Design and construction of a Maxwell-type induction coil for magnetic nanoparticle hyperthermia.

Purpose: We describe a modified Helmholtz induction coil, or Maxwell coil, that generates alternating magnetic fields (AMF) having field uniformity (≤10%) within a = 3000 cm3 volume of interest for magnetic hyperthermia research.Materials and methods: Two-dimensional finite element analysis (2D-FEA) was used for electromagnetic design of the induction coil set and to develop specifications for the required matching network. The matching network and induction coil set were fabricated using best available practices and connected to a 120 kW industrial induction heating power supply. System performance was evaluated by magnetic field mapping with a magnetic field probe, and tests were performed using gel phantoms.Results: Tests verified that the system generated a target peak AMF amplitude along the coil axis of ∼35 kA/m (peak) at a frequency of 150 ± 10 kHz while maintaining field uniformity to >90% of peak for a volume of ∼3000 cm3.Conclusions: The induction coil apparatus comprising three independent loops, i.e., Maxwell-type improves upon the performance of simple solenoid and Helmholtz coils by providing homogeneous flux density fields within a large volume while minimizing demands on power and stray fields. Experiments with gel phantoms and analytical calculations show that future translational research efforts should be devoted to developing strategies to reduce the impact of nonspecific tissue heating from eddy currents; and, that an inductor producing a homogeneous field has significant clinical potential for deep-tissue magnetic fluid hyperthermia.

Evaluation of a Balloon Implant for Simultaneous Magnetic Nanoparticle Hyperthermia and High-Dose-Rate Brachytherapy of Brain Tumor Resection Cavities.

Previous work has reported the design of a novel thermobrachytherapy (TBT) balloon implant to deliver magnetic nanoparticle (MNP) hyperthermia and high-dose-rate (HDR) brachytherapy simultaneously after brain tumor resection, thereby maximizing their synergistic effect. This paper presents an evaluation of the robustness of the balloon device, compatibility of its heat and radiation delivery components, as well as thermal and radiation dosimetry of the TBT balloon. TBT balloon devices with 1 and 3 cm diameter were evaluated when placed in an external magnetic field with a maximal strength of 8.1 kA/m at 133 kHz. The MNP solution (nanofluid) in the balloon absorbs energy, thereby generating heat, while an HDR source travels to the center of the balloon via a catheter to deliver the radiation dose. A 3D-printed human skull model was filled with brain-tissue-equivalent gel for in-phantom heating and radiation measurements around four 3 cm balloons. For the in vivo experiments, a 1 cm diameter balloon was surgically implanted in the brains of three living pigs (40-50 kg). The durability and robustness of TBT balloon implants, as well as the compatibility of their heat and radiation delivery components, were demonstrated in laboratory studies. The presence of the nanofluid, magnetic field, and heating up to 77 °C did not affect the radiation dose significantly. Thermal mapping and 2D infrared images demonstrated spherically symmetric heating in phantom as well as in brain tissue. In vivo pig experiments showed the ability to heat well-perfused brain tissue to hyperthermic levels (≥40 °C) at a 5 mm distance from the 60 °C balloon surface.

Modified Solenoid Coil That Efficiently Produces High Amplitude AC Magnetic Fields With Enhanced Uniformity for Biomedical Applications.

In this paper, we describe a modified solenoid coil that efficiently generates high amplitude alternating magnetic fields (AMF) having field uniformity (≤10%) within a 125-cm3 volume of interest. Two-dimensional finite element analysis (2D-FEA) was used to design a coil generating a targeted peak AMF amplitude along the coil axis of ~100 kA/m (peak-to-peak) at a frequency of 150 kHz while maintaining field uniformity to >90% of peak for a specified volume. This field uniformity was realized by forming the turns from cylindrical sections of copper plate and by adding flux concentrating rings to both ends of the coil. Following construction, the field profile along the axes of the coil was measured. An axial peak field value of 95.8 ± 0.4 kA/m was measured with 650 V applied to the coil and was consistent with the calculated results. The region of axial field uniformity, defined as the distance over which field ≥90% of peak, was also consistent with the simulated results. We describe the utility of such a device for calorimetric measurement of nanoparticle heating for cancer therapy and for magnetic fluid hyperthermia in small animal models of human cancer.

Application of high amplitude alternating magnetic fields for heat induction of nanoparticles localized in cancer.

OBJECTIVE: Magnetic nanoparticles conjugated to a monoclonal antibody can be i.v. injected to target cancer tissue and will rapidly heat when activated by an external alternating magnetic field (AMF). The result is necrosis of the microenvironment provided the concentration of particles and AMF amplitude are sufficient. High-amplitude AMF causes nonspecific heating in tissues through induced eddy currents, which must be minimized. In this study, application of high-amplitude, confined, pulsed AMF to a mouse model is explored with the goal to provide data for a concomitant efficacy study of heating i.v. injected magnetic nanoparticles. METHODS: Thirty-seven female BALB/c athymic nude mice (5-8 weeks) were exposed to an AMF with frequency of 153 kHz, and amplitude (400-1,300 Oe), duration (1-20 minutes), duty (15-100%), and pulse ON time (2-1,200 seconds). Mice were placed in a water-cooled four-turn helical induction coil. Two additional mice, used as controls, were placed in the coil but received no AMF exposure. Tissue and core temperatures as the response were measured in situ and recorded at 1-second intervals. RESULTS: No adverse effects were observed for AMF amplitudes of < or = 700 Oe, even at continuous power application (100% duty) for up to 20 minutes. Mice exposed to AMF amplitudes in excess of 950 Oe experienced morbidity and injury when the duty exceeded 50%. CONCLUSION: High-amplitude AMF (up to 1,300 Oe) was well tolerated provided the duty was adjusted to dissipate heat. Results presented suggest that further tissue temperature regulation can be achieved with suitable variations of pulse width for a given amplitude and duty combination. These results suggest that it is possible to apply high-amplitude AMF (> 500 Oe) with pulsing for a time sufficient to treat cancer tissue in which magnetic nanoparticles have been embedded.

Fluoroquinolone- and ceftriaxone-based therapy of community-acquired pneumonia in hospitalized patients: the risk of subsequent isolation of multidrug-resistant organisms.

A retrospective cohort study was performed on 175 adult patients treated for community-acquired pneumonia with moxifloxacin or ceftriaxone/azithromycin in a nonintensive care unit. Both cohorts were very similar with regard to a wide range of characteristics including age, severity of disease, comorbidities, length of stay, and mortality. Multidrug-resistant organisms were subsequently isolated from 6 (15%) moxifloxacin-treated patients and 5 (4%) ceftriaxone/azithromycin-treated patients within 90 days after beginning of therapy (P = .026 on logistic regression analysis).

The safety of deep sedation without intubation for abortion in the outpatient setting.

STUDY OBJECTIVE: To determine the rate of perioperative pulmonary aspiration in patients undergoing first and second-trimester surgical abortion during deep sedation with propofol, without intubation. DESIGN: Retrospective review of cases of surgical and anesthetic complications reported to the Office of Quality Management of the surgical facility between August 1, 2001 and April 30, 2008. SETTING: Large urban surgical abortion outpatient facility. MEASUREMENTS: The medical records of all surgical abortion patients who underwent hospital transfer were reviewed. From billing records, all patients who underwent abortion during deep sedation were identified. The primary outcome was the rate of perioperative pulmonary aspiration. Secondary outcomes included the rates of other anesthesia-related adverse events resulting in hospital transfer. MAIN RESULTS: During the 81-month study period, the facility performed 62,125 surgical abortions during deep sedation, including 11,039 second-trimester abortions. Only one patient received endotracheal intubation. No cases of perioperative pulmonary aspiration occurred. CONCLUSIONS: Deep sedation without intubation is a viable method of anesthesia for both first and second-trimester surgical abortions in the outpatient setting.