Endorectal surface coil MR imaging of prostatic carcinoma with the inversion-recovery sequence

The value of inversion-recovery (IR) sequences in the diagnosis and staging of prostatic carcinoma with magnetic resonance (MR) imaging was studied. Twenty-six patients with carcinoma of the prostate were imaged at 1.5 T with an endorectal surface coil and with a variety of IR sequences and a set of spin-echo (SE) sequences for comparison. Ex vivo prostate specimens were imaged again at the same field strength. The two images were correlated with histologic sections. Cancer was identified with MR imaging in 96% of patients. Of the tumors more than 4 mm in diameter, 87% were identified on T2-weighted SE images, whereas only 26% were identified on IR images. However, IR images may be more useful in local staging of carcinoma. Gross capsular infiltration was present in only two patients; however, it was detectable (and excluded in five other patients) by means of IR images. It was not detectable on SE images. The high quality of images obtained with the endorectal coil was confirmed. The authors conclude that addition of the IR sequence to MR imaging with the endorectal coil may improve the usefulness of this examination.     

Multicoil Dixon chemical species separation with an iterative least-squares estimation method.

This work describes a new approach to multipoint Dixon fat-water separation that is amenable to pulse sequences that require short echo time (TE) increments, such as steady-state free precession (SSFP) and fast spin-echo (FSE) imaging. Using an iterative linear least-squares method that decomposes water and fat images from source images acquired at short TE increments, images with a high signal-to-noise ratio (SNR) and uniform separation of water and fat are obtained. This algorithm extends to multicoil reconstruction with minimal additional complexity. Examples of single- and multicoil fat-water decompositions are shown from source images acquired at both 1.5T and 3.0T. Examples in the knee, ankle, pelvis, abdomen, and heart are shown, using FSE, SSFP, and spoiled gradient-echo (SPGR) pulse sequences. The algorithm was applied to systems with multiple chemical species, and an example of water-fat-silicone separation is shown. An analysis of the noise performance of this method is described, and methods to improve noise performance through multicoil acquisition and field map smoothing are discussed.     

TiN: A Suitable Coating for Defibrillator Electrodes?

The electrochemical behavior of porous TiN coating for defibrillator electrodes was investigated by in vitro studies. A commercially available Ti patch was compared with a Ti patch coated with a layer of porous TiN. Similarly, the influence of the TiN coating on a Pt/Ir intracardial electrode was tested. Porous TiN coatings were made by reactive sputtering on the plain electrodes. Electrode potential measurements were performed during monophasic anodic and cathodic defibrillator shocks delivering energies between 1 J and 49 J. Porous TiN coating of Pt/Ir coils was found suitable to deliver cathodal pulses, while a plain coil remains recommended for anodic shocks. TiN coating was of benefit for conventional Ti patches. Particularly, in the case of anodic shocks, the TiN layer protected the Ti-mesh from immediate oxidation. However, above 70 anodic shocks of 49 J, the TiN coating underwent oxidation to an oxynitride. An estimated 180 anodic shocks of 10 J could be delivered before TiN oxidation became measurable by increased polarization.     

Techniques for high-resolution MR imaging of atherosclerotic plaque

Atherosclerotic cardiovascular disease is the most common cause of death in the United States. Investigation of atherosclerotic plaque morphology and composition is important because the findings may be useful in predicting prognosis or response to therapy. This study presents high-resolution magnetic resonance (MR) imaging techniques developed on a 1.5-T whole-body imager with a custom-built surface coil, for characterizing the composition and morphology of plaque removed at carotid endarterectomy. The initial comparison of MR imaging and histologic results showed good correlation. In conjunction with MR angiography, these techniques could be used in in vivo imaging to define the size, location, and contents of atherosclerotic plaque at the carotid bifurcation.     

Chinese-made electrolytic detachable coil in the embolization of a dog aneurysmal model

Objective To develop a Chinese-made electrolytic detachable coil (CEDC) that would allow patients to enjoy the benefit of electrolytic detachable coil without having to rely on the expensive Guglielmi detachable coil (GDC), and to test the safety and efficiency of CEDC. Methods Radiopacity of the marker of the CEDC was tested. The anti-strain force of coils and connection points were measured. In vitro and in vivo electrolyses were conducted. We produced 21 aneurysm models including lateral, bifurcation, and terminal aneurysm models, and embolized 18 models with CEDC. Results Radiopacity of the marker was satisfactory. Anti-strain of the coil and the connection point have shown the safety and efficiency of CEDC. Electrolysis in vitro and vivo, was similar to that of GDC. 83% of the aneurysm models were completely occluded. Coils were found to induce thrombosis in the aneurysm cavity, and could lead to a new endothelium over the entrance of the aneurysm, with organized tissue replacing thrombosis in 2 months. Conclusions CEDC is as efficient and safe as GDC. The marker, the ability to induce thrombosis inside the sac and the growth of new endothelium over the orifice are very satisfactory.     

Detachable shape-memory sewing ring for heart valves

The novel sewing ring concept consists of a detachable ring snap connection between valve housing or stent and suture cuff. The suture cuff itself is a memory metal ring of nickel-titanium (NiTi) that is embedded within a textile fabric torus. After a special training program the ring can assume two geometric shapes when alternately cooled and heated. Due to this physical property, the sewing ring can be safely fixed within a groove of the housing or stent by changing between room and physiological temperature. This allows the surgeon first to implant the sewing ring followed by arbitrary positioning and final fixation of the valve by the shape-memory effect. Additional advantages are an increased stiffening of the valve base for minimizing potential leaflet dysfunction, and reduced time and risk of implantation, particularly when a reoperation is necessary.     

High‐permittivity solid ceramic resonators for high‐field human MRI

The properties of a ceramic‐based annular dielectric resonator designed for 7 T MRI have been examined. Electromagnetic simulations and experimentally determined modal frequencies agree to within ~1%. The dependence of the resonance frequency of the degenerate quadrature HEM₁₁ modes on hole diameter and shield diameter was also investigated. The constructed coil, with a 2.5 cm diameter hole, had an unloaded Q value of 400, which was reduced to 150 when loaded with a human finger. Simulated and experimental B₁⁺ maps show a high degree of homogeneity with a sensitivity of ~11.5 μT/√W at the centre. A comparison with a loop gap resonator showed an approximately 25% higher sensitivity for the dielectric resonator. High‐resolution images of the digital interphalangeal (DIP) and proximal interphalangeal (PIP) joints of volunteers were acquired in imaging times of less than 2 min. Finally, novel methods of double tuning such ceramic resonators to two relatively close frequencies, e.g. proton and fluorine, have been shown. Copyright © 2013 John Wiley & Sons, Ltd.     

A low‐cost,mechanically simple apparatus for measuring eddy current‐induced magnetic fields in MRI

The fidelity of gradient waveforms in MRI pulse sequences is essential to the acquisition of images and spectra with minimal distortion artefacts. Gradient waveforms can become nonideal when eddy currents are created in nearby conducting structures; however, the resultant magnetic fields can be characterised and compensated for by measuring the spatial and temporal field response following a gradient impulse. This can be accomplished using a grid of radiofrequency (RF) coils. The RF coils must adhere to strict performance requirements: they must achieve a high sensitivity and signal‐to‐noise ratio (SNR), have minimal susceptibility field gradients between the sample and surrounding material interfaces and be highly decoupled from each other. In this study, an apparatus is presented that accomplishes these tasks with a low‐cost, mechanically simple solution. The coil system consists of six transmit/receive RF coils immersed in a high‐molarity saline solution. The sensitivity and SNR following an excitation pulse are sufficiently high to allow accurate phase measurements during free‐induction decays; the intrinsic susceptibility matching of the materials, because of the unique design of the coil system, results in sufficiently narrow spectral line widths (mean of 19 Hz), and adjacent RF coils are highly decoupled (mean S₁₂ of ?47 dB). The temporal and spatial distributions of eddy currents following a gradient pulse are measured to validate the efficacy of the design, and the resultant amplitudes and time constants required for zeroth‐ and first‐order compensation are provided. Copyright © 2013 John Wiley & Sons, Ltd.     

Novel use of a modified Amplatzer Vascular Plug® to occlude a patent ductus arteriosus in two patients

We describe two cases in which a patent ductus arteriosus (PDA) was successfully occluded percutaneously, using the novel approach of prefilling an Amplatzer Vascular Plug® with embolization coils to decrease the risk of residual shunting through the device. One patient was a small premature neonate, and the other was a child with an aneurismal, tubular PDA with no aortic ampulla. These are situations in which more popular PDA devices such as the Amplatzer Duct Occluder® may be contraindicated. © 2008 Wiley‐Liss, Inc.