Imaging-based Quantification of Hepatic Fat: Methods and Clinical Applications
 Moderate hepatic steatosis in a 58-year-old man with a history of alcohol abuse. Opposed-phase MR imaging was performed with a 1.5-T system. (a) In-phase (TR/TE = 139/4.76) MR image obtained at the level of the right liver lobe and spleen shows a signal intensity ratio of 309/187 = 1.65. (b) Out-of-phase (TR/TE = 139/2.38) MR image, obtained at the same level as a, shows a signal intensity ratio of 207/198 = 1.05. Calculated by using the Dixon method, the percentage of liver fat is [(1.65 -1.05)/(2 • 1.65)] • 100 = 18 percent, a finding indicative of mild to moderate steatosis. (RadioGraphics 2009;29:1253-1280) © RSNA, 2009. All rights reserved. Printed with permission. |
Imaging is a valuable noninvasive alternative to histopathologic analysis. It allows assessment of the entire liver, thereby avoiding sampling errors; permits both qualitative and quantitative evaluation of fat content; is well suited for repeated assessments; and allows concomitant screening for other liver abnormalities, including hepatocellular carcinoma. Because early recognition is critical, selecting an appropriate imaging method for detecting and quantifying liver fat requires an understanding of the advantages and limitations of each modality and the suitable clinical setting.
In an article in the September-October issue of RadioGraphics (RSNA.org/RadioGraphics), Xiaozhou Ma, M.D., and colleagues from Massachusetts General Hospital in Boston review imaging methods and clinical applications for quantification of hepatic fat. Specifically, the authors:
• Discuss the advantages and limitations of ultrasound, CT and MR imaging methods for liver fat quantification
• Describe imaging features that are indicative of fatty liver disease and suggestive of its cause
• Identify the unique advantages of MR spectroscopy for quantifying liver fat in specific settings
"Although CT and ultrasound allow qualitative and quantitative measurements of hepatic fat, MR techniques—in particular, chemical shift imaging and spectroscopy—provide higher sensitivity for more accurate detection of small amounts of fat, allowing more reliable disease characterization and thus better guidance for patient management," the authors conclude.
Air (CO2) Double-Contrast Barium Enteroclysis
Although air (CO2) double-contrast barium enteroclysis compares favorably with wireless capsule endoscopy and double-balloon endoscopy in the diagnosis of mucosal abnormalities of the small bowels, the technique is underused due to its technical demands and discomfort to the patient.
In a review article in the "How I Do It" section of the September issue of Radiology, (RSNA.org/Radiology), Dean D.T. Maglinte, M.D., of the Indiana University School of Medicine, Indiana University Hospital, Indianapolis, and colleagues describe their technique for performing air (CO2) double-contrast barium enteroclysis as well as its clinical indications and pitfalls. Authors discuss the following technical considerations:
 Double-contrast barium enteroclysis image obtained following initial administration of methylcellulose shows poorly defined defect in pelvic segment of ileum (arrow). (Radiology 2009;252:633–641) © RSNA, 2009. All rights reserved. Printed with permission. |
• Pre-procedural assessment and use of conscious sedation
• Catheter balloon and tip position
• Single-contrast barium infusion
• Use of analgesic boost prior to CO2 insufflation
• Administration of CO2 and sequential segmental double-contrast radiography
• Gastric suction and catheter removal
• Post-processing and image interpretation
Attention to such technical details will result in a faster examination with less discomfort, the authors write.
"Proper performance of this method of small-bowel examination can result in earlier diagnosis of diseases that are now evaluated with capsule endoscopy, which is more expensive, and with double-balloon and newer enteroscopic modifications, which are not only costly but invasive and time consuming," the authors conclude.
This article is accompanied by a "How I Do It" video that can be downloaded at Radiology.RSNA.org/site/video/index.xhtml.
RSNA Journals Join GO RAD
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Radiology and RadioGraphics are now among the 11 radiology publications participating in GO RAD, a new global outreach program developed by the International Society of Radiology.
GO RAD was developed to advance radiology education throughout a global radiology community by aggregating current, practical and timely radiology literature with content targeted and dedicated to developing nations and underserved populations. The RSNA Board of Directors approved the participation of the journals in June.
GO RAD, www.isRadiology.org/gorad/index.php, provides immediate open access to a limited amount of journal content otherwise restricted to subscribers of the participating journals, providing an electronic link to the original online article at the time of first publication. Radiology and RadioGraphics will identify suitable articles for the virtual journal offering free access for readers.
The first Radiology article to appear on GO RAD is from July 2009: "Rotator Cuff Calcific Tendonitis: Short-term and 10-year Outcomes after Two-Needle US-guided Percutaneous Treatment— Nonrandomized Controlled Trial." The first RadioGraphics article, "US Artifacts," to appear on the site is from the May-June issue.
RadioGraphics Editor William W. Olmsted, M.D., and Radiology Editor Herbert Y. Kressel, M.D., serve on the GO RAD Editorial Committee headed by Eric J. Stern, M.D. Dr. Stern is GO RAD editor-in-chief.
The Web site will provide open access up to at least one article per issue. Other participating journals are: Academic Radiology, American Journal of NeuroRadiology, American Journal of Roentgenology, Current Problems in Diagnostic Radiology, Journal of Medical Imaging and Radiation Oncology, Korean Radiology Journal, Mexican Annals of Radiology, Radiología and Journal of the American College of Radiology.
