Diffusion-weighted MRI for the assessment of liver fibrosis: principles and applications.

The importance of an early identification of hepatic fibrosis has been emphasized, in order to start therapy and obtain fibrosis regression. Biopsy is the gold-standard method for the assessment of liver fibrosis in chronic liver diseases, but it is limited by complications, interobserver variability, and sampling errors. Several noninvasive methods have been recently introduced into clinical routine, in order to detect liver fibrosis early. One of the most diffuse approaches is represented by diffusion-weighted liver MRI. In this review, the main technical principles are briefly reported in order to explain the rationale for clinical applications. In addition, roles of apparent diffusion coefficient, intravoxel incoherent motion, and relative apparent diffusion coefficient are also reported, showing their advantages and limits.

Diffusion weighted imaging and diffusion tensor imaging in the evaluation of transplanted kidneys.

OBJECTIVE: The aim of this study is to investigate the relation between renal indexes and functional MRI in a population of kidney transplant recipients who underwent MR with diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) of the transplanted graft. METHOD: Study population included 40 patients with single kidney transplant. The patients were divided into 3 groups, on the basis of creatinine clearance (CrCl) values calculated using Cockcroft-Gault formula: group A, including patients with normal renal function (CrCl ≥ 60 mL/min); group B, which refers to patients with moderate renal impairment (CrCl > 30 but <60 mL/min); and, finally, group C, which means severe renal deterioration (CrCl ≤ 30 mL/min). All patients were investigated with a 1.5 Tesla MRI scanner, acquiring DWI and DTI sequences. A Mann-Whitney U test was adopted to compare apparent diffusion coefficients (ADCs) and fractional anisotropy (FA) measurements between groups. Receiver operating characteristic (ROC) curves were created for prediction of normal renal function (group A) and renal failure (group C). Pearson correlation was performed between renal clearance and functional imaging parameter (ADC and FA), obtained for cortical and medullar regions. RESULTS: Mann-Whitney U test revealed a highly significant difference (p < 0.01) between patients with low CrCl (group C) and normal CrCl (group A) considering both medullar ADC and FA and cortical ADC. Regarding contiguous groups, the difference between group B and C was highly significant (p < 0.01) for medullar ADC and significant (p < 0.05) for cortical ADC and medullar FA. No difference between these groups was found considering cortical FA. Analyzing groups A and B, we found a significant difference (p < 0.05) for medullar both ADC and FA, while no difference was found for cortical ADC and FA. Strongest Pearson correlation was found between CrCl and medullar ADC (r = 0.65). For predicting normal renal function or severe renal impairment, highest values of AUC were observed using medullar ADC cut-off values (respectively 0.885 and 0.871); medullar FA showed also high accuracy (respectively 0.831 and 0.853). CONCLUSIONS: DWI and DTI are promising tools for non-invasive monitoring of renal function; medullar ADC proved to be the best parameter for renal function assessment.

Imaging findings of mucopolysaccharidoses: a pictorial review.

INTRODUCTION: Mucopolysaccharidosis (MPS) represent a heterogeneous group of inheritable lysosomal storage diseases in which the accumulation of undegraded glycosaminoglycans (GAGs) leads to progressive damage of affected tissues. The typical symptoms include organomegaly, dysostosis multiplex, mental retardation and developmental delay. Definitive diagnosis is usually possible through enzymatic assays of the defective enzyme in cultured fibroblasts or leukocytes. IMAGING FINDINGS: Radiological and neuroradiological findings are reported. The most important neuroradiological features include abnormal signal intensity in the white matter, dilatation of periventricular spaces, widening of cortical sulci, brain atrophy, enlargement of extraventricular spaces and spinal cord compression. With reference to the skeletal system, most important radiological findings include multiplex dysostosis, which is represented by several bone malformations found in the skull, hands, legs, arms and column. The abnormal storage of GAGs leads to liver and spleen enlargement; it also damages cartilage layers and synovial recesses in the joints. CONCLUSION: The aim of this pictorial essay is to describe the imaging findings of MPS, represented by skeletal and neurological features; skeletal X-ray and MR allow an assessment of the severity of disease, to plan medical and surgical therapy and to evaluate response to treatment. TEACHING POINTS: • To describe the imaging findings common to different types of MPS. • To describe multiplex dysostosis encountered in the axial and appendicular skeleton. • To evaluate neuroradiological features of MPS, including brain abnormal signal intensity and atrophy. • To evaluate important otorhinolaryngological problems, such as otitis media and airways obstruction.