MP4A (Nagatsuka RLS Ref): Multi-linear Reference Tissue Model for [11C]-MP4A (RLS)

The MP4A (Nagatsuka RLS Ref) model has been developed for the non-invasive quantification method (RLS) of the acetylcholinesterase (AChE) activity in the human brain from measurements with the ¹¹C-MP4A acetylcholine analog. In contrast to reference methods for receptor tracers which use a reference devoid of specific binding, the present method uses a reference with very high AChE activity.

By applying the method of Blomqvist, the following multi-linear equation is derived

C(t) is the TAC from a cortical target region, and C'(t) the TAC from the reference region (striatum or cerebellum). It can be solved using multi-linear regression, yielding three regression coefficients from which three parameters of interest can be calculated:

R₁ = K₁/K'₁ = p₁, the delivery in the target region relative to the reference;
k₂ = -p₃ -p₂/p₁ , the rate of back-diffusion from brain to blood;
k₃ = p₂/p₁ , the rate of tracer hydrolysis by AChE.