Biomedical Engineering Reference
In-Depth Information
characterization, treatment planning, and assessment of therapeutic
outcomes
• The design and development of radionuclide imaging and measure-
ment devices for performing molecular examinations of patients
• The use of the tracer technique to perform these procedures with
minimal or no mass effects that could alter the biological process being
imaged or measured
•
The ability to measure molecular concentrations and rates of bio-
logical processes involving substrate concentrations down to micro-
moles to femtomoles per gram of tissue
Nuclear medicine images demonstrate function, rather than anatomy. Some
of the limitations of nuclear medicine imaging studies include limited spatial
resolution, poor signal-to-noise ratio, and frequently poor uptake of the
radiotracer in the diseased condition. Registration with a structural or ana-
tomical image can be useful in addressing a number of these issues. The main
applications at present are
•
Intramodality and intermodality spatial registration
—intramodality
registration in positron emission tomography (PET) and single
photon emission computed tomography (SPECT), e.g., PET-PET,
SPECT-SPECT, and intermodality registration with other func-
tional or structural data such as from x-ray CT and magnetic res-
onance imaging (MRI), e.g., PET-MRI
•
Correcting nuclear medicine emission data
—correction for pho-
ton attenuation and scattering, partial volume correction to compen-
sate for limited spatial resolution, and guiding image reconstruction
algorithms where anatomical priors can be used to “encourage” a
reconstruction towards a particular solution, based on the known
biodistribution of the radiotracer
•
Intersubject registration (spatial normalization)
—standardizing
the geometric conformation of uptake in an organ for comparisons
with normal databases or for use in cohort studies
The methods used to achieve the above, and examples of their use, are the
subject of this chapter. Some discussion of MR-PET registration is included
here, but this topic is treated in more detail in Chapter 9.
11.2
Early Uses of Image Registration in Nuclear Medicine
Functional images do not necessarily follow anatomy, and therefore nuclear
medicine studies have often benefited from the use of patient or organ out-
lines from other imaging devices as anatomical guides. As long ago as 1966,
