|
 |
 |
|
| |
|  | Magnetic Resonance Spectrometry and Positron Emission Tomography |
|
| |
| Positron Emission Tomography (PET) and Magnetic Resonance Spectrometry (MRS) are non-invasive techniques and, when used in man, allow a molecule to be monitored in real time. |
| |
| PET has many applications, some examples of which are discussed below. PET allows the study of the progress of the drug in the body, mainly at the level of in vivo target-organs. In this way, for example, the tissue concentration of erythromycin can be assessed during the course of a pulmonary infection. |
| |
| This technique is also used to demonstrate the possible correlation between a therapeutic effect and the pharmacokinetics of a drug. It is possible to show that the therapeutic effectiveness diphenylhydantoin (phenytoin) in epileptic fits is linked to its concentration in various cerebral structures. |
| |
| The effect of a drug on a physiological or biochemical process which reflects the activity of an organ or a tissue can also be monitored by PET, particularly when the object is to monitor oxygen consumption or utilisation of glucose by the brain. |
| |
| PET also permits characterisation of ligand - receptor binding, either directly with the labelled drug studied (affinity, saturation, stereospecificity studies or determination of number of receptors), or indirectly by using a labelled probe specific to the type of receptor involved in the pharmacological effect. Examples of receptors studied include: benzodiazepinic, GABAergic, dopaminergic and muscarinic. It is also possible to assess the interaction of metabolites with receptors with a view to determining their possible implication in the pharmacological activity of the drug. On the other hand, in kinetic studies PET is unable to distinguish between the active drug and its metabolites. |
| |
| The advantage of MRS lies in its capacity to monitor the appearance of the metabolites of a molecule pre-sent in tissues during physiological or pharmacological stimulation or in clinical situations. It is thus pos-sible to explore in vivo the metabolic fate of a sub-stance in the organs of the body in both healthy and diseased subjects. | |
| MRS also permits monitoring of the physiological variations of hepatic glycogen in man, measurement of intracellular pH and study of energy metabolism of the heart. MRS and PET are therefore two complementary methods for the collection of pharmacological and biochemical information obtained in local areas of the body. This information may be superimposed upon high-resolution morphological information obtained by Magnetic Resonance Imaging (MRI). X.M. |
| |
| | Back to Scientific Section Page | |
