Two new contrast agents with unprecedented high relaxivity have been made by Italian scientists. 

Contrast agents are used in magnetic resonance imaging (MRI) to make parts of the body easier to see. They work by decreasing the time it takes for water protons in tissues to return to their original energy states, known as the relaxation time. The ability of an agent to increase the relaxation rate is called its relaxivity. 

Around one third of MRI scans recorded in clinics use contrast agents, mainly gadolinium (III) complexes. However, all the complexes used have a lower relaxivity than the possible relaxivity predicted by theory. 

Mauro Botta at Università del Piemonte Orientale and colleagues synthesised and measured the relaxivity of two Gd (III) complexes conjugated to human serum albumin. They found that the relaxivity of the complexes was far greater than previously reported for Gd complexes. 

'This result confirms the validity of the predictions made by existing theory,' said Botta. 'This opens the way for chemists to further increase the relaxivity through fine tuning of the complex.' 

A major challenge in the area is the design of contrast agents suitable for use in the new generation of MRI scanners, which operate at much higher magnetic fields. 

'This will require a different approach: the consideration of paramagnetic systems of medium molecular weight and new ideas for enhancing the efficacy of the water-metal ion interaction. A difficult but fascinating task,' said Botta. 

Joanne Thomson