Speaker - Dr. Li Da

It is a great honor to invite Dr. Li Da from the Institute of Anthropology of East China Normal University to give a report in this lecture. The topic of the report is: clinical application of transcranial magnetic diagnosis and treatment technology in precise neuromodulation. The following is an excerpt from Dr. Li Da’s live broadcast:

Live Broadcast Excerpts

1 What is the precision of TMS

One is energy accuracy. This energy includes the energy given to the brain and the energy actually given by the device. One is the dose of the drug given, and the other is the drug concentration level.

The second is accurate location. Similar to pharmacodynamics, transcranial magnetism also requires a target. Its target is the brain, but sometimes it is not a region, but a node of a circuit, or even multiple sites of a circuit.

The third is accurate operation. The operation and treatment process of transcranial magnetism directly determine the curative effect. It is recommended to use the logic of precision medicine to understand the precise treatment of transcranial magnetism.

2 Factors that affect accuracy

The energy of physical therapy and the energy acting on the brain are two concepts. The output of an energy by the instrument does not mean that this energy has completely reached the brain to produce benefits. What we need to capture is actually the energy that our therapeutic devices really stimulate the brain. We address this issue by measuring thresholds in transcranial magnetic therapy. Threshold determination is generally performed by transcranial magnetic contralateral stimulation of the thumb abductor muscle or the corresponding motor area of the index finger. One TMS pulse can be evoked after the stimulation, and when the evoked potential exceeds 50μv five times per ten times of stimulation, we define it as a threshold energy. We think this energy is just enough to stimulate the cerebral cortex. Since the thickness of the cortex is different for each person, the sensitivity of the cortex is different, so when the energy of the same physical parameter is given, their biological effect energy may not necessarily be the same. We're going to titrate the physical therapy energy against the biological effect energy. The premise of all precision therapy is that the energy is accurate, which requires the use of supporting electromyography.

In most clinical cases, the combination of drugs and transcranial magnetic therapy is used. Basic drugs can directly affect cortical excitability, and further affect the energy of transcranial magnetic therapy. When the drug acts on the voltage-gated channel, it will affect the excitability of the cortex. When we stimulate the motor area with the same energy, its evoked motor potential level will change, which requires us to re-determine the threshold. If there is a change in the drug category or dosage during the entire transcranial magnetic therapy process, it is necessary for us to adjust the threshold to ensure the accuracy of the energy.

There are three main types of coils commonly used in clinical practice: figure-8 coils, circular coils and deep coils. Figure-8 coils can focus on a more accurate range, and circular coils can cover more ranges, which need to be selected according to specific clinical needs. Depth and accuracy cannot be achieved at the same time with transcranial magnetic alone.. Deep coils can stimulate deeper areas such as the ACC, but the focusing performance is not as good as figure-8 and circular coils, and its accuracy cannot be guaranteed.

The placement of the coils determines the true spread of the energy. Clinical stimulation of the brain area and the placement of the coil is closely related. Before navigation, our precision treatment was actually based on the experience of the clinician.

In addition, the head of the treatment patient should be fixed in a certain position and cannot be deviated at will.

3 The needs?for precision therapy?

In the absence of brain image imaging, the EEG cap was used, and the electrode points marked on the cap corresponded to the position under the cortex. Although this traditional method is widely used, there are some errors in fact. Individual differences in the way caps are worn, size, and head size, etc., can lead to errors of more than 2cm.

4? How to treat with precision

Anatomical image navigation based on T1 image: After scanning the brain MRI, match it with the skull and reconstruct the brain image. And use the near-infrared imaging camera to capture the position of the head shell, and at the same time carry out optical marking on the coil.

TMS precision treatment based on fMRI navigation: The reconstruction of the navigation structure image has low requirements on the magnetic field strength of the equipment, and the reconstruction can be completed by adjusting the scanning parameters when the magnetic field strength is small. But the function like strongly recommends that the magnetic field strength is 3T.

The navigation and positioning system developed by West China Hospital: the method based on 3D model reconstruction is faster than traditional navigation and more suitable for clinical use. Many targets are integrated in the system, and targets can be selected by inputting coordinate axes or based on clinical evidence. After the coil automatically marks the target, the coil with an adjusted angle can be moved to the target area to achieve stimulation perpendicular to the cortical target. In addition, targets can be selected based on functional maps.

The navigation and positioning system developed by Professor Zhu Chaozhe of Beijing Normal University: It can realize the precise positioning of the target without T1 image or based on near-infrared imaging. Navigation and positioning based on the external marking method is equivalent to topping the cortex to the scalp, which can be measured manually or based on software. Compared with traditional navigation, the positioning time is faster and the convenience is better.

5 The possibility of precision therapy

PTSD: The patient's cortical excitability (threshold) differs between the two hemispheres. The specific performance is a sharp decrease in cortical excitability and obvious lateralization of cortical excitation. However, there was no such situation in the normal control group. It can be seen that this threshold difference can be used as a reference for PTSD diagnosis and evaluation. We therefore encourage determination of bilateral thresholds. Since different symptom groups of PTSD have different stimulation targets, different thresholds are used to stimulate different brain regions, which is helpful for precise treatment.

MDD: The effective rate of treatment based on navigation coordinates is significantly higher than that based on traditional positioning methods.

Suicide: The point coordinates with significant differences in left dorsolateral frontal cortex activation between depression with suicide and depression without suicide were registered to MRI. Saturation dose (3000 pulses in the morning and 3000 pulses in the afternoon), high frequency (10Hz), 90% MT, and stimulation of registration sites, the results showed that the symptoms of depression were significantly improved.

Sleep disorders: Taking the most typical insomnia as an example, it generally stimulates the parietal lobe of the patient. This is because rTMS stimulation along the midline region from front to back was found to elicit the greatest slow potential response when stimulating the parietal lobe. With the increase of research, it is found that sleep disorders such as depression, anxiety, insomnia, or lethargy often have different stimulation sites, and navigation technology is required to achieve more precise positioning.

Other clinical application scenarios: Conventional transcranial magnetism can only stimulate the cortex, but not the subcortex. The cerebral cortex is widely connected with subcortical brain regions. This connection is based on neurophysiological anatomy and functional network connection. The treatment area of the disease is under the cortex, while the area of functional damage is presented on the cortex, such as Parkinson's and stroke. Based on the cortical areas with abnormal functional connections, we can find a direction to intervene. See if activation is increased or decreased compared to normal or after medication. If the activation increases, we suppress it with low frequencies, otherwise we boost it with high frequencies. Based on brain imaging technology, guiding transcranial magnetism to develop new clinical treatments is the main task of the current navigation and positioning system.

Application of preoperative navigation and positioning to optimize the rehabilitation outcome: When the tumor has spread to the motor area, and it is intended to conduct functional localization before craniotomy to investigate the degree of damage and the degree of deformation after being squeezed, individualized detection based on navigation can be performed before surgery to mark the functional normal or damaged area. This is also important in guiding postoperative outcomes to optimize rehabilitation outcomes and to sacrifice the least amount of healthy brain area with the least amount of cost when the affected area is removed.

Note: The above content is part of the text without changing the original meaning from the speakers. To watch the full live video (in Chinese), please go to Live Broadcast Entrance.