Cardiac Flow from Acetate PET

Van den Hoff et al. [1] have investigated and validated ¹¹C-acetate as a flow tracer. This methodology is implemented as the Card Acetate (1 Compartment) model. It employs a single tissue compartment model

with tracer exchange between arterial plasma C_P(t) and myocardial tissue C_myo(t).

Operational Model Curve

The differential equation C_myo(t) is given by

K₁ is the product of flow F and extraction E

For acetate, the extraction is flow dependent [1]

Furthermore a metabolite correction is necessary to derive the plasma activity from whole blood measured in the left cavity [1]

with T_1/2=5.3 min. Including these relations into the differential equation yields

which is non-linear in F. 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. No metabolite correction needs to be enabled on the Blood panel of PKIN because it is included in the tissue model.
• 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, k2, vLV, vRV. Please inspect the %SE standard error to get information about the reliability of the parameter estimates. The parameters for the correction of the flow-dependent extraction (EF scale, EF exp) and the metabolites (MC scale, MC T12) are initialized with the published values [1], but can be edited if needed. The K1 parameter of the 1-tissue compartment model equivalent to the EF product is provided as s macro parameter.

Reference

1. van den Hoff J, Burchert W, Borner AR, Fricke H, Kuhnel G, Meyer GJ, Otto D, Weckesser E, Wolpers HG, Knapp WH: [1-(11)C]Acetate as a quantitative perfusion tracer in myocardial PET. J Nucl Med 2001, 42(8):1174-1182. PDF