our data indicate that , provided the tracer is injected directly into the left ventricle , there is little back diffusion from normal brain to blood under physiological conditions for at least 35 min following the tracer injection and an injection of unlabelled imp , in a dose larger than that used for blood flow determination , does not displace any labelled imp previously taken up by the brain , nor does it displace any labelled imp previously accumulated in the lung that would lead to secondary brain uptake .
C0006104
brain
C0220650
to secondary brain