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。

fmri-participant-preparation-and-visual-cortex-scanning

Research

JoVE Journal

Neuroscience

fMRI Participant Preparation and Visual Cortex Scanning

154 次观看.  Renaissance School of Medicine at Stony Brook University. 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?...

视频: 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 used to functionally map the peripheral and central visual cortex. This method for measuring functional changes of the visual brain allows for functional mapping of the occipital lobe, stimulating &gt;100&#176; (&plusmn;50&#176;) or more of the visual field, compared to standard fMRI visual presentation setups which usually cover &lt;30&#176; of the visual field. A simple wide-view stimulation system for BOLD fMRI can be set up using common MR-compatible projectors by placing a large mirror or screen close to the subject's face and using only the posterior half of a standard head coil to provide a wide-viewing angle without obstructing their vision. The wide-view retinotopic fMRI map can then be imaged using various retinotopic stimulation paradigms, and the data can be analyzed to determine the functional activity of visual cortical regions corresponding to central and peripheral vision. This method provides a practical, easy-to-implement visual presentation system that can be used to evaluate changes in the peripheral and central visual cortex due to eye diseases such as glaucoma and the vision loss that may accompany them.

We have developed techniques for mapping the visual cortex function utilizing more of the visual field than is commonly used. This approach has the potential to enhance the evaluation of vision disorders and eye diseases.

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

科研

神经科学

MRI Scanner Setup for Human Visual Functional Imaging

Begin by using a 3T MRI scanner equipped with multi-channel receiver head coils for functional magnetic resonance imaging. Use the posterior half to ensure a larger viewing angle without obstruction. Next, set up a T1 weighted MPRAGE sequence by inputting a repetition time of 2.2 seconds and a field of view of 176 by 256 by 208 millimeters.Provide a spatial resolution of 1 by 1 by 1 millimeter. Bandwidth of 190 hertz per pixel. Flip angle of 13 degrees.And a scan duration of 3.1 minutes. Set up a gradient echo EPI sequence with a repetition time of 2 seconds, echo time of 30 milliseconds, field of view of 220 by 220 millimeters, in-plane resolution of 1.7 by 1.7 millimeters with 29 slices of 3 millimeters thickness, and a bandwidth of about 1500 hertz per pixel. Now, measure the dimensions of the head coil and scanner bore.Then, connect the PVC tubes with PVC elbows to construct a simple PVC pipe frame, and with nylon screws, attach the ends of the plastic rod holding the mirror to the frame. Note that the mirror is attached to the plastic rod with plastic screws. Make sure that the screws are loose enough for the mirror to be manually rotated to an optimum angle.After screwing a segmented rear projection screen to a frame, place the screen inside the back of the scanner, positioning it behind the head coil to maximize the field of view.

用于人体视觉功能成像的 MRI 扫描仪设置

Begin by instructing the participant to fixate on the central cross during the imaging scans. Briefly demonstrate the visual stimulation to familiarize the participant with the procedure. Position the participant comfortably on the scanner table and immobilize the participant's head in the posterior half of the head coil array with foam padding to reduce motion artifacts.Provide ear plugs to protect their hearing. Use the scanner's positioning system to move the table into the scanner bore. Place the wide-view mirror 10 centimeters from the participant's eyes.Adjust the mirror to maintain a consistent viewing angle. Begin fMRI scanning with a localizer scan, incorporating three orthogonal planes and adjusting the scanner for frequency and shimming calibration. Proceed with an MP-RAGE anatomical scan for enhanced EPI slice positioning.At the start of the fMRI protocol, instruct the participant to fixate on the white cross atop a gray background at the stimuli's center for 10 seconds. Create visual stimuli using a compatible program by displaying a series of rotating wedges for 30 seconds. The wedges should extend to the edge of the screen or mirror with an eight-hertz contrast-reversing black and white checkerboard pattern.Present the white cross for an additional 10 seconds. Repeat cross fixation and stimulation display with the second 30-second visual stimulation paradigm, consisting of expanding and contracting rings. Maintain an eight-hertz contrast-reversing black and white checkerboard pattern at 100%contrast during the experiment.Upon completion of imaging, slide the table out of the scanner bore, ensuring the participant remains still. Next, remove the screen and then remove the mirror before placing the anterior portion of the head coil. Position the table back into the center of the scanner.Acquire a quick localizer scan to account for any movement, followed by an MP-RAGE scan using the full head coil. The polar maps revealed no obvious differences between the primary open-angle glaucoma participants and healthy participants. The eccentricity maps showed that the central region of the parafovea that was activated by the smaller ring stimuli appeared larger in the primary open-angle Glaucoma patient.BOLD percent changes at different eccentricities were reduced in primary open-angle glaucoma patients, especially at more peripheral eccentricities. The BOLD changes were significantly reduced between the two groups, more so at larger eccentricities. The BOLD percent changes averaged for central vision were only slightly and not significantly reduced in primary open-angle glaucoma patients, while the changes were significantly reduced for peripheral vision.