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A practical way to improve contrast‐to‐noise ratio and quantitation for statistical‐based iterative reconstruction in whole‐body PET imaging
Author(s) -
Fin Loïc,
Bailly Pascal,
Daouk Joël,
Meyer MarcEtienne
Publication year - 2009
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 - 10.1118/1.3152116
Subject(s) - imaging phantom , iterative reconstruction , signal to noise ratio (imaging) , noise (video) , image resolution , contrast to noise ratio , gaussian , smoothing , computer science , statistical noise , contrast (vision) , image quality , algorithm , mathematics , artificial intelligence , computer vision , physics , optics , image (mathematics) , statistics , quantum mechanics
In whole‐body positron emission tomography (PET) imaging, the detection of small uptake foci (i.e., around two or three times the tomograph's spatial resolution) is a critical issue. Indeed, spatial resolution is altered by postreconstruction smoothing operations used to reduce the noise introduced by (among other things) an inaccurate system matrix. The authors previously proposed a device‐dedicated projector, easily applicable on a clinical gantry, based on point‐source measurements, which introduces less noise than a geometrical model. In the present study, they took advantage of the lower noise levels by reducing the postfilter and then quantified the approach's impact on image quality. This study was performed on an IEC Body Phantom Set™ filled with F18 (sphere‐to‐background activity ratio: 4:1). The same 3 min acquisition was reconstructed with either (i) a clinical system based on a geometrical tomographic operator (OSEM̱CL) or (ii) an OSEM algorithm using the suggested system matrix (OSEM̱DR). In order to compare the resulting images, they set the 3D Gaussian postfilter (3DGPF) for OSEM̱DR so as to obtain similar background signal‐to‐noise ratio (SNR) to that of OSEM̱CL with a Gaussian postfilter full width at half maximum of 5 mm (as recommended for whole‐body imaging on a Biograph™6). They then assessed the contrast‐to‐noise ratio (CNR) and quantitation [contrast recovery (CR)] for the phantom's four smallest spheres (with internal diameters of 10, 13, 17, and 22 mm ). Evaluation of 3DGPFs ranging from 2.2 to 2.6 mm showed that a value of 2.4 mm in OSEM̱DR gave the closest background SNR to that of OSEM̱CL with a 3DGPF of 5 mm . For all studied targets, the CNR was higher with OSEM̱DR than with OSEM̱CL. For the 10 and 13 mm spheres, OSEM̱DR increased the size of the CNR peaks by 37% and 20%, relative to OSEM̱CL. The OSEM̱DR technique yielded higher CR values than OSEM̱CL did. For the 10, 13, 17, and 22 mm spheres, the CR values at eight iterations were 0.5, 0.6, 1.1, and 1.0 for OSEM̱DR and 0.3, 0.4, 0.9, and 0.8 for OSEM̱CL. They evaluated a practical method for determining a device‐dedicated system matrix based on point‐source acquisitions. This tomographic operator is more realistic than geometrical system matrix and introduces less noise into PET images during statistical reconstruction; it thus reduces the extent of postfiltering operations required. Thus, spatial resolution is better maintained with OSEM̱DR than with clinical reconstruction. They showed that this method improves the contrast‐to‐noise ratio and quantification of uptake foci (especially those that are at the system's limit of detection) and, in a clinical context, could allow better detection and earlier diagnosis.