). In a multiple regression model, knee extensor muscle volume was a predictor (partial r = −0.87; P = 0.001) of GU heterogeneity for old men (R² = 0.78; P < 0.001), and MVC force predicted GU heterogeneity for young men (partial r = −0.95, P < 0.001). The findings demonstrate that GU is more spatially variable for old than young men and especially so for old men who exhibit greater muscle atrophy.

An ¹⁸F-FDG PET study of cervical muscle in parkinsonian anterocollis

The underlying etiology of parkinsonian anterocollis has been the subject of recent debate. The purpose of this study is to test the hypothesis that anterocollis in parkinsonian syndromes is associated with dystonia of the deep cervical flexors (longus colli and capitis). Eight patients with anterocollis, six in the setting of parkinsonism and two primary cervical dystonia control subjects with anterocollis underwent prospective structured clinical evaluations (interview, examination and rating scales), systematic electromyography of the cervical extensor musculature and (18)F-FDG PET/CT studies of cervical muscles to examine evidence of hypermetabolism or overactivity of deep cervical flexors. Subjects with parkinsonian anterocollis were found to have hypermetabolism of the extensor and sub-occipital muscles but not in the cervical flexors (superficial or deep). EMG abnormalities were observed in all evaluated patients, but only one patient was definitely myopathic. Meanwhile, both dystonia controls exhibited hypermetabolism of cervical flexors (including the longus colli). In conclusion, we were able to demonstrate hypermetabolism of superficial and deep cervical flexors with muscle (18)F-FDG PET/CT in dystonic anterocollis patients, but not in parkinsonian anterocollis patients. The hypermetabolic changes seen in parkinsonian anterocollis patients in posterior muscles may be compensatory. Alternative explanations for anterocollis include myopathy of the cervical extensors, or unbalanced rigidity of the cervical flexors, but this remains to be proven.

Estimation and visualization of longitudinal muscle motion using ultrasonography: a feasibility study

Ultrasonography is a convenient and widely used technique to look into the longitudinal muscle motion as it is radiation-free and real-time. The motion of localized parts of the muscle, disclosed by ultrasonography, spatially reflects contraction activities of the corresponding muscles. However, little attention was paid to the estimation of longitudinal muscle motion, especially towards estimation of dense deformation field at different depths under the skin. Yet fewer studies on the visualization of such muscle motion or further clinical applications were reported in the literature. A primal-dual algorithm was used to estimate the motion of gastrocnemius muscle (GM) in longitudinal direction in this study. To provide insights into the rules of longitudinal muscle motion, we proposed a novel framework including motion estimation, visualization and quantitative analysis to interpret synchronous activities of collaborating muscles with spatial details. The proposed methods were evaluated on ultrasound image sequences, captured at a rate of 25 frames per second from eight healthy subjects. In order to estimate and visualize the GM motion in longitudinal direction, each subject was asked to perform isometric plantar flexion twice. Preliminary results show that the proposed visualization methods provide both spatial and temporal details and they are helpful to study muscle contractions. One of the proposed quantitative measures was also tested on a patient with unilateral limb dysfunction caused by cerebral infarction. The measure revealed distinct patterns between the normal and the dysfunctional lower limb. The proposed framework and its associated quantitative measures could potentially be used to complement electromyography (EMG) and torque signals in functional assessment of skeletal muscles.

FDG-PET/CT assessment of differential chemotherapy effects upon skeletal muscle metabolism in patients with melanoma

OBJECTIVES

To quantify the differential effects of chemotherapy on the metabolic activity of skeletal muscle in vivo using molecular imaging with [18F]-fluorodeoxyglucose (FDG)-positron emission tomography/computed tomography (PET/CT).

METHODS

In this retrospective study, 21 subjects with stage IV melanoma who underwent pre- and post-chemotherapy whole-body FDG-PET/CT imaging were included. The mean standardized uptake value (SUVmean) of 8 different skeletal muscles was measured per subject. Pre- and post-treatment measurements were then averaged across all subjects for each muscle and compared for statistically significant differences between the muscles and following different chemotherapy regimens including dacarbazine (DTIC) and temozolomide (TMZ).

RESULTS

Analysis of FDG-PET/CT images reliably detected changes in skeletal muscle metabolic activity based on muscle location. The percent change in metabolic activity of each skeletal muscle in each subject following chemotherapy was observed to be related to the type of chemotherapy received. Subjects receiving DTIC generally had a decrease in metabolic activity of all muscle groups, whereas subjects receiving TMZ generally had an increase in muscle activity of all muscle groups.

CONCLUSION

FDG-PET/CT can reveal baseline metabolic differences between different muscles of the body. Different chemotherapies are associated with differential changes in the metabolic activity of skeletal muscle, which can be detected and quantified with FDG-PET/CT.

PET/CT in the thorax: pitfalls

PET/CT is widely used in the staging and assessment of therapeutic response in patients with malignancies. Accurate interpretation of PET/CT requires knowledge of the normal physiologic distribution of [18F]-fluoro-2-deoxy-d-glucose, artifacts due to the use of CT for attenuation correction of the PET scan and potential pitfalls due to malignancies that are PET negative and benign conditions that are PET positive. Awareness of these artifacts and potential pitfalls is important in preventing misinterpretation that can alter patient management.

Whole body muscle activity during the FIFA 11+ program evaluated by positron emission tomography

Purpose

This study investigated the effect of the FIFA 11+ warm-up program on whole body muscle activity using positron emission tomography.

Methods

Ten healthy male volunteers were divided into a control group and a group that performed injury prevention exercises (The 11+). The subjects of the control group were placed in a sitting position for 20 min and 37 MBq of ¹⁸F-fluorodeoxyglucose (FDG) was injected intravenously. The subjects then remained seated for 45 min. The subjects of the exercise group performed part 2 of the 11+for 20 min, after which FDG was injected. They then performed part 2 of the 11+for 20 min, and rested for 25 min in a sitting position. Positron emission tomography-computed tomography images were obtained 50 min after FDG injection in each group. Regions of interest were defined within 30 muscles. The standardized uptake value was calculated to examine the FDG uptake of muscle tissue per unit volume.

Results

FDG accumulation within the abdominal rectus, gluteus medius and minimus were significantly higher in the exercise group than in the control group (P<0.05).

Conclusion

The hip abductor muscles and abdominal rectus were active during part 2 of the FIFA 11+ program.

PET/CT imaging of age- and task-associated differences in muscle activity during fatiguing contractions

The study compared positron emission tomography/computed tomography (PET/CT) of [(18)F]-2-fluoro-2-deoxy-D-glucose ([(18)F]-FDG) uptake by skeletal muscles and the amount of muscle activity as indicated by surface electromyographic (EMG) recordings when young and old men performed fatiguing isometric contractions that required either force or position control. EMG signals were recorded from thigh muscles of six young men (26 ± 6 yr) and six old men (77 ± 6 yr) during fatiguing contractions with the knee extensors. PET/CT scans were performed immediately after task failure. Glucose uptake in 24 leg muscles, quantified as standardized uptake values, was greater for the old men after the force task and differed across tasks for the young men (force, 0.64 ± 0.3 g/ml; position, 0.73 ± 0.3 g/ml), but not the old men (force, 0.84 ± 0.3 g/ml; position, 0.79 ± 0.26 g/ml) (age × task interaction; P < 0.001). In contrast, the rate of increase in EMG amplitude for the agonist muscles was greater for the young men during the two contractions and there was no difference for either group of subjects in the rate of increase in EMG amplitude across the two tasks. The imaging estimates of glucose uptake indicated age- and task-dependent differences in the spatial distribution of [(18)F]-FDG uptake by skeletal muscles during fatiguing contractions. The findings demonstrate that PET/CT imaging of [(18)F]-FDG uptake, but not surface EMG recordings, detected the modulation of muscle activity across the fatiguing tasks by the young men but not the old men.

Myoelectric activity along human gastrocnemius medialis: different spatial distributions of postural and electrically elicited surface potentials

It has recently been shown that motor units in human medial gastrocnemius (MG), activated during standing, occupy relatively small territories along the muscle's longitudinal axis. Such organisation provides potential for different motor tasks to produce differing regional patterns of activity. Here, we investigate whether postural control and nerve electrical stimulation produce equal longitudinal activation patterns in MG. Myoelectric activity, at different proximal-distal locations of MG, was recorded using a linear electrode array. To ensure differences in signal amplitude between channels did not result from local, morphological factors two experimental protocols were completed: (i) quiet standing; (ii) electrical stimulation of the tibial nerve. Averaged, rectified values (ARVs) were calculated for each channel in each condition. The distribution of signals along electrode channels was described using linear regression and differences between protocols at each channel determined as the ratio between mean ARV from standing: stimulation protocols. Ratio values changed systematically across electrode channels in seven (of eight) participants, with larger values in distal channels. The distribution of ARV along MG therefore differed between experimental conditions. Compared to fibres of units activated during MG nerve stimulation, units activated during standing may have a tendency to be more highly represented in the distal muscle portion.

Relationship between whole body oxygen consumption and skeletal muscle glucose metabolism during walking in older adults: FDG PET study

BACKGROUND AND AIMS

The purpose of this study was to determine the relationship between whole body energy metabolism measured as oxygen consumption (VO2) and local muscle activity measured by positron emission tomography (PET) and [18F]fluorodeoxyglucose (FDG).

METHODS

Ten community- dwelling older women (73-83 yrs) had FDG PET and VO2 measured while walking at a comfortable speed.

RESULTS

A significant positive correlation was found between VO2 and FDG uptake in the biceps femoris (r=0.83), gluteus minimus (r=0.67), gluteus medius (r=0.77) and pelvis section muscles (r=0.76). The subjects who showed high FDG uptake in the hip muscle group had significantly higher VO2 while walking, compared with subjects without high FDG uptake in the hip muscles.

CONCLUSIONS

These results indicate that FDG PET provides an index which reflects whole body energy metabolism during walking, and revealed that excess muscle activity in the hip muscles during walking plays a key role in increasing VO2 in older adults.

Quantitative analysis of masticatory activity during unilateral mastication using muscle fMRI

OBJECTIVE

Quantitative analysis of the activities of all masticatory muscles is required to elucidate the mechanism of stomatognathic dysfunction. Electromyography can be used to record the activity of masticatory muscles, but quantification of the overall activity of every masticatory muscle has not been accomplished because of methodological limitations. In this study, we used muscle functional magnetic resonance imaging for simultaneous quantification of the overall activities of the masseter, medial pterygoid and lateral pterygoid muscles during unilateral gum chewing.

METHODS

Seven healthy male volunteers participated in the study. We evaluated changes in the mean proton transverse relaxation time in the bilateral masseter, medial pterygoid and lateral pterygoid muscles before and after unilateral gum chewing, and to quantify the overall activity of these muscles simultaneously during unilateral gum chewing.

RESULTS

After 5 min of chewing, the activity of the ipsilateral masseter was highest among the six muscles, followed by the ipsilateral medial pterygoid, contralateral lateral pterygoid and contralateral masseter muscles.

CONCLUSION

These results affirm the importance of the ipsilateral masseter muscle and quantitatively demonstrate the important contribution of the ipsilateral medial pterygoid and contralateral lateral pterygoid muscles during unilateral mastication.

Relationship between a chronically painful trapezius muscle and its metabolic state analyzed with PET/CT

OBJECTIVES

The aim of this study was to investigate the intramuscular metabolic state in chronically painful muscles using positron-emission tomography/computerized tomography (PET/CT).

STUDY DESIGN

The study included 140 consecutive noncancer subjects who underwent PET/CT screening for a physical checkup (mean age 56.0 +/- 10.22 y). The demographic data and information on pain in the neck/shoulder region were obtained using a questionnaire. The subjects who had an awareness of pain in the neck/shoulder region for >6 months were regarded to be pain subjects (n = 39). The minimal and maximal standardized uptake values (SUV) of [(18)F]fluorodeoxyglucose ((18)F-FDG) of the trapezius muscle in each subject were automatically calculated.

RESULTS

The unpaired t test revealed that both the minimal and the maximal SUVs were significantly lower in the pain subjects than in the asymptomatic subjects. A multiple linear regression analysis also demonstrated a significant association between pain in the neck/shoulder region and the SUVs in the trapezius muscle.

CONCLUSIONS

Uptake of (18)F-FDG was lower in the chronically painful trapezius muscle.

Muscle use during double poling evaluated by positron emission tomography

Due to the complexity of movement in cross-country skiing (XCS), the muscle activation patterns are not well elucidated. Previous studies have applied surface electromyography (SEMG); however, recent gains in three-dimensional (3D) imaging techniques such as positron emission tomography (PET) have rendered an alternative approach to investigate muscle activation. The purpose of the present study was to examine muscle use during double poling (DP) at two work intensities by use of PET. Eight male subjects performed two 20-min DP bouts on separate days. Work intensity was ∼ 53 and 74% of peak oxygen uptake (Vo(2peak)), respectively. During exercise 188 ± 8 MBq of [(18)F]fluorodeoxyglucose ([(18)F]FDG) was injected, and subsequent to exercise a full-body PET scan was conducted. Regions of interest (ROI) were defined within 15 relevant muscles, and a glucose uptake index (GUI) was determined for all ROIs. The muscles that span the shoulder and elbow joints, the abdominal muscles, and hip flexors displayed the greatest GUI during DP. Glucose uptake did not increase significantly from low to high intensity in most upper body muscles; however, an increased GUI (P < 0.05) was seen for the knee flexor (27%) and extensor muscles (16%), and for abdominal muscles (21%). The present data confirm previous findings that muscles of the upper limb are the primary working muscles in DP. The present data further suggest that when exercise intensity increases, the muscles that span the lumbar spine, hip, and knee joints contribute increasingly. Finally, PET provides a promising alternative or supplement to existing methods to assess muscle activation in complex human movements.

[¹¹C]acetate PET/CT visualizes skeletal muscle exercise participation, impaired function, and recovery after hip arthroplasty; first results

Purpose

Based on skeletal muscle acetate physiology we aimed studying muscle function after hip arthroplasty with [¹¹C]acetate PET.

Procedures

Two male patients were investigated 3 and 12 weeks after hip arthroplasty with muscle [¹¹C]acetate PET/CT performed at rest and exercise. Median muscle SUV_mean were calculated on three non-consecutive transverse PET slices.

Results

The four exercise PET/CT showed, compared with rest, consistent increase in [¹¹C]acetate uptake in active muscles contralateral to surgery. On the arthroplasty side most muscles showed symmetric activity increase under exercise both at 3 and 12 weeks after surgery, but four muscles showed only minor activity increase at 3 weeks. At 3 months, functional recovery of the latter four muscles was observed.

Conclusion

Consistent increase in [¹¹C]acetate uptake in healthy muscles under exercise compared with rest was observed by PET/CT. Transiently impaired muscle function 3 weeks after surgery recovered at 3 months. These first observations merit further investigation.

Comparison between (18)F-FDG PET/CT and EMG Mapping for Identifying Dystonic Superficial Muscles in Primary Cervical Dystonia: Preliminary Results

PURPOSE

This study was conducted to compare (18)F-FDG PET/CT and electromyography (EMG) mapping in patients with primary cervical dystonia (PCD) to find dystonic superficial cervical muscles.

METHODS

Ten consecutive patients with PCD (M:F = 5:5, age 44 ± 13 years) whose dystonic posture was not relieved with conventional muscle relaxant therapy were included. Target cervical muscles for the comparison between (18)F-FDG PET/CT and EMG mapping were four representative superficial bilateral cervical muscles: splenius capitis muscle, sternocleidomstoid muscle, upper trapezius muscle, and leavator scapulae muscle. The diagnostic efficacy was compared between (18)F-FDG PET/CT and EMG mapping using physical exam and measurement of rotation angle as the gold standard.

RESULTS

Among 80 muscles evaluated, there were 21 (26%) dystonic superficial cervical muscles assessed with physical exam and motion analysis. The sensitivity, specificity, and accuracy for localizing dystonic muscles were 76, 92, and 88% for (18)F-FDG PET/CT, and 95, 66, and 74% for EMG mapping, respectively. The sensitivity of EMG mapping was significantly higher than that of (18)F-FDG PET/CT. In contrast, (18)F-FDG PET/CT was significantly superior to EMG mapping for specificity and accuracy.

CONCLUSIONS

(18)F-FDG PET/CT is more specific and accurate than EMG mapping for finding superficial dystonic cervical muscles. The high sensitivity of EMG mapping suggests that (18)F-FDG PET/CT and EMG mapping are complementary for finding dystonic superficial cervical muscles.

Function of the shoulder muscles during arm elevation: an assessment using positron emission tomography

Although 2-deoxy-2-[(18)F]fluoro-D-glucose (FDG) positron emission tomography (PET) has been used for the assessment of skeletal muscle activities, its application to the shoulder muscles is only sparse. The purpose of this study was to investigate the activities of the shoulder muscles during arm elevation using PET. Six healthy volunteers performed an arm elevation exercise before and after FDG injection. The exercise consisted of 200 repetitions of arm elevation in the scapular plane with a 0.25-kg weight fixed to the wrist on both arms. PET examination was performed 50 min after FDG injection. For control data, PET scan was repeated for each subject on a separate day without any exercise. The volume of interest was established for each shoulder muscle. The subscapularis was divided into three portions (superior, middle, and inferior). The standardized uptake value (SUV) was calculated in each muscle to quantify its activity. The SUVs increased significantly after exercise in the deltoid, supraspinatus, and the superior portion of subscapularis. Among three divided portions of the subscapularis, the SUV of the superior one-third was significantly greater than the rest of the muscle after exercise. Our current study clearly indicated that there were two functionally different portions in the subscapularis muscle and the superior one-third played an important role during arm elevation in the scapular plane.

Evaluation of individual skeletal muscle activity by glucose uptake during pedaling exercise at different workloads using positron emission tomography

Skeletal muscle glucose uptake closely reflects muscle activity at exercise intensity levels <55% of maximal oxygen consumption (V̇o2max). Our purpose was to evaluate individual skeletal muscle activity from glucose uptake in humans during pedaling exercise at different workloads by using [18F]fluorodeoxyglucose (FDG) and positron emission tomography (PET). Twenty healthy male subjects were divided into two groups (7 exercise subjects and 13 control subjects). Exercise subjects were studied during 35 min of pedaling exercise at 40 and 55% V̇o2max exercise intensities. FDG was injected 10 min after the start of exercise or after 20 min of rest. PET scanning of the whole body was conducted after completion of the exercise or rest period. In exercise subjects, mean FDG uptake [standardized uptake ratio (SUR)] of the iliacus muscle and muscles of the anterior part of the thigh was significantly greater than uptake in muscles of control subjects. At 55% V̇o2max exercise, SURs of the iliacus muscle and thigh muscles, except for the rectus femoris, increased significantly compared with SURs at 40% V̇o2max exercise. Our results are the first to clarify that the iliacus muscle, as well as the muscles of the anterior thigh, is the prime muscle used during pedaling exercise. In addition, the iliacus muscle and all muscles in the thigh, except for the rectus femoris, contribute when the workload of the pedaling exercise increases from 40 to 55% V̇o2max.

False-positive positron emission tomography appearance with 18F-fluorodeoxyglucose after definitive radiotherapy for cancer of the mobile tongue

(18)F-fluorodeoxyglucose-positron emission tomography (FDG-PET) is an effective tool for evaluating the results of radiotherapy. However, some false-positive appearances caused by physiological or pathological accumulation are reported. We report on three patients who showed a high accumulation of FDG in the lingual muscles but had no recurrent tumour after definitive radiotherapy for the mobile tongue. All patients had squamous cell carcinoma of the tongue and received interstitial radiotherapy with small sources. High uptake was seen in the lingual muscles without recurrence or inflammation, based on physical and MR examinations. This false-positive appearance is thought to relate to ill-balanced high activity of the lingual muscles after definitive radiotherapy.

The use of positron emission tomography and [18F]fluorodeoxyglucose for functional imaging of muscular activity during exercise with a stride assistance system

The aim of this study was to investigate the use of [18F]fluorodeoxyglucose and positron emission tomography (FDG PET) for quantitative evaluation of glucose metabolism in skeletal muscle during walking. Ten young males underwent FDG PET twice during walks, which were done with or without an automated stride assistance system (SAS). Walk ratios were significantly increased by the SAS in seven subjects. Regional glucose metabolism in muscles between the crista iliaca and the planta was clearly visualized in all ten subjects. Glucose utilization increased significantly in the tibialis posterior and medial gastrocnemius muscles of the seven subjects in whom walk ratios were increased by the SAS. FDG PET is useful for analysis of muscle activity during exercise and rehabilitation.

Scalene muscle uptake: a potential pitfall in head and neck PET/CT

PURPOSE

To describe increased 2-deoxy-2-[(18)F] fluoro-D-glucose (FDG) uptake in the scalene muscles in a large population of patients referred for evaluation with FDG positron emission tomography/computed tomography (PET/CT) imaging.

METHODS

The study met criteria for institutional review board exemption. FDG PET/CT images from 410 patients (179 males; mean age 56.8 years, range 6-88) were retrospectively reviewed for the presence or absence of FDG uptake in the neck that corresponded to the scalene muscles on the concurrent CT scan. Medical records were reviewed and data including age, sex, smoking history, reason for referral, and history of obstructive airways disease, thoracotomy, and thoracic radiation were recorded and evaluated.

RESULTS

One hundred and forty-seven of the 410 scans (36%) demonstrated increased FDG uptake on PET that corresponded to the scalene muscles on the CT scan. The uptake was most often bilateral, symmetrical, and linear (n = 117). Other patterns of scalene muscle uptake included unilateral and linear uptake (n = 27) and unilateral and focal uptake (n = 3). Scalene muscle uptake was more common in patients referred for evaluation of lung carcinomas compared to other types of tumors (52% vs. 32%, p = 0.05).

CONCLUSION

Linear FDG uptake in scalene muscles is a commonly seen pattern on PET/CT. This finding should be recognized as a distinct entity and not misinterpreted on transverse images as metastatic disease.

Biceps brachii myoelectric and oxygenation changes during static and sinusoidal isometric exercises

Surface myoelectric signal changes occurring during sustained isometric contractions have been extensively studied with quantitative surface electromyography (sEMG) and are described by means of some sEMG global variables in time and frequency domain (such as the median power spectral frequency). Recently, the possibility of studying local muscle O(2) saturation during exercise using non-invasive methods has been enhanced thanks to the use of near-infrared spectroscopy (NIRS). The purpose of this work was to combine NIRS and sEMG techniques to analyze the relationship between modifications of sEMG parameters and the underlying metabolic status of the exercising biceps brachii muscle. This relationship was tested under different isometric contraction modalities, namely static (ST) at 20, 40, 60 and 80%MVC and sinusoidal (SIN) at 40+/-20 and 60+/-20%MVC. Results clearly indicated the presence of an initial fast phase of muscle O(2) desaturation followed by a slow phase, regardless of the contraction modality. Moreover, the initial rate of muscle O(2) desaturation was related to the level of force output (R=0.92), but it was independent on the contraction modality (p<0.05). Similarly, changes in sEMG parameters were related to force level (Conduction Velocity-CV vs. Force: R=0.87; sEMG Median Frequency-MDF vs. Force: R=0.86). The high correlation found between CV-MDF and Tissue Oxygenation Index (TOI) slope (R=0.73 and 0.72, respectively) suggests a strong relationship between NIRS and sEMG data. This study indicates that muscle O(2) demand during isometric contractions from low to high force levels is influenced by the type of active motor units and not from the type of isometric exercise modality.

A musculoskeletal model of low grade connective tissue inflammation in patients with thyroid associated ophthalmopathy (TAO): the WOMED concept of lateral tension and its general implications in disease

Background

Low level connective tissue inflammation has been proposed to play a role in thyroid associated ophthalmopathy (TAO). The aim of this study was to investigate this postulate by a musculoskeletal approach together with biochemical parameters.

Methods

13 patients with TAO and 16 controls were examined. Erythrocyte levels of Zn, Cu, Ca²⁺, Mg, and Fe were determined. The musculoskeletal evaluation included observational data on body posture with emphasis on the orbit-head region. The angular foot position in the frontal plane was quantified following gait observation. The axial orientation of the legs and feet was evaluated in an unloaded supine position. Functional propioceptive tests based on stretch stimuli were done by using foot inversion and foot rotation.

Results

Alterations in the control group included neck tilt in 3 cases, asymmetrical foot angle during gait in 2, and a reaction to foot inversion in 5 cases. TAO patients presented facial asymmetry with displaced eye fissure inclination (mean 9.1°) as well as tilted head-on-neck position (mean 5.7°). A further asymmetry feature was external rotation of the legs and feet (mean 27°). Both foot inversion as well as foot rotation induced a condition of neuromuscular deficit. This condition could be regulated by gentle acupressure either on the lateral abdomen or the lateral ankle at the acupuncture points gall bladder 26 or bladder 62, respectively. In 5 patients, foot rotation produced a phenomenon of moving toes in the contra lateral foot. In addition foot rotation was accompanied by an audible tendon snapping. Lower erythrocyte Zn levels and altered correlations between Ca²⁺, Mg, and Fe were found in TAO.

Conclusion

This whole body observational study has revealed axial deviations and body asymmetry as well as the phenomenon of moving toes in TAO. The most common finding was an arch-like displacement of the body, i.e. eccentric position, with foot inversion and head tilt to the contra lateral side and tendon snapping. We propose that eccentric muscle action over time can be the basis for a low grade inflammatory condition. The general implications of this model and its relations to Zn and Se will be discussed.

Pitfalls in Integrated CT-PET of the Thorax: Implications in Oncologic Imaging

Integrated computed tomography-positron emission tomography (CT-PET) scanners improve localization of regions of increased [18F]-fluoro-2-deoxy-D-glucose (FDG) uptake and staging accuracy by allowing the near-simultaneous acquisition of coregistered, spatially matched functional and morphologic data in the same examination. However, many benign lesions can accumulate FDG and be potential pitfalls in interpretation. With the increased use of CT-PET in oncologic imaging, misinterpretation of these potential pitfalls can have significant clinical ramifications and alter staging and management. In this article, we review the physiologic uptake of FDG, normal variants, and potential pitfalls in the integrated CT-PET imaging of the thorax and their implications in oncologic imaging.

Demonstration of excessive metabolic activity of thoracic and abdominal muscles on FDG-PET in patients with chronic obstructive pulmonary disease

PURPOSE

The purpose of this study was to determine if an FDG-PET study was able to visualize muscle uptake of the chest and abdomen in patients with chronic obstructive pulmonary disease (COPD).

METHODS

This study included 25 patients with COPD and 25 patients without COPD who had undergone a FDG-PET study. The nonattenuation-corrected images were used to determine the degree of FDG uptake in the intercostals, subscapular, abdominal rectus, and abdominal oblique muscles. The intensity of uptake in the muscles was rated on a 4-point grading scale with 1 being less, 2 the same, 3 slightly more, and 4 markedly more intense than the sternum.

RESULTS

Thirteen patients with COPD demonstrated FDG activity in the intercostal muscles that was equal to or greater than the sternum and the tracer was demonstrated predominantly in the inferolateral chest wall (n = 8), the entire lateral chest wall (n = 2), the posteroinferior chest wall (n = 2), and the entire chest wall (n = 1). In all 13 patients with COPD who demonstrated FDG activity in the abdominal oblique muscles, the site of muscle activity was predominantly in the anteroinferior abdominal wall (n = 8), the lateral wall (n = 4), and the anterior wall (n = 1). In patients without known COPD, the frequency and intensity of uptake in the muscles were less than those with the disease.

CONCLUSION

This study demonstrates the ability of FDG-PET imaging to assess muscle function in respiratory disorders and may prove to be of some value in further characterizing this disorder.