Comparison of transient arterial occlusion and muscle exercise provocation for assessment of perfusion reserve in skeletal muscle with real-time contrast-enhanced ultrasound

Contrast-enhanced ultrasound for musculoskeletal indications in children

The increasing use of contrast-enhanced ultrasound (CEUS) has opened exciting new frontiers for musculoskeletal applications in adults and children. The most common musculoskeletal-related CEUS applications in adults are for detecting inflammatory joint diseases, imaging skeletal muscles and tendon perfusion, imaging postoperative viability of osseous and osseocutaneous tissue flaps, and evaluating the malignant potential of soft-tissue masses. Pediatric musculoskeletal-related CEUS has been applied for imaging juvenile idiopathic arthritis and Legg-Calvé-Perthes disease and for evaluating femoral head perfusion following surgical hip reduction in children with developmental hip dysplasia. CEUS can improve visualization of the capillary network in superficial and deep tissues and also in states of slow- or low-volume blood flow. In addition, measurements of blood flow imaging parameters performed by quantitative CEUS are valuable when monitoring the outcome of treatment interventions. In this review article we present current experience regarding a wide range of CEUS applications in musculoskeletal conditions in adults and children, with emphasis on the latter, and discuss imaging techniques and CEUS findings in musculoskeletal applications.

Quantifiable Contrast-Enhanced Ultrasound Explores the Role of Protection, Rest, Ice (Cryotherapy), Compression and Elevation (PRICE) Therapy on Microvascular Blood Flow

The aim of this randomized controlled laboratory study was to evaluate the role of standardized protection, rest, ice (cryotherapy), compression and elevation (PRICE) therapy on microvascular blood flow in human skeletal muscle. Quantifiable contrast-enhanced ultrasound was used to analyze intramuscular tissue perfusion (ITP) of the rectus femoris (RF) and vastus intermedius (VI) muscles in 20 healthy athletes who were randomly assigned to PRICE or control groups. Baseline perfusion measurements (resting conditions, T₀) were compared with cycling exercise (T₁), intervention (PRICE or control, T₂) and follow-up at 60 min post-intervention (T₃). The 20 min PRICE intervention included rest, cryotherapy (3°C), compression (35 mm Hg) and elevation. After intervention, PRICE demonstrated a decrease of ITP in VI (-47%, p = 0.01) and RF (-50%, p = 0.037) muscles. At T_3, an ongoing decreased ITP for the RF (p = 0.003) and no significant changes for the VI were observed. In contrast, the control group showed an increased ITP at T₂ and no significant differences at T₃. PRICE applied after exercise led to a down-regulation of ITP, and the termination of PRICE does not appear to be associated with a reactive hyperemia for at least 60 min after treatment.

Evaluation of Skeletal Muscle Microcirculation and Reserve Function of the Type 2 Diabetes with Contrast-Enhanced Ultrasonography

OBJECTIVE

This study aimed to discuss clinical application value of contrast-enhanced ultrasonography on lesion skeletal muscle microcirculation and arterial perfusion reserve in type 2 diabetes mellitus and complicated microvessels.

METHODS

Patients in the control group, type 2 diabetes mellitus (DM) group, diabetic microangiopathy (DM + MC) group underwent contrast-enhanced ultrasonography before and after temporary arterial occlusion to observe blood perfusion of gastrocnemius muscle; draw the time-intensity curve of arteriole, muscular tissue, and venule, and obtain perfusion parameters such as contrast agent arrival time and contrast agent transit time. Blood glucose, insulin, insulin resistance index, and relevant blood rheology parameters were measured.

RESULTS

Contrast agent transit time of the DM + MC group before arterial occlusion was significantly longer than that of the DM group and control group (P < 0.05). Contrast agent transit time of the DM + MC group after temporary arterial occlusion was significantly longer than that of the DM group and control group (P < 0.05). Contrast agent transit time of △artery-muscle, △artery-vein, and △muscle-vein of the DM group and control group and △artery-muscle of the DM + MC group after arterial occlusion was significantly shortened, when compared with that before arterial occlusion (P < 0.05). For △muscle-vein and △artery-vein contrast agent transit time in the DM + MC group, the difference was not statistically significant. By comparing blood glucose, insulin, insulin resistance index, and relevant blood rheology parameters among the DM + MC group, DM group, and control group, the difference was statistically significant, and there was a good correlation.

CONCLUSION

Contrast-enhanced ultrasonography can be used to evaluate skeletal muscle microcirculation disturbance and arterial reserve function of patients who had type 2 diabetic microangiopathy.

Potential value of three-dimensional ultrasonography in diagnosis of diabetic nephropathy in Chinese diabetic population with kidney injury

Background

To explore the potential value of three-dimensional ultrasonography (3DUS) and contrast-enhanced ultrasound (CEUS) in the diagnosis of diabetic nephropathy (DN) in Chinese diabetic patients with kidney injury.

Methods

Patients with type 2 diabetes mellitus and kidney injury in our hospital were enrolled, and the clinical characteristics as well as the laboratory data of patients were collected; 3DUS and CEUS were used to evaluate the morphological structure and blood perfusion of kidneys. Eligible patients were categorized into two groups based on renal biopsy results: DN group and non-diabetic renal diseases (NDRD) group. Correlation analysis and logistic regression analysis were applied to identify the risk factors of DN development.

Results

A total of 115 patients aged from 24 to 78 years old were recruited in the experiment, of which 64 patients (55.65%) and 51 patients (44.35%) were in the DN group and NDRD group, respectively. After correction to CKD stage, BMI and right kidney volume index were retained to identify patients with DN. The ROC of the logistic regression model had an AUC of 0.703 (95% CI: 0.591–0.815) and it was higher than both indicators.

Conclusion

3DUS has potential value in the diagnosis of diabetic nephropathy in Chinese diabetic population with kidney injury and may act as an auxiliary diagnosis for DN. More prospective and well-designed studies with larger samples are needed to verify the result.

Contrast-Enhanced Ultrasound for Musculoskeletal Applications: A World Federation for Ultrasound in Medicine and Biology Position Paper

This World Federation for Ultrasound in Medicine and Biology position paper reviews the diagnostic potential of ultrasound contrast agents for clinical decision-making and provides general advice for optimal contrast-enhanced ultrasound performance in musculoskeletal issues. In this domain, contrast-enhanced ultrasound performance has increasingly been investigated with promising results, but still lacks everyday clinical application and standardized techniques; therefore, experts summarized current knowledge according to published evidence and best personal experience. The goal was to intensify and standardize the use and administration of ultrasound contrast agents to facilitate correct diagnoses and ultimately to improve the management and outcomes of patients.

[CEUS-application possibilities in the musculoskeletal system]

METHODICAL ISSUE

Contrast-enhanced ultrasound (CEUS) offers easily accessible visualization and quantification of the skeletal muscle microcirculation and other tissues in vivo and in real-time with almost no side effects.

AIM

The aim of this review is to present the increasing number of musculoskeletal CEUS applications.

METHODICAL INNOVATIONS/PERFORMANCE

CEUS applications regarding the musculoskeletal system include applications at bone and joints extending beyond the visualization of only the muscular microcirculation. Besides basic muscle physiology, impaired microcirculation in patients with peripheral artery disease or diabetes mellitus and the diagnosis of inflammatory myopathies have been the subject of previous CEUS studies. More recent studies in orthopedics and traumatology have focused on osseous and muscular perfusion characteristics, e. g., in differentiating infected and aseptic non-unions or the impact of different types of implants and prostheses on muscular microcirculation as a surrogate marker of clinical success.

PRACTICAL RECOMMENDATIONS

CEUS of the musculoskeletal system is used in clinical trials or off-label. Therefore, it is not well established in clinical routine. However, considering the increasing number of musculoskeletal CEUS applications, this could change in the future.

Contrast Enhanced Ultrasound Perfusion Imaging in Skeletal Muscle

The ability to accurately evaluate skeletal muscle microvascular blood flow has broad clinical applications for understanding the regulation of skeletal muscle perfusion in health and disease states. Contrast-enhanced ultrasound (CEU) perfusion imaging, a technique originally developed to evaluate myocardial perfusion, is one of many techniques that have been applied to evaluate skeletal muscle perfusion. Among the advantages of CEU perfusion imaging of skeletal muscle is that it is rapid, safe and performed with equipment already present in most vascular medicine laboratories. The aim of this review is to discuss the use of CEU perfusion imaging in skeletal muscle. This article provides details of the protocols for CEU imaging in skeletal muscle, including two predominant methods for bolus and continuous infusion destruction-replenishment techniques. The importance of stress perfusion imaging will be highlighted, including a discussion of the methods used to produce hyperemic skeletal muscle blood flow. A broad overview of the disease states that have been studied in humans using CEU perfusion imaging of skeletal muscle will be presented including: (1) peripheral arterial disease; (2) sickle cell disease; (3) diabetes; and (4) heart failure. Finally, future applications of CEU imaging in skeletal muscle including therapeutic CEU imaging will be discussed along with technological developments needed to advance the field.

Triggered intravoxel incoherent motion MRI for the assessment of calf muscle perfusion during isometric intermittent exercise

The main aim of this paper was to propose triggered intravoxel incoherent motion (IVIM) imaging sequences for the evaluation of perfusion changes in calf muscles before, during and after isometric intermittent exercise. Twelve healthy volunteers were involved in the study. The subjects were asked to perform intermittent isometric plantar flexions inside the MRI bore. MRI of the calf muscles was performed on a 3.0 T scanner and diffusion-weighted (DW) images were obtained using eight different b values (0 to 500 s/mm² ). Acquisitions were performed at rest, during exercise and in the subsequent recovery phase. A motion-triggered echo-planar imaging DW sequence was implemented to avoid movement artifacts. Image quality was evaluated using the average edge strength (AES) as a quantitative metric to assess the motion artifact effect. IVIM parameters (diffusion D, perfusion fraction f and pseudo-diffusion D*) were estimated using a segmented fitting approach and evaluated in gastrocnemius and soleus muscles. No differences were observed in quality of IVIM images between resting state and triggered exercise, whereas the non-triggered images acquired during exercise had a significantly lower value of AES (reduction of more than 20%). The isometric intermittent plantar-flexion exercise induced an increase of all IVIM parameters (D by 10%; f by 90%; D* by 124%; fD* by 260%), in agreement with the increased muscle perfusion occurring during exercise. Finally, IVIM parameters reverted to the resting values within 3 min during the recovery phase. In conclusion, the IVIM approach, if properly adapted using motion-triggered sequences, seems to be a promising method to investigate muscle perfusion during isometric exercise.

Perfusion dynamics assessment with Power Doppler ultrasound in skeletal muscle during maximal and submaximal cycling exercise

PURPOSE

Assessment of limitations in the perfusion dynamics of skeletal muscle may provide insight in the pathophysiology of exercise intolerance in, e.g., heart failure patients. Power doppler ultrasound (PDUS) has been recognized as a sensitive tool for the detection of muscle blood flow. In this volunteer study (N = 30), a method is demonstrated for perfusion measurements in the vastus lateralis muscle, with PDUS, during standardized cycling exercise protocols, and the test-retest reliability has been investigated.

METHODS

Fixation of the ultrasound probe on the upper leg allowed for continuous PDUS measurements. Cycling exercise protocols included a submaximal and an incremental exercise to maximal power. The relative perfused area (RPA) was determined as a measure of perfusion. Absolute and relative reliability of RPA amplitude and kinetic parameters during exercise (onset, slope, maximum value) and recovery (overshoot, decay time constants) were investigated.

RESULTS

A RPA increase during exercise followed by a signal recovery was measured in all volunteers. Amplitudes and kinetic parameters during exercise and recovery showed poor to good relative reliability (ICC ranging from 0.2-0.8), and poor to moderate absolute reliability (coefficient of variation (CV) range 18-60%).

CONCLUSIONS

A method has been demonstrated which allows for continuous (Power Doppler) ultrasonography and assessment of perfusion dynamics in skeletal muscle during exercise. The reliability of the RPA amplitudes and kinetics ranges from poor to good, while the reliability of the RPA increase in submaximal cycling (ICC = 0.8, CV = 18%) is promising for non-invasive clinical assessment of the muscle perfusion response to daily exercise.

Prospects of Contrast-Enhanced Ultrasonography for the Diagnosis of Peripheral Arterial Disease: A Meta-analysis

OBJECTIVES

Contrast-enhanced ultrasonography (CEUS) is a modern diagnostic method that can also be used to study microperfusion. This study compared the time to peak intensity measured by CEUS in patients with peripheral arterial disease (PAD) and healthy control participants.

METHODS

After a comprehensive literature search in multiple electronic databases and study selection, a random-effect meta-analysis was performed to compare the time to peak intensity measured by CEUS in patients with PAD and healthy controls, which followed meta-regression analyses for identification of factors affecting the outcomes.

RESULTS

Fourteen studies (data for 322 patients with PAD and 314 healthy individuals) were used for the meta-analysis. The age of this sample of patients with PAD was 64.92 (95% confidence interval, 62.53, 67.31) years, and that of the healthy controls was 55.32 (51.67, 58.98) years. The times to peak intensity were 18.55 (15.62, 21.48) seconds in healthy controls, 33.40 (27.65, 39.15) seconds in patients with PAD, and 76.22 (36.23, 116.22) seconds in patients with PAD and diabetes mellitus. The difference between patients with PAD and healthy controls in the time to peak intensity was statistically significant (mean difference, 24.80 [10.16, 39.44] seconds; P < .00009). The ABI was not significantly associated with the time to peak intensity in patients with PAD. Age and sex were also not significantly associated with the time to peak intensity.

CONCLUSIONS

Contrast-enhanced ultrasonography is a valuable tool for the diagnosis of PAD based on its ability to differentiate the time to peak intensity between patients with PAD and healthy individuals, but little data are yet available to assess its diagnostic ability in clinical practice.

Correlation between microcirculation and contrast-enhanced ultrasonography after crush injury of limbs

PURPOSE

To explore the microcirculation formation mechanism of contrast-enhanced (CE) ultrasonography imaging performance in rabbits with limb muscle crush injury.

METHODS

Seventy-two New Zealand white rabbits were randomly divided into two groups. A limb muscle crush injury model was created by airing a balloon cuff device with a force of 40 kpa. CE ultrasonography parameters were detected in the first group. In vivo microcirculation parameters were detected in the second group. Fine blood vessel diameter and blood flow velocity were calculated before extrusion and 0.5, 2, 6, 24 h, and 3 days after decompression.

RESULTS

Compared with the uninjured muscle, reperfusion of the injured muscles showed early and high enhancement in CE ultrasonography images. The time-intensity curve showed a trend of rapid elevation and gradual drop. Compared with the control group, fine artery and vein diameters in the experimental group were wider and the blood flow velocity was slower, especially in the fine veins.

CONCLUSION

In vivo microcirculation detection can reflect changes in muscle microvascular diameter and blood flow velocity, which have a correlation with quantitative ultrasound imaging parameters.

A Temporal and Spatial Analysis Approach to Automated Segmentation of Microbubble Signals in Contrast-Enhanced Ultrasound Images: Application to Quantification of Active Vascular Density in Human Lower Limbs

Contrast-enhanced ultrasound (CEUS) using microbubble contrast agents has shown great promise in visualising and quantifying active vascular density. Most existing approaches for vascular density quantification using CEUS are calculated based on image intensity and are susceptible to confounding factors and imaging artefact. Poor reproducibility is a key challenge to clinical translation. In this study, a new automated temporal and spatial signal analysis approach is developed for reproducible microbubble segmentation and quantification of contrast enhancement in human lower limbs. The approach is evaluated in vitro on phantoms and in vivo in lower limbs of healthy volunteers before and after physical exercise. In this approach, vascular density is quantified based on the relative areas microbubbles occupy instead of their image intensity. Temporal features of the CEUS image sequences are used to identify pixels that contain microbubble signals. A microbubble track density (MTD) measure, the ratio of the segmented microbubble area to the whole tissue area, is calculated as a surrogate for active capillary density. In vitro results reveal a good correlation (r² = 0.89) between the calculated MTD measure and the known bubble concentration. For in vivo results, a significant increase (129% in average) in the MTD measure is found in lower limbs of healthy volunteers after exercise, with excellent repeatability over a series of days (intra-class correlation coefficient = 0.96). This compares to the existing state-of-the-art approach of destruction and replenishment analysis on the same patients (intra-class correlation coefficient ≤0.78). The proposed new approach shows great potential as an accurate and highly reproducible clinical tool for quantification of active vascular density.

Contrast-Enhanced Ultrasound Reveals Exercise-Induced Perfusion Deficits in Claudicants

Background

Contrast-Enhanced Ultrasonography (CEUS) is an imaging modality allowing perfusion quantification in targeted regions of interest of the lower extremity that has not been possible with color-flow imaging or with measurement of ankle brachial indices. We developed a protocol to quantify lower extremity muscle perfusion impairment in PAD patients in response to exercise.

Methods and findings

Thirteen patients with Rutherford Class I-III Peripheral Arterial Disease (PAD) and no prior revascularization procedures were recruited from the Baltimore Veterans Affairs Medical Center and compared with eight control patients without PAD. CEUS interrogation of the index limb gastrocnemius muscle was performed using an intravenous bolus of lipid-stabilized microsphere contrast before and after a standardized treadmill protocol. Peak perfusion (PEAK) and time to peak perfusion (TTP) were measured before and after exercise. Between and within group differences were assessed. Control subjects demonstrated a more rapid TTP (p<0.01) and an increase in peak perfusion (PEAK, p=0.02) after exercise, when compared to their baseline measures. Patients with PAD demonstrated TTP and PEAK measures equivalent to controls at baseline (p=0.39, p=0.71, respectively). However, they exhibited no significant exercise-induced changes in perfusion (TTP p=0.49 and PEAK 0.67, respectively compared to baseline). After exercise, normal subjects had significantly shorter TTP (p=0.04) and greater PEAK (p=0.02) than PAD patients.

Conclusion

Consistent with their lack of ischemic symptoms at rest, class I to III claudicant PAD patients showed similar perfusion measures (TTP and PEAK) at rest. PAD patients, however, were unable to increase perfusion in response to exercise, whereas controls increased perfusion significantly. This corresponds with claudication and limited walking capacity observed in PAD. CEUS with bolus injection offers a convenient, objective, quantitative and visual physiologic assessment of perfusion limitation in specific muscle groups of PAD patients. This has the potential for substantial clinical and research utility.

Effect of Peripheral Artery Sympathetic Denervation on Muscle Microperfusion and Macroperfusion in an Animal Peripheral Artery Disease Model Using Contrast-Enhanced Ultrasound and Doppler Flow Measurement

PURPOSE

To determine the effects of catheter-based peripheral sympathetic denervation (CPSD) on peripheral artery sympathetic tone and peripheral microperfusion (PMP).

MATERIALS AND METHODS

The effects of bilateral CPSD in common iliac arteries on PMP of the biceps femoris were determined in pigs using contrast-enhanced ultrasound, and mean transit time (mTT) and wash-in rate (WiR) were calculated during steady-state infusion of INN-sulfur-hexafluoride. Measurements were performed bilaterally at rest and during infusion of adenosine 70 μg/kg/min after unilateral moderate left external iliac artery stenosis.

RESULTS

Before CPSD, PMP decreased significantly (P < .05) under adenosine stress compared with resting conditions, with right mTT of 7.5 seconds ± 3.6 versus 16.9 seconds ± 11.9 and WiR of 63.1 arbitrary units (AU) ± 49.0 versus 25.0 AU ± 17.5 and left mTT of 29.2 seconds ± 18.0 versus 56.3 seconds ± 38.7 and WiR of 13.6 AU ± 8.4 versus 6.0 AU ± 4.1. After CPSD, PMP did not differ significantly (P > .05) between conditions of adenosine stress and rest, with right mTT of 19.9 seconds ± 24.7 versus 23.2 seconds ± 21.0 and WiR of 16.2 AU ± 25.0 versus 20.5 AU ± 19.7 and left mTT of 23.3 seconds ± 23.1 versus 25.8 seconds ± 21.7 and WiR of 12.5 AU ± 6.2 versus 20.0 AU ± 12.1.

CONCLUSIONS

CPSD reduced peripheral artery sympathetic tone and may be an alternative to surgical or computed tomography-guided sympathectomy for the treatment of end-stage peripheral artery disease and Raynaud phenomenon.

Contrast-enhanced ultrasonography to assess blood perfusion of skeletal muscles in normal dogs

This study evaluated perfusion of skeletal muscle using contrast enhanced ultrasonography in humerus, radius, femur and tibia in normal dogs. Contrast enhanced ultrasonography for each region was performed after injecting 0.5 mL and 1 mL of contrast medium (SonoVue) in every dog. Blood perfusion was assessed quantitatively by measuring the peak intensity, time to the peak intensity and area under the curve from the time-intensity curve. Vascularization in skeletal muscle was qualitatively graded with a score of 0-3 according to the number of vascular signals. A parabolic shape of time-intensity curve was observed from muscles in normal dogs, and time to the peak intensity, the peak intensity and area under the curve of each muscle were not significantly different according to the appendicular regions examined and the dosage of contrast agent administered. This study reports that feasibility of contrast enhanced ultrasonography for assessment of the muscular perfusion in canine appendicular regions.

Reliability of contrast-enhanced ultrasound for the assessment of muscle perfusion in health and peripheral arterial disease

We investigated the reliability of contrast-enhanced ultrasound (CEUS) in assessing calf muscle microvascular perfusion in health and disease. Response to a post-occlusive reactive hyperaemia test was repeated on two occasions >48 h apart in healthy young (28 ± 7 y) and elderly controls (70 ± 5 y), and in peripheral arterial disease patients (PAD, 69 ± 7 y; n = 10, 9 and 8 respectively). Overall, within-individual reliability was poor (coefficient of variation [CV] range: 15-87%); the most reliable parameter was time to peak (TTP, 15-48% CV). Nevertheless, TTP was twice as long in elderly controls and PAD compared to young (19.3 ± 10.4 and 22.0 ± 8.6 vs. 8.9 ± 6.2 s respectively; p < 0.01), and area under the curve for contrast intensity post-occlusion (a reflection of blood volume) was ∼50% lower in elderly controls (p < 0.01 versus PAD and young). Thus, CEUS assessment of muscle perfusion during reactive hyperaemia demonstrated poor reliability, yet still distinguished differences between PAD patients, elderly and young controls.

Application of contrast-enhanced ultrasonography in the diagnosis of skeletal muscle crush injury in rabbits

OBJECTIVE

To explore the diagnostic value of quantitative contrast-enhanced (CE) ultrasonography for crush injury in the hind limb muscles of rabbits.

METHODS

A total of 120 New Zealand white rabbits were randomized to receive compression on the left hind limb for either 2 h (n = 56) or 4 h (n = 56) to induce muscle crush injury. Another eight animals were not injured and served as normal controls. CE ultrasonography parameters such as peak intensity (PI), ascending slop, descending slop and area under curve (AUC) were measured at 0.5, 2, 6 and 24 h and 3, 7 and 14 days after decompression.

RESULTS

Compared with the uninjured muscles, reperfusion of the injured muscles showed early and high enhancement in CE ultrasonography images. The time-intensity curve showed a trend of rapid lift and gradual drop. The PI and AUC values differed significantly among the three groups and were positively correlated with serum and tissue biomarkers. Rabbits of the 4-h compression group showed significantly higher PI and AUC values, and serum and tissue parameters than the 2-h compression group at each time points.

CONCLUSION

CE ultrasonography can effectively detect muscle crush injury and monitor dynamic changes of the injured muscles in rabbits. PI and AUC are promising diagnostic parameters for this disease.

ADVANCES IN KNOWLEDGE

CE ultrasonography might play an important role in the pre-hospital and bedside settings for the diagnosis of muscle crush injury.

Assessment of peripheral skeletal muscle microperfusion in a porcine model of peripheral arterial stenosis by steady-state contrast-enhanced ultrasound and Doppler flow measurement

OBJECTIVE

Noninvasive measurement of peripheral muscle microperfusion could potentially improve diagnosis, management, and treatment of peripheral arterial disease (PAD) and thus improve patient care. Contrast-enhanced ultrasound (CEUS) as a noninvasive diagnostic tool allows quantification of muscle perfusion. Increasing data on bolus technique CEUS reflecting microperfusion are becoming available, but only limited data on steady-state CEUS for assessment of muscle microperfusion are available. Therefore, the aim of this study was to evaluate steady-state CEUS for assessment of peripheral muscle microperfusion in a PAD animal model.

METHODS

In a porcine animal model, peripheral muscle microperfusion was quantified by steady-state CEUS replenishment kinetics (mean transit time [mTT] and wash-in rate [WiR]) of the biceps femoris muscle during intravenous steady-state infusion of INN-sulfur hexafluoride (SonoVue; Bracco, Geneva, Switzerland). In addition, macroperfusion was quantified at the external femoral artery with a Doppler flow probe. Peripheral muscle microperfusion and Doppler flow measurements were performed bilaterally at rest and under adenosine stress (70 μg/kg body weight) before and after unilateral creation of a moderate external iliac artery stenosis.

RESULTS

All measurements could be performed completely in 10 pigs. Compared with baseline measurements, peripheral muscle microperfusion decreased significantly during adenosine stress (rest vs adenosine stress: mTT, 7.8 ± 3.3 vs 21.2 ± 17.8 s, P = .0006; WiR, 58.4 ± 38.1 vs 25.3 ± 15.6 arbitrary units [a.u.]/s, P < .0001; Doppler flow, 122.3 ± 31.4 vs 83.6 ± 28.1 mL/min, P = .0067) and after stenosis creation (no stenosis vs stenosis: mTT, 8.1 ± 3.1 vs 29.2 ± 18.0 s, P = .0469; WiR, 53.0 ± 22.7 vs 13.6 ± 8.4 a.u./s, P = .0156; Doppler flow, 124.2 ± 41.8 vs 65.9 ± 40.0 mL/min, P = .0313). After stenosis creation, adenosine stress led to a further significant decrease of peripheral muscle microperfusion but had no effect on macroperfusion (mTT, 29.2 ± 18.0 vs 56.3 ± 38.7 s, P = .0078; WiR, 13.6 ± 8.4 vs 6.0 ± 4.1 a.u./s, P = .0078; Doppler flow, 65.9 ± 40.0 vs 79.2 ± 29.6 mL/min, P = .8125). Receiver operating characteristic curves for the presence of inflow stenosis showed an excellent area under the curve of 0.93 for mTT at rest and 0.86 for Doppler flow.

CONCLUSIONS

Peripheral muscle microperfusion measurement by steady-state CEUS with replenishment kinetics is feasible and allows detection of muscle microperfusion changes caused by vasodilative stress alone or in combination with a moderate inflow stenosis. Steady-state CEUS offers superior diagnostic performance compared with Doppler flow measurements. Therefore, steady-state CEUS may prove to be a useful tool in diagnosis of PAD and for evaluation of new therapies.

Assessment of skeletal muscle microcirculation in type 2 diabetes mellitus using dynamic contrast-enhanced ultrasound: a pilot study

PURPOSE

To investigate muscular micro-perfusion by employing dynamic contrast-enhanced ultrasound (CEUS) and performing transient arterial occlusion in patients with type 2 diabetes mellitus (DM-2).

METHODS

Twenty DM-2 patients (mean age, 58 ± 8.6 years; duration of diabetes, 15.4 ± 12.1 years) and 20 healthy volunteers (mean age, 54 ± 5.4 years) participated. CEUS was applied to the calf, while 4.8 mL of SonoVue(®) was injected intravenously. At the thigh level, arterial occlusion (60 s) was performed. CEUS parameters (tmax, max, AUCpost and m) were evaluated and Pearson-product-moment correlation coefficients were computed.

RESULTS

A moderate negative correlation of HbA1c and max was established (-0.53). Max in patients with DM-2 >10 years was 79.89 ± 37.4. Max in patients with DM-2 duration <10 years was 137.62 ± 71.72 (p = 0.04). AUCpost in patients with DM-2 duration >10 years was 3924.01 ± 1630.52. AUCpost in patients with DM-2 duration <10 years was 6453.59 ± 3206.23 (p = 0.04).

CONCLUSION

Patients with long history of DM-2 present with impaired muscular perfusion. CEUS and transient arterial occlusion may provide appropriate methods for semi-quantitative evaluation of muscular micro-perfusion in patients with DM-2.

Microvascular perfusion increases after eccentric exercise of the gastrocnemius

OBJECTIVES

The purpose of this study was to assess microvascular perfusion immediately after eccentric exercise using contrast-enhanced sonography.

METHODS

An intravenous catheter was placed in the antecubital vein of the arm contralateral to the leg being tested for the delivery of microbubbles to 18 healthy volunteers (mean age ± SD, 22.2 ± 2.2 years; height, 166.0 ± 11.9 cm; weight, 69.4 ± 25.0 kg). Eccentric exercises were performed unilaterally in a randomized leg. Calf-lowering repetitions off a raised step were performed to the beat of a metronome over 3 seconds in the sequence of 50 repetitions, 5 minutes of rest, and 50 repetitions. Microvascular perfusion (blood volume, blood flow, and blood flow velocity) was measured before and immediately after exercise using replenishment kinetics.

RESULTS

Blood volume and flow both significantly increased after exercise (P < .001). Baseline measurements were 5.88 ± 1.33 dB and 2.34 ± 0.41 dB/s and increased to 12.20 ± 3.31 dB and 4.52 ± 1.05 dB/s, respectively. There was a significant decrease in blood flow velocity (P = .035) after exercise (0.38 ± 0.03 s(-1)) from baseline (0.41 ± 0.06 s(-1)).

CONCLUSIONS

Circulatory responses were altered after eccentric exercise, which may be due to the metabolic demand placed on the body. On the basis of this finding, eccentric exercise may be used as a model to assess the effect modalities have on the circulatory system after an elevated state of microvascular perfusion is reached.

Dynamic contrast-enhanced ultrasound for assessment of therapy effects on skeletal muscle microcirculation in peripheral arterial disease: pilot study

OBJECTIVE

To assess with dynamic contrast-enhanced ultrasound (CEUS) and transient arterial occlusion whether the muscular micro-perfusion in patients with peripheral arterial disease (PAD) is improved after angioplasty or surgery.

MATERIALS AND METHODS

This study had local institutional review board approval. Written informed consent was obtained from all 20 patients with PAD, Fontaine stage IIb (mean age, 64 years), who participated in the study. Low-MI CEUS (7MHz; MI, 0.28) was applied to the mainly affected lower leg after start of a continuous automatic intravenous injection of 4.8mL SonoVue(®). Muscle-perfusion was monitored by CEUS before, during, and after provocation by arterial occlusion at the thigh level lasting for 60s. CEUS examination was performed a second time within 14 days after angioplasty (n=15), thrombendarterectomy (n=2), angioplasty and thrombendarterectomy (n=1), or bypass (n=2). Clinical amelioration was re-evaluated within 6 months after the intervention using a 4-point scale.

RESULTS

Ankle-brachial-index (ABI) increased from 0.8±0.2 to 0.9±0.3 after treatment (p=0.01). Time to maximum CEUS signal (tmax) shortened from 26±14s to 14±4s (p=0.004). The slope to maximum after transient occlusion (m2) changed to steeper values (6.4±5.8∼mL/s versus 10.2±5.0∼mL/s; p=0.04). Shortened tmax predicted improvement in the patients' intermittent leg pain and therefore successful therapy outcome.

CONCLUSION

Dynamic CEUS with transient arterial occlusion can visualize the treatment-induced improvement of muscular micro-perfusion in patients with PAD.

Microvascular perfusion and intramuscular temperature of the calf during cooling

PURPOSE

The study's purpose was to examine how the microvascularity of the gastrocnemius changed after a cryotherapy intervention based on subcutaneous tissue thickness. A secondary purpose was to compare intramuscular temperature change to subcutaneous tissue thickness.

METHODS

This was a single-blinded crossover study; each subject received both conditions (cryotherapy or sham). Subjects had baseline measurements of blood flow, blood volume, and intramuscular temperature recorded at 1 cm into the muscle belly of the medial gastrocnemius. The randomized condition was applied for 10, 25, 40, or 60 min, depending on subcutaneous tissue thickness. Immediate posttreatment microvascular measures were taken. After a designated rewarming period, again based on subcutaneous tissue thickness, measurements were retaken. At least 48 h separated the two conditions.

RESULTS

There were significant condition × time interactions for blood flow (P = 0.01), blood volume (P = 0.022), and intramuscular temperature (P < 0.001). For blood flow and volume, the cryotherapy condition maintained baseline levels, whereas the sham condition increased immediately after treatment and rewarming. For intramuscular temperature, the cryotherapy condition caused a decrease in intramuscular temperature from baseline compared with no change in the sham condition from baseline. Intramuscular temperature change was significantly correlated to subcutaneous tissue thickness (r = 0.49, P = 0.05).

CONCLUSIONS

Cryotherapy did not decrease blood flow and blood volume from resting levels, although the intramuscular temperature decreased. An intramuscular change of 7°C-9°C may not be cold enough to cause local vasoconstriction.

Dynamic contrast-enhanced ultrasound and transient arterial occlusion for quantification of arterial perfusion reserve in peripheral arterial disease

OBJECTIVE

To quantify muscular micro-perfusion and arterial perfusion reserve in peripheral arterial disease (PAD) with dynamic contrast-enhanced ultrasound (CEUS) and transient arterial occlusion.

MATERIALS AND METHODS

This study had local institutional review board approval and written informed consent was obtained from all subjects. We examined the dominant lower leg of 40 PAD Fontaine stage IIb patients (mean age, 65 years) and 40 healthy volunteers (mean age, 54 years) with CEUS (7 MHz; MI, 0.28) during continuous intravenous infusion of 4.8 mL microbubbles. Transient arterial occlusion at mid-thigh level simulated physical exercise. With time-CEUS-intensity curves obtained from regions of interest within calf muscles, we derived the maximum CEUS signal after occlusion (max) and its time (tmax), slope to maximum (m), vascular response after occlusion (AUC(post)), and analysed accuracy, receiver operating characteristic (ROC) curves, and correlations with ankle-brachial index (ABI) and walking distance.

RESULTS

All parameters differed in PAD and volunteers (p<0.014). In PAD, tmax was delayed (31.2±13.6 vs. 16.7±8.5 s, p<0.0001) and negatively correlated with ankle-brachial-index (r=-0.65). m was decreased in PAD (4.3±4.6 mL/s vs. 13.1±8.4 mL/s, p<0.0001) and had highest diagnostic accuracy (sensitivity/specificity, 75%/93%) for detection of diminished muscular micro-perfusion in PAD (cut-off value, m<5∼mL/s). Discriminant analysis and ROC curves revealed m, and AUC(post) as optimal parameter combination for diagnosing PAD and therefore impaired arterial perfusion reserve.

CONCLUSIONS

Dynamic CEUS with transient arterial occlusion quantifies muscular micro-perfusion and arterial perfusion reserve. The technique is accurate to diagnose PAD.

Functional imaging in muscular diseases

OBJECTIVE: The development of morphological and functional imaging techniques has improved the diagnosis of muscular disorders. METHODS: With the use of whole-body magnetic resonance imaging (MRI) the possibility of imaging the entire body has been introduced. In patients with suspected myositis, oedematous and inflammatory changed muscles can be sufficiently depicted and therefore biopsies become more precise. RESULTS: Functional MR methods visualise different aspects of muscular (patho)physiology: muscular sodium (Na(+)) homeostasis can be monitored with (23)Na MRI; the muscular energy and lipid metabolism can be monitored using (31)P and (1)H MR spectroscopy. (23)Na MRI has reached an acceptable value in the diagnosis and follow-up of patients with muscular Na(+) channelopathies that are characterised by myocellular Na(+) overload and consecutive muscle weakness. Besides MRI, low mechanical index contrast-enhanced ultrasound (CEUS) methods have also been introduced. For evaluation of myositis, CEUS is more efficient in the diagnostic work-up than usual b-mode ultrasound, because CEUS can detect the inflammatory-induced muscular hyperperfusion in acute myositis. Moreover, the arterial perfusion reserve in peripheral arterial disease can be adequately examined using CEUS. CONCLUSION: Modern muscular imaging techniques offer deeper insights in muscular (patho)physiology than just illustrating unspecific myopathic manifestations like oedematous or lipomatous changes, hypertrophy or atrophy.