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Positron emission tomography (PET) is a molecular imaging technology that provides quantitative information about function and metabolism in biological processes in vivo for disease diagnosis and therapy assessment. The broad application and rapid advances of PET has led to an increased demand for new radiochemical methods to synthesize highly specific molecules bearing positron-emitting radionuclides. This article provides an overview of commonly-used labeling chemistry in the examples of clinically relevant PET tracers, and highlights most recent development and breakthroughs over the past decade with focus on 11C, 18F, 13N, and 15O.

Field mapping in northern Tibet reveals that the normal slip along late Cenozoic northsouth-trending faults is comparable to that estimated for equivalent structures in southern Tibet. The orientation of fault striations in two north-south-trending rifts suggests an eastnortheast-west-northwest direction of extension in northern Tibet, which in turn implies that northeast-striking active faults in northern Tibet have significant left-slip components. Initiation of rifting in northern Tibet postdates the early Oligocene, and possibly occurred after 4 Ma. The broad similarities in the magnitude of slip and the direction of extension for normal faults in both northern and southern Tibet imply that the entire plateau has been extending. This precludes significant eastward extrusion of north Tibet relative to south Tibet and requires a regional boundary condition as the cause of east-west extension for the entire Tibet plateau.