Quantitative ultrasound (QUS) methods have been widely used for soft tissue characterization. Spatial resolution (i.e. ultrasound frequency) is an important factor for QUS methods. In a previous study, a double Nakagami (DN) distribution model to echo signals from fatty livers using a 15 MHz transducer was used to permit fine-resolution QUS. This study used a filtering approach to quantify steatosis progression using three QUS parameters obtained by fitting a DN distribution model to experimental envelope data. The filter was designed using QUS parameters obtained from three healthy liver. A strong correlation ( r = 0.96, p < 0.001) was found between histologically quantified steatosis percentage and the percentage of the liver having non-healthy liver features. This approach was able to successfully diagnose fatty livers (>20% steatosis percentage) in a dataset of 12 livers ranging from 0% to 90% steatosis.

Ultrasound imaging is a first-line assessment tool for hepatic steatosis. Properties of tissue microstructures correlate with the statistical distribution of ultrasound backscattered signals, which can be described by the Nakagami distribution (a widely adopted approximation of backscattered statistics). The double Nakagami distribution (DND) model, which combines two Nakagami distributions, was recently proposed for using high-frequency ultrasound to analyze backscattered statistics corresponding to lipid droplets in the fat-infiltrated liver. This study evaluated the clinical feasibility of the DND model in ultrasound parametric imaging of hepatic steatosis by conducting clinical experiments using low-frequency ultrasound dedicated to general abdominal examinations. A total of 204 patients were recruited, and ultrasound image raw data were acquired using a 3.5 MHz array transducer for DND parametric imaging using the sliding window technique. The DND parameters were compared with hepatic steatosis grades identified histologically. A receiver operating characteristic (ROC) curve analysis was used to evaluate the diagnostic performance. The results indicated that DND parametric imaging constructed using a sliding window with the side length of five times the pulse length of the transducer provided stable and reliable DND parameter estimations and visualized changes in the backscattered statistics caused by hepatic steatosis. The DND parameter increased with the hepatic steatosis grade. The areas under the ROC curve for identifying hepatic steatosis were 0.76 (≥mild), 0.81 (≥moderate), and 0.82 (≥severe). When using low-frequency ultrasound, DND imaging allows the clinical detection of hepatic steatosis and reflects information associated with lipid droplets in the fat-infiltrated liver.

In previous studies, the double-Nakagami (DN) model has been proposed for fatty liver assessment and applied to in vivo rat livers and clinical data sets. The healthy liver structure filter (HLSF) method, which extracts non-healthy areas using two DN parameters, has also been proposed. In this paper, we first verify the accuracy of the DN model and the HLSF method for acoustic fields at 15 and 5 MHz, which were reproduced using numerical simulation. We then apply the method to clinical data sets of livers observed using a frequency of 3 MHz and investigate the method’s clinical usefulness. A positive correlation ( r = 0.28 ) was found between the ratio of the non-healthy area and fat mass. Although the results were inferior to the results produced using 15 MHz ultrasound ( r = 0.96 ), we found that it was possible to detect the difference between a normal liver and a fatty liver even at a lower frequency.

The elasticity of biological tissues is one of the physical characteristics of tissues and has attracted attention as a clinical diagnostic parameter. The elasticity can be determined on the microscopic scale with speed of sound (SoS) measurements using acoustic microscopy. In SoS measurements, a thin-sliced section is attached to a glass slide in the same manner as a light microscopic specimen. There are two main methods for preparing thin sections: paraffin-embedding and frozen-section. The frozen-section method requires fewer processing steps from sectioning to measurement and is considered to reduce artifacts in the sample compared with the paraffin-embedding method. Both methods need fixatives to keep tissue structures. Many reports of measurements using frozen sections are focused on soft tissues with relatively high protein contents. In this study, we determined the SoS in thin sections of four types of organs (brain, heart, liver, and kidney) prepared using two different methods (paraffin-embedding and frozen-section) and four different chemical fixatives (formalin, Karnovsky fixative (KF) 0.5% and 2.0% glutaraldehyde, and ethanol). The SoS in heart and liver samples prepared using KF showed good agreement with reported values for raw samples. For samples fixed with KF, the SoS increased as the glutaraldehyde concentration increased from 0.5% to 2.0%. A brain tumor sample was processed with KF 0.5%, and the SoS in the tumor was significantly higher than that in the non-tumor area. The results confirmed that it is possible to measure the SoS in brain samples with low protein contents using appropriate fixatives.

We compared the evaluation accuracy of amplitude envelope statistics under the transmission and reception conditions of compounded plane wave imaging (CPWI) and focused beam imaging (FBI). In a basic study using a homogeneous phantom, we found that the amplitude gradient in the depth direction and the point spread function in the lateral direction spread in the FBI reduced the accuracy of evaluation in amplitude envelope statistics. On the other hand, CPWI showed a more stable evaluation than FBI because of the elimination of sound field characteristics. In CPWI, the multi-Rayleigh model discriminated signals from two types of scatterer with high accuracy in the evaluation using phantoms mimicking fatty liver. It was confirmed that the combination of CPWI and the multi-Rayleigh model is effective for detecting early fatty liver disease. The results show that CPWI is effective for improving the robustness of amplitude envelope statistics.

Background: Clinically insignificant hemolytic anemia is occasionally a complication of prosthetic valve replacement. However, hemolysis related to kinked grafts is a very rare complication after central repair for acute aortic dissection. Case presentation: A 42-year-old man had undergone replacement of the ascending aorta and a root repair for type A aortic dissection 6 months previously. Laboratory data showed mild hemolysis 5 months later, and he began to complain of fatigue on exertion. The serum hemoglobin level reduced to 8.6 g/dL, and lactate dehydrogenase levels increased to 3071 IU/L with gross change in urine color, indicating hemoglobinuria. We diagnosed mechanical hemolytic anemia caused by a kinked graft and planned a repeat operation. The kinked graft was resected and graft-graft anastomosis was performed. Postoperatively, the clinical course was uneventful, and the hemolytic anemia completely resolved. Conclusion: We herein report a case of hemolytic anemia caused by kinking of the graft 6 months after acute aortic dissection repair. The diagnosis was swiftly made, and the patient was successfully managed with redo surgery.