Simultaneous acquisition of 99mTc- and 123I-labeled radiotracers using a preclinical SPECT scanner with CZT detectors
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Simultaneous acquisition of 99mTc and 123I was evaluated using a preclinical SPECT scanner with cadmium zinc telluride (CZT)-based detectors.
10-ml cylindrical syringes contained about 37 MBq 99mTc-tetrofosmin (99mTc-TF) or 37 MBq 123I-15-(p-iodophenyl)-3R,S-methyl pentadecanoic acid (123I-BMIPP) were used to assess the relationship between these SPECT radioactive counts and radioactivity. Two 10-ml syringes contained 100 or 300 MBq 99mTc-TF and 100 MBq 123I-BMIPP to assess the influence of 99mTc upscatter and 123I downscatter, respectively. A rat-sized cylindrical phantom also contained both 100 or 300 MBq 99mTc-TF and 100 MBq 123I-BMIPP. The two 10-ml syringes and phantom were scanned using a pinhole collimator for rats. Myocardial infarction model rats were examined using 300 MBq 99mTc-TF and 100 MBq 123I-BMIPP. Two 1-ml syringes contained 105 MBq 99mTc-labeled hexamethylpropyleneamine oxime (99mTc-HMPAO) and 35 MBq 123I-labeled N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl) nortropane (123I-FP-CIT). The two 1-ml syringes were scanned using a pinhole collimator for mice. Normal mice were examined using 105 MBq 99mTc-HMPAO and 35 MBq 123I-FP-CIT.
The relationship between SPECT radioactive counts and radioactivity was excellent. Downscatter contamination of 123I-BMIPP exhibited fewer radioactive counts for 300 MBq 99mTc-TF without scatter correction (SC) in 125–150 keV. There was no upscatter contamination of 99mTc-TF in 150–175 keV. In the rat-sized phantom, the radioactive count ratio decreased to 4.0 % for 300 MBq 99mTc-TF without SC in 125–150 keV. In the rats, myocardial images and radioactive counts of 99mTc-TF with the dual tracer were identical to those of the 99mTc-TF single injection. Downscatter contamination of 123I-FP-CIT was 4.2 % without SC in 125–150 keV. In the first injection of 99mTc-HMPAO and second injection of 123I-FP-CIT, brain images and radioactive counts of 99mTc-HMPAO with the dual tracer in normal mice also were the similar to those of the 99mTc-HMPAO single injection. In the first injection of 123I-FP-CIT and second injection of 99mTc-HMPAO, the brain images and radioactive counts with the dual tracer were not much different from those of the 123I-FP-CIT single injection.
Dual-tracer imaging of 99mTc- and 123I-labeled radiotracers is feasible in a preclinical SPECT scanner with CZT detector. When higher radioactivity of 99mTc-labeled radiotracers relative to 123I-labeled radiotracers is applied, correction methods are not necessarily required for the quantification of 99mTc- and 123I-labeled radiotracers when using a preclinical SPECT scanner with CZT detector.
KeywordsDual tracer 99mTc 123I Small animal SPECT scanner Cadmium zinc telluride
The author would like to thank Akiko Hayashi and Ryoko Komatsu, Takafumi Tsujiuchi, Masatoshi Sakashita and members of the medical staff at the Ishikawa prefectural government and Kanazawa University.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Sources of funding
This study was partly funded by Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (24601008, 24659558, 25293260 and 15K09949), the Society of Nuclear Medicine Technology, Japanese Society of Radiological Technology and Ishikawa Prefecture Commission Research.
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