3D MRI provides prognostic possibilities for liver fibrosis
Although new infections of hepatitis C in the United States have declined from their peak in the 1980s of approximately a quarter million new cases annually, patients presenting with this chronic viral disease are at risk for liver fibrosis and cirrhosis. As this is a principle cause of morbidity and mortality in this patient group, the early detection of liver fibrosis is important for determining antiviral treatments and prognosis.

Conventional detection of liver fibrosis has rested mainly on histologic findings after a liver biopsy, which is prone to sampling errors, interobserver variability and dangers inherent to interventional procedures. A possible alternative to this procedure is the use of perfusion MRI, which has the potential to enable physicians to noninvasively detect and assess vascular alterations associated with collagen deposition in patients with chronic liver disease, according to researchers who conducted a prospective study with the modality.

“Three-dimensional (3D) perfusion MR imaging with coverage of the entire liver has the advantage of depicting perfusion changes in the liver on both a global basis and a regional basis,” wrote the authors of the study published in this month’s Radiology. “This could be useful in the diagnosis of fibrosis and the detection of interval changes during antiviral treatment monitoring.”

The study cohort contained 27 members, 7 control subjects with normal liver function and no history of liver disease and 20 patients with a known diagnosis of liver disease.  The patients presenting with liver disease included 16 with hepatitis C, 2 with chronic autoimmune hepatitis, 1 with hepatitis B, and 1 with nonalcoholic steatohepatitis. A pair of hepatopathologists working in consensus diagnosed fibrosis or cirrhosis from blinded liver biopsy specimens.

Scientists from the departments of radiology and pathology at New York University Medical Center in New York City performed their imaging studies on one of two 1.5-Tesla MRI systems with torso phased-array coils (Magnetom Symphony or Avanto; Siemens Medical Solutions). The mean time between biopsy and imaging for the patient cohort was 105 days.

Patients were imaged with and without gadolinium contrast (Magnevist; Berlex Laboratories), followed by a saline flush delivered via an MRI-compatible power injector (Spectris; Medrad).

“The rationale behind the use of 3D acquisition was to ensure that the entire liver was imaged and to account for regional perfusion differences in the liver,” the authors wrote.

Perfusion MR images of the liver in a 66-year-old female patient with chronic hepatitis C and stage 2 fibrosis obtained by using a coronal 3D interpolated spoiled gradient-recalled-echo sequence (1.7–3.2/0.8, 9° flip angle, generalized autocalibrating partially parallel acquisition acceleration factor of three) to cover the entire liver before and after injection of 10 mL of gadopentetate dimeglumine. Selected time points from 20 measurements are shown in chronologic order. The total acquisition time was approximately 120 seconds. (Each volume was acquired in 5.6 seconds.) Progressive opacification of the aorta and hepatic artery (short arrows), portal vein (long arrow), and liver parenchyma and hepatic vein (dashed arrow) was noted. Image and caption courtesy of the Radiological Society of North America.  

The researchers noted that the 3D protocol was incorporated into the routine MR imaging protocol and added only about 5 minutes to the total procedure time, which was 45 minutes. By measuring the distribution volume (DV) of gadolinium through the liver compartment and the portal venous (PV) fraction, they were able to detect regional changes in liver perfusion, which presented as more heterogeneous in patients with advanced fibrosis and cirrhosis.

Although the study was limited by the small sample size, the researchers believe that the potential clinical applications of perfusion MR imaging are numerous, and they need to be further investigated and validated. In addition to its role in detection of liver fibrosis, it could play a role in the detection and characterization of angiogenic activity in patients with hepatocellular carcinoma or metastatic lesions, according to the researchers.

Advanced visualization technology will play a large role in determining how clinically successful and widespread 3D MR perfusion imaging becomes.

“Future work will need to focus on improved image post-processing, with automated registration, vessel segmentation, and parametric mapping of perfusion parameters performed on a voxel-by-voxel basis,” the authors wrote. “This could improve assessment of regional differences in patients with fibrosis, help to assess differentiation of mild and moderate fibrosis, and be useful in the detection and characterization of liver lesions.”