The Card. 99mTc Tetrofosmin (Shrestha) model has been developed by Shrestha et al. [1] for cardiac SPECT studies using 99mTc Tetrofosmin bolus injection. It is based on a 1-tissue compartment model with plasma activity CP(t) and total uptake in myocardium Cmyo(t).
Operational Model Curve
The differential equation is given by
The model uses the activity in the left ventricular cavity Clv(t) is used as the input curve (CP(t)=CLV(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
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 Shrestha et al. [1] are
A = 0.91
B = 0.34 [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
VLV = spill-over fraction of the blood activity in the left ventricular cavity CLV(t),
VRV = spill-over fraction of the blood activity in the right ventricular cavity CRV(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 VRV 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. If necessary, the scale factor A (EF scale) and the exponent B (EF exp) of the extraction function can be interactively edited.
Reference
1.Shrestha U, Sciammarella M, Alhassen F, Yeghiazarians Y, Ellin J, Verdin E, Boyle A, Seo Y, Botvinick EH, Gullberg GT: Measurement of absolute myocardial blood flow in humans using dynamic cardiac SPECT and (99m)Tc-tetrofosmin: Method and validation. J Nucl Cardiol 2017, 24(1):268-277.