Card. Rb-82 (1 Compartment)

The Card. Rb82(1 Compartment) model has been developed by Lortie et al. [1] for cardiac PET studies using ⁸²Rb bolus injection. It is based on a 1-tissue compartment model with plasma activity C_P(t) and total uptake in myocardium C_myo(t).

Operational Model Curve

The differential equation is given by

Equation Rb 1Compartment

The model uses the activity in the left ventricular cavity C_lv(t) is used as the input curve (C_P(t)=C_LV(t)). Rb is known to have a flow-dependent extraction fraction, so that K₁, which is the product of flow F times extraction fraction E, is described by the expression

Equation Rb 1 Compartment K1

This expression is inserted for K₁ into the differential equation, so that F becomes a fit parameter, and K₁ is derived from it. The values of the extraction parameters reported by Lortie et al. [1] are

A = 0.77
B = 0.63 [ml/min/g]

They can be entered as input parameters into the model for changing the form of the extraction function. The model curve incorporates a cardiac dual spillover correction, resulting in the operational equation

where
V_LV = spill-over fraction of the blood activity in the left ventricular cavity C_LV(t),
V_RV = spill-over fraction of the blood activity in the right ventricular cavity C_RV(t)

Implementation

When using the model from the PCARD module, the data are transferred appropriately. When using it in PKIN the blood data have to be loaded as follows:

The left ventricle curve must be loaded as the Plasma activity curve.
The right ventricle curve must be loaded as the Whole blood curve.

The following automatic adjustment is performed within the model:

The spill-over fraction from the right ventricle V_RV is automatically fixed to zero if the string "Sep" is not contained in the name a region. The assumption is that such a TAC is not from septal tissue and should thus be modeled with spill-over from the left ventricle only.

Parameter Fitting

The model includes the 4 fitable parameters F, vRV, vLV and k2. Please inspect the %SE standard error to get information about the reliability of the parameter estimates. The scale factor A (EF scale) and the exponent B (EF exp) of the extraction function can be entered as input parameters.

Reference

1. Lortie M, Beanlands RS, Yoshinaga K, Klein R, Dasilva JN, DeKemp RA: Quantification of myocardial blood flow with 82Rb dynamic PET imaging. Eur J Nucl Med Mol Imaging 2007, 34(11):1765-1774.