Axon tracing in the adult rat optic nerve and tract after intravitreal injection of MnDPDP using a semiautomatic segmentation technique
✍ Scribed by Øystein Olsen; Marte Thuen; Martin Berry; Vassili Kovalev; Maria Petrou; Pål Erik Goa; Axel Sandvig; Olav Haraldseth; Christian Brekken
- Publisher
- John Wiley and Sons
- Year
- 2007
- Tongue
- English
- Weight
- 617 KB
- Volume
- 27
- Category
- Article
- ISSN
- 1053-1807
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✦ Synopsis
Abstract
Purpose
To develop and validate an objective technique for 3D segmentation of manganese‐enhanced MR images of the optic nerve/tract (ON) in adult rats to improve contrast‐to‐noise (CNR) calculations and use the technique to ascertain if manganese dipyridoxyl diphosphate (MnDPDP) gives sufficient Mn^2+^ enhancement compared to MnCl~2~ when used for functional imaging of the visual pathway.
Materials and Methods
Intravitreous injection of the manganese‐releasing MR contrast agent MnDPDP (30 nmol Mn^2+^) was performed to trace the ON in adult rats (n = 4). A positive control group of rats (n = 5) received a standard preparation of MnCl~2~ (200 nmol Mn^2+^), while gadodiamide (1500 nmol Gd^3+^) was administered in negative control rats (n = 2). An objective technique for 3D segmentation of the enhanced ON was developed. CNR profiles along the ON were calculated by resampling the 3D image‐volume in 2D planes perpendicular to the Mn^2+^ enhanced ON in 0.2 mm steps, 4 mm along the segmented ON measured from the lamina cribrosa.
Results
The ON was successfully segmented and CNR calculated accurately within 2 minutes in a representative 3D MR image volume. Intravitreal MnDPDP injection resulted in significant MRI contrast enhancement of the retina and ON after 12–24 hours similar to that of MnCl~2~ injection.
Conclusion
3D semiautomated image segmentation and the use of MnDPDP can improve in vivo axon tracing based on MRI. Mn^2+^ was found to be released from MnDPDP after intravitreal injection in sufficient amounts to obtain functional tracing of the adult rat primary visual pathway. J. Magn. Reson. Imaging 2007. © 2007 Wiley‐Liss, Inc.