Determining the Minimal Required Ultra-Low-Dose CT Dose Level for Reliable Attenuation Correction of 18F-FDG PET/CT: A Phantom Study

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FIGURE 1.
Representative images of PET (attenuation-corrected), CT, and PET/CT for phantom and spheres at various CT settings. CT settings of first and second rows are reference regular adult imaging protocol and pediatric imaging protocols, respectively, at Yale New Haven Hospital. In bottom 3 rows, delineation of spheres was not clear on CT images at lower radiation dose settings.
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FIGURE 2.
Impact on SUV_max from attenuation correction with various CT settings: 120 kVp (A), 100 kVp (B), and 80 kVp (C). Attenuation-corrected SUV_max measures are overall consistent for all spheres with CT settings of 120 kVp and 10–600 mA (A), 100 kVp and 10–600 mA (B), and 80 kVp and 30–160 mA (C). Attenuation-corrected SUV_max measures are slightly decreased (>10%) for some spheres with CT settings of 80 kVp and 10–20 mA (C).
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FIGURE 3.
Impact on SUV_ave from attenuation correction with various CT settings: 120 kVp (A), 100 kVp (B), and 80 kVp (C). Attenuation-corrected SUV_ave measures are overall consistent for all spheres with CT settings of 120 kVp and 10–600 mA (A), 100 kVp and 10–600 mA (B), and 80 kVp and 30–160 mA (C). Attenuation-corrected SUV_ave measures are slightly decreased (>10%) for some spheres with CT settings of 80 kVp and 10–20 mA (C).

TABLE 1

Estimated CT Doses (mGy) and Effective Doses (mSv) from Various Combinations of kVp and mA

kVp	mA	CT dose index volume (mGy)	mSv
120	600	19.61	32.4
120	300	10.18	16.2
120	80	2.63	4.3
120	40	1.32	2.2
120	30	0.99	1.6
120	20	0.66	1.1
120	10	0.33	0.5
100	600	15.25	20.6
100	300	7.68	10.3
100	80	2.06	2.7
100	40	1.03	1.4
100	30	0.77	1.0
100	20	0.55	0.7
100	10	0.26	0.3
80	160	1.73	2.7
80	80	0.87	1.4
80	30	0.43	0.5
80	20	0.22	0.3
80	10	0.11	0.2
80	10*	0.08	0.1

All 120-kVp CT scans use 0.4-s rotation time and pitch of 0.984. All 100- and 80-kVp CT scans use 0.5-s rotation time and pitch of 0.984, except for 0.4-s rotation time and pitch of 1.375, where noted by asterisk.