Magnetic resonance measurement of diffusion in the abdomen
ABSTRACT Diffusion-weighted (DW) magnetic resonance imaging is an emerging noninvasive technique increasing its spectrum of use in the abdomen. Diffusion-weighted imaging has been used as add-on to routine abdominal protocol because it may potentially substitute contrast-enhanced imaging in cases under risk of nephrogenic systemic fibrosis. The apparent diffusion coefficient (ADC) images calculated from DW images enable qualitative and quantitative evaluations of tissue water mobility and functional environment because of changes in intracellular, extracellular, and intravascular tissue compartments. This article presents the basic physics of the ADC measurement, the techniques for performing ADC measurements of the liver and the pancreas, and the clinical applications of DW imaging.
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ABSTRACT: At least 40% of survivors of biliary atresia have progressive cirrhosis even after undergoing Kasai operation. The values of hepatic apparent diffusion coefficient and apparent-diffusion-coefficient-related indices were applied to biliary atresia patients and correlated with cirrhotic severity scores of model for end-stage liver disease or pediatric end-stage liver disease model, Child-Turcotte, and Child-Pugh systems. Thirty-three biliary atresia patents (mean=1140, 61-4314 days of age) received magnetic resonance image examinations due to complications of biliary atresia from April 2008 to August 2009. Two non-breath-hold diffusion weighted imaging sequences were performed with motion-probing gradients in three directions with two b values: 0/100 and 0/500 s/mm2; 1000 ms/61.1 ms, time to repeat/time to echo; number of excitation, 1.0; 8 mm section thickness; 40 cm×40 cm field of view; 128×256 matrix in all biliary atresia patients and 18 control subjects. We used the Spearman rank correlation test to analyze the relationship among the scores of model for end-stage liver disease or pediatric end-stage liver disease model, Child-Turcotte and Child-Pugh scores and right hepatic apparent diffusion coefficients, apparent diffusion coefficient using b factor of 500-albumin product and alanine transaminase/apparent diffusion coefficient with b factor of 500 ratio. The right hepatic apparent diffusion coefficient using b factor of 100, apparent diffusion coefficient with b factor of 500 and product of apparent diffusion coefficient with b factor of 500-albumin level were significantly negatively correlated (p≤0.0125) with model for end-stage liver disease or pediatric end-stage liver disease model, Child-Turcotte, and Child-Pugh scores of biliary atresia patients. The ratio of alanine transaminase level/right hepatic apparent diffusion coefficient with b factor of 500 was also significantly (p≤0.0251), moderately correlated with Child-Turcotte and Child-Pugh scores (rho=0.5256 and 0.7518, respectively). Right hepatic apparent diffusion coefficient with b factor of 500 and alanine transaminase/right hepatic apparent diffusion coefficient with b factor of 500 can be useful for long-term follow-up of cirrhotic severity in biliary atresia patients.European journal of radiology 11/2010; 80(3):e253-7. DOI:10.1016/j.ejrad.2010.11.002 · 2.16 Impact Factor
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ABSTRACT: Objective Clinical hepatic diffusion weighted imaging (DWI) generally relies on mono-exponential diffusion. The aim was to demonstrate that mono-exponential diffusion in the liver is contaminated by microperfusion and that the bi-exponential model is required. Methods Nineteen fasting healthy volunteers were examined with DWI (seven b-values) using fat suppression and respiratory triggering (1.5 T). Five different regions in the liver were analysed regarding the mono-exponentially fitted apparent diffusion coefficient (ADC), and the bi-exponential model: molecular diffusion (D slow ), microperfusion (D fast ) and the respective fractions (f slow/fast ). Data were compared using ANOVA and Kruskal–Wallis tests. Simulations were performed by repeating our data analyses, using just the DWI series acquired with b-values approximating those of previous studies. Results Median mono-exponentially fitted ADCs varied significantly (P −3 mm2/s for the five regions. Bi-exponential fitted Dslow varied between 0.923 and 1.062 × 10−3 mm2/s without significant differences (P = 0.140). D fast varied significantly, between 17.8 and 46.8 × 10−3 mm2/s (P F > 21.4, P Conclusion ADCs of normal liver tissue are significantly dependent on the measurement location because of substantial microperfusion contamination; therefore the bi-exponential model should be used. Key Points Diffusion weighted MR imaging helps clinicians to differentiate tumours by diffusion properties Fast moving water molecules experience microperfusion, slow molecules diffusion Hepatic diffusion should be measured by bi-exponential models to avoid microperfusion contamination Mono-exponential models are contaminated with microperfusion, resulting in apparent regional diffusion differences Bi-exponential models are necessary to measure diffusion and microperfusion in the liverEuropean Radiology 11/2011; 22(4):891-9. DOI:10.1007/s00330-011-2313-1 · 4.34 Impact Factor
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ABSTRACT: Purpose:To evaluate the value of diffusion-weighted (DW) imaging in differentiation of an intrapancreatic accessory spleen (IPAS) from a small (<3 cm) solid pancreatic tumor.Materials and Methods:This retrospective study was approved by the institutional review board, and informed consent was waived. Twenty patients with IPAS and 22 patients with small solid pancreatic tumors were included. All patients underwent abdominal magnetic resonance (MR) imaging with DW and gadoxetic acid-enhanced imaging. Qualitative (signal intensity) and quantitative (signal intensity and apparent diffusion coefficient [ADC]) evaluations were performed by two observers. Fisher exact test and Mann-Whitney U test were used for comparing groups.Results:Compared with the spleen, the IPAS showed isointensity more frequently than did small pancreatic tumors on T2-weighted images (95% [19 of 20] vs 41% [nine of 22]), arterial phase images (100% [20 of 20] vs 18% [four of 22]), portal phase images (100% [20 of 20] vs 23% [five of 22]), late phase images (100% [20 of 20] vs 41% [nine of 22]), and DW images with b value of 0 sec/mm(2) (100% [20 of 20] vs 9% [two of 22]), b value of 100 sec/mm(2) (95% [19 of 20] vs 27% [six of 22]), and b value of 800 sec/mm(2) (100% [20 of 20] vs 27% [six of 22]), with significant differences (P < .01). The means of the absolute value of relative signal intensity and ADC ratio on DW images of IPAS were significantly lower and closer to zero than those of pancreatic tumors (P < .05). Visual assessment of the similarity between pancreatic lesion and spleen on DW images for diagnosis of IPAS yielded diagnostic accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of 95% (40 of 42), 100% (20 of 20), 91% (20 of 22), 91% (20 of 22), and 100% (20 of 20), respectively, for observer 1 and 90% (38 of 42), 95% (19 of 20), 86% (19 of 22), 86% (19 of 22), and 95% (19of 20), respectively, for observer 2.Conclusion:In addition to conventional morphologic MR imaging, DW imaging can be used as a tool for differentiating IPAS from solid pancreatic tumors.© RSNA, 2012© RSNA, 2012Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12112765/-/DC1.Radiology 10/2012; 266(1). DOI:10.1148/radiol.12112765 · 6.21 Impact Factor