Parathyroid Scintigraphy - European Association of Nuclear Medicine

1a) is defined by a fixed distance from the axis
of rotation to the centre of the camera surface
for all angles. Elliptical orbits (Fig. 1b) follow
the body outline more closely.
Figure 1a Figure 1b
Figure 1a circular orbit
Figure 1b elliptical orbit
With a circular orbit, the camera is distant from
the body at some angles, causing a reduction
in spatial resolution in these projections. This
will reduce the resolution of the reconstructed
images.
With an elliptical orbit, spatial resolution will be
improved as the camera passes closer to the
body at all angles. Nevertheless, the distance
from the organ to the detector varies more
significantly with an elliptical orbit than with
a circular orbit. This may generate artefacts
simulating small photopenic areas when reconstructing
using filtered back projection.
Programmes that allow the camera to learn
and closely follow the contours of the body
1
Chapter 3: Imaging equipment - preparation and use
are available and improve resolution, although
at the expense of computing power to modify
the data before reconstruction.
The loss of spatial resolution with a circular
orbit has to be offset against the potential artefacts
that may be generated by an elliptical
or contoured orbit.
Filtered back projection image
reconstruction: some considerations
The main goal of nuclear medicine parathyroid
imaging procedures is to identify the
site of parathyroid hormone production,
usually a single parathyroid adenoma. However,
parathyroid adenomas can be found in
diverse locations: alongside, beside or within
the thyroid, or in anatomical regions distant
from thyroid, such as high or low in the neck
and mediastinum. The diversity of these anatomical
locations makes SPECT a useful tool
in parathyroid imaging.
Furthermore, parathyroid adenomas are small
structures with increased uptake often close
to normal thyroid activity. The choice of an
optimum filter when using filtered back projection
for reconstruction is crucial (Pires Jorge
et al. 1998).
A filter in SPECT is a data processing algorithm
that enhances image information, without
significantly altering the components of the
input data, creating artefacts or losing information.
It should produce results that lead to
EANM