Flexible Metamaterial Wrap for Improved Head Imaging at 3 T MRI With Low-Cost and Easy Fabrication Method.

Magnetic resonance imaging (MRI) requires spatial uniformity of the radiofrequency (RF) field inside the subject for maximum signal-to-noise ratio (SNR) and image contrast. Bulky high permittivity dielectric pads (HPDPs) focus magnetic fields into the region of interest (ROI) and increase RF field uniformity when placed between the patient and RF coils in the MR scanner. Metamaterials could replace HPDPs and reduce system bulkiness, but those in the literature often require a complicated fabrication process and cannot conform to patient body shape. Proposed is a flexible metamaterial for brain imaging made with a scalable fabrication process using conductive paint and a plastic laminate substrate. The effects of single and double-sided placement of the metamaterial around a human head phantom were investigated in a 3 T scanner. When two metamaterial sheets were wrapped around a head phantom (double-sided placement), the total average signal in the resulting image increased by 10.14% compared to placing a single metamaterial sheet underneath the phantom (single-sided placement). The difference between the maximum and minimum signal intensity values decreased by 57% in six different ROIs with double-sided placement compared to single-sided placement.

A Comparison of Aesthetic Outcomes of Umbilicoplasty in Breast Reconstruction with Abdominal Flap: Inverted-U Versus Vertical Oval Incision.

BACKGROUND: The umbilicus is a key aesthetic unit of the abdominal wall. It contributes to the natural curvature of the abdomen and is now considered as one of the most important factors in the overall results and patient satisfaction. In this study, we present an inverted-U incisional technique for umbilicoplasty. This study aims to describe the senior author's approach to umbilicoplasty and compare the aesthetic outcomes of the inverted-U method with those of the vertical oval incisional technique. METHODS: In this retrospective cohort study, we analyzed a total of 109 patients including 51 who underwent umbilicoplasty with the inverted-U incisional technique and 58 who had surgery with the vertical oval incisional method. With the description of our operative technique, the aesthetic outcomes of both techniques were compared by two independent surgeons using a 5-point Likert scale in terms of shape, size, depth, natural appearance and periumbilical scarring. Also, the total scores of the five items were calculated to give a final score for each patient (range, from 5 to 25 points). RESULTS: On all measured parameters, the inverted-U incisional technique produced favorable outcomes compared with the vertical oval incisional technique. Also, the inverted-U incisional technique was given significantly higher total scores than was the vertical oval incisional technique (inverted-U 14.73 ± 2.47 vs. vertical oval 11.26 ± 3.02, p = 0.002). CONCLUSIONS: In this study, an inverted-U incisional technique produced significantly favorable outcomes in terms of shape, size, depth, natural appearance and overall score compared to a vertical oval incision (p < 0.05). We believe that this technique enables surgeons to achieve a better shape, natural retrusive appearance and superior hood. LEVEL OF EVIDENCE III: In this study, an inverted-U incisional technique produced significantly favorable outcomes in terms of shape, size, depth, natural appearance and overall score compared to a vertical oval incision (p < 0.05). We believe that this technique enables surgeons to achieve a better shape, natural retrusive appearance and superior hood.

Development and testing of implanted carbon electrodes for electromagnetic field mapping during neuromodulation.

PURPOSE: Deep brain stimulation electrodes composed of carbon fibers were tested as a means of administering and imaging magnetic resonance electrical impedance tomography (MREIT) currents. Artifacts and heating properties of custom carbon-fiber deep brain stimulation (DBS) electrodes were compared with those produced with standard DBS electrodes. METHODS: Electrodes were constructed from multiple strands of 7-µm carbon-fiber stock. The insulated carbon electrodes were matched to DBS electrode diameter and contact areas. Images of DBS and carbon electrodes were collected with and without current flow and were compared in terms of artifact and thermal effects in phantoms or tissue samples in 7T imaging conditions. Effects on magnetic flux density and current density distributions were also assessed. RESULTS: Carbon electrodes produced magnitude artifacts with smaller FWHM values compared to the magnitude artifacts around DBS electrodes in spin echo and gradient echo imaging protocols. DBS electrodes appeared 269% larger than actual size in gradient echo images, in sharp contrast to the negligible artifact observed in diameter-matched carbon electrodes. As expected, larger temperature changes were observed near DBS electrodes during extended RF excitations compared with carbon electrodes in the same phantom. Magnitudes and distribution of magnetic flux density and current density reconstructions were comparable for carbon and DBS electrodes. CONCLUSION: Carbon electrodes may offer a safer, MR-compatible method for administering neuromodulation currents. Use of carbon-fiber electrodes should allow imaging of structures close to electrodes, potentially allowing better targeting, electrode position revision, and the facilitation of functional imaging near electrodes during neuromodulation.

In vivo MR imaging with simultaneous RF transmission and reception.

PURPOSE: To present a practical scheme of a simultaneous radiofrequency (RF) transmit (Tx) and receive (Rx) (STAR) system for MRI, discuss the challenges and solutions, and show preliminary in vivo MR images obtained with this new technique. METHODS: A remotely controlled STAR system was built and tested with a transverse electromagnetic head coil on a 4T (Oxford, 90 cm-bore) MRI scanner equipped with an Agilent DirectDrive console (Agilent, Santa Clara, CA). In vivo head images have been acquired using continuous sweep excitation and acquisition. RESULTS: The bench test and MR experimental results show our STAR system to have high isolation (60 dB) between Tx and Rx, with insensitivity to load swings created by head motion. To acquire in vivo head images, ultralow RF peak power of 50 mW was used. CONCLUSION: A novel motion-insensitive STAR MRI technique was developed and experimentally tested. The first in vivo MR images using this method were acquired. Magn Reson Med 76:1932-1938, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

A Compact, High Power Capable, and Tunable High Directivity Microstrip Coupler.

A coupler is an indispensable component to sample the forward and reflected power for the real-time radio frequency (RF) power monitoring system. The directivity of a coupler is a critical factor to achieve accurate RF power measurements. This paper proposes a microstrip coupler with a tunable high directivity circuit to accurately measure the reflected RF power. The directivity tuner composed of passive components adjusts phase and amplitude of the coupled RF signal, and cancel out the leakage signal from the RF input port at the coupled reflection port. The experimental results, which agree with simulation results, show that the microstrip coupler with the directivity tuner circuit has a compact size (~ 0.07 λg x 0.05 λg), high power capability (up to 1 kW), and high directivities (more than 40 dB) at operating frequency bands (f = 297.3 MHz, 400 MHz, and 447 MHz, respectively) for magnetic resonance imaging (MRI) applications.

RF Head Coil Design with Improved RF Magnetic Near-Fields Uniformity for Magnetic Resonance Imaging (MRI) Systems.

Higher magnetic field strength in magnetic resonance imaging (MRI) systems offers higher signal-to-noise ratio (SNR), contrast, and spatial resolution in MR images. However, the wavelength in ultra-high fields (7 tesla and beyond) becomes shorter than the human body at the Larmor frequency with increasing static magnetic field (B0) of MRI system. At short wavelengths, interference effect appears resulting in non- uniformity of the RF magnetic near-field (B1) over the subject and MR images may have spatially anomalous contrast. The B1 near-field generated by the transverse electromagnetic (TEM) RF coil's microstrip line element has a maximum near the center of its length and falls off towards both ends. In this study, a double trapezoidal shaped microstrip transmission line element is proposed to obtain uniform B1 field distribution by gradual impedance variation. Two multi-channel RF head coils with uniform and trapezoidal shape elements were built and tested with a phantom at 7T MRI scanner for comparison. The simulation and experimental results show stronger and more uniform B1+ near-field with the trapezoidal shape.

Difference in the outcomes of anterior tenting and wrapping techniques for acellular dermal matrix coverage in prepectoral breast reconstruction.

BACKGROUND: Acellular dermal matrices (ADMs) play an essential role in prepectoral implant-based breast reconstructions; however, the most appropriate method for ADMs is unknown. METHODS: We conducted a retrospective analysis of our institutional database. Patients who underwent mastectomy and prepectoral breast reconstruction using tissue expanders or breast implants covered with ADMs between March 2018 and June 2021 were included. Patient characteristics, postoperative complications, and long-term outcomes were investigated. RESULTS: In total, 112 patients (126 breasts) were included. The anterior tenting and wrapping techniques were used in the reconstruction of 32 (25.3%) and 94 (74.7%) breasts, respectively. Using propensity score matching, nine breasts were selected for each technique within the direct-to-implant reconstruction group, while 16 breasts were selected for each technique within the 2-stage reconstruction group. The choice of technique (anterior vs. wrapping) in implementing ADM did not generate any significant differences in postoperative complications, including seroma formation and capsular contracture, for the direct-to-implant and 2-stage reconstruction groups. Regarding the direct-to-implant reconstruction group, the average postoperative drain volume was less in the anterior tenting group than that in the wrapping group (anterior tenting vs. wrapping; 495.09 ± 156.118 mL vs. 673.43 ± 307.954 mL, p = 0.006), but the difference was insignificant after propensity score matching. CONCLUSION: We report our experience with covering prosthetic devices with ADMs during postmastectomy breast reconstruction. No differences in the postoperative drain volume or postoperative outcomes were found between the study groups. Future studies are needed to determine the method that provides the most satisfactory results.

Standalone RF Self-Interference Cancellation System for In-Vivo Simultaneous Transmit and Receive (STAR) MRI.

Demonstrated is a standalone RF self-interference canceller for simultaneous transmit and receive (STAR) magnetic resonance imaging (MRI) at 1.5T. Standalone STAR cancels the leakage signal directly coupled between transmit and receive RF coils. A cancellation signal, introduced by tapping the input of a transmit coil with a power divider, is manipulated with voltage-controlled attenuators and phase shifters to match the leakage signal in amplitude, 180° out of phase, to exhibit high isolation between the transmitter and receiver. The cancellation signal is initially generated by a voltage-controlled oscillator (VCO); therefore, it does not require any external RF or synchronization signals from the MRI console for calibration. The system employs a field programmable gate array (FPGA) with an on-board analog to digital converter (ADC) to calibrate the cancellation signal by tapping the receive signal, which contains the leakage signal. Once calibrated, the VCO is disabled and the transmit signal path switches to the MRI console for STAR MR imaging. To compensate for the changes of parameters in RF sequences after the automatic calibration and to further improve isolation, a wireless user board that uses an ESP32 microcontroller was built to communicate with the FPGA for final fine-tuning of the output state. The standalone STAR system achieved 74.2 dB of isolation with a 94 second calibration time. With such high isolation, in-vivo MR images were obtained with approximately 40 mW of RF peak power.

Design of standalone wireless impedance matching (SWIM) system for RF coils in MRI.

The radio frequency (RF) power transfer efficiency of transmit coils and the signal-to-noise ratio (SNR) at the receive signal chain are directly dependent on the impedance matching condition presented by a loaded coil, tuned to the Larmor frequency. Sub-optimal impedance condition of receive coils significantly reduces coil sensitivity and image quality. In this study we propose a Standalone Wireless Impedance Matching (SWIM) system for RF coils to automatically compensate for the impedance mismatch caused by the loading effect at the target frequency. SWIM uses a built-in RF generator to produce a calibration signal, measure reflected power as feedback for loading change, and determine an optimal impedance. The matching network consists of a capacitor array with micro-electromechanical system (MEMS) RF switches to electronically cycle through different input impedance conditions. Along with automatic calibration, SWIM can also perform software detuning of RF receive coils. An Android mobile application was developed for real-time reflected power monitoring and controlling the SWIM system via Bluetooth. The SWIM system can automatically calibrate an RF coil in 3 s and the saline sample SNR was improved by 24% when compared to a loaded coil without retuning. Four different tomatoes were imaged to validate the performance of SWIM.

Transient lower extremity lymphedema following COVID-19 vaccination: A case report.

RATIONALE: Complications from COVID-19 vaccines have yet to be sufficiently analyzed because they are rapidly approved without long-term data. In particular, there are no case reports of lymphedema in a healthy patient following vaccination. Herein, we report a patient who underwent transient lymphedema after vaccination with BNT16b2. PATIENT CONCERNS: A 79-year-old woman with pitting edema in both lower legs after administration of a second dose of Pfizer vaccine was referred to our clinic. In the absence of clinical evidence of swelling during the laboratory evaluation, we suspected deep vein thrombosis. However, ultrasonographic findings revealed no evidence of venous thrombosis or varicose veins. DIAGNOSIS: On the basis of lymphoscintigraphy, the patient was diagnosed with transient lymphedema with decreased lymphatic transport in both lower extremities. INTERVENTION: The patient received intensive physiotherapy, including complex decongestive physiotherapy and pneumatic pump compression, to improve the lymphatic circulation. Furthermore, the patient was trained to apply a multilayer compressive bandage to the lower extremities. OUTCOMES: At 2 months follow-up after rehabilitative treatment, the patient's symptoms improved without recurring lymphedema. LESSONS: In the absence of clinical evidence of swelling during laboratory evaluation or ultrasonographic investigations suggesting deep vein thrombosis, we should consider the possibility of lymphatic disorders.

Effects of pre-existing abdominal scar on postoperative complications after autologous breast reconstruction using abdominal flaps: A systematic review and meta-analysis.

BACKGROUND: A previous abdominal scar is generally considered as a challenge for breast reconstruction using abdominal flaps. Since it may interfere with the perfusion of abdominal tissue and weaken the abdominal fascia, many plastic surgeons are concerned about the theoretical risk of postoperative complications. This study aims to assess the effects of previous scar on complications in abdominal flap-based breast reconstruction. METHODS: This systematic review of the literature was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline using MEDLINE, Ovid, and Cochrane databases in March 2020. All studies comparing the complication rates between patients with previous abdominal scars and control group without a scar were included. However, articles such as case series fewer than 10 patients, letters and animal studies were excluded. RESULTS: A total of 2109 patients underwent 2792 abdominal flap tissue transfers for breast reconstruction in the 11 studies reviewed. A previous scar increased the risk of overall flap complications (RR 1.12; 95% CI, 0.95-1.32; fixed-effect model, I2 = 13%) and donor-site complications (RR 1.35; 95% CI, 1.13-1.62; fixed-effect model, I2 = 42%, p > 0.05). In particular, the risk of donor-site wound problem was significantly higher than that in the control group (RR 1.83; 95% CI, 1.35-2.46; fixed-effect model, I2 = 19%, p > 0.05). CONCLUSIONS: This study result showed that the previous scar increased the risk for all types of complications compared with the control group. In patients with a vertical midline scar, it requires careful preoperative planning with CT angiography and attentive follow-up. However, with careful preoperative planning and an appropriate strategy, it is possible to overcome the detrimental effect of previous scar. LEVEL OF EVIDENCE: I.

Use of a biopsy punch for end-to-side anastomosis in free-tissue transfer.

Background: In end-to-side vessel-anastomoses, a side fenestration should be made by a slit incision or partial excision of the vessel wall. However, a slit incision might restrict blood flow across the anastomosis, and a partial vessel wall excision using micro-scissors may be time-consuming and result in irregular edges, which may weaken the vessel wall and cause flow disturbances. We used a biopsy punch for end-to-side anastomosis, and obtained satisfactory results.Methods: Between September 2015 and August 2017, 27 end-to-side anastomoses using punch biopsies were performed. Two vessel clamps were applied to the recipient vessel proximal and distal to the point planned for the side anastomosis. The flap side vessel size was measured, and an appropriately sized punch was selected. The clamped recipient vessel was supported by a wooden tongue depressor and the punch was applied to the vessel wall. An end-to-side anastomosis was performed in the usual manner, and immediate patency was tested with a refill test.Results: The vessel patency rate was 96 percent. The mean arteriotomy or venotomy time was 65 s and entire anastomosis procedure time was 1065 s. Both the vessel preparation and the micro-anastomosis procedure times were shorter than those of the conventional procedure group with statistical significance. (p < .05) There was only one case of venous failure by deep vein thrombosis - and it was resolved with thrombectomy and re-anastomosis.Conclusion: Use of a biopsy punch in end-to-side anastomosis can offer a uniform circular edge and reduce operating time.

Impact of alcohol drinking on acetylcholine-induced coronary artery spasm in Korean populations.

BACKGROUND AND AIMS: Generally, immoderate alcohol consumption is associated with variant angina and accepted as one of the risk factors for coronary artery spasm (CAS), but evidence is lacking in this regard. The aim of this study is to evaluate the impact of alcohol consumption and drinking pattern on CAS by acetylcholine (ACH) provocation test and long-term clinical outcomes. METHODS: A total of 5491 patients with typical or atypical chest pain, without significant coronary artery disease, who underwent intracoronary ACH provocation test, were enrolled prospectively, and retrospectively analyzed in this study. They were divided into two groups according to their alcohol drinking status; the current alcohol (CA) drinking group (n = 1792), and non-CA group (n = 3699). To adjust for potential confounders, a propensity score matching (PSM) analysis was performed. The primary endpoint was incidence of CAS, and secondary endpoints were major adverse cardiac events (MACE) and recurrent angina requiring repeat coronary angiography (CAG) at 5 years. RESULTS: After PSM analysis, alcohol consumption was a strong risk factor for CAS. Furthermore, excessive alcohol consumption was correlated with a higher risk for CAS. As compared with the non-CA group, the CA group showed worse angiographic and clinical findings, including higher incidence of CAS (58% vs. 62%, p = 0.016), spontaneous spasm (17% vs. 22%, p = 0.004), multi-vessel spasm (31% vs. 37%, p = 0.009), proximal epicardial spasm (39% vs. 46%, p = 0.002), ischemic electrocardiography changes such as T-inversion (0.4% vs. 1.2%, p < 0.001) and chest pain (42% vs. 46%, p = 0.047) during ACH provocation test. However, the status and pattern of alcohol drinking had no influence on long-term clinical outcomes such as MACE or recurrent angina. CONCLUSIONS: Alcohol consumption is a strong risk factor for CAS, and excessive alcohol consumption was correlated with a higher risk for CAS. Further well-designed studies are needed to confirm the results.

Design of an Electrically Automated RF Transceiver Head Coil in MRI.

Magnetic resonance imaging (MRI) is a widely used nonionizing and noninvasive diagnostic instrument to produce detailed images of the human body. The radio-frequency (RF) coil is an essential part of MRI hardware as an RF front-end. RF coils transmit RF energy to the subject and receive the returning MR signal. This paper presents an MRI-compatible hardware design of the new automatic frequency tuning and impedance matching system. The system automatically corrects the detuned and mismatched condition that occurs due to loading effects caused by the variable subjects (i.e., different human heads or torsos). An eight-channel RF transceiver head coil with the automatic system has been fabricated and tested at 7 Tesla (T) MRI system. The automatic frequency tuning and impedance matching system uses digitally controlled capacitor arrays with real-time feedback control capability. The hardware design is not only compatible with current MRI scanners in all aspects but also it operates the tuning and matching function rapidly and accurately. The experimental results show that the automatic function increases return losses from 8.4 dB to 23.7 dB (maximum difference) and from 12.7 dB to 19.6 dB (minimum difference) among eight channels within 550 ms . The reflected RF power decrease from 23.1% to 1.5% (maximum difference) and from 5.3% to 1.1% (minimum difference). Therefore, these results improve signal-to-noise ratio (SNR) in MR images with phantoms.

Stepped impedance resonators for high-field magnetic resonance imaging.

Multi-element volume radio-frequency (RF) coils are an integral aspect of the growing field of high-field magnetic resonance imaging. In these systems, a popular volume coil of choice has become the transverse electromagnetic (TEM) transceiver coil consisting of microstrip resonators. In this paper, to further advance this design approach, a new microstrip resonator strategy in which the transmission line is segmented into alternating impedance sections, referred to as stepped impedance resonators (SIRs), is investigated. Single-element simulation results in free space and in a phantom at 7 T (298 MHz) demonstrate the rationale and feasibility of the SIR design strategy. Simulation and image results at 7 T in a phantom and human head illustrate the improvements in a transmit magnetic field, as well as RF efficiency (transmit magnetic field versus specific absorption rate) when two different SIR designs are incorporated in 8-element volume coil configurations and compared to a volume coil consisting of microstrip elements.