Layer‐specific functional and anatomical MRI of the retina with passband balanced SSFP

Purpose To verify that a visual fixation protocol with cued eye blinks achieves sufficient stability for magnetic resonance imaging (MRI) blood-flow measurements and to determine if choroidal blood flow (ChBF) changes with age in humans. Methods The visual fixation stability achievable during an MRI scan was measured in five normal subjects using an eye-tracking camera outside the MRI scanner. Subjects were instructed to blink immediately after recorded MRI sound cues but to otherwise maintain stable visual fixation on a small target. Using this fixation protocol, ChBF was measured with MRI using a 3 Tesla clinical scanner in 17 normal subjects (24–68 years old). Arterial and intraocular pressures (IOP) were measured to calculate perfusion pressure in the same subjects. Results The mean temporal fluctuations (standard deviation) of the horizontal and vertical displacements were 29 ± 9 μm and 38 ± 11 μm within individual fixation periods, and 50 ± 34 μm and 48 ± 19 μm across different fixation periods. The absolute displacements were 67 ± 31 μm and 81 ± 26 μm. ChBF was negatively correlated with age (R =−0.7, p = 0.003), declining 2.7 ml/100 ml/min per year. There were no significant correlations between ChBF versus perfusion pressure, arterial pressure, or IOP. There were also no significant correlations between age versus perfusion pressure, arterial pressure, or IOP. Multiple regression analysis indicated that age was the only measured independent variable that was significantly correlated with ChBF (p = 0.03). Conclusions The visual fixation protocol with cued eye blinks was effective in achieving sufficient stability for MRI measurements. ChBF had a significant negative correlation with age.

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“…32 Quantitative BF maps in units of ml/100 ml/min were calculated using the following equation: 24,33

BF = \frac{6000}{2 \cdot λ \cdot α \cdot α_{italicinv} \cdot T_{1, blood}} \cdot \frac{Δ M_{italicASL}}{M_{o}} \cdot e^{T 1 ∕ T_{1}, blood} \cdot e^{TE ∕ T_{2} blood},

where ΔM ASL is the difference of the control and label images. λ is the water content of blood in ml water/ml arterial blood (0.85).…”

Section: Methodsmentioning

confidence: 99%

Choroidal Blood Flow Decreases with Age: An MRI Study

Nateras

Harrison

Muir

et al. 2014

Current Eye Research

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“…A recent bSSFP MRI study on anesthetized mice could detect additional anatomic layers and layer-specific "physiologically evoked" BOLD responses. 46 Similarly, MRI of layer-specific, quantitative retinal and choroidal blood flow in the rodent retina is feasible. 22 MRI provides blood-flow values with classical units reflecting tissue perfusion, in contrast to blood-cell velocity measurements in large vessels often measured using optical approaches.…”

Section: Drawbacks and Challenges Of Retinal Mrimentioning

confidence: 99%

Lamina-Specific Anatomic Magnetic Resonance Imaging of the Human Retina

Zhang¹,

Nateras²,

Peng³

et al. 2011

Invest. Ophthalmol. Vis. Sci.

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“…MRI, by contrast, offers depth-resolved information with large field of view. MRI has recently been applied to image anatomical layers, [4][5][6] relaxation time and diffusion constants, [6][7][8] blood-oxygenation level dependent (BOLD) responses to physiological 5 and visual [9][10][11] stimulations, and quantitative blood flow 12,13 of the retinas in animal models. These approaches have been applied to study retinal degeneration, 5,12 diabetic retinopathy, 14 and glaucoma 15 in animal models.…”

mentioning

confidence: 99%