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| Dr. Patrick Reinartz is Assistant
Medical Director of the
Department of Nuclear Medicine
at the University Hospital in
Aachen. He started his training in
1997 and received board
certification in 2002. He is
currently involved in research on
methodological optimization of
ventilation/perfusion lung
scintigraphy. His other research
interests include osteology with a
particular emphasis on SPECT
imaging in bone metastases and
positron emission tomography in
patients with joint replacements,
as well as molecular imaging of
hypoxia in oncology. |
Pulmonary embolism from a nuclear medicine perspective
Patrick Reinartz, MD
Ulrich Buell, MD
Department of Nuclear Medicine, University Hospital
Aachen, Aachen, Germany
Corresponding author:
Dr. med. Patrick Reinartz
Department of Nuclear Medicine
University Hospital Aachen
Pauwelsstrasse 30, 52074 Aachen, Germany
Tel: +49-241-80-88-743
Fax: +49-241-80-82-424
Email: preinartz@compuserve.com
Abstract
Lung scintigraphy is an indirect imaging method which
non-invasively visualizes the perfusion defect caused by
an embolus instead of the embolus itself. Since the
perfusion defect is a great deal larger than the clot
causing it, the procedure is highly sensitive and easily
detects even small embolisms on a subsegmental level.
To improve the specificity of the method, each
perfusion scintigraphy should be coupled with a
ventilation scan. For best results, single photon emission
computed tomography (SPECT) should be used; this
technique increases the diagnostic accuracy of the
method to 0.94. In addition to SPECT imaging, the use
of the new ultrafine aerosol Technegas as ventilation
agent is highly recommended. In the field of image
interpretation, the use of the complex PIOPED system
and its unsatisfactory probability classes can no longer
be advised. Instead, definitive diagnoses should be given
by assessing all mismatch defects of at least half
segment size as pulmonary embolisms. As far as the
diagnostic efficiency of lung scintigraphy in clinical trials
is concerned, there is a trend to compare advanced
tomographic imaging modalities such as multislice or
electron beam CT with planar scintigraphy acquired in a
technique similar to that of the 20-year-old PIOPED
study. For a balanced comparison, it is essential to use
state-of-the-art techniques for all modalities.
Lung scintigraphy was introduced in 1964, making it
one of the longest established non-invasive imaging modalities in the diagnosis of pulmonary embolism.1
Unlike angiography, lung scintigraphy is an indirect
imaging procedure which detects the perfusion defect
caused by an embolus instead of the embolus itself.
Such an indirect approach has advantages as well as
disadvantages. On the one hand, the method is
exceptionally sensitive because the perfusion defect is a
great deal larger than the clot causing it. Therefore, even
small embolisms at the sub-segmental level are easily
detected by this method. In addition, only lung
scintigraphy is able to exactly quantify the functional
fraction of lung tissue that is unaffected by an
embolism. On the other hand, specificity is a weak
point of the procedure since pulmonary perfusion
defects are not only caused by emboli but by a
multitude of other diseases and pathological processes.
To amend this deficit, the acquisition protocol of lung
scintigraphy was complemented by the ventilation scan
in 1968.2 Today, the term ‘lung scintigraphy’ always
implies both the perfusion and the ventilation scan.
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