Raman Spectroscopy for Urea Breath Test

Abstract

The urea breath test is a non-invasive diagnostic method for Helicobacter pylori infections, which relies on the change in the proportion of ¹³CO₂ in exhaled air. Nondispersive infrared sensors are commonly used for the urea breath test in laboratory equipment, but Raman spectroscopy demonstrated potential for more accurate measurements. The accuracy of the Helicobacter pylori detection via the urea breath test using ¹³CO₂ as a biomarker is affected by measurement errors, including equipment error and δ¹³C measurement uncertainty. We present a Raman scattering-based gas analyzer capable of δ¹³C measurements in exhaled air. The technical details of the various measurement conditions have been discussed. Standard gas samples were measured. ¹²CO₂ and ¹³CO₂ calibration coefficients were determined. The Raman spectrum of the exhaled air was measured and the δ¹³C change (in the process of the urea breath test) was calculated. The total error measured was 6% and does not exceed the limit of 10% that was analytically calculated.

Keywords: Helicobacter pylori; Raman spectroscopy; exhaled breath; urea breath test; δ13C.

Figure 1

The scheme of the gas analyzer (not in scale): 1—laser; 2—objective; 3—gas cell; 4—f-matcher; 5—spectrometer; 6—specimen; 7—pressure boosting system; and 8—vacuum pump.

Figure 2

Example of Raman spectrum–Lorentz contour fit: dots—measured values; line—Lorentz function.

Figure 3

Influence of SNR on a relative standard deviation of volume fraction for two methods: via intensity calculation (blue line) and via the area measurement calculation (orange line).

Figure 4

Correspondence of absolute error of the ¹³CO₂ volume fraction measurement from change in δ¹³C and the CO₂ volume fraction in exhaled air.

Figure 5

Noise standard deviation as a function of exposure time via different temperatures of CCD camera, points—experimental results, line—fit with Equation (6).

Figure 6

SNR as a function of exposure time via different temperatures of CCD camera.

Figure 7

Influence of spectral broadening on signal measured, red stars—with correction of spectral broadening, black dots—without correction of spectral broadening.

Figure 8

Raman spectrum of the exhaled air: (a) the broad range; (b) ¹²CO₂ and ¹³CO₂ peaks.

Figure 9

Results of measuring volume fraction in base and diagnostic probes for: (a) ¹²CO₂; (b) ¹³CO₂.