Novel Approaches in the Diagnostics of Ear-Nose-Throat Diseases Using High-Resolution THz Spectroscopy
, Elena Domracheva 1,2, Kseniya Glushkova 1,3, Roman Larin 1,4 and Maria Shakhova 1,5Round 1
Reviewer 1 Report
First of all, I must say that I can only evaluate the technical side of the work under review. I cannot assess the use of the device in medical diagnostics because I do not have sufficient competence for that.
From a technical point of view, the work is new and important. In the 118 - 178 GHz frequency range, the authors identified about 20 species of absorption lines, the number and intensity of which differed in mucosal samples taken from healthy and sick patients. This is roughly the same amount of material as was identified in exhaled air in previous work using higher frequencies of 250-350 GHz (N. Rothbart et.al., Sensors, 19, 2719 (2019). It was necessary to make certain comparisons with the above-mentioned work: for example, spectral and temporal resolution, the sensitivity of determining the absorption coefficient, etc. By the way, it remains unclear from the text (lines 128-129) what is meant by ".. sensitivity of the spectrometer" - the absorption coefficient or its linewidth. The English of the manuscript also needs some improvement. The adjective built-in is used by the author as a verb (lines 144-145); verb tenses should also be adjusted in several places.
So, as far as the purely technical content of the article is concerned, it could be published after minor corrections.
Author Response
Answers for reviewer N1
From a technical point of view, the work is new and important. In the 118 - 178 GHz frequency range, the authors identified about 20 species of absorption lines, the number and intensity of which differed in mucosal samples taken from healthy and sick patients. This is roughly the same amount of material as was identified in exhaled air in previous work using higher frequencies of 250-350 GHz (N. Rothbart et.al., Sensors, 19, 2719 (2019). It was necessary to make certain comparisons with the above-mentioned work: for example, spectral and temporal resolution, the sensitivity of determining the absorption coefficient, etc.
The sensitivity of spectrometer proposed by reviewer was presented in ref 30 of proposed work (N. Rothbart et.al., Sensors, 19, 2719 (2019)). The ref.30 is Schmalz, K.; Rothbart, N.; Eissa, M.H.; Borngraber, J.; Kissinger, D.; Hubers, H.-W. Transmitters and receivers in SiGe BiCMOS technology for sensitive gas spectroscopy at 222–270 GHz. AIP Adv. 2019, 9, 015213. Here the sensitivity at concentration for “OCS and Acetonitrile were approximately 2 – 3 ppm” for the absorption lines at the a frequencies of 279.685 GHz (OCS) and 294.251 GHz (Acetonitrile) with the integrated absorption coefficients of these lines (1.21*10-21 cm and 7.07*10-21 cm). The integrated intensity in nm2*MHz (the lg of integrated intensity was presented in databases of jpl or cologne database) is recalculated to integrated intensity in cm as presented in HITRAN database as follows: I[nm2*MHz] =10lgI* (10-7)2cm2*1Hz*106 =10lgI *10-14cm2*106Hz/3*1010cm/s =10lgI*0.333*10-18cm. For comparison we must take the lines with lg I =-3 or more. The H2S absorption line with characteristics (f=168762.7624 MHz and lgI= -2.8376) has the necessary integrated intensity. The absorption coefficient for pure H2S at working pressure 5*10-2 torr (at these conditions we can considered that this working pressure is equal the partial pressure of H2S) the absorption coefficient is about 0.06 cm-1 (alfa=151.194*10lgI*p/Δνdoppl) (see the description of “Submillimeter, Millimeter, and Microwave Spectral Line Catalog” (https://spec.jpl.nasa.gov/ftp/pub/catalog/doc/catintro.pdf) for minimal absorption coefficient (which can be registered) of 5*10-10 the minimal detected concentration at the same working pressure (5*10-2 torr) of mixture is about 8.3 ppb (from proportion). At the second case (for minimal absorption coefficient of 3*10-9cm-1) the minimal detected concentration is about 50 ppb. But the most of absorption lines in 118-178 GHz detected in gas mixture under study have the lgI at the level of -4 or-5. For those lines the minimal concentration would be at the level of 100 ppb -1¸10 ppm. The last levels of concentrations are better or comparable with the sensitivity (relatively of concentration) in the works proposed by reviewer.
The manuscript is added now by next parts.
One of the human excretions investigated with using THz high-resolution spectroscopy is exhaled breath. The high-resolution spectrometer (with frequency range from 220 to 330 GHz) in scanning mode was used with revealing the 21 different molecular species in exhaled breath samples of 3 volunteers [10]. But ENT-organs were not studied with using THz high-resolution methods earlier.
For phase switching spectrometer:
If the absorption lines have integrated intensity at the level of 0.001 nm2*MHz (the lgI=-3 presented in database [11,12]) as for H2S (f=168762.7624 MHz, lgI=-2.8376) [11], the concentration sensitivity (for absorption coefficient sensitivities of spectrometers presented in our work) is about 8.3 ppb (for for minimal absorption coefficient of 5*10-10 cm-1) and 50 ppb (for minimal absorption coefficient of 3*10-9cm-1). The most of absorption lines in 118-178 GHz detected in gas mixture under study have the lgI at the level of -4 or-5. For those lines the minimal concentration would be at the level of 100 ppb -1¸10 ppm. The levels of concentration sensitivities are better (for H2S) or comparable (for some other substances) with the sensitivity (relatively of concentration) in [10,13]
For fast sweep spectrometer:
“The sensitivities of concentration are 1.6 ppm¸250ppb for H2S (f=168762.7624 MHz, lgI=-2.8376) [11] for this case.”
The references have been added by two items (10 and 13) now.
By the way, it remains unclear from the text (lines 128-129) what is meant by ".. sensitivity of the spectrometer" - the absorption coefficient or its linewidth.
The sensitivity of the spectrometer means the minimal absorption coefficient. The sentence is added by explanation:
“…the sensitivity (minimal absorption coefficient) of the phase switching spectrometer reaches 5*10-10cm-1, and in the second case 3*10-9cm-1”.
The adjective built-in is used by the author as a verb (lines 144-145).
The phrase is changed now:
The radiation source has a built-in module– a commercial reference frequency synthesizer LMX2594, used as the reference oscillator
The conclusions have been added now by next part:
In the spectra of the polypous tissues of the sphenoid sinus for such substances as acetone, hydroxyacetone, methylbutironitrile, acetonitrile, pentannitrile and furan many times more absorption lines correspond than for relatively healthy mucosas and cysts of the maxillary sinus. A similar analysis was performed for cyst tissue and potential markers of pathology were identified, which do not coincide with the markers of the polyp. These are acetic and acrylic acids, methanol, propanediol, propanal, glycroaldehyde, butyronitril, methylmercaptan and azole
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript describes an attempt to analyze the metabolites composition of the ear-nose-throat (ENT) tissues using high-resolution THz spectroscopy, and compare the metabolites formed during thermal decomposition of relatively healthy mucosa polyps and cysts.
Perhaps the authors may disagree with me, but as far as I’m concerned, this work seems not well structured a long with some statements not in every way scientifically understandable. From my opinion, the work will need an exhaustive and careful review by the authors to become an acceptable input and be welcomed by the topic’s research community and the wide science research and readership.
The conclusions, although a bit in accordance with the carried-out work, it must be extensively improved. I placed some annotations and suggestions throughout the manuscript to be considered thoroughly by the authors.
Comments for author File: 
Comments.pdf
Author Response
Answers for reviewer N2
Previous version: The chemical compounds were identified with using
Now: The chemical compounds were identified using
Previous version: In all samples there are methanol…
Now: In all samples there are such substances as methanol,…
I suggest this abstract to be double-checked and eventually be re-edited.
Some corrections to abstract are carried out.
94th line “The goal of the work is to use high-resolution spectrometers on non-stationary effects…” - This part lacks in the abstract
Now: The next sentence in abstract “The goal of the study is analyzing the metabolites composition of the ear-nose-throat (ENT) tissues by the high resolution THz spectroscopy based on nonstationary effects and comparing metabolites formed during thermal decomposition of relatively healthy mucosas, polyps and cysts” is added by the words about nonstationaty effects.. .
100th line – “nonstationary “ - Non-stationary as was above written
All variants of “non-stationary” or “nonstationary” are changed to “nonstationary”
116th-117th lines “This signal is recorded … then arrived” - Directed/sent
The sentence now is “This signal is recorded … then sent…”
122nd line “Figure 1. The scheme of phase switching spectrometer” - I suggest a bit more description on the schematic
Now: “Figure 1. The scheme of phase switching spectrometer, where PC is personal computer, ADC – is analog-to-digital converter” and “horns “, “inlet” and “pumping out” are labeled in the figure.
131st lime – “2-mm spectrometer” - ???
The frequency range of 118-178 GHz matches the wavelength range of 2 millimeters. Now the values for frequency range of radiation source based on BWO are presented.
134th line “The scheme of the fast frequency sweep spectrometer is shown in Fig.2.” - How is the operation carried out regarding the samples cell? Are you firstly extracting the air from and then the gas sample, right?
The sample of tissue under study was put in a flask connected via vacuum valve to a measuring cell pre-evacuated to 0.0005 mbar. The sample was dehydrated under low vacuum pressure, then the flask was pre-evacuated to 0.005 mbar. After that the flask was heated up o 200–250°C and the vapors and products of thermal decomposition of the sample was let into the measuring cell increasing the pressure up to about 0.05 mbar (working pressure).
This part was presented in manuscript three paragraphs later (the 156th-159th lines). But the sentence about dehydration of sample and next pre-evacuation is added now to manuscript.
136th line “Figure 2. The scheme of fast frequency sweep spectrometer” - The same as on the above schematic
Now: ” Figure 2. The scheme of fast frequency sweep spectrometer, where PC is personal computer, ADC – is analog-to-digital converter.” and “horns “, “inlet” and “pumping out” are labeled in the figure.
140nd line “The bands of frequency are controlled by the PC”
Now: “The frequency bands are controlled by the PC”
142nd line “This signal is recorded and then arrived to the amplifier” - With the radiation contained in the mixture ???
The signal from the radiation source and the signal after interaction with molecules go to detector. If the interaction with molecules is presented with absorption of radiation, the power received by detector is changed.
There are not any changes of text here.
Besides all changes above, the conclusions have been added now by next part:
In the spectra of the polypous tissues of the sphenoid sinus for such substances as acetone, hydroxyacetone, methylbutironitrile, acetonitrile, pentannitrile and furan many times more absorption lines correspond than for relatively healthy mucosas and cysts of the maxillary sinus. A similar analysis was performed for cyst tissue and potential markers of pathology were identified, which do not coincide with the markers of the polyp. These are acetic and acrylic acids, methanol, propanediol, propanal, glycroaldehyde, butyronitril, methylmercaptan and azole
The references have been added by two items (10 and 13)
Author Response File: Author Response.docx
