Panel Disdussion

3rd International Congress of of Nuclear Medicine & & 15th 15th Iranian Annual Annual Congress of
Congress of Nuclear Medicine
Shahid Beheshti Shahid Beheshti University University of Medical of Medical Sciences Sciences 19-21 19-21 May May 2011
Dual isotope cardiac imaging using Tl-Tc cross-contamination
correction by subtraction method
Mohsen Kohanpour 1 , Hossein Rajabi 2 , Mohsen Beheshti 3 , Faraz
Kalantari 2 , Majid Pouladian 1
1 Islamic Azad University
2 Department of Medical Physics, Tarbiat Modares University
3 Paracelsus Medical University
Introduction: Separate dual isotope, rest 201Tl-stress 99mTc, is a
common protocol for heart imaging. Theoretically, this imaging
protocol can perform simultaneously by defining different energy
windows for each radionuclide. However, a potential limitation of
simultaneous dual isotope SPECT imaging is contribution of scattered
photons from technetium-99m and lead X-rays produced in the
collimator into the thallium-201 energy window, referred to here as
cross-contamination. The aim of this study is introducing a modified
middle energy window method to compensate for this crosscontamination.
Material and Methods: This investigation was performed in clinical
study, that 30 men is gone for cardiac study. In simulation step, the
most suitable functions by their ability to modeling crosscontamination
were determined. To achieve this goal, Root Mean
Square errors between our estimated and real cross-contamination
for each view were used. SPECT images of patients who had
angiographic data were acquired in different energy windows. In each
step of this study, in addition to 201Tl and 99mTc windows centered
at 77 keV and 140 keV respectively; a third window centered at 100
keV is established. at each projection angle, the contaminant image
to be subtracted from the image in the 201Tl window was estimated
as a linear combination of a scatter-window (90-110 keV) image,
convolved by a 2D modified exponential function, and the 99mTc
photopeak image, convolved by a different Gaussian function. All of
these images were compared by determining defect or left ventricle
cavity to myocardium contrast.
Results: Significant improvements in contrasts of simultaneous dual
201Tl images were found in each step . Better results in comparison
with other similar methods also were acquired by our suggested
functions.
Discussion and Conclusion: Our results showed contrast
improvement, however many other parameters should be evaluated
for clinical approaches. Simultaneous dual-isotope201Tl/99mTc
myocardial imaging is seems feasible with 99mTc crosscontamination
correction specific. There are many advantages by
simultaneous dual isotope imaging. It halves imaging time and
doubles patient throughput, improves scheduling flexibility, and
reduces patient waiting time and discomfort. Identical rest/stress
registration of images also makes motion or attenuation correction
easy by physicist and image interpretation by physicians.
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