The purpose of this study was to evaluate the diagnostic accuracy of the ultrasound-guided attenuation parameter (UGAP) using the LOGEQ E10 for hepatic steatosis in non-alcoholic fatty liver disease (NAFLD) patients and directly compare UGAP with attenuation imaging (ATI) and controlled attenuation parameter (CAP). We prospectively analyzed 105 consecutive patients with NAFLD who underwent UGAP, ATI, CAP, and liver biopsy on the same day between October 2019 and April 2021. The diagnostic ability of the UGAP-determined attenuation coefficient (AC) was evaluated using receiver operating characteristic (ROC) curve analysis, and its correlation with ATI-determined AC values or CAP values was investigated. The success rate of UGAP was 100%. The median IQR/med obtained by UGAP was 4.0%, which was lower than that of ATI and CAP (P < 0.0001). The median ACs obtained by UGAP for grades S0 (control), S1, S2, and S3 were 0.590, 0.670, 0.750, and 0.845 dB/cm/MHz, respectively, demonstrating a stepwise increase with increasing hepatic steatosis severity (P < 0.0001). The areas under the ROC curve of UGAP for identifying ≥ S1, ≥ S2, and S3 were 0.890, 0.906, and 0.912, respectively, which were significantly better than the results obtained with CAP for identifying S3. Furthermore, the correlation coefficient between UGAP-AC and ATI-AC values was 0.803 (P < 0.0001), indicating a strong relationship. Our results indicate that UGAP has high diagnostic accuracy for detecting and grading hepatic steatosis in patients with NAFLD.

Liver fat is one of the main clinical features in chronic liver disease, and the number of fatty liver patients is increasing as the prevalence of obesity and metabolic syndrome increases globally. Noninvasive and quantitative assessment of liver fat content was made possible by recent technological advances. Attenuation coefficient (ATT) measurement is a noninvasive and quantitative liver fat measurement method used in clinical practice. The ATT value is significantly associated with histological steatosis grade. The diagnostic accuracy of ATT for histological steatosis grade is equivalent to controlled attenuation parameter (CAP), and ATT has a lower measurement failure rate than CAP because ATT can be measured on a B-mode image with the exact location of the region of interest. Furthermore, ATT measurement has high interobserver reproducibility. Since ATT measurement and other ultrasound-based modalities for liver fat quantification are easy to perform and inexpensive, these modalities are suitable for point-of-care and screening. Although emerging data suggest that quantitative liver fat content and its changes over time may be associated with disease progression in nonalcoholic fatty liver disease, the association between ATT and disease progression has not been evaluated yet. Therefore, further investigation and validation studies are necessary to strengthen the clinical significance of ATT measurement in chronic liver disease.

Reflecting the growing interest in early diagnosis of nonalcoholic fatty liver disease in recent years, the development of noninvasive and reliable fat quantification methods is required. Fat quantification by magnetic resonance imaging (MRI), especially MRI-derived proton density fat fraction (MRI-PDFF) obtained by quantitative chemical shift imaging such as the multi-point Dixon method, is highly correlated with histological evaluation and fat quantification with MR spectroscopy (MRS). In recent years, MRI-PDFF has been increasingly used as a reference standard for image-based fat quantification instead of MRS because it is possible to evaluate the whole liver with a single breath-hold. Furthermore, recent advances in MR imaging have led to the application of multiparametric MRI for the diagnosis of nonalcoholic fatty liver disease with specific liver tissue quantification of fat, iron, and fibrosis. One of the advantages of multiparametric MRI is that whole organ imaging to exclude sampling variability and organ-specific tissue quantification can be done simultaneously. Therefore, multiparametric MRI methods offer an attractive option for noninvasive and comprehensive liver assessment beyond the quantitative assessment of liver steatosis. In this review article, we mainly focus on a technical explanation and clinical interpretation of MRI-PDFF in the quantitative assessment of liver steatosis. Furthermore, we would like to mention future perspectives of MR imaging of the liver in relation to elastography and other specific multiparametric MRI methods such as R2* and T1 mapping.

Reflecting the growing interest in early diagnosis of non-alcoholic fatty liver disease in recent years, the development of noninvasive and reliable fat quantification methods is needed. Dual-energy computed tomography (DE-CT) is a quantitative diagnostic imaging method that estimates the composition of the imaging target using a material decomposition technique based on the X-ray absorption characteristics peculiar to substances from DE-CT scanning using X-rays generated with different energies (tube voltage). In this review article, we first explain the basic principles and technical aspects of DE-CT. Then, we will present the current diagnostic ability of DE-CT and the factors influencing the quantitative evaluation of liver steatosis using DE-CT as compared to multi-modal methods including ultrasound and magnetic resonance imaging-based methods. In brief, DE-CT may have comparable diagnostic performance to the modern US-based liver fat measurement methods. However, the current material decomposition technique using DE-CT does not seem to have added value to the simple quantitative assessment of liver steatosis, because DE-CT measurement does not improve the accuracy of fat quantification over conventional single-energy computed tomography (SE-CT) attenuation. The most significant influencing factor for the quantitative assessment of liver steatosis using DE-CT can be hepatic iron deposition. An iron-specific multi-material decomposition algorithm correcting for the influences of iron in the liver has been under development. The current material decomposition algorithm can still have added value in a specific situation such as the quantitative assessment of liver steatosis using contrast-enhanced DE-CT. However, there is a lack of evidence for the influence of liver fibrosis in the quantitative assessment of liver steatosis using DE-CT.

Although new ultrasound (US) methods able to quantitatively assess liver fat content have been recently developed, B-mode US is still the major method for detecting liver steatosis during medical checkups. However, some pathological cases yield false-positive or false-negative liver steatosis results using B-mode US. In addition, histologically, the degree of fat deposits and the size of fat droplets in the liver can affect the sensitivity and specificity of the diagnosis of liver steatosis using B-mode US. As B-mode US evaluation of fatty liver relies on operator expertise, the operator should be aware that there are some cases of liver steatosis that are difficult to evaluate with B-mode US. Here, we describe the pathological findings of liver steatosis that is difficult to evaluate with US.

Papillary cystadenoma of the epididymis (PCE) is a rare benign tumor of the epididymis. It occurs in association with von Hippel-Lindau disease (VHLD), an autosomal manifestation of the disease, and also occurs solitarily. However, there have been few imaging reports, and in the absence of a history of VHLD, a preoperative diagnosis is difficult. As such, orchiectomy is often performed. In this report, we describe a case of PCE that was thought to be solitary, focusing on ultrasound images. The patient was a man in his 70s. A mass with hypervascularity was incidentally detected in the left scrotum on contrast-enhanced computed tomography (CT), suggesting a right inguinal hernia. On ultrasonography, the mass was located adjacent to the cephalic side of the left testis, with clear boundaries in B-mode, and the interior was isoechoic to the testis, with a high echo area with acoustic shadows that appeared to be calcification. Color Doppler showed abundant color in most of the mass, and although PCE was considered as a possible diagnosis, a primary sarcoma in the paratesticular area could not be ruled out, and high orchiectomy was performed. Histopathologically, the tumor was a papillary growth of cells with pale cytoplasm and chromatin-enhanced, similarly round or slightly distorted nuclei. The possibility of metastasis from clear cell renal cell carcinoma and PCE was considered. Ultimately, PCE was clinically diagnosed due to absence of a history of renal cell carcinoma.