PT  - JOURNAL ARTICLE
AU  - Zheng, Jiabei
AU  - Chun, Se Young
AU  - Fessler, Jeffrey
AU  - Dewaraja, Yuni
TI  - Optimization and application of non-local means (NLM) filtering of SPECT/CT
DP  - 2014 May 01
TA  - Journal of Nuclear Medicine
PG  - 542--542
VI  - 55
IP  - supplement 1
4099  - http://jnm.snmjournals.org/content/55/supplement_1/542.short
4100  - http://jnm.snmjournals.org/content/55/supplement_1/542.full
SO  - J Nucl Med2014 May 01; 55
AB  - 542 Objectives NLM filtering with high-quality side information (CT in our case) provides excellent image denoising. We optimized NLM filtering for SPECT/CT dosimetry applications where accurate quantification of total target activity and 3D activity distribution is of interest. Methods SPECT and CT NLM weight maps were combined by multiplication (NLM-CTM) or by summation (NLM-CTS). With XCAT simulation, we optimized filter parameters for SPECT (σf) and CT (σa) by maximizing an objective function based on recovery coefficients (RC) and normalized root mean squared errors (NRMSE) of spherical lesions. By scaling SPECT range to CT range when forming weight maps, we removed count-rate dependency of the optimal parameters. The optimized filters were applied to OSEM reconstructed I-131 SPECT of both experimental phantoms (with known uniform or nonuniform activity in spheres) and patient studies. For phantom studies, σf was scaled to account for differences in sphere and background CT numbers compared with XCAT. Results of filtered and unfiltered OSEM were compared. Results In XCAT, RCs and NRMSEs calculated for different σa and σf had similar distributions for different lesion sizes and count rates, making it possible to find two broadly applicable filters (optimal NLM-CTM and optimal NLM-CTS). For high- and low-count cases, optimal filters increased RCs by 3.4% to 8.1% and reduced NRMSEs by 20.8% to 29.6%. The dose-rate-volume histograms (DVH) also better matched truth. In the experimental phantom with uniform spheres, RCs increased by -0.7% to 8.9% and NRMSEs decreased by 14.6% to 37.2%. In the phantom with nonuniform spheres, RCs remained unchanged while NRMSEs decreased by -1.5% to 14.1%. In the patient study, changes in image quality and DVHs were observed. Conclusions We proposed two optimized NLM filters for SPECT/CT that were effective for a range of count levels and lesion sizes and practical for clinical application. They improved estimates of both total target activity and 3D activity distribution in simulated and experimental studies. Research Support NIH 2RO1 EB001994