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Impact of target‐to‐background ratio, target size, emission scan duration, and activity on physical figures of merit for a 3D LSO‐based whole body PET/CT scanner
Author(s) -
Brambilla M.,
Matheoud R.,
Secco C.,
Sacchetti G.,
Comi S.,
Rudoni M.,
Carriero A.,
Inglese E.
Publication year - 2007
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2776242
Subject(s) - imaging phantom , scanner , figure of merit , image quality , optics , nuclear medicine , signal to noise ratio (imaging) , physics , medical imaging , materials science , computer science , artificial intelligence , medicine , image (mathematics)
The aim of our work is to describe the way in which physical figures of merit such as contrast‐to‐noise ratio (CNR) behave when varying acquisition parameters such as emission scan duration (ESD) or activity at the start of acquisition ( A acq ) that in clinical practice can be selected by the user, or object properties such as target dimensions or target‐to‐background (T/B) ratio, which depend uniquely on the intrinsic characteristics of the object being imaged. Figures of merit, used to characterize image quality and quantitative accuracy for a 3D‐LSO based PET/CT scanner, were studied as a function of ESD andA acqfor different target sizes and T/B ratios using a multivariate approach in a wide range of conditions approaching the ones that can be encountered in clinical practice. An annular ring of water bags of 3 cm thickness was fitted over an IEC phantom in order to obtain counting rates similar to those found in average patients. The average scatter fraction (SF) of the modified IEC phantom was similar to the mean SF measured on patients with a similar scanner. A supplemental set of micro‐hollow spheres was positioned inside the phantom. The NEMA NU 2‐2001 scatter phantom was positioned at the end of the IEC phantom to approximate the clinical situation of having activity that extends beyond the scanner. The phantoms were filled with a solution of water andF18( 12 kBq ∕ mL ) and the spheres with various T/B ratios of 22.5, 10.3, and 3.6. Sequential imaging was performed to acquire PET images with varying background activity concentrations of about 12, 9, 6.4, 5.3, and 3.1 kBq ∕ mL , positioned on the linear portion of the phantom's NECR curve, well below peak NECR of 61.2 kcps that is reached at 31.8 kBq ∕ mL . The ESD was set to 1, 2, 3, and 4 min ∕ bed . With T/B ratios of 3.6, 10.3, and 22.5, the 13.0, 8.1, and 6.5 mm spheres were detectable for the whole ranges of background activity concentration and ESD, respectively. The ESD resulted as the most significant predictor of CNR variance, followed by T/B ratio and the cross sectional area of the given sphere. Only last comesA acqwith a weight more than halved with respect to ESD. Thus, raising ESD seems to be much more effective than raisingA acqin order to obtain higher CNR, which is the physical figure of merit closely related with target detectability, at least in the simple task of the signal known exactly background known exactly model.