具有宽视网膜刺激的视觉皮层功能性磁共振成像 （fMRI）
Summary
我们已经开发了利用比常用更多的视野来绘制视觉皮层功能的技术。这种方法有可能加强对视力障碍和眼部疾病的评估。
Abstract
具有宽视角表现的高分辨率视网膜血氧水平依赖性 （BOLD） 功能性磁共振成像 （fMRI） 可用于功能性地绘制外周和中央视觉皮层。这种测量视觉大脑功能变化的方法允许枕叶的功能映射，刺激>100°（±50°）或更多的视野，而标准fMRI视觉呈现设置通常覆盖<30°的视野。BOLD fMRI的简单宽视角刺激系统可以使用普通的MR兼容投影仪进行设置，方法是将大镜子或屏幕放置在靠近受试者脸部的位置，并仅使用标准头部线圈的后半部分来提供宽视角而不会阻碍他们的视线。然后可以使用各种视网膜刺激范式对宽视网膜 fMRI 图进行成像，并且可以分析数据以确定与中央和周边视觉相对应的视觉皮层区域的功能活动。这种方法提供了一个实用的、易于实施的视觉呈现系统，可用于评估由于青光眼等眼部疾病以及可能伴随的视力丧失而导致的外周和中央视觉皮层的变化。
Introduction
功能性磁共振成像 （fMRI） 是一种有价值的方法，用于评估视觉皮层内区域神经血管功能对刺激的反应，因为区域血流的变化与大脑区域的激活相关 1,2。高分辨率视网膜血氧水平依赖性 （BOLD） 信号测量表示脱氧血红蛋白的变化，这是由脑内血流和血氧的局部变化驱动的 1,2。从 fMRI 数据中收集的 BOLD 活动模式可用于功能性地绘制外周和中央视觉皮层，以及检测视网膜位图的变化以响应视觉障碍和神经退行性变3。
以前的大多数 fMRI 研究使用窄视距（中央视野约 ±12°）非视网膜刺激或具有窄视视网膜刺激的简单视网膜刺激，这为视网膜皮层中的视网膜表征提供了有限的功能性包裹，并且仅对中央视野（不包括外周）的评估有限3。因此，窄视 fMRI 数据显示青光眼患者的 BOLD 百分比变化不一致 4,5,6。因此，需要改进功能磁共振成像方法来评估周边和中央视野，特别是在评估青光眼等疾病时。
青光眼是不可逆转失明的主要原因，影响 10% 的 80 岁7 人。青光眼是由视网膜神经节细胞进行性、不可逆的神经退行性变引起的，视网膜神经节细胞负责通过视神经将视觉刺激传递到大脑。在原发性开角型青光眼 （POAG） 中，最常见的青光眼形式，眼压升高会导致视网膜神经纤维层 （RNFL） 变薄，导致周边视力丧失，随后出现周边和中央失明 8,9,10,11。来自动物研究的组织学证据表明，青光眼还会导致视神经、视束、外侧膝状核、视辐射和视觉皮层的进行性神经退行性变12,13。MRI 技术提供了一种评估视觉皮层血氧和神经退行性变的微创方法。在青光眼患者中，MRI 发现视觉通路13、14、15、16 有灰质萎缩的证据，视交叉、视束和视辐射 1,17,18 有异常白质的证据。
为了进一步探索对视觉处理的影响，fMRI可用于检测大脑功能对视觉线索的反应。本文的协议描述了一种使用具有宽视场 （>100°） 刺激的高分辨率视网膜 fMRI 获得低成本、宽视角视网膜图的新方法，如 周 等人3 所述。使用膨胀环和旋转楔形的视觉刺激来引出 fMRI 的偏心率和极角的视网膜定位。将 BOLD fMRI 百分比变化分析为偏心率的函数，以评估大脑功能，对应于中央和周边视觉。BOLD fMRI 百分比变化可用于可视化整个视觉皮层的激活。这些功能磁共振成像测量提供了一种可靠的新方法来评估神经退行性变化及其对涉及视野缺陷的眼部疾病（如青光眼）中视觉皮层的功能影响。
Protocol
德克萨斯大学健康科学中心和石溪大学根据机构指南对人类参与者进行研究，并获得参与者的知情同意，并使用他们的数据。 1. MRI扫描仪和成像协议的设置 对于 fMRI，请使用带有多通道接收器头线圈的 3T MRI 扫描仪。也可以使用不同的场强，但可能会遇到信噪比 （SNR） 或失真伪影的困难，因此请进行相应调整。仅使用头部线圈的后半部分进行 fMRI，以允?…
Representative Results
如周等人之前描述的那样，使用上述宽视fMRI协议评估了9名被诊断患有POAG的参与者（4名男性，36-74岁）和9名年龄匹配的健康志愿者（6名男性，53-65岁）。通过评估与青光眼、视盘拔罐和/或眼内压 （IOP） 大于 21 mmHg3 一致的视野缺损的表现，在开角患者中临床确诊 POAG。使用广视角视觉呈现 （±55°） 评估每组的中央和周边视力3。 <p class="jov…
Discussion
上述利用广视网膜视网膜 fMRI 的方案是评估视力丧失和眼部疾病对大脑影响的创新方法。通过使用更宽的视野屏幕对视觉皮层进行宽视网膜定位，这种方法可以更全面地了解视觉系统的功能组织。这可以更好地了解大脑视觉处理系统的异常，这发生在神经退行性疾病中，例如青光眼24,25。该技术还可用于检测和分析导致失明的其他条件下的大脑退化和重…
Disclosures
The authors have nothing to disclose.
Acknowledgements
这项工作得到了美国国立卫生研究院的支持[R01EY030996]。
Materials
| 1/4"-20 nylon machine screws, knurled head thumb screw | to attach rod to PVC frame | ||
| 1-1/4 inch PVC pipe | length of ~5-10 ft is needed | ||
| 3T MRI scanner | Siemens | ||
| 6-32 nylon machine screws, rounded head | to attach mirror/screen to rod | ||
| 8-channel head array coil | Siemens | ||
| 90 degree PVC elbow, 1-1/4 inch fitting | |||
| Acrylic mirror | Width and length of 25-30cm | ||
| Acrylic rod | 1 inch width, ~ 2 ft long depening on size of scanner bore and head coil | ||
| E-Prime | Psychology Software Tools | to prepare and present visual stimuli paradigms | |
| Plywood sheet, 1/2 inch thick | Size should be at least as large as the scanner bore. Cut as bore-sized frame for the projection screen | ||
| Rear projection screen | Size should be at least as large as the scanner bore |
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Cite This Article
Galenchik-Chan, A., Chernoff, D., Zhou, W., Duong, T. Q., Muir, E. R. Functional Magnetic Resonance Imaging (fMRI) of the Visual Cortex with Wide-View Retinotopic Stimulation. J. Vis. Exp. (202), e65597, doi:10.3791/65597 (2023).