Development of a bio-magnetic measurement system and sensor configuration analysis for rats.

Magnetoencephalography (MEG) based on superconducting quantum interference devices enables the measurement of very weak magnetic fields (10-1000 fT) generated from the human or animal brain. In this article, we introduce a small MEG system that we developed specifically for use with rats. Our system has the following characteristics: (1) variable distance between the pick-up coil and outer Dewar bottom (∼5 mm), (2) small pick-up coil (4 mm) for high spatial resolution, (3) good field sensitivity (45∼ 80fT/cm/Hz), (4) the sensor interval satisfies the Nyquist spatial sampling theorem, and (5) small source localization error for the region to be investigated. To reduce source localization error, it is necessary to establish an optimal sensor layout. To this end, we simulated confidence volumes at each point on a grid on the surface of a virtual rat head. In this simulation, we used locally fitted spheres as model rat heads. This enabled us to consider more realistic volume currents. We constrained the model such that the dipoles could have only four possible orientations: the x- and y-axes from the original coordinates, and two tangentially layered dipoles (local x- and y-axes) in the locally fitted spheres. We considered the confidence volumes according to the sensor layout and dipole orientation and positions. We then conducted a preliminary test with a 4-channel MEG system prior to manufacturing the multi-channel system. Using the 4-channel MEG system, we measured rat magnetocardiograms. We obtained well defined P-, QRS-, and T-waves in rats with a maximum value of 15 pT/cm. Finally, we measured auditory evoked fields and steady state auditory evoked fields with maximum values 400 fT/cm and 250 fT/cm, respectively.

Diagnostic techniques to detect the epileptogenic zone: Pathophysiological and presurgical analysis of epilepsy in dogs and cats.

The use and availability of magnetic resonance imaging (MRI) and other neurosurgical devices is rapidly increasing in the field of veterinarian medicine. Coincident with these technological advances, there is an increased expectation to treat drug resistant epilepsy in dogs and cats by epilepsy surgery. However, the presurgical evaluation of epileptic animals, by using methodologies to detect the epileptogenic zone for example, have yet to become established in common practice. The epileptogenic zone, defined as the minimum amount of cortex to produce seizure freedom, consists of five conceptual cortical abnormal 'zones': symptomatogenic, irritative, seizure-onset, structurally abnormal (epileptogenic lesion) and functional deficit. These zones can now be detected by suitable modalities including ictal video monitoring, interictal non-invasive or invasive electroencephalography (EEG), ictal video-EEG, magnetoencephalography, structural and functional MRIs, or nuclear imaging. These diagnostic techniques are essential for selecting both appropriate patients and surgical techniques, and are also important in understanding the pathophysiology of epilepsy. This review describes the diagnostic techniques available for detecting each abnormal zone while considering the current veterinary status to realise future surgery for canine and feline epilepsy.