Axon tracing in the adult rat optic nerve and tract after intravitreal injection of MnDPDP using a semiautomatic segmentation technique

• Published in: Journal of magnetic resonance imaging 2008-01, Vol.27 (1), p.34-42
• Main Authors: Olsen, Øystein, Thuen, Marte, Berry, Martin, Kovalev, Vassili, Petrou, Maria, Goa, Pål Erik, Sandvig, Axel, Haraldseth, Olav, Brekken, Christian
• Format: Article
• Language: English
• Subjects: 3D image segmentation; Analysis of Variance; Animals; Chlorides - administration & dosage; Chlorides - pharmacology; Contrast Media - administration & dosage; Contrast Media - pharmacology; Edetic Acid - administration & dosage; Edetic Acid - analogs & derivatives; Edetic Acid - pharmacology; Female; Gadolinium DTPA - administration & dosage; Gadolinium DTPA - pharmacology; Imaging, Three-Dimensional; Injections; Magnetic Resonance Imaging; manganese; Manganese Compounds - administration & dosage; Manganese Compounds - pharmacology; MEMRI; optic nerve; Optic Nerve - anatomy & histology; Pyridoxal Phosphate - administration & dosage; Pyridoxal Phosphate - analogs & derivatives; Pyridoxal Phosphate - pharmacology; rat; Rats; Rats, Inbred F344; Regression Analysis; Tissue Distribution; Vitreous Body
• ISSN: 1053-1807; 1522-2586
• DOI: 10.1002/jmri.21234

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 Mn2+ enhancement compared to MnCl2 when used for functional imaging of the visual pathway. Materials and Methods Intravitreous injection of the manganese‐releasing MR contrast agent MnDPDP (30 nmol Mn2+) was performed to trace the ON in adult rats (n = 4). A positive control group of rats (n = 5) received a standard preparation of MnCl2 (200 nmol Mn2+), while gadodiamide (1500 nmol Gd3+) 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 Mn2+ 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 MnCl2 injection. Conclusion 3D semiautomated image segmentation and the use of MnDPDP can improve in vivo axon tracing based on MRI. Mn2+ 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.