Waveguide Manufacturing Technologies for Next-Generation Millimeter-Wave Antennas.

Some recent waveguide-based antennas are presented in this paper, designed for the next generation of communication systems operating at the millimeter-wave band. The presented prototypes have been conceived to be manufactured using different state-of-the-art techniques, involving subtractive and additive approaches. All the designs have used the latest developments in the field of manufacturing to guarantee the required accuracy for operation at millimeter-wave frequencies, where tolerances are extremely tight. Different designs will be presented, including a monopulse antenna combining a comparator network, a mode converter, and a spline profile horn; a tunable phase shifter that is integrated into an array to implement reconfigurability of the main lobe direction; and a conformal array antenna. These prototypes were manufactured by diverse approaches taking into account the waveguide configuration, combining parts with high-precision milling, electrical discharge machining, direct metal laser sintering, or stereolithography with spray metallization, showing very competitive performances at the millimeter-wave band till 40 GHz.

The techniques of uniportal video-assisted thoracoscopic surgery: lower lobectomies and lymphadenectomy.

Uniportal video-assisted thoracoscopic surgery (VATS) is probably the most successful single-incision approach worldwide, probably secondary to several specific circumstances: multiportal VATS was hardly getting his recognition in the thoracic surgeon's community; the extraordinary effort by his creators and believers for developing the technique and giving massive diffusion; the subjective feeling by surgeons who performed the approach about its benefits and advantages. Despite this, many efforts have focused on extending new indications and describing variations of the original intercostal uniportal VATS, but few quality papers have analyzed the real impact of the approach and its real advantages or disadvantages comparing to multiportal VATS. Thus, many surgeons still feel little confidence on the approach and reject his performance. With the aim of standardizing the approach and the technical aspects for non-experienced or beginners, the Uniportal VATS Interest Group (UVIG) of the European Society of Thoracic Surgery (ESTS) decided to set the basis for homogenization of the technique to cement the development of high-level evidence works that shed light on the real outcomes of uniportal compared to multiportal VATS. This article describes the main specific technical aspects while performing lower lobectomies and lymphadenectomy, which were described as the most suitable cases for initiating the learning curve.

Tubeless major pulmonary resections.

From its inception, cutting edge minimally invasive thoracic surgery has pursued to barely produce patient perturbation. Although state of the art techniques such as uniportal approach have achieved a remarkable reduction in postoperative morbidity, there is still a way to go in patient comfort. A new 'tubeless' concept has surfaced as an alternative to double-lumen intubation with general anaesthesia combining non-intubated spontaneous breathing video-assisted thoracic surgery (VATS) surgery under loco-regional blockade with the avoidance of central line, epidural or urinary catheter and chest tube in selected patients. Those procedures combine the most evolved and less invasive techniques in anaesthesia, video-assisted surgery and perioperative care to cause the least trauma and allow for faster recovery. Non-intubated thoracic surgery used to rise some concerns regarding spontaneous breathing collapse, oxygenation, cough reflex triggering and mediastinal shift. Today, experienced teams in high-volume centers have proven non-intubated major lung resections are feasible and safe once those drawbacks have been overcome with the proper techniques and extensive previous expertise in VATS. Tubeless thoracic surgery is currently evolving, challenging former exclusion criteria and expanding indications to major lung resections or even tracheal and carinal resections to provide better intraoperative status and promote minimal need for recovery.

Nonintubated uniportal VATS pulmonary anatomical resections.

Nonintubated procedures have widely developed during the last years, thus nowadays major anatomical resections are performed in spontaneously breathing patients in some centers. In an attempt for combining less invasive surgical approaches with less aggressive anesthesia, nonintubated uniportal video-assisted thoracic surgery (VATS) lobectomies and segmentectomies have been proved feasible and safe, but there are no comparative trials and the evidence is still poor. A program in nonintubated uniportal major surgery should be started in highly experienced units, overcoming first a learning period performing minor procedures and a training program for the management of potential crisis situations when operating on these patients. A multidisciplinary approach including all the professionals in the operating room (OR), emergency protocols and a comprehensive knowledge of the special physiology of nonintubated surgery are mandatory. Some concerns about regional analgesia, vagal block for cough reflex control and oxygenation techniques, combined with some specific surgical tips can make safer these procedures. Specialists must remember an essential global concept: all the efforts are aimed at decreasing the invasiveness of the whole procedure in order to benefit patients' intraoperative status and postoperative recovery.

On the estimation of the worst-case implant-induced RF-heating in multi-channel MRI.

The increasing use of multiple radiofrequency (RF) transmit channels in magnetic resonance imaging (MRI) systems makes it necessary to rigorously assess the risk of RF-induced heating. This risk is especially aggravated with inclusions of medical implants within the body. The worst-case RF-heating scenario is achieved when the local tissue deposition in the at-risk region (generally in the vicinity of the implant electrodes) reaches its maximum value while MRI exposure is compliant with predefined general specific absorption rate (SAR) limits or power requirements. This work first reviews the common approach to estimate the worst-case RF-induced heating in multi-channel MRI environment, based on the maximization of the ratio of two Hermitian forms by solving a generalized eigenvalue problem. It is then shown that the common approach is not rigorous and may lead to an underestimation of the worst-case RF-heating scenario when there is a large number of RF transmit channels and there exist multiple SAR or power constraints to be satisfied. Finally, this work derives a rigorous SAR-based formulation to estimate a preferable worst-case scenario, which is solved by casting a semidefinite programming relaxation of this original non-convex problem, whose solution closely approximates the true worst-case including all SAR constraints. Numerical results for 2, 4, 8, 16, and 32 RF channels in a 3T-MRI volume coil for a patient with a deep-brain stimulator under a head imaging exposure are provided as illustrative examples.

Pregnant women models analyzed for RF exposure and temperature increase in 3T RF shimmed birdcages.

PURPOSE: MRI is increasingly used to scan pregnant patients. We investigated the effect of 3 Tesla (T) two-port radiofrequency (RF) shimming in anatomical pregnant women models. THEORY AND METHODS: RF shimming improves B1+ uniformity, but may at the same time significantly alter the induced current distribution and result in large changes in both the level and location of the absorbed RF energy. In this study, we evaluated the electrothermal exposure of pregnant women in the third, seventh, and ninth month of gestation at various imaging landmarks in RF body coils, including modes with RF shimming. RESULTS: Although RF shimmed configurations may lower the local RF exposure for the mother, they can increase the thermal load on the fetus. In worst-case configurations, whole-body exposure and local peak temperatures-up to 40.8°C-are equal in fetus and mother. CONCLUSIONS: Two-port RF shimming can significantly increase the fetal exposure in pregnant women, requiring further research to derive a very robust safety management. For the time being, restriction to the CP mode, which reduces fetal SAR exposure compared with linear-horizontal polarization modes, may be advisable. Results from this study do not support scanning pregnant patients above the normal operating mode. Magn Reson Med 77:2048-2056, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Virtual population-based assessment of the impact of 3 Tesla radiofrequency shimming and thermoregulation on safety and B1 + uniformity.

PURPOSE: To assess the effect of radiofrequency (RF) shimming of a 3 Tesla (T) two-port body coil on B1 + uniformity, the local specific absorption rate (SAR), and the local temperature increase as a function of the thermoregulatory response. METHODS: RF shimming alters induced current distribution, which may result in large changes in the level and location of absorbed RF energy. We investigated this effect with six anatomical human models from the Virtual Population in 10 imaging landmarks and four RF coils. Three thermoregulation models were applied to estimate potential local temperature increases, including a newly proposed model for impaired thermoregulation. RESULTS: Two-port RF shimming, compared to circular polarization mode, can increase the B1 + uniformity on average by +32%. Worst-case SAR excitations increase the local RF power deposition on average by +39%. In the first level controlled operating mode, induced peak temperatures reach 42.5°C and 45.6°C in patients with normal and impaired thermoregulation, respectively. CONCLUSION: Image quality with 3T body coils can be significantly increased by RF shimming. Exposure in realistic scan scenarios within guideline limits can be considered safe for a broad patient population with normal thermoregulation. Patients with impaired thermoregulation should not be scanned outside of the normal operating mode. Magn Reson Med 76:986-997, 2016. © 2015 Wiley Periodicals, Inc.

Convex optimization of MRI exposure for mitigation of RF-heating from active medical implants.

Local RF-heating of elongated medical implants during magnetic resonance imaging (MRI) may pose a significant health risk to patients. The actual patient risk depends on various parameters including RF magnetic field strength and frequency, MR coil design, patient's anatomy, posture, and imaging position, implant location, RF coupling efficiency of the implant, and the bio-physiological responses associated with the induced local heating. We present three constrained convex optimization strategies that incorporate the implant's RF-heating characteristics, for the reduction of local heating of medical implants during MRI. The study emphasizes the complementary performances of the different formulations. The analysis demonstrates that RF-induced heating of elongated metallic medical implants can be carefully controlled and balanced against MRI quality. A reduction of heating of up to 25 dB can be achieved at the cost of reduced uniformity in the magnitude of the B(1)(+) field of less than 5%. The current formulations incorporate a priori knowledge of clinically-specific parameters, which is assumed to be available. Before these techniques can be applied practically in the broader clinical context, further investigations are needed to determine whether reduced access to a priori knowledge regarding, e.g. the patient's anatomy, implant routing, RF-transmitter, and RF-implant coupling, can be accepted within reasonable levels of uncertainty.

Non-intubated video-assisted thoracic surgery management of secondary spontaneous pneumothorax.

Secondary spontaneous pneumothorax (SSP) is serious entity, usually due to underlying disease, mainly chronic obstructive pulmonary disease (COPD). Its morbidity and mortality is high due to the pulmonary compromised status of these patients, and the recurrence rate is almost 50%, increasing mortality with each episode. For persistent or recurrent SSP, surgery under general anesthesia (GA) and mechanical ventilation (MV) with lung isolation is the gold standard, but ventilator-induced damages and dependency, and postoperative pulmonary complications are frequent. In the last two decades, several groups have reported successful results with non-intubated video-assisted thoracic surgery (NI-VATS) with thoracic epidural anesthesia (TEA) and/or local anesthesia under spontaneous breathing. Main benefits reported are operative time, operation room time and hospital stay reduction, and postoperative respiratory complications decrease when comparing to GA, thus encouraging for further research in these moderate to high risk patients many times rejected for the standard regimen. There are also reports of special situations with satisfactory results, as in contralateral pneumonectomy and lung transplantation. The aim of this review is to collect, analyze and discuss all the available evidence, and seek for future lines of investigation.

Enfermedad de Whipple: una infrecuente causa bacteriana de demencia / Whipple’s Disease: an uncommon cause of dementia

Presentamos un caso de demencia diagnosticada como Alzheimer, cuya evolución condujo al diagnóstico final de una enfermedad de Whipple cerebral (AU)

We present a dementia case, diagnosed as Alzheimer type. Nevertheless, the final diagnosis of Whipple’s disease was delayed (AU)