The present invention provides a process for the production of an organic iodinated X-ray contract agent, characterized in that process control comprises vibrational (e.g., infrared, Raman or preferably near-infrared) spectroscopic monitoring of the reaction mixture in at least one of the process steps, preferably one of the final reaction steps.

The present invention relates to a method of generating an electron spin resonance enhanced magnetic resonance image of a sample which comprises introducing into the sample a magnetic resonance signal enhancing amount of a free radical and generating an enhanced electron spin resonance image of the sample. The method comprises using as the free radical an inert triarylmethyl free radical, wherein each aryl moiety of said triarylmethyl radical, which may be identical or different, comprises an optionally substituted 6-membered carbocyclic or thienyl ring. The invention also relates to the use of trityls in ESR imaging.