Standard Coil Research Articles

Volumetric wireless coil based on periodically coupled split-loop resonators for clinical wrist imaging.

Design and characterization of a new inductively driven wireless coil (WLC) for wrist imaging at 1.5 T with high homogeneity operating due to focusing the B1 field of a birdcage body coil. The WLC design has been proposed based on a volumetric self-resonant periodic structure of inductively coupled split-loop resonators with structural capacitance. The WLC was optimized and studied regarding radiofrequency fields and interaction to the birdcage coil (BC) by electromagnetic simulations. The manufactured WLC was characterized by on-bench measurements and in vivo and phantom study in comparison to a standard cable-connected receive-only coil. The WLC placed into BC gave the measured B1+ increase of the latter by 8.6 times for the same accepted power. The phantom and in vivo wrist imaging showed that the BC in receiving with the WLC inside reached equal or higher signal-to-noise ratio than the conventional clinical setup comprising the transmit-only BC and a commercial receive-only flex-coil and created no artifacts. Simulations and on-bench measurements proved safety in terms of specific absorption rate and reflected transmit power. The results showed that the proposed WLC could be an alternative to standard cable-connected receive coils in clinical magnetic resonance imaging. As an example, with no cable connection, the WLC allowed wrist imaging on a 1.5 T clinical machine using a full-body BC for transmitting and receive with the desired signal-to-noise ratio, image quality, and safety.

Distributed Diameter Subcoil Twisted Loop Antenna in Nonradiative WPT

This letter focuses on the high-frequency wireless power transfer by electromagnetic induction and its dependence on the lateral misalignment and tilt of the small receiving coil relative to the transmitting coil. We combine two structures, the twisted loop antenna (TLA) and subcoils of a distributed diameter coil (DDC) for transmitting designs. Our system is then referred to as TLA-DDC. The radius of the subcoils is parametrically varied for different distances between the coils and performed in two positions for each distance (coaxial position when the receiving coil is parallel to the plane of the transmitting coil, and center position for the perpendicular orientation of both coils). Then, using different radii for the transmitting DDC TLA when the receiving coil is moved onto its surface allows us to obtain a greater value of efficiency at different positions: up to 2.4 times for the peak value and 1.5 for the average value for receiving coil in parallel plane. The efficiency of the magnetic coupling is determined by means of power efficiency with a comparison between the DDC TLA antennas and a standard coil antenna corresponding to the same inductance value.

Application of surface coil in nuclear magnetic resonance studies of physical properties of quasi-2D materials.

We conduct a comprehensive set of tests of performance of surface coils used for nuclear magnetic resonance (NMR) study of quasi-2-dimensional samples. We report 115In and 31P NMR measurements on InP, semi-conducting thin substrate samples. Surface coils of both zig-zag meander-line and concentric spiral geometries were used. We compare reception sensitivity and signal-to-noise ratio of the NMR signal obtained by using surface-type coils to that obtained by standard solenoid-type coils. As expected, we find that surface-type coils provide better sensitivity for NMR study of thin film samples. Moreover, we compare the reception sensitivity of different types of the surface coils. We identify the optimal geometry of the surface coils for a given application and/or direction of the applied magnetic field.

Improved simultaneous multislice magnetic resonance imaging using total variation regularization**Project supported by the National Natural Science Foundation of China (Grant No. 61671026) and the Natural Science Foundation of Beijing, China (Grant No. 7162112).

Controlled aliasing in parallel imaging results in higher acceleration (CAIPIRINHA) for simultaneous multislice imaging has been proposed recently, which combines multiband excitation and phase cycling techniques to reduce scan time and improve subsequent imaging reconstruction. In this work, the total variation (TV) regularization method is used to further improve CAIPIRINHA. The TV regularization uses an edge-preserving prior, which establishes a relationship between neighboring pixels for image reconstruction. It reduces artifacts and suppresses noise amplification simultaneously. The results are presented with a standard eight-channel head coil with an acceleration factor of 4, where the TV-regularized CAIPIRINHA generates an improved reconstruction as compared with a typical nonregularized CAIPIRINHA.

Clinical utility of an endorectal MRI-guided prostate probe: preliminary examinations

Abstract Prostate cancer (PCa) is one of the most common cancer diseases in men in the western countries [1]. Besides the palpation, and the amount of prostate-specific-antigen’s (PSA) inside the blood, the current diagnostic imaging technologies are not appropriate. Early diagnosis defining the exact tumor location, spread and margins could make efficient targeted biopsies and image-guided surgery. A multimodal imaging technique containing a transmit-receive surface coil for anatomical MR imaging, a (S)PET detector module, consisting of silicon photomultipliers (SiPM), for functional imaging and an ultrasound (US) probe are placed as close as possible to the prostate designed as an endorectal tube to increase sensitivity and spatial resolution. All materials that are used are non-magnetic. Advantages of the SiPM are diversified, like non-sensitive to magnetic fields, higher gain (105–106) than standard avalanche photodiodes (APD), good timing properties and compactness. The PET detector should reach approximately 1mm3 spatial resolution together with 60ps FWHM Time-of-Flight resolution and a high efficiency to reduce scanning time and injected dose. A home-made transmit-receive coil surrounding the PET module improves signal-to-noise-ratio (SNR) with respect to standard coils will be present. The system will be used as a MRI-insert and be able to visualize anatomic and metabolic information together. The US-probe is guiding examination for correct overlapping of the multimodal images. This procedure will save time, costs and the need of co-registration. By combining all advantages of each system, it will necessarily update the non-invasive treatment of PCa. The system is adapted and tested to a 3 Tesla MR scanner called Trio A Tim system and Allegra system from the company Siemens healthcare with a larmor frequency of 123.2 MHz and an input of 50 Ω free from artifacts. First results on homogeneity of the transmit-receive coil will be presented. Preliminary measurements showing the proposed device is challenging but feasible.

Mapping the complex topological organization of the human parietal face area

The macaque monkey ventral intraparietal area (VIP) contains neurons with aligned visual-tactile receptive fields anchored to the face and upper body. Our previous fMRI studies using standard head coils found a human parietal face area (VIP+ complex; putative macaque VIP homologue) containing superimposed topological maps of the face and near-face visual space. Here, we construct high signal-to-noise surface coils and used phase-encoded air puffs and looming stimuli to map topological organization of the parietal face area at higher resolution. This area is consistently identified as a region extending between the superior postcentral sulcus and the upper bank of the anterior intraparietal sulcus (IPS), avoiding the fundus of IPS. Using smaller voxel sizes, our surface coils picked up strong fMRI signals in response to tactile and visual stimuli. By analyzing tactile and visual maps in our current and previous studies, we constructed a set of topological models illustrating commonalities and differences in map organization across subjects. The most consistent topological feature of the VIP+ complex is a central-anterior upper face (and upper visual field) representation adjoined by lower face (and lower visual field) representations ventrally (laterally) and/or dorsally (medially), potentially forming two subdivisions VIPv (ventral) and VIPd (dorsal). The lower visual field representations typically extend laterally into the anterior IPS to adjoin human area AIP, and medially to overlap with the parietal body areas at the superior parietal ridge. Significant individual variations are then illustrated to provide an accurate and comprehensive view of the topological organization of the parietal face area.

O17 Controlled stimulation of deep brain areas using navigated TMS with a standard coil

Introduction TMS has mainly been used- and is often believed to only be suitable for stimulation of superficial cortical areas. However, standard coils have also been used to target deeper volumes, alternatively specially designed coils have been developed for this purpose. We aimed to validate the use of standard coils for the stimulation of deep volumes. We used a system for navigated TMS where the stimulus induced electrical field strength in any location of the brain can be estimated. In the process, we also studied if the use of a midline parieto-occipital location as site for sham-stimulation could be justified. Methods Healthy adults were stimulated using a standard figure-of-eight coil in the Eximia system (Nexstim Ltd). The RMT for activation of the APB and AH muscles on the dominant side were defined. Four scalp locations were stimulated, each with three different intensities in relation to the RMTs: Three scalp locations with shortest Euclidian distance to dACC, insular and hippocampal cortices respectively, one location at the proposed site for sham-stimulation. Results All locations could be stimulated in all subjects. The intensity at the superficial cortical area under the coil, needed to produce sufficient (as compared to the RMTs) electrical field strengths at the deep locations dACC and insula were within a reasonable range (1.5–2 RMT), whereas hippocampal structures were not possible to stimulate using this set up. The sham stimulation location seems to be adequate in terms of not producing significant field strengths over motor cortices. Discussion If navigated stimulation and estimation of electrical field strengths are utilised, a standard TMS setup can be used to stimulate deep structures such as the dACC and insular cortex in a biologically reasonable fashion. A midline parieto-occipital location may be used as a locus for sham-stimulation in studies investigating motor cortex stimulation.

Decreased olfactory bulb volumes in patients with fibromyalgia syndrome.

Among the other symptoms, impaired olfactory function such as odor identification, threshold, and discrimination have been reported in patients with fibromyalgia syndrome (FMS). To investigate olfactory bulb (OB) volumes in FMS, by using magnetic resonance imaging (MRI), and to make reasonable suggestions are the goals of the present study. The study included 62 individuals as the FMS group (n=30) and the control group (n=32). MRI examinations were performed by a 1.5-T scanner and a standard head coil was used for the images. The coronal T2-weighted images were used for to measure OB volumes. Right, left, and total OB volumes were calculated with the aid of these images. The mean age of the FMS group was 44.2±8.3years and the control group was 41.7±3.53years. The mean volume of the right OB was 74.9±12.4mm3 in the FMS group and was 92.6±12.9mm3 in the control group. The mean value of the left OB volume was 74.3±10.8mm3 in the FMS group and 92.8±12.6mm3 in the control group. The mean of the total OB volume was 146.6±20.81mm3 in the FMS group and 186.5±23.5mm3 in the control group. Left, right, and total OB volumes were significantly lower in the FMS group than in the control group (all p<0.05). Female patients with FMS are under the risk of the decreased olfactory bulb volumes. This situation should be kept in mind for proper and reasonable management of this tough syndrome.

Diagnostic accuracy of high-resolution MRI as a method to predict potentially safe endoscopic and surgical planes in patients with early rectal cancer

IntroductionEarly rectal cancer (ERC) assessment should include prediction of the potential excision plane to safely remove lesions with clear deep margins and feasibility of organ preservation.MethodMRI accuracy for differentiating ≤T1sm2...

Robust EPI Nyquist ghost removal by incorporating phase error correction with sensitivity encoding (PEC-SENSE).

The existing approach of Nyquist ghost correction by parallel imaging in echo planar imaging (EPI) can suffer from image noise amplification. We propose a method that estimates a phase error map from multi-channel data itself and incorporates it into the sensitivity encoding (SENSE) reconstruction for Nyquist ghost correction without compromising the image SNR. This method first reconstructs two ghost-free images from positive and negative echoes using SENSE, respectively, from which the phase error map is computed. This map is then incorporated into the coil sensitivity maps for the negative echo image during the joint SENSE reconstruction of all k-space data to obtain the final ghost-free image. Phantom and in vivo EPI experiments at 7 T and 3 T were performed to evaluate the proposed method. Nyquist ghost was effectively removed in all images even under oblique imaging and poor eddy current conditions. Resulting image signal-to-noise ratio (SNR) was comparable to that by the traditional linear phase error correction method and higher than that by a previous SENSE-based parallel imaging correction approach. The proposed correction method can robustly eliminate Nyquist ghost while preserving the image SNR. This approach requires no additional calibration data beyond standard coil sensitivity maps and can be readily applied to all EPI applications. Magn Reson Med 79:943-951, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Heavy Prenatal Alcohol Exposure is Related to Smaller Corpus Callosum in Newborn MRI Scans.

Magnetic resonance imaging (MRI) studies have consistently demonstrated disproportionately smaller corpus callosa in individuals with a history of prenatal alcohol exposure (PAE) but have not previously examined the feasibility of detecting this effect in infants. Tissue segmentation of the newborn brain is challenging because analysis techniques developed for the adult brain are not directly transferable, and segmentation for cerebral morphometry is difficult in neonates, due to the latter's incomplete myelination. This study is the first to use volumetric structural MRI to investigate PAE effects in newborns using manual tracing and to examine the cross-sectional area of the corpus callosum (CC). Forty-three nonsedated infants born to 32 Cape Coloured heavy drinkers and 11 controls recruited prospectively during pregnancy were scanned using a custom-designed birdcage coil for infants, which increases signal-to-noise ratio almost 2-fold compared to the standard head coil. Alcohol use was ascertained prospectively during pregnancy, and fetal alcohol spectrum disorders diagnosis was conducted by expert dysmorphologists. Data were acquired using a multi-echo FLASH protocol adapted for newborns, and a knowledge-based procedure was used to hand-segment the neonatal brains. CC was disproportionately smaller in alcohol-exposed neonates than controls after controlling for intracranial volume. By contrast, CC area was unrelated to infant sex, gestational age, age at scan, or maternal smoking, marijuana, or methamphetamine use during pregnancy. Given that midline craniofacial anomalies have been recognized as a hallmark of fetal alcohol syndrome in humans and animal models since this syndrome was first identified, the CC deficit identified here in newborns may support early identification of a range of midline structural impairments. Smaller CC during the newborn period may provide an early indicator of fetal alcohol-related cognitive deficits that have been linked to this critically important brain structure in childhood and adolescence.

High-sensitivity TMS/fMRI of the Human Motor Cortex Using a Dedicated Multichannel MR Coil

PurposeTo validate a novel setup for concurrent TMS/fMRI in the human motor cortex based on a dedicated, ultra-thin, multichannel receive MR coil positioned between scalp and TMS system providing greatly enhanced sensitivity compared to the standard birdcage coil setting. MethodsA combined TMS/fMRI design was applied over the primary motor cortex based on 1Hz stimulation with stimulation levels of 80%, 90%, 100%, and 110% of the individual active motor threshold, respectively. Due to the use of a multichannel receive coil we were able to use multiband-accelerated (MB=2) EPI sequences for the acquisition of functional images. Data were analysed with SPM12 and BOLD-weighted signal intensity time courses were extracted in each subject from two local maxima (individual functional finger tapping localiser, fixed MNI coordinate of the hand knob) next to the hand area of the primary motor cortex (M1) and from the global maximum. ResultsWe report excellent image quality without noticeable signal dropouts or image distortions. Parameter estimates in the three peak voxels showed monotonically ascending activation levels over increasing stimulation intensities. Across all subjects, mean BOLD signal changes for 80%, 90%, 100%, 110% of the individual active motor threshold were 0.43%, 0.63%, 1.01%, 2.01% next to the individual functional finger tapping maximum, 0.73%, 0.91%, 1.34%, 2.21% next to the MNI-defined hand knob and 0.88%, 1.09%, 1.65%, 2.77% for the global maximum, respectively. ConclusionOur results show that the new setup for concurrent TMS/fMRI experiments using a dedicated MR coil array allows for high-sensitivity fMRI particularly at the site of stimulation. Contrary to the standard birdcage approach, the results also demonstrate that the new coil can be successfully used for multiband-accelerated EPI acquisition. The gain in flexibility due to the new coil can be easily combined with neuronavigation within the MR scanner to allow for accurate targeting in TMS/fMRI experiments.

Controlled stimulation of deep brain areas using navigated TMS with a standard coil

Introduction: TMS has mainly been used- and is often believed to only be suitable for stimulation of superficial cortical areas. However, standard coils have also been used to target deeper volumes, alternatively specially designed coils have been developed for this purpose. We aimed to validate the use of standard coils for the stimulation of deep volumes. We used a system for navigated TMS where the stimulus induced electrical field strength in any location of the brain can be estimated. In the process, we also studied if the use of a midline parieto-occipital location as site for sham-stimulation could be justified.

T033 Right prefrontal rTMS for the treatment of ADHD: Electrophysiological correlates and prognostic biomarkers

Background Reduced excitability of the right prefrontal cortex (rPFC) has been implicated in attention deficit/hyperactivity disorder (ADHD). Despite its high prevalence, chronic treatments for ADHD are not tolerable by many patients. Modulation of the rPFC with rTMS may become a novel treatment alternative. Methods Drug-free adults with ADHD (n = 53) received 15 daily sessions of high-frequency repetitive TMS directed to the rPFC, using either deep (H-6r, dTMS), standard (Figure-8, 8TMS), or sham coils. Standard ADHD questionnaires were administered, and EEG recordings were taken before, during, and after the first and the last days of treatment. In addition, EEG was recorded during a Stop Signal task (SST), following single TMS pulses over the rPFC, and during the treatment session itself. Additional comparison group of healthy subjects (n = 41) was recorded under the same conditions, but did not undergo the chronic rTMS treatment. Results At baseline, amplitudes of TMS evoked potential (TEP) and the SST’s N200 and P300 components, were significantly lower in subjects with ADHD than those of healthy controls. Moreover, the TEP and SST amplitudes correlated with ADHD symptoms and with the behavioral inhibition measures. Following treatment, improvement in ADHD total symptoms was only evident in the dTMS group. Moreover, TEP was enhanced following the first treatment session with either 8TMS or dTMS, but long-term cumulative enhancement was evident only in the dTMS group. Finally, specific EEG bands recorded at rest and during the first treatment session were highly correlated with dTMS outcomes; yielding a prognostic marker that explains 90% of variance in therapeutic outcome. Discussion These findings suggest that 3 weeks high frequency dTMS treatment can serve as a novel treatment for ADHD in adults, possibly by enhancing excitability of the rPFC. Furthermore, electrophysiological activity elicited during the first treatment session can serve as a high quality prognostic marker. This predictor may promote superior treatment response rates under proper selection of patients and is a first step towards the development of personalized dTMS treatment.

1H- and 31P-myocardial magnetic resonance spectroscopy in non-obstructive hypertrophic cardiomyopathy patients and competitive athletes.

The clinical differentiation between athlete's heart and mild forms of non-obstructive hypertrophic cardiomyopathy (HCM) is crucial. We hypothesized that differences do exist between the myocardial metabolism of patients with non-obstructive HCM and competitive athletes (CAs). Our aim was to evaluate myocardial metabolism with 31P-MRS and 1H-MRS in HCM patients and CAs. After Ethics Committee approval, 15 CAs and 7 HCM patients were prospectively enrolled. They underwent a 1.5-T cardiac MR including electrocardiographically triggered cine images, single-voxel 1H-MRS and multivoxel 31P-MRS. 1H-MRS was performed after imaging using standard coil with the patient in the supine position; thereafter, 31P-MRS was performed using a dedicated coil, in the prone position. Data were reported as median and interquartile range. Mann-Whitney U test was used. In CAs, left ventricular mass index was 72 (66-83)g/m2, septal thickness 10 (10-11)mm, end diastolic volume index 95 (85-102)ml/m2, end systolic volume index 30 (28-32)ml/m2 and ejection fraction 68% (65-69%); in HCM patients, 81 (76-111)g/m2 (P=0.052), 18 (15-21)mm (P=0.003), 73 (58-76)ml/m2 (P=0.029), 20 (16-34)ml/m2 (P=0.274) and 68% (55-73%) (P=1.000), respectively. At 1H-MRS, total lipids were 35 (0-183) arbitrary units (au) for CA and 763 (155-1994) au for HCM patients (P=0.046). At 31P-MRS, PCr/γATP was 5 (4-6) au for CA and 4 (2-5) au for HCM patients (P=0.230). Examination time was 20min for imaging only, 5min for 1H-MRS and 15min for 31P-MRS. We observed a significant increase of myocardial lipids, but a preserved PCr/γATP ratio in the metabolism of HCM patients compared with competitive CAs.

Diffusion Tensor Imaging for Glioma Grading: Analysis of Fiber Density Index.

Introduction:The most common primary tumors of brain are gliomas and tumor grading is essential for designing proper treatment strategies. The gold standard choice to determine grade of glial tumor is biopsy which is an invasive method. The purpose of this study was to investigate the role of fiber density index (FDi) by means of diffusion tensor imaging (DTI) (as a noninvasive method) in glial tumor grading.Methods:A group of 20 patients with histologically confirmed diagnosis of gliomas were evaluated in this study. We used a 1.5 Tesla MR system (AVANTO; Siemens, Germany) with a standard head coil for scanning. Multidirectional diffusion weighted imaging (measured in 12 noncollinear directions), and T1 weighted nonenhanced were performed for all patients. We defined two regions of interest (ROIs); 1) White matter fibers near the tumor and 2) Similar fibers in the contralateral hemisphere.Results:FDi of the low-grade gliomas was higher than those of high-grade gliomas, which was significant (P=0.017). FDi ratio (ratio of fiber density in vicinity of the tumor to homologous fiber tracts in the contralateral hemisphere) is higher in low-grade than high-grade tumors, (P=0.05). In addition, we performed ROC (receiver operating characteristic) curve and the area under curve (AUC) was 0.813(P=0.013).Conclusion:Our findings prove significant difference in FDi near by low-grade and high-grade gliomas. Therefore, FDi values and ratios are helpful in glial tumor grading.

The effect of quality control on the function of magnetic resonance imaging (MRI), using American College of Radiology (ACR) phantom

ObjectiveTo study image quality of MRI scanner using the American College of Radiology (ACR) phantom. Material and methodsImage quality of 1.5T MRI scanner was tested using ACR phantom. A standard head coil with standard restraints was used to fix the phantom head position. The phantom included seven modules for measuring MRI scanner image quality. MRI images for each module were analyzed. ResultsFor the Geometric accuracy test the inside length of the phantom was 146mm and the inside diameter was 189.4mm. For the High-contrast spatial resolution, individual small bright spots on the image were three pairs of hole arrays and were distinguishable. For the slice thickness test, the top signal ramp length was 54.4mm and bottom signal ramp length was 54.8mm so the slice thickness was 5.46mm. For the slice position accuracy, the bar length differences of intensity uniformity a value, called percent integral uniformity (PIU), was 96.15%. For the percent-signal ghosting, ghosting ratio was 0.0002. For the low contrast object detectability, the sum of numbers of complete spokes scored was 30 spokes. ConclusionsImage quality tests were very important in acceptance of any MRI scanner after installation and during maintenance. Using ACR phantom, these tests approve that the image parameters are acceptable.

Spherical and Improved Helmholtz Coil with High B&lt;sub&gt;1&lt;/sub&gt; Homogeneity for Magnetic Resonance Imaging

Several types of volume RF coils such as Helmholtz pair have been used for Magnetic Resonance Imaging. However, the field uniformity of a coil has always been suffering from a critical issue in imaging accuracy. The presented work is a study and design of spherical and improved radiofrequency Helmholtz coil which produces a high B1 magnetic field homogeneity. This coil is composed of four coaxial rings of wire, which are symmetrically located on a spherical surface. Each two rings on the same side have the same tuning capacitor. In contrast with the standard Helmholtz pair, which is of 2nd-order magnetic field homogeneity, the proposed coil provides fourth-order magnetic field homogeneity. The developed spherical structure is tested experimentally in free space and compared with results obtained with equivalent standard Helmholtz coil. The results lead to conclude that the proposed structure provides better B1 Homogeneity than the Standard Helmholtz type coil. Thus, the relative width at 1% of the profile is 1.37 times greater for the spherical Helmholtz coil. Similarly, the spherical Helmholtz coil has shown to have an increased efficiency and quality factor is of great interest.

A 32-channel coil system for MR vessel wall imaging of intracranial and extracranial arteries at 3T

PurposeTo develop a RF coil system for joint imaging of intracranial and extracranial arterial vessel wall at 3T. Materials and methodThe coil system consists of a 24-channel head coil combined with an 8-channel carotid coil. It is compared with a standard coil configuration (12-channel head coil+4-channel neck coil+8-channel carotid coil) for SNR and g-factors in phantoms and healthy volunteers. The clinical relevance of the proposed coil system is also evaluated in patients. ResultsIn phantom experiments, the SNR of the proposed coil system is 53% higher than the maximum SNR of the standard coil configuration at the center of the phantom which usually corresponds to the intracranial region of the head. The g-factors of the proposed coil system in the sagittal plane are lower than the standard coil configuration (by 10.8% and 26.6% for R=2 and 4 respectively) in the same experiment. In healthy volunteer experiments, 55% of the pixels have SNR above 100 for the proposed coil system, which is 33% more than that of the standard coil configuration. The maximum g-factors in the standard configuration are higher than those from the new coil design by 12% at R=2 and up to 36% at R=4 in the sagittal plane. In patients, in-vivo intracranial and extracranial arterial wall images at an isotropic spatial resolution of 0.6mm can be acquired using the proposed coil system. Plaques are well depicted from the images. ConclusionsThe performance of the proposed coil set is superior to the standard coil configuration, providing high SNR, low g-factor and good spatial coverage needed for simultaneous high resolution imaging of intracranial and extracranial arterial walls. Images acquired in 7.6min using the proposed coil system can achieve an isotropic spatial resolution of 0.6mm and can be used to depict plaques on the intracranial and extracranial arterial walls in patients.

Real-time MRI of the temporomandibular joint at 15 frames per second—A feasibility study

The purpose of this study was to develop and evaluate a novel method for real-time MRI of TMJ function at high temporal resolution and with two different contrasts. Real-time MRI was based on undersampled radial fast low angle shot (FLASH) acquisitions with iterative image reconstruction by regularized nonlinear inversion. Real-time MRI movies with T1 contrast were obtained with use of a radiofrequency-spoiled FLASH sequence, while movies with T2/T1 contrast employed a gradient-refocused FLASH version. TMJ function was characterized in 40 randomly selected volunteers by sequential 20s acquisitions of both the right and left joint during voluntary opening and closing of the mouth (in a medial, central and lateral oblique sagittal section perpendicular to the long axis of the condylar head). All studies were performed on a commercial MRI system at 3T using the standard head coil, while online reconstruction was achieved with a bypass computer fully integrated into the MRI system. As a first result, real-time MRI studies of the right and left TMJ were successfully performed in all 40 subjects (80 joints) within a total examination time per subject of only 15min. Secondly, at an in-plane resolution of 0.75mm and 5mm section thickness, the achieved temporal resolution was 66.7ms per image or 15 frames per second. Thirdly, both T1-weighted and T2/T1-weighted real-time MRI movies provided information about TMJ function such as disc position, condyle mobility and disc-condyle relationship. While T1 contrast offers a better delineation of structures during rapid jaw movements, T2/T1 contrast was rated superior for characterizing the articular disc. In conclusion, the proposed real-time MRI method may become a robust and efficient tool for the clinical assessment of TMJ function.