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Access to MRI is limited for patients with deep brain stimulation (DBS) implants due to safety hazards, including radiofrequency (RF) heating of tissue surrounding the leads. Computational models provide an exquisite tool to explore the multi-variate problem of RF heating and help better understand the interaction of electromagnetic fields and biological tissues. This paper presents a computational approach to assess RF-induced heating, in terms of specific absorption rate (SAR) in the tissue, around the tip of bilateral DBS leads during MRI at 64MHz/1.5 T and 127 MHz/3T. Patient-specific realistic lead models were constructed from post-operative CT images of nine patients operated for sub-thalamic nucleus DBS. Finite element method was applied to calculate the SAR at the tip of left and right DBS contact electrodes. Both transmit head coils and transmit body coils were analyzed. We found a substantial difference between the SAR and temperature rise at the tip of right and left DBS leads, with the lead contralateral to the implanted pulse generator (IPG) exhibiting up to 7 times higher SAR in simulations, and up to 10 times higher temperature rise during measurements. The orientation of incident electric field with respect to lead trajectories was explored and a metric to predict local SAR amplification was introduced. Modification of the lead trajectory was shown to substantially reduce the heating in phantom experiments using both conductive wires and commercially available DBS leads. Finally, the surgical feasibility of implementing the modified trajectories was demonstrated in a patient operated for bilateral DBS.

Background Several lines of research suggest that prefrontal cortex dysfunctions observed in obsessive compulsive disorder (OCD) and schizophrenia (SKZ) are linked to two partially independent neuroanatomic systems: the ventromedial prefrontal cortex and the dorsolateral prefrontal cortex, with different neuroanatomic connections, including the striatum. The primary aim of this study was to test this hypothesis using a double dissociation study of neuropsychological tasks performance of the dorsolateral prefrontal cortex and ventromedial prefrontal cortex. Methods We administered the Wisconsin Card Sorting Test, the Gambling Task, and the four-disk version of the Tower of Hanoi to 110 SKZ and 67 OCD patients and 56 control subjects. Results A clear double dissociation of Wisconsin Card Sorting Test and Gambling Task performances was found, with SKZ patients performing the Wisconsin Card Sorting test significantly worse than OCD patients and control subjects and OCD patients performing the Gambling Task significantly worse than SKZ and control subjects. Both SKZ and OCD patients performed the Tower of Hanoi significantly worse than control subjects. Conclusions Results from our double dissociation study confirm the hypothesis of involvement of different frontal lobe subsystems within basal–corticofrontal circuits function in SKZ and OCD.

The paper presents the collection and the analyse of data coming out from operating experiences gained in the Joint European Torus (JET) for the Ion Cyclotron Resonance Heating (ICRH) system. The main goal of the activity is to enrich the data collection on failures of components used in fusion facilities. Alarms/failures and malfunctions occurred in the years of operations from March 1996 to November 2005, including information on failure modes and, where possible, causes of the failures, have been identified. About 3400 events classified as alarms or failures related to specific components or sub-systems were identified by analysing hand-written logbooks made available by the ICRH operation staff. By analysing the tick sheets covering the whole considered time interval it results that the ICRH was operated during about 12,000 plasma pulses. Main statistical values, such as rates of alarms/failures and corresponding standard errors and confidence intervals, have been estimated. Failure rates of systems and components have been evaluated both with regard to the ICRH operation pulses and operating days (in which at least one ICRH module was requested to operate). Failure probabilities on demand have been evaluated with regard to number of pulses operated. © 2008 Elsevier B.V. All rights reserved.