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Proton resonance frequency shift (PRFS) MR thermometry is the most common method used in clinical thermal treatments because of its fast acquisition and high sensitivity to temperature. However, motion is the biggest obstacle in PRFS MR thermometry for monitoring thermal treatment in moving organs. This challenge arises because of the introduction of phase errors into the PRFS calculation through multiple methods, such as image misregistration, susceptibility changes in the magnetic field, and intraframe motion during MRI acquisition. Various approaches for motion correction have been developed for real-time, motion-robust, and volumetric MR thermometry. However, current technologies have inherent trade-offs among volume coverage, processing time, and temperature accuracy. These tradeoffs should be considered and chosen according to the thermal treatment application. In hyperthermia treatment, precise temperature measurements are of increased importance rather than the requirement for exceedingly high temporal resolution. In contrast, ablation procedures require robust temporal resolution to accurately capture a rapid temperature rise. This paper presents a comprehensive review of current cutting-edge MRI techniques for motion-robust MR thermometry, and recommends which techniques are better suited for each thermal treatment. We expect that this study will help discern the selection of motion-robust MR thermometry strategies and inspire the development of motion-robust volumetric MR thermometry for practical use in clinics.

The current project undertakes a kinematic examination of vertical larynx actions and intergestural timing stability within multi-gesture complex segments such as ejectives and implosives that may possess specific temporal goals critical to their articulatory realization. Using real-time MRI (rtMRI) speech production data from Hausa non-pulmonic and pulmonic consonants, this study illuminates speech timing between oral constriction and vertical larynx actions within segments and the role this intergestural timing plays in realizing phonological contrasts and processes in varying prosodic contexts. Results suggest that vertical larynx actions have greater magnitude in the production of ejectives compared to their pulmonic counterparts, but implosives and pulmonic consonants are differentiated not by vertical larynx magnitude but by the intergestural timing patterns between their oral and vertical larynx gestures. Moreover, intergestural timing stability/variability between oral and non-oral (vertical larynx) actions differ among ejectives, implosives, and pulmonic consonants, with ejectives having the most stable temporal lags, followed by implosives and pulmonic consonants, respectively. Lastly, the findings show how contrastive linguistic 'molecules' – here, segment-sized phonological complexes with multiple gestures – interact with phrasal context in speech in such a way that it variably shapes temporal organization between participating gestures as well as respecting stability in relative timing between such gestures comprising a segment. [ABSTRACT FROM AUTHOR]

INTRODUCTION: Image-guided endovascular interventions, performed using the insertion and navigation of catheters through the vasculature, have been increasing in number over the years, as minimally invasive procedures continue to replace invasive surgical procedures. Such endovascular interventions are almost exclusively performed under x-ray fluoroscopy, which has the best spatial and temporal resolution of all clinical imaging modalities. Magnetic resonance imaging (MRI) offers unique advantages and could be an attractive alternative to conventional x-ray guidance, but also brings with it distinctive challenges. AREAS COVERED: In this review, the benefits and limitations of MRI-guided endovascular interventions are addressed, systems and devices for guiding such interventions are summarized, and clinical applications are discussed. EXPERT OPINION: MRI-guided endovascular interventions are still relatively new to the interventional radiology field, since significant technical hurdles remain to justify significant costs and demonstrate safety, design, and robustness. Clinical applications of MRI-guided interventions are promising but their full potential may not be realized until proper tools designed to function in the MRI environment are available. Translational research and further preclinical studies are needed before MRI-guided interventions will be practical in a clinical interventional setting.

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: To develop an efficient and flexible water/fat separated real‐time MRI (RT‐MRI) method using spiral out‐in‐out‐in (OIOI) sampling and balanced SSFP (bSSFP) at 0.55T. Methods: A bSSFP sequence with golden‐angle spiral OIOI readout was developed, capturing three echoes to allow water/fat separation. A low‐latency reconstruction that combines all echoes was available for online visualization. An offline reconstruction provided water and fat RT‐MRI in two steps: (1) image reconstruction with spatiotemporally constrained reconstruction (STCR) and (2) water/fat separation with hierarchical iterative decomposition of water and fat with echo asymmetry and least‐squares estimation (HIDEAL). In healthy volunteers, spiral OIOI was acquired in the wrist during a radial‐to‐ulnar deviation maneuver, in the heart without breath‐hold and cardiac gating, and in the lower abdomen during free‐breathing for visualizing small bowel motility. Results: We demonstrate successful water/fat separated RT‐MRI for all tested applications. In the wrist, resulting images provided clear depiction of ligament gaps and their interactions during the radial‐to‐ulnar deviation maneuver. In the heart, water/fat RT‐MRI depicted epicardial fat, provided improved delineation of epicardial coronary arteries, and provided high blood‐myocardial contrast for ventricular function assessment. In the abdomen, water‐only RT‐MRI captured small bowel mobility clearly with improved water‐fat contrast. Conclusions: We have demonstrated a novel and flexible bSSFP spiral OIOI sequence at 0.55T that can provide water/fat separated RT‐MRI with a variety of application‐specific temporal resolution and spatial resolution requirements. [ABSTRACT FROM AUTHOR]

Purpose: To demonstrate speech‐production real‐time MRI (RT‐MRI) using a contemporary 0.55T system, and to identify opportunities for improved performance compared with conventional field strengths. Methods: Experiments were performed on healthy adult volunteers using a 0.55T MRI system with high‐performance gradients and a custom 8‐channel upper airway coil. Imaging was performed using spiral‐based balanced SSFP and gradient‐recalled echo (GRE) pulse sequences using a temporal finite‐difference constrained reconstruction. Speech‐production RT‐MRI was performed with three spiral readout durations (8.90, 5.58, and 3.48 ms) to determine trade‐offs with respect to articulator contrast, blurring, banding artifacts, and overall image quality. Results: Both spiral GRE and bSSFP captured tongue boundary dynamics during rapid consonant‐vowel syllables. Although bSSFP provided substantially higher SNR in all vocal tract articulators than GRE, it suffered from banding artifacts at TR > 10.9 ms. Spiral bSSFP with the shortest readout duration (3.48 ms, TR = 5.30 ms) had the best image quality, with a 1.54‐times boost in SNR compared with an equivalent GRE sequence. Longer readout durations led to increased SNR efficiency and blurring in both bSSFP and GRE. Conclusion: High‐performance 0.55T MRI systems can be used for speech‐production RT‐MRI. Spiral bSSFP can be used without suffering from banding artifacts in vocal tract articulators, provide better SNR efficiency, and have better image quality than what is typically achieved at 1.5 T or 3 T. [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]

Extensive spread of the coronavirus disease (COVID-19) prompted an investigation of its diagnostic features. Acute viral pneumonia associated with COVID-19 has been described in detail using CT, radiography, and MRI. There is no data in the literature on the descriptive picture observed with dynamic MRI. Considering a comprehensive diagnostic approach, radiologists should know how to correctly recognize and interpret COVID-19 on MRI. This case series demonstrated the ability of dynamic MRI to detect the cloudy sky sign and distinguish it from consolidation in COVID-19 patients, thus presumably distinguishing between early or mild changes and a progressive clinical course. These changes in dynamic lung images on MRI can be recorded depending on the phase of the respiratory cycle. Thus, MRI, as a radiation-free tool that can be used to examine a patient with acute viral pneumonia COVID-19, can be useful in cases where access to computed tomography is limited and dynamic morphofunctional imaging is required.

Purpose: Conventional sequences are static in nature, fixing measurement parameters in advance in anticipation of a wide range of expected tissue parameter values. We set out to design and benchmark a new, personalized approach—termed adaptive MR—in which incoming subject data is used to update and fine‐tune the pulse sequence parameters in real time. Methods: We implemented an adaptive, real‐time multi‐echo (MTE) experiment for estimating T2s. Our approach combined a Bayesian framework with model‐based reconstruction. It maintained and continuously updated a prior distribution of the desired tissue parameters, including T2, which was used to guide the selection of sequence parameters in real time. Results: Computer simulations predicted accelerations between 1.7‐ and 3.3‐fold for adaptive multi‐echo sequences relative to static ones. These predictions were corroborated in phantom experiments. In healthy volunteers, our adaptive framework accelerated the measurement of T2 for n‐acetyl‐aspartate by a factor of 2.5. Conclusion: Adaptive pulse sequences that alter their excitations in real time could provide substantial reductions in acquisition times. Given the generality of our proposed framework, our results motivate further research into other adaptive model‐based approaches to MRI and MRS. [ABSTRACT FROM AUTHOR]

PURPOSE: MRI-guided cardiovascular intervention using standard metal guidewires can produce focal tissue heating caused by induced radiofrequency guidewire currents. It has been shown that safe operation is made possible by using parallel transmit radiofrequency coils driven in the null current mode, which does not induce radiofrequency currents and hence allows safe tissue visualization. We propose that the maximum current modes, usually considered unsafe, be used at very low power levels to visualize conductive wires, and we investigate pulse sequences best suited for this application. METHODS: Spoiled gradient echo, balanced steady-state free precession, and turbo spin echo sequences were evaluated for their ability to visualize a conductive guidewire embedded in a gel phantom when run in maximum current modes at very low power level. Temperature at the guidewire tip was monitored for safety assessment. RESULTS: Excellent guidewire visualization could be achieved using maximum current modes excitation, with the turbo spin echo sequence giving the best image quality. Although turbo spin echo is usually considered to be a high-power sequence, our method reduced all pulses to 1% amplitude (0.01% power), and heating was not detected. In addition, visualization of background tissue can be achieved using null current mode, also with no recorded heating at the guidewire tip even when running at 100% (reported) specific absorption rate. CONCLUSION: Parallel transmit is a promising approach for both guidewire and tissue visualization using maximum and null current modes, respectively, for interventional cardiac MRI. Such systems can switch excitation mode instantaneously, allowing for flexible integration into interactive sequences.

Introduction: Musculoskeletal problems in professional brass musicians are very common and often involve the muscles of the embouchure. In rare cases, embouchure dystonia (EmD), a task-specific movement disorder with a wide symptomatic and phenotypic variability, occurs. Following trumpeters and horn players, professional tuba players with and without EmD have now been studied using the latest real-time MRI technology to better understand the underlying pathophysiology. Materials and methods: In the present study, the tongue movement patterns of 11 healthy professional artists and one subject suffering from EmD were compared. The tongue position in the anterior, intermediary and posterior oral cavity were converted into pixel positions based on seven previously generated profile lines, using the established software MATLAB. These data allow a structured comparison of tongue movement patterns between the patient and the healthy subjects, as well as between individual exercises. The main focus of the analysis was on an ascending 7-note harmonic series performed in different playing techniques (slurred, tongued, tenuto and staccato). Results: Playing the ascending harmonics, a noticeable ascending tongue movement could be observed in the anterior part of the oral cavity in healthy tubists. In the posterior region, there was a slight decrease in oral cavity space. In the EmD patient, hardly any movement was observed at the tongue apex, but in the middle and posterior regions of the oral cavity there was an increase in size the higher the tone became. These distinct differences are relevant for the characterization and a better understanding of the clinical presentation of EmD. Concerning different playing techniques, it was apparent, that notes played slurred or staccato resulted in a larger oral cavity when compared to notes played tongued or tenuto, respectively. Conclusion: By using real-time MRI videos, the tongue movements of tuba players can be clearly observed and analyzed. The differences between healthy and diseased tuba players demonstrate the great effects of movement disorders in a small area of the tongue. In order to better understand the compensation of this motor control dysfunction, further studies should investigate further parameters of tone production in all brass players with a larger number of EmD patients additional to the observed movement patterns. [ABSTRACT FROM AUTHOR]

IntroductionMusculoskeletal problems in professional brass musicians are very common and often involve the muscles of the embouchure. In rare cases, embouchure dystonia (EmD), a task-specific movement disorder with a wide symptomatic and phenotypic variability, occurs. Following trumpeters and horn players, professional tuba players with and without EmD have now been studied using the latest real-time MRI technology to better understand the underlying pathophysiology.Materials and methodsIn the present study, the tongue movement patterns of 11 healthy professional artists and one subject suffering from EmD were compared. The tongue position in the anterior, intermediary and posterior oral cavity were converted into pixel positions based on seven previously generated profile lines, using the established software MATLAB. These data allow a structured comparison of tongue movement patterns between the patient and the healthy subjects, as well as between individual exercises. The main focus of the analysis was on an ascending 7-note harmonic series performed in different playing techniques (slurred, tongued, tenuto and staccato).ResultsPlaying the ascending harmonics, a noticeable ascending tongue movement could be observed in the anterior part of the oral cavity in healthy tubists. In the posterior region, there was a slight decrease in oral cavity space. In the EmD patient, hardly any movement was observed at the tongue apex, but in the middle and posterior regions of the oral cavity there was an increase in size the higher the tone became. These distinct differences are relevant for the characterization and a better understanding of the clinical presentation of EmD. Concerning different playing techniques, it was apparent, that notes played slurred or staccato resulted in a larger oral cavity when compared to notes played tongued or tenuto, respectively.ConclusionBy using real-time MRI videos, the tongue movements of tuba players can be clearly observed and analyzed. The differences between healthy and diseased tuba players demonstrate the great effects of movement disorders in a small area of the tongue. In order to better understand the compensation of this motor control dysfunction, further studies should investigate further parameters of tone production in all brass players with a larger number of EmD patients additional to the observed movement patterns.

The purpose of this study was to evaluate and compare three kinds of scan plane manipulation tools for real-time magnetic resonance imaging (MRI). The first one was a Line-Projection tool which was clinically used on a General Electric's MRI system (Signa™) in its real-time imaging mode. The second one was called rtViewer, which was a custom designed tri-planner graphical user interface for volumetric image visualization. The third kind, using a Plane Navigator (PN) as a representative, was an arm-like mechanical armature with coordinated 6-degree-of-freedom (DoF) input capability. Two usability experiments were conducted to compare their effects in a simulated interactive MRI setting. Twelve cardiac practitioners were recruited to prescribe diagnostic views of a familiar object, i.e., a beating heart, and to prescribe an unfamiliar object, i.e., a custom designed phantom. Results indicated that the coordinated 6-DoF Plane Navigator outperformed both the Line-Projection tool and rtViewer in terms of task completion time and accuracy for prescribing both simple and complex views, though rtViewer performed best for through plane translation. The Plane Navigator saved about 50% of the time needed by the Line-Projection tool or rtViewer for prescribing unfamiliar double-oblique phantom views. Thanks to its desirable features including coordinated 6-DoF input, rich kinesthetic feedback, visual cue, and stay-put due to its static balance, the Plane Navigator tool may be used to manipulate the scan plane for fast visualization of a dynamic beating heart during real-time cardiac MRI and for the visualization of a surgical tool during an interventional MRI-guided minimum invasive surgery, or for interactive visualization of large-sized volumetric dataset including pre-acquired medical volumetric images. [ABSTRACT FROM AUTHOR]

We present a method for speech enhancement of data collected in extremely noisy environments, such as those obtained during magnetic resonance imaging (MRI) scans. We propose an algorithm based on dictionary learning to perform this enhancement. We use complex nonnegative matrix factorization with intra-source additivity (CMF-WISA) to learn dictionaries of the noise and speech+noise portions of the data and use these to factor the noisy spectrum into estimated speech and noise components. We augment the CMF-WISA cost function with spectral and temporal regularization terms to improve the noise modeling. Based on both objective and subjective assessments, we find that our algorithm significantly outperforms traditional techniques such as Least Mean Squares (LMS) filtering, while not requiring prior knowledge or specific assumptions such as periodicity of the noise waveforms that current state-of-the-art algorithms require.

Purpose: Overall there is a lack of evidence on the accuracy and precision of phase-contrast (PC) MRI in patients with cardiac implantable electronic devices (CIEDs). The purpose of this study is to determine whether aortic velocity measurements are influenced by a CIED., Methods: We scanned 21 adult patients and 8 pediatric volunteers using clinical standard PC and real-time PC (rt-PC) sequences with and without a CIED generator taped on human subjects (below the left clavicle for adults and children; also on the abdomen for children) to mimic image artifacts. Peak and mean velocities above the aortic valve were calculated., Results: The Bland-Altman analyses on peak velocity measurements in pediatric subjects showed that both the accuracy and precision worsen as the distance between the CIED and aortic valve decreases (i.e., from abdomen to below the left clavicle). Specifically, both the bias and the coefficient of variation (CV) for both clinical PC and rt-PC increased from the abdominal position (clinical: bias = -1.1%, CV = 4.3%; rt-PC: bias = -0.3%, CV = 3.4%) to the clavicle position (clinical: bias = -4.0%, CV = 8.1%; rt-PC: bias = 8.2%, CV = 7.3%). A similar trend was observed for mean velocity. The mean difference in peak and mean velocity measurements between rt-PC with CIED (either position) and clinical standard PC with no CIED was within 7.5%. In adult patients, the mean difference between rt-PC with CIED and clinical standard PC with CIED in peak velocity was 6.9%, and the CV was 7.9%., Conclusion: This study demonstrates that aortic velocity measurements are influenced by CIED in both adult and pediatric subjects., (© 2024 The Author(s). Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)

Purpose: To determine the feasibility of simultaneous multi-slice (SMS) real-time MRI (RT-MRI) at 0.55T for the evaluation of cardiac function., Methods: Cardiac CINE MRI is routinely used to evaluate left-ventricular (LV) function. The standard is sequential multi-slice balanced SSFP (bSSFP) over a stack of short-axis slices using electrocardiogram (ECG) gating and breath-holds. SMS has been used in CINE imaging to reduce the number of breath-holds by a factor of 2-4 at 1.5T, 3T, and recently at 0.55T. This work aims to determine if SMS is similarly effective in the RT-MRI evaluation of cardiac function. We used an SMS bSSFP pulse sequence with golden-angle spirals at 0.55T with an SMS factor of three. We cover the LV with three acquisitions for SMS, and nine for single-band (SB). Imaging was performed on 9 healthy volunteers and 1 patient with myocardial fibrosis and sternal wires. A spatio-temporal constrained reconstruction is used, with regularization parameters selected by a board-certified cardiologist. Images were quantitatively analyzed with a normalized contrast and an Edge Sharpness (ES) score., Results: There was a statistically significant 2-fold difference in contrast between SMS and SB and no significant difference in ES score. The contrast for SMS and SB were 13.38/29.05 at mid-diastole and 10.79/22.26 at end-systole; the ES scores for SMS and SB were 1.77/1.83 at mid-diastole and 1.50/1.72 at end-systole., Conclusions: SMS cardiac RT-MRI at 0.55T is feasible and provides sufficient blood-myocardium contrast to evaluate LV function in three slices simultaneously without any gating or periodic motion assumptions., (© 2024 The Author(s). Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)

Background: Transcutaneous auricular vagus nerve stimulation (taVNS) has been investigated regarding its therapeutic properties in several several conditions such as epilepsy, migraine and major depressive disorder and was shown to access similar neural pathways as invasive vagus nerve stimulation. While the vagus nerve's role in gut motility is physiologically established, the effect of taVNS has scarcely been investigated in humans and yielded conflicting results. Real-time gastric magnetic resonance imaging (rtMRI) is an established reproducible method to investigate gastric motility non-invasively. Objective: To investigate the influence of taVNS on gastric motility of healthy participants using rtMRI. Methods: We conducted a randomized, double-blind study using high-frequency (HF) stimulation at 25Hz or low-frequency (LF) taVNS at 1Hz after ingestions of a standardized meal in 57 healthy participants. The gastric motility index (GMI) was determined by measuring the amplitude and velocity of the peristaltic waves using rtMRI. Results: After HF taVNS, GMI was significantly higher than after LF stimulation (p = 0.005), which was mainly attributable to a higher amplitude of the peristaltic waves (p = 0.003). Conclusion: We provide evidence that 4-h of taVNS influences gastric motility in healthy human participants for the first time using rtMRI. HF stimulation is associated with higher amplitudes of peristaltic waves in the gastric antrum compared to LF stimulation. Further studies are needed to investigate the effect of different frequencies of taVNS and its therapeutic properties in conditions with impaired gastric motility.

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]

BackgroundChildren 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.MethodsWe 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.ResultsDuring 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.ConclusionsComprehensive 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 registrationClinicalTrials.gov NCT02739087 registered February 17, 2016.

BackgroundQuantification 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.MethodsOne 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.ResultsRHC 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

We report a summary of developmental work to explore, develop, and establish clinical applications of real-time magnetic resonance imaging (rtMRI) with a temporal resolution of 70 frames/second in oral and maxillofacial surgery (OMFS). Real-time MRI can contribute to procedure planning, diagnostics, rehabilitation, monitoring, and patient education. At present, conventional MRI is used extensively in the diagnosis, staging, and follow up of head and neck cancer patients, with scanning durations typically of several minutes and temporal resolution of up to 0.5 frames/second. The potential for rtMRI, where function can be assessed, could go far beyond the established clinical application of conventional MRI. Preliminary prototyping is a first stage in the establishment of rtMRI in OMFS. We follow best-practice approaches in co-creation across multiple disciplines, an indispensable aspect in the development of new methodologies and diagnostic tools. [ABSTRACT FROM AUTHOR]

Purpose: Few studies have examined the effects of body position on urination efficiency morphologically. We aimed to dissect out the anatomical changes of pelvic organs during urination in the upright and supine positions by a real‐time magnetic resonance imaging (rtMRI) system. Methods: Thirteen healthy male volunteers aged 26–60 years were included in the study. The sagittal real‐time two‐dimensional images were taken to evaluate urinary efficiency, along with change in six morphological indices at the time of storage and the beginning of voiding, in both upright ant supine positions. Results: Urination was more efficient in upright position than in supine position, as expressed by higher average rate of bladder emptying (9.9 ± 4.2 vs. 6.8 ± 2.9 ml/s, p < 0.05) and also by fewer participants showing significant residual urine (1/13 vs. 7/13, p < 0.05). At the onset of voiding in standing position, the levator ani (LA) muscle moves downward and backward followed by descent of the bladder neck and rotation of the prostate around the symphysis. Such changes were expressed by two morphological indices. One was posterior vesicourethral angle at the start of voiding, 152 ± 7 versus 140 ± 1 in upright and supine position (p < 0.05). The other index was the change in angle between the LA line and pubo‐coccygeal line in upright and supine position, 9.4 ± 9.9 versus 1.6 ± 7.9 before voiding (p < 0.05) and 30.2 ± 14.0 versus 17.3 ± 12.9 after the start of voiding (p < 0.05). Conclusion: The dynamic relaxation of LA seemed to be a key movement that enables more efficient urination in standing position than in supine position. [ABSTRACT FROM AUTHOR]

Purpose: To develop a real‐time radial tagging MRI for accurate measurement of rotational motion and twist of the left ventricle (LV). Methods: A FLASH‐based radial tagging sequence with an undersampled radial reading scheme was developed for both single and double‐slice imaging in real‐time. The Polar Fourier Transform was used for reconstruction to push the undersampling artifacts out of a reduced FOV. The developed technique was used to image five normal subjects during rest, plus one during both exercise and rest conditions. LV rotational motions were estimated for five consecutive cardiac cycles in all cases. The process was validated using a numerical phantom. The real‐time measurement of global rotational motion was compared with those measured from a non‐real‐time exam using linear regression analysis and the Bland‐Altman plot. Results: The real‐time acquisition was performed successfully with a temporal resolution of 46.2 ms. Image quality was sufficient for the reproducible calculation of rotation at rest and exercise. The feasibility of double‐slice acquisition on human was further studied and a real‐time twist of the left ventricle was demonstrated. The difference between LV global rotations from real‐time and non‐real‐time approaches was 0.27 degrees. A significant reverse recoiling, induced by exercise, was reproducibly measured by the technique. Conclusion: A real‐time radial tagging MRI technique was developed based on the undersampled radial acquisition and Polar Fourier Transform reconstruction, for accurate measuring of the heart rotational motion and twist. The technique was able to extract a meaningful change of diastolic recoiling under stress test conditions during physical activities (cycling). [ABSTRACT FROM AUTHOR]

Purpose: To assess the esophagogastric junction (EGJ) on real-time MRI and compare imaging parameters to EGJ morphology on high-resolution manometry (HRM). Methods: A total of 105 of 117 eligible patients who underwent real-time MRI and high-resolution manometry for GERD-like symptoms between 2015 and 2018 at a single center were retrospectively evaluated (male n = 57; female n = 48; mean age 52.5 ± 15.4 years). Real-time MRI was performed at a median investigation time of 15 min (1 frame/40 ms). On HRM, EGJ morphology was assessed according to the Chicago classification of esophageal motility disorders. Real-time MRI was performed at 3 T using highly undersampled radial fast low-angle shot acquisitions with NLINV image reconstruction. A 10 mL pineapple juice bolus served as oral contrast agent at supine position. Real-time MRI films of the EGJ were acquired during swallowing events and during Valsalva maneuver. Anatomic and functional MRI parameters were compared to EGJ morphology on HRM. Results: On HRM, n = 42 patients presented with EGJ type I (40.0%), n = 33 with EGJ type II (31.4%), and n = 30 with EGJ type III (28.6%). On real-time MRI, hiatal hernia was more common in patients with EGJ type III (66.7%) than in patients with EGJ type I (26.2%) and EGJ type II (30.3%; p < 0.001). Sliding hiatal hernia was more frequent in patients with EGJ type II (33.3%) than in patients with EGJ type III (16.7%) and EGJ type I (7.1%; p = 0.017). The mean esophagus–fundus angle of patients was 85 ± 31° at rest and increased to 101 ± 36° during Valsalva maneuver. Conclusion: Real-time MRI is a non-invasive imaging method for assessment of the esophagogastric junction. Real-time MRI can visualize dynamic changes of the EGJ during swallowing events. [ABSTRACT FROM AUTHOR]

Purpose: To develop an auto‐calibrated image reconstruction for highly accelerated multi‐directional phase‐contrast (PC) MRI that compensates for (1) reconstruction instabilities occurring for phase differences near ±π and (2) phase errors by concomitant magnetic fields that differ for individual radial spokes. Theory and Methods: A model‐based image reconstruction for real‐time PC MRI based on nonlinear inversion is extended to multi‐directional flow by exploiting multiple flow‐encodings for the estimation of velocity vectors. An initial smoothing constraint during iterative optimization is introduced to resolve the ambiguity of the solution space by penalizing phase wraps. Maxwell terms are considered as part of the signal model on a line‐by‐line basis to address phase errors by concomitant magnetic fields. The reconstruction methods are evaluated using simulated data and cross‐sectional imaging of a rotating‐disc, as well as in vivo for the aortic arch and cervical spinal canal at 3T. Results: Real‐time three‐directional velocity mapping in the aortic arch is achieved at 1.8 × 1.8 × 6 mm3 spatial and 60 ms temporal resolution. Artificial phase wraps are avoided in all cases using the smoothness constraint. Inter‐spoke differences of concomitant magnetic fields are effectively compensated for by the model‐based image reconstruction with integrated radial Maxwell correction. Conclusion: Velocity vector reconstructions based on nonlinear inversion allow for high degrees of radial data undersampling paving the way for multi‐directional PC MRI in real time. Whether a spoke‐wise treatment of Maxwell terms is required or a computationally cheaper frame‐wise approach depends on the individual application. [ABSTRACT FROM AUTHOR]

Real‐time magnetic resonance imaging (RT‐MRI) allows for imaging dynamic processes as they occur, without relying on any repetition or synchronization. This is made possible by modern MRI technology such as fast‐switching gradients and parallel imaging. It is compatible with many (but not all) MRI sequences, including spoiled gradient echo, balanced steady‐state free precession, and single‐shot rapid acquisition with relaxation enhancement. RT‐MRI has earned an important role in both diagnostic imaging and image guidance of invasive procedures. Its unique diagnostic value is prominent in areas of the body that undergo substantial and often irregular motion, such as the heart, gastrointestinal system, upper airway vocal tract, and joints. Its value in interventional procedure guidance is prominent for procedures that require multiple forms of soft‐tissue contrast, as well as flow information. In this review, we discuss the history of RT‐MRI, fundamental tradeoffs, enabling technology, established applications, and current trends. Level of Evidence: 5 Technical Efficacy Stage: 1 [ABSTRACT FROM AUTHOR]

Proton resonance frequency shift (PRFS) MR thermometry is the most common method used in clinical thermal treatments because of its fast acquisition and high sensitivity to temperature. However, motion is the biggest obstacle in PRFS MR thermometry for monitoring thermal treatment in moving organs. This challenge arises because of the introduction of phase errors into the PRFS calculation through multiple methods, such as image misregistration, susceptibility changes in the magnetic field, and intraframe motion during MRI acquisition. Various approaches for motion correction have been developed for real-time, motion-robust, and volumetric MR thermometry. However, current technologies have inherent trade-offs among volume coverage, processing time, and temperature accuracy. These tradeoffs should be considered and chosen according to the thermal treatment application. In hyperthermia treatment, precise temperature measurements are of increased importance rather than the requirement for exceedingly high temporal resolution. In contrast, ablation procedures require robust temporal resolution to accurately capture a rapid temperature rise. This paper presents a comprehensive review of current cutting-edge MRI techniques for motion-robust MR thermometry, and recommends which techniques are better suited for each thermal treatment. We expect that this study will help discern the selection of motion-robust MR thermometry strategies and inspire the development of motion-robust volumetric MR thermometry for practical use in clinics., (© 2024 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)

Transcutaneous auricular vagus nerve stimulation (taVNS) has been investigated regarding its therapeutic properties in several several conditions such as epilepsy, migraine and major depressive disorder and was shown to access similar neural pathways as invasive vagus nerve stimulation. While the vagus nerve's role in gut motility is physiologically established, the effect of taVNS has scarcely been investigated in humans and yielded conflicting results. Real-time gastric magnetic resonance imaging (rtMRI) is an established reproducible method to investigate gastric motility non-invasively. To investigate the influence of taVNS on gastric motility of healthy participants using rtMRI. We conducted a randomized, double-blind study using high-frequency (HF) stimulation at 25Hz or low-frequency (LF) taVNS at 1Hz after ingestions of a standardized meal in 57 healthy participants. The gastric motility index (GMI) was determined by measuring the amplitude and velocity of the peristaltic waves using rtMRI. After HF taVNS, GMI was significantly higher than after LF stimulation (p = 0.005), which was mainly attributable to a higher amplitude of the peristaltic waves (p = 0.003). We provide evidence that 4-h of taVNS influences gastric motility in healthy human participants for the first time using rtMRI. HF stimulation is associated with higher amplitudes of peristaltic waves in the gastric antrum compared to LF stimulation. Further studies are needed to investigate the effect of different frequencies of taVNS and its therapeutic properties in conditions with impaired gastric motility. • Transcutaneous vagus nerve stimulation influences gut motility on healthy subjects. • First use of real-time MRI in humans to asses the effect of taVNS on gut motility. • High frequency stimulation is associated with higher GMI than low frequency. [ABSTRACT FROM AUTHOR]

Purpose: To mitigate a common artifact in spiral real‐time MRI, caused by aliasing of signal outside the desired FOV. This artifact frequently occurs in midsagittal speech real‐time MRI. Methods: Simulations were performed to determine the likely origin of the artifact. Two methods to mitigate the artifact are proposed. The first approach, denoted as "large FOV" (LF), keeps an FOV that is large enough to include the artifact signal source during reconstruction. The second approach, denoted as "estimation‐subtraction" (ES), estimates the artifact signal source before subtracting a synthetic signal representing that source in multicoil k‐space raw data. Twenty‐five midsagittal speech‐production real‐time MRI data sets were used to evaluate both of the proposed methods. Reconstructions without and with corrections were evaluated by two expert readers using a 5‐level Likert scale assessing artifact severity. Reconstruction time was also compared. Results: The origin of the artifact was found to be a combination of gradient nonlinearity and imperfect anti‐aliasing in spiral sampling. The LF and ES methods were both able to substantially reduce the artifact, with an averaged qualitative score improvement of 1.25 and 1.35 Likert levels for LF correction and ES correction, respectively. Average reconstruction time without correction, with LF correction, and with ES correction were 160.69 ± 1.56, 526.43 ± 5.17, and 171.47 ± 1.71 ms/frame. Conclusion: Both proposed methods were able to reduce the spiral aliasing artifacts, with the ES‐reduction method being more effective and more time efficient. [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]

Cell therapy is an emerging approach to stroke treatment with a potential to limit brain damage and enhance its restoration after the acute phase of the disease. In this study we tested directly reprogrammed neural precursor cells (drNPC) derived from adult human bone marrow cells in the rat middle cerebral artery occlusion (MCAO) model of acute ischemic stroke using human placenta mesenchymal stem cells (pMSC) as a positive control with previously confirmed efficacy. Cells were infused into the ipsilateral (right) internal carotid artery of male Wistar rats 24 h after MCAO. The main goal of this work was to evaluate real-time distribution and subsequent homing of transplanted cells in the brain. This was achieved by performing intra-arterial infusion directly inside the MRI scanner and allowed transplanted cells tracing starting from their first pass through the brain vessels. Immediately after transplantation, cells were observed in the periphery of the infarct zone and in the brain stem, 15 min later small numbers of cells could be discovered deep in the infarct core and in the contralateral hemisphere, where drNPC were seen earlier and in greater numbers than pMSC. Transplanted cells in both groups could no longer be detected in the rat brain 48–72 h after infusion. Histological and histochemical analysis demonstrated that both the drNPC and pMSC were localized inside blood vessels in close contact with the vascular wall. No passage of labeled cells through the blood brain barrier was observed. Additionally, the therapeutic effects of drNPC and pMSC were compared. Both drNPC and pMSC induced substantial attenuation of neurological deficits evaluated at the 7th and 14th day after transplantation using the modified neurological severity score (mNSS). Some of the effects of drNPC and pMSC, such as the influence on the infarct volume and the survival rate of animals, differed. The results suggest a paracrine mechanism of the positive therapeutic effects of IA drNPC and pMSC infusion, potentially enhanced by the cell-cell interactions. Our data also indicate that the long-term homing of transplanted cells in the brain is not necessary for the brain’s functional recovery.

Cell therapy is an emerging approach to stroke treatment with a potential to limit brain damage and enhance its restoration after the acute phase of the disease. In this study we tested directly reprogrammed neural precursor cells (drNPC) derived from adult human bone marrow cells in the rat middle cerebral artery occlusion (MCAO) model of acute ischemic stroke using human placenta mesenchymal stem cells (pMSC) as a positive control with previously confirmed efficacy. Cells were infused into the ipsilateral (right) internal carotid artery of male Wistar rats 24 h after MCAO. The main goal of this work was to evaluate real-time distribution and subsequent homing of transplanted cells in the brain. This was achieved by performing intra-arterial infusion directly inside the MRI scanner and allowed transplanted cells tracing starting from their first pass through the brain vessels. Immediately after transplantation, cells were observed in the periphery of the infarct zone and in the brain stem, 15 min later small numbers of cells could be discovered deep in the infarct core and in the contralateral hemisphere, where drNPC were seen earlier and in greater numbers than pMSC. Transplanted cells in both groups could no longer be detected in the rat brain 48–72 h after infusion. Histological and histochemical analysis demonstrated that both the drNPC and pMSC were localized inside blood vessels in close contact with the vascular wall. No passage of labeled cells through the blood brain barrier was observed. Additionally, the therapeutic effects of drNPC and pMSC were compared. Both drNPC and pMSC induced substantial attenuation of neurological deficits evaluated at the 7th and 14th day after transplantation using the modified neurological severity score (mNSS). Some of the effects of drNPC and pMSC, such as the influence on the infarct volume and the survival rate of animals, differed. The results suggest a paracrine mechanism of the positive therapeutic effects of IA drNPC and pMSC infusion, potentially enhanced by the cell-cell interactions. Our data also indicate that the long-term homing of transplanted cells in the brain is not necessary for the brain's functional recovery. [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]

We present a method of using generalized additive mixed models (GAMMs) to analyze midsagittal vocal tract data obtained from real-time magnetic resonance imaging (rt-MRI) video of speech production. Applied to rt-MRI data, GAMMs allow for observation of factor effects on vocal tract shape throughout two key dimensions: time (vocal tract change over the temporal course of a speech segment) and space (location of change within the vocal tract). Examples of this method are provided for rt-MRI data collected at a temporal resolution of 20 ms and a spatial resolution of 1.41 mm, for 36 native speakers of German. The rt-MRI data were quantified as 28-point semi-polar-grid aperture functions. Three test cases are provided as a way of observing vocal tract differences between: (1) /aː/ and /iː/, (2) /aː/ and /aɪ/, and (3) accentuated and unstressed /aː/. The results for each GAMM are independently validated using functional linear mixed models (FLMMs) constructed from data obtained at 20% and 80% of the vowel interval. In each case, the two methods yield similar results. In light of the method similarities, we propose that GAMMs are a robust, powerful, and interpretable method of simultaneously analyzing both temporal and spatial effects in rt-MRI video of speech.

Abstract 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 (

Purpose: To develop and evaluate a fast and effective method for deblurring spiral real‐time MRI (RT‐MRI) using convolutional neural networks. Methods: We demonstrate a 3‐layer residual convolutional neural networks to correct image domain off‐resonance artifacts in speech production spiral RT‐MRI without the knowledge of field maps. The architecture is motivated by the traditional deblurring approaches. Spatially varying off‐resonance blur is synthetically generated by using discrete object approximation and field maps with data augmentation from a large database of 2D human speech production RT‐MRI. The effect of off‐resonance range, shift‐invariance of blur, and readout durations on deblurring performance are investigated. The proposed method is validated using synthetic and real data with longer readouts, quantitatively using image quality metrics and qualitatively via visual inspection, and with a comparison to conventional deblurring methods. Results: Deblurring performance was found superior to a current autocalibrated method for in vivo data and only slightly worse than an ideal reconstruction with perfect knowledge of the field map for synthetic test data. Convolutional neural networks deblurring made it possible to visualize articulator boundaries with readouts up to 8 ms at 1.5 T, which is 3‐fold longer than the current standard practice. The computation time was 12.3 ± 2.2 ms per frame, enabling low‐latency processing for RT‐MRI applications. Conclusion: Convolutional neural networks deblurring is a practical, efficient, and field map‐free approach for the deblurring of spiral RT‐MRI. In the context of speech production imaging, this can enable 1.7‐fold improvement in scan efficiency and the use of spiral readouts at higher field strengths such as 3 T. [ABSTRACT FROM AUTHOR]

Purpose: Accurate needle tracking provides essential information for MRI-guided percutaneous interventions. Passive needle tracking using MR images is challenged by variations of the needle-induced signal void feature in different situations. This work aimed to develop an automatic needle tracking algorithm for MRI-guided interventions based on the Mask Region Proposal-Based Convolutional Neural Network (R-CNN). Methods: Mask R-CNN was adapted and trained to segment the needle feature using 250 intra-procedural images from 85 MRI-guided prostate biopsy cases and 180 real-time images from MRI-guided needle insertion in ex vivo tissue. The segmentation masks were passed into the needle feature localization algorithm to extract the needle feature tip location and axis orientation. The proposed algorithm was tested using 208 intra-procedural images from 40 MRI-guided prostate biopsy cases, and 3 real-time MRI datasets in ex vivo tissue. The algorithm results were compared with human-annotated references. Results: In prostate datasets, the proposed algorithm achieved needle feature tip localization error with median Euclidean distance (dxy) of 0.71 mm and median difference in axis orientation angle (dθ) of 1.28°, respectively. In 3 real-time MRI datasets, the proposed algorithm achieved consistent dynamic needle feature tracking performance with processing time of 75 ms/image: (a) median dxy = 0.90 mm, median dθ = 1.53°; (b) median dxy = 1.31 mm, median dθ = 1.9°; (c) median dxy = 1.09 mm, median dθ = 0.91°. Conclusions: The proposed algorithm using Mask R-CNN can accurately track the needle feature tip and axis on MR images from in vivo intra-procedural prostate biopsy cases and ex vivo real-time MRI experiments with a range of different conditions. The algorithm achieved pixel-level tracking accuracy in real time and has potential to assist MRI-guided percutaneous interventions. [ABSTRACT FROM AUTHOR]

Objectives: To evaluate a novel method for real‐time tagged MRI with increased tag persistence using phase sensitive tagging (REALTAG), demonstrated for speech imaging. Methods: Tagging is applied as a brief interruption to a continuous real‐time spiral acquisition. REALTAG is implemented using a total tagging flip angle of 180° and a novel frame‐by‐frame phase sensitive reconstruction to remove smooth background phase while preserving the sign of the tag lines. Tag contrast‐to‐noise ratio of REALTAG and conventional tagging (total flip angle of 90°) is simulated and evaluated in vivo. The ability to extend tag persistence is tested during the production of vowel‐to‐vowel transitions by American English speakers. Results: REALTAG resulted in a doubling of contrast‐to‐noise ratio at each time point and increased tag persistence by more than 1.9‐fold. The tag persistence was 1150 ms with contrast‐to‐noise ratio >6 at 1.5T, providing 2 mm in‐plane resolution, 179 frames/s, with 72.6 ms temporal window width, and phase sensitive reconstruction. The new imaging window is able to capture internal tongue deformation over word‐to‐word transitions in natural speech production. Conclusion: Tag persistence is substantially increased in intermittently tagged real‐time MRI by using the improved REALTAG method. This makes it possible to capture longer motion patterns in the tongue, such as cross‐word vowel‐to‐vowel transitions, and provides a powerful new window to study tongue biomechanics. [ABSTRACT FROM AUTHOR]

Purpose: MRI‐guided cardiovascular intervention using standard metal guidewires can produce focal tissue heating caused by induced radiofrequency guidewire currents. It has been shown that safe operation is made possible by using parallel transmit radiofrequency coils driven in the null current mode, which does not induce radiofrequency currents and hence allows safe tissue visualization. We propose that the maximum current modes, usually considered unsafe, be used at very low power levels to visualize conductive wires, and we investigate pulse sequences best suited for this application. Methods: Spoiled gradient echo, balanced steady‐state free precession, and turbo spin echo sequences were evaluated for their ability to visualize a conductive guidewire embedded in a gel phantom when run in maximum current modes at very low power level. Temperature at the guidewire tip was monitored for safety assessment. Results: Excellent guidewire visualization could be achieved using maximum current modes excitation, with the turbo spin echo sequence giving the best image quality. Although turbo spin echo is usually considered to be a high‐power sequence, our method reduced all pulses to 1% amplitude (0.01% power), and heating was not detected. In addition, visualization of background tissue can be achieved using null current mode, also with no recorded heating at the guidewire tip even when running at 100% (reported) specific absorption rate. Conclusion: Parallel transmit is a promising approach for both guidewire and tissue visualization using maximum and null current modes, respectively, for interventional cardiac MRI. Such systems can switch excitation mode instantaneously, allowing for flexible integration into interactive sequences. [ABSTRACT FROM AUTHOR]

Purpose: To develop a rapid and motion‐robust technique for volumetric MRI, which is based on cross‐sectional real‐time MRI acquisitions with automatic advancement of the slice position. Methods: Real‐time MRI with a frame‐by‐frame moving cross‐section is performed with use of highly undersampled radial gradient‐echo sequences offering spin density, T1, or T2/T1 contrast. Joint reconstructions of serial images and coil sensitivity maps from spatially overlapping sections are accomplished by nonlinear inversion with regularization to the preceding section—formally identical to dynamic real‐time MRI. Shifting each frame by 20% to 25% of the section thickness ensures 75% to 80% overlap of successive sections. Acquisition times of 40 to 67 ms allow for rates of 15 to 25 sections per second, while volumes are defined by the number of cross‐sections times the section shift. Results: Preliminary realizations at 3T comprise studies of the human brain, carotid arteries, liver, and prostate. Typically, coverage of a 90‐ to 180‐mm volume at 0.8‐ to 1.2‐mm in‐plane resolution, 4‐ to 6‐mm section thickness, and 0.8‐ to 1.5‐mm section shift is accomplished within total measuring times of 4 to 6 seconds and a section speed of 15 to 37.5 mm per second. However, spatiotemporal resolution, contrast including options such as fat saturation and total measuring time are highly variable and may be adjusted to clinical needs. Promising volumetric applications range from fetal MRI to dynamic contrast‐enhanced MRI. Conclusion: The proposed method allows for rapid and motion‐robust volume coverage in a variety of imaging scenarios. [ABSTRACT FROM AUTHOR]

Recent MRI studies of blood flow in the inferior vena cava (IVC) resulted in findings which are inconsistent with earlier observations by invasive procedures – most likely because ECG‐gated MRI techniques are unable to resolve dynamic adjustments due to respiration. The purpose of this work was to apply real‐time phase‐contrast MRI at 50 ms resolution to re‐evaluate IVC flow in response to normal and deep breathing as well as breath holding and Valsalva maneuver (11 young healthy subjects). Real‐time flow MRI relied on highly undersampled radial gradient‐echo sequences and a model‐based nonlinear inverse reconstruction. A frequency analysis of the predominant pulsatility classified IVC flow in individual subjects as "cardiac", "respiratory" or "mixed" type. Peak flow velocities during free breathing ranged from 30 to 58 cm s−1, while flow rates varied from 15 to 37 ml s−1. The subject‐specific IVC flow pattern persists during deep breathing although the enhanced respiratory influence may shift subjects form "cardiac" to "mixed" or from "mixed" to "respiratory" type. Peak velocities increased relative to normal breathing but led to similar flow rates of 16 to 34 ml s−1. Inspiration during deep breathing elicited brief periods of flow reversal in all subjects with mean peak velocities of −21 cm s−1. The observation of only mildly flattened parabolic velocity distributions within the IVC indicated mostly laminar flow. Breath holding reduced blood flow velocities and rates by more than 40% on average, while Valsalva maneuvers completely abolished venous return. In conclusion, IVC blood flow is dominated by the acquired respiratory behavior of individual subjects and its pressure‐induced alterations relative to cardiac pulsation. The responses to breath holding and Valsalva maneuver are in full agreement with previous invasive observations of reduced or even ceased flow, respectively. [ABSTRACT FROM AUTHOR]

Motion of the target during radiotherapy negatively impacts the effectiveness and can cause damage to nearby tissue. MRI offers great soft-tissue contrast to visualize the target but its long acquisition time requires high undersampling of k-space to monitor this motion in real time. This typically limits the achievable latency even though every saved millisecond can increase the effectiveness of the treatment. In this study, a recurrent neural network (RNN) is used to continuously estimate motion directly from incoming k-space data. A golden-angle radial k-space trajectory continuously scans the target region and feeds the acquired data spoke-by-spoke into the RNN. Skipping image reconstruction and focusing only on the motion in the data allows for very fast motion monitoring in the order of milliseconds. To improve network training and generalization, different amounts of peripheral values are removed from the k-space spokes during preprocessing. To train and evaluate the network, 2D MRI motion datasets with different motion characteristics were generated by synthetically transforming slices of 25 MRI head scans. The RNN takes less than a millisecond to accurately estimate motion. By keeping only the inner 10% of each spoke, a mean rotational error of 0. 37 ° and a mean translational error of 0.26 mm are achieved. No patient-specific preparation or retraining is necessary. The network gives very fast motion estimations with sub-millimeter accuracy. The results demonstrate the feasibility of this approach and provide the groundwork to further reduce latency in real-time motion monitoring systems for radiotherapy without sacrificing accuracy. • Continuous motion estimation in MRI using an RNN and a golden-angle trajectory. • Improved generalization by only considering central k-space data. • Very low latency of less than a millisecond while keeping sub-millimeter accuracy. • No patient-specific training or periodic motion pattern requirement. [ABSTRACT FROM AUTHOR]

Abstract 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 NCT02739087 registered February 17, 2016

Abstract 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