Biomedical Engineering Reference
In-Depth Information
negative coefficients of exponentials are also possible if the input and output are
not taken from the same compartment [90]. Furthermore, repeated eigenvalues
may be inherent in the data and the impulse response function of the underlying
system could have different formats [91].
2.14.7 Weighted Integration
Another approach for dynamic PET data analysis is by means of
weighted inte-
gration
or
integrated projection
methods. Different from the techniques men-
tioned before which calculate parameters of interest from a series of
recon-
structed images
based on the framework of compartmental model fitting, these
methods eliminate the need to reconstruct the dynamic projection data. Instead,
the parameters of interest are calculated from the weighted integrals of the pro-
jection data based on the relationship between the time-dependent weighting
functions and the projection data [92-95]. Indeed, the weighted integration ap-
proach can be applied to the reconstructed data by integrating the full set of
dynamic images. Reconstruction load, however, can be significantly reduced if
the weighted integration is performed on the projection data because only the
integrated projection data is reconstructed. This relies on the fact that image re-
construction is a linear operation in the spatial domain and the linear operations
in time is communicative with image reconstruction [96, 62]. Therefore, the or-
der of reconstruction and integration can be interchanged. It is apparent that
integration of the projection data prior to image reconstruction has an attractive
computational advantage.
Typically weighted integration or integrated projection methods are used to
determine the rate of blood flow and the tissue-to-blood partition coefficient. In
fact, the use of weighted integration does not limit to one-compartment model
such as that used to measure cerebral blood flow. With the use of additional
weighting functions, physiologic parameters in two- and three-compartment
models can also be estimated. As might be expected, the formulation is consid-
erably more complicated.
2.15 Applications of PET
As PET is a physiological/functional imaging modality, which provides infor-
mation about the physiology in tissue, it is therefore complementary to the
