title: Multi-isotope SPECT imaging of the225Ac decay chain: feasibility studies.
abstract: Effective use of the [Formula: see text] decay chain in targeted internal radioimmunotherapy requires the retention of both [Formula: see text] and progeny isotopes at the target site. Imaging-based pharmacokinetic tests of these pharmaceuticals must therefore separately yet simultaneously image multiple isotopes that may not be colocalized despite being part of the same decay chain. This work presents feasibility studies demonstrating the ability of a microSPECT/CT scanner equipped with a high energy collimator to simultaneously image two components of the [Formula: see text] decay chain: [Formula: see text] (218 keV) and [Formula: see text] (440 keV). Image quality phantoms were used to assess the performance of two collimators for simultaneous [Formula: see text] and [Formula: see text] imaging in terms of contrast and noise. A hotrod resolution phantom containing clusters of thin rods with diameters ranging between 0.85 and 1.70 mm was used to assess resolution. To demonstrate ability to simultaneously image dynamic [Formula: see text] and [Formula: see text] activity distributions, a phantom containing a [Formula: see text] generator from [Formula: see text] was imaged. These tests were performed with two collimators, a high-energy ultra-high resolution (HEUHR) collimator and an ultra-high sensitivity (UHS) collimator. Values consistent with activity concentrations determined independently via gamma spectroscopy were observed in high activity regions of the images. In hotrod phantom images, the HEUHR collimator resolved all rods for both [Formula: see text] and [Formula: see text] images. With the UHS collimator, no rods were resolvable in [Formula: see text] images and only rods  ⩾1.3 mm were resolved in [Formula: see text] images. After eluting the [Formula: see text] generator, images accurately visualized the reestablishment of transient equilibrium of the [Formula: see text] decay chain. The feasibility of evaluating the pharmacokinetics of the [Formula: see text] decay chain in vivo has been demonstrated. This presented method requires the use of a high-performance high-energy collimator.
authors.affiliation: Life Sciences Division, TRIUMF, 4004 Wesbrook Mall, Vancouver BC, V6T 2A3, Canada. Department of Physics and Astronomy, University of British Columbia (UBC), 6224 Agronomy Road, Vancouver BC, V6T 1Z1, Canada.
authors.forename: A K H
authors.initials: AKH
authors.lastname: Robertson
authors.forename: C F
authors.initials: CF
authors.lastname: Ramogida
authors.forename: C
authors.initials: C
authors.lastname: Rodríguez-Rodríguez
authors.forename: Stephan
authors.initials: S
authors.lastname: Blinder
authors.forename: Peter
authors.initials: P
authors.lastname: Kunz
authors.forename: Vesna
authors.initials: V
authors.lastname: Sossi
authors.forename: Paul
authors.initials: P
authors.lastname: Schaffer
mesh_terms: D000186:Actinium / Q000378:metabolism*; D005240:Feasibility Studies; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D019047:Phantoms, Imaging; D011877:Radionuclide Imaging / Q000379:methods*; D019275:Radiopharmaceuticals / Q000378:metabolism*; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
chemical_list: D019275:Radiopharmaceuticals; D000186:Actinium