Diffusion-weighted magnetic resonance imaging of human skeletal muscles: gender-, age- and muscle-related differences in apparent diffusion coefficient

Repeatability of diffusion kurtosis tensor parameters in muscles of the lower legs

PURPOSE

The aim of this study was to provide measurements from and investigate the repeatability of diffusion kurtosis tensor parameters in the muscles of the lower legs.

METHODS

Test-retest acquisition of a kurtosis tensor sequence was performed in 13 healthy volunteers. Quantitative kurtosis tensor parameters were derived, and repeatability of each parameter was evaluated by muscle group and over the whole muscle through intraclass correlation coefficient (ICC) and within-subject coefficient of variation (wsCV). Bland-Altman analysis was also conducted. Differences in parameter values by muscle group were investigated through an analysis of variance.

RESULTS

Axial kurtosis and radial kurtosis values from the test data were 0.63 ± 0.04 and 0.70 ± 0.05, respectively. Kurtosis tensor parameters from all muscle groups and over the whole muscle had wsCV below 15%. ICC for the parameters from most muscle groups was above 85%, with the lowest ICC over the whole muscle being 88.39%. The medial gastrocnemius and extensor digitorum longus showed highest repeatability. Mean, axial, and radial diffusivity had higher wsCV despite being lower-order terms than kurtosis.

CONCLUSION

This study sought to examine the repeatability of diffusion kurtosis tensor-derived parameters in the legs and verify that they could potentially be used as longitudinal imaging metrics. wsCV values from test-retest data indicated high repeatability throughout all examined muscle groups. There were minimal differences in kurtosis and diffusivity parameters between muscle groups in this healthy volunteer cohort.

Volumetric and multispectral DWI near metallic implants using a non-linear phase Carr-Purcell-Meiboom-Gill diffusion preparation

PURPOSE

DWI near metal implants has not been widely explored due to substantial challenges associated with through-slice and in-plane distortions, the increased encoding requirement of different spectral bins, and limited SNR. There is no widely adopted clinical protocol for DWI near metal since the commonly used EPI trajectory fails completely due to distortion from extreme off-resonance ranging from 2 to 20 kHz. We present a sequence that achieves DWI near metal with moderate b-values (400-500 s/mm² ) and volumetric coverage in clinically feasible scan times.

THEORY AND METHODS

Multispectral excitation with Cartesian sampling, view angle tilting, and kz phase encoding reduce in-plane and through-plane off-resonance artifacts, and Carr-Purcell-Meiboom-Gill (CPMG) spin-echo refocusing trains counteract T2* effects. The effect of random phase on the refocusing train is eliminated using a stimulated echo diffusion preparation. Root-flipped Shinnar-Le Roux refocusing pulses permits preparation of a high spectral bandwidth, which improves imaging times by reducing the number of excitations required to cover the desired spectral range. B₁ sensitivity is reduced by using an excitation that satisfies the CPMG condition in the preparation. A method for ADC quantification insensitive to background gradients is presented.

RESULTS

Non-linear phase refocusing pulses reduces the peak B₁ by 46% which allows RF bandwidth to be doubled. Simulations and phantom experiments show that a non-linear phase CPMG pulse pair reduces B₁ sensitivity. Application in vivo demonstrates complementary contrast to conventional multispectral acquisitions and improved visualization compared to DW-EPI.

CONCLUSION

Volumetric and multispectral DW imaging near metal can be achieved with a 3D encoded sequence.

Diffusion tensor imaging indices of acute muscle damage are augmented after exercise in peripheral arterial disease

PURPOSE

Although it is known that peripheral arterial disease (PAD) is associated with chronic myopathies, the acute muscular responses to exercise in this population are less clear. This study used diffusion tensor imaging (DTI) to compare acute exercise-related muscle damage between PAD patients and healthy controls.

METHODS

Eight PAD patients and seven healthy controls performed graded plantar flexion in the bore of a 3T MRI scanner. Exercise began at 2 kg and increased by 2 kg every 2 min until failure, or completion of 10 min of exercise. DTI images were acquired from the lower leg pre- and post-exercise, and were analyzed for mean diffusivity, fractional anisotropy (FA), and eigenvalues 1-3 (λ1-3) of the medial gastrocnemius (MG) and tibialis anterior (TA).

RESULTS

Results indicated a significant leg by time interaction for mean diffusivity, explained by a significantly greater increase in diffusivity of the MG in the most affected legs of PAD patients (11.1 × 10-4 ± 0.5 × 10-4 mm2/s vs. 12.7 × 10-4 ± 1.2 × 10-4 mm2/s at pre and post, respectively, P = 0.02) compared to healthy control subjects (10.8 × 10-4 ± 0.3 × 10-4 mm2/s vs. 11.2 × 10-4 ± 0.5 × 10-4 mm2/s at pre and post, respectively, P = 1.0). No significant differences were observed for the TA, or λ1-3 (all P ≥ 0.06). Moreover, no reciprocal changes were observed for FA in either group (all P ≥ 0.29).

CONCLUSION

These data suggest that calf muscle diffusivity increases more in PAD patients compared to controls after exercise. These findings are consistent with the notion that acute exercise results in increased muscle damage in PAD.

Musculoskeletal trauma imaging in the era of novel molecular methods and artificial intelligence

Over the past decade rapid advancements in molecular imaging (MI) and artificial intelligence (AI) have revolutionized traditional musculoskeletal radiology. Molecular imaging refers to the ability of various methods to in vivo characterize and quantify biological processes, at a molecular level. The extracted information provides the tools to understand the pathophysiology of diseases and thus to early detect, to accurately evaluate the extend and to apply and evaluate targeted treatments. At present, molecular imaging mainly involves CT, MRI, radionuclide, US, and optical imaging and has been reported in many clinical and preclinical studies. Although originally MI techniques targeted at central nervous system disorders, later on their value on musculoskeletal disorders was also studied in depth. Meaningful exploitation of the large volume of imaging data generated by molecular and conventional imaging techniques, requires state-of-the-art computational methods that enable rapid handling of large volumes of information. AI allows end-to-end training of computer algorithms to perform tasks encountered in everyday clinical practice including diagnosis, disease severity classification and image optimization. Notably, the development of deep learning algorithms has offered novel methods that enable intelligent processing of large imaging datasets in an attempt to automate decision-making in a wide variety of settings related to musculoskeletal trauma. Current applications of AI include the diagnosis of bone and soft tissue injuries, monitoring of the healing process and prediction of injuries in the professional sports setting. This review presents the current applications of novel MI techniques and methods and the emerging role of AI regarding the diagnosis and evaluation of musculoskeletal trauma.

The repeatability of bilateral diffusion tensor imaging (DTI) in the upper leg muscles of healthy adults

Objectives

Assessment of the repeatability of diffusion parameter estimations in the upper leg muscles of healthy adults over the time course of 2 weeks, from a simultaneous bilateral upper leg DTI measurement.

Methods

SE-EPI DTI datasets were acquired at 3 T in the upper legs of 15 active adults at a time interval of 2 weeks. ROIs were manually drawn for four quadriceps and three hamstring muscles of both legs. The following DTI parameters were analyzed: 1st, 2nd, and 3rd eigenvalue (λ₁, λ₂, and λ₃), mean diffusivity (MD), and fractional anisotropy (FA). DTI parameters per muscle were calculated with and without intravoxel incoherent motion (IVIM) correction together with SNR levels per muscle. Bland-Altman plots and within-subject coefficient of variation (wsCV) were calculated. Left-right differences between muscles were assessed.

Results

The Bland-Altman analysis showed good repeatability of all DTI parameters except FA for both the IVIM-corrected and standard data. wsCV values show that MD has the highest repeatability (4.5% IVIM; 5.6% standard), followed by λ₂ (4.9% IVIM; 5.5% standard), λ₁ (5.3% IVIM; 7.5% standard), and λ₃ (5.7% IVIM; 5.7% standard). wsCV values of FA were 15.2% for the IVIM-corrected data and 13.9% for the standard analysis. The SNR (41.8 ± 16.0 right leg, 41.7 ± 17.1 left leg) and wsCV values were similar for the left and right leg and no left-right bias was detected.

Conclusions

Repeatability was good for standard DTI data and slightly better for IVIM-corrected DTI data. Our protocol is suitable for DTI of the upper legs with overall good SNR.

Key Points

• The presented DTI protocol is repeatable and therefore suitable for bilateral DT imaging of the upper legs.

• Additional B1⁺calibrations improve SNR and repeatability.

• Correcting for perfusion effects improves repeatability.

Electronic supplementary material

The online version of this article (10.1007/s00330-019-06403-5) contains supplementary material, which is available to authorized users.

Normal values and test-retest variability of stimulated-echo diffusion tensor imaging and fat fraction measurements in the muscle

OBJECTIVES

To assess the test-retest variability of both diffusion parameters and fat fraction (FF) estimates in normal muscle, and to assess differences in normal values between muscles in the thigh.

METHODS

29 healthy volunteers (mean age 37 years, range 20-60 years, 17/29 males) completed the study. Magnetic resonance images of the mid-thigh were acquired using a stimulated echo acquisition mode-echoplanar imaging (STEAM-EPI) imaging sequence, to assess diffusion, and 2-point Dixon imaging, to assess FF. Imaging was repeated in 19 participants after a 30 min interval in order to assess test-retest variability of the measurements.

RESULTS

Intraclass correlation coefficients (ICCs) for test-retest variability were 0.99 [95% confidence interval, (CI): 0.98, 1] for FF, 0.94 (95% CI: 0.84, 0.97) for mean diffusivity and 0.89 (95% CI: 0.74, 0.96) for fractional anisotropy (FA). FF was higher in the hamstrings than the quadriceps by a mean difference of 1.81% (95% CI:1.63, 2.00)%, p < 0.001. Mean diffusivity was significantly lower in the hamstrings than the quadriceps (0.26 (0.13, 0.39) x10^-3 mm²s^-1, p < 0.001) whereas fractional anisotropy was significantly higher in the hamstrings relative to the quadriceps with a mean difference of 0.063 (0.05, 0.07), p < 0.001.

CONCLUSIONS

This study has shown excellent test-retest, variability in MR-based FF and diffusion measurements and demonstrated significant differences in these measures between hamstrings and quadriceps in the healthy thigh.

ADVANCES IN KNOWLEDGE

Test-retest variability is excellent for STEAM-EPI diffusion and 2-point Dixon-based FF measurements in the healthy muscle. Inter- and intraobserver variability were excellent for region of interest placement for STEAM-EPI diffusion and 2-point Dixon-based FF measurements in the healthy muscle. There are significant differences in FF and diffusion measurements between the hamstrings and quadriceps in the normal muscle.

Quantitative MRI Musculoskeletal Techniques: An Update

OBJECTIVE. For many years, MRI of the musculoskeletal system has relied mostly on conventional sequences with qualitative analysis. More recently, using quantitative MRI applications to complement qualitative imaging has gained increasing interest in the MRI community, providing more detailed physiologic or anatomic information. CONCLUSION. In this article, we review the current state of quantitative MRI, technical and software advances, and the most relevant clinical and research musculoskeletal applications of quantitative MRI.

Short- and long-term reproducibility of diffusion-weighted magnetic resonance imaging of lower extremity musculature in asymptomatic individuals and a comparison to individuals with spinal cord injury

Background

Diffusion-weighted magnetic resonance imaging (DW-MRI) of skeletal muscle has the potential to be a sensitive diagnostic and/or prognostic tool in complex, enigmatic neuromusculoskeletal conditions such as spinal cord injury and whiplash associated disorder. However, the reliability and reproducibility of clinically accessible DW-MRI parameters in skeletal muscle remains incompletely characterized – even in individuals without neuromusculoskeletal injury – and these parameters have yet to be characterized for many clinical populations. Here, we provide normative measures of the apparent diffusion coefficient (ADC) in healthy muscles of the lower limb; assess the rater-based reliability and short- and long-term reproducibility of the ADC in the same muscles; and quantify ADC of these muscles in individuals with motor incomplete spinal cord injury.

Methods

Twenty individuals without neuromusculoskeletal injury and 14 individuals with motor incomplete spinal cord injury (SCI) participated in this investigation. We acquired bilateral diffusion-weighted MRI of the lower limb musculature in all participants at 3 T using a multi-shot echo-planar imaging sequence with b-values of 0, 100, 300 and 500 s/mm² and diffusion-probing gradients applied in 3 orthogonal directions. Outcome measures included: (1) average ADC in the lateral and medial gastrocnemius, tibialis anterior, and soleus of individuals without neurological or musculoskeletal injury; (2) intra- and inter-rater reliability, as well as short and long-term reproducibility of the ADC; and (3) estimation of average muscle ADC in individuals with SCI.

Results

Intra- and inter-rater reliability of the ADC averaged 0.89 and 0.79, respectively, across muscles. Least significant change, a measure of temporal reproducibility, was 4.50 and 11.98% for short (same day) and long (9-month) inter-scan intervals, respectively. Average ADC was significantly elevated across muscles in individuals with SCI compared to individuals without neurological or musculoskeletal injury (1.655 vs. 1.615 mm²/s, respectively).

Conclusions

These findings provide a foundation for future studies that track longitudinal changes in skeletal muscle ADC of the lower extremity and/or investigate the mechanisms underlying ADC changes in cases of known or suspected pathology.

Probabilistic classification of tumour habitats in soft tissue sarcoma

The purpose of this work is to propose a method to characterize tumour heterogeneity on MRI, using probabilistic classification based on a reference tissue. The method uses maps of the apparent diffusion coefficient (ADC), T₂ relaxation, and a calculated map representing high-b-value diffusion-weighted MRI (denoted simDWI) to identify up to five habitats (i.e. sub-regions) of tumours. In this classification method, the parameter values (ADC, T₂ , and simDWI) from each tumour voxel are compared against the corresponding parameter probability distributions in a reference tissue. The probability that a tumour voxel belongs to a specific habitat is the joint probability for all parameters. The classification can be visualized using a custom colour scheme. The proposed method was applied to data from seven patients with biopsy-confirmed soft tissue sarcoma, at three time-points over the course of pre-operative radiotherapy. Fast-spin-echo images with two different echo times and diffusion MRI with three b-values were obtained and used as inputs to the method. Imaging findings were compared with pathology reports from pre-radiotherapy biopsy and post-surgical resection. Regions of hypercellularity, high-T₂ proteinaceous fluid, necrosis, collagenous stroma, and fibrosis were identified within soft tissue sarcoma. The classifications were qualitatively consistent with pathological observations. The percentage of necrosis on imaging correlated strongly with necrosis estimated from FDG-PET before radiotherapy (R²  = 0.97) and after radiotherapy (R²  = 0.96). The probabilistic classification method identifies realistic habitats and reflects the complex microenvironment of tumours, as demonstrated in soft tissue sarcoma.

Skeletal Muscle Quantitative Nuclear Magnetic Resonance Imaging and Spectroscopy as an Outcome Measure for Clinical Trials

Recent years have seen tremendous progress towards therapy of many previously incurable neuromuscular diseases. This new context has acted as a driving force for the development of novel non-invasive outcome measures. These can be organized in three main categories: functional tools, fluid biomarkers and imagery. In the latest category, nuclear magnetic resonance imaging (NMRI) offers a considerable range of possibilities for the characterization of skeletal muscle composition, function and metabolism. Nowadays, three NMR outcome measures are frequently integrated in clinical research protocols. They are: 1/ the muscle cross sectional area or volume, 2/ the percentage of intramuscular fat and 3/ the muscle water T2, which quantity muscle trophicity, chronic fatty degenerative changes and oedema (or more broadly, “disease activity”), respectively. A fourth biomarker, the contractile tissue volume is easily derived from the first two ones. The fat fraction maps most often acquired with Dixon sequences have proven their capability to detect small changes in muscle composition and have repeatedly shown superior sensitivity over standard functional evaluation. This outcome measure will more than likely be the first of the series to be validated as an endpoint by regulatory agencies. The versatility of contrast generated by NMR has opened many additional possibilities for characterization of the skeletal muscle and will result in the proposal of more NMR biomarkers. Ultra-short TE (UTE) sequences, late gadolinium enhancement and NMR elastography are being investigated as candidates to evaluate skeletal muscle interstitial fibrosis. Many options exist to measure muscle perfusion and oxygenation by NMR. Diffusion NMR as well as texture analysis algorithms could generate complementary information on muscle organization at microscopic and mesoscopic scales, respectively. ³¹P NMR spectroscopy is the reference technique to assess muscle energetics non-invasively during and after exercise. In dystrophic muscle, ³¹P NMR spectrum at rest is profoundly perturbed, and several resonances inform on cell membrane integrity. Considerable efforts are being directed towards acceleration of image acquisitions using a variety of approaches, from the extraction of fat content and water T2 maps from one single acquisition to partial matrices acquisition schemes. Spectacular decreases in examination time are expected in the near future. They will reinforce the attractiveness of NMR outcome measures and will further facilitate their integration in clinical research trials.

Intravoxel incoherent motion MRI as a means to measure in vivo perfusion: A review of the evidence

The idea that in vivo intravoxel incoherent motion magnetic resonance signal is influenced by blood motion in the microvasculature is exciting, because it suggests that local and quantitative perfusion information can be obtained in a simple and elegant way from a few diffusion-weighted images, without contrast injection. When the method was proposed in the late 1980s some doubts appeared as to its feasibility, and, probably because the signal to noise and image quality at the time was not sufficient, no obvious experimental evidence could be produced to alleviate them. Helped by the tremendous improvements seen in the last three decades in MR hardware, pulse design, and post-processing capabilities, an increasing number of encouraging reports on the value of intravoxel incoherent motion perfusion imaging have emerged. The aim of this article is to review the current published evidence on the feasibility of in vivo perfusion imaging with intravoxel incoherent motion MRI.

The diagnostic value of biexponential apparent diffusion coefficients in myopathy

To investigate the performance of a biexponential signal decay model using DWI in myopathies and to differentiate Polymyositis (PM)/Dermatomyositis (DM), Glycogen Storage Diseases (GSDs) and Muscular Dystrophies (MDs) utilizing diffusion-weighted imaging. 11 healthy volunteers (control group) and 46 patients with myopathy were enrolled in the retrospective study. 27 of 46 patients had PM/DM, 7 patients GSDs and 12 patients MDs. After conventional MR sequences, diffusion weighted imaging with a b-factor ranging from 0 to 1200 s/mm(2) was performed on both thighs. The intra-muscular signal-to-noise ratios (SNRs) on multiple-b DWI images were measured for 7 different muscles and compared among the different groups. The median T2 signal intensity and biexponential apparent diffusion coefficients (ADC), including standard ADC, fast ADC, and slow ADC values, were compared among the different groups. The intra-muscular SNRs were statistically significantly different depending on the b value, and also found among the 4 groups (p < 0.05). The median T2 signal intensity of the normal muscles in control group was statistically significantly lower than that of edematous muscles in the PM/DM, GSDs and MDs groups (p = 0.000), while there were no statistically significant differences among the PM/DM, GSDs, and MDs groups (p > 0.05). The median standard ADC value of the edematous muscles in GSDs was statistically significantly lower than that of normal muscles in the control group (p = 0.000) and the median ADC value of the edematous muscles in PM/DM patients was statistically significantly greater than that of the GSDs (p = 0.000) and MDs groups (p = 0.005). The median slow ADC value of the edematous muscles in MDs patients and PM/DM patients was statistically significantly greater than that of GSDs patients (p < 0.05). Intra-muscular SNR decay curves and biexponential ADC parameters are useful in distinguishing among PM/DM, GSDs, and MDs.

Multi-parametric MR imaging of quadriceps musculature in the setting of clinical frailty syndrome

OBJECTIVE

Frailty is a common geriatric syndrome associated with loss of skeletal muscle mass (sarcopenia) conferring an increased risk of rapid decline in health and function with increased vulnerability to adverse outcomes. The purpose of this study was to investigate the correlation between diffusion tensor, T2 and intramuscular fat content values of the quadriceps muscle group and clinical frailty status using diffusion tensor MR imaging.

MATERIAL AND METHODS

Subjects were recruited from the Arizona Frailty cohort composed of all females with frailty status based on the Fried criteria, including 6 non-frail and 10 pre-frail/frail adults, as well as a community sample of 11 young, healthy controls. Axial images of both thighs were obtained on a 3-T magnet with T1, T2 and diffusion tensor imaging as well as intramuscular fat analysis. Diffusion tensor and T2 values were determined by region-of-interest measurements at the proximal, mid and distal thirds of both thighs. Data were evaluated to determine differences between measured values and frailty status.

RESULTS

The mean fractional anisotropy (FA) values in the bilateral quadriceps muscles demonstrated significant differences (F = 7.558, p = 0.0030) between the control and pre-frail/frail and non-frail and pre-frail/frail groups. There was a significant difference in mean T2 (F = 21.675, p < 0.0001) and lipid content (F = 19.266, p < 0.0001) among all three groups in the total quadriceps muscle group.

CONCLUSION

The quadriceps musculature of pre-frail/frail adults demonstrated increased FA compared to young controls and non-frail adults with increasing T2 and intramuscular fat among the control, non-frail and pre-frail/frail categories.

MR imaging of skeletal muscle signal alterations: Systematic approach to evaluation

Muscle edema or edema-like signal alterations are commonly encountered findings in musculoskeletal magnetic resonance (MR) imaging. Although such signal alterations are very sensitive for detection of the underlying muscle pathology, these are often non-specific findings. Encompassing knowledge of their typical clinical presentations, characteristic appearances and patterns of muscle signal alterations and following a systematic approach towards their assessment, a reader can effectively narrow down the differential diagnosis. This article outlines the role of conventional imaging and advanced anatomic and functional musculoskeletal MR imaging techniques in the evaluation of various muscle disorders and presents a systematic approach towards their diagnosis and management.

Application of intravoxel incoherent motion perfusion imaging to shoulder muscles after a lift-off test of varying duration

Intravoxel incoherent motion (IVIM) MRI is a method to extract microvascular blood flow information out of diffusion-weighted images acquired at multiple b-values. We hypothesized that IVIM can identify the muscles selectively involved in a specific task, by measuring changes in activity-induced local muscular perfusion after exercise. We tested this hypothesis using a widely used clinical maneuver, the lift-off test, which is known to assess specifically the subscapularis muscle functional integrity. Twelve shoulders from six healthy male volunteers were imaged at 3 T, at rest, as well as after a lift-off test hold against resistance for 30 s, 1 and 2 min respectively, in three independent sessions. IVIM parameters, consisting of perfusion fraction (f), diffusion coefficient (D), pseudo-diffusion coefficient D* and blood flow-related fD*, were estimated within outlined muscles of the rotator cuff and the deltoid bundles. The mean values at rest and after the lift-off tests were compared in each muscle using a one-way ANOVA. A statistically significant increase in fD* was measured in the subscapularis, after a lift-off test of any duration, as well as in D. A fD* increase was the most marked (30 s, +103%; 1 min, +130%; 2 min, +156%) and was gradual with the duration of the test (in 10(-3) mm(2) /s: rest, 1.41 ± 0.50; 30 s, 2.86 ± 1.17; 1 min, 3.23 ± 1.22; 2 min, 3.60 ± 1.21). A significant increase in fD* and D was also visible in the posterior bundle of the deltoid. No significant change was consistently visible in the other investigated muscles of the rotator cuff and the other bundles of the deltoid. In conclusion, IVIM fD* allows the demonstration of a task-related microvascular perfusion increase after a specific task and suggests a direct relationship between microvascular perfusion and the duration of the effort. It is a promising method to investigate non-invasively skeletal muscle physiology and clinical perfusion-related muscular disorders.

Techniques and applications of skeletal muscle diffusion tensor imaging: A review

Diffusion tensor imaging (DTI) is increasingly applied to study skeletal muscle physiology, anatomy, and pathology. The reason for this growing interest is that DTI offers unique, noninvasive, and potentially diagnostically relevant imaging readouts of skeletal muscle structure that are difficult or impossible to obtain otherwise. DTI has been shown to be feasible within most skeletal muscles. DTI parameters are highly sensitive to patient-specific properties such as age, body mass index (BMI), and gender, but also to more transient factors such as exercise, rest, pressure, temperature, and relative joint position. However, when designing a DTI study one should not only be aware of sensitivity to the above-mentioned factors but also the fact that the DTI parameters are dependent on several acquisition parameters such as echo time, b-value, and diffusion mixing time. The purpose of this review is to provide an overview of DTI studies covering the technical, demographic, and clinical aspects of DTI in skeletal muscles. First we will focus on the critical aspects of the acquisition protocol. Second, we will cover the reported normal variance in skeletal muscle diffusion parameters, and finally we provide an overview of clinical studies and reported parameter changes due to several (patho-)physiological conditions.

Age-related structural and functional changes of low back muscles

During aging declining maximum force capacity with more or less unchanged fatigability is observed with the underlying mechanisms still not fully understood. Therefore, we compared morphology and function of skeletal muscles between different age groups. Changes in high-energy phosphate turnover (PCr, Pi and pH) and muscle functional MRI (mfMRI) parameters, including proton transverse relaxation time (T2), diffusion (D) and vascular volume fraction (f), were investigated in moderately exercised low back muscles of young and late-middle-aged healthy subjects with (31)P-MR spectroscopy, T2- and diffusion-weighted MRI at 3T. In addition, T1-weighted MRI data were acquired to determine muscle cross-sectional areas (CSA) and to assess fat infiltration into muscle tissue. Except for pH, both age groups showed similar load-induced MR changes and rates of perceived exertion (RPE), which indicates comparable behavior of muscle activation at moderate loads. Changes of mfMRI parameters were significantly associated with RPE in both cohorts. Age-related differences were observed, with lower pH and higher Pi/ATP ratios as well as lower D and f values in the late-middle-aged subjects. These findings are ascribed to age-related changes of fiber type composition, fiber size and vascularity. Interestingly, post exercise f was negatively associated with fat infiltration with the latter being significantly higher in late-middle-aged subjects. CSA of low back muscles remained unchanged, while CSA of inner back muscle as well as mean T2 at rest were associated with maximum force capacity. Overall, applying the proposed MR approach provides evidence of age-related changes in several muscle tissue characteristics and gives new insights into the physiological processes that take place during aging.

Association between muscle hydration measures acquired using bioelectrical impedance spectroscopy and magnetic resonance imaging in healthy and hemodialysis population

Establishing the effect of fluctuating extracellular fluid (ECF) volume on muscle strength in people with end-stage renal disease (ESRD) on hemodialysis (HD) is essential, as inadequate hydration of the skeletal muscles impacts its strength and endurance. Bioelectrical impedance spectroscopy (BIS) has been a widely used method for estimating ECF volume of a limb or calf segment. Magnetic resonance imaging (MRI)-acquired transverse relaxation times (T2) has also been used for estimating ECF volumes of individual skeletal muscles. The purpose of this study was to determine the association between T2 (gold standard) of tibialis anterior (TA), medial (MG), and lateral gastrocnemius (LG), and soleus muscles and calf BIS ECF, in healthy and in people with ESRD/HD. Calf BIS and MRI measures were collected on two occasions before and after HD session in people with ESRD/HD and on a single occasion for the healthy participants. Linear regression analysis was used to establish the association between these measures. Thirty-two healthy and 22 participants on HD were recruited. The association between T2 of TA, LG, MG, and soleus muscles and ratio of calf BIS-acquired ECF and intracellular fluids (ICF) were: TA: β = 0.30, P > 0.05; LG: β = 0.37, P = 0.035; MG: β = 0.43, P = 0.014; soleus: β = 0.60, P < 0.001. For the HD group, calf ECF was significantly associated with T2 of TA (β = 0.44, P = 0.042), and medial gastrocnemius (β = 0.47, P = 0.027) following HD only. Hence BIS-acquired measures cannot be used to measure ECF volumes of a single muscle in the ESRD/HD population; however, BIS could be utilized to estimate ratio of ECF: ICF in healthy population for the LG, MG, and soleus muscles.

Interrelations of muscle functional MRI, diffusion-weighted MRI and (31) P-MRS in exercised lower back muscles

Exercise-induced changes of transverse proton relaxation time (T2 ), tissue perfusion and metabolic turnover were investigated in the lower back muscles of volunteers by applying muscle functional MRI (mfMRI) and diffusion-weighted imaging (DWI) before and after as well as dynamic (31) P-MRS during the exercise. Inner (M. multifidus, MF) and outer lower back muscles (M. erector spinae, ES) were examined in 14 healthy young men performing a sustained isometric trunk-extension. Significant phosphocreatine (PCr) depletions ranging from 30% (ES) to 34% (MF) and Pi accumulations between 95% (left ES) and 120%-140% (MF muscles and right ES) were observed during the exercise, which were accompanied by significantly decreased pH values in all muscles (∆pH ≈ -0.05). Baseline T2 values were similar across all investigated muscles (approximately 27 ms at 3 T), but revealed right-left asymmetric increases (T2 ,inc ) after the exercise (right ES/MF: T2 ,inc  = 11.8/9.7%; left ES/MF: T2 ,inc  = 4.6/8.9%). Analyzed muscles also showed load-induced increases in molecular diffusion D (p = .007) and perfusion fraction f (p = .002). The latter parameter was significantly higher in the MF than in the ES muscles both at rest and post exercise. Changes in PCr (p = .03), diffusion (p < .01) and perfusion (p = .03) were strongly associated with T2,inc , and linear mixed model analysis revealed that changes in PCr and perfusion both affect T2,inc (p < .001). These findings support previous assumptions that T2 changes are not only an intra-cellular phenomenon resulting from metabolic stress but are also affected by increased perfusion in loaded muscles.

Feasibility of semiquantitative liver perfusion assessment by ferucarbotran bolus injection in double-contrast hepatic MRI

PURPOSE

To evaluate the feasibility of semiquantitative measurement of liver perfusion from analysis of ferucarbotran induced signal-dynamics in double-contrast liver MR-imaging (DC-MRI).

MATERIALS AND METHODS

In total 31 patients (21 men; 58 ± 10 years) including 18 patients with biopsy proven liver cirrhosis prospectively underwent clinically indicated DC-MRI at 1.5 Tesla (T) with dynamic T2-weighted gradient-echo imaging after ferucarbotran bolus injection. Breathing artefacts in tissue and input time curves were reduced by Savitzky-Golay-filtering and semiquantitative perfusion maps were calculated using a model free approach. Hepatic blood flow index (HBFI) and splenic blood flow index (SBFI) were determined by normalization of arbitrary perfusion values to the perfusion of the erector spinae muscle resulting in a semiquantitative perfusion measure.

RESULTS

In 30 of 31 patients the evaluated protocol could successfully be applied. Mean HBF was 7.7 ± 2.46 (range, 4.6-12.8) and mean SBF was 13.20 ± 2.57 (range, 8.5-17.8). A significantly lower total HBF was seen in patients with cirrhotic livers as compared to patients with noncirrhotic livers (P < 0.05). In contrast, similar SBF was observed in cirrhotic and noncirrhotic patients (P = 0.11).

CONCLUSION

Capturing the signal dynamics during bolus injection of ferucarbotran in DC-MRI of the liver allows for semiquantitative assessment of hepatic perfusion that may be helpful for a more precise characterisation of liver cirrhosis and focal liver lesions.

Diffusion-weighted MRI, dynamic susceptibility contrast MRI and ultrasound perfusion quantification of denervated muscle in rabbits

OBJECTIVE

The purpose of this study was to assess denervated muscle perfusion using dynamic susceptibility contrast MRI (DSCMRI) and contrast-enhanced ultrasound (CEUS), and to measure denervated muscle apparent diffusion coefficient (ADC) on b1000 diffusion-weighted MRI (DWMRI) at 3 T in order to clarify whether muscle denervation leads to an increase in the extracellular extravascular space, or an increase in blood flow-or both.

MATERIALS AND METHODS

Axotomy of the right sciatic nerve of six white rabbits was performed at day 0. At day 9, hind limb muscles MRI and CEUS were performed to assess the consequences of denervation and both semimembranosus muscles of each rabbit were explanted for histological studies. Signal intensity on T2- and T1-weighted MRI, ADC on DWMRI, maximum signal drop (MSD) on DSCMRI and the area under the curve (AUC) on CEUS were measured over circular regions of interest (ROI), in both semimembranosus muscles. Non-parametric Wilcoxon matched-pairs tests were used to assess the mean differences between denervated and normal muscles.

RESULTS

T2 fat-saturated (FS) MRI studies showed a strong signal in the right semimembranosus muscles compared with the left side, and gadolinium enhancement was observed on T1 FS MRI. Denervated muscles show a significant increase in ADC on DWMRI (p < 0.01) and a significant signal enhancement on DSCMR imaging (p < 0.05) and on first-pass CEUS (p < 0.05).

CONCLUSION

The results of this study--based on perfusion- and diffusion-weighted images--suggest that, after denervation, both increased blood flow through muscle tissue and expansion of the extracellular water volume are present.

Diffusion-weighted magnetic resonance imaging of the musculoskeletal system: an emerging technology with potential to impact clinical decision making

Diffusion-weighted imaging (DWI) is an application of magnetic resonance imaging that allows the measurement of water movement within and between tissues. Originally developed as a way of detecting early signs of stroke or brain disease, DWI is now being used to study physiologic events within the musculoskeletal system. The accurate measurement of water diffusion can provide important information regarding tissue responses associated with trauma and disease, as well as offer insight toward the mechanism by which physical therapy interventions affect tissues. The purpose of this paper is to discuss the rationale for DWI and its potential clinical and research applications for patients with musculoskeletal disorders. Specific examples of the use of DWI for patients with painful spinal disorders are used as illustrations.

Alterations in intramuscular water movement associated with mechanical changes in human skeletal muscle fibers: an evaluation using magnetic resonance diffusion-weighted imaging and B-mode ultrasonography

BACKGROUND

Intramuscular water movement is expected to be affected by the mechanical changes of the muscle fibers. However, the effect of changes in fiber length (FL) and pennation angle (PA) on the water movement has not been sufficiently investigated in human skeletal muscles.

PURPOSE

To determine the relationship between intramuscular water movement and the mechanical changes in human muscle fibers.

MATERIAL AND METHODS

Axial magnetic resonance diffusion-weighted images of the right leg (eight men) were taken using a 1.5-Tesla device with the ankle joint maximally dorsiflexed and maximally plantar flexed. The apparent diffusion coefficient (ADC) values of both the dorsiflexors (the superficial and deep parts of the tibialis anterior) and the plantar flexors (medial gastrocnemius and soleus) were calculated along three orthogonal axes (S-I: superior-to-inferior, A-P: anterior-to-posterior, and R-L: right-to-left). FL and PA of both muscle groups were also calculated from longitudinal B-mode ultrasound images with the ankle joint maximally dorsiflexed and plantar flexed.

RESULTS

There was a significant increase in the ADC in superficial (P < 0.05) and deep (P < 0.05) parts of the dorsiflexors in the S-I direction when the ankle was plantar flexed and in the A-P and R-L directions when the ankle was dorsiflexed (P < 0.05). The plantar flexors showed significantly elevated ADC in the S-I direction when the ankle was dorsiflexed (P < 0.05), and in the A-P and R-L directions when the ankle was plantar flexed (P < 0.05). The dorsiflexors also showed significantly increased PA and decreased FL values when the ankle was dorsiflexed (P < 0.05). The plantar flexors displayed similar morphological changes when the ankle was plantar flexed (P < 0.05).

CONCLUSION

Water diffusion is affected by structural changes in the long axis of the muscle fibers, namely the changes in PA and FL.

Diffusion-weighted magnetic resonance imaging for the healthy cervical multifidus: a potential method for studying neck muscle physiology following spinal trauma

STUDY DESIGN

Cross-sectional.

OBJECTIVE

To develop a new magnetic resonance imaging (MRI) measure for the diffusive properties of the healthy cervical multifidus and to determine the interrater and intrarater reliability of the measurement.

BACKGROUND

Diffusion-weighted MRI, via calculation of the apparent diffusion coefficient (ADC), provides a representation of microscopic movements of water molecules in human tissues and may be useful to assess structural changes in neck muscle, as has been observed following whiplash. The optimal imaging parameters, however, have not been established.

METHODS

A diffusion-weighted MRI measure was developed, and, for the basic examination, the right cervical multifidus muscle at the C5 level was studied. A total of 6 asymptomatic volunteer individuals (3 females and 3 males) underwent a single diffusion-weighted MRI scan. Interrater and intrarater agreement was evaluated using Bland-Altman plots and intraclass correlation coefficients.

RESULTS

Mean ADCb0-b50 and ADCb50-250 were significantly different from one another (P=.03). The plots confirmed the agreement of raters for ADC of the right cervical multifidus at C5.

CONCLUSIONS

A quantitative and reliable diffusion-weighted MRI measure of cervical multifidus ADC has been described. There appears to be a fast and slow component ADC for the healthy multifidus, suggesting changes in extracellular and intracellular volume. Further comparative study is needed to quantify ADCs in the neck muscles in patients with traumatic whiplash.

Value of diffusion-weighted MRI for assessing liver fibrosis and cirrhosis

OBJECTIVE

The objective of our study was to determine the usefulness of the apparent diffusion coefficient (ADC) of liver parenchyma for determining the severity of liver fibrosis.

MATERIALS AND METHODS

This study investigated 78 patients who underwent diffusion-weighted imaging (DWI) with 1.5-T MRI and pathologic staging of liver fibrosis based on biopsy. DWI was performed with b values of 50 and 400 s/mm(2). ADCs of liver were measured using 2.0- to 3.0-cm(2) regions of interest in the right and left lobes of the liver; the mean ADC value was used for analysis. Pathologic METAVIR scores for liver fibrosis stage were used as a reference standard.

RESULTS

The mean ADC values for fibrosis pathologically staged using the METAVIR classification system as F0 (n = 11), F1 (n = 16), F2 (n = 10), F3 (n = 14), and F4 (n = 27) were 125.9, 105.0, 104.5, 103.2, and 99.1 x 10(-5) s/mm(2), respectively. The correlation between the ADC values and the degree of liver fibrosis was moderate (Spearman's test, rho = -0.36). There was a significant difference in ADC values between patients with nonfibrotic liver (F0) and those with cirrhotic liver (F4) (p = 0.008). The best cutoff ADC value to distinguish between these groups was 118 x 10(-5) s/mm(2). However, ADC values were not useful for differentiating viral hepatitis patients with F2 fibrosis or higher from those with a lower degree of fibrosis (area under the receiver operating characteristic curve [AUC] = 0.66) or for differentiating low-stage fibrosis in all patients from high-stage fibrosis in all patients (AUC = 0.54).

CONCLUSION

The ADCs in cirrhotic livers are significantly lower than those in nonfibrotic livers. However, ADC values measured using the current generation of scanners are not reliable enough to replace liver biopsy for staging hepatic fibrosis.

Evaluation of exercised or cooled skeletal muscle on the basis of diffusion-weighted magnetic resonance imaging

In this study, we assessed the physiological changes after exercising or cooling skeletal muscles on the basis of the apparent diffusion coefficient (ADC) values in magnetic resonance (MR) diffusion-weighted images (DWIs). DWIs of the ankle dorsiflexors were acquired with a 1.5-T MR device before and after exercising (22 subjects) or cooling (19 subjects). The exercise comprised a 5-min walk with the ankles dorsiflexed and a 30-time ankle dorsiflexion. Cooling (0 degrees C) of the ankle dorsiflexors was performed for 30 min. ADC values were calculated as ADC1-reflecting diffusion and perfusion and ADC2-approximating the true diffusion coefficient of the ankle dorsiflexors before and after exercising or cooling. ADC1 and ADC2 significantly increased with exercise and decreased with cooling (P < 0.05). Considering both diffusion and perfusion, ADC values allowed us to evaluate the intramuscular changes induced by exercising or cooling in terms of the motion of water molecules and microcirculation.