Nimish Vakil

Correction of distortion in endoscope images

Images formed with endoscopes suffer from a spatial distortion due to the wide-angle nature of the endoscopes objective lens. This change in the size of objects with position precludes quantitative measurement of the area of the objects, which is important in endoscopy for accurately measuring ulcer and lesion sizes over time. A method for correcting the distortion characteristic of endoscope images is presented. A polynomial correction formula was developed for the endoscope lens and validated by comparing quantitative test areas before and after the distortion correction. The distortion correction has been incorporated into a computer program that could readily be applied to electronic images obtained at endoscopy using a desk-top computer. The research presented here is a key step towards the quantitative determination of the area of regions of interest in endoscopy.

Optical performance of electronic imaging systems for the colon

Electronic (video) endoscopes are a significant new development in gastroenterology, offering the potential of enhanced teaching and permanent storage of pictorial data. The primary concern of gastroenterologists is the resolution and color performance of these instruments, as these parameters have important bearings on the ability to discern pathological changes in mucosa. We sought to determine the resolution and color capabilities of electronic colonoscopes and compare them with a conventional fiber colonoscope. Resolution was determined using a standard test chart at various distances and the number of picture elements (a measure of resolution) was calculated. The mean number of picture elements was Fujinon (219), Fiber (172), Pentax (169), Toshiba (142), Olympus (140), and Welch Allyn (133). In close focus examination (target distances less than 1 cm), the Fujinon and Toshiba endoscopes had significantly higher resolution than the other instruments. Color was measured quantitatively using a standard color chart and a color analyzer. Color polygons were plotted for each endoscope on a reference chromaticity diagram. All systems had an acceptable overall performance but color was undersaturated with some systems. The optical performance of electronic endoscopes has improved considerably since the inception of electronic endoscopy.

The effects of synthetic human secretin on calcium carbonate solubility in human bile

This study sought to determine the effects of synthetic human secretin on ionized calcium and carbonate concentrations in human hepatic bile. Five patients with a nasobiliary drain in the right hepatic duct were studied. Three basal samples of bile were collected, each over a 15-minute period. Synthetic human secretin was then infused IV at 0.05 micrograms.kg-1.h-1 for 45 minutes followed by 0.5 micrograms.kg-1.h-1 for 45 minutes. Bile was sampled over 15-minute periods. To document return to baseline conditions, two further samples of bile were obtained over 15-minute periods 2 hours after the infusion was terminated. Bile acid concentration was determined by an enzymatic method; pH and PCO2 were measured with an automated analyzer. Total calcium was determined by inductively coupled plasma emission spectrometry and ionized calcium by an ion-specific electrode. Bicarbonate and carbonate concentrations were calculated using Henrys law and the Henderson-Hasselbalch equation. The fraction of bile sampled by the catheter was determined by Indocyanin Green recovery at the end of the experiment. Secretin caused an increase in bile flow and bicarbonate output. Bicarbonate concentrations increased from 26 +/- 3 mmol/L to 41 +/- 3 mmol/L (P less than 0.05), and chloride concentrations decreased. Mean bile acid concentrations declined significantly from 14.6 +/- 2 mmol/L to 4.7 +/- 1 mmol/L (P less than 0.05). Ionized calcium concentrations decreased from 0.7 +/- 0.005 mmol/L to 0.5 +/- 0.02 mmol/L (P less than 0.05) while pH increased significantly from 7.44 +/- 0.06 to 7.6 +/- 0.04 (P less than 0.05). Carbonate concentrations increased significantly from 0.15 +/- 0.02 mmol/L to 0.26 +/- 0.03 mmol/L, and the ion product for calcium carbonate increased significantly from 0.099 +/- 0.002 (mmol/L)2 to 0.135 +/- 0.015 (mmol/L)2 (P less than 0.05). Synthetic human secretin augments the ion product of calcium and carbonate in human hepatic bile, increasing the tendency for calcium carbonate precipitation.

Bile composition, microspheroliths, antinucleating activity, and gallstone calcification

This study examined if abnormalities in bile composition and antinucleating activity are associated with gallstone calcification. Nineteen controls without gallbladder disease and 42 patients with cholesterol stones were studied. Bile was obtained at surgery and analyzed for pH and PCO2, ionized calcium, and total calcium. The pH and carbonate concentrations of gallbladder bile were significantly higher in patients with calcified stones than in patients with noncalcified stones and in controls, resulting in significantly higher levels of the ion product in patients with calcified gallstones. Microspheroliths of calcium carbonate, seen on microscopic examination of bile, predicted stone calcification with a sensitivity of 86%, a specificity of 86%, and a predictive value of 86%. Bile from control subjects completely inhibited precipitation of calcium carbonate from a supersaturated solution, whereas bile from subjects with calcified and noncalcified gallstones did not. It is concluded that gallstone calcification is related to elevated bile pH and carbonate concentrations, resulting in an elevated ion production of calcium carbonate in gallbladder bile. In addition, bile from subjects with calcified and noncalcified gallstones lacks antinucleating activity for calcium carbonate.

Gas in gallstones: Quantitative determinations and possible effects on fragmentation by shock waves

The presence of gas in a gallstone can profoundly affect the ability of shock waves to fragment the stone by various mechanisms. In the present study, the aim was to determine the gas content of gallstones and determine if increasing the gas content of the stone affected the outcome of lithotripsy. Thirty human gallstones, transferred directly from gallbladder bile into sterile saline, were studied. The initial gas content of all stones was determined by differential weighing under saline before and after degassing. Eighteen gallstones were pairs; each pair was from a single patient and of similar size and composition. One gallstone of each of the pairs was exposed to air and the other was kept under saline. Then each of the paired gallstones was subjected to 1000 pulses at power level 3 (highest) in a Diasonics Therasonic lithotripter (Diasonics, Milpitas, CA). The volume of gas present at the beginning of the experiment in all groups of stones was 2.4 +/- 2.1 mm3, and 27% of all gallstones tested contained measurable amounts of gas initially. There was no significant difference in the volume of gas present in the paired stones at the beginning of the experiment (group A, 1 +/- 0.4 mm3; group B, 2 +/- 1 mm3). After group A stones were exposed to air, the gas content was significantly higher (36 +/- 18 mm3) than in the paired group B stones stored under saline (3 +/- 2 mm3; P less than 0.05). Stones exposed to air fragmented more easily than stones stored under saline. The mean number of pulses required to cause initial fragmentation was significantly lower in the group of stones exposed to air (22 +/- 7) compared with those stored under saline (610 +/- 139; P less than 0.05). The fragments were smaller and more numerous in the group of stones exposed to air than in those stored under saline. It is concluded that gas is present in some gallstones and that the efficacy of lithotripsy increases with increasing stone gas content. Our data suggest that alterations in the physical characteristics of gallstones can have profound effects on the outcome of lithotripsy.

The appreciation of colour in endoscopy

The perception of colour at endoscopy has been taken for granted since the discovery of the fibreoptic bundle and the advent of fibreoptic endoscopy. Fibreoptic and lens assemblies can distort the impression of colour by selectively absorbing some wavelengths of light. In the case of electronic endoscopes, the principal sensor is the charge-coupled device (CCD), a small microelectronic device that converts an image into a sequence of electronic signals which, after appropriate processing, are transformed into an image on the monitor screen. The image is therefore visualized as a mosaic of small images, one from each sensing element. Colour is synthesized by using sequential illumination using filters or by filters placed over the CCD. Fibre-endoscopes may alter colour by selectively transmitting certain portions of the visible spectrum, while electronic endoscopes are susceptible to errors due to poor calibration of the instrument and manipulation of the colour controls by endoscopists. Colour information provides the endoscopist with clues to the nature of the lesion and also a site for biopsy. In experimental situations, colour information has been used to determine blood flow and classify lesions. Much work needs to be done to define normal and abnormal colour in the gastrointestinal tract and to develop a standard terminology for colour nomenclature in endoscopy.

Improved biliary stenting using a balloon catheter and the combined technique for difficult stenoses

target and accurately define and position the bleeding site. To obtain a wider operative field, we developed a transparent ligating device with an operative field angle of 120 degrees and were able to successfully obtain the same endoscopic view as that without using the ligating device. Because the operative field mainly depends on the transparency of the hoods but not on the diameter of the opening, the non-transparent, original device has a narrow operative field. Even in patients with acute bleeding the bleeding site was as quickly and easily found with the transparent device as in patients treated without the device. The larger diameter of the device allows for larger esophageal varices or gastric varices to be ligated, but additional caution should also be paid to the possibility of accidentally ligating tissue deep in the submucosa. In conclusion,

Viscosity of human bile and its role in gallstone lithotripsy

Acoustic cavitation has been shown to play an important role in gallstone lithotripsy [Vakil et al., J. Acoust. Soc. Am. 90, 2340 (A) (1991)]. The bile surrounding a gallstone has been assumed to behave as a Newtonian fluid, with a viscosity independent of shear rate. Calculations show, however, that collapsing cavitation bubbles can produce shear rates nine orders of magnitude larger than those at which reported bile viscosities have been measured. Measurements of bile viscosity over a range of shear rates will be presented that show the non‐Newtonian behavior of human bile, whose effective viscosity increases with shear rate. These results have implications for models of the behavior of collapsing cavitation bubbles during gallstone lithotripsy, and suggest the usefulness of clinical medical procedures that modify patients’ bile viscosity prior to lithotripsy.

The role of gallstone and bile properties in stone breakup in lithotripsy.

The fragmentation mechanisms of gallstones exposed to both in vitro and in vivo lithotripsy with a Diasonics Therasonic piezoelectric litho‐ tripter were studied. Mechanical properties of stones, including air content, microhardness, acoustic attenuation, and shear and longitudinal wave speeds were measured and correlated with objective measures of fragmentation rates. These measures included the number of shocks to the development of the first crack, and the mass of the stone fragments larger than 3 mm in diameter remaining after 2000 shocks. The relationship of the volume of the surrounding liquid to the efficacy of litho‐ tripsy was studied for gallstones that were removed from the same patient. Finally, gallstones removed surgically from three patients who underwent lithotripsy and had incomplete fragmentation were examined under a scanning electron microscope for signs of damage. The results of these studies point to the combined roles of cavitation and stone properties as the principal determinants ...