Dose Reduction in Computed Tomography of the Chest: Image Quality of Iterative Reconstructions at a 50% Radiation Dose Compared to Filtered Back Projection at a 100% Radiation Dose

Abstract

Purpose: The aim of this study was to evaluate the potential of iterative reconstruction (IR) in chest computed tomography (CT) to reduce radiation exposure. The qualitative and quantitative image quality of standard reconstructions with filtered back projection (FBP) and half dose (HD) chest CT data reconstructed with FBP and IR was assessed.

Materials and Methods: 52 consecutive patients underwent contrast-enhanced chest CT on a dual-source CT system at 120 kV and automatic exposure control. The tube current was equally split on both tube detector systems. For the HD datasets, only data from one tube detector system was utilized. Thus, FD and HD data was available for each patient with a single scan. Three datasets were reconstructed from the raw data: standard full dose (FD) images applying FBP which served as a reference, HD images applying FBP and IR. Objective image quality analysis was performed by measuring the image noise in tissue and air. The subjective image quality was evaluated by 2 radiologists according to European guidelines. Additional assessment of artifacts, lesion conspicuity and edge sharpness was performed.

Results: Image noise did not differ significantly between HD-IR and FD-FBP (p = 0.254) but increased substantially in HD-FBP (p < 0.001). No statistically significant differences were found for the reproduction of anatomical and pathological structures between HD-IR and FD-FBP, subsegmental bronchi and bronchioli. The image quality of HD-FBP was rated inferior because of increased noise.

Conclusion: A 50 % dose reduction in contrast-enhanced chest CT is feasible without a loss of diagnostic confidence if IR is used for image data reconstruction. Iterative reconstruction is another powerful tool to reduce radiation exposure and can be combined with other dose-saving techniques.

Key Points:

• Iterative reconstructions allow for image noise and artifact reduction.

• Comparable image data can thus be attained even at 50 % radiation dose.

• Diagnostic confidence remains unaffected.

Citation Format:

• May MS, Eller A, Stahl C et al. Dose Reduction in Computed Tomography of the Chest: Image Quality of Iterative Reconstructions at a 50% Radiation Dose Compared to Filtered Back Projection at a 100% Radiation Dose. Fortschr Röntgenstr 2014; 186: 576 – 584

Zusammenfassung

Ziel: Evaluation der iterativen Rekonstruktionstechnik (IR) zur Dosisreduktion in der Thorax-CT. Vergleich quantitativer und qualitativer Kriterien zur Bildqualität bei um 50 % reduzierter Dosis (HD) mit den mittels gefilterter Rückprojektion (FBP) rekonstruierten Datensätzen bei voller (FD) und HD.

Material und Methode: Bei 52 konsekutiven Patienten wurde der anatomisch modulierte Röhrenstrom bei 120 kV zu gleichen Teilen auf die zwei Röhren-Detektor-Einheiten eines Dual-Source-CT aufgeteilt. Aus jeder Untersuchung wurden je 3 Datensätze rekonstruiert: FD-FBP durch Auswertung der Rohdaten aus beiden, sowie HD-FBP und HD-IR aus Rohdaten eines einzelnen Röhren-Detektor-Systems. Die objektive Bewertung der Bildqualität erfolgte durch Messung des Bildrauschens, die subjektive durch 2 Untersucher analog europäischer Richtlinien. Zusätzlich wurden Bildartefakte sowie die Abgrenzbarkeit und Randschärfe von Läsionen evaluiert.

Ergebnisse: Das Bildrauschen in HD-IR und FD-FBP zeigte keine signifikanten Unterschiede (p = 0,254) und war in HD-FBP deutlich erhöht (p < 0,001). Mit Ausnahme der Subsegmentbronchien und Bronchiolen zeigten FD-FBP und HD-IR sowohl bzgl. der scharfen Darstellung pulmonaler und mediastinaler Strukturen als auch der pathologischen Läsionen keine signifikanten Unterschiede. Die HD-FBP-Bilddaten wurden hingegen überwiegend qualitativ signifikant schlechter bewertet.

Schlussfolgerung: Bei der Kontrastmittel-CT des Thorax kann eine vergleichbare Bildqualität und diagnostische Wertigkeit bei halber Strahlendosis mittels IR dank Rausch- und Artefaktreduktion erreicht werden. Iterative Rekonstruktionen ermöglichen eine deutliche Verringerung der CT-Strahlendosis und können mit anderen Reduktionsalgorithmen kombiniert werden.

Key words

thorax - CT - technical aspects - image manipulation/reconstruction

• References

• 1 Cohnen M, Poll LJ, Puettmann C et al. Effective doses in standard protocols for multi-slice CT scanning. Eur Radiol 2003; 13: 1148-1153
• 2 Brix G, Nagel HD, Stamm G et al. Radiation exposure in multi-slice versus single-slice spiral CT: results of a nationwide survey. Eur Radiol 2003; 13: 1979-1991
• 3 Harrieder A, Geyer LL, Korner M et al. Evaluation der Strahlendosis bei Polytrauma-CT-Untersuchungen eines 64-Zeilen-CT im Vergleich zur 4-Zeilen-CT. Fortschr Röntgenstr 2012; 184: 443-449
• 4 Agency HP, Centre for Radiation CaEH, Division RP. European Commission Radiation Protection N° 154, European Guidance on Estimating Population Doses from Medical X-Ray Procedures, Annex 1 – DD Report 1 Review of recent National Surveys of Population Exposure from Medical X-rays in Europe. Chilton, Didcot, Oxfordshire: 2008. In:
• 5 Widmann G, Fasser M, Schullian P et al. Substantial dose reduction in modern multi-slice spiral computed tomography (MSCT)-guided craniofacial and skull base surgery. Fortschr Röntgenstr 2012; 184: 136-142
• 6 Danova D, Keil B, Kastner B et al. Reduction of uterus dose in clinical thoracic computed tomography. Fortschr Röntgenstr 2010; 182: 1091-1096
• 7 Hidajat N, Schroder RJ, Vogl T et al. Effektivität der Bleiabdeckung zur Dosisreduktion beim Patienten in der Computertomographie. Fortschr Röntgenstr 1996; 165: 462-465
• 8 Wang J, Duan X, Christner JA et al. Bismuth shielding, organ-based tube current modulation, and global reduction of tube current for dose reduction to the eye at head CT. Radiology 2012; 262: 191-198
• 9 Gosch D, Stumpp P, Kahn T et al. Performance of an automatic dose control system for CT: anthropomorphic phantom studies. Fortschr Röntgenstr 2011; 183: 154-162
• 10 Greess H, Wolf H, Baum U et al. Dosisreduktion in der Computertomographie durch anatomieorientierte schwächungsbasierte Röhrenstromregelung: Erste klinische Ergebnisse. Fortschr Röntgenstr 1999; 170: 246-250
• 11 Deak PD, Langner O, Lell M et al. Effects of adaptive section collimation on patient radiation dose in multisection spiral CT. Radiology 2009; 252: 140-147
• 12 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 2011; 84: 335-341
• 13 Pontana F, Pagniez J, Flohr T et al. Chest computed tomography using iterative reconstruction vs filtered back projection (Part 1): Evaluation of image noise reduction in 32 patients. Eur Radiol 2011; 21: 627-635
• 14 Pontana F, Duhamel A, Pagniez J et al. Chest computed tomography using iterative reconstruction vs filtered back projection (Part 2): image quality of low-dose CT examinations in 80 patients. Eur Radiol 2011; 21: 636-643
• 15 Hu XH, Ding XF, Wu RZ et al. Radiation dose of non-enhanced chest CT can be reduced 40% by using iterative reconstruction in image space. Clin Radiol 2011; 66: 1023-1029
• 16 Mueck FG, Michael L, Deak Z et al. Upgrade to lterative Image Reconstruction (lR) in MDCT lmaging: A Clinical Study for Detailed Parameter Optimization Beyond Vendor Recommendations Using the Adaptive Statistical lterative Reconstruction Environment (ASIR) Part2: The Chest. Fortschr Röntgenstr 2013;
• 17 Deak PD, Smal Y, Kalender WA. Multisection CT protocols: sex- and age-specific conversion factors used to determine effective dose from dose-length product. Radiology 2010; 257: 158-166
• 18 Bongartz GGS, Jurik AG, Leonardi M et al. European Guidelines on Quality Criteria for Computed Tomography. Danish Society of Radiology 1998; www.drs.dk/guidelines/ct/quality/
• 19 Julious SA. Sample sizes for clinical trials with normal data. Stat Med 2004; 23: 1921-1986
• 20 Schaich E, Hamerle A. Verteilungsfreie statistische Prüfverfahren. Berlin: Springer; 1984
• 21 Conover WJ. Practical nonparametric statistics. New York: Wiley; 1980
• 22 Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977; 33: 159-174
• 23 Ghetti C, Ortenzia O, Serreli G. CT iterative reconstruction in image space: a phantom study. Physica medica 2012; 28: 161-165
• 24 Morsbach F, Desbiolles L, Plass A et al. Stenosis quantification in coronary CT angiography: impact of an integrated circuit detector with iterative reconstruction. Invest Radiol 2013; 48: 32-40
• 25 Mieville FA, Berteloot L, Grandjean A et al. Model-based iterative reconstruction in pediatric chest CT: assessment of image quality in a prospective study of children with cystic fibrosis. Pediatric radiology 2013; 43: 558-567
• 26 Ebersberger U, Tricarico F, Schoepf UJ et al. CT evaluation of coronary artery stents with iterative image reconstruction: improvements in image quality and potential for radiation dose reduction. Eur Radiol 2013; 23: 125-132
• 27 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
• 28 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
• 29 Mueck FG, Korner M, Scherr MK et al. 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). Fortschr Röntgenstr 2012; 184: 229-238
• 30 Hwang HJ, Seo JB, Lee JS et al. Radiation dose reduction of chest CT with iterative reconstruction in image space – Part I: studies on image quality using dual source CT. Korean J Radiol 2012; 13: 711-719
• 31 Hwang HJ, Seo JB, Lee JS et al. Radiation dose reduction of chest CT with iterative reconstruction in image space – Part II: assessment of radiologists’ preferences using dual source CT. Korean J Radiol 2012; 13: 720-727