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LETTERS TO THE EDITOR

(eg, N-acetylcysteine regimens, sodium bicarbonate) (2,3). More surprisingly, there are no data from controlled studies to suggest that intravenous fluid therapy reduces the risk of emergent dialysis or mortality among cases of suspected contrast material–mediated AKI (4–6). Even in the critical care setting, studies of intravenous fluid therapies among patients with contrast material–independent causes of AKI have shown conflicting results, with some data suggesting that intravenous fluid use actually has a negative effect on mortality rates (7). These equivocal results might be interpreted as evidence that the prevention of serum creatinine–defined CIN by using intravenous fluid therapies is nothing more than a predictable physiologic response to increased intravascular volume, as there is little evidence to suggest these therapies prevent renal injury, dialysis, or death. Disclosures of Conflicts of Interest: disclosed no relevant relationships. disclosed no relevant relationships. disclosed no relevant relationships. disclosed no relevant relationships. disclosed no relevant relationships. disclosed no relevant relationships. disclosed no relevant relationships.

R.J.M. J.S.M. R.E.C. R.P.H. R.W.K. D.F.K. E.E.W.

References 1. McDonald RJ, McDonald JS, Carter RE, et al. Intravenous contrast material exposure is not an independent risk factor for dialysis or mortality. Radiology 2014;273(3):714–725. 2. Pannu N, Manns B, Lee H, Tonelli M. Systematic review of the impact of N-acetylcysteine on contrast nephropathy. Kidney Int 2004;65(4):1366–1374. 3. Weisbord SD, Palevsky PM. Strategies for the prevention of contrast-induced acute kidney injury. Curr Opin Nephrol Hypertens 2010;19(6):539–549. 4. Zoungas S, Ninomiya T, Huxley R, et al. Systematic review: sodium bicarbonate treatment regimens for the prevention of contrast-induced nephropathy. Ann Intern Med 2009;151(9):631–638. 5. Hsu TF, Huang MK, Yu SH, Yen DH, Kao WF, Chen YC, Huang MS. N-acetylcysteine for the prevention of contrast-induced nephropathy in the emergency department. Intern Med 2012;51(19):2709–2714.

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6. Schiffl H. Sodium bicarbonate infusion for prevention of acute kidney injury: no evidence for superior benefit, but risk for harm? Int Urol Nephrol 2015;47(2):321–326. 7. Zarychanski R, Abou-Setta AM, Turgeon AF, et al. Association of hydroxyethyl starch administration with mortality and acute kidney injury in critically ill patients requiring volume resuscitation: a systematic review and meta-analysis. JAMA 2013;309(7):678–688.

Review Articles From Matthew McInnes, MD, FRCPC Department of Radiology, University of Ottawa Faculty of Medicine, Ottawa Hospital Research Institute, 1053 Carling Ave, Room c159, Ottawa, ON, Canada K1Y 4E9 e-mail: [email protected] Editor: In the January 2015 issue of Radiology, Dr Barral and colleagues (1) present an excellent review of diffusionweighted magnetic resonance (MR) imaging of the pancreas. This work is categorized as a review article and is not presented as original research, like a systematic review and metaanalysis would be (2–4). The manner in which the authors have presented their data offers an opportunity to consider the optimal methods for performing reviews. In this review, the authors evaluate data from multiple studies. Data are presented in a table format, including number of studies, number of patients, and mean apparent diffusion coefficient (ADC) (eg, table 3 presents mean ADCs for pancreatitis from up to seven studies). This raises concerns about whether appropriate techniques for systematic review and meta-analysis have been applied. Because there is no Materials and Methods section, the reader is left guessing at how the authors arrived at their conclusions (a thorough description of the search strategy is noted in the appendix). This approach is problematic for several reasons. First, the basic characteristics of the included studies are not pro-

vided; this limits the ability of readers to assess whether the characteristics of the included studies allow generalizability of the conclusions to their patients. Second, the authors have not assessed for risk of bias in the included studies; readers are left guessing regarding important study design elements that might impact the interpretation of results, such as whether an appropriate reference standard was used. Finally, the method used for pooling data from multiple studies is not described. The authors seem to have performed a metaanalysis without specifying whether established methods for pooling of data across studies were used. This approach is problematic because simple averaging of data across multiple studies will not appropriately account for differences in sample size and variability and will not provide an estimate of the heterogeneity between studies (5). Overall, “traditional” review articles are an important part of our literature; however, if an article aims to present summary estimates of results across studies, a formal systematic review and meta-analysis may be a more appropriate format for the reasons described above. Disclosures of Conflicts of Interest: disclosed no relevant relationships.

References 1. Barral M, Taouli B, Guiu B, et al. Diffusionweighted MR imaging of the pancreas: current status and recommendations. Radiology 2015;274(1):45–63. 2. Lee YJ, Lee JM, Lee JS, et al. Hepatocellular carcinoma: diagnostic performance of multidetector CT and MR imaging: a systematic review and meta-analysis. Radiology 2015: 275(1):97–109. 3. Spick C, Baltzer PA. Diagnostic utility of second-look US for breast lesions identified at MR imaging: systematic review and metaanalysis. Radiology 2014;273(2):401–409. 4. Wu MZ, McInnes MD, Macdonald DB, Kielar AZ, Duigenan S. CT in adults: systematic review and meta-analysis of interpretation discrepancy rates. Radiology 2014;270(3):717– 735. 5. Higgins JPT, Green S, Cochrane Collaboration. Cochrane handbook for systematic re-

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views of interventions. Chichester, England; Hoboken, NJ: Wiley-Blackwell, 2008.

Response From Philippe Soyer, MD, PhD,*† Bachir Taouli, MD,‡ Boris Guiu, MD, PhD,§ Doh-Mu Koh, MD, MRCP, FRCR,# Alain Luciani, MD, PhD,|| Riccardo Manfredi, MD,** Valérie Vilgrain, MD,††† Christine Hoeffel, MD, PhD,‡‡ Masayuki Kanematsu, MD, PhD,§§ and Eric Vicaut, MD, PhD## Department of Body and Interventional Imaging, Hôpital Lariboisière, AP-HP, 2 rue Ambroise Paré, 75475 Paris Cedex 10, France* e-mail: [email protected] Université Paris-Diderot, Paris, France† Department of Radiology, Body MR imaging and Translational and Molecular Imaging Institute, Mount Sinai Medical Center, New York, NY‡ Department of Medical Imaging, Hopital Universitaire Saint-Éloi, Montpellier, France§ Department of Radiology, Royal Marsden Hospital, Royal Marsden NHS Foundation Trust, Sutton, England# Department of Radiology, Hôpital Henri-Mondor, AP-HP, Créteil, France|| Department of Radiology, University of Verona, Verona, Italy** Department of Radiology, Hôpital Beaujon, AP-HP, Clichy, France†† Department of Radiology, Hôpital Robert Debré, Reims, France‡‡ Department of Radiology, Gifu University Hospital, Gifu, Japan§§ Department of Clinical Research, Hôpital Lariboisière, AP-HP, Paris, France## Dr McInnes raises several concerns regarding meta-analyses. Meta-analysis must follow strict criteria. Included studies must have acceptable reference standards, sources of bias must be strictly assessed, and statis-

tical analysis must include data pooling, heterogeneity testing, and metaregression (1–3). However, these concerns do not directly apply to our article, which was a review article and correctly identified and further appropriately categorized by the editor (4). Our article was a review article aimed to provide a current overview of the use, potential advantages and limitations of diffusionweighted MR imaging in the field of pancreatic diseases in light of recent improvements of this promising technique (5–7). In addition, our article was constructed to provide future recommendations for well-designed studies using the experience and personal insight of the authors who have substantially contributed to the current knowledge in this area. We assume that our search strategy as described in the appendix was misleading. We apologize for the misunderstanding. However, please note that this search was described in detail to convince the readers that we actually did a comprehensive search. In this regard, many otherwise excellent review articles published in reputable journals do not explain how the literature analysis was made so that it is difficult for the reader to know if a comprehensive and exhaustive analysis was actually made. This is why we adopted this presumably “virtuous” approach for our review article. Dr McInnes has raised other concerns regarding our methodology. Most meta-analyses in the field of imaging have assessed the sensitivity of imaging techniques (1–3). We did not pool results of several studies regarding the sensitivity or diagnostic capabilities of diffusion-weighted MR imaging. In our review, we have just provided mean values of the ADC for a variety of pancreatic conditions along with ranges of ADCs reported in different studies. Neither standard deviation values nor 95% confidence intervals were given. ADCs are commonly used for pancreatic lesion characterization (5,7); we assumed that this information given

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in our article could be helpful to the readers. Disclosures of Conflicts of Interest: P.S. Activities related to the present article: disclosed no relevant relationships. Activities not related to the present article: received personal fees from the Guerbet Group and Ipsen. Other relationships: disclosed no relevant relationships. B.T. Activities related to the present article: disclosed no relevant relationships. Activities not related to the present article: received a grant from Bayer and General Electric; is on the advisory board at Siemens. Other relationships: disclosed no relevant relationships. B.G. disclosed no relevant relationships. D.M.K. Activities related to the present article: disclosed no relevant relationships. Activities not related to the present article: received a grant from NIHR Biomedical Research Centre, Royal Marsden Hospital. Other relationships: disclosed no relevant relationships. A.L. disclosed no relevant relationships. R.M. disclosed no relevant relationships. V.V. disclosed no relevant relationships. C.H. disclosed no relevant relationships. M.K. disclosed no relevant relationships. E.V. disclosed no relevant relationships.

References 1. Soyer P, Aout M, Hoeffel C, Vicaut E, Placé V, Boudiaf M. Helical CT-enteroclysis in the detection of small-bowel tumours: a metaanalysis. Eur Radiol 2013;23(2):388–399. 2. Lin P, Chen M, Liu B, Wang S, Li X. Diagnostic performance of shear wave elastography in the identification of malignant thyroid nodules: a meta-analysis. Eur Radiol 2014;24(11): 2729–2738. 3. Spick C, Baltzer PA. Diagnostic utility of second-look US for breast lesions identified at MR imaging: systematic review and metaanalysis. Radiology 2014;273(2):401–409. 4. Barral M, Taouli B, Guiu B, et al. Diffusionweighted MR imaging of the pancreas: current status and recommendations. Radiology 2015;274(1):45–63. 5. Barral M, Sebbag-Sfez D, Hoeffel C, et al. Characterization of focal pancreatic lesions using normalized apparent diffusion coefficient at 1.5-Tesla: preliminary experience. Diagn Interv Imaging 2013;94(6):619-627. 6. Barral M, Soyer P, Ben Hassen W, et al. Diffusion-weighted MR imaging of the normal pancreas: reproducibility and variations of apparent diffusion coefficient measurement at 1.5- and 3.0-Tesla. Diagn Interv Imaging 2013;94(4):418–427. 7. Soyer P, Kanematsu M, Taouli B, et al. ADC normalization: a promising research track for diffusion-weighted MR imaging of the

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abdomen. Diagn Interv Imaging 2013;94(6): 571–573.

Iodinated Contrast Media: A Semantic Somersault From Ulf Nyman, MD, PhD,* Peter Aspelin, MD, PhD,† and Torsten Almén, MD, PhD* Department of Translational Medicine, Division of Medical Radiology, Skåne University Hospital, SE-205 02 Malmö, Sweden* e-mail: [email protected] Division of Medical Imaging and Technology, Department of Clinical Science, Intervention and Technology (CLINTEC), Karolinska Institute and University Hospital, Stockholm, Sweden† Editor: Having been involved with contrast media research (1) and having followed the scientific literature with regard to contrast media since the 1960s–1970s, we have observed that intravascular contrast media based on iodine are nowadays almost invariably designated as iodinated contrast media in the scientific literature (2,3). As an example, when you start to fill in “iodinated” in the search field on the PubMed home page you will get a number of choices for “iodinated contrast.” If you put “iodine” in the search field, you get only one choice: “iodine contrast.” The simple question then arises: How is it possible to iodinate a contrast medium that is already saturated with iodine? In the context of contrast media, for example, those used with intravenous urography, computed tomography, and catheter-based angiography and interventions, the term contrast medium itself implies that it is based on iodine. Thus, the term iodinated contrast medium is tautological. It is the benzene molecule (C6H6) that is iodinated by substitution of three iodine atoms for three hydrogen atoms, which results in an iodine or iodinebased contrast medium including re934

placement of the remaining three hydrogen atoms with side chains containing, for example, hydroxyl groups (OH) to allow for high hydrophilicity of nonionic contrast media. Contrast media based on gadolinium for magnetic resonance imaging are almost always correctly denoted as gadolinium contrast media. Is it just because the term gadolinated is difficult to articulate? Who has heard of bariuminated contrast media? So why overelaborate with the word iodinated for contrast media? So far there exists no iodinated contrast media, and the correct term should simply be iodine contrast media. We would appreciate if scientific journals would set a standard for a correct language in this respect. Disclosures of Conflicts of Interest: U.N. Activities related to the present article: disclosed no relevant relationships. Activities not related to the present article: receives speakers fees from GE Healthcare; is paid to be on the advisory board at GE Healthcare. Other relationships: disclosed no relevant relationships. P.A. Activities related to the present article: disclosed no relevant relationships. Activities not related to the present article: is a paid consultant for GE Healthcare. Other relationships: disclosed no relevant relationships. T.A. disclosed no relevant relationships.

material. I suspect this reflects the fact that the benzene molecule has been “iodinated.” Moreover, it is shorter, easier to read, and universally understood by our readers than is other suggested terminology. We do not have strict style guidelines for the description and would certainly allow the use of the terms iodine-based or iodine-containing contrast material. Similarly, the preferred terminology for the gadolinium agents is gadolinium-based contrast agents, often abbreviated as GBCAs, or gadolinium chelates. The copy editors inform me that we would accept the term gadolinated if used by an author, although we have not encountered such usage. We would not accept the term gadolinium contrast medium as it might imply the use of elemental gadolinium, which of course is toxic. A review of the literature on the terminology used shows wide variability, and our current style approach to this allows for a good deal of flexibility, which is probably a realistic approach in view of the range of common usage patterns.

Errata

References 1. Almen T. Contrast agent design: some as pects on the synthesis of water soluble contrast agents of low osmolality. J Theor Biol 1969;24(2):216–226. 2. Barrett BJ, Carlisle EJ. Metaanalysis of the relative nephrotoxicity of high- and low-osmolality iodinated contrast media. Radiology 1993;188(1):171–178. 3. McDonald RJ, McDonald JS, Carter RE, et al. Intravenous contrast material exposure is not an independent risk factor for dialysis or mortality. Radiology 2014;273(3):714–725.

Originally published in: Radiology 2009;252(2):577–586 DOI: 10.1148/radiol.2522081956 Tracheomalacia in Adults with Cystic Fibrosis: Determination of Prevalence and Severity with Dynamic Cine CT Shaunagh McDermott, Sinead C. Barry, Eoin E. Judge, Susan Collins, Pim A. de Jong, Harm A. W. M. Tiddens, Edward F. McKone, Charles G. Gallagher, and Jonathan D. Dodd

From Herbert Y. Kressel, MD, Editor, Radiology

Erratum in: Radiology 2015;275(3):934 DOI:10.1148/radiol.2015154012 In the author list, the third author should be listed as Eoin P. Judge.

I thank the authors for their thoughtful comments. As they note, current common terminology for iodine-based contrast media is iodinated contrast

Originally published in: Radiology 2015;275(3):755–762 DOI: 10.1148/radiol.14141400

Editor’s Note

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