Orthopedic implants affect the electric field induced by switching gradients in MRI.

Purpose: To investigate whether the risk of peripheral nerve stimulation increases in the presence of bulky metallic prostheses implanted in a patient's body.

Methods: A computational tool was used to calculate the electric field (E-field) induced in a realistic human model due to the action of gradient fields. The calculations were performed both on the original version of the anatomical model and on a version modified through "virtual surgery" to incorporate knee, hip, and shoulder prostheses.

Nivolumab plus docetaxel in patients with chemotherapy-naïve metastatic castration-resistant prostate cancer: results from the phase II CheckMate 9KD trial.

Background: Docetaxel has immunostimulatory effects that may promote an immunoresponsive prostate tumour microenvironment, providing a rationale for combination with nivolumab (programmed death-1 inhibitor) for metastatic castration-resistant prostate cancer (mCRPC).

Methods: In the non-randomised, multicohort, global phase II CheckMate 9KD trial, 84 patients with chemotherapy-naive mCRPC, ongoing androgen deprivation therapy and ≤2 prior novel hormonal therapies (NHTs) received nivolumab 360 mg and docetaxel 75 mg/m every 3 weeks with prednisone 5 mg twice daily (≤10 cycles) and then nivolumab 480 mg every 4 weeks (≤2 years). The co-primary end-points were objective response rate (ORR) and prostate-specific antigen response rate (PSA-RR; ≥50% decrease from baseline).

Recurrence rate of localized prostate cancer after radical prostatectomy according to D'amico risk classification in a tertiary referral hospital: association study.

Objetivo: Determinar la tasa de recurrencia del cáncer de próstata localizado después de la prostatectomía radical según la clasificación D'Amico.

MÉtodos: Estudio de cohorte retrospectivo comparativo de 5 años. Se obtuvieron datos de registros clínicos de pacientes con cáncer de próstata localizado, que se sometieron a prostatectomía radical y se evaluó la tasa de recurrencia de la enfermedad.

Efficacy of the Endoscopic Combined Intrarenal Surgery for the Treatment of a Staghorn Calculus in Crossed Fused Renal Ectopia.

Crossed fused renal ectopia (CFRE) is an unusual anomaly in which both kidneys lie fused on one side, with double pelvis and ureters draining into both sides of the bladder. Complex renal stones are a considerable challenge to endourologists, and when a staghorn stone is associated with abnormal anatomy, its treatment is even more difficult. Today there is no consensus about the right treatment for complex renal stones in CFRE.

Intra-coil interactions in split gradient coils in a hybrid MRI-LINAC system.

An MRI-LINAC system combines a magnetic resonance imaging (MRI) system with a medical linear accelerator (LINAC) to provide image-guided radiotherapy for targeting tumors in real-time. In an MRI-LINAC system, a set of split gradient coils is employed to produce orthogonal gradient fields for spatial signal encoding. Owing to this unconventional gradient configuration, eddy currents induced by switching gradient coils on and off may be of particular concern.

Numerical prediction of temperature elevation induced around metallic hip prostheses by traditional, split, and uniplanar gradient coils.

Purpose: The paper presents a computational study for the estimation of the temperature elevation occurring in a human subject carrying metallic hip prostheses when exposed to the magnetic field produced by gradient coils.

Methods: The simulations are performed through validated numerical codes, which solve the electromagnetic and thermal equations applied to a high-resolution anatomical human model. Three different sets of gradient coils (traditional, split and uniplanar) are considered to evaluate the maximum steady-state temperature elevation in the human body.

Skin and proximity effects in the conductors of split gradient coils for a hybrid Linac-MRI scanner.

In magnetic resonance imaging (MRI), rapidly changing gradient fields are applied to encode the magnetic resonance signal with spatial position; however eddy currents are induced in the surrounding conducting structures depending on the geometry of the conductor and the excitation waveform. These alternating fields change the spatial profile of the current density within the coil track with the applied frequencies of the input waveform and by their proximity to other conductors. In this paper, the impact of the conductor width and the excited frequency over the parameters that characterise the performance of split transverse and longitudinal gradient coils are studied.

An analysis of the gradient-induced electric fields and current densities in human models when situated in a hybrid MRI-LINAC system.

MRI-LINAC is a new image-guided radiotherapy treatment system that combines magnetic resonance imaging (MRI) with a linear accelerator (LINAC) in a single unit. One drawback is that the pulsing of the split gradient coils of the system induces an electric field and currents in the patient which need to be predicted and evaluated for patient safety. In this novel numerical study the in situ electric fields and associated current densities were evaluated inside tissue-accurate male and female human voxel models when a number of different split-geometry gradient coils were operated.

Numerical safety study of currents induced in the patient during rotations in the static field produced by a hybrid MRI-LINAC system.

MRI-LINAC is a new image-guided radiotherapy treatment system that combines magnetic resonance imaging (MRI) and a linear particle accelerator (LINAC) into a single unit. Moving (i.e.

Multilayer integral method for simulation of eddy currents in thin volumes of arbitrary geometry produced by MRI gradient coils.

Purpose: This article aims to present a fast, efficient and accurate multi-layer integral method (MIM) for the evaluation of complex spatiotemporal eddy currents in nonmagnetic and thin volumes of irregular geometries induced by arbitrary arrangements of gradient coils.

Methods: The volume of interest is divided into a number of layers, wherein the thickness of each layer is assumed to be smaller than the skin depth and where one of the linear dimensions is much smaller than the remaining two dimensions. The diffusion equation of the current density is solved both in time-harmonic and transient domain.

Flanged-edge transverse gradient coil design for a hybrid LINAC-MRI system.

MRI can be combined with other systems, such as linear accelerators (LINACs) to provide image-guided therapy. However, in some configurations this requires splitting the MRI scanner to provide a central gap large enough to ensure dual access for the accelerator and the patient. This raises technical difficulties for maintaining a high gradient coil performance.

Simulation and analysis of the interactions between split gradient coils and a split magnet cryostat in an MRI-PET system.

Splitting a magnetic resonance imaging (MRI) magnet into two halves can provide a central region to accommodate other modalities, such as positron emission tomography (PET). This approach, however, produces challenges in the design of the gradient coils in terms of gradient performance and fabrication. In this paper, the impact of a central gap in a split MRI system was theoretically studied by analysing the performance of split, actively-shielded transverse gradient coils.

Minimax current density gradient coils: analysis of coil performance and heating.

Standard gradient coils are designed by minimizing the inductance or resistance for an acceptable level of gradient field nonlinearity. Recently, a new method was proposed to minimize the maximum value of the current density in a coil additionally. The stated aim of that method was to increase the minimum wire spacing and to reduce the peak temperature in a coil for fixed efficiency.

Simulation and analysis of split gradient coil performance in MRI.

Split magnet systems for hybrid imaging, such as positron emission tomography-magnetic resonance imaging (PET-MRI) and Radiotherapy-MRI, require gradient coils designed with similar shapes as their corresponding main magnet. This introduces challenges in the gradient coil design of good performance and manufacturing. In this paper the effect of the gap size in shielded transverse split gradient coils and split cryostat "warm" bore over the coil efficiency, shielding efficiency, wire spacing, cryostat ohmic power loss and mechanical vibration have been simulated and studied.

Eddy current simulation in thick cylinders of finite length induced by coils of arbitrary geometry.

Eddy currents are inevitably induced when time-varying magnetic field gradients interact with the metallic structures of a magnetic resonance imaging (MRI) scanner. The secondary magnetic field produced by this induced current degrades the spatial and temporal performance of the primary field generated by the gradient coils. Although this undesired effect can be minimized by using actively and/or passively shielded gradient coils and current pre-emphasis techniques, a residual eddy current still remains in the MRI scanner structure.

An improved equivalent magnetization current method applied to the design of local breast gradient coils.

Magnetic resonance imaging (MRI) is an important tool in the diagnosis of breast cancer. Increased gradient strengths and slew rates assist in terms of the potential to image with increased spatial and/or temporal resolution. Strong gradients also facilitate diffusion studies; one well-known method of increasing gradient strength is to design local gradient coils, those with reduced diameter where the gradient conductors are closer to the region of interest.

The equivalent magnetizing method applied to the design of gradient coils for MRI.

This paper presents a new method for the design of gradient coils for Magnetic Resonance Imaging systems. The method is based on the equivalence between a magnetized volume surrounded by a conducting surface and its equivalent representation in surface current/charge density. We demonstrate that the curl of the vertical magnetization induces a surface current density whose stream line defines the coil current pattern.