Magnetic resonance imaging of focal liver lesions

Magnetic resonance imaging (MRI) and diseases of the liver and biliary tract. Part 1. Basic principles, MRI in the assessment of diffuse and focal hepatic disease

Magnetic resonance imaging (MRI) relies on the physical properties of unpaired protons in tissues to generate images. Unpaired protons behave like tiny bar magnets and will align themselves in a magnetic field. Radiofrequency pulses will excite these aligned protons to higher energy states. As they return to their original state, they will release this energy as radio waves. The frequency of the radio waves depends on the local magnetic field and by varying this over a subject, it is possible to build the images we are familiar with. In general, MRI has not been sufficiently sensitive or specific in the assessment of diffuse liver disease for clinical use. However, because of the specific characteristics of fat and iron, it may be useful in the assessment of hepatic steatosis and iron overload. Magnetic resonance imaging is useful in the assessment of focal liver disease, particularly in conjunction with contrast agents. Haemangiomas have a characteristic bright appearance on T2 weighted images because of the slow flowing blood in dilated sinusoids. Focal nodular hyperplasia (FNH) has a homogenous appearance, and enhances early in the arterial phase after gadolinium injection, while the central scar typically enhances late. Hepatic adenomas have a more heterogenous appearance and also enhance in the arterial phase, but less briskly than FNH. Hepatocellular carcinoma is similar to an adenoma, but typically occurs in a cirrhotic liver and has earlier washout of contrast. The appearance of metastases depends on the underlying primary malignancy. Overall, MRI appears more sensitive and specific than computed tomography with contrast for the detection and evaluation of malignant lesions.

Clinical efficacy of portal vein stent placement in patients with hepatocellular carcinoma invading the main portal vein

BACKGROUND/AIMS

Hepatocellular carcinoma frequently invades the portal veins, and when it invades the main portal vein, the patient's prognosis is extremely poor. This study was undertaken to evaluate the clinical efficacy of stent placement into the portal vein in these patients.

METHODS

Twenty-one patients with hepatocellular carcinoma invading the main portal vein were studied. Stents were placed in the portal veins to compress tumor thrombi after percutaneous transhepatic portography.

RESULTS

Stents were successfully placed in the portal veins in all patients. Portal venous pressure significantly decreased from 25.3 +/- 7.4 mmHg to 22.4 +/- 6.6 mmHg (p < 0.0001) immediately after stent placement, leading to improvement in gastroesophageal varices, melena and ascites. Although a pseudoaneurysm of the hepatic artery related to portal vein puncture developed in one patient, there were no major complications in the other 20 patients. Blood flow through the stent was maintained during the survival period in 15 patients. The mean stent patency period was 12.4 months. Fifteen patients underwent transcatheter arterial chemoembolization without major complications after stent placement. The survival rate was 64.2% at 6 months and 29.2% at 1 and 2 years, respectively. The mean survival period was 13.7 months.

CONCLUSION

Stent placement into the portal vein is a relatively safe and feasible procedure. It improves portal hypertension, expands treatment options, and helps to prolong the survival period in patients with hepatocellular carcinoma invading the main portal vein.

MRI of the liver

MRI of the liver is a powerful imaging modality for detection and characterization of liver pathology. MRI technology continues to evolve with developments in scanner hardware performance and refinements in imaging sequences, particularly in respect to fast imaging techniques, improving the quality of images that can be routinely achieved. Fast imaging techniques allow dynamic contrast-enhanced scanning to assist in lesion detection and characterization. An array of tissue-specific contrast agents are also becoming available; the clinical utility of some of these agents is yet to be fully established. An overview of scanning technique, contrast media, and the role of MRI in liver lesion detection and characterization is presented, with a review of the typical imaging characteristics of common focal and diffuse hepatic diseases. Where possible, emphasis has been placed on features that allow distinction between the various pathologic entities described.

Comparison of breath-hold multishot echo-planar and respiratory triggered fast-spin-echo sequences for T2-weighted MRI of liver lesions

The purpose of this study was to evaluate the usefulness of multishot echo-planar imaging in detecting liver tumors in comparison with respiratory triggered T2-weighted fast-spin-echo (FSE) imaging. Thirty-two patients with 70 focal liver lesions were imaged using a 1.5-T high speed MR imager. Eight-shot echo-planar images covering the whole liver were acquired during a single breath-hold period. FSE images were acquired with respiratory triggering in approximately 4 minutes. Lesion detectability and image quality of the two pulse sequences were analyzed qualitatively. Quantitative analysis was performed by means of signal-to-noise and tumor-liver contrast-to-noise analysis. Lesion detectability was comparable in both solid (86.3% vs 90.2%: .3 < P < .5) and nonsolid lesions (89.5% vs 100%: .3 < P < .5) between echo-planar and FSE images. Echo-planar imaging provided significantly reduced image artifact, better lesion conspicuity, and anatomic detail compared with FSE imaging. The signal-to-noise and contrast-to-noise ratios of echo-planar images were significantly higher than those of FSE images. Breath-hold eight-shot echo-planar imaging can be an alternative to T2-weighted FSE imaging because it can provide comparable image quality in a substantially decreased acquisition time.