New developments in liver MR imaging

Transcription

1 Parallel symposium B. 간질환에대한영상검사및중재적시술 (What are new in imaging diagnosis and interventional treatment of liver diseases) 울산대학교의과대학서울아산병원영상의학과 New developments in liver MR imaging Hyung Jin Won, M.D. Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea 국문초록 최근간자기공명영상 (Magnetic Resonance Imaging, MRI) 의발전에힘입어, 간영상에서 MR의중요성이커지고있다. 그중에서새로운간세포특이적조영제인 gadoxetate (Gd-EOB-DTPA) 는기존의비특이적세포외액조영제의역동적영상뿐만아니라간세포의기능적영상을함께얻을수있어서주목받고있다. Gadoxetate는간국소병변의특성화에추가적인진단적가치를보이며, 간세포암등의발견에있어서도다중검출 CT (Multidetector CT) 보다우수한성적이보고되고있다. 또다른새로운영상기법으로는확산강조영상 (Diffusion-weighted imaging, DWI) 을들수있다. 확산강조영상은조직내의물분자의확산특성을영상화하는자기공명영상기법이며, 간국소병변의검출과감별진단에도움을준다. 이글에서는 gadoxetate와확산강조영상의기본원리를소개하고, 흔하게마주치는간국소병변, 특히간세포암에대하여영상소견과진단적가치를기술하고자한다. 색인단어 : 간신생물, 자기공명영상, gadolinium ethoxybenzyl DTPA, 확산강조영상 Keywords: Liver neoplasms, Magnetic Resonance Imaging, gadolinium ethoxybenzyl DTPA, Diffusion Magnetic Resonance imaging - S112 -

2 Introduction Technical advances in magnetic resonance imaging (MRI) of the liver, in terms of hardware, software and contrast agents, have been made in recent years such that it now offers many advantages over computed tomography (CT) and ultrasonography (US) for liver imaging. 1,2 In this article, among various new developments, new hepatocyte-specific contrast agent gadoxetic acid is presented with emphasis on detection and characterization of the common focal liver lesions including hepatocellular carcinoma (HCC). Furthermore, clinical value of diffusion weighted imaging in the field of liver MRI is discussed. Gadoxetate-enhanced liver MR imaging 1. Overview of contrast agents for MR imaging Non-tissue specific, extracellular gadolinium chelates were the first category of MR contrast agents approved for clinical use. Gadolinium chelates have an excellent safety profiles and lesion detection and characterization is based on tumor perfusion properties with dynamic imaging, which are similar to those seen with iodinated contrast agents used in CT. 3 The other two categories of MR contrast agents are targeted to reticuloendothelial systems and hepatocytes, respectively. Superparamagnetic iron oxide particles (SPIO), such as ferumoxide and ferucarbotran is taken up by the reticuloendothelial systems (Kupffer cells in the liver) and produces a decrease in signal intensity on T2-weighted images, while tissue which do not contain RES cells remain unaffected. 4 Hepatocyte-specific contrast media includes the gadolinium- and manganese based agents. 5 The gadolinium-based agents have both hepatocyte and perfusion imaging properties. Gadobenate dimeglumine (Multihance ç, Bracco, Milan, Italy; formerly known as Gd-BOPTA) and gadoxetate (Primovist ç, Bayer-Schering, Berlin, Germany; formerly known as Gd-EOB-DTPA) are available in this category. The manganese-based agent mangafodipir trisodium (Teslascan ç, GE Healthcare, Oslo, Norway; formerly known as Mn-DPDP) is predominantly a T1-shotening agent. With mangafodipir, tumors of non-hepatocyte origin show no enhancement, while hepatocellular lesions show uptake depending on the grade of differentiation Characteristics of gadoxetate Gadoxetate (Gadolinium-ethoxybenzyl-diethylene triamine penta-acetic acid, Gd-EOB-DTPA; Primovist ç, Bayer Schering Pharma, Berlin, Germany) is a hepatocyte-specific contrast agent that is eliminated in equal quantities by the urinary and biliary systems. Gadoxetate is specifically taken up by hepatocytes and thereby provides increased lesion-liver contrast not achievable with the extracellular gadolinium-based contrast agents. After bolus administration, dynamic T1-weighted GRE pulse sequences are obtained. Whereas only 4% of the injected dose of gadobenate is taken up by hepatocytes, 50% of the injected dose of gadoxetate is taken up by hepatocytes, reaching a plateau after a plateau - S113 -

3 2010 년대한간학회추계학술대회 after approximately 20 min and lasting for approximately 2 h. Due to the small fraction of gadobenate taken up by the hepatocytes, the delayed phase MR acquisition is started at least 60 min after administration. Both gadobenate and gadoxetate have biliary excretion. Therefore a high degree of enhancement of the biliary tract is seen in the delayed phase images, especially after administration of gadoxetate. 3. Imaging features of focal liver lesions With gadoxetate-enhanced dynamic imaging, the enhancement pattern of focal nodular hyperplasia (FNH) is very much like the enhancement pattern observed with non-specific gadolinium chelates. On delayed phase T1-weighted images, however, a substantial hepatocellular enhancement is noted within the lesion, while the central scar appears hypointense. Enhancement in the hepatocyte-specific phase after 20 minutes was observed in 90% of FNH in a multicenter trial. 7 Iso- to hyperintensity in the hepatocyte phase after gadolinium injection allows differentiation between FNHs and hepatic adenomas. The MR appearance of HCC is variable, but it is typically moderately hypointense on T1-weighted images and mildly hypointense on T2-weighted images. 8 The pseudocapsule, if present, may be visible as a thin hypointense rim on T1-weighted images with mild hyperintensity on T2-weighted images. 9 HCCs are in most cases hypervascular and therefore enhance strongly on arterial phase. A typical feature of HCC which helps differentiate dysplastic nodules from HCC is wash-out of contrast agent, which renders HCC hypointense on equilibrium phase images. Some severely dysplastic nodules, however, may also show intense early enhancement and may mimic early HCC. Gadoxetate has limitation in characterization of hepatocellular nodules in cirrhosis, because well-differentiated HCC and dysplastic nodules may show variable degree of contrast agent uptake in hepatobiliary phase. 10,11 High-flow hemangiomas might show relatively low signal intensity because of gadoxetate uptake in the surrounding normal liver parenchyma during the equilibrium (3-minute delay) phase. Such findings are called pseudo washout and can mimic hypervascular hepatic tumors such as HCC or hypervascular metastasis. 12 However, high-flow hemangioma can be diagnosed by observing bright signal intensity on T2-weighted imaging and isointense or slightly increased signal intensity on subtraction images. Because of the absence of hepatocytes, hemangioma appears hypointense during hepatobiliary phase. 4. Diagnostic performance Data suggest that the sensitivity of gadoxetate-enhanced MRI is significantly superior to multi-detector row CT for the detection of HCC. 13,14 But some reports failed to show statistically significant difference. 15,16 Gadoxetate-enhanced MRI during the hepatobiliary phase can identify small HCC lesions more clearly than dynamic-phase imaging or dynamic CT due to increased liver-lesion contrast after uptake of gadoxetate by functioning hepatocytes. - S114 -

4 Diffusion weighted imaging (DWI) DWI in the liver is a relatively new and increasingly used imaging technique in addition to conventional unenhanced and contrast enhanced MRI. 17 DWI is an imaging technique which provides tissue contrast by the measurement of diffusion properties of water molecules within tissues. Diffusion is expressed in an apparent diffusion coefficient (ADC), which reflects the diffusion properties unique to each type of tissue. 18 DWI proved to be helpful in the characterization of focal liver lesions, but should always be used in conjunction with traditional MRI since there is a great overlap between ADC values of benign and malignant lesions. 19,20 DWI is useful in the detection of small HCC in the cirrhotic liver, with higher sensitivity, specificity and positive predictive value compared to conventional contrast enhanced MR imaging due to better lesion to liver contrast and background suppression of signals arising from vessels and bile ducts. 21,22 This is also the case for the detection of metastases in the liver. 23,24 However, it should be noted that DWI images are difficult to interpret since DWI is very sensitive to artifacts. DWI in the follow-up after RFA and TACE shows promising results in the detection of ablation site recurrences, especially in combination with conventional contrast enhanced MR imaging. 25,26 Conclusions The new hepatocyte-specific contrast agent gadoxetate increases the diagnostic confidence of MR imaging for the characterization of focal liver lesions by providing additional functional information. Gadoxetate also seems to be superior in detecting HCC compared with MDCT. Diffusion-weighted imaging of liver is helpful in detection and characterization of focal liver lesions when used in conjunction with conventional contrast enhanced MR imaging. REFERENCES 1. Ba-Ssalamah A, Uffmann M, Saini S, Bastati N, Herold C, Schima W. Clinical value of MRI liver-specific contrast agents: a tailored examination for a confident non-invasive diagnosis of focal liver lesions. Eur Radiol 2009;19: Tanimoto A, Lee JM, Murakami T, Huppertz A, Kudo M, Grazioli L. Consensus report of the 2 nd international forum for liver MRI. Eur Radiol 2009;19(Suppl 5):S975-S Semelka RC, Helmberger TK. Contrast agents for MR imaging of the liver. Radiology 2001;218(1): Bluemke DA, Weber TM, Rubin D, de Lange EE, Semelka R, Redvanly RD, et al. Hepatic MR imaging with ferumoxides: multicenter study of safety and effectiveness of direct injection protocol. Radiology 2003;228(2): Reimer P, Schneider G, Schima W. Hepatobiliary contrast agents for contrast-enhanced MRI of the liver: properties, clinical development and applications. Eur Radiol 2004;14(4): Oudkerk M, Torres CG, Song B, Konig M, Grimm J, Fernandez-Cuadrado J. Characterization of liver lesions with mangafodipir trisodium-enhanced MR imaging: multicenter study comparing MR and dual-phase spiral CT. Radiology 2002;223(2): Zech CJ, Grazioli L, Breuer J, Reiser MF, Schoenberg SO. Diagnostic performance and description of morphological features of focal nodular hyperplasia in Gd-EOB-DTPA-enhanced MRI: results of a multicenter trial. Invest Radiol - S115 -

5 2010 년대한간학회추계학술대회 2008;43(7): Taouli B, Losada M, Holland A, Krinsky G. Magnetic resonance imaging of hepatocellular carcinoma. Gastroenterology 2004;127(5 Suppl 1):S144-S Grazioli L, Olivetti L, Fugazzola C, Benetti A, Stanga C, Dettori E, et al. The pseudocapsule in hepatocellular carcinoma: correlation between dynamic MR imaging and pathology. Eur Radiol 1999;9(1): Huppertz A, Haraida S, Kraus A, Zech CJ, Scheidler J, Breuer J, et al. Enhancement of focal liver lesions at gadoxetic acid-enhanced MR imaging: correlation with histopathologic findings and spiral CT-initial observations. Radiology 2005;234: Bartolozzi C, Crocetti L, Lencioni R, Cioni D, Della pina C, Campani D. Biliary and reticuloendothelial impairment in hepatocarcinogenesis: the diagnostic role of tissue-specific MR contrast media. Eur Radiol 2007;17: Doo KW, Lee CH, Choi JW, Lee J, Kim KA, Park CM. Pseudo washout sign in high-flow hemangioma on gadoxetic acid contrast-enhanced MRI mimicking hypervascular tumor. AJR Am J Roentgenol 2009;193:W490-W Kim YK, Kim CS, Han YM, Kwak HS, Jin GY, Hwang SB, et al. Detection of hepatocellular carcinoma: gadoxetic acid-enhanced 3-dimensional magnetic resonance imaging versus multi-detector row computed tomography. J Comput Assist Tomogr 2009;33: Di Martino M, Marin D, Guerrisi A, Baski M, Galati F, Rossi M, et al. Intraindividual comparison of gadoxetate disodium-enhanced MR imaging and 64-section multidetector CT in the detection of hepatocellular carcinoma in patients with cirrhosis. Radiology 2010;256: Kim SH, Kim SH, Lee J, Kim MJ, Jeon YH, Park Y, et al. Gadoxetic-acid enhanced MRI versus triple-phase MDCT for the preoperative detection of hepatocellular carcinoma. AJR Am J Roentgenol 2009;192: Akai H, Kiryu S, Matsuda I, Satou J, Takao H, Tajima T, et al. Detection of hepatocellular carcinoma by Gd-EOB-DTPA-enhanced liver MRI: comparision with triple phase 64 detector row helical CT. Eur J Radiol (2010), doi: /j.ejrad Kele PG, van der Jagt EJ. Diffusion weighted imaging in the liver. World J Gastroenterol 2010;16: Bammer R. Basic principles of diffusion-weighted imaging. Eur J Radiol 2003;45: Feuerlein S, Pauls S, Juchems MS, Stuber T, Hoffmann MH, Brambs HJ, et al. Pitfalls in abdominal diffusion-weighted imaging: how predictive is restricted water diffusion for malignancy. AJR Am J Roentgenol 2009;193: Sandrasegaran K, Akisik FM, Lin C, Tahir B, Rajan J, Aisen AM. The value of diffusion-weighted imaging in characterizing focal liver masses. Acad Radiol 2009;16: Zech CJ, Reiser MF, Herrmann KA. Imaging of hepatocellular carcinoma lesions by computed tomography and magnetic resonance imaging: state of the art. Dig Dis 2009;27: Vandecaveye V, De Keyzer F, Verslype C, Op de Beeck K, Komuta M, Topal B, et al. Diffusion-weighted MRI provides additional value to conventional dynamic contrast-enhanced MRI for detection of hepatocellular carcinoma. Eur Radiol 2009;19: Koh DM, Brown G, Riddell AM, Scurr E, Collins DJ, Allen SD, et al. Detection of colorectal hepatic metastases using MnDPDP MR imaging and diffusion-weighted imaging(dwi) alone and in combination. Eur Radiol 2008;18: Nasu K, Kuroki Y, Nawano S, Kuroki S, Tsukamoto T, Yamamoto S, et al. Hepatic metastases: diffusion-weighted sensitivity-encoding versus SPIO-enhanced MR imaging. Radiology 2006;239: Schraml C, Schwenzer NF, Clasen S, Rempp HJ, Martirosian P, Claussen CD, et al. Navigator respiratory-triggered diffusion-weighted imaging in the follow-up after hepatic radiofrequency ablation-initial results. J Magn Reson Imaging 2009;29: Yu JS, Kim JH, Chung JJ, Kim KW. Added value of diffusion-weighted imaging in the MRI assessment of perilesional tumor recurrence after chemoembolization of hepatocellular carcinomas. J Magn Reson Imaging 2009;30: S116 -