Simultaneous magnetic resonance angiography and perfusion (MRAP) measurement: initial application in lower extremity skeletal muscle

Four functional magnetic resonance imaging techniques for skeletal muscle exploration, a systematic review

BACKGROUND

The study of muscle health has become more relevant lately, due to global aging and a higher incidence of musculoskeletal pathologies. Current exploration techniques, such as electromyography, do not provide accurate spatial information.

OBJECTIVE

The objective of this work is to perform a systematic review of the literature to synthesize the contributions that can offer functional MRI techniques commonly used in neuroimaging, applied to skeletal muscle: Blood Oxygen Level Dependent (BOLD), IntraVoxel Incoherent Motion (IVIM), Arterial Spin Labeling (ASL) and Dynamic Contrast Enhanced (DCE).

EVIDENCE ACQUISITION

Web of Science and Medline databases were searched, over the last 10 years, focused on the use of BOLD, ASL, IVIM or DCE in skeletal muscle.

EVIDENCE SYNTHESIS

59 articles were included after applying the selection criteria. 37 studies were performed in healthy subjects, and 22 in patients with different pathologies: in peripheral arterial disease, systemic sclerosis, diabetes, osteoporosis, adolescent idiopathic scoliosis, and dermatomyositis. Reference values in healthy subjects still vary in some cases.

CONCLUSION

The studies show the feasibility of implementing functional MRI through BOLD, ASL, IVIM or DCE imaging in several muscles and their possible utility in different pathologies. A synthesis of how to implement such exploration is given here.

CLINICAL IMPACT

These four techniques are based on sequences already present in clinical MRI scanners, therefore, their use for functional muscle exploration does not require additional investment. These techniques allow visualization and quantification of parameters associated with the vascular health of the muscles and represent interesting support for musculoskeletal exploration.

Evaluation of microvascular permeability of skeletal muscle and texture analysis based on DCE-MRI in alloxan-induced diabetic rabbits

OBJECTIVES

To estimate the microvascular permeability and perfusion of skeletal muscle by using quantitative dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and explore the feasibility of using texture analysis (TA) to evaluate subtle structural changes of diabetic muscles.

METHODS

Twenty-four rabbits were randomly divided into diabetic (n = 14) and control (n = 10) groups, and underwent axial DCE-MRI of the multifidus muscle (0, 4, 8, 12, and 16 weeks after alloxan injection). The pharmacokinetic model was used to calculate the permeability parameters; texture parameters were extracted from volume transfer constant (K^trans) map. The two-sample t test/Mann-Whitney U test, repeated measures analysis of variance/Friedman test, and Pearson correlations were used for data analysis.

RESULTS

In the diabetic group, K^trans and rate constant (K_ep) increased significantly at week 8 and then showed a decreasing trend. Extravascular extracellular space volume fraction (V_e) increased and plasma volume fraction (V_p) decreased significantly from the 8th week. Skewness began to decrease at the 4th week. Median K^trans and entropy increased significantly, while inverse difference moment decreased from the 8th week. Energy decreased while contrast increased only at week 8. Muscle fibre cross-sectional area was negatively correlated with V_e. The capillary-to-fibre ratio was positively correlated with V_p (p < 0.05, all).

CONCLUSIONS

Quantitative DCE-MRI can be used to evaluate microvascular permeability and perfusion in diabetic skeletal muscle at an early stage; TA based on K^trans map can identify microarchitectural modifications in diabetic muscles.

KEY POINTS

• Four quantitative parameters of DCE-MRI can be used to evaluate microvascular permeability and perfusion of skeletal muscle in diabetic models at early stages. • Texture analysis based on K^trans map can identify subtle structural changes in diabetic muscles.

Combined angiography and perfusion using radial imaging and arterial spin labeling

PURPOSE

To demonstrate the feasibility of a novel noninvasive MRI technique for the comprehensive evaluation of blood flow to the brain: combined angiography and perfusion using radial imaging and arterial spin labeling (CAPRIA).

METHODS

In the CAPRIA pulse sequence, blood labeled with a pseudocontinuous arterial spin labeling pulse train is continuously imaged as it flows through the arterial tree and into the brain tissue using a golden ratio radial readout. From a single raw data set, this flexible imaging approach allows the reconstruction of both high spatial/temporal resolution angiographic images with a high undersampling factor and low spatial/temporal resolution perfusion images with a low undersampling factor. The sparse and high SNR nature of angiographic images ensures that radial undersampling artifacts are relatively benign, even when using a simple regridding image reconstruction. Pulse sequence parameters were optimized through sampling efficiency calculations and the numerical evaluation of modified pseudocontinuous arterial spin labeling signal models. A comparison was made against conventional pseudocontinuous arterial spin labeling angiographic and perfusion acquisitions.

RESULTS

2D CAPRIA data in healthy volunteers demonstrated the feasibility of this approach, with good vessel visualization in the angiographic images and clear tissue perfusion signal when reconstructed at 108-ms and 252-ms temporal resolution, respectively. Images were qualitatively similar to those from conventional acquisitions, but CAPRIA had significantly higher SNR efficiency (48% improvement on average, P = 0.02).

CONCLUSION

The CAPRIA technique shows potential for the efficient evaluation of both macrovascular blood flow and tissue perfusion within a single scan, with potential applications in a range of cerebrovascular diseases.

Advantages of time-resolved contrast-enhanced 4D MR angiography in splenic arterial steal syndrome

Splenic artery steal syndrome (SASS) is a severe complication affecting up to 10% of orthotopic liver transplant (OLT) patients. In this case report, we present a 35-year-old male with OLT secondary to liver failure due to hemochromatosis, who developed SASS. We describe potential application of different imaging techniques for diagnosis of SASS with focus on the value of time-resolved contrast enhanced 4D magnetic resonance angiography (MRA).

Spinal Cord Stimulation Improves the Microvascular Perfusion Insufficiency Caused by Critical Limb Ischemia

OBJECTIVE

This retrospective case-controlled study intended to identify the benefits and efficacy of spinal cord stimulation (SCS) as a therapeutic strategy for patients with perfusion problems caused by critical limb ischemia (CLI). The outcomes of patients who received SCS were compared with those of patients who did not receive SCS.

METHODS

This study recruited 78 patients who were diagnosed with perfusion problems over the period of 2003-2011. Lower-limb Thallium-201 (²⁰¹ Tl) scintigraphy revealed that the patients exhibited a perfusion difference of <0.95. Thirty-seven of the recruited patients received SCS treatment and 41 did not receive SCS treatment. All patients received the same medication: 100 mg aspirin once a day and 500 mg paracetamol thrice a day. The outcomes of walking distance, walking time, and sleeping quality were measured and recorded. Pain intensities were evaluated using the visual analog scale (VAS) scoring system.

RESULTS

Prior to SCS implantation, patients in the SCS treatment group had worse walking distance (64.86 ± 40.80 vs. 613.70 ± 535.00, p < 0.001), walking time (2.65 ± 1.64 vs. 13.90 ± 11.91, p < 0.001), and sleep quality (1.70 ± 0.78 vs. 3.32 ± 1.17, p < 0.001) than patients in the non-SCS treatment group. At the one-year follow-up, however, patients in the SCS treatment group had significantly better walking distance (1595.00 ± 483.60, p < 0.001), walking time (48.92 ± 14.10, p < 0.001), and sleep quality (4.65 ± 0.92, p < 0.001) than patients in the non-SCS treatment group. Moreover, the VAS score of patients in the SCS treatment group improved one week (8.63 ± 0.54 vs. 4.48 ± 0.59, p < 0.001) and one year after SCS implantation (2.35 ± 0.62, p < 0.001). By contrast, at the one-year follow-up, the walking distance (277.60 ± 374.80, p = 0.002), walking time (9.44 ± 10.73, p = 0.078), sleep quality (2.20 ± 1.10, p < 0.001), and VAS score (7.98 ± 0.43, p = 0.020) of patients in the non-SCS treatment group worsened. Furthermore, lower-limb ²⁰¹ Tl scintigraphy revealed that microcirculation intensity increased in the lower extremities of patients in the SCS treatment group after SCS implantation relative to that before SCS implantation. Most importantly, 10 of the 41 patients in the non-SCS treatment group required the use of wheelchairs, whereas none of the patients in the SCS treatment group required the use of wheelchairs.

CONCLUSION

Treatment of CLI patient with SCS improved patient's walking ability, pain severity, and sleep quality. SCS should be considered as an effective treatment toward limb salvage in CLI.

The impact of injector-based contrast agent administration in time-resolved MRA

OBJECTIVES

Time-resolved contrast-enhanced MR angiography (4D-MRA), which allows the simultaneous visualization of the vasculature and blood-flow dynamics, is widely used in clinical routine. In this study, the impact of two different contrast agent injection methods on 4D-MRA was examined in a controlled, standardized setting in an animal model.

METHODS

Six anesthetized Goettingen minipigs underwent two identical 4D-MRA examinations at 1.5 T in a single session. The contrast agent (0.1 mmol/kg body weight gadobutrol, followed by 20 ml saline) was injected using either manual injection or an automated injection system. A quantitative comparison of vascular signal enhancement and quantitative renal perfusion analyses were performed.

RESULTS

Analysis of signal enhancement revealed higher peak enhancements and shorter time to peak intervals for the automated injection. Significantly different bolus shapes were found: automated injection resulted in a compact first-pass bolus shape clearly separated from the recirculation while manual injection resulted in a disrupted first-pass bolus with two peaks. In the quantitative perfusion analyses, statistically significant differences in plasma flow values were found between the injection methods.

CONCLUSIONS

The results of both qualitative and quantitative 4D-MRA depend on the contrast agent injection method, with automated injection providing more defined bolus shapes and more standardized examination protocols.

KEY POINTS

• Automated and manual contrast agent injection result in different bolus shapes in 4D-MRA. • Manual injection results in an undefined and interrupted bolus with two peaks. • Automated injection provides more defined bolus shapes. • Automated injection can lead to more standardized examination protocols.

Perfusion measures for symptom severity and differential outcome of revascularization in limb ischemia: Preliminary results with arterial spin labeling reactive hyperemia

BACKGROUND

Previously, a theoretical model based on microvascular physiology was established to facilitate the interpretation of calf perfusion dynamics recorded by arterial spin labeling (ASL).

PURPOSE

To investigate the clinical relevance of novel perfusion indices by comparing them to the symptoms, response to revascularization, and short-term functional outcome in patients with peripheral arterial disease (PAD).

STUDY TYPE

Prospective cohort study.

POPULATION

Nineteen patients with PAD.

FIELD STRENGTH/SEQUENCE

Pulsed ASL at 3T.

ASSESSMENT

The mid-calf reactive hyperemia induced by 2 minutes of arterial occlusion was recorded in PAD patients. The perfusion responses were characterized by the peak, time-to-peak, and physiological model-derived indices including the baseline perfusion f_r , arterial resistance R_a , and compliance C_a , and sensitivity g_ATP and response time τ_ATP of downstream microvasculature to metabolic stress. These indices were compared to the disease severity and outcome within 6 months after revascularization assessed by self-reported symptoms and the ankle-brachial index. Disease severity was categorized as asymptomatic, claudication, or critical limb ischemia. The outcome was categorized as symptom resolved or limited improvement.

STATISTICAL TESTS

Severity and outcome groups were compared using Mann-Whitney and Kruskal-Wallis tests with Holm-Sidak adjustments.

RESULTS

The peak perfusion decreased and model arterial resistance increased progressively with increasing severity of limb ischemia (P = 0.0402 and 0.0413, respectively). Eleven patients had a successful endovascular procedure, including six patients who had symptoms resolved, four patients who had remaining leg pain, and one patient lost to follow-up. The subjects with limited improvement had significantly lower preintervention microvascular sensitivity g_ATP than those with symptoms resolved (8.72 ± 1.46 vs. 4.93 ± 0.91, P = 0.0466).

DATA CONCLUSION

ASL reactive hyperemia reflects multiple aspects of the pathophysiology. Measures of macrovascular arterial disease are related to the manifested symptom severity, whereas preintervention g_ATP associated with microvascular dysfunction is related to prognosis following revascularization.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 4 J. Magn. Reson. Imaging 2018;47:1578-1588.

Baseline assessment and comparison of arterial anatomy, hyperemic flow, and skeletal muscle perfusion in peripheral artery disease: The Cardiovascular Cell Therapy Research Network "Patients with Intermittent Claudication Injected with ALDH Bright Cells" (CCTRN PACE) study

BACKGROUND

Peripheral artery disease (PAD) is important to public health as a major contributor to cardiovascular morbidity and mortality. Recent developments in magnetic resonance imaging (MRI) techniques permit improved assessment of PAD anatomy and physiology, and may serve as surrogate end points after proangiogenic therapies.

METHODS

The PACE study is a randomized, double-blind, placebo-controlled clinical trial designed to assess the physiologic impact and potential clinical efficacy of autologous bone marrow-derived ALDH^br stem cells. The primary MRI end points of the study are as follows: (1) total collateral count, (2) calf muscle plasma volume (a measure of capillary perfusion) by dynamic contrast-enhanced MRI, and (3) peak hyperemic popliteal flow by phase-contrast MRI (PC-MRI).

RESULTS

The interreader and intrareader and test-retest results demonstrated good-to-excellent reproducibility (interclass correlation coefficient range 0.61-0.98) for all magnetic resonance measures. The PAD participants (n=82) had lower capillary perfusion measured by calf muscle plasma volume (3.8% vs 5.6%) and peak hyperemic popliteal flow (4.1 vs 13.5mL/s) as compared with the healthy participants (n=16), with a significant level of collateralization.

CONCLUSIONS

Reproducibility of the MRI primary end points in PACE was very good to excellent. The PAD participants exhibited decreased calf muscle capillary perfusion as well as arterial flow reserve when compared with healthy participants. The MRI tools used in PACE may advance PAD science by enabling accurate measurement of PAD microvascular anatomy and perfusion before and after stem cell or other PAD therapies.

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.

Insights Into Microcirculation Underlying Critical Limb Ischemia by Single-Photon Emission Computed Tomography

Perfusion difference is used as a parameter to evaluate microcirculation. This study aims to differentiate lower-limb perfusion insufficiency from neuropathy to prevent possible occurrence of failed back surgery syndrome (FBSS).Patients were retrospectively gathered from 134 FBSS cases diagnosed in the past 7 years. Up to 82 cases that were excluded from neuralgia by radiologic imaging, electrodiagnostic electromyography, and nerve conduction velocity were enrolled in this study. Perfusion difference was evaluated by single-photon emission computed tomography, and pain intensities were recorded via visual analog scale (VAS) score.Lower perfusion at the left leg comprises 51.2% (42 of 82) of the patients. The mean perfusion difference of the 82 patients was 0.86 ± 0.05 (range: 0.75-0.93). Patients with systemic vascular diseases exhibited significantly higher perfusion difference than that of patients without these related diseases (P < 0.05), except for renal insufficiency (P = 0.134). Significant correlation was observed between perfusion difference and VAS score (r = -0.78; P < 0.0001; n = 82).In this study, we presented perfusion difference as a parameter for evaluating microcirculation, which cannot be detected by ultrasonography or angiography.

Recent advances in 3D time-resolved contrast-enhanced MR angiography

Contrast-enhanced magnetic resonance angiography (CE-MRA) was first introduced for clinical studies approximately 20 years ago. Early work provided 3-4 mm spatial resolution with acquisition times in the 30-second range. Since that time there has been continuing effort to provide improved spatial resolution with reduced acquisition time, allowing high resolution 3D time-resolved studies. The purpose of this work is to describe how this has been accomplished. Specific technical enablers have been: improved gradients allowing reduced repetition times, improved k-space sampling and reconstruction methods, parallel acquisition, particularly in two directions, and improved and higher count receiver coil arrays. These have collectively made high-resolution time-resolved studies readily available for many anatomic regions. Depending on the application, ∼1 mm isotropic resolution is now possible with frame times of several seconds. Clinical applications of time-resolved CE-MRA are briefly reviewed.

Current Phase II drugs under investigation for the treatment of limb ischemia

INTRODUCTION

More than 20 million people in Europe suffer from peripheral arterial disease and nearly 3% develop critical limb ischemia (CLI). Without any medical treatment, CLI has poor prognosis, resulting in limb loss and high mortality rate. Until today, no systemic drug is available for the treatment of CLI and the gold standard method of treatment includes risk factor modification and open surgical or endovascular revascularization. Endovascular local drug delivery devices and novel antithrombotic agents, currently under investigation, aim to improve outcomes of revascularization procedures. The pioneering concept of therapeutic angiogenesis induced by gene and stem cell therapy has been proposed, in an attempt to increase ischemic tissue perfusion.

AREAS COVERED

This review summarizes local and systemic pharmacological treatment of CLI using endovascular or pharmaco-biological therapy and focuses on Phase II trials available for these drugs.

EXPERT OPINION

Novel endovascular technologies combining angioplasty and local drug-delivery continuously improve and will come to be standard of practice for the management of limb ischemia, while new antithrombotic agents will further improve outcomes. Therapeutic angiogenesis represents a safe and promising treatment option. The combination of revascularization with microcirculation improvement induced by gene or stem cell therapy could enhance limb salvage.

Reducing view-sharing using compressed sensing in time-resolved contrast-enhanced magnetic resonance angiography

PURPOSE

To study temporal and spatial blurring artifacts from k-space view-sharing in time-resolved MR angiography (MRA) and to propose a technique for reducing these artifacts.

METHODS

We acquired k-space data sets using a three-dimensional time-resolved MRA view-sharing sequence and retrospectively reformatted them into two reconstruction frameworks: full view-sharing via time-resolved imaging with stochastic trajectories (TWIST) and minimal k-space view-sharing and compressed sensing (CS-TWIST). The two imaging series differed in temporal footprint but not in temporal frame rate. The artifacts from view-sharing were compared qualitatively and quantitatively in nine patients in addition to a phantom experiment.

RESULTS

CS-TWIST was able to reduce the imaging temporal footprint by two- to three-fold compared with TWIST, and the overall subjective image quality of CS-TWIST was higher than that for TWIST (P < 0.05). View sharing caused a delay in the visualization of small blood vessels, and the mean transit time of the carotid artery calculated based on TWIST reconstruction was 0.6 s longer than that for CS-TWIST (P < 0.01). In thoracic MRA, the shorter temporal footprint decreased the sensitivity to physiological motion blurring, and vessel sharpness was improved by 8.8% ± 6.0% using CS-TWIST (P < 0.05).

CONCLUSION

In time-resolved MRA, the longer temporal footprint due to view-sharing causes spatial and temporal artifacts. CS-TWIST is a promising method for reducing these artifacts.

High-field (11.75T) multimodal MR imaging of exercising hindlimb mouse muscles using a non-invasive combined stimulation and force measurement device

We have designed and constructed an experimental set-up allowing electrical stimulation of hindlimb mouse muscles and the corresponding force measurements at high-field (11.75T). We performed high-resolution multimodal MRI (including T2 -weighted imaging, angiography and diffusion) and analysed the corresponding MRI changes in response to a stimulation protocol. Mice were tested twice over a 1-week period to investigate the reliability of mechanical measurements and T2 changes associated with the stimulation protocol. Additionally, angiographic images were obtained before and immediately after the stimulation protocol. Finally, multislice diffusion imaging was performed before, during and immediately after the stimulation session. Apparent diffusion coefficient (ADC) maps were calculated on the basis of diffusion weighted images (DWI). Both force production and T2 values were highly reproducible as illustrated by the low coefficient of variation (<8%) and high intraclass correlation coefficient (≥0.75) values. Maximum intensity projection angiographic images clearly showed a strong vascular effect resulting from the stimulation protocol. Although a motion sensitive imaging sequence was used (echo planar imaging) and in spite of the strong muscle contractions, motion artifacts were minimal for DWI recorded under exercising conditions, thereby underlining the robustness of the measurements. Mean ADC values increased under exercising conditions and were higher during the recovery period as compared with the corresponding control values. The proposed experimental approach demonstrates accurate high-field multimodal MRI muscle investigations at a preclinical level which is of interest for monitoring the severity and/or the progression of neuromuscular diseases but also for assessing the efficacy of potential therapeutic interventions.

Multi-parametric MRI characterization of inflammation in murine skeletal muscle

Myopathies often display a common set of complex pathologies that include muscle weakness, inflammation, compromised membrane integrity, fat deposition, and fibrosis. Multi-parametric, quantitative, non-invasive imaging approaches may be able to resolve these individual pathological components. The goal of this study was to use multi-parametric MRI to investigate inflammation as an isolated pathological feature. Proton relaxation, diffusion tensor imaging (DTI), quantitative magnetization transfer (qMT-MRI), and dynamic contrast enhanced (DCE-MRI) parameters were calculated from data acquired in a single imaging session conducted 6-8 hours following the injection of λ-carrageenan, a local inflammatory agent. T2 increased in the inflamed muscle and transitioned to bi-exponential behavior. In diffusion measurements, all three eigenvalues and the apparent diffusion coefficient increased, but λ3 had the largest relative change. Analysis of the qMT data revealed that the T1 of the free pool and the observed T1 both increased in the inflamed tissue, while the ratio of exchanging spins in the solid pool to those in the free water pool (the pool size ratio) significantly decreased. DCE-MRI data also supported observations of an increase in extracellular volume. These findings enriched the understanding of the relation between multiple quantitative MRI parameters and an isolated inflammatory pathology, and may potentially be employed for other single or complex myopathy models.