Polyp detection with MDCT: a phantom-based evaluation of the impact of dose and spatial resolution.
OBJECTIVE
The objective of our study was to evaluate the impact of dose and spatial resolution on the detection of colonic polyps using a 4-MDCT scanner.


METHODS
Twenty-four latex phantoms that simulate the large bowel and contain artificial polyps of different sizes and shapes were constructed. The polyps were divided into three size groups (diameter, 0-2, 2-5, and 5-10 mm) and were classified into four shape groups: pedunculated; broad-based; ulcerated or depressed; and sessile or flat. The colon phantoms were submerged in a water tank and scanned on a 4-MDCT scanner using 12 protocols with various settings of slice thickness, pitch, and tube current. The images were independently evaluated by three radiologists using axial 2D multiplanar reconstruction images and a 3D surface-rendering technique (fly-through).


RESULTS
At a constant dose (i.e., dose-length product [DLP]), the polyp detection rate increased with increasing axial spatial resolution. For the standard protocol (2.50-mm slice thickness, 1.5 pitch), the detection rate for all polyp sizes decreased from approximately 70% at 100 mA to 55% at 40 mA. Between a 60- and 100-mA tube current, the detection rate for the largest polyps (> 5 mm) was almost constant, close to 90%.


CONCLUSIONS
The detection of polyps in the large bowel using a standard protocol can be improved without dose penalty by increasing the axial spatial resolution of the image acquisition and adjusting the tube current setting. If the analysis can be restricted to polyps larger than 5 mm, the dose can be substantially reduced without compromising the detection rate.
Ozgün
Abdülvahit
A
Department of Medical Physics, S-171 76 Karolinska University Hospital, Stockholm, Sweden. vahit123@hotmail.com
Rollvén
Erik
E
Blomqvist
Lennart
L
Bremmer
Staffan
S
Odh
Richard
R
Fransson
Annette
A
D003111:Colonic Polyps / Q000000981:diagnostic imaging*; D023881:Colonography, Computed Tomographic; D006801:Humans; D007091:Image Processing, Computer-Assisted; D019047:Phantoms, Imaging; D011829:Radiation Dosage