Abstract
Objective: Although Iodine-125 (125I) has been widely used for in vitro studies because of its relatively long half-life (60.1 days), 125I imaging is limited because of its low energy (27 - 35 keV), even in an animal-dedicated system. In this study, imaging characteristics of 125I were assessed using a small animal-dedicated imaging system and clinical scanner. Methods: Using the Siemens Inveon and Siemens Symbia TruePoint systems, imaging characteristics such as resolution, sensitivity, and image quality were compared. Mouse high resolution (MHR-0.5), mouse general purpose (MGP-1.0), and mouse high sensitivity (MHS-2.0) collimators were used for the Inveon scanner, and low energy high-resolution (LEHR) and low energy all-purpose (LEAP) collimators were used for the Symbia TruePoint. For animal imaging, 16.8 MBq of 125I was administered to BALB/c mice intravenously, and the planar image and single-photon emission computed tomography (SPECT) were obtained using both scanners. Results: The resolution of 125I for the Inveon scanner was 3.98 mm full width at half maximum (FWHM) at a 30-mm distance with the MHR-0.5 collimator, and the value of Symbia scanner was 8.72 mm FWHM at a 30-mm distance with the LEHR collimator. The sensitivity of 125I for the Inveon scanner was 21.87 cps/MBq, and the value for the clinical scanner was 30.55 cps/MBq. The planar images of mice were successfully obtained at the level of evaluating specific binding in both scanners. Conclusion: 125I small animal imaging can be achieved with a clinical scanner. This result may enhance the utilization of 125I small animal imaging using a clinical scanner.
Highlights
Iodine-125 (125I) has been widely used for in vitro research because of its relatively long half-life (60.1 days)
We investigated the feasibility for 125I imaging using a clinical scanner without a pinhole collimator and compared its performance characteristics to a small animal scanner
The resolution of the clinical scanner compared to the small animal scanner presented as a function of the source-to-collimator distance with each collimator. (a) Idoine-125 (125I) point source and (b) Technetium-99m (99mTc) point source
Summary
Iodine-125 (125I) has been widely used for in vitro research because of its relatively long half-life (60.1 days). In vivo 125I imaging methods were developed, and both in vivo and in vitro experiments were performed using the same 125I-labeled tracers [3]-[7]. In vivo imaging in animals using 125I is limited because of its low energy (27 - 35 keV) compared to Technetium-99m (99mTc) or Iodine-123 (123I) [8]. Small animal imaging using a clinical scanner with a pinhole collimator and 99mTc or 123I has been reported [6] [9]-[12]. A small animal-dedicated scanner provides high resolution (submillimeter range), the clinical scanner is ready to use in clinics. Another advantage of the clinical scanner is the large field of view
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