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Absolute Quantification in Dopaminergic Neurotransmission SPECT Using a Monte Carlo–Based Scatter Correction and Fully 3-Dimensional Reconstruction

¹ Unitat de Biofísica i Bioenginyeria, Departament Ciències Fisiològiques I, Facultat de Medicina, Universitat de Barcelona, Barcelona, Spain
² Secció d’Enginyeria Nuclear, Departament Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Barcelona, Spain
³ Institut de Tècniques Energètiques, Universitat Politècnica de Catalunya, Barcelona, Spain
⁴ Servei de Medicina Nuclear, Hospital Clínic i Provincial de Barcelona, Barcelona, Spain
⁵ Institut d’Investigacions Biomèdiques August Pi i Sunyer, Barcelona, Spain

Dopamine transporter (DAT) ligands have been developed for in vivo imaging of the dopaminergic system in SPECT. Although the visual analysis of SPECT images is, in general, suitable for clinical assessment, the accurate quantification of the striatal uptake might increase the sensitivity of the technique and help in the early diagnosis, follow-up, and eventual treatment response of Parkinson’s disease (PD). This work is focused on assessment of the quantification of specific uptake of ^99mTc-DAT ligands when compensation for all degrading phenomena is performed. Methods: The SimSET Monte Carlo (MC) code was used to generate a set of SPECT projections of a numeric striatal phantom with different specific uptake ratios (SURs). An absolute quantification method (AQM), which performs a MC-based scatter compensation and a fully 3-dimensional (3D) reconstruction, was implemented. The scatter estimate was included in the reconstruction algorithm. Results: The use of attenuation, point-spread-function (PSF), and scatter corrections resulted in an improvement in the value of the SUR of 37% on average with respect to the reconstruction without corrections. The magnitude of each improvement corresponded to 7% for the attenuation correction, 12% for the PSF correction using a 2-dimensional reconstruction algorithm and a further 11% for the PSF correction using a 3D reconstruction algorithm, and 7% for the scatter correction. Conclusion: Our findings indicate that the PSF correction plays a major role in the quantification of striatal uptake in comparison with the attenuation correction and the scatter correction. The implemented method also provides an absolute quantification procedure based on MC methods that do not depend on empiric approximations. The relative quantification results using the proposed AQM accounted for 96%–97% of the nominal SUR, whereas the limit achieved using only primary photons attained 98%–99%. The volumetric activity values obtained using the AQM converged toward the nominal values.

Key Words: scatter correction • fully 3D reconstruction • dopamine transporter • Monte Carlo methods

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