Development of low cost instrumentation for non-invasive detection of Helicobacter pylori

Abstract

A new clinical diagnostic instrument for urea breath test (UBT) based non-invasive detection of Helicobacter Pylori is presented here. Its compact and low cost design makes it an economical and commercial alternative for the more expensive Isotope Ratio Mass Spectrometer (IRMS). The instrument is essentially a two channel non-dispersive IR spectrometer that performs high precision ratio measurements of the two carbon isotopomers ( 12 CO 2 and 13 CO 2 ) present in exhaled breath. A balanced absorption system configuration was designed where the two channel path lengths would roughly be in the ratio of their concentrations. Equilibrium between the transmitted channel intensities was maintained by using a novel feedback servo mechanism to adjust the length of the 13 C channel cell. Extensive computational simulations were performed to study the effect of various possible interferents and their results were considered in the design of the instrument so as to achieve the desired measurement precision of 1‰. Specially designed gas cells and a custom made gas filling rig were also developed. A complete virtual interface for both instrument control and data acquisition was implemented in LABVIEW. Initial tests were used to validate the theory and a basic working device was demonstrated.

Optical gas sensing: a review

“…These fringes can be the limiting source of uncertainty as they are liable to drift with temperature changes and can be indistinguishable from the spectral signature of the gas absorption lines. Because gas lines can be inherently narrow, interference fringes can also be a significant performance-limiting factor in broadband absorption measurements [23] .…”

“…Ideally, the two beams will be well matched in all respects other than the absorption (or not) of the reference gas. However, in practice some separation of the beams becomes inevitable such that researchers need to correct for minor differences in reflectivity of cell windows or interference fringes generated by low finesse etalons in the system [23] . Such differences can be responsible for the limiting signal to noise ratio and drift effects in these systems.…”

“…The advantages of this system were a reduced reliance on bulk optics and a very small reference cell volume (5 μl). Problems with the correlation approach can occur with linearity and calibration [137] , and with gas selectivity, should a proportion of the target gas lines overlap with those of other species [23] . Changes in atmospheric temperature and pressure in either the sample or reference cells can affect the linewidth of narrow gas absorption lines and therefore introduce calibration errors [23] .…”

“…Problems with the correlation approach can occur with linearity and calibration [137] , and with gas selectivity, should a proportion of the target gas lines overlap with those of other species [23] . Changes in atmospheric temperature and pressure in either the sample or reference cells can affect the linewidth of narrow gas absorption lines and therefore introduce calibration errors [23] . A further problem is the need to maintain a reference cell with a fixed concentration of the target gas that is stable over the lifetime or calibration interval of the instrument, ruling out the use of reactive or unstable gases.…”