Commentary:clinical imaging in measuring visceral adipose tissue and other body components

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(1.Obesity Research Center Department of Medicine and Institute of Human Nutrition ColumbiaUniversity Medical Center 1150 Saint Nicholas Avenue,Suite 121 New York,New York,10032 USA;2.Department of Radiology,Beijing Jishuitan Hospital,Peking University,Beijing,100035,China)

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Commentary:clinical imaging in measuring visceral adipose tissue and other body components

ShenWei1，ChengXiaoguang2

(1.ObesityResearchCenterDepartmentofMedicineandInstituteofHumanNutritionColumbiaUniversityMedicalCenter1150SaintNicholasAvenue,Suite121NewYork,NewYork,10032USA;2.DepartmentofRadiology,BeijingJishuitanHospital,PekingUniversity,Beijing,100035,China)

In recent years it has been recognized that not only total amount of fat,but also fat distribution plays an important role in metabolism.Visceral adipose tissue(VAT),the most important component of central obesity,is closely related to insulin resistance and hyperlipidemia.It is hypothesized that an overflow of free-fatty acid and an increased secretion of inflammatory factors toward liver impairs insulin resistance and lipid metabolism[1].Obesity is a risk factor for many chronic diseases and obesity may interact with the underlying pathophysiology of different diseases.

1 VAT measurement techniques

Among the methods that characterize obesity,body mass index(BMI) is the most widely used tool,however BMI does not provide any information on fat distribution.Waist circumference(WC) is a proxy for central obesity but does not differentiate between VAT and subcutaneous adipose tissue(SAT).In this issue,a study compared anthropometric measures with QCT in measuring VAT.It is found that the error for WC to estimate VAT was relatively high.These findings in a Chinese sample are consistent with previous reports in western population.Some models of dual-energy X-ray absorptiometry(DXA) provide VAT reading,which are derived from DXA geometric models and are validated against VAT measured by computed tomography(CT) in cross-sectional studies.CT and magnetic resonance imaging (MRI) are the only technologies that can directly quantify VAT.VAT is quantified by using single-slice or multi-slice techniques[2].A single-slice scan best estimates VAT at 5 to 10 cm above L4-L5,at T12-L1,or at the L1-L2 level[2-4].Although single slice imaging is adequate in estimating total VAT in large scale cross-sectional studies,multi-slice imaging is more accurate in predicting SAT and VAT changes during weight loss[5].

2 Clinical imaging capacity on body composition measurements

Although CT and MRI are the most accurate methods in measuring VAT,they are not widely used due to the radiation involved in CT and the high cost of both CT and MRI[6].However,CT and MRI are clinically collected for diagnosis,classification,and treatment evaluation in various diseases.Compared to imaging that is collected only for the purpose of research,clinical imaging has the advantage of adding no additional burden or radiation to patients.Recent advances of CT and MRI made it possible to quantify total body and regional adiposity,to map adipose tissue distribution,and to evaluate ectopic fat.Quantitative CT(QCT) has advantage of quantifying organ fat such as liver fat more accurately than conventional CT(ref).Radiomics is another emerging field that takes advantage of clinically collected image scans by post-processing tumor scans[7].In this issue,a study found that QCT and MRI are comparable in measuring VAT and SAT.Although CT and MRI are generally considered comparable in measuring VAT,the analysis of CT is less technical demanding as CT,and is less likely to be affected by artifacts compared with MRI.In this issue,clinically collected imaging has been used to quantifying both muscle and adipose tissue.

3 Disease and Obesity

There is no controversy that obesity is a risk factor for cardiovascular diseases,diabetes,strokes,cancer,etc.In recent years it has been found that obesity may also influence the outcomes and prognoses of different diseases including cancer,chronic obstructive pulmonary disease(COPD),osteoporosis,and acromegaly.In this issue a study found that malignant gynecologic tumor patients had higher amount of fat than benign gynecologic disease.The American Society of Clinical Oncology (ASCO) position statement on obesity and cancer stated that obesity is a major risk for cancer prognosis,and is called for researching to understand the pathophysiology of obesity in cancer outcomes[8].Recent understanding is that obesity does not translate to the same outcomes for everyone[9].Each malignancy may be also distinctly interact with the underlying pathophysiology of obesity.

4 In summary

MRI and CT are increasingly employed in both clinical trials and clinical care.These scans are used for diagnosis,disease staging,as well as treatment evaluation.Image measured VAT as well as other body components might be used for evaluating improving disease outcomes.The digitalization and centralization of these images are allowed for clarifying obesity related questions in various diseases.Imaging offers enormous opportunities in obesity care and prevention in diseases.

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[3]Shen W，Punyanitya M，Wang ZM，et al．Visceral adipose tissue:relations between single-slice areas and total volume[J]．Am J Clin Nutr，2004，80(2)：271-278．

[4]Irlbeck T，Massaro JM，Bamberg F，et al．Association between single-slice measurements of visceral and abdominal subcutaneous adipose tissue with volumetric measurements:the Framingham Heart Study[J]． Int J Obes (Lond)，2010，34(4)：781-787．

[5]Shen W，Chen J，Gantz M，et al．A Single MRI slice does not accurately predict visceral and subcutaneous adipose tissue changes during weight loss[J]．Obesity (Silver Spring)，2012，20(12)：2458-2463．

[6]Shen W，Wang ZM，Punyanita M，et al．Adipose tissue quantification by imaging methods:a proposed classification[J].Obes Res，2003，11(1)：5-16．

[7]Aerts HJ，Velazquez ER，Leijenaar RT，et al．Decoding tumour phenotype by noninvasive imaging using a quantitative radiomics approach[J]．Nat Commun，2014(5)：4006．

[8]Ligibel JA，Alfano CM，Courneya KS，et al．American Society of Clinical Oncology position statement on obesity and cancer[J]．J Clin Oncol，2014，32(31)：3568-3574．

[9]Azvolinsky A．Cancer prognosis:role of BMI and fat tissue[J]．J Natl Cancer Inst，2014，106(6)：dju177．

R445

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1671-8348(2016)30-4177-02

2016-03-18

2016-07-06)

沈溦

程曉光

?家述評·

10.3969/j.issn.1671-8348.2016.30.001

沈溦：研究員，美國哥倫比亞大學醫學院醫學系和營養學院助理教授，哥倫比亞大學肥胖研究中心影像分析實驗室主任、人體組成實驗室副主任，是美國國立衛生院(NIH)資助的多個肥胖領域MRI和CT項目的首席科學家(Principal Investigator)。目前她的R01項目研究減肥過程中和能量代謝變化有關的器官大小變化。其最新研究方向是疾病、肥胖及人體組成的關系。目前已發表70多篇SCI同行評議文章，并和多位臨床醫師和科學家合作將影像學人體組成方法應用于肥胖、糖尿病、肢端肥大癥、神經性厭食癥、癌癥、柯興氏病、非酒精性脂肪肝炎、特發性骨質疏松、艾滋病、多囊卵巢綜合征、肌萎縮等病癥的研究。其領導的影像分析實驗室是世界領先的人體組成影像分析的中心實驗室，完成了美國和國際的多個NIH和藥廠的多中心臨床試驗的影像分析，包括大于10萬份MRI、MRS、CT和DXA的影像分析。

程曉光：現任北京積水潭醫院放射科主任醫師/主任/教授/博導。北京市創傷骨科研究所碩士，比利時魯汶大學博士，美國加州大學舊金山分校博士后。現任亞洲骨骼學會(AMS)副主席，中華醫學會骨質疏松與骨礦鹽疾病分會常委，中國醫師協會放射醫師分會常務兼總干事長。中華醫學會放射學分會骨肌放射影像專委會副主任委員，北京醫學會骨質疏松與骨礦鹽疾病分會常委等。任《中國骨質疏松雜志》副主編，《中國臨床醫學影像雜志》編委，《中國醫學影像技術》編委，《中華骨質疏松與骨礦鹽疾病雜志》編委，《中華放射學雜志》特邀編委，《中國CT和MRI雜志》編委，《臨床放射學雜志》編委。長期從事放射學，在肌骨影像診斷和研究方面具有豐富經驗和成果，尤其是骨質疏松研究領域成果在國內得到廣泛應用，并得到國際學術界的認可。