Blood Oxygenation Level Dependent FMRI Psychology Essay

Blood Oxygenation Level Dependent FMRI Psychology Essay Functional magnetic resonance (fMRI) is the most widely used and powerful method of understanding the brain function and mapping neuroanatomy of the human brain. The most basic fMRI technique is blood oxygen level dependent (BLOD-fMRI). Paramagnetic deoxyhemoglobin in venous blood is a natural contrast agent for magnetic resonance imaging (MRI). Basic principles and methodological applications of BOLD-MRI as an introduction are presented in this article, and the relationship between neural activation and a magnetic resonance signal change is represented in much detail. Introduction Functional magnetic resonance (fMRI) is a widely recognized technique for brain mapping and providing the anatomical information of brain activity. It has been demonstrated that this method bases on the local hemodynamic changes that influence deoxyhemoglobin changes in venous blood. Furthermore, susceptibility changes produced by deoxyhemoglobin changes lead to the changes of MR signal strength. This effect is called blood oxygenation level dependent (BOLD) contract (1). High spatial and temporal resolution brain mapping can be structured by this basic method. Currently, it has become the most powerful study of brain function techniques. Compared with the traditional neuroimaging methods, including positron emission tomography (PET) and intrinsic signal optical reflection imaging, BOLD-fMRI can provide high spatial and temporal resolution sufficiently using internal concentration of oxygenation in human bodies as a natural contrast agent. Blood oxygen level dependent (BOLD) effect was firstly presented by Ogawa etc in 1990. They found that the magnetic resonance signal reduces when the concentration of oxyhemoglobin decreases. Also, their research showed that the reduction of signal not only occurs in blood, but also outside the blood vessels. Thus, they assert that this effect is caused by the property of magnetic field changes. After that, many researchers performed a large number of theoretical and experimental works to summarize the basis of BOLD-fMRI imaging. When neuron is activated, regional cerebral blood flow and oxygen consumption volume increase, but there are differences between the two increases, which is that the increase in cerebral blood flow is more than the oxygen consumption. Due to this difference, the venous oxygen concentration in active regions is significantly higher than the surrounding tissue and the concentration of deoxyhemoglobin reduces relatively. BOLD contrast has its origin in the fact that when normally diamagnetic oxyhemoglobin gives up its oxygen, the resulting deoxyhemoglobin is paramagnetic (2). Deoxyhemoglobin is a paramagnetic material which can produce local gradient magnetic field in the blood vessels and surroundings. Hence, it has effect on reducing T2. When brain areas are activated, the effect of reducing T2 decreases result from the reduction of deoxyhemoglobin. Compared with the resting state, T2 or T2* is relatively extended in local brain regions. Therefore, the signal is relatively enhanced on the T2 weighting or T2* weighting functional magnetic resonance imaging maps. Current MRI brain mapping studies all focus on off-on subtraction mode, which is the fMRI signal in active condition minus the signal under control conditions. The signal is extremely weak, and the relative increasing strength is 2%-5% generally. During imaging, the functional image of corresponding brain areas can be obtained if superimposing the high signal in different colors of active area on the high-resolution T1 weighting anatomical maps. This method is called blood oxygen level dependent contrast fMRI due to it depends on the level of oxygen in local blood vessels (1). This article reviews the basic principles and available methodological information and research on blood oxygen level dependent (BLOD-fMRI). This review begins with some basic principles on BOLD-fMRI. Furthermore, the methods for BOLD-fMRI will be described in detail including block design and event-related design. Also, the results of BOLD-fMRI studies will be presented and the advantages and limitations of the current research will be discussed as well. Finally, the key points and important aspects of the BOLD-fMRI will be summarized as a conclusion. Materials and Methods BOLD-fMRI experiment steps include: firstly, make experimental planning and determine the most optimal stimulus or task programs. Secondly, high T1 WL resolution anatomical images and a great number of original images in stimulation and rest states can be obtained by scanning. Lastly, functional active maps should be obtained by experimental data analysis. Block design bases on cognitive subtraction mode to show the stimulus task in block form. A tropical block design contains two basic tasks which are experimental tasks and control tasks, and the two intervals of blocks appear. Task-related brain activities can be understudied by the comparison of regional cerebral blood oxygen reaction through stimulation and control tasks. It is widely used in locating brain function. It is the early main method to do functional magnetic resonance imaging experiments. The advantages are simple and easy to perform tasks. However, the drawback is that the BOLD signal changes larger result in long stimulation time and the high rate of oxygen reaction. In blocked designs, regardless of stimulus presentation or task performance interdigitated with rest, observing the relationship of the time course of BOLD response to activation paradigm is possible (3). Also, more than one image can be obtained during every experimental and rest period. The signal time course should be assumed to be activated, and it can be tested. A simple example is presented in Figure 1(a). Firstly, switch on and off the visual stimulation (black and green) quickly for 10 times. It is shown that the time course of pixels follows the stimulation paradigm. However, the difference between the stimulation and time course is quite obviously (p