Biomedical Engineering Reference
In-Depth Information
2.16 Discussion and Concluding Remarks
This chapter presented an overview of quantitative PET imaging, including the
basic principles and instrumentation, methods of image reconstruction from
projections, and some specific correction factors necessary to achieve quantita-
tive images. Techniques for absolute physiologic parameters estimation based on
the framework of tracer kinetic modeling are also introduced. Recent advances
in instrumentation and detector technologies have partially resolved some of
the challenges. Research is still under way to develop new detector materials
not only for improving the spatial resolution but also the system sensitivity,
while keeping the cost of the instrument acceptable. Another active research
area is image reconstruction. Although the filtered backprojection method is still
widely used nowadays, it is not an optimal reconstruction technique. Iterative
algorithms have been shown to improve the signal-to-noise ratio of the recon-
structed images and provide more accurate image reconstruction for low count
studies, but the computational complexity and appreciably long reconstruction
times as compared with filtered backprojection, as well as the requirement of
using some
ad hoc
techniques to control the visual quality of the reconstructed
images, remain a substantial obstacle for routine implementation. It should be
noted, however, that a good reconstructed image is not only dependent on the
reconstruction algorithm, but also dependent on the sufficient axial and angu-
lar sampling of projection data such that the reconstruction artifacts can be
minimized. In order to achieve accurate absolute or relative quantification, ap-
propriate data corrections have to be applied prior to image reconstruction.
The use of SPECT for studying physiologic functions deserves mention here.
SPECT is another form of emission computed tomography which had its begin-
ning in the early 1960s, initiated by the work of Kuhl and Edwards on transverse-
and longitudinal-section scanning with single-photon-emitting radiotracers [15],
and the work of Anger on the development of scintillation camera (also known
as gamma camera or Anger camera) coupled with photomultiplier tubes [108].
Although the innovative idea of how gamma rays interact with inorganic crystal
(scintillator) to produce scintillation light and how optical coupling with pho-
tomultiplier tubes helps amplify the scintillation signal may shed some light on
detector design in PET, the development of SPECT imaging, however, has been
overshadowed by PET for reasons to be detailed. The principles for detecting
