3D ultrasound guidance for radiofrequency ablation in an anthropomorphic thyroid nodule phantom.

Background: The use of two-dimensional (2D) ultrasound for guiding radiofrequency ablation (RFA) of benign thyroid nodules presents limitations, including the inability to monitor the entire treatment volume and operator dependency in electrode positioning. We compared three-dimensional (3D)-guided RFA using a matrix ultrasound transducer with conventional 2D-ultrasound guidance in an anthropomorphic thyroid nodule phantom incorporated additionally with temperature-sensitive albumin.

Methods: Twenty-four phantoms with 48 nodules were constructed and ablated by an experienced radiologist using either 2D- or 3D-ultrasound guidance.

Navigated intraoperative ultrasound in pediatric brain tumors.

Purpose: The aim of this study was to evaluate the diagnostic value and accuracy of navigated intraoperative ultrasound (iUS) in pediatric oncological neurosurgery as compared to intraoperative magnetic resonance imaging (iMRI).

Methods: A total of 24 pediatric patients undergoing tumor debulking surgery with iUS, iMRI, and neuronavigation were included in this study. Prospective acquisition of iUS images was done at two time points during the surgical procedure: (1) before resection for tumor visualization and (2) after resection for residual tumor assessment.

Flexible metasurface for improving brain imaging at 7T.

Purpose: Ultra-high field MRI offers unprecedented detail for noninvasive visualization of the human brain. However, brain imaging is challenging at 7T due to the B field inhomogeneity, which results in signal intensity drops in temporal lobes and a bright region in the brain center. This study aims to evaluate using a metasurface to improve brain imaging at 7T and simplify the investigative workflow.

The Development and External Validation of Artificial Intelligence-Driven MRI-Based Models to Improve Prediction of Lesion-Specific Extraprostatic Extension in Patients with Prostate Cancer.

Adequate detection of the histopathological extraprostatic extension (EPE) of prostate cancer (PCa) remains a challenge using conventional radiomics on 3 Tesla multiparametric magnetic resonance imaging (3T mpMRI). This study focuses on the assessment of artificial intelligence (AI)-driven models with innovative MRI radiomics in predicting EPE of prostate cancer (PCa) at a lesion-specific level. With a dataset encompassing 994 lesions from 794 PCa patients who underwent robot-assisted radical prostatectomy (RARP) at two Dutch hospitals, the study establishes and validates three classification models.

Deep learning for automated contouring of neurovascular structures on magnetic resonance imaging for prostate cancer patients.

Background And Purpose: Manual contouring of neurovascular structures on prostate magnetic resonance imaging (MRI) is labor-intensive and prone to considerable interrater disagreement. Our aim is to contour neurovascular structures automatically on prostate MRI by deep learning (DL) to improve workflow and interrater agreement.

Materials And Methods: Segmentation of neurovascular structures was performed on pre-treatment 3.

Radiofrequency safety of high permittivity pads in MRI-Impact of insulation material.

Purpose: High permittivity dielectric pads are known to be effective for tailoring the RF field and improving image quality in high field MRI. Despite a number of studies reporting benign specific absorption rate (SAR) effects, their "universal" safety remains an open concern. In this work, we evaluate the impact of the insulation material in between the pad and the body, using both RF simulations as well as phantom experiments.

Personalized local SAR prediction for parallel transmit neuroimaging at 7T from a single T1-weighted dataset.

Purpose: Parallel RF transmission (PTx) is one of the key technologies enabling high quality imaging at ultra-high fields (≥7T). Compliance with regulatory limits on the local specific absorption rate (SAR) typically involves over-conservative safety margins to account for intersubject variability, which negatively affect the utilization of ultra-high field MR. In this work, we present a method to generate a subject-specific body model from a single T1-weighted dataset for personalized local SAR prediction in PTx neuroimaging at 7T.

Design and evaluation of a modular multimodality imaging phantom to simulate heterogeneous uptake and enhancement patterns for radiomic quantification in hybrid imaging: A feasibility study.

Background: Accuracy and precision assessment in radiomic features is important for the determination of their potential to characterize cancer lesions. In this regard, simulation of different imaging conditions using specialized phantoms is increasingly being investigated. In this study, the design and evaluation of a modular multimodality imaging phantom to simulate heterogeneous uptake and enhancement patterns for radiomics quantification in hybrid imaging is presented.

Optimal sequences and sequence parameters for GBCA-enhanced MRI of the glymphatic system: a systematic literature review.

Background: The glymphatic system (GS) is a recently discovered waste clearance system in the brain.

Purpose: To evaluate the most promising magnetic resonance imaging (MRI) sequence(s) and the most optimal sequence parameters for glymphatic MRI (gMRI) 4-24 h after administration of gadolinium-based contrast agent (GBCA).

Material And Methods: Multiple literature databases were systematically searched for articles regarding gMRI or MRI of the perilymph in the inner ear until 11 May 2020.

Accelerating implant RF safety assessment using a low-rank inverse update method.

Purpose: Patients who have medical metallic implants, e.g. orthopaedic implants and pacemakers, often cannot undergo an MRI exam.

3-D Contrast Source Inversion-Electrical Properties Tomography.

Contrast source inversion-electrical properties tomography (CSI-EPT) is an iterative reconstruction method to retrieve the electrical properties (EPs) of tissues from magnetic resonance data. The method is based on integral representations of the electromagnetic field and has been shown to allow EP reconstructions of small structures as well as tissue boundaries with compelling accuracy. However, to date, the CSI-EPT has been implemented for 2-D configurations only, which limits its applicability.

A simple head-sized phantom for realistic static and radiofrequency characterization at high fields.

Purpose: To demonstrate a simple head-sized phantom for realistic static and RF field characterization in high field systems.

Methods: The head-sized phantom was composed of an ellipsoidal compartment and a spherical cavity to mimic the nasal cavity. The phantom was filled with an aqueous solution of polyvinylpyrrolidone (PVP), to mimic the average dielectric properties of brain tissue.

Passive radiofrequency shimming in the thighs at 3 Tesla using high permittivity materials and body coil receive uniformity correction.

Purpose: To explore the effects of high permittivity dielectric pads on the transmit and receive characteristics of a 3 Tesla body coil centered at the thighs, and their implications on image uniformity in receive array applications.

Theory And Methods: Transmit and receive profiles of the body coil with and without dielectric pads were simulated and measured in healthy volunteers. Parallel imaging was performed using sensitivity encoding (SENSE) with and without pads.

The effect of high-permittivity pads on specific absorption rate in radiofrequency-shimmed dual-transmit cardiovascular magnetic resonance at 3T.

Background: Dual-channel transmit technology improves the image quality in cardiovascular magnetic resonance (CMR) at 3 T by reducing the degree of radiofrequency (RF) shading over the heart by using RF shimming. Further improvements in image quality have been shown on a dual-transmit system using high permittivity pads. The aim of this study is to investigate the transmit field (B 1 (+)) homogeneity and the specific absorption rate (SAR) using high permittivity pads as a function of the complete range of possible RF-shim settings in order to gauge the efficacy and safety of this approach.

Diffusion-prepared neurography of the brachial plexus with a large field-of-view at 3T.

Purpose: To study diffusion-prepared neurography optimized for a large field-of-view (FOV) to include the neck and both shoulders. In a large FOV poor homogeneity of the magnetic field (B0 ) often leads to poor image quality and possibly to poor diagnostic accuracy. The aim was therefore to find an optimal (combination of) shimming method(s) for diffusion-prepared neurography in a large FOV.

A theoretical approach based on electromagnetic scattering for analysing dielectric shimming in high-field MRI.

Purpose: In this study, we analyzed dielectric shimming by formulating it as an electromagnetic scattering problem using integral equations.

Methods: Three-dimensional simulations of the radiofrequency field in two configurations using different materials were analyzed in terms of induced currents and secondary fields. A two-dimensional integral equation method with different backgrounds was used to identify the underlying physical mechanisms.

Clinical applications of dual-channel transmit MRI: A review.

This article reviews the principle of dual-channel transmit MRI and highlights current clinical applications which are performed primarily at 3 Tesla. The main benefits of dual-channel transmit compared with single-transmit systems are the increased image contrast homogeneity and the decreased scanning time due to the more accurate local specific absorption ratio estimation, meaning that less conservative safety limits are needed. The dual-transmit approach has been particularly beneficial in body imaging applications, and is also promising in terms of cardiac, spine, and fetal imaging.

Ventricular B1 (+) perturbation at 7 T - real effect or measurement artifact?

The objective of this work was to explore the origin of local B1 (+) perturbations in the ventricles measured at 7 T. The B1 (+) field in the human brain was mapped using four different MRI techniques: dual refocusing echo acquisition mode (DREAM), actual flip-angle imaging (AFI), saturated double-angle method (SDAM) and Bloch-Siegert shift (BSS). Electromagnetic field simulations of B1 (+) were performed in male and female subject models to assess the dependence of the B1 (+) distribution on the dielectric properties of cerebrospinal fluid and subject anatomy.

High permittivity dielectric pads improve high spatial resolution magnetic resonance imaging of the inner ear at 7 T.

Objectives: The objective of this study was to evaluate the use of dielectric pads for improving high spatial resolution imaging of the inner ear at 7 T.

Materials And Methods: Two sets of dielectric pads were designed using electromagnetic simulations and implemented using a deuterated suspension of barium titanate. Their effect on transmit efficiency, contrast homogeneity, and diagnostic image quality was evaluated in vivo (N = 10).

High permittivity pads reduce specific absorption rate, improve B1 homogeneity, and increase contrast-to-noise ratio for functional cardiac MRI at 3 T.

Purpose: To improve image quality and reduce specific absorption rate in functional cardiac imaging at 3 T.

Methods: Two high permittivity dielectric pads on the anterior and posterior sides of the thorax were numerically designed and implemented using an aqueous suspension of barium titanate. The effects on the average transmit efficiency, B(1) homogeneity, reception sensitivity, and contrast-to-noise ratio were verified in vivo on a dual-transmit system with the body coil driven in conventional quadrature and radiofrequency-shimmed mode.

Quantitative assessment of the effects of high-permittivity pads in 7 Tesla MRI of the brain.

The use of high-permittivity materials has been shown to be an effective method for increasing transmit and receive sensitivity in areas of low-signal intensity in the brain at high field. Results in this article show that the use of these materials does not increase the intercoil coupling for a phased array receive coil, does not have any detrimental effects on the B(0) homogeneity within the brain, and does not affect the specific absorption rate distribution within the head. Areas of the brain close to the pads exhibit significant increases (>100%) in transmit field efficiency, but areas further away show a less pronounced (~10%) decrease due to the homogenization of the transmit field and the loss introduced by the dielectric pads.