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Optimal collimator choice for sequential iodine-123 and technetium-99m imaging
F D Geeter1, P R Franken, M Defrise
1Department of Nuclear Medicine, University Hospital, Free University of Brussels (VUB), Brussels, Belgium.
European Journal of Nuclear Medicine
|July 1, 1996
Summary
Dual-isotope imaging with technetium-99m and iodine-123 requires accurate activity ratios. The medium-energy collimator better preserves these ratios for iodine-123 compared to the low-energy high-resolution collimator, improving accuracy in sequential studies.
Area of Science:
- Nuclear Medicine
- Medical Imaging Physics
Background:
- Dual-isotope imaging using technetium-99m (99mTc) and iodine-123 (123I) is valuable for imaging organs like the brain and myocardium.
- Accurate comparison of images from different isotopes requires preservation of activity ratios by the imaging system.
Purpose of the Study:
- To investigate the impact of collimator response on activity ratio preservation in dual-isotope SPECT imaging.
- To compare the performance of low-energy high-resolution (LEHR) and medium-energy (ME) collimators for 99mTc and 123I imaging.
Main Methods:
- Utilized a Rollo phantom filled with 99mTc or 123I.
- Performed imaging on a Siemens Orbiter 3700 camera with LEHR and ME collimators.
- Measured count densities in regions of interest (ROIs) and assessed accuracy using mean square error (MSE) against known activity ratios.
Main Results:
- For 99mTc, both LEHR and ME collimators showed good approximation of activity ratios (MSE < 0.020).
- For 123I, the LEHR collimator resulted in significant overestimation of activity ratios (MSE=0.235), while the ME collimator performed well (MSE=0.013).
- ME collimator offers higher contrast accuracy for sequential 99mTc/123I studies, despite lower spatial resolution.
Conclusions:
- The medium-energy collimator is preferred for sequential 99mTc/123I studies due to superior contrast accuracy and activity ratio preservation for 123I.
- While spatial resolution is reduced with the ME collimator, it remains consistent between the two isotopes, facilitating accurate dual-isotope imaging.