Deep brain stimulation in flat coil signal coupling technology (1)

Parkinson's disease (Parkinson ' s Disease, PD) is a common middle and old age, disease of the nervous system degeneration diseases occur in parts of the brain, which in a group of neurons, synthesis in substantia nigra can be called the "dopamine," neurotransmitter, projected onto certain areas in the brain, motor function for adjusting [1].

If the substantia nigra of Neuron degeneration killed more than 80%, the brain neurotransmitters dopamine can no longer regulate the normal function of the nervous system, there will be the symptoms of Parkinson's disease. In our country, 55 years old, approximately 170 million, prevalence in patients with Parkinson's and European and American countries.

At this stage, in addition to drug therapy, surgery can also play a very good effect, common methods are: brain cell transplantation, pallidotomy and stimulation of brain depth (Deep Brain Stimulation, DBS) i.e. brain pacemaker.

Brain cell transplantation and gene therapy while already in animal experiments and achieved great success, but due to lack of ideal transplant clinical organizations [3], currently remains in the laboratory stage, should not be widely used. Pallidotomy is the use of electrical Cauterization method destroys brain dysfunction excited nuclei, although the effect has been recognized, but as a destructive operation complications, easy, and recurrence in patients with age, indications, and is quite high, there is an obvious shortcomings [4]. Deep brain stimulation [5] is the use of brain stereotaxic surgery on the brain in a special location implantation, through high-frequency electrical stimulation to suppress abnormal electrical activity of neurons, thereby play a treatment effect. The technique most major characteristic is the efficacy, safety, available through the control of postoperative adjust to optimally, side effects, not destroy brain organization, and does not affect future other new methods of treatment. As a result, the current DBS technology has basically replaces the damage of a surgical treatment of Parkinson's disease.

Clinical application of brain pacemaker mainly consists of four parts [6], the implant body parts: Nerve Stimulator, brain pacemaker wires, extension cords, in part to control the magnet.

Nerve Stimulator consists of a battery and a set of micro-circuit system, subcutaneous implantation of clavicle, near to the extended line will produce electrical signal transmission to the destinations in the brain of the deep. Each brain pacemaker wire includes 4 thin insulation coil and State-of-the-art 4 1.5mm electrodes, wire or using a combination of electrodes to deliver stimulating electrodes. Extension cord implant to subcutaneous, through the head, neck, shoulder of insulated wire to wire and implanted nerve Stimulator. Control of magnetic part for patients, patients can be manipulated to control magnet placed above the nerve Stimulator to control stimulator of the switch. This brain pacemaker pulse generator is usually only the maintenance of the battery 5 ~ 8 years battery exhaustion after the need to replace the clavicle subcutaneous and pulse generators, multiple implants in foreign bodies may cause skin ulcers. Only the United States of Medtronic Inc. (Medtronic Inc.) Production of brain pacemaker (Activa Therapy) for the United States food and Drug Administration (FDA) approved by [6], Medtronic company occupies a clinical required brain pacemaker monopoly to China's patients, which is very expensive. In view of this, the depth of brain stimulation system for independent research and development and further improvement has become particularly important.

This article discusses a new brain pacemaker — external brain pacemaker, the brain pacemakers in the traditional brain pacemaker have improved on the basis of the signal generator, control devices and power all move to in vitro, intracranial leaving stimulation electrode.

The advantages of this design is to avoid a wound, below the clavicle and avoid a lot of conductors in the body, reduces the risk of infection, minimize the pain of the patient. External pulse generator free replacement so that patients are no longer under battery power, use more convenient and easier.

System design

External brain pacemaker use coil can coupling characteristics of AC signal to pass stimulus signals.

The system is divided into two parts, which are located in both sides of the human head, scalp in section includes signal generator, controllers, power supplies and display devices, in vitro and in vivo part mainly Stimulator, System block diagram shown in Figure 1. Two relatively independent part consists of a pair of coil, will stimulate the signal coupling by in vitro to in vivo Stimulator. External brain pacemaker brings to patients with easily, but also to design a certain challenge. Because the signal is transmitted through the scalp in the past, so in order to guarantee the intracranial accept to pulse signal waveform and power to meet the requirements of the treatment.

Brain coil (secondary coils) and brain-coil (primary)

Secondary coils as needed and stimulating electrode attached coil, as a secondary coils to implantation in human brain, use exceptional shape coil to save space, the smaller the thin coil is ideal.

This article is designed as a flat disc-shaped coil, theoretically the coiling into single layer, like a mosquito's shape, but considering the actual winding of technical reasons, the coil is divided into 10 layers Planar disc, 100 turn on each floor. Choose the diameter of the wire for 0.06mm, so the whole coil thickness only 0.6mm, outer diameter d1 = bore diameter d2 = 30mm, 18mm.

Since the primary coil can be placed in the brain to the scalp, so the primary coil size and shape of requirements than the secondary coils, as long as possible and try to be thin.

Design of the primary coil windings for 800, the diameter of the wire-wound 0.2mm, also as far as possible around the plane the original disc, you can allow certain thickness. After measuring, coil thickness 5 mm, outside diameter d1 = bore diameter d2 = 20mm, 12mm.

Inductance and mutual inductance