Quantification of Liver Steatosis

The prevalence of non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) is increasing in the modern world. Fatty infiltration of the liver can be assessed by standard ultrasound, by controlled attenuation parameter (CAP) using the FibroScan device or, more recently, by ultrasound systems that evaluate the attenuation in the liver. Standard ultrasound (US) for steatosis evaluation was used for a long time as a semi-quantitative method for steatosis assessment in the liver. A “bright liver” with “posterior attenuation” is the typical US sign of liver steatosis. Considering the attenuation severity, steatosis is subjectively graded as mild, moderate or severe. Using the kidney/liver ratio, a more accurate evaluation can be made. Controlled attenuation parameter (CAP) was developed by EchoSens, France, and implemented into the FibroScan device. CAP manages an objective assessment of steatosis severity with rather good accuracy. More recently, ultrasound companies such as Hitachi, General Electric and Canon, implemented in their system algorithms which allow an objective assessment of liver steatosis, using the attenuation of the ultrasound beams

2D Shear Wave Elastography for Liver Fibrosis Evaluation

2D shear wave elastography is a technique embedded in ultrasound machines which allows the interrogation of the tissue by acoustic radiation force impulses induced into the tissues by focused ultrasonic beams and captures the propagation of resulting shear waves in real time. Elasticity is displayed using a color-coded image superimposed on a B-mode image, and at the same time, a quantitative estimation of liver stiffness (LS) can be performed in a certain region of interest (ROI). The published data showed a real value of this method for liver stiffness estimation in patients with chronic hepatitis. It has the following advantages: it is integrated into standard ultrasound systems; it is a real-time elastographic method; and it is also feasible in patients with ascites and with large and adjustable size of the ROI that will be evaluated

Liver Fibrosis Assessment by Point Shear-Wave Elastography Techniques

Point shear-wave elastographic (pSWE) techniques use acoustic radiation force impulse (ARFI) to stimulate the liver tissue and to generate shear waves that propagate into the liver. The shear-wave velocity (SWV) increases with the severity of fibrosis. The first type of pSWE was Virtual Touch Quantification (VTQ) developed by Siemens, followed by ElastPQ by Philips, and nowadays pSWE is available on other systems (Hitachi, Esaote, Samsung). To evaluate liver fibrosis by pSWE, ten valid measurements are performed in the right liver lobe; a median value is calculated, with the results expressed in meters/second or in kilopascals (kPa) (if the operator chooses). VTQ is a reproducible method, the intraclass correlation coefficient (ICC) for inter- and intraobserver measurements ranging from 0.81 to 0.87. Confounding factors for VTQ are non-fasting conditions, elevated aminotransferases, congestive heart failure, and extrahepatic cholestasis. In patients with chronic hepatopathies, the AUROCs for predicting significant fibrosis range between 0.75 and 0.85 and for predicting cirrhosis between 0.85 and 0.95. There were promising results regarding the value of VTQ to predict liver cirrhosis complications, especially portal hypertension. ElastPQ is a newly developed point shear-wave elastographic method (from Philips). Only few data were published but with promising results

Design and practical implementation of a fractional order proportional integral controller (FOPI) for a poorly damped fractional order process with time delay

One of the most popular tuning procedures for the development of fractional order controllers is by imposing frequency domain constraints such as gain crossover frequency, phase margin and iso-damping properties. The present study extends the frequency domain tuning methodology to a generalized range of fractional order processes based on second order plus time delay (SOPDT) models. A fractional order PI controller is tuned for a real process that exhibits poorly damped dynamics characterized in terms of a fractional order transfer function with time delay. The obtained controller is validated on the experimental platform by analyzing staircase reference tracking, input disturbance rejection and robustness to process uncertainties. The paper focuses around the tuning methodology as well as the fractional order modeling of the process' dynamics