Speaker
Mrs
Irène Buvat
(U678 Inserm UPMC)
Description
Objective: Emission tomography (Single Photon Emission Tomography – SPECT – and
Positron Emission Tomography – PET) offers a great potential for the quantitative
characterization of functional and molecular processes in vivo. Indeed, voxel values in the
reconstructed SPECT and PET images can theoretically be translated into a well-understood
physical quantity, namely radiotracer concentration, from which all kinds of parameters
characterizing molecular processes can be derived using appropriate modeling. Such
quantitative interpretation of SPECT and PET images is often referred to as “quantification”.
The objective of this tutorial is to examine how far we are in this quest for quantification by
presenting the different problems that have to be addressed, the methods that have been
developed to solve these problems, and the current performance of these methods.
Contents: To successfully achieve quantitative interpretation of SPECT and PET images, the
very first step consists in establishing a linear relationship between radiotracer concentration
and voxel values. To do so, many phenomena have to be taken into account, among which
motion, photon attenuation and photon scatter, non stationary spatial resolution and partial
volume effect are the most critical. For each of these phenomena, the resulting biases will be
explained and illustrated in different configurations, the most relevant compensation methods
will be described and the current performance that can be achieved using these methods will
be presented. The influence of the random correction in PET, of the tomographic
reconstruction algorithm, and the very way measurements are performed from the images will
also be discussed. The respective importance of the different factors affecting the accuracy
with which activity concentration can be estimated from the images will be illustrated.
Once proper methods have been used to ensure that radiotracer concentration can be
accurately deduced from voxel values, a second step in the quantification process is the
estimation of physiological parameters from radiotracer concentrations measured in different
physiological compartments and possibly over time. Such estimation is based on modeling the
physiological system under study. Examples will be shown to demonstrate that relevant
modeling is of foremost importance to take full advantage of accurate estimates of radiotracer
concentration from the SPECT and PET images and successfully complete the quantification
process.
Author
Mrs
Irène Buvat
(U678 Inserm UPMC)
