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Muir ER, Chandra SB, De La Garza BH, Velagapudi C, Abboud HE, Duong TQ. Layer-Specific Manganese-Enhanced MRI of the Diabetic Rat Retina in Light and Dark Adaptation at 11.7 Tesla. Invest Ophthalmol Vis Sci 2015; 56:4006-12. [PMID: 26098468 DOI: 10.1167/iovs.14-16128] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To employ high-resolution manganese-enhanced MRI (MEMRI) to study abnormal calcium activity in different cell layers in streptozotocin-induced diabetic rat retinas, and to determine whether MEMRI detects changes at earlier time points than previously reported. METHODS Sprague-Dawley rats were studied 14 days (n = 8) and 30 days (n = 5) after streptozotocin (STZ) or vehicle (n = 7) injection. Manganese-enhanced MRI at 20 × 20 × 700 μm, in which contrast is based on manganese as a calcium analogue and an MRI contrast agent, was obtained in light and dark adaptation of the retina in the same animals in which one eye was covered and the fellow eye was not. The MEMRI activity encoding of the light and dark adaptation was achieved in awake conditions and imaged under anesthesia. RESULTS Manganese-enhanced MRI showed three layers, corresponding to the inner retina, outer retina, and the choroid. In normal animals, the outer retina showed higher MEMRI activity in dark compared to light; the inner retina displayed lower activity in dark compared to light; and the choroid showed no difference in activity. Manganese-enhanced MRI activity changed as early as 14 days after hyperglycemia and decreased with duration of hyperglycemia in the outer retina in dark relative to light adaptation. The choroid also had altered MEMRI activity at 14 days, which returned to normal by 30 days. No differences in MEMRI activity were detected in the inner retina. CONCLUSIONS Manganese-enhanced MRI detects progressive reduction in calcium activity with duration of hyperglycemia in the outer retina as early as 14 days after hyperglycemia, earlier than any other time point reported in the literature.
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Affiliation(s)
- Eric R Muir
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, Texas, United States 2Departments of Ophthalmology, Radiology, and Physiology, University of Texas Health Science Center, San Antonio, Texas, United States
| | - Saurav B Chandra
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, Texas, United States
| | - Bryan H De La Garza
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, Texas, United States
| | - Chakradhar Velagapudi
- Department of Medicine, University of Texas Health Science Center, San Antonio, Texas, United States
| | - Hanna E Abboud
- Department of Medicine, University of Texas Health Science Center, San Antonio, Texas, United States
| | - Timothy Q Duong
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, Texas, United States 2Departments of Ophthalmology, Radiology, and Physiology, University of Texas Health Science Center, San Antonio, Texas, United States 4South Texas Ve
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Tan O, Liu G, Liang L, Gao SS, Pechauer AD, Jia Y, Huang D. En face Doppler total retinal blood flow measurement with 70 kHz spectral optical coherence tomography. JOURNAL OF BIOMEDICAL OPTICS 2015; 20:066004. [PMID: 26062663 PMCID: PMC4462711 DOI: 10.1117/1.jbo.20.6.066004] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Accepted: 05/14/2015] [Indexed: 05/03/2023]
Abstract
An automated algorithm was developed for total retinal blood flow (TRBF) using 70-kHz spectral optical coherence tomography (OCT). The OCT was calibrated for the transformation from Doppler shift to speed based on a flow phantom. The TRBF scan pattern contained five repeated volume scans (2 x 2 mm) obtained in 3 s and centered on central retinal vessels in the optic disc. The TRBF was calculated using an en face Doppler technique. For each retinal vein, blood flow was measured at an optimal plane where the calculated flow was maximized. The TRBF was calculated by summing flow in all veins. The algorithm tracked vascular branching so that either root or branch veins are summed, but never both. The TRBF in five repeated volumes were averaged to reduce variation due to cardiac cycle pulsation. Finally, the TRBF was corrected for eye length variation. Twelve healthy eyes and 12 glaucomatous eyes were enrolled to test the algorithm. The TRBF was 45.4 ± 6.7 μl/min for healthy control and 34.7 ± 7.6 μl/min for glaucomatous participants (p-value = 0.01). The intravisit repeatability was 8.6% for healthy controls and 8.4% for glaucoma participants. The proposed automated method provided repeatable TRBF measurement.
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Affiliation(s)
- Ou Tan
- Oregon Health and Science University, Casey Eye Institute, 3375 NW Terwilliger Boulevard, Portland, Oregon 97239, United States
- Address all correspondence to: Ou Tan, E-mail:
| | - Gangjun Liu
- Oregon Health and Science University, Casey Eye Institute, 3375 NW Terwilliger Boulevard, Portland, Oregon 97239, United States
| | - Liu Liang
- Oregon Health and Science University, Casey Eye Institute, 3375 NW Terwilliger Boulevard, Portland, Oregon 97239, United States
| | - Simon S. Gao
- Oregon Health and Science University, Casey Eye Institute, 3375 NW Terwilliger Boulevard, Portland, Oregon 97239, United States
| | - Alex D. Pechauer
- Oregon Health and Science University, Casey Eye Institute, 3375 NW Terwilliger Boulevard, Portland, Oregon 97239, United States
| | - Yali Jia
- Oregon Health and Science University, Casey Eye Institute, 3375 NW Terwilliger Boulevard, Portland, Oregon 97239, United States
| | - David Huang
- Oregon Health and Science University, Casey Eye Institute, 3375 NW Terwilliger Boulevard, Portland, Oregon 97239, United States
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Türksever C, Valmaggia C, Orgül S, Schorderet DF, Flammer J, Todorova MG. Retinal vessel oxygen saturation and its correlation with structural changes in retinitis pigmentosa. Acta Ophthalmol 2014; 92:454-60. [PMID: 24767408 DOI: 10.1111/aos.12379] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2013] [Accepted: 01/29/2014] [Indexed: 12/15/2022]
Abstract
PURPOSE To study the influence of retinal structural changes on oxygen saturation in retinitis pigmentosa (RP) patients. METHODS Oximetry measurements were performed on 21 eyes of 11 RP patients and compared to 24 eyes of 12 controls. Retinal oxygen saturation was measured in all major retinal arterioles (A-SO₂) and venules (V-SO₂) with an oximetry unit of the retinal vessel analyser (IMEDOS Systems UG, Jena, Germany). Oximetry data were compared with morphological changes measured by Cirrus optical coherence tomography (OCT) (Carl Zeiss Meditec, Dublin, CA, USA, macular thickness protocol). RESULTS In RP patients, the retinal A-SO₂ and V-SO₂ levels were higher at 99.3% (p = 0.001, anova based on mixed-effects model) and 66.8% (p < 0.001), respectively, and the difference between the two (A-V SO₂) was lower at 32.5% (p < 0.001), when compared to the control group (92.4%; 54.0%; 38.4%, respectively). With the RP group, the A-V SO₂ correlated positively, not only with central macular thickness, but also with retinal thickness, in zones 2 and 3 (p = 0.006, p = 0.007, p = 0.014). CONCLUSION These data indicate that oxygen metabolism was altered in RP patients. Based on our preliminary results, retinal vessel saturation correlated with structural alterations in RP. This method could be valuable in monitoring disease progression and evaluating a potential therapeutic response.
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Affiliation(s)
- Cengiz Türksever
- Department of Ophthalmology; University of Basel; Basel Switzerland
| | | | - Selim Orgül
- Department of Ophthalmology; University of Basel; Basel Switzerland
| | - Daniel F. Schorderet
- IRO - Institut for Research in Ophthalmology; Sion Switzerland
- Department of Ophthalmology; University of Lausanne; Lausanne Switzerland
- School of Life Sciences; Federal Institute of Technology; Lausanne Switzerland
| | - Josef Flammer
- Department of Ophthalmology; University of Basel; Basel Switzerland
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Ho LC, Conner IP, Do CW, Kim SG, Wu EX, Wollstein G, Schuman JS, Chan KC. In vivo assessment of aqueous humor dynamics upon chronic ocular hypertension and hypotensive drug treatment using gadolinium-enhanced MRI. Invest Ophthalmol Vis Sci 2014; 55:3747-57. [PMID: 24764067 DOI: 10.1167/iovs.14-14263] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
PURPOSE Although glaucoma treatments alter aqueous humor (AH) dynamics to lower intraocular pressure, the regulatory mechanisms of AH circulation and their contributions to the pathogenesis of ocular hypertension and glaucoma remain unclear. We hypothesized that gadolinium-enhanced magnetic resonance imaging (Gd-MRI) can visualize and assess AH dynamics upon sustained intraocular pressure elevation and pharmacologic interventions. METHODS Gadolinium contrast agent was systemically administered to adult rats to mimic soluble AH components entering the anterior chamber (AC) via blood-aqueous barrier. Dynamic Gd-MRI was applied to examine the signal enhancement in AC and vitreous body upon microbead-induced ocular hypertension and unilateral topical applications of latanoprost, timolol maleate, and brimonidine tartrate to healthy eyes. RESULTS Gadolinium signal time courses in microbead-induced hypertensive eyes possessed faster initial gadolinium uptake and higher peak signals in AC than control eyes, reflective of reduced gadolinium clearance upon microbead occlusion. Opposite trends were observed in latanoprost- and timolol-treated eyes, indicative of their respective drug actions on increased uveoscleral outflow and reduced AH production. The slowest initial gadolinium uptake but strongest peak signals were found in AC of both brimonidine-treated and untreated fellow eyes. These findings drew attention to the systemic effects of topical hypotensive drug treatment. Gadolinium leaked into the vitreous of microbead-induced hypertensive eyes and brimonidine-treated and untreated fellow eyes, suggestive of a compromise of aqueous-vitreous or blood-ocular barrier integrity. CONCLUSIONS Gadolinium-enhanced MRI allows spatiotemporal and quantitative evaluation of altered AH dynamics and ocular tissue permeability for better understanding the physiological mechanisms of ocular hypertension and the efficacy of antiglaucoma drug treatments.
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Affiliation(s)
- Leon C Ho
- NeuroImaging Laboratory, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Ian P Conner
- UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States Louis J. Fox Center for Vision Restoration, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Chi-Wai Do
- School of Optometry, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, China
| | - Seong-Gi Kim
- NeuroImaging Laboratory, University of Pittsburgh, Pittsburgh, Pennsylvania, United States UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States Center for Neuroscience Imaging Research, Institute for Basic Science, Department of Biological Science, Sungkyunkwan University, Suwon, Korea Center for the Neural Basis of Cognition, University of Pittsburgh and Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
| | - Ed X Wu
- Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong, China
| | - Gadi Wollstein
- UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States Louis J. Fox Center for Vision Restoration, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Joel S Schuman
- UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States Louis J. Fox Center for Vision Restoration, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Kevin C Chan
- NeuroImaging Laboratory, University of Pittsburgh, Pittsburgh, Pennsylvania, United States UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States Louis J. Fox Center for Vision Restoration, University of Pittsburgh, Pittsburgh, Pennsylvania, United States Center for the Neural Basis of Cognition, University of Pittsburgh and Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
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Duong TQ. Magnetic resonance imaging of the retina: from mice to men. Magn Reson Med 2014; 71:1526-30. [PMID: 23716429 PMCID: PMC3783549 DOI: 10.1002/mrm.24797] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Revised: 03/25/2013] [Accepted: 04/15/2013] [Indexed: 11/09/2022]
Abstract
This mini-review provides an overview of magnetic resonance imaging (MRI) applications to study rodent, cat, non-human primate, and human retinas. These techniques include T(1) - and T(2) -weighted anatomical, diffusion, blood flow, blood volume, blood-oxygenation level dependent, manganese-enhanced, physiological, and functional MRI. Applications to study the retinas in diabetic retinopathy, glaucoma, and retinal degeneration are also reviewed. MRI offers some unique advantages compared with existing imaging techniques and has the potential to further our understanding of physiology and function in healthy and diseased retinas.
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Affiliation(s)
- Timothy Q Duong
- South Texas Veterans Health Care System, Research Imaging Institute, Department of Ophthalmology, University of Texas Health Science Center, San Antonio, Texas, USA
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Li G, Shih YYI, Kiel JW, De La Garza BH, Du F, Duong TQ. MRI study of cerebral, retinal and choroidal blood flow responses to acute hypertension. Exp Eye Res 2013; 112:118-24. [PMID: 23623996 DOI: 10.1016/j.exer.2013.04.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2013] [Revised: 04/03/2013] [Accepted: 04/05/2013] [Indexed: 11/17/2022]
Abstract
Blood flow (BF) in many tissues is stable during significant fluctuations in systemic arterial blood pressure or perfusion pressure under normal conditions. The regulatory mechanisms responsible for this non-passive BF behavior include both local and neural control mechanisms. This study evaluated cerebral BF (CBF), retinal BF (RBF) and choroidal BF (ChBF) responses to acute blood pressure increases in rats using magnetic resonance imaging (MRI). A transient increase in blood pressure inside the MRI scanner was achieved by mechanically inflating a balloon catheter to occlude the descending aorta near the diaphragm. We verified the rat model of mechanical occlusion and MRI approach by first measuring blood-flow regulatory responses to changing BP in the brain under normoxia and hypercapnia where the phenomenon is well documented. Retinal and choroidal blood-flow responses to transient increased arterial pressure were then investigated. In response to an acute increase in blood pressure, RBF exhibited autoregulatory behavior and ChBF exhibited baroregulation similar to that seen in the cerebral circulation. This approach may prove useful to investigate retinal and choroidal vascular dysregulation in rat models of retinal diseases with suspected vascular etiology.
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Affiliation(s)
- Guang Li
- Research Imaging Institute, University of Texas Health Science Center, USA
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Zhang Y, Harrison JM, Nateras OSE, Chalfin S, Duong TQ. Decreased retinal-choroidal blood flow in retinitis pigmentosa as measured by MRI. Doc Ophthalmol 2013; 126:187-97. [PMID: 23408312 DOI: 10.1007/s10633-013-9374-1] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2012] [Accepted: 01/28/2013] [Indexed: 11/25/2022]
Abstract
PURPOSE To evaluate retinal and choroidal blood flow (BF) using high-resolution magnetic resonance imaging (MRI) as well as visual function measured by the electroretinogram (ERG) in patients with retinitis pigmentosa (RP). METHODS MRI studies were performed in 6 RP patients (29-67 years) and 5 healthy volunteers (29-64 years) on a 3-Tesla scanner with a custom-made surface coil. Quantitative BF was measured using the pseudo-continuous arterial spin-labeling technique at 0.5 × 0.8 × 6.0 mm. Full-field ERGs of all patients were recorded. Amplitudes and implicit times of standard ERGs were analyzed. RESULTS Basal BF in the posterior retinal-choroid was 142 ± 16 ml/100ml/min (or 1.14 ± 0.13 μl/mm(2)/min) in the control group and was 70 ±19 ml/100ml/min (or 0.56 ± 0.15 μl/mm(2)/min) in the RP group. Retinal-choroidal BF was significantly reduced by 52 ± 8 % in RP patients compared to controls (P<0.05). ERG a- and b-wave amplitudes of RP patients were reduced, and b-wave implicit times were delayed. There were statistically significant correlations between a-wave amplitude and BF value (r=0.9, P<0.05) but not between b-wave amplitude and BF value (r =0.7, P=0.2). CONCLUSIONS This study demonstrates a novel non-invasive MRI approach to measure quantitative retinal and choroidal BF in RP patients. We found that retinal-choroidal BF was markedly reduced and significantly correlated with reduced amplitudes of the a-wave of the standard combined ERG.
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Affiliation(s)
- Yi Zhang
- Research Imaging Institute, University of Texas Health Science Center, 8403 Floyd Curl Dr, San Antonio, TX 78229, USA
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Fanea L, Fagan AJ. Review: magnetic resonance imaging techniques in ophthalmology. Mol Vis 2012; 18:2538-60. [PMID: 23112569 PMCID: PMC3482169] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2011] [Accepted: 10/10/2012] [Indexed: 11/19/2022] Open
Abstract
Imaging the eye with magnetic resonance imaging (MRI) has proved difficult due to the eye's propensity to move involuntarily over typical imaging timescales, obscuring the fine structure in the eye due to the resulting motion artifacts. However, advances in MRI technology help to mitigate such drawbacks, enabling the acquisition of high spatiotemporal resolution images with a variety of contrast mechanisms. This review aims to classify the MRI techniques used to date in clinical and preclinical ophthalmologic studies, describing the qualitative and quantitative information that may be extracted and how this may inform on ocular pathophysiology.
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Affiliation(s)
- Laura Fanea
- Department of Biomedical Physics, Physics Faculty, Babes-Bolyai University, Cluj-Napoca, Romania,Department of Radiology, Cluj County Emergency Hospital, Cluj-Napoca, Romania
| | - Andrew J. Fagan
- Centre for Advanced Medical Imaging, St. James’s Hospital Dublin / University of Dublin Trinity College, Ireland
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Muir ER, Rentería RC, Duong TQ. Reduced ocular blood flow as an early indicator of diabetic retinopathy in a mouse model of diabetes. Invest Ophthalmol Vis Sci 2012; 53:6488-94. [PMID: 22915034 DOI: 10.1167/iovs.12-9758] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To investigate ocular blood flow and visual function in the Ins2(Akita) diabetic retinopathy mouse model at early and late time points after onset of hyperglycemia. METHODS Mice heterozygous for the Ins2(Akita) mutation, which become hyperglycemic at approximately 4 weeks old, were studied at 2.5 and 7.5 months of age, with age-matched wild-type littermates used as controls. Retinal and choroidal blood flows were noninvasively imaged at 42 × 42 × 400 μm using magnetic resonance imaging. Visual function was measured using optokinetic tracking to determine spatial frequency and contrast thresholds from the same mice. RESULTS At 2.5 months, choroidal blood flow was significantly reduced (P < 0.01) by 20% in Ins2(Akita) mice (n = 13) compared with age-matched controls (n = 16), whereas retinal blood flow and visual function were not significantly affected (P > 0.05). At 7.5 months, both choroidal and retinal blood flow were significantly reduced (P < 0.05) by 27% and 28%, respectively, in Ins2(Akita) mice (n = 11) compared with age-matched controls (n = 15). Visual functions were also significantly worse (P < 0.05) in Ins2(Akita) mice at 7.5 months, as indicated by a 19% decreased spatial frequency threshold and 135% increased contrast threshold compared with age-matched controls. The magnitudes of the blood flow and vision deficits, however, were not correlated. CONCLUSIONS Although both choroidal and retinal blood flow and vision were altered after prolonged diabetes in the Ins2(Akita) mouse, choroidal blood flow was reduced even in young diabetic animals, suggesting ocular blood flow deficit could be an early pathological change in diabetic retinopathy.
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Affiliation(s)
- Eric R Muir
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, Texas 78229, USA
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De La Garza BH, Li G, Shih YYI, Duong TQ. Layer-specific manganese-enhanced MRI of the retina in light and dark adaptation. Invest Ophthalmol Vis Sci 2012; 53:4352-8. [PMID: 22669725 DOI: 10.1167/iovs.11-8826] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To employ functional manganese-enhanced MRI (MEMRI) to image layer-specific changes in calcium-dependent activities in the rat retina during light versus dark adaptation. METHODS Functional MEMRI at 20 × 20 × 700 μm was used to study light and dark adaptation in the same animals (N = 10) in which one eye was covered and the fellow eye was not. The activity encoding of the light and dark adaptation was achieved in awake conditions and imaged under anesthesia. T(1)-weighted MRI at 11.7 tesla (T) was performed using two identical radiofrequency transceiver coils to allow interleaved MRI acquisitions of the two eyes. An intravascular contrast agent was also used to verify layer assignments. RESULTS MEMRI detected contrasts among the inner retina, outer retina, and choroid. Independent confirmation of the vascular layers and boundaries between layers was documented with an intravascular contrast agent. The retinal layer thicknesses agreed with published data. The outer retina had lower MEMRI activity in light compared with dark adaption (P < 0.001), consistent with the increased metabolic demand associated with the "dark current." The inner retina had higher MEMRI activity in light compared with dark adaption (P < 0.05). The choroid MEMRI activity was not statistically different between light and dark adaptation (P > 0.05). CONCLUSIONS This study demonstrated a high-resolution MEMRI protocol to image functional activities among different layers of the retinas in awake animals during light and dark adaptation. This approach could have potential applications in animal models of retinal dysfunction.
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Affiliation(s)
- Bryan H De La Garza
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, TX 78229, USA
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Zhang Y, San Emeterio Nateras O, Peng Q, Rosende CA, Duong TQ. Blood flow MRI of the human retina/choroid during rest and isometric exercise. Invest Ophthalmol Vis Sci 2012; 53:4299-305. [PMID: 22661466 DOI: 10.1167/iovs.11-9384] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To investigate blood flow (BF) in the human retina/choroid during rest and handgrip isometric exercise using magnetic resonance imaging (MRI). METHODS Four healthy volunteers (25-36 years old) in multiple sessions (1-3) on different days. MRI studies were performed on a 3-Tesla scanner using a custom-made surface coil (7×5cm in diameter) at the spatial resolution of 0.5×0.8×6.0 mm. BF was measured using the pseudo-continuous arterial-spin-labeling technique with background suppression and turbo-spin-echo acquisition. During MRI, subjects rested for 1 minute followed by 1 minute of handgrip, repeating three times, while maintaining stable eye fixation on a target with cued eye blinks at the end of each data acquisition (every 4.6 seconds). RESULTS Robust BF of the unanesthetized human retina/choroid was detected. Basal BF in the posterior retina/choroid was 149±48 mL/100 mL/min with a mean heart rate of 60±5 beats per minute, mean arterial pressure of 78±5 mm Hg, ocular perfusion pressure of 67±4 mm Hg at rest (mean±SD, n=4 subjects). Handgrip significantly increased retina/choroid BF by 25%±7%, heart rate by 19%±8%, mean arterial pressure by 22%±5% (measured at the middle of the handgrip task), and ocular perfusion pressure by 25%±6% (averaged across the entire handgrip task) (P<0.01), but did not change intraocular pressure, arterial oxygen saturation, end-tidal CO2, and respiration rate (P>0.05). CONCLUSIONS This study demonstrates a novel MRI application to image quantitative BF of the human retina/choroid during rest and isometric exercise. Retina/choroid BF increases during brief handgrip exercise, paralleling increases in mean arterial pressure. Handgrip exercise changes ocular perfusion pressure free of potential drug side effect and can be done in the MRI scanner. MRI offers quantitative BF with large field of view without depth limitation, potentially providing insights into retinal pathophysiology.
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Affiliation(s)
- Yi Zhang
- Research Imaging Institute, Department of Ophthalmology, University of Texas Health Science Center, San Antonio, TX 78229, USA
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12
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Layer-specific blood-flow MRI of retinitis pigmentosa in RCS rats. Exp Eye Res 2012; 101:90-6. [PMID: 22721720 DOI: 10.1016/j.exer.2012.06.006] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Revised: 05/23/2012] [Accepted: 06/11/2012] [Indexed: 02/04/2023]
Abstract
The Royal College of Surgeons (RCS) rat is an established animal model of retinitis pigmentosa, a family of inherited retinal diseases which starts with loss of peripheral vision and progresses to eventual blindness. Blood flow (BF), an important physiological parameter, is intricately coupled to metabolic function under normal physiological conditions and is perturbed in many neurological and retinal diseases. This study reports non-invasive high-resolution MRI (44 × 44 × 600 μm) to image quantitative retinal and choroidal BF and layer-specific retinal thicknesses in RCS rat retinas at different stages of retinal degeneration compared with age-matched controls. The unique ability to separate retinal and choroidal BF was made possible by the depth-resolved MRI technique. RBF decreased with progressive retinal degeneration, but ChBF did not change in RCS rats up to post-natal day 90. We concluded that choroidal and retinal circulations have different susceptibility to progressive retinal degeneration in RCS rats. Layer-specific retinal thickness became progressively thinner and was corroborated by histological analysis in the same animals. MRI can detect progressive anatomical and BF changes during retinal degeneration with laminar resolution.
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Passi N, Degnan AJ, Levy LM. MR imaging of papilledema and visual pathways: effects of increased intracranial pressure and pathophysiologic mechanisms. AJNR Am J Neuroradiol 2012; 34:919-24. [PMID: 22422187 DOI: 10.3174/ajnr.a3022] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Papilledema, defined as swelling of the optic disc, frequently occurs in the setting of increased ICP and in a variety of medical conditions, including pseudotumor cerebri, sinus thrombosis, intracerebral hemorrhage, frontal lobe neoplasms, and Chiari malformation. Noninvasive imaging of the ON is possible by using MR imaging, with a variety of findings occurring in the setting of papilledema, including flattening of the posterior sclera, protrusion of the optic disc, widening of the ONS, and tortuosity of the ON. Early recognition of papilledema and elevated ICP is of paramount importance for ensuring restoration of vision. Newer advanced MR imaging techniques such as fMRI and DTI may prove useful in the future to assess the potential effects of papilledema on retinal and visual pathway integrity.
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Affiliation(s)
- N Passi
- Department of Radiology, George Washington University Hospital, Washington, DC 20037, USA
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Shih YYI, Li G, Muir ER, De La Garza BH, Kiel JW, Duong TQ. Pharmacological MRI of the choroid and retina: blood flow and BOLD responses during nitroprusside infusion. Magn Reson Med 2011; 68:1273-8. [PMID: 22183830 DOI: 10.1002/mrm.24112] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2011] [Revised: 10/06/2011] [Accepted: 11/18/2011] [Indexed: 11/10/2022]
Abstract
Nitroprusside, a vasodilatory nitric oxide donor, is clinically used during vascular surgery and to lower blood pressure in acute hypertension. This article reports a novel application of blood flow (BF) and blood oxygenation level dependent (BOLD) MRI on an 11.7T scanner to image the rat chorioretinal BF and BOLD changes associated with graded nitroprusside infusion. At low doses (1 or 2 μg/kg/min), nitroprusside increased BF as expected but decreased BOLD signals, showing an intriguing BF-BOLD uncoupling. At high doses (3-5 μg/kg/min), nitroprusside decreased BF and markedly decreased BOLD signals. To our knowledge, this is the first pharmacological MRI application of the retina. This approach has potential to open up new avenues to study the drug-related hemodynamic functions and to evaluate the effects of novel therapeutic interventions on BOLD and BF in the normal and diseased retinas.
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Affiliation(s)
- Yen-Yu I Shih
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, Texas 78229, USA.
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15
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Shen Q, Duong TQ. Background suppression in arterial spin labeling MRI with a separate neck labeling coil. NMR IN BIOMEDICINE 2011; 24:1111-1118. [PMID: 21294207 PMCID: PMC3116975 DOI: 10.1002/nbm.1666] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2010] [Revised: 12/02/2010] [Accepted: 12/05/2010] [Indexed: 05/30/2023]
Abstract
In arterial spin labeling (ASL) MRI to measure cerebral blood flow (CBF), pair-wise subtraction of temporally adjacent non-labeled and labeled images often can not completely cancel the background static tissue signal because of temporally fluctuating physiological noise. While background suppression (BS) by inversion nulling improves CBF temporal stability, imperfect pulses compromise CBF contrast. Conventional BS techniques may not be applicable in small animals because the arterial transit time is short. This study presents a novel approach of BS to overcome these drawbacks using a separate 'neck' radiofrequency coil for ASL and a 'brain' radiofrequency coil for BS with the inversion pulse placed before spin labeling. The use of a separate 'neck' coil for ASL should also improve ASL contrast. This approach is referred to as the inversion-recovery BS with the two-coil continuous ASL (IR-cASL) technique. The temporal and spatial contrast-to-noise characteristics of basal CBF and CBF-based fMRI of hypercapnia and forepaw stimulation in rats at 7 Tesla were analyzed. IR-cASL yielded two times better temporal stability and 2.0-2.3 times higher functional contrast-to-noise ratios for hypercapnia and forepaw stimulation compared with cASL without BS in the same animals. The Bloch equations were modified to provide accurate CBF quantification at different levels of BS and for multislice acquisition where different slices have different degree of BS and residual degree of labeling. Improved basal CBF and CBF-based fMRI sensitivity should lead to more accurate CBF quantification and should prove useful for imaging low CBF conditions such as in white matter and stroke.
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Affiliation(s)
- Qiang Shen
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, TX, USA
- Department of Ophthalmology, University of Texas Health Science Center, San Antonio, TX, USA
- Department of Radiology, University of Texas Health Science Center, San Antonio, TX, USA
| | - Timothy Q. Duong
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, TX, USA
- Department of Ophthalmology, University of Texas Health Science Center, San Antonio, TX, USA
- Department of Radiology, University of Texas Health Science Center, San Antonio, TX, USA
- Department of Physiology, University of Texas Health Science Center, San Antonio, TX, USA
- South Texas Veterans Health Care System, Department of Veterans Affairs, San Antonio, TX, USA
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16
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De La Garza BH, Muir ER, Shih YYI, Duong TQ. 3D magnetic resonance microscopy of the ex vivo retina. Magn Reson Med 2011; 67:1154-8. [PMID: 22009721 DOI: 10.1002/mrm.23082] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2011] [Revised: 05/17/2011] [Accepted: 06/14/2011] [Indexed: 11/12/2022]
Abstract
3D-MR microscopy at 11.7T and 20 × 20 × 57 μm resolution was performed on formalin-fixed rat eyes with: (I) no contrast agent and (II) Gadodiamide (Omniscan(®) ) added to the fixative. Group I data showed generally poor contrast among layers. Group II data showed markedly better lamina-specific contrast with the nerve fiber + ganglion cell layer and inner nuclear layer being hypointense, and the inner plexiform, outer plexiform, outer nuclear layer, and the segments being hyperintense. The signal-to-noise ratio in group II was higher than group I, consistent with Gadodiamide acting as a T(1) -contrast agent. All major retinal layers were assigned and their thicknesses quantified with corroboration by histology. MR microscopy allows nondestructive examination of valuable specimens and could have applications in disease and in vivo.
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Zhang Y, Nateras OSE, Peng Q, Kuranov RV, Harrison JM, Milner TE, Duong TQ. Lamina-specific anatomic magnetic resonance imaging of the human retina. Invest Ophthalmol Vis Sci 2011; 52:7232-7. [PMID: 21828153 DOI: 10.1167/iovs.11-7623] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Magnetic resonance imaging (MRI) of the human retina faces two major challenges: eye movement and hardware limitation that could preclude human retinal MRI with adequate spatiotemporal resolution. This study investigated eye-fixation stability and high-resolution anatomic MRI of the human retina on a 3-Tesla (T) MRI scanner. Comparison was made with optical coherence tomography (OCT) on the same subjects. METHODS Eye-fixation stability of protocols used in MRI was evaluated on four normal volunteers using an eye tracker. High-resolution MRI (100 × 200 × 2000 μm) protocol was developed on a 3-T scanner. Subjects were instructed to maintain stable eye fixation on a target with cued blinks every 8 seconds during MRI. OCT imaging of the retina was performed. Retinal layer thicknesses measured with MRI and OCT were analyzed for matching regions of the same eyes close to the optic nerve head. RESULTS The temporal SDs of the horizontal and vertical displacements were 78 ± 51 and 130 ± 51 μm (±SD, n = 4), respectively. MRI detected three layers within the human retina, consistent with MRI findings in rodent, feline, and baboon retinas. The hyperintense layer 1 closest to the vitreous likely consisted of nerve fiber, ganglion cell, and inner nuclear layer; the hypointense layer 2, the outer nuclear layer and the inner and outer segments; and the hyperintense layer 3, the choroid. The MRI retina/choroid thickness was 711 ± 37 μm, 19% (P < 0.05) thicker than OCT thickness (579 ± 34 μm). CONCLUSIONS This study reports high-resolution MRI of lamina-specific structures in the human retina. These initial results are encouraging. Further improvement in spatiotemporal resolution is warranted.
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Affiliation(s)
- Yi Zhang
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, Texas 78229, USA
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18
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Shih YYI, De la Garza BH, Muir ER, Rogers WE, Harrison JM, Kiel JW, Duong TQ. Lamina-specific functional MRI of retinal and choroidal responses to visual stimuli. Invest Ophthalmol Vis Sci 2011; 52:5303-10. [PMID: 21447679 DOI: 10.1167/iovs.10-6438] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To demonstrate lamina-specific functional magnetic resonance imaging (MRI) of retinal and choroidal responses to visual stimulation of graded luminance, wavelength, and frequency. MATERIALS AND METHODS High-resolution (60 × 60 μm) MRI was achieved using the blood-pool contrast agent, monocrystalline iron oxide nanoparticles (MION) and a high-magnetic-field (11.7 T) scanner to image functional changes in the normal rat retina associated with various visual stimulations. MION functional MRI measured stimulus-evoked blood-volume (BV) changes. Graded luminance, wavelength, and frequency were investigated. Stimulus-evoked fMRI signal changes from the retinal and choroidal vascular layers were analyzed. RESULTS MRI revealed two distinct laminar signals that corresponded to the retinal and choroidal vascular layers bounding the retina and were separated by the avascular layer in between. The baseline outer layer BV index was 2-4 times greater than the inner layer BV, consistent with higher choroidal vascular density. During visual stimulation, BV responses to flickering light of different luminance, frequency, and wavelength in the inner layer were greater than those in the outer layer. The inner layer responses were dependent on luminance, frequency, and wavelength, whereas the outer layer responses were not, suggesting differential neurovascular coupling between the two vasculatures. CONCLUSIONS This is the first report of simultaneous resolution of layer-specific functional responses of the retinal and choroid vascular layers to visual stimulation in the retina. This imaging approach could have applications in early detection and longitudinal monitoring of retinal diseases where retinal and choroidal hemodynamics may be differentially perturbed at various stages of the diseases.
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Affiliation(s)
- Yen-Yu I Shih
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, Texas, USA
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19
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Muir ER, Duong TQ. Layer-specific functional and anatomical MRI of the retina with passband balanced SSFP. Magn Reson Med 2011; 66:1416-21. [PMID: 21604296 DOI: 10.1002/mrm.22935] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2010] [Revised: 02/23/2011] [Accepted: 03/07/2011] [Indexed: 11/09/2022]
Abstract
The retina consists of multiple cellular and synaptic layers and is nourished by two distinct (retinal and choroidal) circulations bounding the retina, separated by an avascular layer. High spatiotemporal resolution, layer-specific MRI of the retina remains challenging due to magnetic inhomogeneity-induced artifacts. This study reports passband balanced steady-state free-precession (bSSFP) MRI at 45×45×500 μm and 1.6 s temporal resolution to image the mouse retina, overcoming geometric distortion and signal dropout while maintaining rapid acquisition and high signal-to-noise ratio. bSSFP images revealed multiple alternating dark-bright-dark-bright retinal layers. Hypoxic (10% O(2) ) inhalation decreased bSSFP signals in the two layers bounding the retina, corresponding to the retinal and choroidal vasculatures. The layer in between showed no substantial response and was assigned the avascular photoreceptor layers. Choroidal responses (-25.9 ± 6.4%, mean ± SD, n=6) were significantly (P<0.05) larger than retinal vascular responses (-11.6±2.4%). bSSFP offers very high spatiotemporal resolution and could have important applications in imaging layer-specific changes in retinal diseases.
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Affiliation(s)
- Eric R Muir
- Department of Ophthalmology, Research Imaging Institute, University of Texas Health Science Center, San Antonio, Texas, USA
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20
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Effects of common anesthetics on eye movement and electroretinogram. Doc Ophthalmol 2011; 122:163-76. [PMID: 21519880 DOI: 10.1007/s10633-011-9271-4] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2010] [Accepted: 04/04/2011] [Indexed: 10/18/2022]
Abstract
High-resolution magnetic resonance imaging (MRI) provides non-invasive images of retinal anatomy, physiology, and function with depth-resolved laminar resolution. Eye movement and drift, however, could limit high spatial resolution imaging, and anesthetics that minimize eye movement could significantly attenuate retinal function. The aim of this study was to determine the optimal anesthetic preparations to minimize eye movement and maximize visual-evoked retinal response in rats. Eye movements were examined by imaging of the cornea with a charge-coupled device (CCD) camera under isoflurane, urethane, ketamine/xylazine, and propofol anesthesia at typical dosages in rats. Combination of the paralytic pancuronium bromide with isoflurane or ketamine/xylazine anesthesia was also examined for the eye movement studies. Visual-evoked retinal responses were evaluated using full-field electroretinography (ERG) under isoflurane, ketamine/xylazine, urethane, and ketamine/xylazine + pancuronium anesthesia in rats. The degree of eye movement, measured as displacement per unit time, was the smallest under 1% isoflurane + pancuronium anesthesia. The ketamine/xylazine groups showed larger dark-adapted ERG a- and b-waves than other anesthetics tested. The isoflurane group showed the shortest b-wave implicit times. Photopic ERGs in the ketamine/xylazine groups showed the largest b-waves with the isoflurane group showing slightly shorter implicit times at the higher flash intensities. Oscillatory potentials revealed an early peak in the isoflurane group compared with ketamine/xylazine and urethane groups. Pancuronium did not affect the a- and b-wave, but did increase oscillatory potential amplitudes. Compared with the other anesthetics tested here, ketamine/xylazine + pancuronium was the best combination to minimize eye movement and maximize retinal function. These findings should set the stage for further development and application of high-resolution functional imaging techniques, such as MRI, to study retinal anatomy, physiology, and function in anesthetized rats.
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Duong TQ. Magnetic resonance imaging of the retina: A brief historical and future perspective. Saudi J Ophthalmol 2011; 25:137-43. [PMID: 23960915 PMCID: PMC3729810 DOI: 10.1016/j.sjopt.2011.01.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2011] [Accepted: 01/21/2011] [Indexed: 11/30/2022] Open
Abstract
This invited review starts with a brief introduction of retinal anatomy and magnetic resonance imaging techniques with contrast to optics, followed by a history and future perspective on MRI applications to investigate the retinas of rodents, non-human primates and humans.
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Affiliation(s)
- Timothy Q. Duong
- Address: University of Texas Health Science Center at San Antonio, Research Imaging Institute, 8403 Floyd Curl Dr, San Antonio, TX 78229, USA. Tel.: +1 567 8100; fax: +1 210 567 8152.
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22
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Zhang Y, Wey HY, San Emeterio Nateras O, Peng Q, De La Garza BH, Duong TQ. Anatomical, blood oxygenation level-dependent, and blood flow MRI of nonhuman primate (baboon) retina. Magn Reson Med 2011; 66:546-54. [PMID: 21360746 DOI: 10.1002/mrm.22853] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2010] [Revised: 12/04/2010] [Accepted: 01/05/2011] [Indexed: 11/10/2022]
Abstract
The goal of this study was to demonstrate high-resolution anatomical, blood oxygenation level-dependent, and blood flow MRI on large nonhuman primate retinas using a 3-Tesla clinical scanner as a first step toward translation. Baboon was chosen because of its evolutionary similarity to human. Anesthetized preparation, free of eye-movement artifacts, was used to evaluate clinical scanner hardware feasibility and optimize multimodal protocols for retinal MRI. Anatomical MRI (0.1×0.2×2.0 mm3) before contrast-agent injection detected three alternating bright-dark-bright layers. The hyperintense inner strip nearest to the vitreous was enhanced by an intravascular contrast agent, which likely included the ganglion and bipolar cell layer and the embedded retinal vessels. The hypointense middle strip showed no contrast enhancement, which likely included the avascular outer unclear layer and photoreceptor segments. The hyperintense outer strip showed contrast enhancement, which likely corresponded to the choroid vascular layer. In the posterior retina, the total thickness including the choroid was 617±101 μm (±standard deviation, n=7). Blood oxygenation level-dependent functional MRI (0.3×0.6×2.0 mm3) of oxygen inhalation relative to air increased the signals by 6.5±1.4%. Basal blood flow (2×2×2 mm3) was 83±30 mL/100 g/min (air), and hypercapnia increased blood flow by 25±9% (P<0.05). This study demonstrates multimodal MRI to image anatomy, physiology, and function on large nonhuman primate retinas using a clinical scanner, offering encouraging data to explore human applications.
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Affiliation(s)
- Yi Zhang
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, Texas, USA; Department of Radiology, University of Texas Health Science Center, San Antonio, Texas 78229, USA
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Peng Q, Zhang Y, Nateras OSE, van Osch MJP, Duong TQ. MRI of blood flow of the human retina. Magn Reson Med 2011; 65:1768-75. [PMID: 21590806 DOI: 10.1002/mrm.22763] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2010] [Revised: 10/25/2010] [Accepted: 11/24/2010] [Indexed: 12/25/2022]
Abstract
This study reports a high-resolution MRI approach to image basal blood flow and hypercapnia-induced blood-flow changes in the unanesthetized human retina on a 3-T MRI scanner. Pseudocontinuous arterial spin labeling technique with static tissue suppression was implemented to minimize movement artifacts and improve blood-flow sensitivity. Turbo spin-echo acquisition was used to achieve high spatial resolution free of susceptibility artifacts. The size, shape, and position of a custom-made receive radiofrequency coil were optimized for sensitivity in the posterior retina. Synchronized eye blink and respiration to the end of each data readout minimized eye movement and physiological fluctuation. Robust high-contrast blood-flow MRI of the unanesthetized human retina was obtained at 500 × 800 μm(2) in-plane resolution. Blood flow in the posterior retina was 93 ± 31 mL/(100 mL min) (mean ± standard deviation, N = 5). Hypercapnic inhalation (5% CO(2)) increased blood flow by 12 ± 4% relative to air (P < 0.01, N = 5). This study demonstrates the feasibility of blood-flow MRI of the retina of unanesthetized human. Because blood flow is tightly coupled to metabolic function under normal conditions and it is often perturbed in diseases, this approach could provide unique insights into retinal physiology and serve as an objective imaging biomarker for disease staging and testing of novel therapeutic strategies. This approach could open up new avenue of retinal research.
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Affiliation(s)
- Qi Peng
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, Texas 78229, USA
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De La Garza BH, Muir ER, Li G, Shih YYI, Duong TQ. Blood oxygenation level-dependent (BOLD) functional MRI of visual stimulation in the rat retina at 11.7 T. NMR IN BIOMEDICINE 2011; 24:188-193. [PMID: 21344533 PMCID: PMC3057875 DOI: 10.1002/nbm.1571] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2010] [Revised: 04/21/2010] [Accepted: 04/28/2010] [Indexed: 05/30/2023]
Abstract
Although optically based imaging techniques provide valuable functional and physiological information of the retina, they are mostly limited to the probing of the retinal surface and require an unobstructed light path. MRI, in contrast, could offer physiological and functional data without depth limitation. Blood oxygenation level-dependent functional MRI (BOLD fMRI) of the thin rat retina is, however, challenging because of the need for high spatial resolution, and the potential presence of eye movement and susceptibility artifacts. This study reports a novel application of high-resolution (111 × 111 × 1000 µm(3)) BOLD fMRI of visual stimulation in the anesthetized rat retina at 11.7 T. A high-field MRI scanner was utilized to improve the signal-to-noise ratio, spatial resolution and BOLD sensitivity. Visual stimuli (8 Hz diffuse achromatic light) robustly increased BOLD responses in the retina [5.0 ± 0.8% from activated pixels and 3.1 ± 1.1% from the whole-retina region of interest (mean ± SD), n = 12 trials on six rats, p < 0.05 compared with baseline]. Some activated pixels were detected surrounding the pupil and ciliary muscle because of accommodation reflex to visual stimuli, and were reduced with atropine and phenylephrine eye drops. BOLD fMRI scans without visual stimulations showed no significantly activated pixels (whole-retina BOLD changes were 0.08 ± 0.34%, n = 6 trials on five rats, not statistically different from baseline, p > 0.05). BOLD fMRI of visual stimulation has the potential to provide clinically relevant data to probe hemodynamic neurovascular coupling and dysfunction of the retina with depth resolution.
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Affiliation(s)
- Bryan H. De La Garza
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, TX, USA
| | - Eric R. Muir
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, TX, USA
- Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA, USA
| | - Guang Li
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, TX, USA
- Department of Radiology, University of Texas Health Science Center, San Antonio, TX, USA
| | - Yen-Yu I. Shih
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, TX, USA
| | - Timothy Q. Duong
- Research Imaging Institute, University of Texas Health Science Center, San Antonio, TX, USA
- Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA, USA
- Department of Radiology, University of Texas Health Science Center, San Antonio, TX, USA
- Department of Ophthalmology, University of Texas Health Science Center, San Antonio, TX, USA
- Department of Physiology, University of Texas Health Science Center, San Antonio, TX, USA
- South Texas Veterans Health Care System, San Antonio, TX, USA
- Southwest National Primate Research Center, San Antonio, TX, USA
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25
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Muir ER, Duong TQ. MRI of retinal and choroidal blood flow with laminar resolution. NMR IN BIOMEDICINE 2011; 24:216-23. [PMID: 20821409 PMCID: PMC3026903 DOI: 10.1002/nbm.1576] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2010] [Revised: 05/12/2010] [Accepted: 05/14/2010] [Indexed: 05/11/2023]
Abstract
The retina is nourished by two distinct circulations: the retinal vessels within the inner retina and the choroidal vessels behind the neural retina. The outer nuclear layer and the inner and outer segments of the photoreceptors in between are avascular. The aim of this study was to determine whether arterial spin labeling MRI could provide sufficient resolution to differentiate between quantitative retinal blood flow (rBF) and choroidal blood flow (chBF), and whether this technique is sufficiently sensitive to detect vascular-specific blood flow (BF) changes modulated by anesthetics. Arterial spin labeling MRI was performed at 42 × 42 × 400 µm(3) in the mouse retina at 7 T, and was used to investigate the effects of isoflurane and ketamine/xylazine anesthesia on rBF and chBF. MRI yielded unambiguous differentiation of rBF, chBF and the avascular layer in between. Under isoflurane, chBF was 7.7 ± 2.1 mL/g/min and rBF was 1.3 ± 0.44 mL/g/min (mean ± SD, n = 7, p < 0.01). Under ketamine/xylazine anesthesia in the same animals, chBF was 4.3 ± 1.9 mL/g/min and rBF was 0.88 ± 0.22 mL/g/min (p < 0.01). Under ketamine/xylazine anesthesia, rBF was lower by 29% (P < 0.01) and chBF by 42% (P < 0.01) relative to isoflurane. This study demonstrates, for the first time, the quantitative imaging of rBF and chBF in vivo, providing a new method to study basal values and alterations of rBF and chBF.
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Affiliation(s)
- Eric R. Muir
- Research Imaging Center, Departments of Ophthalmology, Radiology and Physiology, University of Texas Health Science Center, San Antonio, TX, USA
- Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA, USA
| | - Timothy Q. Duong
- Research Imaging Center, Departments of Ophthalmology, Radiology and Physiology, University of Texas Health Science Center, San Antonio, TX, USA
- South Texas Veterans Health Care System, San Antonio, TX, USA
- Southwest National Primate Research Center, San Antonio, TX, USA
- Correspondence to: T. Q. Duong, Research Imaging Center, University of Texas Health Science Center at San Antonio (UTHSCSA), 8403 Floyd Curl Dr., San Antonio, TX 78229, USA.
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26
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Muir ER, Duong TQ. MRI of retinal and choroidal blood flow with laminar resolution. NMR IN BIOMEDICINE 2011. [PMID: 20821409 DOI: 10.1002/nbm.v24.2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
The retina is nourished by two distinct circulations: the retinal vessels within the inner retina and the choroidal vessels behind the neural retina. The outer nuclear layer and the inner and outer segments of the photoreceptors in between are avascular. The aim of this study was to determine whether arterial spin labeling MRI could provide sufficient resolution to differentiate between quantitative retinal blood flow (rBF) and choroidal blood flow (chBF), and whether this technique is sufficiently sensitive to detect vascular-specific blood flow (BF) changes modulated by anesthetics. Arterial spin labeling MRI was performed at 42 × 42 × 400 µm(3) in the mouse retina at 7 T, and was used to investigate the effects of isoflurane and ketamine/xylazine anesthesia on rBF and chBF. MRI yielded unambiguous differentiation of rBF, chBF and the avascular layer in between. Under isoflurane, chBF was 7.7 ± 2.1 mL/g/min and rBF was 1.3 ± 0.44 mL/g/min (mean ± SD, n = 7, p < 0.01). Under ketamine/xylazine anesthesia in the same animals, chBF was 4.3 ± 1.9 mL/g/min and rBF was 0.88 ± 0.22 mL/g/min (p < 0.01). Under ketamine/xylazine anesthesia, rBF was lower by 29% (P < 0.01) and chBF by 42% (P < 0.01) relative to isoflurane. This study demonstrates, for the first time, the quantitative imaging of rBF and chBF in vivo, providing a new method to study basal values and alterations of rBF and chBF.
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Affiliation(s)
- Eric R Muir
- Research Imaging Center, Departments of Ophthalmology, Radiology and Physiology, University of Texas Health Science Center, San Antonio, TX 78229, USA
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27
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Zhang Y, Peng Q, Kiel JW, Rosende CA, Duong TQ. Magnetic resonance imaging of vascular oxygenation changes during hyperoxia and carbogen challenges in the human retina. Invest Ophthalmol Vis Sci 2011; 52:286-91. [PMID: 20847121 PMCID: PMC3053278 DOI: 10.1167/iovs.10-6108] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2010] [Revised: 08/11/2010] [Accepted: 08/11/2010] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To demonstrate blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) of vascular oxygenation changes in normal, unanesthetized human retinas associated with oxygen and carbogen challenge. METHODS MRI was performed with a 3-T human scanner and a custom-made surface-coil detector on normal volunteers. BOLD MRI with inversion recovery was used to suppress the vitreous signal. During MRI measurements, volunteers underwent three episodes of air and 100% oxygen or carbogen (5% CO(2) and 95% O(2)) breathing. Eye movement was effectively managed with eye fixation, synchronized blinks, and postprocessing image coregistration. BOLD time-series images were analyzed using the cross-correlation method. Percent changes due to oxygen or carbogen inhalation versus air were tabulated for whole-retina and different regions of the retina. RESULTS Robust BOLD responses were detected. BOLD MRI percent change from a large region of interest at the posterior pole of the retina was 5.2 ± 1.5% (N = 9 trials from five subjects) for oxygen inhalation and 5.2 ± 1.3% (N = 11 trials from five subjects) for carbogen inhalation. Group-averaged BOLD percent changes were not significantly different between oxygen and carbogen challenges (P > 0.05). The foveal region had greater BOLD response compared with the optic nerve head region for both challenges. CONCLUSIONS BOLD retinal responses to oxygen and carbogen breathing in unanesthetized humans can be reliably imaged at high spatiotemporal resolution. BOLD MRI has the potential to provide a valuable tool to study retinal physiology and pathophysiology, such as how vascular oxygenation at the tissue level is regulated in the normal retina, and how retinal diseases may affect oxygen response.
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Affiliation(s)
- Yi Zhang
- From the Research Imaging Institute and
- the Departments of Radiology
| | - Qi Peng
- From the Research Imaging Institute and
- the Departments of Radiology
| | | | | | - Timothy Q. Duong
- From the Research Imaging Institute and
- the Departments of Radiology
- Ophthalmology, and
- Physiology, University of Texas Health Science Center, San Antonio, Texas; and
- South Texas Veterans Health Care System, San Antonio, Texas
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CHAN KEVINC, CHEUNG MATTHEWM, WU EDX. IN VIVOMULTIPARAMETRIC MAGNETIC RESONANCE IMAGING AND SPECTROSCOPY OF RODENT VISUAL SYSTEM. J Integr Neurosci 2010; 9:477-508. [DOI: 10.1142/s0219635210002524] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2010] [Accepted: 11/04/2010] [Indexed: 01/27/2023] Open
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Nair G, Tanaka Y, Kim M, Olson DE, Thulé PM, Pardue MT, Duong TQ. MRI reveals differential regulation of retinal and choroidal blood volumes in rat retina. Neuroimage 2010; 54:1063-9. [PMID: 20850550 DOI: 10.1016/j.neuroimage.2010.09.020] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2010] [Revised: 08/10/2010] [Accepted: 09/08/2010] [Indexed: 10/19/2022] Open
Abstract
The retina is nourished by two unique (retinal and choroidal) circulations. The lack of depth-resolved blood volume (BV) imaging techniques hampers investigation of vascular-specific regulation of the retina in vivo. This study presents a high-resolution, laminar-specific magnetic resonance imaging (MRI) study to image retinal and choroidal BVs, their responses to physiologic challenges in normal and Royal-College-of-Surgeons (RCS) rats (a model of retinal degeneration). Retinal and choroidal BVs were imaged by MRI (30×30×800 μm) with intravascular administration of monocrystalline iron oxide nanocolloid (MION) contrast agent. Relative baseline BV and BV changes due to physiologic challenges were calculated in normal and RCS rat retinas. BV-MRI revealed two well-resolved retinal and choroidal vascular layers located on either side of the retina and an intervening avascular layer. The ratio of choroidal:retinal BV in normal rats at baseline was 9.8±3.2 in control rat retinas (N=7). Hyperoxia decreased retinal BV (-51±17%, p<0.05) more than choroidal BV (-28±14%), and hypercapnia increased retinal BV (52±11%, p<0.01) more than choroidal BV (12±11%). BV-MRI in degenerated retinas of RCS rats (N=7) revealed thinning of the avascular layer and an increase in relative baseline retinal and choroidal BVs. Only hypercapnia-induced BV changes in the retinal vasculature of RCS rats were significantly different (smaller) from controls (p<0.05). These findings suggest that BV in both retinal vasculatures is regulated. The relative baseline BV in both vasculatures increased in retinal degeneration. BV-MRI provides clinically relevant data that may prove useful for early detection and longitudinal probing of retinal diseases, and could complement optical imaging techniques.
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Affiliation(s)
- Govind Nair
- Graduate School of Biomedical Science, University of Massachusetts Medical School, Worcester, MA, USA
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Duong TQ, Muir ER. Magnetic resonance imaging of the retina. Jpn J Ophthalmol 2009; 53:352-67. [PMID: 19763752 DOI: 10.1007/s10384-009-0688-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2009] [Accepted: 03/27/2009] [Indexed: 02/06/2023]
Abstract
This paper reviews recent developments in high-resolution magnetic resonance imaging (MRI) and its application to image anatomy, physiology, and function in the retina of animals. It describes technical issues and solutions in performing retinal MRI, anatomical MRI, blood oxygenation level-dependent functional MRI (fMRI), and blood-flow MRI both of normal retinas and of retinal degeneration. MRI offers unique advantages over existing retinal imaging techniques, including the ability to image multiple layers without depth limitation and to provide multiple clinically relevant data in a single setting. Retinal MRI has the potential to complement existing retinal imaging techniques.
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Affiliation(s)
- Timothy Q Duong
- Research Imaging Center, Department of Ophthalmology, University of Texas Health Science Center, San Antonio, TX, USA.
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Pouliot M, Deschênes MC, Hétu S, Chemtob S, Lesk MR, Couture R, Vaucher E. Quantitative and regional measurement of retinal blood flow in rats using N-isopropyl-p-[14C]-iodoamphetamine ([14C]-IMP). Exp Eye Res 2009; 89:960-6. [PMID: 19698709 DOI: 10.1016/j.exer.2009.08.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2009] [Revised: 07/24/2009] [Accepted: 08/12/2009] [Indexed: 11/26/2022]
Abstract
Quantitative and regional measurement of retinal blood flow in rodents is of prime interest for the investigation of regulatory mechanisms of ocular circulation in physiological and pathological conditions. In this study, a quantitative autoradiographic method using N-isopropyl-p-(14)C-iodoamphetamine ([(14)C]-IMP), a diffusible radioactive tracer, was evaluated for its ability to detect changes in retinal blood perfusion during hypercapnia. Findings were compared to cerebral blood flow values measured simultaneously. Hypercapnia was induced in awaken Wistar rats by inhalation of 5% or 8% CO(2) in medical air for 5 min. [(14)C]-IMP (100 microCi/kg) was injected in the femoral vein over a 30 s period and the rats were sacrificed 2 min later. Blood flow was calculated from whole-mount retinae and 20 microm thick brain sections in discrete regions of interest by quantitative autoradiography or from digested samples of retina and brain by liquid scintillation counting. Retinal blood flow values measured with quantitative and regional autoradiography were higher in the central (108 +/- 20 ml/100 g/min) than in peripheral (84 +/- 15 ml/100 g/min) retina. These values were within the same range as cortical blood flow values (97 +/- 4 ml/100 g/min). The retinal blood flow values obtained on whole-mount retinae were validated by the sampling method. Hypercapnia significantly increased overall blood flow in the retina (24-53%) with a maximal augmentation in the peripheral region and in the brain (22-142%). The changes were stronger in the brain compared to retina (p = 0.016). These results demonstrate that retinal blood flow can be quantified using [(14)C]-IMP and compared with cerebral blood flow. This technique is a powerful tool to study how retinal blood flow is regulated in different regions of the rat retina.
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Affiliation(s)
- Mylène Pouliot
- School of Optometry, University of Montreal, C.P. 6128, succursale Centre-Ville, Montréal, QC H3C 3J7, Canada
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