title: Ultra-high-sensitivity submillimeter mouse SPECT.
abstract: SPECT with submegabecquerel amounts of tracer or subsecond time resolution would enable a wide range of new imaging protocols such as screening tracers with initially low yield or labeling efficiency, imaging low receptor densities, or even performing SPECT outside regular radiation laboratories. To this end we developed dedicated ultra-high-sensitivity pinhole SPECT.
  
  
  METHODS
  A cylindric collimator with 54 focused 2.0-mm-diameter conical pinholes was manufactured and mounted in a stationary small-animal SPECT system. The system matrix for image reconstruction was calculated via a hybrid method based on both (99m)Tc point source measurements and ray-tracing analytic modeling. SPECT images were reconstructed using pixel-based ordered-subsets expectation maximization. Performance was evaluated with phantoms and low-dose bone, dynamic kidney, and cardiac mouse scans.
  
  
  RESULTS
  The peak sensitivity reached 1.3% (13,080 cps/MBq). The reconstructed spatial resolution (rod visibility in a micro-Jaszczak phantom) was 0.85 mm. Even with only a quarter megabecquerel of activity, 30-min bone SPECT scans provided surprisingly high levels of detail. Dynamic dual-isotope kidney and (99m)Tc-sestamibi cardiac scans were acquired with a time-frame resolution down to 1 s.
  
  
  CONCLUSIONS
  The high sensitivity achieved increases the range of mouse SPECT applications by enabling in vivo imaging with less than a megabecquerel of tracer activity or down to 1-s frame dynamics.
authors: Section of Radiation, Detection, and Medical Imaging, Delft University of Technology, Delft, The Netherlands MILabs B.V., Utrecht, The Netherlands; and Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, Utrecht, The Netherlands o.ivashchenko-1@tudelft.nl.
authors: Oleksandra
authors: O
authors: Ivashchenko
authors: Section of Radiation, Detection, and Medical Imaging, Delft University of Technology, Delft, The Netherlands MILabs B.V., Utrecht, The Netherlands; and Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, Utrecht, The Netherlands.
authors: Frans
authors: F
authors: van der Have
authors: Section of Radiation, Detection, and Medical Imaging, Delft University of Technology, Delft, The Netherlands.
authors: Marlies C
authors: MC
authors: Goorden
authors: Section of Radiation, Detection, and Medical Imaging, Delft University of Technology, Delft, The Netherlands MILabs B.V., Utrecht, The Netherlands; and Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, Utrecht, The Netherlands.
authors: Ruud M
authors: RM
authors: Ramakers
authors: Section of Radiation, Detection, and Medical Imaging, Delft University of Technology, Delft, The Netherlands MILabs B.V., Utrecht, The Netherlands; and Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, Utrecht, The Netherlands.
authors: Freek J
authors: FJ
authors: Beekman
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000000981:diagnostic imaging; D002138:Calibration; D004867:Equipment Design; D006321:Heart / Q000000981:diagnostic imaging; D007091:Image Processing, Computer-Assisted; D007668:Kidney / Q000000981:diagnostic imaging; D051379:Mice; D008810:Mice, Inbred C57BL; D019047:Phantoms, Imaging; D019275:Radiopharmaceuticals; D012680:Sensitivity and Specificity; D013667:Technetium / Q000737:chemistry; D017256:Technetium Tc 99m Sestamibi; D013997:Time Factors; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D019275:Radiopharmaceuticals; D013667:Technetium; D017256:Technetium Tc 99m Sestamibi
keywords: SPECT; dynamic imaging; low-dose; molecular imaging; pinhole