title: Cold wall effect eliminating method to determine the contrast recovery coefficient for small animal PET scanners using the NEMA NU-4 image quality phantom.
abstract: The contrast recovery coefficients (CRC) were evaluated for five different small animal PET scanners: GE Explore Vista, Genisys4, MiniPET-2, nanoScan PC and Siemens Inveon. The NEMA NU-4 2008 performance test with the suggested image quality phantom (NU4IQ) does not allow the determination of the CRC values for the hot regions in the phantom. This drawback of NU4IQ phantom motivated us to develop a new method for this purpose. The method includes special acquisition and reconstruction protocols using the original phantom, and results in an artificially merged image enabling the evaluation of CRC values. An advantageous feature of this method is that it stops the cold wall effect from distorting the CRC calculation. Our suggested protocol results in a set of CRC values contributing to the characterization of small animal PET scanners. GATE simulations were also performed to validate the new method and verify the evaluated CRC values. We also demonstrated that the numerical values of this parameter depend on the actual object contrast of the hot region(s) and this mainly comes from the spillover effect. This effect was also studied while analysing the background activity level around the hot rods. We revealed that the calculated background mean values depended on the target contrast in a scanner specific manner. Performing the artificially merged imaging procedure and additional simulations using the micro hollow sphere (MHS) phantom geometry, we also proved that the inactive wall around the hot spheres can have a remarkable impact on the calculated CRC. In conclusion, we have shown that the proposed artificial merging procedure and the commonly used NU4IQ phantom prescribed by the NEMA NU-4 can easily deliver reliable CRC data otherwise unavailable for the NU4IQ phantom in the conventional protocol or the MHS phantom.
authors.affiliation: Department of Nuclear Medicine, Medical Center, University of Debrecen, 4032 Debrecen, Nagyerdei krt. 98, Hungary.
authors.forename: Imre
authors.initials: I
authors.lastname: Lajtos
authors.forename: Johannes
authors.initials: J
authors.lastname: Czernin
authors.forename: Magnus
authors.initials: M
authors.lastname: Dahlbom
authors.forename: Freddie
authors.initials: F
authors.lastname: Daver
authors.forename: Miklos
authors.initials: M
authors.lastname: Emri
authors.forename: Salman
authors.initials: S
authors.lastname: Farshchi-Heydari
authors.forename: Attila
authors.initials: A
authors.lastname: Forgacs
authors.forename: Carl K
authors.initials: CK
authors.lastname: Hoh
authors.forename: Istvan
authors.initials: I
authors.lastname: Joszai
authors.forename: Aron K
authors.initials: AK
authors.lastname: Krizsan
authors.forename: Judit
authors.initials: J
authors.lastname: Lantos
authors.forename: Peter
authors.initials: P
authors.lastname: Major
authors.forename: Jozsef
authors.initials: J
authors.lastname: Molnar
authors.forename: Gabor
authors.initials: G
authors.lastname: Opposits
authors.forename: Lajos
authors.initials: L
authors.lastname: Tron
authors.forename: David R
authors.initials: DR
authors.lastname: Vera
authors.forename: Laszlo
authors.initials: L
authors.lastname: Balkay
mesh_terms: D000818:Animals; D016477:Artifacts; D003080:Cold Temperature; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000295:instrumentation*