Journal of Neuroscience Methods 176 (2009) 152–156 Contents lists available at ScienceDirect Journal of Neuroscience Methods journal homepage: www.elsevier.com/locate/jneumeth Unilateral intracarotid injection of holmium microspheres to induce bilateral MRI-validated cerebral embolization in rats Fellery de Lange a,∗ , Jan M. Dieleman a,1 , Erwin L.A. Blezer b,2 , Ralph J.F. Houston a,1 , Cor J. Kalkman a,1 , J. Frank W. Nijsen c,3 a Division of Perioperative Care and Emergency Medicine, University Medical Center Utrecht, mail stop Q04-2-313, P.O. Box 85500, 3508 GA Utrecht, The Netherlands b Image Sciences Institute, University Medical Center Utrecht, Bolognalaan 50, 3584 CJ Utrecht, The Netherlands c Department of Nuclear Medicine, University Medical Center Utrecht, mail stop E 02.222, P.O. Box 85500, 3508 GA Utrecht, The Netherlands article info Article history: Received 19 May 2008 Received in revised form 31 August 2008 Accepted 2 September 2008 Keywords: Animal model Cerebral embolization Holmium Microspheres MRI Rat abstract Background: Cerebral embolization models have been hindered by the fact that delivery is predominantly one-sided and cannot be quantified easily. We have developed a model for bilateral cerebral micro- embolization. By using holmium microspheres, it is possible to quantify intracerebral delivery using MRI. Methods: To validate the quantification of holmium microspheres a phantom study was performed in which concentration of microspheres in solution was compared with the number of holmium-induced artifacts on MRI. After that identical microspheres were administered by unilateral injection in the carotid artery, while the opposite carotid artery was clamped. On post-injection MRI scans, intracerebral delivery and right/left distribution of the microspheres was determined. Results: In the phantom study it was shown that quantification by MRI is possible and that MRI artifacts represent single microspheres. In the rat brain, about one-third of the injected dose was consistently located on the contralateral side. The administration was reproducible regarding distribution and number of microspheres. Conclusions: The use of holmium microspheres enables quantification of delivered dose as single micro- spheres induce artifacts on MRI. By clamping the contralateral carotid artery, one-third of the dose is diverted to the contralateral hemisphere. © 2008 Elsevier B.V. All rights reserved. 1. Introduction In the last few decades, many animal models of cerebral micro- embolization have been employed to study pathophysiological mechanisms of diffuse cerebral ischemia. In these microsphere animal models (Bralet et al., 1979; Zivin et al., 1987; Takeo et al., 1992; Omae et al., 2000) an attempt is made to mimic the dislodging of particles as occurs during cardiac, orthopedic or cere- brovascular surgery and in stroke. However, all of these models have been hindered by the fact that injection in the carotid artery results in unpredictable delivery to the ipsilateral hemisphere (and sometimes to the contralateral hemisphere) which cannot be quan- tified directly (Takeo et al., 1992; Omae et al., 2000). We therefore ∗ Corresponding author. Tel.: +31 88 7559677; fax: +31 30 2541828. E-mail address: f.delange@umcutrecht.nl (F. de Lange). 1 Tel.: +31 88 7559677; fax: +31 30 2541828. 2 Tel.: +31 30 2535521; fax: +31 30 2535561. 3 Tel.: +31 88 7556295; fax: +31 30 2542531. developed a method of unilateral intracarotid injection for bilat- eral distribution of holmium-containing micro-embolic spheres. Because holmium is highly paramagnetic it can be used for quan- titative detection in the rat brain by magnetic resonance imaging (MRI) (Nijsen et al., 2004). By using phantoms with different con- centrations of microspheres, we investigated whether individual microspheres cause detectable distortions on MRI imaging. 2. Materials and methods 2.1. Microspheres The microspheres used in the studies were poly(l-lactic-acid) microspheres containing 17.1% holmium acetylacetonate (Nijsen et al., 2001; Zielhuis et al., 2006). Because of the paramagnetic prop- erties of holmium, the microspheres cause pixel distortion on MRI images and can thus be quantified (Nijsen et al., 2004). The microspheres had a diameter of 30 m (outer limits 20–50 m). 0165-0270/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jneumeth.2008.09.011