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.

In vivo enhancement of calf MRI at 7 T via optimized flexible metasurfaces.

Purpose: Ultrahigh field (≥7 T) MRI is at the cutting edge of medical imaging, enabling enhanced spatial and spectral resolution as well as enhanced susceptibility contrast. However, transmit ( ) field inhomogeneity due to standing wave effects caused by the shortened RF wavelengths at 7 T is still a challenge to overcome. Novel hardware methods such as dielectric pads have been shown to improve the field inhomogeneity but are currently limited in their corrective effect by the range of high-permittivity materials available and have a fixed shelf life.

A review of recent developments and applications of high-permittivity dielectric shimming in magnetic resonance.

We present a review outlining the basic mechanism, background, recent technical developments, and clinical applications of aqueous dielectric padding in the field of MRI. Originally meant to be a temporary solution, it has gained traction as an effective method for correcting B inhomogeneities due to the unique properties of the calcium titanate and barium titanate perovskites used. Aqueous dielectric pads have used a variety of high-permittivity materials over the years to improve the quality of MRI acquisitions at 1.

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.

Electrical Properties Tomography: A Methodological Review.

Electrical properties tomography (EPT) is an imaging method that uses a magnetic resonance (MR) system to non-invasively determine the spatial distribution of the conductivity and permittivity of the imaged object. This manuscript starts by providing clear definitions about the data required for, and acquired in, EPT, followed by comprehensively formulating the physical equations underlying a large number of analytical EPT techniques. This thorough mathematical overview of EPT harmonizes several EPT techniques in a single type of formulation and gives insight into how they act on the data and what their data requirements are.

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.

A simulation study on the effect of optimized high permittivity materials on fetal imaging at 3T.

Purpose: One of the main concerns in fetal MRI is the radiofrequency power that is absorbed both by the mother and the fetus. Passive shimming using high permittivity materials in the form of "dielectric pads" has previously been shown to increase the efficiency and homogeneity in different applications, while reducing the specific absorption rate (SAR). In this work, we study the effect of optimized dielectric pads for 3 pregnant models.

Developments in Electrical-Property Tomography Based on the Contrast-Source Inversion Method.

The main objective of electrical-property tomography (EPT) is to retrieve dielectric tissue parameters from B ^ 1 + data as measured by a magnetic-resonance (MR) scanner. This is a so-called hybrid inverse problem in which data are defined inside the reconstruction domain of interest. In this paper, we discuss recent and new developments in EPT based on the contrast-source inversion (CSI) method.

High-permittivity pad design tool for 7T neuroimaging and 3T body imaging.

Purpose: High-permittivity materials in the form of flexible "dielectric pads" have proved very useful for addressing RF inhomogeneities in high field MRI systems. Finding the optimal design of such pads is, however, a tedious task, reducing the impact of this technique. We present an easy-to-use software tool which allows researchers and clinicians to design dielectric pads efficiently on standard computer systems, for 7T neuroimaging and 3T body imaging applications.

Studying neurons and glia non-invasively via anomalous subdiffusion of intracellular metabolites.

Cells in the central nervous system, neurons and glia, display a wide range of structural features. Molecular diffusion properties in the intracellular space of these cells reflect this structural diversity, deviating from standard Gaussian dynamics and resulting in anomalous subdiffusion. By tracking the displacement of intracellular metabolites, diffusion-weighted magnetic resonance spectroscopy allows for in vivo compartment-specific and cell-preferential morphological analysis of neurons and glia in the human brain.

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.

Improved image quality and reduced power deposition in the spine at 3 T using extremely high permittivity materials.

Purpose: To explore the effect of using extremely high permittivity (ε ∼1,000) materials on image quality and power requirements of spine imaging at 3 T.

Theory And Methods: A linear array of high permittivity dielectric blocks made of lead zirconate titanate (PZT) was designed and characterized by electromagnetic simulations and experiments. Their effect on the transmit efficiency, receive sensitivity, power deposition, and diagnostic image quality was analyzed in vivo in 10 healthy volunteers.

An Efficient Methodology for the Analysis of Dielectric Shimming Materials in Magnetic Resonance Imaging.

Interference effects in the transmit B field can severely degrade the image quality in high-field Magnetic Resonance Imaging (MRI). High-permittivity pads are increasingly used to counteract these effects, but designing such pads is not trivial. In this paper, we present an efficient solution methodology for this dielectric RF shimming problem.

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.