Effects of spatial resolution and tube current on computer-aided detection of polyps on CT colonographic images: phantom study.
OBJECTIVE
To prospectively evaluate the effects of z-axis spatial resolution and tube current on the sensitivity of a commercially available computed tomographic (CT) colonography computer-aided diagnosis (CAD) system for polyp detection by using pig colon phantoms.


METHODS
Ninety-six polyps were created and analyzed in 14 pig colon phantoms. CT colonography was performed by using a 16-detector CT scanner at 0.75-mm collimation; 10, 50, 100, and 160 mAs; and a pitch of 1.5. At each milliampere-second setting, the CT images were reconstructed with a section thickness (ST) of 1.5 mm and a reconstruction increment (RI) of 1.3 mm. To evaluate the effect of z-axis spatial resolution, CT images were also reconstructed at 100 mAs with various SI and RI combinations (respectively: 1.0 and 0.7 mm, 3.0 and 2.0 mm, 3.0 and 3.0 mm, 5.0 and 5.0 mm). The phantom data were then analyzed by using a CAD program. CAD performance with different CT parameters was calculated and compared in terms of per-polyp sensitivity and number of false-positive (FP) findings per data set.


RESULTS
At a constant tube current of 100 mAs, the polyp detection rate was significantly higher in data sets obtained with SI and RI combinations of 1.0 and 0.7 mm, respectively (81% [78/96]), and 1.5 and 1.3 mm, respectively (75% [72/96]), than in those obtained with the three thicker ST-RI settings (27% [26/96] to 64% [61/96]) (P < .01). A similar trend was observed, regardless of polyp size or morphology. However, the number of FP findings at the 1.0 mm and 0.7 mm setting (8.9 per phantom) was also significantly greater than that at the thicker ST-RI settings (4.0-6.1 per phantom) (P < .05). At a constant z-axis spatial resolution (1.5-mm ST, 1.3-mm RI), CAD polyp detection rate and number of FP findings per phantom remained nearly constant-close to 78% (75/96) and 6.1, respectively-at various tube current settings.


CONCLUSIONS
CAD performance in polyp detection at CT colonography is highly dependent on z-axis spatial resolution. However, tube current is not an influencing factor in CAD performance at a given z-axis spatial resolution.


BACKGROUND
http://radiology.rsnajnls.org/cgi/content/full/2482071025/DC1.
Kim
Se Hyung
SH
Department of Radiology, Institute of Radiation Medicine, Seoul National University College of Medicine, Chongno-gu, Seoul, Korea.
Lee
Jeong Min
JM
Shin
Cheong-Il
CI
Kim
Hyo Chul
HC
Lee
Joon-Goo
JG
Kim
Jong Hyo
JH
Choi
Jin Young
JY
Eun
Hyo Won
HW
Han
Joon Koo
JK
Lee
Jae Young
JY
Choi
Byung Ihn
BI
D000465:Algorithms; D000818:Animals; D003111:Colonic Polyps / Q000000981:diagnostic imaging*; D023881:Colonography, Computed Tomographic; D005189:False Positive Reactions; D019047:Phantoms, Imaging; D011446:Prospective Studies; D011857:Radiographic Image Interpretation, Computer-Assisted; D012680:Sensitivity and Specificity; D013552:Swine