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Extraction and Retention of Technetium-99m-ECD in Human Brain: Dynamic SPECT and Oxygen-15-Water PET Studies

Departments of Nuclear Medicine and Neurology, Faculty of Medicine, Kyoto University, Kyoto
Biomedical Imaging Research Center, Fukui Medical School, Fukui, Japan

Correspondence: For correspondence or reprints contact: Koichi Ishizu, MD, Department of Nuclear Medicine, Faculty of Medicine, Kyoto University, Shogoin, Sakyo-ku, Kyoto 606-01, Japan.

ABSTRACT

The kinetic behavior of ^99mTc-ethyl cysteinate dimer (^99mTc-ECD) in the human brain was investigated in six normal volunteers. Methods: Dynamic SPECT and a three-compartmental model were used to estimate the rate constants of ^99mTc-ECD in normal human brain. Extraction fraction (E), retention fraction (R) and permeability surface area product (PS product) of ^99mTc-ECD were calculated using the rate constants. Regional cerebral blood flow (rCBF) was measured by PET with ¹⁵O-water. Results: The rate constants in the cerebral cortex were estimated as 0.307 ± 0.021 for K1 (influx constant), 0.201 ± 0.047 for k2 (backdiffusion rate constant), 0.547 ± 0.103 for k3 (lipophilic-to-hydrophilic conversion constant) and 0.0028 ± 0.0012 for k5 (rate constant from lipophilic compartment to blood) at rCBF of 0.509 ± 0.055 ml/g/min (mean ± s.d.). The first-pass extraction, retention fraction and PS product were calculated as 0.608 ± 0.069, 0.734 ± 0.047 and 0.477 ± 0.060, respectively. The first- pass extraction of ^99mTc-ECD decreased significantly with increases in rCBF. The retention fraction and PS product of ^99mTc-ECD did not show significant changes within the normal range of rCBF. The net extraction of ^99mTc-ECD calculated from the static SPECT image obtained from 20 to 40 min was 0.358 ± 0.039 in the cortex. Conclusion: Technetium-99m-ECD has a fairly high brain extraction, and its retention fraction and PS product appear to be independent of rCBF in the healthy human brain.

Key Words: technetium-99m-ECD • brain perfusion • SPECT • permeability surface area product

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