Роль 13N-аммония в оценке перфузии миокарда(при ПЭТ)

[Eukariot]

Помогите студенту 6го курса, который не был достаточно внимателен на лекциях по биохимии года 2 назад.
На Лучевой диагностике проходим ПЭТ.Мне не понятно почему распределение 13N-аммония позволяет судить о перфузии миокарда. Есть 2 основных мысли:
1. 13N-аммоний включается в цикл клеточного дыхания
2. 13N-аммоний как-то связан а) с эндотелиоцитами
б)с белками(альбумины?)кровеносного русла...
Одним словом я не знаю,а главное не совсем прелставляю в каком направлении копать.
Заранее благодарю.

[Yariko]

Medical and Statistical Review of N-13 Ammonia Positron Emission
Tomography—August 9, 1999
Florence Houn, MD MPH FACP, Medical Officer
[Ссылки доступны только зарегистрированным пользователям ]

Journal of Nuclear Medicine Vol. 48 No. 5 783-793
Clinical Myocardial Perfusion PET/CT
Marcelo F. Di Carli, Sharmila Dorbala, Jolene Meserve, Georges El Fakhri, Arkadiusz Sitek and Stephen C. Moore
[Ссылки доступны только зарегистрированным пользователям ]

In arterial blood, 13N-ammonia consists of neutral ammonia (NH3) in equilibrium with its charged ammonium (NH4) ion. The neutral NH3 molecule readily diffuses across plasma and cell membranes, leading to virtually complete extraction from the vascular pool. Inside the myocyte, it reequilibrates with its ammonium form, which is trapped in glutamine via the enzyme glutamine synthase. Once inside the myocyte, 13N-ammonia is incorporated into the glutamine pool and becomes metabolically trapped. Only a small fraction diffuses back into the intravascular space. Its retention by the myocardium has a nonlinear and inverse relationship with blood flow. In healthy humans, the fraction of 13N-ammonia retained by the myocardium during its first pass is 0.83 when blood flow is 1 mL/min/g, and decreases to 0.60 as flow increases to 3 mL/min/g. As with other nondiffusible tracers, the net tissue extraction (the product of the retained fraction during first pass and myocardial blood flow) decreases as myocardial blood flow increases. For 13N-ammonia, the relation between net tissue extraction and blood flow is linear for values of blood flow up to 2.5 mL/min/g. At high flow rates, "metabolic trapping" of 13N-ammonia becomes the rate-limiting factor affecting tracer retention. This leads to underestimation of blood flow at high flow rates. Therefore, to quantify myocardial blood flow using 13N-ammonia, it becomes necessary to correct for flow-dependent changes in net tissue extraction.