title: Counting Rate Characteristics and Image Distortion in Preclinical PET Imaging During Radiopharmaceutical Therapy.
abstract: PET may provide important information on the response during radiopharmaceutical therapy (RPT). Emission of radiation from the RPT radionuclide may disturb coincidence detection and impair image resolution. In this study, we tested the feasibility of performing intratherapeutic PET on 3 preclinical PET systems.
  
  
  METHODS
  Using22Na point sources and phantoms filled with18F, as well as a phantom filled with either99mTc or177Lu, we evaluated the coincidence counting rate and spatial resolution when both a PET and a therapeutic radionuclide were in the PET system. Because99mTc has a suitable half-life and is easy obtainable, we used it as a substitute for a generic therapeutic radionuclide.
  
  
  RESULTS
  High activities of99mTc deteriorated the coincidence counting rate from the18F-filled phantom and the22Na point source on all 3 systems. The counting rate could be corrected to a high degree on one of the systems by its dead-time correction. Spatial resolution was degraded at high99mTc activities for all systems. On one of the systems,177Lu increased the coincidence counting rate and slightly affected the spatial resolution. The results for high177Lu activities were similar to those for99mTc.
  
  
  CONCLUSIONS
  Intratherapeutic imaging might be a feasible method of studying the response to RPT. However, some sensitive preclinical PET systems, unable to handle high counting rates, will have count losses and may also introduce image artifacts.
authors.affiliation: Division of Oncology and Pathology, Department of Clinical Sciences-Lund, Lund University, Lund, Sweden emma.mellhammar@med.lu.se.
authors.forename: Emma
authors.initials: E
authors.lastname: Mellhammar
authors.affiliation: Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, UCLA, Los Angeles, California.
authors.forename: Magnus
authors.initials: M
authors.lastname: Dahlbom
authors.affiliation: Department of Physics, LTH, Lund, Sweden; and.
authors.forename: Johan
authors.initials: J
authors.lastname: Axelsson
authors.affiliation: Division of Oncology and Pathology, Department of Clinical Sciences-Lund, Lund University, Lund, Sweden.|Division of Oncology and Pathology, Department of Clinical Sciences-Lund, Lund University, Lund, Sweden.
authors.forename: Sven-Erik
authors.initials: SE
authors.lastname: Strand
mesh_terms: D016477:Artifacts; D005240:Feasibility Studies; D006207:Half-Life; D007091:Image Processing, Computer-Assisted; D036103:Nanotechnology; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals / Q000378:metabolism / Q000627:therapeutic use*
chemical_list: D019275:Radiopharmaceuticals
keywords: PET; dead time; image distortion; pile up; radionuclide therapy