[Diffusion-weighted MR imaging of liver pathology: principles and clinical applications]

Latest developments in the imaging of fibrotic liver disease

According to the World Health Organization, liver cirrhosis accounted for 1.8% of all deaths in Europe, causing about 170,000 deaths per year. Approximately 29 million persons in the EU suffer from chronic liver disease and this trend is on the rise. Liver disease is the EU's fifth most common cause of death accounting for at least one in six deaths. Early detection and monitoring of fibrosis has the potential to direct management of these chronic liver diseases and avert morbidity and mortality. Although the available techniques are in their infancy and the very early stages of fibrosis are difficult to detect, there have been significant advances in imaging over the last decade that has resulted in the use of these new imaging techniques being introduced into the patient pathway. This review explores the accuracies of these imaging techniques, their role in the management of patients, and the potential for the future.

Intravoxel incoherent motion model-based liver lesion characterisation from three b-value diffusion-weighted MRI

OBJECTIVE

To evaluate intravoxel incoherent motion (IVIM) model-based liver lesion characterisation from three b-value diffusion-weighted imaging (DWI).

METHODS

The 1.5-T DWI data from a respiratory gated spin-echo echo-planar magnetic resonance imaging sequence (b = 0, 50, 800 s/mm(2)) were retrospectively analysed in 38 patients with different liver lesions. Conventional apparent diffusion coefficient ADC = ADC(0,800) as well as IVIM-based parameters D' = ADC(50,800), ADC_low = ADC(0,50), and f' were calculated voxel-wise. Sixty-one regions of interest in hepatocellular carcinomas (HCCs, n = 24), haemangiomas (HEMs, n = 11), focal nodular hyperplasias (FNHs, n = 11), and healthy liver tissue (REFs, n = 15) were analysed. Group differences were investigated using Student's t-test and receiver-operating characteristic (ROC) analysis.

RESULTS

Mean values ± standard deviations of ADC, D', ADC_low (in 10(-5) mm(2)/s), and f' (in %) for REFs/FNHs/HEMs/HCCs were 130 ± 11/143 ± 27/168 ± 16/113 ± 25, 104 ± 12/123 ± 25/162 ± 18/102 ± 23, 518 ± 66/437 ± 97/268 ± 69/283 ± 120, and 18 ± 3/14 ± 4/6 ± 3/9 ± 5, respectively. Differences between lesions and REFs were more significant for IVIM-based parameters than for conventional ADC. ROC analysis showed the best discriminability between HCCs and FNHs for ADC_low and f' and between HEMs and FNHs or HCCs for D'.

CONCLUSION

Three instead of two b-value DWI enables a numerically stable and voxel-wise IVIM-based analysis for improved liver lesion characterisation with tolerable acquisition time.

KEY POINTS

• Quantitative analysis of diffusion-weighted MRI helps liver lesion characterisation. • Analysis of intravoxel incoherent motion is superior to apparent diffusion coefficient determination. • Only three b-values enable separation of diffusion and microcirculation effects. • The method presented is numerically stable, with voxel-wise results and short acquisition times.

Dynamic characteristics of MR diffusion-weighted imaging in a rabbit liver VX-2 tumor model

PURPOSE

To investigate prospectively dynamic characteristics of the apparent diffusion coefficient (ADC) on MR diffusion-weighted imaging (DWI) in a rabbit VX-2 tumor model.

MATERIALS AND METHODS

Forty New Zealand rabbits were included in the study, and 47 rabbit VX-2 tumor models were developed by direct and intrahepatic implantation after opening the abdominal cavities. DWI was carried out periodically and respectively on days 7, 14 and 21 after implantation. The VX-2 tumor samples were studied by pathology. The distinction of VX-2 tumors on DWI was assessed by their ADC values by analysis of variance (ANOVA) using SPSS12.0 software.

RESULTS

The ADC values (mean ± SD) × 10(-3) mm(2)/s of 47 VX-2 tumors in the peripheral and central areas were 2.18 ± 0.29, 1.96 ± 0.33, 1.80 ± 0.35, 2.20 ± 0.29, 2.05 ± 0.30 and 1.96 ± 0.48, respectively, on days 7, 14 and 21 after implantation. ADC values of 47 VX-2 tumors in the area of the tumor periphery, center and normal parenchyma were higher when the b-value was 100 s/mm(2) than those when the b-value was 300 s/mm(2) (F = 17.964, p < 0.001; F = 13.986, p < 0.001; F = 128.681, p < 0.001). ADC values in the area of normal liver parenchyma were higher than those in the area of the VX-2 tumor periphery and center when the b-value was 100 or 300 s/mm(2). ADCs of viable tumor cells in VX-2 tumors were lower on DWI than those in the area of normal liver parenchyma around the tumor, and ADCs of dead tumor cells in VX-2 tumors were unequal, including high, equal and low values, but they were higher than in the area of normal liver parenchyma around tumors after dead tumor cells had been liquefied or had become cystic.

CONCLUSION

ADC is correlated with the tumor histology and degree of malignancy, and DWI has potential value for dynamically monitoring tumors and evaluating the degree of malignancy and therapeutic effect.

MRI and pelvic abscesses: a pictorial review

OBJECTIVE

The purpose of our article was to review the magnetic resonance imaging (MRI) features of pelvic abscesses. Pelvic abscesses account for a wide range of abnormalities from various etiologies.

CONCLUSION

MRI is being increasingly used for pelvic exploration. Radiologists must thus be aware of their features and characteristics.

Superinfection of focal liver lesions after bile duct procedures

OBJECTIVES

Pyogenic liver abscess is a rare condition in the general population. The source of infection is most often biliary, and more rarely gastrointestinal via the portal tract, or even hematogenic. Other than in special contexts (scarring after radiofrequency ablation), focal liver lesions are not a usual risk factor for hepatic abscesses in patients with a history of bile duct procedures (sphincterotomy, biliary stenting, biliary enteric anastomosis). MATERIALS AND METHOD - RESULTS: We report four cases of focal liver lesions (two patients with benign lesions of the biliary cyst type and two other patients with lesions due to pancreatic cancer) complicated by a superinfection in patients with a history of bile duct procedures. There were no predisposing factors other than a context of cancer or diabetes.

CONCLUSION

Superinfection of a focal liver lesion should be considered when there is a suggestive clinical picture and a change in the appearance of the lesion in patients with a history of bile duct procedures in a context of cancer or diabetes.

Imaging of malignant neoplasms of the mesenteric small bowel: new trends and perspectives

This article describes the recent advances in radiological imaging of malignant neoplasms of the mesenteric small bowel and provides an outline of new trends and perspectives that can be anticipated. The introduction of multidetector row technology, which allows the acquisition of submillimeter and isotropic voxels, has dramatically improved the capabilities of computed tomography in the investigation of the mesenteric small bowel. This technology combined with optimal filling of small bowel loops through the use of appropriate enteral contrast agents has markedly changed small bowel imaging. Computed tomography-enteroclysis, which is based on direct infusion of enteral contrast agent into the mesenteric small bowel through a naso-jejunal tube, provides optimal luminal distension. By contrast, computed tomography-enterography is based on oral administration of enteral contrast agent. These two techniques are now well-established ones for the detection and the characterization of small bowel neoplasms. During the same time, combining the advantages of unsurpassed soft tissue contrast and lack of ionizing radiation, magnetic resonance imaging has gained wide acceptance for the evaluation of patients with suspected small bowel neoplasms. Rapid magnetic resonance imaging sequences used in combination with specific enteral contrast agents generate superb images of the mesenteric small bowel so that magnetic resonance-enteroclysis and magnetic resonance-enterography are now considered as effective diagnostic tools for both the detection and the characterization of neoplasms of the mesenteric small bowel. Recent improvements in image post-processing capabilities help obtain realistic three-dimensional representations of tumors and virtual enteroscopic views of the small bowel that are useful for the surgeon and the gastroenteroenteologist to plan surgical or endoscopic interventions. Along with a better knowledge of the potential and limitations of wireless capsule endoscopy and new endoscopic techniques, these recent developments in radiological imaging reasonably suggest that substantial changes in the investigation of small bowel tumors may be anticipated in a near future, thus potentially create a new paradigm shift after standard small bowel follow-through study has been universally abandoned.

The diffusion-weighted imaging perfusion fraction f is a potential marker of sorafenib treatment in advanced hepatocellular carcinoma: a pilot study

OBJECTIVE

To determine the total Apparent Diffusion Coefficient (ADC), the pure Diffusion coefficient (D) and the perfusion fraction (f) in advanced hepatocellular carcinoma (HCC) under sorafenib treatment.

MATERIALS AND METHODS

Two target tumors were prospectively analyzed in 12 patients at baseline, 2-weeks and 2-months treatment using b values of 0, 200, 400, 800 s/mm. Repeatability error was estimated on a healthy volunteer.

RESULTS

Lesion sizes, ADC and D values did not significantly change during treatment (overall mean values, respectively, 47.8 ± 31.0 mm, 1.34 ± 0.14 × 10⁻³ mm² s and 1.18 ± 0.22 × 10⁻³ mm²/s). However, f values significantly increased in seven responder patients (+38.39% at 2-weeks, +50.94% at 2-months, P = 0.005) while they decreased in five non responder patients (-41.93% at 2-weeks, P = 0.006). Furthermore, f was inversely correlated with αFP levels (P = 0.032) and responder patients had a higher mean overall survival (OS) than non responder patients (12.29 ± 4.46 vs. 7.80 ± 4.9 months). The % variation of f relative to baseline at 2-months was correlated with OS (P = 0.038) and symptomatic time to progression (P = 0.022).

CONCLUSION

Contrary to ADC and D, the perfusion fraction f is a valuable marker of sorafenib treatment in advanced HCC.