Functional Magnetic Resonance Imaging: An Overview of Technical Advances and Clinical Applications

1. Introduction

In the second half of the 19th century, researchers first observed the effect of brain circulation on brain activity. In 1890s, C. Roy (1836-1914) and Charles Scott Sherrington (1857-1952) suggested that blood circulation in the brain may be related to metabolism, thereby establishing the relationship between neuronal activity and brain circulation (Molnár and Brown 2010). Since then, the investigation of brain is no longer limited to its anatomy (Smitha et al. 2017). After Edward M. Pelcell (1912-1997) and Felix Bloch (1905-1983) discovered the phenomenon of nuclear magnetic resonance in 1946, magnetic resonance imaging (MRI) techniques have been developed for physiological research and clinical diagnosis.

In 1990, Ogawa and colleagues at AT&T Bell Laboratories began investigating how the blood oxygen level dependent (BOLD) mechanism could be used to detect brain function in mice at 7T and 8.4T magnetic resonance (Ogawa and Sung 2019, Ogawa and Lee 1990, Ogawa et al. 1990). In 1991, the first fMRI images were obtained using endogenous BOLD comparisons (Uğurbil 2012). The same year, Belliveau's blood volume silhouette, published in Science, opened the door to exploring human brain with MRI (Belliveau et al. 1991). In subsequent years, functional magnetic resonance imaging (fMRI) has become one of the most important imaging methods for investigating human brain activities and clinical diagnosis of neurological diseases.

Figure 1 shows the trend of publication since 1990s. The literature search was performed using the keyword “functional magnetic resonance imaging” on three mainstream research databases: Scopus, PubMed, and ScienceDirect. The results revealed rapid growth of publications on fMRI since 2000s.

Figure 1.

Number of publications on functional magnetic resonance imaging in three mainstream research databases from 1990 to 2023

3. Classification Of Fmri

fMRI can be divided into resting state fMRI (RS-fMRI) and task based fMRI (TB-fMRI) according to the brain state. The former refers to the state when the brain does not perform specific cognitive tasks, keeps quiet, relaxed and awake, and is the most basic state, while the latter refers to the state when the brain performs specific tasks such as memory, recognition and movement (Ott et al. 2021).