Corrections for Scanner-Related Factors - Correction Techniques in Emission Tomography - page 114

that for the translation between the CFOV of the SPECT and the CT scan-
ner. Furthermore, differences in the diameter of the FOV between the two
modalities may influence reconstruction accuracy. For myocardial perfusion
SPECT/CT this issue is addressed in [8].
Furthermore, the intrinsic dependency of collimator resolution on source-
to-collimator distance (see Figure 6.3) leads to the requirement that a patient
is placed as close to the collimator as possible (within constraints of patient
comfort, and sometimes the wish to keep this distance as equal as possible
during a whole body acquisition).
6.2.2 Motion correction
For certain applications such as cardiac SPECT-CT imaging, advanced
methods are available for compensation of motion. One form is compensation
for cardiac motion by taking a measured ECG signal into account to sort
measured data over various phases of the cardiac cycle (e.g., end-systolic or
end-diastolic phases). Another form is an automated detection of patient mo-
tion during acquisition. If, for instance, during rotation of the gamma camera
heads around the patient one of the projections is measured on a patient that
moved between the former and the latter projection, this can be detected as
well as automatically corrected (see Figure 6.4).
FIGURE 6.3: Collimator resolution versus source-to-collimator distance for
three different collimators. Taken from [6].