功能磁共振成像在弱视中的应用

功能性磁共振基于血管内血氧浓度的变化,可以无损伤地反映活体大脑功能,其在脑功能相关的视觉问题中的应用,使人们有机会从整体水平了解弱视患者脑功能的损害特点,还能通过它观察眼优势柱转移,比较不同类型弱视的脑功能改变,以及药物治疗的监测等。本文就功能性磁共振成像基本原理特点、实验设计、技术要求及其在弱视中应用作一综述。     

Functional magnetic resonance imaging of the retina

PURPOSE: This study explored the feasibility of mapping the retina's responses to visual stimuli noninvasively, by using functional magnetic resonance imaging (fMRI). METHODS: fMRI was performed on a 9.4-Tesla scanner to map activity-evoked signal changes of the retina-choroid complex associated with visual stimulation in anesthetized cats (n = 6). Three to 12 1-mm slices were acquired in a single shot using inversion-recovery, echo-planar imaging with a nominal in-plane resolution of 468 x 468 microm(2). Visual stimuli were presented to the full visual field and to the upper and lower visual fields. The stimuli were drifting or stationary gratings, which were compared with the dark condition. Activation maps were computed using cross-correlation analysis and overlaid on anatomic images. Multislice activation maps were reconstructed and flattened onto a two-dimensional surface. RESULTS: fMRI activation maps showed robust increased activity in the retina-choroid complex after visual stimulation. The average stimulus-evoked fMRI signal increase associated with drifting-grating stimulus was 1.7% +/- 0.5% (P < 10(-4), n = 6) compared with dark. Multislice functional images of the retina flattened onto a two-dimensional surface showed relatively uniform activation. No statistically significant activation was observed in and around the optic nerve head. Hemifield stimulation studies demonstrated that stimuli presented to the upper half of the visual field activated the lower part of the retina, and stimuli presented to the lower half of the visual field activated the upper part of the retina, as expected. Signal changes evoked by the stationary gratings compared with the dark basal condition were positive but were approximately half that evoked by the drifting gratings (1.0% +/- 0.1% versus 2.1% +/- 0.3%, P < 10(-4)). CONCLUSIONS: To the best of our knowledge, this is the first fMRI study of the retina, demonstrating its feasibility in imaging retinal function dynamically in a noninvasive manner and at relatively high spatial resolution.     

Functional magnetic resonance imaging of the visual system.

Functional magnetic resonance imaging (fMRI), which is a technique useful for non-invasive mapping of brain function, is well suited for studying the visual system. This review highlights current clinical applications and research studies involving patients with visual deficits. Relevant reports regarding the investigation of the brain's role in visual processing and some newer fMRI techniques are also reviewed. Functional magnetic resonance imaging has been used for presurgical mapping of visual cortex in patients with brain lesions and for studying patients with amblyopia, optic neuritis, and residual vision in homonymous hemianopia. Retinotopic borders, motion processing, and visual attention have been the topics of several fMRI studies. These reports suggest that fMRI can be useful in clinical and research studies in patients with visual deficits.     

JJO special issue: Functional imaging of the retina

Preface to Reviews

JJO special issue: Functional imaging of the retina     

急性视神经炎的功能磁共振成像研究

目的应用功能磁共振成像技术探讨急性视神经炎的皮层功能变化。方法以1.5T磁共振成像系统采集14例单眼急性视神经炎、12例正常人视皮层BOLD-fMRI数据,比较正常组与视神经炎组两眼分别刺激时的视皮层激活像素数与激活信号平均强度,分析BOLD-fMRI数据与PVEPP100波潜时的相关性。结果正常组与视神经炎组枕叶视皮层、颞下回、后顶叶都有不同程度的兴奋,主要兴奋区位于枕叶距状裂周围。与对侧眼相比,视神经炎患眼刺激的皮层激活像素减少、激活信号平均强度降低。治疗4周后,患眼视力提高,皮层激活像素明显增多,屏状核、额前叶、丘脑亦有不同程度的兴奋。P100波潜时与皮层激活像素数呈负相关。结论功能磁共振成像技术可以反映视神经炎的皮层功能改变,为视神经炎的临床诊断和预后评估提供新的依据。     

共同性斜视患者大脑皮层激活强度的功能磁共振研究

目的　采用血氧水平依赖性功能磁共振成像（ｂｌｏｏｄｏｘｙｇｅｎｌｅｖｅｌｄｅｐｅｎｄｅｎｔｆｕｎｃ-ｔｉｏｎａｌｍａｇｎｅｔｉｃｒｅｓｏｎａｎｃｅｉｍａｇｉｎｇ,ＢＯＬＤ-ｆＭＲＩ）技术比较共同性斜视患者与正常受试者在接受不同视差的立体图刺激下激活脑区和激活强度的差异。方法　选取共同性斜视患者１２例,立体视觉正常者１０例,进行组块设计的ｆＭＲＩ研究。采用ＳＰＭ５对数据进行预处理及分析。结果　两组激活强度比较差异有统计学意义（Ｐ＜０．０５）。在视差１２００″刺激下,共同性斜视组激活强度低于正常组的区域表现为双侧枕中回（ＢＡ１８）、双侧额下回（ＢＡ４５／４７）、右侧颞下回（ＢＡ３７）、左侧顶下小叶（ＢＡ４０）、左侧中央后回（ＢＡ２）、左侧岛叶（ＢＡ１３）。在视差２４００″刺激下,共同性斜视组激活强度低于正常组的区域表现为双侧枕中回（ＢＡ１８）、右侧颞下回（ＢＡ３７）、双侧海马（ＢＡ２８）、左侧颞上回（ＢＡ２０）;共同性斜视组激活强度高于正常组的区域表现为右侧舌回（ＢＡ１８）。在视差３６００″刺激下,共同性斜视组激活强度低于正常组的区域表现为右侧额下回（ＢＡ４７）、左侧枕中回（ＢＡ１８）、右侧枕下回（ＢＡ１８）、左侧岛叶（ＢＡ１３）;共同性斜视组激活强度高于正常组的区域表现为右侧额中回（ＢＡ８／１０）。结论　共同性斜视患者右侧舌回、额中回的激活强度高于正常人,双侧枕叶、颞叶、额叶及左侧岛叶、顶叶的激活强度均低于正常人。     

Functional MRI of brain activation by eye blinking.

Functional magnetic resonance imaging (fMRI) was used to map cortical areas that control eye blinking. T2*-weighted asymmetric spin-echo MRI (or BOLD-blood oxygen level dependent-MRI) was used to detect changes caused by focal variations in blood oxygenation. Six normal volunteers and two cases of dry eye (less than 5-mm Schirmer's test) entered the study. The experimental scheme consisted of three cycles of a two-step sequence: (eyes closed)-(blink or blink inhibition). And to minimize contamination from photic activation, the experiments were carried out in a dark environment and the volunteers reported no light perception during the MR scans.In all eight cases, normal blinking (about one blink every 4 sec) activated areas in the orbitofrontal cortex and in some cases, the visual cortex including the anterior portion of the visual cortex and the primary visual cortex. In severe dry eye, blink-inhibition strongly activated the visual cortex even after irritation due to corneal desiccation was removed by topical anesthesia.The blinking process, especially the rate, appears to be controlled in the orbitofrontal cortex. The significance of visual cortex activation in the dark and in the case of severe dry eye still remains unclear; although it may be associated with attention and arousal.     

Functional magnetic resonance imaging of eye dominance at 4 tesla

We studied eye dominance in visual cortex and lateral geniculate nucleus (LGN) using functional magnetic resonance imaging (fMRI) at a very high magnetic field (4 tesla). Eight normal volunteers were studied with fMRI at 4 tesla during alternating monocular visual stimulation. The acquisition was repeated twice in 4 subjects to confirm reproducibility. In addition, magnetic resonance signal intensities during three conditions (right eye stimulation, left eye stimulation, and control condition) were compared to determine whether the observed area was truly or relatively monocular in 2 subjects. In both the individual and group analyses, the anterior striate cortex was consistently activated by the contralateral eye more than the ipsilateral eye. Additionally, we found evidence that there were areas in the bilateral LGN which were more active during the stimulation of the contralateral eye than during the stimulation of the ipsilateral eye. The activated areas were reproducible, and the mean ratio of the overlapping area was 0.71 for the repeated scans. The additional experiment revealed that the area in the anterior visual cortex could be divided into two parts, one truly monocular and the other relatively monocular. Our finding confirmed previous fMRI results at 1.5 tesla showing that eye dominance was observed in the contralateral anterior visual cortex. However, the eye dominance in the visual cortex was found not only in the most anterior area corresponding to the monocular temporal crescent but also in the more posterior area, presumably showing the greater sensitivity of the temporal visual field (nasal retina) as compared with the nasal visual field (temporal retina) in the peripheral visual field (peripheral retina). In addition, it is suggested that the nasotemporal asymmetry of the retina and the visual fields is represented in the LGN as well as in the visual cortex.     

Functional imaging of mitochondria in retinal diseases using flavoprotein fluorescence

Mitochondria are critical for cellular energy production and homeostasis. Oxidative stress and associated mitochondrial dysfunction are integral components of the pathophysiology of retinal diseases, including diabetic retinopathy (DR), age-related macular degeneration, and glaucoma. Within mitochondria, flavoproteins are oxidized and reduced and emit a green autofluorescence when oxidized following blue light excitation. Recently, a noninvasive imaging device was developed to measure retinal flavoprotein fluorescence (FPF). Thus, oxidized FPF can act as a biomarker of mitochondrial dysfunction. This review article describes the literature surrounding mitochondrial FPF imaging in retinal disease. The authors describe the role of mitochondrial dysfunction in retinal diseases, experiments using FPF as a marker of mitochondrial dysfunction in vitro, the three generations of retinal FPF imaging devices, and the peer-reviewed publications that have examined FPF imaging in patients. Finally, the authors report their own study findings. Goals were to establish normative reference levels for FPF intensity and heterogeneity in healthy eyes, to compare between healthy eyes and eyes with diabetes and DR, and to compare across stages of DR. The authors present methods to calculate a patient’s expected FPF values using baseline characteristics. FPF intensity and heterogeneity were elevated in diabetic eyes compared to age-matched control eyes, and in proliferative DR compared to diabetic eyes without retinopathy. In diabetic eyes, higher FPF heterogeneity was associated with poorer visual acuity. In conclusion, while current retinal imaging modalities frequently focus on structural features, functional mitochondrial imaging shows promise as a metabolically targeted tool to evaluate retinal disease.Subject terms: Predictive markers, Retinal diseases     

Functional imaging of the retinal microvasculature by Scanning Laser Doppler Flowmetry

Purpose: to image functionally perfused retinal vessels and to assess quantitatively the intercapillary space of the retinal microvasculature.Method: The base offunctional imaging and the quantitative assessment of the retinal vasculature is the two-dimensional map of the retina encoded by the laser Doppler frequency shift. By Scanning Laser Doppler Flowmetry (HRF. Heidelberg Engineering) the laser Doppler frequency shift of 16.384 retinal sites (256 pixels × 64 lines, spatial resolution10 m) of a retinal area of 2.7 × 0.7 mm was gained. The image processing was performed by a recently described algorithm (AFFPIA). Using the data of the laser Doppler frequency shift of every retinal site, a color-coded retinal image was establishedshowing perfused vessels and capillaries. By automatic pattern analysis of this image vessels and capillaries were identified and segmented. Based on this image the distances in [m] of every retinal site to the next vessel or capillary were calculated ("distanceto next capillary'). The functional imaging of the retinal perfusion was demonstrated in (1) normal retina, (2) retinal arterial occlusion, and (3) proliferative retinopathy. Intraobserverreliability of the quantitative assessment of the parameter ``distance to next capillary' was estimated by measuring 10 eyes of 10 subjects at 5 different days by one observer. Interobserver reliability of the quantitative assessment was evaluated by analysing10 perfusion maps by 5 different operators. In 93 eyes of 71 normal subjects (mean age 40.4 15 years) the juxtapapillary retina was quantitatively evaluated.Results: Qualitative evaluation: The functional images of the retinal perfusion of eyes with normal retina, with retinal arterial occlusion, and with proliferative retinopathy correspondedwell with the fluorescein angiography. Perfused vessels and capillaries became visible in a high local resolution. Quantititative assessment: The coefficient of reliability of the introobserver and interobserver reproducibility of the parameter ``mean distance to next capillary' was 0.74, and 0.95, respectively. The quantitative assessment of the perfusion showed that the major part of the retinal sites (>700%) had distancesto the next capillary lower than 30 m 46% of the retinal area had distances to the next capillary from 0–20 lm 26% of the retina had distances from 20–30 m, 12% of the retina had distances from 30–40 m 7% of the retina had distances from 40–50 m, 4% of the retina had distances from 50–60 m, and 4% of the retinal sites showed distances to the next capillary greater than 60 m. The mean distance tothe next capillary or vessel was calculated with 21 ± 6.5 m.Conclusion: By non-invasive Scanning Laser Doppler Flowmetry in combination with adequate softwareit is possible to perform a functional imaging of the retinal vasculature and to measure all index for the functional density of retinal capillaries and vessels.     

Three-dimensional modeling of the human eye based on magnetic resonance imaging

PURPOSE: A methodology for noninvasively characterizing the three-dimensional (3-D) shape of the complete human eye is not currently available for research into ocular diseases that have a structural substrate, such as myopia. A novel application of a magnetic resonance imaging (MRI) acquisition and analysis technique is presented that, for the first time, allows the 3-D shape of the eye to be investigated fully. METHODS: The technique involves the acquisition of a T2-weighted MRI, which is optimized to reveal the fluid-filled chambers of the eye. Automatic segmentation and meshing algorithms generate a 3-D surface model, which can be shaded with morphologic parameters such as distance from the posterior corneal pole and deviation from sphericity. Full details of the method are illustrated with data from 14 eyes of seven individuals. The spatial accuracy of the calculated models is demonstrated by comparing the MRI-derived axial lengths with values measured in the same eyes using interferometry. RESULTS: The color-coded eye models showed substantial variation in the absolute size of the 14 eyes. Variations in the sphericity of the eyes were also evident, with some appearing approximately spherical whereas others were clearly oblate and one was slightly prolate. Nasal-temporal asymmetries were noted in some subjects. CONCLUSIONS: The MRI acquisition and analysis technique allows a novel way of examining 3-D ocular shape. The ability to stratify and analyze eye shape, ocular volume, and sphericity will further extend the understanding of which specific biometric parameters predispose emmetropic children subsequently to develop myopia.     

基于红外成像原理的睑板腺图像量化分析系统

目的:分析人眼的睑板腺形态学特征,探索睑板腺分析系统在眼表疾病的应用研究.方法:中山眼科中心入组正常受试者24例(42眼),进行睑板腺红外摄影.选取受试者中的10例(20眼)在同型号的设备上由二名操作员分别进行睑板腺红外摄影.图像通过自行设计的分析软件对上睑结膜中央5条腺体形态学参数进行定量分析,对数据进行重复性测试....