Factor Analysis

From the lung TAC three synthetic TACs are calculated which will be used in the factor analysis:

the TAC of blood in the left ventricle (LV): approximated by the lung TAC shifted to a later time (positive delay),
the TAC of blood in the right ventricle (RV): approximated by the lung TAC shifted to an earlier time (negative delay),
the TAC in myocardium: calculated from the LV TAC as the input curve (shifted by a specified delay) with a single-tissue compartment model, a Mean myocardial perfusion value, and the Partition coefficient of water.

Note that these three TACs are only used internally and are not shown in the user interface.

The parameters for generating the TACs can be entered in the FACTOR ANALYSIS Parameters area:

PCARD FA Parameters

In this area there are two additional configuration boxes:

FA input is decay corrected	Check the box if the dynamic data used in the FA is decay corrected. If it is not checked, a decay correction to the scan starting time will be performed using the half-time of ¹⁵O (the kinetic model in the factor analysis assumes decay-corrected data).
FA input is time normalized	Check the box if the dynamic images have units of counts/sec or kBq/cc. Otherwise it is assumed that the images contain counts and a normalization is performed by dividing the pixel values by the acquisition durations.

The Run button

PCARD FA Run Button

starts the factor analysis.

The factors are calculated, one set for myocardium, and another set for the blood volume.
These factors are used in a weighted averaging of the dynamic frames to generate the factor images of the myocardium and the factor images of the blood pool.
To make the images look smoother a Gaussian Smoothing filter is applied.
The smoothed factor images together with the dynamic images are transferred to the Reorientation page. To direct them into the right image container, please set the Stress/Rest radio button accordingly.

Note: If rest and stress studies are to be analyzed in parallel, the factor analysis must be performed sequentially, directing the results once to Rest, and once to Stress.

From then on processing continues with short axis reorientation, VOI definition and kinetic modeling as described above for the other tracers.