title: Simultaneous (99m)Tc/(201)Tl dual-isotope SPET with Monte Carlo-based down-scatter correction.
abstract: In simultaneous technetium-99m/thallium-201 dual-isotope (DI) single-photon emission tomography (SPET), down-scatter of (99m)Tc photons contaminates the (201)Tl image, which leads to a decrease in lesion contrast and loss of quantitative accuracy. Correction for down-scatter can be achieved by first reconstructing the (99m)Tc activity distribution. Subsequently, the (99m)Tc down-scatter in the (201)Tl photopeak window is simulated and used for correction during iterative reconstruction of the (201)Tl image. In this work, the down-scatter projections are calculated using a dedicated Monte Carlo simulator which is able to efficiently model the detection of lead X-rays from the collimator. An anthropomorphic torso phantom with a cardiac insert with and without cold lesions was used for evaluation of the proposed method. Excellent agreement in lesion contrast and quantitative accuracy was found between the down-scatter corrected DI-SPET (201)Tl image and the virgin (i.e. separately acquired) (201)Tl image, in particular when the effects of lead X-rays were included. Compensation for the noise added by down-scatter to the (201)Tl image can be achieved by using a 15% lower dose of (99m)Tc, a 15% increase in scan time and a 12% increase in (201)Tl dose. In conclusion, the Monte Carlo-based down-scatter correction recovers lesion contrast and quantitative accuracy in DI-SPET (201)Tl images almost perfectly. In addition, degradations due to the added noise of down-scatter in simultaneous DI-SPET can be prevented by slight adaptations to the data acquisition protocol.
authors.affiliation: Image Sciences Insitute, University Medical Center Utrecht, The Netherlands. hwam.jong@vumc.nl
authors.forename: H W A M
authors.initials: HW
authors.lastname: de Jong
authors.forename: F J
authors.initials: FJ
authors.lastname: Beekman
authors.forename: M A
authors.initials: MA
authors.lastname: Viergever
authors.forename: P P
authors.initials: PP
authors.lastname: van Rijk
mesh_terms: D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D015233:Models, Statistical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011786:Quality Control; D019275:Radiopharmaceuticals; D012542:Scattering, Radiation; D013269:Stochastic Processes; D013667:Technetium; D013793:Thallium; D013909:Thorax / Q000000981:diagnostic imaging; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation / Q000379:methods*
chemical_list: D019275:Radiopharmaceuticals; C027549:thallium chloride; D013667:Technetium; D013793:Thallium