Technique For Measurement Of Gradients Research Articles

"One stop" liver-focused endoscopy: EUS-guided portal pressure gradient measurement technique.

Referral for abnormal liver chemistry is one of the most frequently encountered reasons for visits to gastroenterologists and hepatologists, particularly given the versatility and vulnerability of the liver.1Kwo P.Y. Cohen S.M. Lim J.K. ACG clinical guideline: evaluation of abnormal liver chemistries.Am J Gastroenterol. 2017; 112: 18-35Crossref PubMed Scopus (395) Google Scholar Here, we present a 40-year-old man with class III obesity, essential hypertension, and hyperlipidemia who was referred for further diagnostic workup of his abnormal liver chemistry. Despite periods of significant weight loss, his liver transaminases had remained elevated over the prior 10 years (alanine aminotransferase 20-93 U/L, aspartate aminotransferase 20-71 U/L). Diagnostic workup included an abdominal ultrasound with evidence of hepatic steatosis and transient elastography (Fibroscan) that demonstrated a liver stiffness of 12.8 kPa, S3 (marked steatosis), and F3 (severe fibrosis). After reviewing the risks, benefits, and alternatives, the decision was made to perform an EGD to evaluate for stigmata of portal hypertension and an EUS to obtain a liver biopsy specimen and portal pressure gradient (PPG) measurements. The patient was intubated and remained in the supine position for the entirety of the procedure (Video 1, available online at www.VideoGIE.org). Initially, an EGD was performed, with no endoscopic evidence of varices or stigmata of portal hypertension. Next, the EUS examination was performed. The left lobe of the liver appeared diffusely hyperechoic, suggestive of steatosis. Real-time elastography was then performed on the left and right lobes of the liver to assess liver stiffness. The region of interest was positioned over the hepatic parenchyma, and an average of 10 measurements was obtained from each lobe of the liver. Mean liver stiffness was 11.5 kPa. The EchoTip Insight Portosystemic Pressure Gradient Measurement System (Cook Medical, Bloomington, Ind, USA) then was set up, involving a 25-gauge FNA needle, noncompressible tubing, a compact digital manometer, and heparinized saline solution. The middle hepatic vein was first identified and punctured using a transgastric approach. Once the needle tip was seen within the vessel, approximately 1 to 2 mL of heparinized saline solution was used to flush the needle. The pressure reading on the manometer was obtained and recorded once stable. This process was repeated a total of 3 times, including repeat flushes of heparinized saline solution to obtain the mean hepatic vein pressure measurement. Next, the umbilical portion of the left portal vein was identified, and using the aforementioned approach, the process was repeated 3 times to obtain the mean portal vein pressure measurement. The PPG was calculated by subtracting the mean hepatic vein pressure (16.4 mm Hg) from the mean portal vein pressure (23.4), which measured 7 mm Hg (consistent with preclinical portal hypertension). Last, EUS-guided liver biopsy was performed. Using a 19-gauge EUS–fine needle biopsy needle primed with heparin, we performed a transgastric puncture to obtain a sample from the left lobe of the liver. This process was then repeated using a transduodenal approach to obtain tissue from the right lobe of the liver. Liver core was then expressed onto a slide and sent to surgical pathology. The patient was discharged home after endoscopy without any adverse events. Surgical pathology from the liver biopsy revealed mild steatohepatitis with stage 0-1/4 fibrosis (Fig. 1). On outpatient follow-up, the patient was started on a stricter diet and exercise regimen for weight loss. EUS-guided applications have been increasing over the past decade; today, both endoscopy and echoendoscopy offer tremendous diagnostic information to help guide management in the workup of liver disease.2Samarasena J. Chang K.J. Endo-hepatology: a new paradigm.Endosc Ultrasound. 2018; 7: 219-222Crossref PubMed Scopus (6) Google Scholar In particular, EUS-guided liver biopsy has emerged as a safe and minimally invasive approach and an alternative to a percutaneous technique and now can be paired with EUS-guided real-time elastography and PPG measurement.3Huang J.Y. Samarasena J.B. Tsujino T. et al.EUS-guided portal pressure gradient measurement with a simple novel device: a human pilot study.Gastrointest Endosc. 2017; 85: 996-1001Abstract Full Text Full Text PDF PubMed Scopus (61) Google Scholar,4Shah A. Martinez I.C. Valentin N. et al.Efficacy and safety of endoscopic ultrasound-guided liver biopsies in parenchymal liver diseases: a systematic review and meta-analysis.Am J Gastroenterol. 2018; 113: S565-S566Crossref Google Scholar Here, we demonstrate the safety and technique of EUS-guided PPG measurement in the diagnostic workup of abnormal liver tests. Dr Sharaiha is a consultant for Boston Scientific and Apollo Endosurgery (terminated). All other authors disclosed no financial relationships. https://www.videogie.org/cms/asset/91a9cbf3-9569-4652-812c-a82edde33120/mmc1.mp4Loading ... Download .mp4 (65.17 MB) Help with .mp4 files Video 1“One stop” liver-focused endoscopy: EUS-guided portal pressure gradient measurement technique.

A rapid and robust gradient measurement technique using dynamic single-point imaging.

We propose a new gradient measurement technique based on dynamic single-point imaging (SPI), which allows simple, rapid, and robust measurement of k-space trajectory. To enable gradient measurement, we utilize the variable field-of-view (FOV) property of dynamic SPI, which is dependent on gradient shape. First, one-dimensional (1D) dynamic SPI data are acquired from a targeted gradient axis, and then relative FOV scaling factors between 1D images or k-spaces at varying encoding times are found. These relative scaling factors are the relative k-space position that can be used for image reconstruction. The gradient measurement technique also can be used to estimate the gradient impulse response function for reproducible gradient estimation as a linear time invariant system. The proposed measurement technique was used to improve reconstructed image quality in 3D ultrashort echo, 2D spiral, and multi-echo bipolar gradient-echo imaging. In multi-echo bipolar gradient-echo imaging, measurement of the k-space trajectory allowed the use of a ramp-sampled trajectory for improved acquisition speed (approximately 30%) and more accurate quantitative fat and water separation in a phantom. The proposed dynamic SPI-based method allows fast k-space trajectory measurement with a simple implementation and no additional hardware for improved image quality. Magn Reson Med 78:950-962, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Gradient measurement technique to identify phase transitions in nano-dispersed liquid crystalline compounds

Characterization and phase transitions in pure and 0.5% BaTiO3 nano-dispersed liquid crystalline (LC) N-(p-n-heptyloxybenzylidene)-p-n-nonyloxy aniline, 7O.O9, com-pounds are carried out using a polarizing microscope attached with hot stage and camera. We observed that when any of these images are distorted, different local structures suffer from various degradations in a gradient magnitude. So, we examined the pixel-wise gradient magnitude similarity between the reference and distorted images combined with a novel pooling strategy – the standard deviation of the GMS map – to determine the overall phase transition variations. In this regard, MATLAB software is used for gradient measurement technique to identify the phase transitions and transition temperature of the pure and nano-dispersed LC compounds. The image analysis of this method proposed is in good agreement with the standard methods like polarizing microscope (POM) and differential scanning calorimeter (DSC). 0.5% BaTiO3 nano-dispersed 7O.O9 compound induces cholesteric phase quenching the nematic phase, which the pure compound exhibits.

STROPE: A new species density gradient measurement technique

In this paper, we have demonstrated both theoretically and experimentally a new diagnostic technique for measuring directly the density gradients of a species. This striation slope technique has the virtues of being relatively simple in both conception and implementation, for although it uses the near-resonance refractive-index properties of the atoms or ions of interest it does not require an interferometric setup or a precisely tuned laser. Indeed, it only requires a broadband well-collimated source that spectrally straddles a resonance doublet of the species of interest. Consequently, this technique could be used at short wavelengths where laser interferometry is impractical.