Name: FMRI Participant Preparation and Visual Cortex Scanning
Uploaded: 2023-12-08T12:40:00
Description: Watch this Scientific Journal Video about FMRI Participant Preparation and Visual Cortex Scanning at JoVE.com

fmri participant preparation and visual cortex scanning

推进视觉皮层映射以增强对视力障碍的评估

Functional magnetic resonance imaging (fMRI) is a valuable method to assess changes in regional neurovascular function within the visual cortex in response to stimuli, as changes in regional blood flow correlate to the activation of brain regions1,2. High-resolution retinotopic blood oxygenation level-dependent (BOLD) signal measurements represent changes in deoxyhemoglobin, which are driven by localized changes in blood flow and blood oxygenation within the brain1,2. BOLD activity patterns collected from fMRI data can be used to functionally map the peripheral and central visual cortex, as well as detect changes in the retinotopic map in response to visual impairment and neurodegeneration3.
Most previous fMRI studies made use of narrow-view (around &#177;12&#176; of the central visual field) non-retinotopic stimuli or simple retinotopic stimuli with narrow-view visual stimuli, which provided limited functional parcellation of the retinotopic representation in the visual cortex and limited assessment to only the central visual field, excluding the periphery3. Consequently, narrow-view fMRI data has reported inconsistent BOLD percent changes in glaucoma patients4,5,6. There is therefore a need for improved fMRI approaches to assessing the peripheral and central visual field, particularly in the evaluation of diseases such as glaucoma.
Glaucoma is the leading cause of irreversible blindness, affecting 10% of people by the age of 807. Glaucoma is caused by the progressive, irreversible neurodegeneration of retinal ganglion cells, which are responsible for transmitting visual stimuli to the brain through the optic nerve. In primary open-angle glaucoma (POAG), the most common form of glaucoma, increased intraocular pressure causes thinning of the retinal nerve fiber layer (RNFL), leading to the loss of peripheral vision followed by peripheral and central blindess8,9,10,11. Histological evidence from animal studies suggests that glaucoma additionally results in progressive neurodegeneration of the optic nerve, optic tract, lateral geniculate nucleus, optic radiation, and visual cortex12,13. MRI technology offers a minimally invasive method of assessing both blood oxygenation and neurodegeneration in the visual cortex. In patients with glaucoma, MRI has found evidence of gray-matter atrophy in the visual pathway13,14,15,16 and abnormal white matter in the optic chiasm, optic tract, and optic radiation1,17,18.
To further explore the effects on visual processing, fMRI can be used to detect brain function in response to visual cues. The protocol herein describes a novel method to obtain a low-cost, wide-view retinotopic map using high-resolution retinotopy fMRI with wide-field (&#62;100&#176;) stimuli, as described by Zhou et al3. Visual stimuli of expanding rings and rotating wedges were used to elicit retinotopic mapping of the eccentricity and polar angle for fMRI. BOLD fMRI percent changes were analyzed as a function of eccentricity to evaluate brain function, corresponding to both central and peripheral vision. The BOLD fMRI percent change may be used to visualize activation throughout the visual cortex. These fMRI measures provide a reliable new method to evaluate neurodegenerative changes and their functional effects on the visual cortex found in eye diseases involving visual field defects, such as glaucoma.

作者聚焦：通过宽视角 fMRI 映射洞察视觉皮层研究 

具有宽视网膜刺激的视觉皮层功能性磁共振成像 （fMRI）

This research focuses on providing a practical, cost-effective visual presentation system to evaluate changes in the visual cortex due to ophthalmic diseases. We provide a method to create a wide viewing angle, retina atopic map, using FMRI to assess the functional activity of the visual cortex. A current experimental challenge is that standard systems for presenting visual stimuli for FMRI only cover small area of the visual fields, and with the view partially obstructed by the head coil.This protocol provides method for wide view and unobstructed stimuli that balances cost, efficacy, and precision. Our protocol provides an affordable, moderately wide view of up to a hundred degrees of the visual field. Compared to other techniques, it avoids distortions, additional costs for projector lenses or fiber optic bundles, and other complexities, such as the need for contact lenses.Our findings can be used to expand the understanding of the visual cortex, enabling the mapping of peripheral and central regions via an affordable, wide view FMRI system. This could enhance the management of visual impairments in eye diseases such as glaucoma, which involves dysfunction of the visual system in the brain.

Watch this Scientific Journal Video about FMRI Participant Preparation and Visual Cortex Scanning at JoVE.com

FMRI Participant Preparation and Visual Cortex Scanning  

fMRI 参与者准备和视觉皮层扫描

首先指示参与者在成像扫描期间注视中央十字架。简要演示视觉刺激，使参与者熟悉该过程。将参与者舒适地放在扫描仪台上，并用泡沫衬垫将参与者的头部固定在头部线圈阵列的后半部分，以减少运动伪影。提供耳塞以保护他们的听力。使用扫描仪的定位系统将工作台移动到扫描仪孔中。将广角镜放置在距离参与者眼睛 10 厘米的地方。调整镜子以保持一致的视角。使用定位器扫描开始 fMRI 扫描，合并三个正交平面并调整扫描仪以进行频率和匀场校准。继续进行 MP-RAGE 解剖扫描以增强 EPI 切片定位。在 fMRI 协议开始时，指示参与者注视刺激中心灰色背景上的白色十字架 10 秒钟。通过显示一系列旋转楔子 30 秒，使用兼容程序创建视觉刺激。楔子应延伸到屏幕或镜子的边缘，并带有 8 赫兹对比度反转黑白棋盘图案。再展示白色十字架 10 秒钟。使用第二个 30 秒视觉刺激范式重复交叉固定和刺激显示，由扩张和收缩环组成。在实验过程中，以 100% 对比度保持 8 赫兹对比度反转黑白棋盘图案。成像完成后，将工作台滑出扫描仪孔，确保参与者保持静止。接下来，在放置头部线圈的前部之前，取下屏幕，然后取下镜子。将工作台放回扫描仪的中心。获取快速定位器扫描以考虑任何运动，然后使用全头线圈进行 MP-RAGE 扫描。极地地图显示，原发性开角型青光眼参与者和健康参与者之间没有明显差异。偏心率图显示，在原发性开角型青光眼患者中，由较小环刺激激活的旁中央凹中心区域显得较大。在原发性开角型青光眼患者中，不同偏心率的BOLD百分比变化降低，特别是在更外周的偏心率下。两组之间的BOLD变化显著减少，在较大的偏心率下更是如此。在原发性开角型青光眼患者中，中心视力的平均 BOLD 百分比变化仅略有减少，没有显着降低，而周边视力的变化显着减少。

Research

JoVE Journal

Neuroscience

fMRI Participant Preparation and Visual Cortex Scanning

Functional Magnetic Resonance Imaging (fMRI) of the Visual Cortex with Wide-View Retinotopic Stimulation

High-resolution retinotopic blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) with a wide-view presentation can be ...