RSNA 2012 

Abstract Archives of the RSNA, 2012


LL-PHS-WE8C

Assessment of Image Quality vs Dose Using an Iterative Reconstruction Algorithm in Multislice CT

Scientific Informal (Poster) Presentations

Presented on November 28, 2012
Presented as part of LL-PHS-WEPM: Physics Afternoon CME Posters

Participants

Lucia Pinali, Presenter: Nothing to Disclose
Fabio Menini, Abstract Co-Author: Nothing to Disclose
Massimiliano Motton MD, Abstract Co-Author: Nothing to Disclose
Gabriele Meliadò, Abstract Co-Author: Nothing to Disclose
Carlo Cavedon DPhil, Abstract Co-Author: Nothing to Disclose
Stefania Montemezzi MD, Abstract Co-Author: Nothing to Disclose

PURPOSE

To assess image quality and patient dose obtained in multi slice CT studies by means of a standard Filtered Backprojection algorithm (FBP) versus a new type of iterative algorithm called iDose4

METHOD AND MATERIALS

Various scans on a Catphan600 phantom (The Phantom Laboratory) were performed with a Brilliance iCT-256 scanner (Philips Healthcare) varying reconstruction algorithm (FBP and iDose4 with six different levels), kernel (B-D-YB), and dose. Image quality has been compared through the following figures of merit: signal-to-noise ratio (SNR) for low-contrast resolution and MTF-50 for high-contrast resolution. Images were analysed with IQworks. Dose was varied through the mAs/slice mean value set to scan the phantom. The fixed scan parameters used for all the studies were: HV=120kVp, FOV=250mm, pitch=0.993, slice thickness=2.5mm, rotation time=0.75s, matrix size=512x512. 188 patients were scanned according to an iDose4 level 3 protocol (30% dose reduction). Five radiologists performed image quality analysis with a 5 point grading scale (1 worst; 5 excellent)

RESULTS

With kernel B and 78mAs/slice the following SNR values have been measured: FBP 1.48, iDose4 (levels 1 to 6) 1.62, 1.70, 1.82, 1.98, 2.28, 2.54; for MTF-50 results were: FBP 3.5 lp/cm, iDose4 (levels 1 to 6) 3.4 to 3.5 lp/cm . With FBP (kernel B) and mAs/slice ranging from 78 to 156 results for SNR were: 1.48-2.12 (R2=0.998), and for MTF-50: 3.4-3.7 lp/cm. Equivalent values of SNR (1.81) and MTF-50 (3.5 lp/cm) were obtained with iDose4 level 3-kernel B-78mAs/slice and with FBP-kernel B-117mAs/slice. MTF-50 as a function of the kernel varied from 3.5lp/cm (B) to 6.2lp/cm (YB), almost independently from dose and reconstruction algorithm. Quality image was 5 level in 66,5% of 188 patient examinations and not inferior to 3 level

CONCLUSION

Phantom assessments showed that the use of the iDose4 algorithm compared to FBP allows SNR to increase up to 70% at equal patient dose and permits to reach a 33% patient dose reduction at equal values of SNR and MTF-50, SNR being the limiting factor.

CLINICAL RELEVANCE/APPLICATION

30% dose reduction not compromise image quality. Higher dose reductions seem to be achievable, possibly up to 70%, if high-contrast resolution is the most critical factor (e.g. vascular studies)

Cite This Abstract

Pinali, L, Menini, F, Motton, M, Meliadò, G, Cavedon, C, Montemezzi, S, Assessment of Image Quality vs Dose Using an Iterative Reconstruction Algorithm in Multislice CT.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12043915.html