PT  - JOURNAL ARTICLE
AU  - Katie Hulme
AU  - S. Cheenu Kappdath
TI  - Propagation of dose- and radial-dependent CT noise into reconstructed SPECT images
DP  - 2009 May 01
TA  - Journal of Nuclear Medicine
PG  - 405--405
VI  - 50
IP  - supplement 2
4099  - http://jnm.snmjournals.org/content/50/supplement_2/405.short
4100  - http://jnm.snmjournals.org/content/50/supplement_2/405.full
SO  - J Nucl Med2009 May 01; 50
AB  - 405 Objectives To investigate the propagation of dose- and radial-dependent noise in CT images used for attenuation correction (AC) into reconstructed SPECT images. Methods SPECT/CT scans of a cylindrical (R=11 cm) 99mTc-water phantom were acquired with 4.8 mm/pixel, 128x128 matrix, 128 views/360 and 500 kCt/view. CT scans were acquired for several different tube currents and potentials (mAs: 12,25,50,200; kVp: 80,110,130) and reconstructed using an AC filter (ACf) and a body filter (Bf) to yield 24 CT datasets. SPECT data was reconstructed iteratively (3D-OSEM) using each CT dataset for CT-based AC. Image noise was estimated on a pixel-by-pixel basis by calculating the pixel variance across 25 reconstructed slices for both CT and SPECT datasets as a function of mAs and radial distance. Results CT image noise exhibited a power-law dependence on mAs (-0.46 to -0.62). The two filters together with 4 mAs values yielded CT images with non-overlapping noise levels: 1-6 HU with ACf and 12-57 HU with Bf at isocenter for 80kVp. AC with all 24 CT datasets resulted in SPECT images with no significant change in signal (<1%) or noise levels (<0.1%). CT noise was found to decrease linearly with distance from isocenter. The largest radial dependence was observed for Bf at 12 mAs and 80 kVp where noise decreased by 2 from center to edge (57 to 28 HU). However, the corresponding SPECT image exhibited no significant (p>0.5) noise dependence with radial position. Conclusions AC using noisy CT datasets with radial noise dependence resulted in negligible changes in SPECT noise for the CT noise levels investigated. The dose (CTDIvol) of the AC CT scan could be decreased to 1.3 mGy (5% of reference dose for abdominal CT) while introducing <0.1% additional noise into the reconstructed SPECT images.