Cyclic motion encoding for enhanced MR visualization of slip interfaces

MR elastography-based slip interface imaging (SII) for functional assessment of myofascial interfaces: A feasibility study

PURPOSE

Abnormal adherence at functional myofascial interfaces is hypothesized as an important phenomenon in myofascial pain syndrome. This study aimed to investigate the feasibility of MR elastography (MRE)-based slip interface imaging (SII) to visualize and assess myofascial mobility in healthy volunteers.

METHODS

SII was used to assess local shear strain at functional myofascial interfaces in the flexor digitorum profundus (FDP) and thighs. In the FDP, MRE was performed at 90 Hz vibration to each index, middle, ring, and little finger. Two thigh MRE scans were performed at 40 Hz with knees flexed and extended. The normalized octahedral shear strain (NOSS) maps were calculated to visualize myofascial slip interfaces. The entropy of the probability distribution of the gradient NOSS was computed for the two knee positions at the intermuscular interface between vastus lateralis and vastus intermedius, around rectus femoris, and between vastus intermedius and vastus medialis.

RESULTS

NOSS map depicted distinct functional slip interfaces in the FDP for each finger. Compared to knee flexion, clearer slip interfaces and larger gradient NOSS entropy at the vastus lateralis-vastus intermedius interface were observed during knee extension, where the quadriceps are not passively stretched. This suggests the optimal position for using SII to visualize myofascial slip interface in skeletal muscles is when muscles are not subjected to any additional force.

CONCLUSION

The study demonstrated that MRE-based SII can visualize and assess myofascial interface mobility in extremities. The results provide a foundation for investigating the hypothesis that myofascial pain syndrome is characterized by changes in the mobility of myofascial interfaces.

Preoperative Magnetic Resonance Elastography (MRE) of Skull Base Tumours: A Review

Conventional magnetic resonance imaging (MRI) can detect tumors consistency, but it can't predict tumor stiffness or adherence of the tumor to nearby structures. Magnetic resonance elastography (MRE) is a known non-invasive MRI based imaging technique used to assess the viscoelasticity of the tissues particularly liver fibrosis. This study discussed the importance of preoperative MRE in skull base tumors and the future implications of this new imaging modality. We did review of the English literature (by searching PubMed) regarding the use of MRE in preoperative assessment of skull base tumours stiffness and adherence to surrounding tissues. Recent research demonstrated that MRE can detect the stiffness and adherence of skull base tumors to surrounding structures by recording the spread of mechanical waves in the different tissues. In addition to non-radiation exposure, this technique is fast and can be incorporated into the conventional (MRI) study. MRE can palpate skull base tumours by imaging, allowing the stiffness of the tumour to be assessed. Preoperative assessment of brain tumours consistency, stiffness, and adherence to surrounding tissues is critical to avoid injury of important nearby structures and better preoperative patient counselling regarding surgical approach (endoscopic or open), operative time, and suspected surgical complications. However, the accuracy of MRE is less in small and highly vascular tumors. Also, MRE can't accurately detect tumour-brain adherence, but the new modality (slip-interface imaging) can. Hence, adding MRE to the conventional MRI study may help in preoperative diagnosis and treatment of skull base tumours.

Magnetic Resonance Elastography in Intracranial Neoplasms: A Scoping Review

BACKGROUND

Magnetic resonance elastography (MRE) allows noninvasive assessment of intracranial tumor mechanics and may thus be predictive of intraoperative conditions. Variations in the use of technical terms complicate reading of current literature, and there is need of a review using consolidated nomenclature.

OBJECTIVES

We present an overview of current literature on MRE relating to human intracranial neoplasms using standardized nomenclature suggested by the MRE guidelines committee. We then discuss the implications of the findings, and suggest approaches for future research.

METHOD

We performed a systematic literature search in PubMed, Embase, and Web of Science; the articles were screened for relevance and then subjected to full text review. Technical terms were consolidated.

RESULTS

We identified 12 studies on MRE in patients with intracranial tumors, including meningiomas, glial tumors including glioblastomas, vestibular schwannomas, hemangiopericytoma, central nervous system lymphoma, pituitary macroadenomas, and brain metastases. The studies had varying objectives that included prediction of intraoperative consistency, histological separation, prediction of adhesiveness, and exploration of the mechanobiology of tumor invasiveness and malignancy. The technical terms were translated using standardized nomenclature. The literature was highly heterogeneous in terms of image acquisition techniques, post-processing, and study design and was generally limited by small and variable cohorts.

CONCLUSIONS

MRE shows potential in predicting tumor consistency, adhesion, and mechanical homogeneity. Furthermore, MRE provides insight into malignant tumor behavior and its relation to tissue mechanics. MRE is still at a preclinical stage, but technical advances, improved understanding of soft tissue rheological impact, and larger samples are likely to enable future clinical introduction.

Stiffness and Beyond: What MR Elastography Can Tell Us About Brain Structure and Function Under Physiologic and Pathologic Conditions

Brain magnetic resonance elastography (MRE) was developed on the basis of a desire to "palpate by imaging" and is becoming a powerful tool in the investigation of neurophysiological and neuropathological states. Measurements are acquired with a specialized MR phase-contrast pulse sequence that can detect tissue motion in response to an applied external or internal excitation. The tissue viscoelasticity is then reconstructed from the measured displacement. Quantitative characterization of brain viscoelastic behaviors provides us an insight into the brain structure and function by assessing the mechanical rigidity, viscosity, friction, and connectivity of brain tissues. Changes in these features are associated with inflammation, demyelination, and neurodegeneration that contribute to brain disease onset and progression. Here, we review the basic principles and limitations of brain MRE and summarize its current neuroanatomical studies and clinical applications to the most common neurosurgical and neurodegenerative disorders, including intracranial tumors, dementia, multiple sclerosis, amyotrophic lateral sclerosis, and traumatic brain injury. Going forward, further improvement in acquisition techniques, stable inverse reconstruction algorithms, and advanced numerical, physical, and preclinical validation models is needed to increase the utility of brain MRE in both research and clinical applications.

Slip interface imaging based on MR-elastography preoperatively predicts meningioma-brain adhesion

Purpose

To investigate the ability of slip interface imaging (SII), a recently developed magnetic resonance elastography (MRE)‐based technique, to predict the degree of meningioma–brain adhesion, using findings at surgery as the reference standard.

Materials and Methods

With Institutional Review Board approval and written informed consent, 25 patients with meningiomas >2.5 cm in maximal diameter underwent preoperative SII assessment. Intracranial shear motions were introduced using a soft, pillow‐like head driver and the resulting displacement field was acquired with an MRE pulse sequence on 3T MR scanners. The displacement data were analyzed to determine tumor–brain adhesion by assessing intensities on shear line images and raw as well as normalized octahedral shear strain (OSS) values along the interface. The SII findings of shear line images, OSS, and normalized OSS were independently and blindly correlated with surgical findings of tumor adhesion by using the Cohen's κ coefficient and chi‐squared test.

Results

Neurosurgeons categorized the surgical plane as extrapial (no adhesion) in 15 patients, mixed in four, and subpial (adhesion) in six. Both shear line images and OSS agreed with the surgical findings in 18 (72%) cases (fair agreement, κ = 0.37, 95% confidence interval [CI]: 0.05–0.69), while normalized OSS was concordant with the surgical findings in 23 (92%) cases (good agreement, κ = 0.86, 95% CI: 0.67–1). The correlation between SII predictions (shear line images, OSS, and normalized OSS) and the surgical findings were statistically significant (chi‐squared test, P = 0.02, P = 0.02, and P < 0.0001, respectively).

Conclusion

SII preoperatively evaluates the degree of meningioma–brain adhesion noninvasively, allowing for improved prediction of surgical risk and tumor resectability.

Level of Evidence: 1

Technical Efficacy: Stage 1

J. Magn. Reson. Imaging 2017;46:1007–1016.

Combining rheology and MRI: Imaging healthy and tumorous brains based on mechanical properties

PURPOSE

It is well known that pathological changes in tissue alter its mechanical properties. This holds also true for brain tissue. In case of the brain, however, obtaining information about these properties is hard due to the surrounding cranial bone. In this paper a novel technique to create an imaging contrast based on the aforementioned properties is presented.

METHODS

The method is based on an excitation of the brain induced by a short fall. The response of the brain tissue is measured using a motion sensitive MRI sequence.

RESULTS

The new method is tested by measurements on phantom material as well as on healthy volunteers. In a proof of principle experiment the capability of the approach to identify local alterations in the mechanical properties is shown by means of measurements on meningioma patients.

CONCLUSION

The presented results show the feasibility of the novel method. Even in this early state of the proposed method, comparisons of measurements on meningioma patients with intraoperative palpation suggest that meningioma tissue responds differently to the excitation depending on their mechanical properties. Magn Reson Med 78:930-940, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Slip Interface Imaging Predicts Tumor-Brain Adhesion in Vestibular Schwannomas

PURPOSE

To test the clinical feasibility and usefulness of slip interface imaging (SII) to identify and quantify the degree of tumor-brain adhesion in patients with vestibular schwannomas.

MATERIALS AND METHOD

S With institutional review board approval and after obtaining written informed consent, SII examinations were performed in nine patients with vestibular schwannomas. During the SII acquisition, a low-amplitude mechanical vibration is applied to the head with a pillow-like device placed in the head coil and the resulting shear waves are imaged by using a phase-contrast pulse sequence with motion-encoding gradients synchronized with the applied vibration. Imaging was performed with a 3-T magnetic resonance (MR) system in less than 7 minutes. The acquired shear motion data were processed with two different algorithms (shear line analysis and calculation of octahedral shear strain [OSS]) to identify the degree of tumor-brain adhesion. Blinded to the SII results, neurosurgeons qualitatively assessed tumor adhesion at the time of tumor resection. Standard T2-weighted, fast imaging employing steady-state acquisition (FIESTA), and T2-weighted fluid-attenuated inversion recovery (FLAIR) imaging were reviewed to identify the presence of cerebral spinal fluid (CSF) clefts around the tumors. The performance of the use of the CSF cleft and SII to predict the degree of tumor adhesion was evaluated by using the κ coefficient and McNemar test.

RESULTS

Among the nine patients, SII agreed with the intraoperative assessment of the degree of tumor adhesion in eight patients (88.9%; 95% confidence interval [CI]: 57%, 98%), with four of four, three of three, and one of two cases correctly predicted as no adhesion, partial adhesion, and complete adhesion, respectively. However, the T2-weighted, FIESTA, and T2-weighted FLAIR images that used the CSF cleft sign to predict adhesion agreed with surgical findings in only four cases (44.4% [four of nine]; 95% CI: 19%, 73%). The κ coefficients indicate good agreement (0.82 [95% CI: 0.5, 1]) for the SII prediction versus surgical findings, but only fair agreement (0.21 [95% CI: -0.21, 0.63]) between the CSF cleft prediction and surgical findings. However, the difference between the SII prediction and the CSF cleft prediction was not significant (P = .103; McNemar test), likely because of the small sample size in this study.

CONCLUSION

SII can be used to predict the degree of tumor-brain adhesion of vestibular schwannomas and may provide a method to improve preoperative planning and determination of surgical risk in these patients.

Magnetic resonance imaging of pediatric muscular disorders: recent advances and clinical applications

This review describes various quantitative magnetic resonance imaging techniques that can be used to objectively analyze the composition (T2 relaxation time mapping, Dixon imaging, and diffusion-weighted imaging), architecture (diffusion tensor imaging), mechanical properties (magnetic resonance elastography), and function (magnetic resonance spectroscopy) of normal and pathologic skeletal muscle in the pediatric population.

Review of MR elastography applications and recent developments

The technique of MR elastography (MRE) has emerged as a useful modality for quantitatively imaging the mechanical properties of soft tissues in vivo. Recently, MRE has been introduced as a clinical tool for evaluating chronic liver disease, but many other potential applications are being explored. These applications include measuring tissue changes associated with diseases of the liver, breast, brain, heart, and skeletal muscle including both focal lesions (e.g., hepatic, breast, and brain tumors) and diffuse diseases (e.g., fibrosis and multiple sclerosis). The purpose of this review article is to summarize some of the recent developments of MRE and to highlight some emerging applications.

Magnetic resonance elastography: a review

Magnetic resonance elastography (MRE) is a rapidly developing technology for quantitatively assessing the mechanical properties of tissue. The technology can be considered to be an imaging-based counterpart to palpation, commonly used by physicians to diagnose and characterize diseases. The success of palpation as a diagnostic method is based on the fact that the mechanical properties of tissues are often dramatically affected by the presence of disease processes, such as cancer, inflammation, and fibrosis. MRE obtains information about the stiffness of tissue by assessing the propagation of mechanical waves through the tissue with a special magnetic resonance imaging technique. The technique essentially involves three steps: (1) generating shear waves in the tissue, (2) acquiring MR images depicting the propagation of the induced shear waves, and (3) processing the images of the shear waves to generate quantitative maps of tissue stiffness, called elastograms. MRE is already being used clinically for the assessment of patients with chronic liver diseases and is emerging as a safe, reliable, and noninvasive alternative to liver biopsy for staging hepatic fibrosis. MRE is also being investigated for application to pathologies of other organs including the brain, breast, blood vessels, heart, kidneys, lungs, and skeletal muscle. The purpose of this review article is to introduce this technology to clinical anatomists and to summarize some of the current clinical applications that are being pursued.