Noise-reducing algorithms do not necessarily provide superior dose optimisation for hepatic lesion detection with multidetector CT

• Published in: British journal of radiology Vol. 86; no. 1023; p. 20120500
• Main Authors: Dobeli, K L, Lewis, S J, Meikle, S R, Thiele, D L, Brennan, P C
• Format: Journal Article
• Language: English
• Published: England The British Institute of Radiology 01-03-2013
• Subjects: Algorithms; Humans; Liver Diseases - diagnostic imaging; Multidetector Computed Tomography - methods; Multidetector Computed Tomography - standards; Phantoms, Imaging; Radiation Dosage
• ISSN: 0007-1285; 1748-880X
• DOI: 10.1259/bjr.20120500

To compare the dose-optimisation potential of a smoothing filtered backprojection (FBP) and a hybrid FBP/iterative algorithm to that of a standard FBP algorithm at three slice thicknesses for hepatic lesion detection with multidetector CT.
A liver phantom containing a 9.5-mm opacity with a density of 10 HU below background was scanned at 125, 100, 75, 50 and 25 mAs. Data were reconstructed with standard FBP (B), smoothing FBP (A) and hybrid FBP/iterative (iDose(4)) algorithms at 5-, 3- and 1-mm collimation. 10 observers marked opacities using a four-point confidence scale. Jackknife alternative free-response receiver operating characteristic figure of merit (FOM), sensitivity and noise were calculated.
Compared with the 125-mAs/5-mm setting for each algorithm, significant reductions in FOM (p<0.05) and sensitivity (p<0.05) were found for all three algorithms for all exposures at 1-mm thickness and for all slice thicknesses at 25 mAs, with the exception of the 25-mAs/5-mm setting for the B algorithm. Sensitivity was also significantly reduced for all exposures at 3-mm thickness for the A algorithm (p<0.05). Noise for the A and iDose(4) algorithms was approximately 13% and 21% lower, respectively, than for the B algorithm.
Superior performance for hepatic lesion detection was not shown with either a smoothing FBP algorithm or a hybrid FBP/iterative algorithm compared with a standard FBP technique, even though noise reduction with thinner slices was demonstrated with the alternative approaches.
Reductions in image noise with non-standard CT algorithms do not necessarily translate to an improvement in low-contrast object detection.