What Is an fMRI Machine?

Functional magnetic resonance imaging (fMRI) detects changes in the cerebral cortex signals of patients / subjects after receiving stimulation (visual, auditory, tactile, etc.), and is used for the in-depth study of the cortical central functional area and other brain functions .

Functional magnetic resonance imaging

Magnetic resonance brain functional imaging (fMRI) is a research method that stimulates specific senses, causes neural activity (functional area activation) in corresponding parts of the cerebral cortex, and displays them through magnetic resonance images.

fMRI was originally adopted

Including basic research and clinical application of normal brain function, the main aspects currently involved include: neurophysiology and neuropsychology.

fMRI was first applied to the study of neurophysiological activities, mainly the study of visual and functional cortex. Later, with the improvement of the precision of the stimulation plan and the advancement of experimental technology, the research of fMRI gradually expanded to the study of the functional cortex of hearing, language, cognition and emotion and psychological activities such as memory.

For fMRI studies of cerebral neuropathy, a large number of papers have been reported, involving epilepsy, Parkinson's syndrome, Alzheimer's disease (AD), multiple sclerosis (MS) and cerebral infarction. Because of its high resolution in time and space, it is of great significance for the early diagnosis, identification, treatment and follow-up of the disease. In terms of mental illness, there are also corresponding studies on patients with schizophrenia and depression.

fMRI can provide sensitive, objective and accurate information evaluation for the research, diagnosis, progress estimation and experimental intervention evaluation of neurological diseases. It is of great significance to formulate surgical and radiotherapy plans for tumor lesions, estimate prognosis, reduce surgical injuries and complications, and improve the quality of life after surgery.

The fMRI experimental design is mainly implemented by the "OFF-ON subtraction mode of baseline-task stimulation".

Through the external regular, interactive task and stationary stimulus, the signals in the same area under the activation and control conditions are obtained. After the Fourier transform, a series of dynamic original images over time are obtained. During image post-processing, the original image in two states is matched and subtracted by setting thresholds. After the subtraction image is subjected to pixel averaging, statistical methods are used to reconstruct a credible functionally-stimulated image. The currently used statistical methods are mainly correlation analysis and t-test. Through these post-processing, we can not only improve the reliability of the experimental results, but also effectively eliminate some image artifacts.

Technically, the BOLD effect for small blood vessels is proportional to the square of the field strength, so the fMRI study is more suitable for systems with high field strength. Studies have shown that systems with field strength below 1.5T are not suitable for brain function research. For imaging sequence requirements, T2 * effect-sensitive fast imaging sequences are generally used, such as GRE, GRE-EPI, and SE-EPI.

At present, most fMRI imaging requires MR equipment with high field strength above 1.5-2.0T. Generally, GRE sequences sensitive to T2 effect and fast imaging EPI sequences are used. The disadvantages of pure GRE sequence imaging are that the image acquisition time is long, the number of imaging layers is limited, and the image is easily affected by motion to generate artifacts. EPI was first described by MansField in 1997 [5]. This technology reduces multiple scans in classic imaging to one scan, which greatly improves the imaging speed. At present, most high field strength MR machines use GRE and EPI phase. Combined sequence EPI. Gradient field switching speed is fast, single or less than one excitation can complete the entire K-space data acquisition, imaging time can be shortened to 30-100ms, which greatly reduces motion artifacts.