Upgrade to Iterative Image Reconstruction (IR) in Abdominal MDCT Imaging: A Clinical Study for Detailed Parameter Optimization Beyond Vendor Recommendations Using the Adaptive Statistical Iterative Reconstruction Environment (ASIR)

Abstract

Purpose: To compare the image quality of dose-reduced 64-row abdominal CT reconstructed at different levels of adaptive statistical iterative reconstruction (ASIR) to full-dose baseline examinations reconstructed with filtered back-projection (FBP) in a clinical setting and upgrade situation.

Materials and Methods: Abdominal baseline examinations (noise index NI = 29; LightSpeed VCT XT, GE) were intra-individually compared to follow-up studies on a CT with an ASIR option (NI = 43; Discovery HD750, GE), n = 42. Standard-kernel images were calculated with ASIR blendings of 0 – 100 % in slice and volume mode, respectively. Three experienced radiologists compared the image quality of these 567 sets to their corresponding full-dose baseline examination (– 2: diagnostically inferior, – 1: inferior, 0: equal, + 1: superior, + 2: diagnostically superior). Furthermore, a phantom was scanned. Statistical analysis used the Wilcoxon – the Mann-Whitney U-test and the intra-class correlation (ICC).

Results: The mean CTDIvol decreased from 19.7 ± 5.5 to 12.2 ± 4.7 mGy (p < 0.001). The ICC was 0.861. The total image quality of the dose-reduced ASIR studies was comparable to the baseline at ASIR 50 % in slice (p = 0.18) and ASIR 50 – 100 % in volume mode (p > 0.10). Volume mode performed 73 % slower than slice mode (p < 0.01).

Conclusion: After the system upgrade, the vendor recommendation of ASIR 50 % in slice mode allowed for a dose reduction of 38 % in abdominal CT with comparable image quality and time expenditure. However, there is still further dose reduction potential for more complex reconstruction settings.

Zusammenfassung

Ziel: Zielsetzung dieser klinischen Studie war im Rahmen eines System-Upgrades ein Vergleich der Bildqualität dosisreduzierter abdomineller 64-Zeilen-CTs, die mit unterschiedlichem Einfluss von adaptiver statistischer iterativer Rekonstruktion (ASIR) rekonstruiert wurden, mit Voll-Dosis-Voruntersuchungen, welche mittels gefilterter Rückprojektion (FBP) rekonstruiert wurden.

Material und Methoden: Abdominelle Baseline-Untersuchungen (Rauschindex NI = 29; LightSpeed VCT XT, GE) wurden intraindividuell mit Follow-up-Untersuchungen eines CT mit ASIR-Option verglichen (NI = 43; Discovery HD750, GE), n = 42. Im Standard-Kernel wurden Bilder mit 0 – 100 % ASIR-Einfluss sowohl im Slice- als auch im Volumen-Modus berechnet. Drei erfahrene Radiologen verglichen die Bildqualität dieser 567 Serien mit der jeweiligen Voll-Dosis-Baseline (– 2: diagnostisch schlechter, – 1: schlechter, 0: gleich, + 1: besser, + 2: diagnostisch besser). Zudem wurde ein Phantom gescannt. Zur statistischen Analyse wurden der Wilcoxon-, der Mann-Whitney-U-Test verwendet und die Intra-Class-Correlation (ICC) errechnet.

Ergebnisse: Der mittlere CTDIvol verringerte sich von 19,7 ± 5,5 auf 12,2 ± 4,7 mGy (p < 0,001). ICC war 0,861. Die mittlere Bildqualität der etwa um 40 % dosis-reduzierten ASIR Studien war für ASIR 50 % im Slice- (p = 0,18) und für ASIR 50 – 100 % im Volumen-Modus mit der Baseline vergleichbar (jeweils p > 0,10). Der Volumen-Modus war hierbei 73 % langsamer als der Slice-Modus (p < 0,01).

Schlussfolgerung: Nach dem Upgrade wurde mit der Herstellerempfehlung von ASIR 50 % im Slice-Modus eine Dosiseinsparung von 38 % bei gleichbleibender Bildqualität und konstantem Zeitaufwand erreicht. Darüber hinaus besteht für komplexere Bildrekonstruktionssettings ein weiteres Potenzial zur Dosiseinsparung.

Key words

abdomen - iterative reconstruction - dose reduction - ASIR - computed tomography

• References

• 1 Brenner DJ, Hall EJ. Computed tomography-an increasing source of radiation exposure. N Engl J Med 2007; 357: 2277-2284
• 2 Mettler Jr FA, Thomadsen BR, Bhargavan M et al. Medical radiation exposure in the U. S. in 2006: preliminary results. Health Phys 2008; 95: 502-507
• 3 Galanski M, Nagel HD, Stamm G. CT-Expositionspraxis in der Bundesrepublik Deutschland. Fortschr Röntgenstr 2001; 173: R1-R66
• 4 Hall EJ, Brenner DJ. Cancer risks from diagnostic radiology. Br J Radiol 2008; 81: 362-378
• 5 Kalra MK, Maher MM, Toth TL et al. Strategies for CT radiation dose optimization. Radiology 2004; 230: 619-628
• 6 Brenner DJ, Elliston CD. Estimated radiation risks potentially associated with full-body CT screening. Radiology 2004; 232: 735-738
• 7 Greess H, Wolf H, Suess C et al. Dosisautomatik bei der Mehrzeilenspiral-CT: Phantommessungen und klinische Ergebnisse. Fortschr Röntgenstr 2004; 176: 862-869
• 8 McCollough CH, Bruesewitz MR, Kofler Jr JM. CT dose reduction and dose management tools: overview of available options. Radiographics 2006; 26: 503-512
• 9 Kropil P, Lanzman RS, Walther C et al. Dosisreduktion und Bildqualitat in der MDCT des Oberbauchs: Potenzial eines adaptiven Nachverarbeitungsfilters. Fortschr Röntgenstr 2010; 182: 248-253
• 10 Fleischmann D, Boas FE. Computed tomography-old ideas and new technology. Eur Radiol 2011; 21: 510-517
• 11 Flicek KT, Hara AK, Silva AC et al. Reducing the radiation dose for CT colonography using adaptive statistical iterative reconstruction: A pilot study. Am J Roentgenol 2010; 195: 126-131
• 12 Hara AK, Paden RG, Silva AC et al. Iterative reconstruction technique for reducing body radiation dose at CT: feasibility study. Am J Roentgenol 2009; 193: 764-771
• 13 Martinsen AC, Saether HK, Hol PK et al. Iterative reconstruction reduces abdominal CT dose. Eur J Radiol 2011; DOI: 10.1016/j.ejrad.2011.04.021
• 14 Prakash P, Kalra MK, Kambadakone AK et al. Reducing abdominal CT radiation dose with adaptive statistical iterative reconstruction technique. Invest Radiol 2010; 45: 202-210
• 15 Prakash P, Kalra MK, Digumarthy SR et al. Radiation dose reduction with chest computed tomography using adaptive statistical iterative reconstruction technique: initial experience. J Comput Assist Tomogr 2010; 34: 40-45
• 16 Leipsic J, Nguyen G, Brown J et al. A prospective evaluation of dose reduction and image quality in chest CT using adaptive statistical iterative reconstruction. Am J Roentgenol 2010; 195: 1095-1099
• 17 Heilbron BG, Leipsic J. Submillisievert coronary computed tomography angiography using adaptive statistical iterative reconstruction – a new reality. Can J Cardiol 2010; 26: 35-36
• 18 Kanal KM, Stewart BK, Kolokythas O et al. Impact of operator-selected image noise index and reconstruction slice thickness on patient radiation dose in 64-MDCT. Am J Roentgenol 2007; 189: 219-225
• 19 Samei E, Badano A, Chakraborty D et al. Assessment of display performance for medical imaging systems: executive summary of AAPM TG18 report. Med Phys 2005; 32: 1205-1225
• 20 EUR 16262. Quality criteria for computed tomography. . Available at: http://www.drs.dk/guidelines/ct/quality/download/eur16262.w51 Accessed March 25 ee.
• 21 May MS, Wust W, Brand M et al. Dose reduction in abdominal computed tomography: intraindividual comparison of image quality of full-dose standard and half-dose iterative reconstructions with dual-source computed tomography. Invest Radiol 2011; 46: 465-470
• 22 Zarb F, Rainford L, McEntee MF. AP diameter shows the strongest correlation with CTDI and DLP in abdominal and chest CT. Radiat Prot Dosimetry 2010; 140: 266-273
• 23 Prakash P, Kalra MK, Ackman JB et al. Diffuse lung disease: CT of the chest with adaptive statistical iterative reconstruction technique. Radiology 2010; 256: 261-269
• 24 Deak Z, Deak P, Wirth S et al. Comparing the effect of two different CT detectors of different generations on image noise (IN): a phantom study. Abstract accepted for RSNA congress 2011.
• 25 Cornfeld D, Israel G, Detroy E et al. Impact of Adaptive Statistical Iterative Reconstruction (ASIR) on radiation dose and image quality in aortic dissection studies: a qualitative and quantitative analysis. Am J Roentgenol 2011; 196: W336-W340
• 26 Singh S, Kalra MK, Hsieh J et al. Abdominal CT: comparison of adaptive statistical iterative and filtered back projection reconstruction techniques. Radiology 2010; 257: 373-383
• 27 Honda O, Yanagawa M, Inoue A et al. Image quality of multiplanar reconstruction of pulmonary ct scans using adaptive statistical iterative reconstruction. Br J Radiol 2010; DOI: 57998586 [pii] 10.1259/bjr/57998586
• 28 Sagara Y, Hara AK, Pavlicek W et al. Abdominal CT: comparison of low-dose CT with adaptive statistical iterative reconstruction and routine-dose CT with filtered back projection in 53 patients. Am J Roentgenol 2010; 195 (03) 713-719