Consistency of vendor-specified activity values for ¹9²Ir brachytherapy sources.

A long-term comparison was done between the manufacturer-stated ¹9²Ir activity and the measured ¹9²Ir activities determined with a well-type ionization chamber. Sources for a Nucletron Micro Selectron high-dose-rate (HDR) unit were used for this purpose. The radioactive sources reference activities were determined using a PTW well-type ionization chamber traceable to the National Institute of Standards and Technology Primary Calibration Laboratory. The measurements were taken in a period of 56 months with 17 different radioactive sources. The manufacturer stated activities were taken from the source calibration certificate provided by the manufacturer. These values were compared with the measured activities. The results have shown that both the percentage deviation of the monthly control measurements with the well-type chamber and the ratio between the measured activities to the manufacturer-stated value lie within ± 2.5%. These results were compared with similar published data and with uncertainty level (3% of the mean and 5% maximum deviation from mean) for brachytherapy sources calibration recommended by the AAPM. It was concluded that a threshold level of ±2.5% can be used as a suitable quality assurance indicator to spot problems in our department. The typical ±5% uncertainty as provided by the manufacturers may be tightened to ±3% to be more in line with published AAPM reports.

Toward a comparison of microelectrodes for acute and chronic recordings.

Several variations of microelectrode arrays are used to record and stimulate intracortical neuronal activity. Bypassing the immune response to maintain a stable recording interface remains a challenge. Companies and researchers are continuously altering the material compositions and geometries of the arrays in order to discover a combination that allows for a chronic and stable electrode-tissue interface. From this interface, they wish to obtain consistent quality recordings and a stable, low impedance pathway for charge injection over extended periods of time. Despite numerous efforts, no microelectrode array design has managed to evade the host immune response and remain fully functional. This study is an initial effort comparing several microelectrode arrays with fundamentally different configurations for use in an implantable epilepsy prosthesis. Specifically, NeuroNexus (Michigan) probes, Cyberkinetics (Utah) Silicon and Iridium Oxide arrays, ceramic-based thin-film microelectrode arrays (Drexel), and Tucker-Davis Technologies (TDT) microwire arrays are evaluated over a 31-day period in an animal model. Microelectrodes are compared in implanted rats through impedance, charge capacity, signal-to-noise ratio, recording stability, and elicited immune response. Results suggest significant variability within and between microelectrode types with no clear superior array. Some applications for the microelectrode arrays are suggested based on data collected throughout the longitudinal study. Additionally, specific limitations of assaying biological phenomena and comparing fundamentally different microelectrode arrays in a highly variable system are discussed with suggestions on how to improve the reliability of observed results and steps needed to develop a more standardized microelectrode design.

Atomic absorption spectrometric determination of the iridium content in tumor cells exposed to an iridium metallodrug.

An electrothermal atomic absorption spectrometric method to quantify the iridium content of HT-29 colon carcinoma cells exposed to iridium metallodrugs was developed. Optimisation of the procedure involved the evaluation of pyrolysis and atomisation conditions (optimal values were 1400 degrees C for pyrolysis and 2400 degrees C for atomisation) and the addition of appropriate additives. The presence of cellular components as well as the addition of nitric acid and hydrochloric acid led to enhanced absorption signals and suggested the use of matrix matched calibration. The described method allows the measurement of iridium in cell suspensions in the low microg/L range (linear dynamic range: 10-450 microg/L) with a detection limit of 11.2 microg/L. The applicability of the method was tested by means of a novel iridium metallodrug. First results on the complex [IrCl3(DMSO)(phen)] indicated a low cellular uptake (21.2 microM at incubation with 100 microM) of this iridium species in HT-29 cells compared to other metal containing antitumor drugs.

Prospective randomized comparison of 8-mm gold-tip, externally irrigated-tip and 8-mm platinum-iridium tip catheters for cavotricuspid isthmus ablation.

INTRODUCTION: Radiofrequency (RF) ablation of the cavotricuspid isthmus (CTI) can be performed using different types of ablation catheter. Gold tip electrodes have the theoretical advantage of creating bigger lesions than standard platinum-iridium electrode. This prospective, randomized study compares the clinical efficacy of 8-mm gold tip catheter, externally irrigated and 8-mm platinum-iridium tip (Pt tip) catheters. METHODS AND RESULTS: Sixty consecutive patients (51 men, 60 +/- 10 years) undergoing de novo CTI ablation for documented typical atrial flutter were randomized to one of the following ablation catheters: 8-mm gold tip catheter, an externally irrigated-tip (Irr. tip) catheter, or an 8-mm Pt tip catheter. The procedural endpoint was achievement of bidirectional isthmus conduction block with < or = 20 minutes of RF energy application. The latter was achieved equally with the 3 catheters (95% for gold tip, 100% for irrigated tip, 95% for Pt tip) and the durations of RF (10 +/- 6, 10 +/- 4, 13 +/- 8 minutes), fluoroscopy (12 +/- 6, 12 +/- 7, 15 +/- 12 minutes) and the procedure (34 +/- 23, 38 +/- 24, 40 +/- 30 minutes) were similar in all groups. The maximal targeted power could not be reached in at least one location in 40% of patients with gold tip and in 35% of patients with Pt tip catheters whereas it was always achieved with an Irr. tip catheter (P = 0.003, P = 0.008). The reduction in impedance during RF delivery was greater with Irr. tip (11 +/- 7 ohms) than with gold (7 +/- 4 ohms, P = 0.02) or Pt tip (5 +/- 3 ohms, P = 0.001) catheters. CONCLUSION: This study demonstrates equivalent efficacies of gold, platinum-iridium and externally Irr. tip catheters for successful de novo ablation of the CTI.

MRI compatible electrodes for the induction of amygdala kindling in rats.

The rat electrical kindling model has been widely utilized in epilepsy research. This study aimed to identify the optimum "MRI compatible" bipolar stimulating and recording electrodes to enable serial MRI acquisition in this model. Two types of custom-made electrodes (gold and carbon) were compared with commercial platinum-iridium alloy electrodes for suitability based on size, effect on image quality and kindling induction. The custom-made gold electrodes, based on these parameters, were found to be most suitable. These electrodes enable the study of epileptogenesis utilizing MRI in this model of temporal lobe epilepsy (TLE).

Safety of 125iodine and 192iridium implants to the canine carotid artery: preliminary report.

Thirty-nine healthy dogs underwent a simulated radical neck dissection followed by implantation of either 125Iodine (125I) or 192Iridium (192Ir) in various dose regimes randomized prospectively from 3,000 to 30,000 rad. Bilateral selective carotid angiography was performed immediately postoperatively and at six months and one year. No significant effects occurred to the animals who received 15,000 rad 125I or 6,000 rad 192Ir. In the higher dosed animals the 125I treated group fared better than the 192Ir treated group, probably due to the lower dose rate delivery. All surviving animals will be maintained an additional year to determine the late effects of brachytherapy irradiation to the carotid artery.