Joint Program in Nuclear Medicine
Attenuation Artifact in Cardiac Imaging
Gaurav M. Patel, MD
J. Anthony Parker, MD PhD
September 9, 2003
A 52-year old man with history of coronary artery disease presented
with acute onset of atypical chest pain.
images show a large, severe, fixed inferior wall defect extending
into the apex (shown
and a medium, moderate severity, partially reversible lateral wall
defect (shown by arrowheads). From top to bottom, the rows are
short-axis stress, short-axis rest, vertical-long-axis stress,
vertical-long-axis rest, horizontal-long-axis stress, and
show resolution of both the fixed inferior wall defect and the
partially reversible lateral wall defect. Gated SPECT images (not
shown) demonstrate normal wall motion and thickening, with a calculated
ejection fraction of 60%.
No Fixed or Reversible Defects
Attenuation is the decrease in intensity of a photon signal along its
path to the detector. During nuclear cardiac imaging, non-uniform
attenuation occurs as photons pass through tissues of varying
densities, such as the sub-diaphragmatic tissues, chest wall, spine,
and breasts. This results in an attenuation artifact whose extent
varies with location of soft tissue, overall patient body size, and
depth of target organ (heart).
Attenuation artifact leads to a loss of diagnostic accuracy as
artifacts may be confused with true perfusion abnormalities, resulting
in an increase in false-positives. There may also be cases of
under-interpretation of true perfusion abnormalities as the effects of
attenuation may be overestimated by the observer.
Clues for Interpretation
One way to minimize the overall negative effects of artifacts is for
the interpreter to recognize them. Some ways of doing so:
- Viewing the planar image or cine loop to look for anatomic causes
- Breast shadow
- Superiorly positioned diaphragm
- Arm position
- Use of quantitative analysis – severe defects are more likely to
- Breast markers (used for planar imaging)
- IV tubing filled with radioactive liquid to outline breast
- Changing patient position
- Repeat imaging with prone positioning if inferior wall defect
is seen on supine imaging
- Functional data
- Fixed perfusion defects which demonstrate normal contractile
defect is unlikely to be myocardial scar
- However, reversible defects are difficult to discern from
artifacts because both show normal function
Attenuation correction is a technique of using quantitative methods to
correct images for the effects of attenuation. While normal nuclear
medicine imaging usually involves an emission image obtained from
radiotracer within the patient’s body, attenuation correction uses
additional transmission data of the patient’s soft tissue distribution
to create a ‘map’ of the body’s attenuation effects.
For the Vantage™ system, a gadolinium-153 line source, collimated
with a narrow slit aperture running its length, is positioned 180
degrees oposite each of the detectors of a dual detector camera. The
line source moves across the field of view, providing transmission data
simultaneously with collection of emission data by means of a sliding
electronic window that is synchronized to the motion of the line
source. The resulting transmission map is used to ‘correct’ the
Attenuation artifacts usually result in fixed defects as the
relative position of the soft tissues with respect to the heart remains
constant between rest and stress imaging. However, reversible defects
can result from attenuation if there is a difference in patient
position between the rest and stress studies, as was likely in this
The joint position statement from the American Society of Nuclear
Cardiology and Society of Nuclear Medicine states, “…it is our
recommendation that the adjunctive technique of attenuation correction
has become a method for which the weight of evidence and opinion favor
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Clinical Use. ADAC Laboratories. 1997.
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J. Anthony Parker, MD PhD, Tony_Parker@CareGroup.Harvard.edu