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Real-time magnetic resonance imaging (rtMRI) is a technique that provides high-contrast videographic data of human anatomy in motion. Applied to the vocal tract, it is a powerful method for capturing the dynamics of speech and other vocal behaviours by imaging structures internal to the mouth and throat. These images provide a means of studying the physiological basis for speech, singing, expressions of emotion, and swallowing that are otherwise not accessible for external observation. However, taking quantitative measurements from these images is notoriously difficult. We introduce a signal processing pipeline that produces outlines of the vocal tract from the lips to the larynx as a quantification of the dynamic morphology of the vocal tract. Our approach performs simple tissue classification, but constrained to a researcher-specified region of interest. This combination facilitates feature extraction while retaining the domain-specific expertise of a human analyst. We demonstrate that this pipeline generalises well across datasets covering behaviours such as speech, vocal size exaggeration, laughter, and whistling, as well as producing reliable outcomes across analysts, particularly among users with domain-specific expertise. With this article, we make this pipeline available for immediate use by the research community, and further suggest that it may contribute to the continued development of fully automated methods based on deep learning algorithms. [ABSTRACT FROM AUTHOR]

Purpose: Pineal region cysts (PCs) may affect the tectum and aqueduct and cause deep central vein congestion. Beside headaches, PC often causes a broad range of symptoms, leading to prolonged diagnosis and therapy. The aims of this study are to reveal parameters that might explain the ambiguity of the symptoms and to identify factors in association with the respiration-driven neurofluid system. Methods: This retrospective study included 28 paediatric patients (mean age 11.6 years) who received surgical treatment and 18 patients (mean age 11.3 years) who were followed conservatively. Symptoms, time to diagnosis, cyst size, ventricular indices, head circumference and postoperative outcome, were analysed. Four patients were investigated for CSF dynamics with real-time MRI. The mean follow-up time was 1.6 years. Results: The most common early onset symptoms were headaches (92%), blurred vision (42.8%), sleep disturbances (39.3%) and vertigo (32.1%). Tectum contact was observed in 82% of patients, and MRI examinations revealed that imaging flow void signals were absent in 32.1% of patients. The maximal cyst diameters were 13.7 × 15.6 mm (mean). Together with a postoperative flow void signal, 4 patients recovered their respiration-driven CSF aqueductal upward flow, which was not detectable preoperatively. After surgery the main symptoms improved. Conclusion: Despite proximity to the aqueduct with frequently absent flow void signals, hydrocephalus was never detected. Data from real-time MRI depicted a reduced preoperative filling of the ventricular CSF compartments, indicating a diminished fluid preload, which recovered postoperatively. [ABSTRACT FROM AUTHOR]

Diagnosis of temporomandibular disorders is currently based on clinical examination and static MRI. Real-time MRI enables tracking of condylar motion and, thus, evaluation of their motion symmetricity (which could be associated with temporomandibular joint disorders). The purpose of this work is to propose an acquisition protocol, an image processing approach, and a set of parameters enabling objective assessment of motion asymmetry; to check the reliability and find the limitations of the approach, and to verify if the automatically calculated parameters are associated with the motion symmetricity. A rapid radial FLASH sequence was used to acquire a dynamic set of axial images for 10 subjects. One more subject was involved to estimate the dependence of the motion parameters on the slice placement. The images were segmented with a semi-automatic approach based on U-Net convolutional neural network, and the condyles' mass centers were projected on the mid-sagittal axis. Resulting projection curves were used for the extraction of various motion parameters including latency, velocity peak delay, and maximal displacement between the right and the left condyle. These automatically calculated parameters were compared with the physicians' scores. The proposed segmentation approach allowed a reliable center of mass tracking. Latency and velocity peak delay were found to be invariant to the slice position, and maximal displacement difference considerably varied. The automatically calculated parameters demonstrated a significant correlation with the experts' scores. The proposed acquisition and data processing protocol enables the automatizable extraction of quantitative parameters that characterize the symmetricity of condylar motion [ABSTRACT FROM AUTHOR]

Objective: Real-time imaging is useful for the evaluation of wrist instability. However, currently available real-time magnetic resonance imaging (MRI) methods are limited due to their 2D nature or provide insufficient temporal resolution and image quality for quantitative kinematic analysis. This work introduces a novel approach for volumetric dynamic MRI of the wrist joint during active motion and demonstrates the feasibility of tracking carpal bone motion.A flexible 8-element 3 T wrist receive coil and 3D-printed support platform for guiding motion were designed for dynamic wrist imaging. 2D real-time images were acquired using a fat-saturated FLASH sequence with radial sampling and reconstructed with the GRASP algorithm. Corresponding volumetric dynamic wrist images were obtained by assembling 2D real-time images into 3D snapshots using autodetected MRI-visible markers for slice alignment. The proposed method was demonstrated for radial-ulnar deviation on five healthy volunteers.The flexible wrist coil provided high SNR while allowing a wide range of wrist movements. 2D real-time wrist images were acquired with a temporal resolution of 48 ms/frame with negligible streaking artifacts. Carpal bones and metacarpal bones were properly aligned in the assembled dynamic volumes for all five subjects. The excellent bone-to-tissue contrast enabled accurate segmentation of the individual carpal bones on the assembled dynamic volumes.This work introduces a novel wrist coil and demonstrates that real-time volumetric dynamic examination of the moving wrist is feasible. The achieved image quality and high temporal resolution could enable automatic segmentation of carpal bones and quantitative kinematic assessment for evaluating wrist instability.Materials and methods: Real-time imaging is useful for the evaluation of wrist instability. However, currently available real-time magnetic resonance imaging (MRI) methods are limited due to their 2D nature or provide insufficient temporal resolution and image quality for quantitative kinematic analysis. This work introduces a novel approach for volumetric dynamic MRI of the wrist joint during active motion and demonstrates the feasibility of tracking carpal bone motion.A flexible 8-element 3 T wrist receive coil and 3D-printed support platform for guiding motion were designed for dynamic wrist imaging. 2D real-time images were acquired using a fat-saturated FLASH sequence with radial sampling and reconstructed with the GRASP algorithm. Corresponding volumetric dynamic wrist images were obtained by assembling 2D real-time images into 3D snapshots using autodetected MRI-visible markers for slice alignment. The proposed method was demonstrated for radial-ulnar deviation on five healthy volunteers.The flexible wrist coil provided high SNR while allowing a wide range of wrist movements. 2D real-time wrist images were acquired with a temporal resolution of 48 ms/frame with negligible streaking artifacts. Carpal bones and metacarpal bones were properly aligned in the assembled dynamic volumes for all five subjects. The excellent bone-to-tissue contrast enabled accurate segmentation of the individual carpal bones on the assembled dynamic volumes.This work introduces a novel wrist coil and demonstrates that real-time volumetric dynamic examination of the moving wrist is feasible. The achieved image quality and high temporal resolution could enable automatic segmentation of carpal bones and quantitative kinematic assessment for evaluating wrist instability.Results: Real-time imaging is useful for the evaluation of wrist instability. However, currently available real-time magnetic resonance imaging (MRI) methods are limited due to their 2D nature or provide insufficient temporal resolution and image quality for quantitative kinematic analysis. This work introduces a novel approach for volumetric dynamic MRI of the wrist joint during active motion and demonstrates the feasibility of tracking carpal bone motion.A flexible 8-element 3 T wrist receive coil and 3D-printed support platform for guiding motion were designed for dynamic wrist imaging. 2D real-time images were acquired using a fat-saturated FLASH sequence with radial sampling and reconstructed with the GRASP algorithm. Corresponding volumetric dynamic wrist images were obtained by assembling 2D real-time images into 3D snapshots using autodetected MRI-visible markers for slice alignment. The proposed method was demonstrated for radial-ulnar deviation on five healthy volunteers.The flexible wrist coil provided high SNR while allowing a wide range of wrist movements. 2D real-time wrist images were acquired with a temporal resolution of 48 ms/frame with negligible streaking artifacts. Carpal bones and metacarpal bones were properly aligned in the assembled dynamic volumes for all five subjects. The excellent bone-to-tissue contrast enabled accurate segmentation of the individual carpal bones on the assembled dynamic volumes.This work introduces a novel wrist coil and demonstrates that real-time volumetric dynamic examination of the moving wrist is feasible. The achieved image quality and high temporal resolution could enable automatic segmentation of carpal bones and quantitative kinematic assessment for evaluating wrist instability.Conclusion: Real-time imaging is useful for the evaluation of wrist instability. However, currently available real-time magnetic resonance imaging (MRI) methods are limited due to their 2D nature or provide insufficient temporal resolution and image quality for quantitative kinematic analysis. This work introduces a novel approach for volumetric dynamic MRI of the wrist joint during active motion and demonstrates the feasibility of tracking carpal bone motion.A flexible 8-element 3 T wrist receive coil and 3D-printed support platform for guiding motion were designed for dynamic wrist imaging. 2D real-time images were acquired using a fat-saturated FLASH sequence with radial sampling and reconstructed with the GRASP algorithm. Corresponding volumetric dynamic wrist images were obtained by assembling 2D real-time images into 3D snapshots using autodetected MRI-visible markers for slice alignment. The proposed method was demonstrated for radial-ulnar deviation on five healthy volunteers.The flexible wrist coil provided high SNR while allowing a wide range of wrist movements. 2D real-time wrist images were acquired with a temporal resolution of 48 ms/frame with negligible streaking artifacts. Carpal bones and metacarpal bones were properly aligned in the assembled dynamic volumes for all five subjects. The excellent bone-to-tissue contrast enabled accurate segmentation of the individual carpal bones on the assembled dynamic volumes.This work introduces a novel wrist coil and demonstrates that real-time volumetric dynamic examination of the moving wrist is feasible. The achieved image quality and high temporal resolution could enable automatic segmentation of carpal bones and quantitative kinematic assessment for evaluating wrist instability. [ABSTRACT FROM AUTHOR]

Purpose: Real-time MRI offers a continuous and dynamic view of the object being imaged. Researchers have applied real-time MRI to speech production, which allows for the visualization of the vocal tract during speech. Methods: This study proposed applying self-navigated subspace reconstruction for real-time vocal tract imaging. We performed experiments on a clinical 3 T MRI using standard RF coils and rapid acquisition. Additionally, 1000 frames were compressed during reconstruction to a few principal components, and iterative low-rank approximation was performed on compressed k-space, in conjunction with the orthogonal basis estimation for the subspace. Results: The simulation study involving a 32-time acceleration showed that the proposed method produced a reasonably small root mean square error (RMSE) of 0.159, compared to 0.278 for sliding window reconstruction, 0.2527 for SToRM and 0.294 for low-rank reconstruction. The study also presented in vivo images of a typical sagittal image with a temporal resolution of 7 ms/frame or 21 ms/frame for the three-slice scan. Conclusion: Our study presented a subspace reconstruction technique that does not require a navigator echo, which can be used for real-time MRI, particularly in speech imaging applications. [ABSTRACT FROM AUTHOR]

New experimental and clinical findings question the historic view of hydrocephalus and its 100-year-old classification. In particular, real-time magnetic resonance imaging (MRI) evaluation of cerebrospinal fluid (CSF) flow and detailed insights into brain water regulation on the molecular scale indicate the existence of at least three main mechanisms that determine the dynamics of neurofluids: (1) inspiration is a major driving force; (2) adequate filling of brain ventricles by balanced CSF upsurge is sensed by cilia; and (3) the perivascular glial network connects the ependymal surface to the pericapillary Virchow–Robin spaces. Hitherto, these aspects have not been considered a common physiologic framework, improving knowledge and therapy for severe disorders of normal-pressure and posthemorrhagic hydrocephalus, spontaneous intracranial hypotension, and spaceflight disease. [ABSTRACT FROM AUTHOR]

Velum movement signals generated from real-time magnetic resonance imaging videos of thirty-five German speakers were used to investigate the physiological conditions that might promote sound change involving the development of contrastive vowel nasality. The results suggest that, in comparison to when a nasal consonant precedes a voiced obstruent, the velum gesture associated with a nasal consonant preceding a voiceless obstruent undergoes gestural rescaling and temporal rephasing. This further suggests that the diachronic development of contrastive vowel nasality comprises two stages: the first stage involves gestural shortening and realignment, while the second stage involves a trading relationship between source and effect. [ABSTRACT FROM AUTHOR]

Magnetic resonance imaging (MRI) can measure cardiac response to exercise stress for evaluating and managing heart patients in the practice of clinical cardiology. However, exercise stress cardiac MRI have been clinically limited by the ability of available MRI techniques to quantitatively measure fast and unstable cardiac dynamics during exercise. The presented work is to develop a new real-time MRI technique for improved quantitative performance of exercise stress cardiac MRI. This technique seeks to represent real-time cardiac images as a sparse Fourier-series along the time. With golden-angle radial acquisition, parallel imaging and compressed sensing can be integrated into a linear system of equations for resolving Fourier coefficients that are in turn used to generate real-time cardiac images from the Fourier-series representation. Fourier-series reconstruction from golden-angle radial data can effectively address data insufficiency due to MRI speed limitation, providing a real-time approach to exercise stress cardiac MRI. To demonstrate the feasibility, an exercise stress cardiac MRI experiment was run to investigate biventricular response to in-scanner biking exercise in a cohort of sixteen healthy volunteers. It was found that Fourier-series reconstruction from golden-angle radial data effectively detected exercise-induced increase in stroke volume and ejection fraction in a healthy heart. The presented work will improve the applications of exercise stress cardiac MRI in the practice of clinical cardiology. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to propose and evaluate a slice‐to‐volume registration (SVR) method integrating an advanced dual‐slice real‐time magnetic resonance image (MRI) and three‐dimensional (3D) MRI volume of the tibiofemoral joint for determining their 3D kinematics. Methods: The real‐time and 3D MRI of the knee were collected from 12 healthy adults at 5 static flexion positions and during dynamic flexion/extension movement. The 3D positions and orientations of the femur and tibia were obtained by registering their volumetric models constructed from the 3D MRI to dual‐slice real‐time MRI using an optimization process. The proposed method was quantitatively evaluated for its performance in terms of the robustness and measurement accuracy, and compared to those of a single‐slice SVR method. Its repeatability in measuring knee kinematics during flexion/extension movement was also determined. Results: In comparison to the single‐slice SVR method, the dual‐slice method was significantly superior, giving a successful registration rate > 95%, a bias less than 0.5 mm in translations and 0.6° in rotations and a precision <0.7 mm in translations and 0.9° in rotations for determining the 3D tibiofemoral poses. For repeatability of the dual‐slice SVR in measuring tibiofemoral kinematics during dynamic flexion/extension, the means of the time‐averaged standard deviations were <0.9° for joint angles and 0.5 mm for joint translations. Conclusion: A dual‐slice SVR method in conjunction with real‐time MRI has been developed and evaluated for its performance in measuring 3D kinematics of the tibiofemoral joint in 12 young adults in terms of the accuracy, robustness, and repeatability. The proposed MRI‐based 3D measurement method provides a noninvasive and ionizing radiation‐free approach for 3D kinematic measurement of the tibiofemoral joint, which will be helpful for future academic and clinical applications. [ABSTRACT FROM AUTHOR]

The purpose of this study was to assess the reproducibility of functional and anatomical parameters of swallowing events as determined by real-time MRI at 40 ms temporal resolution (25 frames per second). Twenty-three consecutive patients with gastroesophageal reflux disease (GERD) underwent real-time MRI of the gastroesophageal junction at 3.0 T. Real-time MRI was based on highly undersampled radial fast low angle shot (FLASH) acquisitions with iterative image reconstruction by regularized nonlinear inversion (NLINV). MRI movies visualized the esophageal transport of a pineapple juice bolus, its passage through the gastroesophageal junction and functional responses during a Valsalva maneuver. His-angle, sphincter position, sphincter length and sphincter transit time were assessed by two radiologists. Interobserver and intraobserver intraclass correlation coefficients (ICC) were evaluated and Bland-Altman plots were constructed to assess the observer agreement. Interobserver agreement was excellent for sphincter transit time (ICC = 0.92), His-angle (ICC = 0.93), His-angle during Valsalva maneuver (ICC = 0.91) and sphincter-to-diaphragm distance (ICC = 0.98). Sphincter length and oesophageal diameter showed good interobserver agreement (ICC = 0.62 and ICC = 0.70). Intraobserver agreement was good for sphincter length (ICC = 0.80) and excellent for sphincter transit time, His-angle and His-angle during Valsalva maneuver, sphincter-to-diaphragm distance, and esophageal diameter (ICC = 0.91; ICC = 0.97; ICC = 0.97; ICC = 0.998; ICC = 0.93). All functional parameters of the gastroesophageal junction had good to excellent reproducibility. Visual assessment of Bland Altman plots did not reveal any systematic interobserver bias. In conclusion, the visualization of swallowing events by real-time MRI has a high potential for clinical application in gastroesophageal reflux disease. [ABSTRACT FROM AUTHOR]

Speech production mechanisms can be characterized at a peripheral level by both their acoustic and articulatory traces along time. Researchers have thus developed very large efforts to measure articulation. Thanks to the spectacular progress accomplished in the last decade, real-time Magnetic Resonance Imaging (RT-MRI) offers nowadays the advantages of frame rates closer than before to those achieved by electromagnetic articulography or ultrasound echography while providing very detailed geometrical information about the whole vocal tract. RT-MRI has thus become inescapable for the study of speech articulators’ movements. However, making efficient use of large sets of images to characterize and model speech tasks implies the development of automatic methods to segment the articulators from these images with sufficient accuracy. The present article describes our approach to develop, based on supervised machine learning techniques, an automatic segmentation method that offers various useful features such as (1) capability of dealing with individual articulators independently, (2) ensuring hard palate, jaw and hyoid bone to be adequately tracked as rigid structures, (3) delivering contours for a full set of articulators, including the epiglottis and the back of the larynx, which partly reflects the vocal fold abduction / adduction state, (4) dealing more explicitly and thus more accurately with contact between articulators, and (5) reaching an accuracy better than one millimeter. The main contributions of this work are the following. We have recorded the first large database of high quality RT-MRI midsagittal images for a French speaker. We have manually segmented the main speech articulators (jaw, lips, tongue, velum, hyoid, larynx, etc.) for a small training set of about 60 images selected by hierarchical clustering to represent the whole corpus as faithfully as possible. We have used these data to train various image and contour models for developing automatic articulatory segmentation methods. The first method, based on Multiple Linear Regression, allows to predict the contour coordinates from the image pixel intensities with a Mean Sum of Distances (MSD) segmentation error over all articulators of 0.91 mm, computed with a Leave-One-Out Cross Validation procedure on the training set. Another method, based on Shape Particle Filtering, reaches an MSD error of 0.66 mm. Finally the modified version of Active Shape Models (mASM) explored in this study gives an MSD error of a mere 0.55 mm (0.68 mm for the tongue). These results demonstrate that this mASM approach performs better than state-of-the-art methods, though at the cost of the manual segmentation of the training set. The same method used on other MRI data leads to similar errors, which testifies to its robustness. The large quantity of contour data that can be obtained with this automatic segmentation method opens the way to various fruitful perspectives in speech: establishing more elaborate articulatory models, analyzing more finely coarticulation and articulatory variability or invariance, implementing machine learning methods for articulatory speaker normalization or adaptation, or illustrating adequate or prototypical articulatory gestures for application in the domains of speech therapy and of second language pronunciation training. [ABSTRACT FROM AUTHOR]

Background: Children with heart disease may require repeated X-Ray cardiac catheterization procedures, are more radiosensitive, and more likely to survive to experience oncologic risks of medical radiation. Cardiovascular magnetic resonance (CMR) is radiation-free and offers information about structure, function, and perfusion but not hemodynamics. We intend to perform complete radiation-free diagnostic right heart catheterization entirely using CMR fluoroscopy guidance in an unselected cohort of pediatric patients; we report the feasibility and safety. Methods: We performed 50 CMR fluoroscopy guided comprehensive transfemoral right heart catheterizations in 39 pediatric (12.7 ± 4.7 years) subjects referred for clinically indicated cardiac catheterization. CMR guided catheterizations were assessed by completion (success/failure), procedure time, and safety events (catheterization, anesthesia). Pre and post CMR body temperature was recorded. Concurrent invasive hemodynamic and diagnostic CMR data were collected. Results: During a twenty-two month period (3/2015 - 12/2016), enrolled subjects had the following clinical indications: post-heart transplant 33%, shunt 28%, pulmonary hypertension 18%, cardiomyopathy 15%, valvular heart disease 3%, and other 3%. Radiation-free CMR guided right heart catheterization attempts were all successful using passive catheters. In two subjects with septal defects, right and left heart catheterization were performed. There were no complications. One subject had six such procedures. Most subjects (51%) had undergone multiple (5.5 ± 5) previous X-Ray cardiac catheterizations. Retained thoracic surgical or transcatheter implants (36%) did not preclude successful CMR fluoroscopy heart catheterization. During the procedure, two subjects were receiving vasopressor infusions at baseline because of poor cardiac function, and in ten procedures, multiple hemodynamic conditions were tested. Conclusions: Comprehensive CMR fluoroscopy guided right heart catheterization was feasible and safe in this small cohort of pediatric subjects. This includes subjects with previous metallic implants, those requiring continuous vasopressor medication infusions, and those requiring pharmacologic provocation. Children requiring multiple, serial X-Ray cardiac catheterizations may benefit most from radiation sparing. This is a step toward wholly CMR guided diagnostic (right and left heart) cardiac catheterization and future CMR guided cardiac intervention. Trial registration: ClinicalTrials.gov registered February 17, 2016 [ABSTRACT FROM AUTHOR]

Background: Quantification of cardiac output and pulmonary vascular resistance (PVR) are critical components of invasive hemodynamic assessment, and can be measured concurrently with pressures using phase contrast CMR flow during real-time CMR guided cardiac catheterization. Methods: One hundred two consecutive patients underwent CMR fluoroscopy guided right heart catheterization (RHC) with simultaneous measurement of pressure, cardiac output and pulmonary vascular resistance using CMR flow and the Fick principle for comparison. Procedural success, catheterization time and adverse events were prospectively collected. Results: RHC was successfully completed in 97/102 (95.1%) patients without complication. Catheterization time was 20 ± 11 min. In patients with and without pulmonary hypertension, baseline mean pulmonary artery pressure was 39 ± 12 mmHg vs. 18 ± 4 mmHg (p < 0.001), right ventricular (RV) end diastolic volume was 104 ± 64 vs. 74 ± 24 (p = 0.02), and RV end-systolic volume was 49 ± 30 vs. 31 ± 13 (p = 0.004) respectively. 103 paired cardiac output and 99 paired PVR calculations across multiple conditions were analyzed. At baseline, the bias between cardiac output by CMR and Fick was 5.9% with limits of agreement -38.3% and 50.2% with r = 0.81 (p < 0.001). The bias between PVR by CMR and Fick was -0.02 WU.m² with limits of agreement -2.6 and 2.5 WU.m² with r = 0.98 (p <0. 001). Correlation coefficients were lower and limits of agreement wider during physiological provocation with inhaled 100% oxygen and 40 ppm nitric oxide. Conclusions: CMR fluoroscopy guided cardiac catheterization is safe, with acceptable procedure times and high procedural success rate. Cardiac output and PVR measurements using CMR flow correlated well with the Fick at baseline and are likely more accurate during physiological provocation with supplemental high-concentration inhaled oxygen. Trial registration: Clinicaltrials.gov NCT01287026, registered January 25, 2011. [ABSTRACT FROM AUTHOR]

Background: Endomyocardial biopsies (EMB) are an important diagnostic tool for myocarditis and other infiltrative cardiac diseases. Routinely, biopsies are obtained under fluoroscopic guidance with a substantial radiation burden. Despite procedural success, there is a large sampling error caused by missing the affected myocardium. Therefore, multiple (>6) biopsies are taken in the clinical setting. In cardiovascular magnetic resonance (CMR), late gadolinium enhancement (LGE) depicts areas of affected myocardium in myocarditis or in other infiltrative cardiomyopathies. Thus, targeted biopsy under real-time CMR image guidance might reduce the problem of sampling error. Methods: Seven minipigs of the Goettingen strain underwent radiofrequency ablation in the left ventricle. At least two focal lesions were induced on the lateral wall in five and the apex in two animals. Each ablation lesion was created by two consecutive 30 sec ablations (max. 30 W, temperature 60-64 °C). Biopsies were taken immediately after lesion induction using a commercially available 7 F conventional bioptome under fluoroscopic guidance at the ablation site. Afterwards the animals underwent CMR and lesion visualization by LGE at 3T. The lesions were then targeted and biopsied under CMR-guidance using a MR-conditional bioptome guided by a steerable catheter. Interactive real-time (RT) visualization of the intervention on an in-room monitor was based on radial FLASH with nonlinear inverse reconstruction (NLINV) at a temporal resolution of 42 ms. All samples underwent a standard histological evaluation. Results: Radiofrequency ablation was successful in all animals. Fluoroscopy-guided biopsies were performed with a success rate of 6/6 minipigs - resulting in a nonlethal pericardial effusion in one animal. Visualization of radiofrequency lesions by CMR was successful in 7/7 minipig, i.e. at least one lesion was clearly visible. Localization and tracking of the catheters and the bioptome using interactive control of the imaging plane was achieved in 6/6 MP; however in the animal with a large pericardial effusion after EMB under fluoroscopy no further EMB was attempted for safety reasons. Biopsies under interactive RT-CMR guidance were successfully performed in 5/6 animals, in one animal the bioptome reached the lesion, however the forceps did not cut out a sample. Specimens obtained under CMR guidance contained part of the lesion in 6/15 (40%) myocardial specimens and in 4/5 (80%) animals in which samples were achieved. Conventional biopsies revealed ablation lesions in 4/17 (23.5%) specimens in 3/6 minipigs (50%). Conclusion: Focal lesions induced by radiofrequency ablation in a minipig model are a useful tool for CMR-guided biopsy studies. In contrast to fluoroscopy, CMR provides excellent visualization of lesions. Interactive real-time CMR allows excellent passive tracking of the instruments and EMB provides significantly superior sampling accuracy compared to fluoroscopy-guided biopsies. Nonetheless, further improvements of MR-compatible bioptomes and guiding catheters are essential before applying this method in a clinical setting. [ABSTRACT FROM AUTHOR]

• MRI thermometry quantifies the spatial temperature distribution in a fixed-bed. • Validation against optical temperature sensors shows an accuracy of ±1.5 °C. • Good agreement was found between MRI-based results and numerical simulations. Controlling the temperature distribution inside catalytic fixed bed reactors is crucial for yield optimization and process stability. Yet, in situ temperature measurements with spatial and temporal resolution are still challenging. In this work, we perform temperature measurements in a cylindrical fixed bed reactor by combining the capabilities of real-time magnetic resonance imaging (MRI) with the temperature-dependent proton resonance frequency (PRF) shift of water. Three-dimensional (3D) temperature maps are acquired while heating the bed from room temperature to 60 ° C using hot air. The obtained results show a clear temperature gradient along the axial and radial dimensions and agree with optical temperature probe measurements with an average error of ± 1.5 ° C. We believe that the MR thermometry methodology presented here opens new perspectives for the fundamental study of mass and heat transfer in gas–solid fixed beds and in the future might be extended to the study of reactive gas–solid systems. [ABSTRACT FROM AUTHOR]

Real-Time MRI Cryo-Ablation Introduction MRI-based ablation provides an attractive capability of seeing ablation-related tissue changes in real time. Here we describe a real-time MRI-based cardiac cryo-ablation system. Methods Studies were performed in canine model (n = 4) using MR-compatible cryo-ablation devices built for animal use: focal cryo-catheter with 8 mm tip and 28 mm diameter cryo-balloon. The main steps of MRI-guided cardiac cryo-ablation procedure (real-time navigation, confirmation of tip-tissue contact, confirmation of vessel occlusion, real-time monitoring of a freeze zone formation, and intra-procedural assessment of lesions) were validated in a 3 Tesla clinical MRI scanner. Results The MRI compatible cryo-devices were advanced to the right atrium (RA) and right ventricle (RV) and their position was confirmed by real-time MRI. Specifically, contact between catheter tip and myocardium and occlusion of superior vena cava (SVC) by the balloon was visually validated. Focal cryo-lesions were created in the RV septum. Circumferential ablation of SVC-RA junction with no gaps was achieved using the cryo-balloon. Real-time visualization of freeze zone formation was achieved in all studies when lesions were successfully created. The ablations and presence of collateral damage were confirmed by T1-weighted and late gadolinium enhancement MRI and gross pathological examination. Conclusion This study confirms the feasibility of a MRI-based cryo-ablation system in performing cardiac ablation procedures. The system allows real-time catheter navigation, confirmation of catheter tip-tissue contact, validation of vessel occlusion by cryo-balloon, real-time monitoring of a freeze zone formation, and intra-procedural assessment of ablations including collateral damage. [ABSTRACT FROM AUTHOR]

Advances on real-time magnetic resonance imaging (RT-MRI) make it suitable to study the dynamic aspects of the upper airway. One of the main challenges concerns how to deal with the large amount of data resulting from these studies, particularly to extract relevant features for analysis such as the vocal tract profiles. A method is proposed, based on a modified active appearance model (AAM) approach, for unsupervised segmentation of the vocal tract from midsagittal RT-MRI sequences. The described approach was designed considering the low inter-frame difference. As a result, when compared to a traditional AAM approach, segmentation is performed faster and model convergence is improved, attaining good results using small training sets. The main goal is to extract the vocal tract profiles automatically, over time, providing identification of different regions of interest, to allow the study of the dynamic features of the vocal tract, for example, during speech production. The proposed method has been evaluated against vocal tract delineations manually performed by four observers, yielding good agreement. [ABSTRACT FROM AUTHOR]

Purpose: Combined magnetic resonance imaging (MRI) systems and linear accelerators for radiotherapy (MR-Linacs) are currently under development. MRI is noninvasive and nonionizing and can produce images with high soft tissue contrast. However, new tracking methods are required to obtain fast real-time spatial target localization. This study develops and evaluates a method for tracking three-dimensional (3D) respiratory liver motion in two-dimensional (2D) real-time MRI image series with high temporal and spatial resolution. Methods: The proposed method for 3D tracking in 2D real-time MRI series has three steps: (1) Recording of a 3D MRI scan and selection of a blood vessel (or tumor) structure to be tracked in subsequent 2D MRI series. (2) Generation of a library of 2D image templates oriented parallel to the 2D MRI image series by reslicing and resampling the 3D MRI scan. (3) 3D tracking of the selected structure in each real-time 2D image by finding the template and template position that yield the highest normalized cross correlation coefficient with the image. Since the tracked structure has a known 3D position relative to each template, the selection and 2D localization of a specific template translates into quantification of both the through-plane and in-plane position of the structure. As a proof of principle, 3D tracking of liver blood vessel structures was performed in five healthy volunteers in two 5.4 Hz axial, sagittal, and coronal real-time 2D MRI series of 30 s duration. In each 2D MRI series, the 3D localization was carried out twice, using nonoverlapping template libraries, which resulted in a total of 12 estimated 3D trajectories per volunteer. Validation tests carried out to support the tracking algorithm included quantification of the breathing induced 3D liver motion and liver motion directionality for the volunteers, and comparison of 2D MRI estimated positions of a structure in a watermelon with the actual positions. Results: Axial, sagittal, and coronal 2D MRI series yielded 3D respiratory motion curves for all volunteers. The motion directionality and amplitude were very similar when measured directly as in-plane motion or estimated indirectly as through-plane motion. The mean peak-to-peak breathing amplitude was 1.6 mm (left-right), 11.0 mm (craniocaudal), and 2.5 mm (anterior-posterior). The position of the watermelon structure was estimated in 2D MRI images with a root-mean-square error of 0.52 mm (in-plane) and 0.87 mm (through-plane). Conclusions: A method for 3D tracking in 2D MRI series was developed and demonstrated for liver tracking in volunteers. The method would allow real-time 3D localization with integrated MR-Linac systems. [ABSTRACT FROM AUTHOR]

Introduction: The aim of this study was to correlate anatomic differences with continence status in male patients after cystoprostatectomy and ileal neobladder using real-time magnetic resonance imaging. Patients and Methods: Anatomic differences of 14 male patients (7 daytime continent and 7 stress incontinent) with ileal neobladder were determined by measuring the orthogonal distance of the bladder neck to the pubococcygeal line (PCL) to correlate anatomic differences with continence status. Results: The median distance of the bladder neck to PCL was +5.4 mm in continent patients before voiding whereas in incontinent patients it was +2 mm (p = 0.012). During the Valsalva maneuver, the median distance in continent patients was +4 and in incontinent patients -3 mm (p = 0.003). At the end of micturition, the median distance was +2.3 mm in continent patients and -12 mm in incontinent patients (p = 0.002). Conclusions: The bladder neck in incontinent patients showed more pronounced mobility in relation to the PCL during micturition and the Valsalva maneuver as compared to continent patients. In addition, the ileal neobladder was positioned significantly lower in the pelvis of incontinent patients. These preliminary results suggest that a stable bladder neck may be an important factor to reach full continence in patients with ileal neobladder. Copyright © 2011 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: Real-time cardiac MRI appears as a promising technique to evaluate the mechanical function of the heart. However, ultra-fast MRI acquisitions come with an important signal-to-noise ratio (SNR) penalty, which drastically reduces the image quality. Hence, a real-time denoising approach would be desirable for SNR amelioration. In the clinical context of cardiac dysfunction assessment, long acquisitions are required and for most patients the acquisition takes place with free breathing. Hence, it is necessary to compensate respiratory motion in real-time. In this article, a real-time and interactive method for sequential registration and denoising of real-time MR cardiac images is presented. The method has been experimented on 60 fast MRI acquisitions in five healthy volunteers and five patients. These experiments assessed the feasibility of the method in a real-time context. [Copyright &y& Elsevier]

Time series of in vivo magnetic resonance images exhibit high levels of temporal correlation. Higher temporal resolution reconstructions are obtained by acquiring data at a fraction of the Nyquist rate and resolving the resulting aliasing using the correlation information. The dynamic imaging experiment is modeled as a linear dynamical system. A Kalman filter based unaliasing reconstruction is described for accelerated dynamic magnetic resonance imaging (MRI). The algorithm handles arbitrary readout trajectories naturally. The reconstruction is causal and very fast, making it applicable to real-time imaging. In vivo results are presented for cardiac MRI of healthy volunteers. [ABSTRACT FROM AUTHOR]

Abstract: In pharmacological magnetic resonance imaging (phMRI) with anesthetized animals, there is usually only a single time window to observe the dynamic signal change to an acute drug administration since subsequent drug injections are likely to result in altered response properties (e.g., tolerance). Unlike the block-design experiments in which fMRI signal can be elicited with multiple repetitions of a task, these single-event experiments require stable baseline in order to reliably identify drug-induced signal changes. Such factors as subject motion, scanner instability and/or alterations in physiological conditions of the anesthetized animal could confound the baseline signal. The unique feature of such functional MRI (fMRI) studies necessitates a technique that is able to monitor MRI signal in a real-time fashion and to interactively control certain experimental procedures. In the present study, an approach for real-time MRI on a Bruker scanner is presented. The custom software runs on the console computer in parallel with the scanner imaging software, and no additional hardware is required. The utility of this technique is demonstrated in manganese-enhanced MRI (MEMRI) with acute cocaine challenge, in which temporary disruption of the blood–brain barrier (BBB) is a critical step for MEMRI experiments. With the aid of real-time MRI, we were able to assess the outcome of BBB disruption following bolus injection of hyperosmolar mannitol in a near real-time fashion prior to drug administration, improving experimental success rate. It is also shown that this technique can be applied to monitor baseline physiological conditions in conventional fMRI experiments using blood oxygenation level-dependent (BOLD) contrast, further demonstrating the versatility of this technique. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to demonstrate and evaluate the performance of real-time color-flow MRI at 3 T using variable-density spiral (VDS) phase contrast. Spiral phase contrast imaging was implemented within a flexible real-time interactive MRI system that provided continuous image reconstruction and an intuitive user interface. The pulse sequence consisted of a spectral–spatial excitation, bipolar gradient, spiral readout and gradient spoiler. VDSs were utilized to increase spatial and/or temporal resolution relative to uniform-density spirals (UDSs). Parameter choices were guided by specific applications. Sliding window reconstruction was used to achieve a maximum display rate of 40 frames/s. No breath-holding or gating was used. Our results demonstrated that real-time color-flow movies using UDS and VDS provided adequate visualization of intracardiac flow, carotid flow and proximal coronary flow in healthy volunteers. Average aortic outflow velocity measured at the aortic valve plane using VDS was 29.4% higher than that using UDS. Peak velocity measured in the common carotid artery using VDS was 9.8% higher than that using UDS. [Copyright &y& Elsevier]

Abstract: Objectives: The purpose of this preliminary study was to analyze the dynamic changes in the configuration of the neobladder and naïve bladder during voiding using real-time MRI. Methods: This study included 10 male patients who had a radical cystectomy and an ileal orthotopic neobladder due to organ-confined bladder cancer and had good urinary function, and 5 male control volunteers. With the subjects in the lateral decubitus position, real-time MRI was performed during micturition. A sagittal slice orientation was used to depict the bladder and the entire length of the urethra; individual movements along the X-axis and Y-axis of the bottom and top of the neobladder and the naïve bladder were recorded and analyzed. Urodynamic studies (UDS) and video voiding cystourethrography were performed in patients. Results: Five of the 10 neobladder patients could void in the lateral decubitus position. In normal controls and patients who could void, the bladder outlet bladder moved ventrocranially during micturition. The ileal bladder outlet moved a significantly longer distance than the naïve bladder during micturition (X-axis, −13.4±1.5 vs. −3.6±4.3cm, p =0.0014; Y-axis, −10.6±0.5 vs. −2.0±6.5cm, p =0.0187). The distance that the bladder top moved between the naïve bladders and the neobladder did not differ. UDS did not show a difference between patients who could and could not void at lateral position. Conclusions: During micturition, the neobladder was found to rotate and move more dynamically than the naïve bladder. Real-time MRI is useful for assessing dynamic voiding function of orthotopic neobladders. [Copyright &y& Elsevier]

The aim of this study was to investigate the value of a real-time magnetic resonance imaging (MRI) approach for the assessment of left-ventricular-wall motion in patients with insufficient transthoracic echocardiography in terms of accuracy and temporal expenditure. Twenty-five consecutive patients were examined on a 1.5-Tesla whole-body MR system (ACS-NT, Philips Medical Systems, Best, NL) using a real-time and ECG-gated (the current gold standard) steady-state free-precession (SSFP) sequence. Wall motion was analyzed by three observers by consensus interpretation. In addition, the preparation, scanning, and overall examination times were measured. The assessment of the wall motion demonstrated a close agreement between the two modalities resulting in a mean kappa coefficient of 0.8. At the same time, each stage of the examination was significantly shortened using the real-time MR approach. Real-time imaging allows for accurate assessment of left-ventricular-wall motion with the added benefit of decreased examination time. Therefore, it may serve as a cost-efficient alternative in patients with insufficient echocardiography. [ABSTRACT FROM AUTHOR]

Purpose: To investigate imaging findings of esophageal motility disorders on dynamic real-time.Material and Methods: 102 patients with GERD-like symptoms were included in this retrospective study between 2015-2018. Dynamic real-time MRI visualized the transit of a 10 mL pineapple juice bolus through the esophagus and EGJ with a temporal resolution of 40 ms. Dynamic and anatomic parameters were measured by consensus reading. Imaging findings were compared to HRM utilizing the Chicago classification of esophageal motility disorders, v3.0.Results: All 102 patients completed real-time MRI in a median examination time of 15 min. On HRM, 14 patients presented with disorders with EGJ outlet obstruction (EGJOO) (13.7 %), 7 patients with major disorders of peristalsis (6.9 %), and 32 patients with minor disorders of peristalsis (31.4 %). HRM was normal in 49 patients (48.0 %). Incomplete bolus clearance was significantly more frequent in patients with esophageal motility disorders on HRM than in patients with normal HRM (p = 0.0002). In patients with motility disorders with EGJOO and major disorders of peristalsis, the esophageal diameter tended to be wider (23.6 ± 8.0 vs. 21.2 ± 3.5 mm, p = 0.089) and the sphincter length longer (19.7 ± 7.3 vs. 16.7 ± 3.0 mm, p = 0.091) compared to patients with normal HRM. 3/7 patients with achalasia type II were correctly identified by real-time MRI and one further achalasia type II patient was diagnosed with a motility disorder on MRI films. The other 3/7 patients presented no specific imaging features.Conclusion: Real-time MRI is an auxiliary diagnostic tool for the assessment of swallowing events. Imaging parameters may assist in the detection of esophageal motility disorders. [ABSTRACT FROM AUTHOR]

Background: Cardiovascular magnetic resonance (CMR) fluoroscopy allows for simultaneous measurement of cardiac function, flow and chamber pressure during diagnostic heart catheterization. To date, commercial metallic guidewires were considered contraindicated during CMR fluoroscopy due to concerns over radiofrequency (RF)-induced heating. The inability to use metallic guidewires hampers catheter navigation in patients with challenging anatomy. Here we use low specific absorption rate (SAR) imaging from gradient echo spiral acquisitions and a commercial nitinol guidewire for CMR fluoroscopy right heart catheterization in patients. Methods: The low-SAR imaging protocol used a reduced flip angle gradient echo acquisition (10° vs 45°) and a longer repetition time (TR) spiral readout (10 ms vs 2.98 ms). Temperature was measured in vitro in the ASTM 2182 gel phantom and post-mortem animal experiments to ensure freedom from heating with the selected guidewire (150 cm × 0.035″ angled-tip nitinol Terumo Glidewire). Seven patients underwent CMR fluoroscopy catheterization. Time to enter each chamber (superior vena cava, main pulmonary artery, and each branch pulmonary artery) was recorded and device visibility and confidence in catheter and guidewire position were scored on a Likert-type scale. Results: Negligible heating (< 0.07°C) was observed under all in vitro conditions using this guidewire and imaging approach. In patients, chamber entry was successful in 100% of attempts with a guidewire compared to 94% without a guidewire, with failures to reach the branch pulmonary arteries. Time-to-enter each chamber was similar (p=NS) for the two approaches. The guidewire imparted useful catheter shaft conspicuity and enabled interactive modification of catheter shaft stiffness, however, the guidewire tip visibility was poor. Conclusions: Under specific conditions, trained operators can apply low-SAR imaging and using a specific fully-insulated metallic nitinol guidewire (150 cm × 0.035" Terumo Glidewire) to augment clinical CMR fluoroscopy right heart catheterization. Trial registration: Clinicaltrials.gov NCT03152773, registered May 15, 2017. [ABSTRACT FROM AUTHOR]