Previous results for the measurement of T1 as a means of monitoring temperature have demonstrated a linear calibration with a coefficient of the order of 1.5%/degrees C. We have studied the changes in T1 further, and observe that changes in tissue perfusion are substantial contributors to the effects observed, and that the model of what is happening is complex and may not permit a simple temperature calibration.

Summary:A new method to measure regional CBF (rCBF) and volume of distribution of water is presented. It centres on recording the tissue build-up and retention of ISO-labelled water during the continuous inhalation of ISO-labelled carbon dioxide. Simultaneously, the arterial concentration is continuously monitored, and corrections for delay and dispersion in the recorded response are made by curve fitting. The values for the volume of disSeveral tracers have been proposed for the mea surement of regional CBF (rCBF) with positron emission tomography (PET). However, in practice most clinical applications have used H2150 as a flow tracer (Lammert sma and Frackowiak, \985). H2150 has been administered intravenously or by inhala tion of C1502. In the latter case the ISO label is rapidly transferred to the water pool in the lung capillary bed (West and Dollery, 1962).The preference for H21S0 as a flow tracer is based on a number of advantages: (a) the relative simplic ity of producing both H21S0 and CIS02 (Clark and Buckingham, 1975); (b) the short half-life of ISO (2.05 min), allowing for repeat measurements dur ing one scanning session and/or combination of rCBF measurements with any other (metabolic, re ceptor, etc.) study; (c) the partition coefficient of

We describe a novel instrument which is capable of measuring the uptake of radioligand in human organs in vivo with the administration of very small doses of positron-emitting radioligands. This technique readily detects the displacement or reduced uptake of radioligand when a competitive agonist or antagonist is administered. This system provides no tomographic information, but the small radioactive doses involved mean that investigations can be repeated at regular intervals and that female volunteers can also participate. We administered [(11) C]flumazenil, [(11)C]diprenorphine, [(11)C]meta -hydroxyephedrine (MHED) and [(11)C]RTI 55 to healthy male volunteers and performed control, pre-loading and displacement experiments. These demonstrate the feasibility of using this technique to investigate benzodiazepine and opiate receptor occupancy, as well as occupancy at dopamine, noradrenaline and serotonin (5-HT) re-uptake sites. This method is likely to be useful in pharmacokinetic/pharmacodynamic experiments, in drug development and discovery and in the development of novel imaging radioligands.