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State of the Art: Iterative CT Reconstruction Techniques See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/280390600 State of the Art: Iterative CT Reconstruction Techniques Article in Radiology · August 2015 Impact Factor: 6.87 · DOI: 10.1148/radiol.2015132766 · Source: PubMed CITATIONS READS 2 52 10 authors, including: Uwe Joseph Schoepf Jonathon Leipsic Medical University of South Carolina Providence Health Care 636 PUBLICATIONS 11,837 CITATIONS 360 PUBLICATIONS 5,432 CITATIONS SEE PROFILE SEE PROFILE Marco Rengo Andrea Laghi Sapienza University of Rome Sapienza University of Rome 122 PUBLICATIONS 462 CITATIONS 450 PUBLICATIONS 6,019 CITATIONS SEE PROFILE SEE PROFILE All in-text references underlined in blue are linked to publications on ResearchGate, Available from: Carlo Nicola De Cecco letting you access and read them immediately. Retrieved on: 31 May 2016 Note: This copy is for your personal non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, contact us at www.rsna.org/rsnarights. REVIEWS AND COMMENTA State of the Art: Iterative CT Reconstruction Techniques1 r Y n STATE OF THE STATE Lucas L. Geyer, MD2 U. Joseph Schoepf, MD Owing to recent advances in computing power, iterative 2 reconstruction (IR) algorithms have become a clinically A Felix G. Meinel, MD RT viable option in computed tomographic (CT) imaging. John W. Nance, Jr, MD3 Substantial evidence is accumulating about the advantages Gorka Bastarrika, MD of IR algorithms over established analytical methods, such Jonathon A. Leipsic, MD as filtered back projection. IR improves image quality Narinder S. Paul, MD through cyclic image processing. Although all available so- Marco Rengo, MD, PhD lutions share the common mechanism of artifact reduc- Andrea Laghi, MD tion and/or potential for radiation dose savings, chiefly Carlo N. De Cecco, MD due to image noise suppression, the magnitude of these effects depends on the specific IR algorithm. In the first section of this contribution, the technical bases of IR are briefly reviewed and the currently available algorithms re- leased by the major CT manufacturers are described. In the second part, the current status of their clinical imple- mentation is surveyed. Regardless of the applied IR algo- rithm, the available evidence attests to the substantial potential of IR algorithms for overcoming traditional limi- tations in CT imaging. © RSNA, 2015 1 From the Department of Radiology and Radiological Science, Medical University of South Carolina, Ashley River Tower, MSC 226, 25 Courtenay Dr, Charleston, SC 29425 (L.L.G., U.J.S., F.G.M., J.W.N., C.N.D.); Department of Radiology, Sunnybrook Health Sciences Centre, Toronto, Ont, Canada (G.B.); Department of Radiology, University of British Columbia, Vancouver, BC, Canada (J.A.L.); Department of Radiology, Toronto General Hospital, University of Toronto, Toronto, Ont, Canada (N.S.P.); and Department of Radiological Sciences, Oncology and Pathology, University of Rome Sapienza–Polo Pontino, Latina, Italy (M.R., A.L., C.N.D.). Received December 17, 2013; revision requested January 15, 2014; final revision received March 18; accepted April 3; final version accepted May 5.Address correspondence to U.J.S. (e-mail: [email protected]). 2 Current address: Institute for Clinical Radiology, Ludwig-Maximilians-University Hospital, Munich, Germany. 3 Current address: The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Hospital, Baltimore, Md. q RSNA, 2015 Radiology: Volume 276: Number 2—August 2015 n radiology.rsna.org 339 STATE OF THE ART: Iterative CT Reconstruction Techniques Geyer et al omputed tomographic (CT) tech- 256- (9), and 320-detector (10) single- general technical evolution providing nology has seen remarkable in- source or dual-source CT systems (11). the required computational power. Fur- Cnovations in the past decade However, the increased number of de- thermore, the increasing number of CT that have substantially improved the tector rows and detector technology examinations worldwide and the asso- diagnostic performance of this modal- are only one domain of CT evolution. ciated radiation dose to the population ity and steadily increased its clinical While advances in CT hardware con- have clearly fostered the rediscovery of indications. Since its first clinical in- tinue to expand the boundaries of phys- IR technology as a promising tool to de- troduction by Sir Godfrey Hounsfield ical limitations, increases in computing crease radiation requirements via noise and James Ambrose in 1972 (1,2), the power have opened additional pathways reduction. evolution of CT technology has mainly for improving the performance of this In this contribution, we review the been driven by advances in hardware. modality via enhanced data process- technical bases of IR and describe the During subsequent decades, important ing methods, such as reconstruction currently available algorithms released milestones have included the introduc- techniques. The most prominent exam- by the major CT manufacturers. Fur- tion of electron-beam CT in the mid- ple of recent years is the renaissance ther, we survey the current status of 1980s (3), spiral (helical) CT imaging of iterative reconstruction (IR) CT al- their clinical implementation. Regard- in 1989 (4), and multi–detector row CT gorithms. IR approaches are not new less of the applied IR algorithm, the in 1998 (5–7). Currently, the major CT and were, in fact, the initially proposed available evidence attests to the sub- manufacturers offer a variety of 64- (8), method for data reconstruction in the stantial potential of IR algorithms for early days of CT technology during the overcoming traditional limitations in Essentials 1970s (2). However, due to its mathe- CT imaging. matically demanding properties and the nn Iterative reconstruction (IR) tech- large amount of data in CT imaging, un- niques allow for substantial radia- til recently IR has not been practical for Technical Background tion dose savings through noise clinical purposes. Instead, this recon- The exact underlying computational al- reduction in CT image processing. struction technique became the default gorithms of the currently available IR nn IR can be used to improve image method for nuclear medicine emission algorithms are mostly considered pro- quality and reduce noise through- tomography imaging modalities with prietary and only partly revealed by out the body, particularly in obese lower spatial and temporal resolution, the manufacturers. However, published patients. such as single photon emission CT and data indicate that these algorithms can nn Besides improvements in general positron emission tomography, because differ substantially with respect to the measures of image quality, an in- of the smaller data volumes and less underlying assumptions of data acqui- creasing number of reports are complex data handling (12). The less sition, data processing, system geome- emerging on enhanced diagnostic perfect, albeit much faster, analytical ap- tries, and noise characteristics. Never- accuracy and artifact suppression proach of filtered back projection (FBP) theless, the following sections attempt with use of IR. has become the standard reconstruction to provide an objective description of nn Special attention should be paid to method for diagnostic CT. the currently available IR techniques. quantitative CT imaging applica- FBP has been established in clinical Pertinent Principles of CT Data tions, as the use of IR may alter routine due to its ability to generate Acquisition standards established on the basis CT studies of adequate image quality of prior analytical image recon- in a robust and fast manner. Despite The fundamental goal of CT data ac- struction methods. its overall acceptable performance, CT quisition and reconstruction is to as- studies that are reconstructed with FBP nn Robust data regarding the impact can be affected by high image noise, and safety of IR in the clinical set- artifacts (eg, streak artifacts), or poor Published online ting are available; thus, routine 10.1148/radiol.2015132766 Content code: low-contrast detectability in specific implementation of IR in CT proto- clinical scenarios. For example, data Radiology 2015; 276:339–357 cols should be strongly considered. acquisition with reduced tube output nn While a multitude of reports high- Abbreviations: or CT imaging of obese patients is of- AIDR = adaptive iterative dose reduction light the promise of IR to enhance ten compromised by high image noise; ASIR = adaptive statistical iterative reconstruction diagnostic performance and high-density structures, such as calci- BMI = body mass index reduce radiation at CT, actual ex- fications or stents, result in blooming CNR = contrast-to-noise ratio amples of adjustment to lower artifacts; metallic implants or bone FBP = filtered back projection radiation dose settings to fully structures might lead to severe streak IR = iterative reconstruction IRIS = iterative reconstruction in image space implement the benefits of IR algo- artifacts. These particular shortcom- SAFIRE = sinogram-affirmed iterative reconstruction rithms in daily clinical practice are ings of FBP likely have driven the re- still limited. naissance of IR algorithms along with Conflicts of interest are listed at the end of this article. 340 radiology.rsna.org n Radiology: Volume 276: Number 2—August 2015 STATE OF THE ART: Iterative CT Reconstruction Techniques Geyer et al sign an attenuation value
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