Biomedical Engineering Reference
In-Depth Information
Chapter 1
Introduction
Molecular imaging is gaining more and more importance, particularly Positron
Emission Tomography (PET) being the tomographic modality with the highest
molecular sensitivity. However, motion is a known problem for many medical
imaging modalities that require a minimum acquisition time to collect the relevant
information for image generation. Emission tomography techniques, such as PET or
Single Photon Emission Computed Tomography (SPECT) are particularly affected
by motion since respiratory and cardiac motion lead to image degradation in thoracic
studies. Image blurring and wrong attenuation correction are possible unwanted
consequences which can impair clinical diagnosis.
The aim of this chapter is to provide insight into the backgrounds necessary for
motion estimation and motion correction in PET. This includes an introduction to
the modality PET itself, gating, and effects which impair image quality, i.e., Partial
Volume Effects (PVE). This chapter concludes with an overview of state-of-the-art
literature regarding motion estimation respectively motion correction.
1.1
Motivation
Both respiratory and cardiac motion are sources of degradation in thoracic PET
since the PET images are acquired over an elongated period of time (in the range of
minutes). During this acquisition time lung and heart motion occurs which leads
to imaging artifacts: wrong attenuation correction and image blur. Attenuation
correction is the method of correcting the PET data for the effects of photon
absorption in the body. Dense tissues like bones absorb a larger part of the photons
than less dense tissues like lungs. Therefore, PET images without attenuation
correction show apparently greater activity in areas with less density. This effect
is corrected by scaling the number of photons registered in the PET scanner in
accordance with the density of tissues. When using Computed Tomography (CT) for
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