In vivo gadolinium nanoparticle quantification with SPECT/CT

Abstract

Background Gadolinium nanoparticles (Gd-NP) combined with radiotherapy are investigated for radiation dose enhancement in radiotherapy treatment. Indeed, NPs concentrated in a tumor could enhance its radiosensitization. The noninvasive quantification of the NP concentration is a crucial task for radiotherapy treatment planning and post-treatment monitoring as it will determine the absorbed dose. In this work, we evaluate the achievable accuracy of in vivo SPECT-based Gd-NP organ concentration on rats. Methods Gd-NPs were labeled with 111 In radionuclide. SPECT images have been acquired on phantom and rats, with various Gd-NP injections. Images have been calibrated and corrected for attenuation, scatter, and partial volume effect. Image-based estimations were compared to both inductively coupled plasma mass spectrometer (ICP-MS) for Gd concentration and ex vivo organ activity measured by gamma counter. Results The accuracy for the Gd mass measurements in organ was within 10% for activity above 2 MBq or concentrations above ∼ 3–4 MBq/mL. The Gd mass calculation is based on In-Gd coefficient which defines the Gd detection limit. It was found to be in a range from 2 mg/MBq to 2 µg/MBq depending on the proportions of initial injection preparations. Measurement was also impaired by free Gd and 111 In formed during metabolic processes. Conclusions Even if SPECT image quantification remains challenging mostly due to partial volume effect, this study shows that it has potential for the Gd mass measurements in organ. The main limitation of the method is its indirectness, and a special care should be taken if the organ of interest could be influenced by different clearance rate of free Gd and 111 In formed by metabolic processes. We also discuss the practical aspects, potential, and limitations of Gd-NP in vivo image quantification with a SPECT.

Consolidation of Gold and Gadolinium Nanoparticles: An Extra Step towards Improving Cancer Imaging and Therapy

“…This selection relies on the fact that GdNPs present R1 relaxation rates higher than commercial contrast agents while, simultaneously, the R2/R1 ratio is close to 1. Therefore, they offer high image quality and vast soft tissue contrast [60,61]. It is worth mentioning that, with the insufficient longitudinal relaxivity (R1) which often describes commercial contrast agents, in MRI imaging it is often required during clinical praxis to inject higher contrast agent doses to achieve adequate contrast enhancement [62].…”

“…Furthermore, the brightness and signal intensity of MR imaging increased as Gd concentrations increased [67]. Almost all studies have shown that Gd ions are toxic [57,60,61], so perhaps a conjugation of Au and Gd could reduce Gd ion leakage and improve system blood compatibility, resulting in extended circulation cycles and active targeting with minimal adverse effects. It is important to mention that all Gd-Cas can be administered intravenously.…”

Metal Nanozymes: New Horizons in Cellular Homeostasis Regulation

“…Due to the possibility to functionalize NPs with targeting molecules, it is possible to increase the drug concentration at desired sites of action and reduce systemic levels of the drug in healthy tissues. In addition, functionalizing of fluorescent or radioactive NPs with targeting molecules allows the imaging of lesions using PET (Positron emission tomography) [199], SPECT (Single-photon emission computed tomography) [200], MRI [199,201], and spectroscopic [202] methods.…”