Next: 2.1.2 Difference in Information
Up: 6.1 Introduction
Previous: 6.1 Introduction
SPECT and MR volumes provide information on the metabolic and
anatomical levels. SPECT/MR registration allows the provision of
information on both levels. Simply viewing images from both modalities
side-by-side is not sufficient for effective study and diagnosis.
This is principally because the images produced by the two modalities
are usually not in the same spatial orientation or scale, unless
imaging was done within the confines of a stereotactic environment or
some other patient immobilization procedure such that position and
orientation was exactly reproducible in both scans. MR provides
images of the brain which are rich in anatomical detail. It has the
capability to image different tissue types, where gray and white
matter in the brain are excellently contrasted from each other.
SPECT images of the brain, on the other hand, give information associated
with radioactive tracer behavior (see section 
) relative to
cerebral blood flow and are greatly lacking in anatomical detail. They
have coarser system tomographic resolution. Gray to white matter blood
uptake ratios in SPECT images of the brain using
Tc-hexamethylpropyleneamine oxime (HMPAO) are thus about 2:1 because of
partial volume effects. When used in clinical diagnosis, the deficit of
anatomical visual cues or landmarks in SPECT images does not allow the
accurate mental placement of areas of abnormal perfusion because of
the modality's inherent lack of anatomical information. Mathematical registration allows the availability of complementary
information by the re-orientation of the position and direction of one of
the brain volume data sets to match the orientation of the other. This is
image registration. The spatial position and orientation of the brain in a
volume data set may be described in terms of points defining a rigid body.
Next: 2.1.2 Difference in Information
Up: 6.1 Introduction
Previous: 6.1 Introduction