MR Safety of Inductively Coupled and Conventional Intraoral Coils.

Purpose: Intraoral coils (IOCs) in magnetic resonance imaging (MRI) significantly improve the signal-to-noise ratio compared with conventional extraoral coils. To assess the safety of IOCs, we propose a 2-step procedure to evaluate radiofrequency-induced heating of IOCs and compare maximum temperature increases in 3 different types of IOCs.

Methods: The 2-step safety assessment consists of electric field measurements and simulations to identify local hotspots followed by temperature measurements during MRI.

An Accelerated PETALUTE MRI Sequence for In Vivo Quantification of Sodium Content in Human Articular Cartilage at 3T.

In this work, we demonstrate the sodium magnetic resonance imaging (MRI) capabilities of a three-dimensional (3D) dual-echo ultrashort echo time (UTE) sequence with a novel rosette petal trajectory (PETALUTE), in comparison to the 3D density-adapted (DA) radial spokes UTE sequence. We scanned five healthy subjects using a 3D dual-echo PETALUTE acquisition and two comparable implementations of 3D DA-radial spokes acquisitions, one matching the number of k-space projections (Radial-Matched Trajectories) and the other matching the total number of samples (Radial-Matched Samples) acquired in k-space. The PETALUTE acquisition enabled equivalent sodium quantification in articular cartilage volumes of interest (168.

Quantification of regional CMRO in human brain using dynamic O-MRI at 3T.

Objective: To investigate the feasibility of cerebral metabolic rate of oxygen consumption (CMRO) measurements with MRI at 3 Tesla in different brain regions.

Methods: CMRO represents a key indicator of the physiological state of brain tissue. Dynamic O-MRI with inhalation of isotopically enriched O gas has been used to quantify global CMRO in brain white (WM) and gray matter (GM).

An improved intraoral transverse loop coil design for high-resolution dental MRI.

Purpose: To improve intraoral transverse loop coil design for high-resolution dental MRI.

Methods: The transverse intraoral loop coil (tLoop) was modified (mtLoop) by overlapping the feed port conductors, bending the posterior section, introducing a parallel plate capacitor, optimizing the insulation thickness, and using it in receive-only mode. In addition, an MR-silent insulation was introduced.

RF-induced heating of interventional devices at 23.66 MHz.

Objective: Low-field MRI systems are expected to cause less RF heating in conventional interventional devices due to lower Larmor frequency. We systematically evaluate RF-induced heating of commonly used intravascular devices at the Larmor frequency of a 0.55 T system (23.

High-resolution 3D ultra-short echo time MRI with Rosette k-space pattern for brain iron content mapping.

Background: The iron concentration increases during normal brain development and is identified as a risk factor for many neurodegenerative diseases, it is vital to monitor iron content in the brain non-invasively.

Purpose: This study aimed to quantify in vivo brain iron concentration with a 3D rosette-based ultra-short echo time (UTE) magnetic resonance imaging (MRI) sequence.

Methods: A cylindrical phantom containing nine vials of different iron concentrations (iron (II) chloride) from 0.

Quantifying myocardial perfusion during MR-guided interventions without exogenous contrast agents: intra-arterial spin labeling.

Purpose: To test intra-arterial spin labeling (iASL) using active guiding catheters for myocardial perfusion measurements during magnetic resonance (MR)-guided interventions in a pig study.

Methods: In this work, a single-loop radiofrequency (RF) coil at the tip of a 6F active coronary catheter was used as a transmit coil for local spin labeling. The transmit magnetic RF field (B) of the coil and the labeling efficiency were determined, and iASL was tested in two pigs after the catheter was engaged in the aortic root, the ostium of the left coronary artery (LCA) under MR-guidance.

Differences of respiratory kinematics in female and male singers - A comparative study using dynamic magnetic resonance imaging.

Breath control is an important factor for singing voice production, but pedagogic descriptions of how a beneficial movement pattern should be performed vary widely and the underlying physiological processes are not understood in detail. Differences in respiratory movements during singing might be related to the sex of the singer. To study sex-related differences in respiratory kinematics during phonation, 12 singers (six male and six female) trained in the Western classical singing tradition were imaged with dynamic magnetic resonance imaging.

Characterizing Off-center MRI with ZTE.

Purpose: To maximize acquisition bandwidth in zero echo time (ZTE) sequences, readout gradients are already switched on during the RF pulse, creating unwanted slice selectivity. The resulting image distortions are amplified especially when the anatomy of interest is not located at the isocenter. We aim to characterize off-center ZTE MRI of extremities such as the shoulder, knee, and hip, adjusting the carrier frequency of the RF pulse excitation for each TR.

Scalable and modular 8-channel transmit and 8-channel flexible receive coil array for F MRI of large animals.

Purpose: To introduce an RF coil system consisting of an 8-channel transmit (Tx) and 8-channel receive (Rx) coil arrays for F MRI of large animals.

Methods: The Tx efficiency and homogeneity of the 8-element loop coil array (loop size: 6 × 15 cm ) were simulated for two different pig models rendered from MR images. An 8-channel Rx coil array consisting of a flexible 6-channel posterior and a 2-channel planar anterior array was designed to fit on the abdomen of an average-sized pig in supine position.

Ultra-short T components imaging of the whole brain using 3D dual-echo UTE MRI with rosette k-space pattern.

Purpose: This study aimed to develop a new 3D dual-echo rosette k-space trajectory, specifically designed for UTE MRI applications. The imaging of the ultra-short transverse relaxation time (uT ) of brain was acquired to test the performance of the proposed UTE sequence.

Theory And Methods: The rosette trajectory was developed based on rotations of a "petal-like" pattern in the k -k plane, with oscillated extensions in the k -direction for 3D coverage.

Single point imaging with radial acquisition and compressed sensing.

Purpose: To accelerate the Pointwise Encoding Time Reduction with Radial Acquisition (PETRA) sequence using compressed sensing while preserving the image quality for high-resolution MRI of tissue with ultra-short values.

Methods: Compressed sensing was introduced in the PETRA sequence (csPETRA) to accelerate the time-consuming single point acquisition of the k-space center data. Random undersampling was applied to achieve acceleration factors up to Acc = 32.

The influence of gravity on respiratory kinematics during phonation measured by dynamic magnetic resonance imaging.

Respiratory kinematics are important for the regulation of voice production. Dynamic MRI is an excellent tool to study respiratory motion providing high-resolution cross-sectional images. Unfortunately, in clinical MRI systems images can only be acquired in a horizontal subject position, which does not take into account gravitational effects on the respiratory apparatus.

Sub-millisecond 2D MRI of the vocal fold oscillation using single-point imaging with rapid encoding.

Objective: The slow spatial encoding of MRI has precluded its application to rapid physiologic motion in the past. The purpose of this study is to introduce a new fast acquisition method and to demonstrate feasibility of encoding rapid two-dimensional motion of human vocal folds with sub-millisecond resolution.

Method: In our previous work, we achieved high temporal resolution by applying a rapidly switched phase encoding gradient along the direction of motion.

Inductively Coupled Intraoral Flexible Coil for Increased Visibility of Dental Root Canals in Magnetic Resonance Imaging.

Objectives: Accurate visualization of dental root canals is vital for the correct diagnosis and subsequent treatment. This work assesses the improvement of a dedicated new coil for dental magnetic resonance imaging (MRI) in comparison to conventional ones in terms of signal-to-noise ratio (SNR) and visibility.

Materials And Methods: A newly developed intraoral flexible coil was used to display dental roots with MRI, and it provides improved sensitivity with a loop design and size adjusted to a single tooth anatomy.

Artifact quantification of venous stents in the MRI environment: Differences between braided and laser-cut designs.

Purpose: To quantify B- and B-induced imaging artifacts of braided venous stents and to compare the artifacts to a set of laser-cut stents used in venous interventions.

Methods: Three prototypes of braided venous stents with different geometries were tested in vitro. B field distortion maps were measured via the frequency shift Δf using multi-echo imaging.

Design of an Intraoral Dipole Antenna for Dental Applications.

Objective: In dental MRI, intraoral coils provide higher signal-to-noise ratio (SNR) than coils placed outside the mouth. This study aims to design an intraoral dipole antenna and demonstrates the feasibility of combining it with an extraoral coil.

Methods: Dipole antenna design was chosen over loop design, as it is open toward the distal; therefore, it does not restrain tongue movement.

Respiratory kinematics and the regulation of subglottic pressure for phonation of pitch jumps - a dynamic MRI study.

The respiratory system is a central part of voice production as it contributes to the generation of subglottic pressure, which has an impact on voice parameters including fundamental frequency and sound pressure level. Both parameters need to be adjusted precisely during complex phonation tasks such as singing. In particular, the underlying functions of the diaphragm and rib cage in relation to the phonation of pitch jumps are not yet understood in detail.

Catheter-based Arterial Input Function Determination for Myocardial Perfusion Measurements.

The quantification of myocardial perfusion with contrast agent (CA) tracers requires the precise knowledge of the arterial input function (AIF). In this study a method for MR-guided vascular interventions is evaluated that determines the AIF via an active tracking catheter during targeted CA injection. A phantom experiment with a dialysis filter was conducted to measure the AIF using an active catheter and a dynamic image series as reference.

Analysis of the RF Excitation of Endovascular Stents in Small Gap and Overlap Scenarios Using an Electro-Optical E-field Sensor.

Objective: To assess the effect of the electro-magnetic coupling of endovascular stents on their RF heating potential in MRI.

Methods: A custom-built electro-optic E-field probe is used to perform measurements of the scattered E-field at a distance of 2 mm to stent samples with submillimeter resolution. Various combinations of stent lengths are measured at 124 MHz (3T MRI Larmor frequency) with varying gap and overlap between the stents, with and without stent coating, and with distilled water and saline solution as surrounding media.

Magnetic Resonance Imaging of Venous Stents at 1.5 T: Susceptibility Artifacts and Radiofrequency Shielding.

Purpose: The aims of this study were to assess radiofrequency (RF) shielding and susceptibility-induced imaging artifacts of venous stents with different designs at 1.5 T and to analyze the relationship between stent designs, that is, cell geometry and RF shielding.

Methods: Twelve dedicated venous stents and 1 stent used for venous pathologies with 8 different designs from 5 different manufacturers were tested: Blueflow (plus medica, Düsseldorf, Germany), Sinus Obliquus, Sinus Venous, Sinus XL (Optimed, Ettlingen, Germany), Vici (Veniti, St.

MR safety watchdog for active catheters: Wireless impedance control with real-time feedback.

Purpose: To dynamically minimize radiofrequency (RF)-induced heating of an active catheter through an automatic change of the termination impedance.

Methods: A prototype wireless module was designed that modifies the input impedance of an active catheter to keep the temperature rise during MRI below a threshold, ΔT . The wireless module (MR safety watchdog; MRsWD) measures the local temperature at the catheter tip using either a built-in thermistor or external data from a fiber-optical thermometer.

Publisher Correction: Real-time magnetic resonance imaging - guided coronary intervention in a porcine model.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.