function Cp = parker(t)
% Cp = parker(t)
% implements the Parker Arterial Input Function (2005)
% Parker et al, Experimentally derived functional form for a
% population-averaged high temporal resolution arterial input function 
% for dynamic contrast enhanced MRI
% MRM: 56(2006)

% t = time  [min]
% Cp = concentration of contrast agent within plasma [mmol/L]

A1     = 0.809;
A2     = 0.330;
T1     = 0.170;
T2     = 0.365;
sigma1 = 0.0563;
sigma2 = 0.132;
alfa   = 1.05;
beta   = 0.1685;
s      = 38.078;
tau    = 0.483;

Cp = A1/sigma1/sqrt(2*pi) * exp(-(t-T1).^2 / 2 / sigma1^2) + ...
     A2/sigma2/sqrt(2*pi) * exp(-(t-T2).^2 / 2 / sigma2^2) + ...
     alfa * exp(-beta * t) ./ (1 + exp(-s*(t-tau)));

Cp(find(t<0)) = 0; 
