Imaging techniques for assessing hepatic fat content in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), an emerging clinical entity with worldwide recognition, is today the most common cause of abnormal liver function tests among adults in the United States. In Mexico City, its prevalence has been reported by our group to be around 14%, but its incidence is higher in the hispanic population in the United States (hispanic population 45%, white population 33%, black population 24%). The main issues in the diagnosis, follow-up, and management of NAFLD are our limited understanding of its pathophysiology and the difficulties involved in developing a noninvasive diagnostic method. Several imaging techniques can detect fatty infiltration of the liver, each with its own advantages and disadvantages. Ultrasound is still in the first option for diagnosis, but its accuracy depends on the operator and the patient's features. Computed tomography can detect hepatic fat content, but only at a threshold of 30%, and it involves ionizing radiation. Magnetic resonance (MR) spectroscopy is probably the most accurate and fastest method of detecting fat, but it is expensive and the necessary software is still not easily available in most MRI units. MR elastography, a new technique to detect liver stiffness, has not been demonstrated to detect NAFLD, and is still undergoing research in patients with hepatitis and cirrhosis. In conclusion, all these imaging tools are limited in their ability to detect coexisting inflammation and fibrosis. In this review, we discuss the radiological techniques currently used to detect hepatic fat content.