Organic photovoltaic cells and methods of forming the same are provided. The cable guide is pivotally attached to a geared oscillation device which cyclically guides the cable to facilitate evenly distributed winding and unwinding of the cable along one end of the drum to an opposite end of the drum. DSA 2-{4,7-bis-carboxymethyl-10-, characterised in that said liposome further comprises a neutral, fully saturated phospholipid component, which are of particular use in the preparation of magnetic resonance contrast agents for enhancing a magnetic resonance image of tumours in a mammal.