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Quantitative magnetic resonance imaging in assessment of the blood-retinal barrier
W E Plehwe1, D W McRobbie, R A Lerski
1Department of Medicine, Royal Postgraduate Medical School, Hammersmith Hospital, London, United Kingdom.
Abstract:
Application of magnetic resonance imaging (MRI) in two-dimensional quantitative assessment of blood-retinal barrier dysfunction was investigated in rabbits using a 0.1 T (4.25 MHz) resistive system. Reliable and consistent measurements of vitreous T1 were obtained repeatedly, in slices of width 5 mm and X-Y resolution of 1.2 mm. Calibration of reduction of T1 in eyes after injection of gadolinium-DTPA (Gd-DTPA) was performed, resulting in a dose-related response of relaxation rate (1/T1) to the dose of Gd-DTPA injected. Follow-up scans of injected eyes demonstrated a gradual spread of the T1 "hot-spot" as the contrast agent diffused through the vitreous. T1 rose gradually to basal levels by 72 hr. No local effect of Gd-DTPA was found by ophthalmoscopy. Xenon arc photocoagulation of rabbit retina reduced T1 from 1638 +/- 54 (n = 6, mean +/- SD) ms to 1408 +/- 118 (n = 4) msec (P less than 0.01) throughout the vitreous 5-7 hr after treatment. In treated rabbits receiving 1.0 mmol/l Gd-DTPA intravenously, T1 adjacent to lesions 90-120 min after injection was further reduced in a 63 microliter voxel to 670 +/- 50 ms (mean +/- SD, n = 5) with a minimum pixel value of 285 +/- 52 ms. It was estimated that this represented leakage into vitreous of 8.3 nmol Gd-DTPA. Plasma Gd-DTPA concentrations declined rapidly, with half-life of 20-40 min. The findings indicate that MRI is a technique with the potential for repeated quantitative three-dimensional assessment of blood-retinal barrier dysfunction.
Insights
Magnetic resonance imaging (MRI) quantifies blood-retinal barrier dysfunction using gadolinium-DTPA (Gd-DTPA) contrast agent in rabbits. MRI shows potential for repeated, quantitative assessment of this barrier
Area of Science:
- Ophthalmology
- Medical Imaging
- Physiology
Background:
- The blood-retinal barrier (BRB) is crucial for retinal health.
- Dysfunction of the BRB is implicated in various ocular diseases.
- Non-invasive quantitative assessment methods for BRB integrity are needed.
Purpose of the Study:
- To investigate the application of magnetic resonance imaging (MRI) for quantitative assessment of blood-retinal barrier (BRB) dysfunction.
- To evaluate the use of gadolinium-DTPA (Gd-DTPA) as a contrast agent for MRI-based BRB assessment in rabbits.
Main Methods:
- Utilized a 0.1 T resistive MRI system for two-dimensional quantitative assessment.
- Measured vitreous T1 relaxation times before and after intravenous injection of Gd-DTPA.
- Induced BRB dysfunction using xenon arc photocoagulation of the rabbit retina.
- Correlated T1 changes with Gd-DTPA concentration in specific retinal regions.
Main Results:
- Reliable and repeatable measurements of vitreous T1 were achieved.
- A dose-dependent reduction in T1 was observed following Gd-DTPA injection.
- Retinal photocoagulation significantly reduced vitreous T1, indicating BRB breakdown.
- MRI detected localized Gd-DTPA leakage into the vitreous adjacent to photocoagulated lesions.
Conclusions:
- MRI, in conjunction with Gd-DTPA, provides a quantitative method for assessing BRB dysfunction.
- The technique allows for repeated, non-invasive measurements of BRB integrity.
- MRI holds potential for the three-dimensional assessment of BRB integrity in vivo.