Positron emission, changes

Silverman, D. H., Small, G. W., Chang, C. Y. et al. Positron emission tomography in evaluation of dementia regional brain metabolism and long-term outcome. JAMA 286 2120-2127, 2001. 

B We know that 19 F is stable, with approximately the same number of neutrons and protons 9 protons, and 10 neutrons. Thus, nuclides of light elements with approximately the same number of neutrons and protons will be stable. In Practice Example 26-1 we saw that positron emission has the effect of transforming a proton into a neutron. /T emission has the opposite effect transforming a neutron into a proton. The mass number does not change in either case. Now let us analyze our two nuclides. 

Positron production occurs for nuclides that are below the zone of stability (those nuclides whose neutron/proton ratios are too small). The net effect of positron emission is to change a proton to a neutron. An example of positron emission would be... 

It is a straightforward matter to understand the physical constraint imposed by the combustion time of silicon. Ashes from silicon will be all the richer in neutrons as the weak interaction is given the time to carry out its work via positron emission and electron capture, changing protons into neutrons and hence enriching the environment with neutrons. 

D.S. Goldstein, P.C. Chang, G. Eisenhofer, R. Miletich, R. Finn, J. Bacher, K.L. Kirk, S. Bacharach, I.J. Kopin, Positron emission tomographic imaging of cardiac sympathetic innervation and function. Circulation 81 (1990) 1606-1621. 

Neuroimaging techniques assessing cerebral blood flow (CBF] and cerebral metabolic rate provide powerful windows onto the effects of ECT. Nobler et al. [1994] assessed cortical CBE using the planar xenon-133 inhalation technique in 54 patients. The patients were studied just before and 50 minutes after the sixth ECT treatment. At this acute time point, unilateral ECT led to postictal reductions of CBF in the stimulated hemisphere, whereas bilateral ECT led to symmetric anterior frontal CBE reductions. Regardless of electrode placement and stimulus intensity, patients who went on to respond to a course of ECT manifested anterior frontal CBE reductions in this acute postictal period, whereas nonresponders failed to show CBF reductions. Such frontal CBF reductions may reflect functional neural inhibition and may index anticonvulsant properties of ECT. A predictive discriminant function analysis revealed that the CBF changes were sufficiently robust to correctly classify both responders (68% accuracy] and nonresponders (85% accuracy]. More powerful measures of CBF and/or cerebral metabolic rate, as can be obtained with positron-emission tomography, may provide even more sensitive markers of optimal ECT administration. 

In PET, positron-emitting isotopes such as C-11, N-13, 0-15, and F-18 are used. Each of these unstable isotopes is characterized by lacking a neutron compared to its stable form for example, C-11 needs one more neutron to become C-12. They undergo positron emission when a proton changes into a neutron ... 

Kennedy, SJU, Evans, K.R., Kruger, S., et al. Changes in regional brain glucose metabolism measured with positron emission tomography after paroxetine treatment of major depression. Am. J. Psychiatry 158(h), 899-905, 2001. 

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