Deuterium magnetic resonance imaging of rabbit eye in vivo

Imaging ocular water inflow in the mouse with deuterium oxide MRI

Abnormal intraocular fluid flow or clearance is involved with a variety of eye diseases such as glaucoma and diabetic retinopathy, but measurement of water exchange dynamics in the vitreous and aqueous remain challenging. 2H MRI can be used to image deuterium oxide (D₂O) as a tracer, but the signal-to-noise ratio for deuterium is low due to its low concentration, which has hampered its application to imaging the eye. To overcome this challenge, we investigated the feasibility of direct D2O MRI to measure water dynamics in the mouse eye. The balanced steady-state free precession (bSSFP) sequence provided substantially higher signal-to-noise ratio for imaging D2O in fluid compared to standard gradient echo and spin echo sequences. bSSFP allowed dynamic imaging of intraocular water inflow in the mouse with 41 s temporal resolution. The inflow rate in the vitreous was found to be faster than in the aqueous. These studies demonstrate the feasibility of in vivo imaging of water inflow dynamics into the both the vitreous and aqueous in mice, which could be useful in studies of abnormal fluid exchange in rodent models of eye disease.

Intraocular Water Movement Visualization Using 1 H-MRI With Eye Drops of O-17-Labeled Saline: First-in-Human Study

BACKGROUND

Visualization of aqueous humor flow in MR contrast images using gadolinium is challenging because of the delayed contrast effects associated with the blood-retinal and blood-aqueous humor barriers. However, oxygen-17 water (H₂ ¹⁷ O) might be used as an ocular contrast agent.

PURPOSE

To observe the distribution of H₂ ¹⁷ O in the human eye, and its flow in and out of the anterior chamber, using dynamic T2-weighted MRI.

STUDY TYPE

Prospective.

POPULATION

Six ophthalmologically normal volunteers (20-37 years, six females).

FIELD STRENGTH/SEQUENCE

A 3 T/dynamic T2-weighted MRI.

ASSESSMENT

H₂ ¹⁷ O eye drops were administered to the right eye. Time-series images were created by subtracting the image before the eye drops from each of the images obtained after the eye drops. The normalized signal intensity of the right anterior chamber (nAC) was obtained by dividing the signal intensity of the right anterior chamber region by that of the left. The inflow and outflow constants of H₂ ¹⁷ O and H₂ ¹⁷ O concentration were calculated from the nAC.

STATISTICAL TESTS

A paired t-test was used to compare the flow-related values and temporal changes in signal intensity. P-values < 0.05 were considered statistically significant.

RESULTS

Significantly decreased signal intensity was observed in the right anterior chamber but not the right vitreous body (P = 0.39). The nAC signal intensity decreased significantly and then recovered. The inflow and outflow constants were 0.36-0.94 min^-1 and 0.023-0.13 min^-1 , respectively. The maximum H₂ ¹⁷ O concentration was 0.078%-0.24%.

DATA CONCLUSION

H₂ ¹⁷ O were distributed in the anterior chamber. The H₂ ¹⁷ O inflow into the anterior chamber was significantly faster than that of the outflow.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY STAGE: 2.

Distribution of intraperitoneally administered deuterium-labeled water in aquaporin-4-knockout mouse brain after middle cerebral artery occlusion

Introduction

As the movement of water in the brain is known to be involved in neural activity and various brain pathologies, the ability to assess water dynamics in the brain will be important for the understanding of brain function and the diagnosis and treatment of brain diseases. Aquaporin-4 (AQP4) is a membrane channel protein that is highly expressed in brain astrocytes and is important for the movement of water molecules in the brain.

Methods

In this study, we investigated the contribution of AQP4 to brain water dynamics by administering deuterium-labeled water (D₂O) intraperitoneally to wild-type and AQP4 knockout (AQP4-ko) mice that had undergone surgical occlusion of the middle cerebral artery (MCA). Water dynamics in the infarct region and on either side of the anterior cerebral artery (ACA) was monitored with proton-density-weighted imaging (PDWI) performed on a 7T animal MRI.

Results

D₂O caused a negative signal change quickly after administration. The AQP4-ko mice showed a delay of the time-to-minimum in both the contralateral and ipsilateral ACA regions compared to wild-type mice. Also, only the AQP4- ko mice showed a delay of the time-to-minimum in the ipsilateral ACA region compared to the contralateral side. In only the wild-type mice, the signal minimum in the ipsilateral ACA region was higher than that in the contralateral ACA region. In the infarct region, the signal attenuation was slower for the AQP4-ko mice in comparison to the wild-type mice.

Discussion

These results suggest that AQP4 loss affects water dynamics in the ACA region not only in the infarct region. Dynamic PDWI after D₂O administration may be a useful tool for showing the effects of AQP4 in vivo.

Visualizing ocular lens fluid dynamics using MRI: manipulation of steady state water content and water fluxes

Studies using various MRI techniques have shown that a water-protein concentration gradient exists in the ocular lens. Because this concentration is higher in the core relative to the lens periphery, a gradient in refractive index is established in the lens. To investigate how the water-protein concentration profile is maintained, bovine lenses were incubated in different solutions, and changes in water-protein concentration ratio monitored using proton density weighted (PD-weighted) imaging in the absence and presence of heavy water (D2O). Lenses incubated in artificial aqueous humor (AAH) maintained the steady state water-protein concentration gradient, but incubating lenses in high extracellular potassium (KCl-AAH) or low temperature (Low T-AAH) caused a collapse of the gradient due to a rise in water content in the core of the lens. To visualize water fluxes, lenses were incubated in D2O, which acts as a contrast agent. Incubation in KCl-AAH and low T-AAH dramatically slowed the movement of D2O into the core but did not affect the movement of D2O into the outer cortex. D2O seemed to preferentially enter the lens cortex at the anterior and posterior poles before moving circumferentially toward the equatorial regions. This directionality of D2O influx into the lens cortex was abolished by incubating lenses in high KCl-AAH or low T-AAH, and resulted in homogenous influx of D2O into the outer cortex. Taken together, our results show that the water-protein concentration ratio is actively maintained in the core of the lens and that water fluxes preferentially enter the lens at the poles.

Quantifying cardiovascular flow dynamics during early development

The relationship between developing biologic tissues and their dynamic fluid environments is intimate and complex. Increasing evidence supports the notion that these embryonic flow-structure interactions influence whether development will proceed normally or become pathogenic. Genetic, pharmacological, or surgical manipulations that alter the flow environment can thus profoundly influence morphologic and functional cardiovascular phenotypes. Functionally deficient phenotypes are particularly poorly described as there are few imaging tools with sufficient spatial and temporal resolution to quantify most intra-vital flows. The ability to visualize biofluids flow in vivo would be of great utility in functionally phenotyping model animal systems and for the elucidation of the mechanisms that underlie flow-related mechano-sensation and transduction in living organisms. This review summarizes the major methodological advances that have evolved for the quantitative characterization of intra-vital fluid dynamics with an emphasis on assessing cardiovascular flows in vertebrate model organisms.

19F-magnetic resonance spectroscopy and chemical shift imaging for schizophrenic patients using haloperidol decanoate

Haloperidol decanoate is widely used in the maintenance treatment of schizophrenia and other psychotic disorders, but knowledge concerning its pharmacokinetics at the injected region is very limited. Because the chemical structure of haloperidol contains fluorine, in vivo 19F-magnetic resonance (MR) spectroscopy (repetition time (TR) = 1 s) and chemical shift imaging (CSI; TR = 1 s, pixel size = 15 x 15 mm) were performed in schizophrenic patients who were treated with haloperidol decanoate (three men and one woman) to measure its diachronic change at the injection point and visualize its local distribution after intramuscular injection. 19F signals (T1 time = 365 ms) were obtained at the haloperidol decanoate-injected region. The decrease rate of the signal-to-noise ratio (SNR) by 19F-MR spectroscopy seemed large in comparison with that of the plasma haloperidol concentration. The distribution was clearly visualized by 19F-CSI for a few days after the injection, but after 1 week could no longer be seen. Although the slow-release characteristics of depot neuroleptics have been explained by the slow diffusion of esterified neuroleptics from the oil vehicle, this result may suggest that there are other mechanisms involved in maintaining the plasma haloperidol concentration. In vivo 19F-MR spectroscopy and CSI are potentially applicable for the pharmacokinetic analysis of haloperidol and other drugs containing fluorine in their structure.

MR in vivo imaging of oxygen suppression effect of soft contact lens on the human cornea

The O(2) suppression effect of a soft contact lens on the human cornea was measured using dynamic magnetic resonance imaging (MRI) of the anterior chamber transcorneally exposed to O(2). Dynamic T(1)-weighted fast spin echo imaging of anterior chambers (TR = 2 s, TE = 15 ms, 5-mm slice) was performed both before and during oxygen supply to a full goggle placed on the face of volunteers wearing a soft contact lens on one eye and nothing on the other eye as a control. Within 15 min after O(2) administration, significantly lower intensity changes were obtained in the anterior chambers of the eyes with the contact lens than in those of the eyes without one, suggesting that dynamic MRI of the anterior chamber transcorneally exposed to O(2) can be used to evaluate the O(2) suppression effect of a soft contact lens on the cornea.

Dynamic MRI of transcorneal dispersion of oxygen into the anterior chamber of human eye

To measure the transcorneal dispersion of oxygen into the anterior chamber, dynamic T1-weighted fast-spin-echo MRI (TR=2 seconds, TE=15 msec, 5-mm slice) of the human eye was performed both before and during oxygen supply to a full goggle placed on the face. During the course of the imaging, a significant increase in the signals in the anterior chamber occurred. This indicated that transcorneal dispersion of oxygen into the anterior chamber can be evaluated by this procedure, suggesting that this method may be useful for diagnosing dysfunction of the cornea or aqueous flow.

Noninvasive analysis of water movement in rat testis using deuterium magnetic resonance imaging

To measure water movement in the testis without the effects from the blood-testis barrier, we performed in vivo deuterium magnetic resonance imaging (2H MRI) of rats administered with deuterated saline. Alcohol was injected into one testis of each animal and the other was administered with normal saline as a control. Dynamic 2H MRI was obtained at 2 T by FLASH pulse sequence (TR, 300 ms; TE, 10 ms; alpha = 90 degrees) using a surface coil (3 cm in diameter). The variation in 2H signal intensity between the two testes as a function of time after deuterated saline injection was examined every 1.1 min up to 20 min. The signal intensity in the testis receiving the alcohol treatment was lower than that in the normal control. Thus, deuterium MRI can be used to analyze functional disorders of the testis.