Original article Respective roles of scatter, attenuation, depth-dependent collimator response and finite spatial resolution in cardiac single-photon emission tomography quantitation: a Monte Carlo study Georges N. El Fakhri 1 , Irène Buvat 1 , Mélanie Pélégrini 1 , Habib Benali 1 , Pedro Almeida 2 , Bernard Bendriem 2 , Andrew Todd-Pokropek 1 , Robert Di Paola 1 1 U494 INSERM, CHU Pitié-Salpêtrière, 91 Boulevard de l’Hôpital, F-75634 Paris cedex 13, France 2 SHFJ, Groupe instrumentation PET/SPET, 4 Place du Général Leclerc, F-91401 Orsay cedex, France &misc:Received 12 November 1998 and in revised form 21 January 1999 &p.1:Abstract. The purpose of this study was to investigate the relative influence of scatter, attenuation, depth-de- pendent collimator response and finite spatial resolution upon the image characteristics in cardiac single-photon emission tomography (SPET). An acquisition of an an- thropomorphic cardiac phantom was performed together with corresponding SPET Monte Carlo simulations. The cardiac phantom and the Monte Carlo simulations were designed so that the effect of scatter, attenuation, depth- dependent collimator response and finite spatial resolu- tion could be studied individually and in combination. The impact of each physical effect and of combinations of effects was studied in terms of absolute and relative quantitative accuracy, spatial resolution and signal-to- noise ratio (SNR) in the resulting images. No corrections for these effects were assessed. Results obtained from Monte Carlo simulations and real acquisitions were in excellent agreement. Attenuation introduced about 90% activity underestimation in a 10-mm-thick left ventricle wall while finite spatial resolution alone introduced about 30% activity underestimation. Scatter had a negli- gible impact on quantitative accuracy in the recontructed slices when attenuation was present. Neither bull’s eye map homogeneity nor contrast between a hot and a cold region were affected by depth-dependent collimator re- sponse or finite spatial resolution. Bull’s eye map homo- geneity was severely affected by attenuation but not by scatter. Attenuation and scatter reduced contrast by about 20% each. Both attenuation and scatter increased the full-width at half-maximum (FWHM) characterizing the spatial resolution of the imaging system by ≈1 mm each but the main effect responsible for the observed 11- mm FWHM spatial resolution was the depth-dependent collimator response. SNR was reduced by a factor of ≈2.5 because of attenuation, while scattered counts in- creased SNR by ≈10%. In conclusion, the quantification of the relative influence of the different physical effects showed that attenuation is definitely the major phenome- non affecting cardiac SPET imaging accuracy, but that finite spatial resolution, scatter and depth-dependent col- limator response also contribute significantly to the er- rors in absolute and relative quantitation and to the poor spatial resolution. &kwd:Key words: Quantitation – Cardiac single-photon emis- sion tomography – Monte Carlo simulation Eur J Nucl Med (1999) 26:437–446 Introduction The accuracy of quantitation in single-photon emission tomography (SPET) is affected by many effects among which attenuation, scatter, depth-dependent collimator response and finite spatial resolution (FSR) play a major role. Studying the impact of each of these effects on the image characteristics (e.g. image resolution, relative and absolute quantitation, and signal-to-noise ratio) is neces- sary to determine what improvement could be expected if we were to perform an ideal correction for a given ef- fect. However, these phenomena are not independent and each one should be considered only as a component re- sponsible for part of the SPET system inaccuracies. Therefore, it is not sufficient to determine how each phe- nomenon taken independently affects the images. The impact of each phenomenon should also be character- ized when it is combined with other phenomena affect- ing the imaging process, to determine the respective role of each phenomenon and the improvements that could be expected when correcting for some effects but ignor- ing the others. Although many studies have been devoted to the in- vestigation of the qualitative and quantitative conse- European Journal of Nuclear Medicine Vol. 26, No. 5, May 1999 – © Springer-Verlag 1999 Correspondence to: I. Buvat&/fn-block: