Fusion Visualization Technique to Improve a Three-Dimensional Isotope-Selective CT Image Based on Nuclear Resonance Fluorescence with a Gamma-CT Image

Round 1

Reviewer 1 Report

1. A section description should be added to the Introduction
2. The introduction section is not very readable, it should introduce the background first, then describe the current status of the study and summarize it, and finally what the paper is going to do.
3. I was expecting a sentence or two from the author about the significance of visualization, especially scientific visualization, for example (https://doi.org/10.1080/13658816.2020.1833016;https://doi.org/10.1016/B978-008044531-1/50437-1

Author Response

Response to Reviewer 1 Comments

First and foremost, we would like to express our grateful to the reviewer 1 for his/her thorough reading of the manuscript. We also thank him/her for appreciating the value of Nuclear Resonance Fluorescence based computed tomography imaging with a quasi-monochromatic Laser Compton Scattering gamma-ray beam for its significant advancement in nuclear engineering by the non-destructive inspection of the hidden isotopic compositions of target materials and the isotope selectivity assessment. We agree with almost all suggestions, and we have revised our manuscript accordingly to improve the manuscript's quality. Our manuscript has undergone English language editing by MDPI. The text has been checked for correct use of grammar and common technical terms and edited to a level suitable for reporting research in a scholarly journal. The manuscript ID for the English editing service is 36180. A detailed point-by-point answer to all comments can be found below (reviewers ‘comments in black, our replies in red). We hope the reviewer approve of our responses to his/her feedback.

Sincerely,

Khaled Ali,

Heishun Zen,

Hideaki Ohgaki,

Toshiteru Kii,

Takehito Hayakawa,

Toshiyuki Shizuma,

Masahiro Katoh.

Yoshitaka Taira,

Masaki Fujimoto,

Hiroyuki Toyokawa.

Point 1: A section description should be added to the Introduction.

Response 1:

• We added a description paragraph on section 1 as follows:

“In section 2 of this article, we outline the experimental setup at the UVSOR synchrotron radiation facility's beamline BL1U. We present a full description of the sample under investigation in section 2.1. The experimental setup to measure the gamma-CT images is described in full in Section 2.2. We provide a brief explanation of the 3D NRF-CT image in section 2.3, which was previously presented [14]. Section 3 provides the obtained results and the FV numerical treatments. Section 3.1 illustrates the obtained 2D gamma-CT images in detail and presents how they were visualized to one 3D image. Additionally, a reference to the original 3D NRF-CT image that need to be improved is provided. The post-multiply FV method between the original NRF-CT and gamma-CT images and its outcomes are shown in Section 3.2. The other possible methods of the FV between the original images followed by our recommendation are also presented. In section 4, we give the conclusions of our research. This article incorporates sub-elementary content (movies 1 and 2)”.

Point 2: The introduction section is not very readable, it should introduce the background first, then describe the current status of the study and summarize it, and finally what the paper is going to do.

Response 2:

• We edited the introduction section and separated it into three paragraphs according to your comments and the academic style required by the Applied Sciences as follows:
• Background

“Nuclear safeguards have a critical role in the non-proliferation of nuclear materials for reprocessing nuclear fuels and the control of nuclear materials. Nuclear resonance fluorescence (NRF) analysis [1] is a promising technology for nuclear safeguards and other nuclear applications [2–4]. Non-destructive inspection (NDI) for isotope based upon NRF has recently attracted a lot of attention because of its capacity to identify shielded isotope substances such as fissile material content in spent fuel and commercial cargo [2–7]. Because the NRF energy is specific to each nuclide, a nuclide of interest can be characterized by measuring the absorption of the incident gamma rays at the NRF energy or of the scattered gamma rays with an energy identical to the NRF energy. Energy-tunable quasi-monochromatic gamma rays generated by laser Compton scattering (LCS) [8,9] are suitable for the NRF measurements. Furthermore, computed tomography (CT) based on the NRF transmission method [10,11] with LCS gamma rays has been proposed as a novel technology for imaging an isotope of interest within massive materials [11]. The NRF-CT imaging technique makes it possible to distinguish an isotope of interest from other isotopes within the same element in a sample. Therefore, the isotope selectivity is one of its strengths. Zen et al. [12] experimentally demonstrated the NRF-CT using an LCS gamma-ray beam. They obtained a two-dimensional (2D) NRF-CT image with a resolution of 5 mm/pixel for the ²⁰⁸Pb isotope in a natural lead rod hidden inside an iron cylinder holder, together with a set of different materials (aluminum, iron, and a vacant area)”.

• The current status

“In our previous study [13], we obtained a 2D isotope-selective CT image based on the NRF transmission method for the distribution of an enriched lead isotope (²⁰⁸Pb) and of another enriched lead isotope (²⁰⁶Pb) implied inside an aluminum cylinder holder. The 2D NRF-CT image had a resolution of 2 mm/pixel with a data acquisition time of 60 hours [13]. As a result, ²⁰⁸Pb and ²⁰⁶Pb were clearly distinguished. In a subsequent study [14], we added another one-dimensional scan to obtain a three-dimensional (3D) NRF-CT image with horizontal and vertical resolutions of 4 and 8 mm/pixel, respectively. The data acquisition time was 48 hours [14]. It is obvious that improving the resolution of NRF-CT images is crucial for realistic applications. To improve the image resolution while keeping a reasonable data acquisition time, upgrading the detection efficiency of the NRF measurement system and/or increasing the gamma-ray beam intensity are possible approach. However, in practice, it is difficult to upgrade the detection system and/or the gamma-ray beams system of existing LCS facilities such as the ultraviolet synchrotron orbital radiation-III (UVSOR-III) synchrotron radiation facility at the Institute of Molecular Science at the National Institutes of Natural Sciences in Japan.”.

• Current Study goals

“In the current study, we proposed an alternative approach that applied a numerical treatment, called the fusion visualization (FV) technique [15–18], to improve the NRF-CT images’ quality. In the case of the NDI for the hidden isotopes within an assembly volume, scientific visualization is representing complex raw data as 2D or 3D images to understand the shape of the hidden isotopes that may be overlooked by standard methods alone. The term “data fusion” refers to a numerical data processing technique that may give more consistent, accurate, and meaningful information by integrating multiple data sources. In the current study, we applied the FV technique to improve the quality of the 3D NRF-CT image that was obtained in our previous study [14]. The FV technique is based on the integration of various data sources. One of the sources is the primary 3D NRF-CT image [14], which supplies the desired isotope distribution, but its image quality needs improvement. Another data source is a high-resolution gamma-CT image for the same CT sample under similar experimental conditions measured at the beamline BL1U in the UVSOR-III facility but with some alterations in the LCS gamma-ray beam parameters. In this article, we describe the numerical treatment procedures of the FV technique for integrating the primary images of the 3D NRF-CT and the 3D gamma-CT to improve the quality of an isotope-selective 3D NRF-CT image. We compared a few different numerical treatments of the FV technique and discussed the quality of the obtained images.”

• Description section
• please see the response to comment 1.

Point 3: I was expecting a sentence or two from the author about the significance of visualization, especially scientific visualization, for example:

https://doi.org/10.1080/13658816.2020.1833016

https://doi.org/10.1016/B978-008044531-1/50437-1

Response 3:

• We added the following statement to the thirds paragraph of the introduction section for the significance of scientific visualization:

“In the case of the NDI for the hidden isotopes within an assembly volume, scientific visualization is representing complex raw data as 2D or 3D images to understand the shape of the hidden isotopes that may be overlooked by standard methods alone.”

 

 

 

 

 

 

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper is good for publising in Applied Sciences.

The only my remark is some disagreement in visibility of the Fe rod in the figures. While in figs 3-4 and 8 the Fe rod is invisible, in fig 7 it is clearly seen. I suggest to either improve the figures or to comment on this.

Author Response

Response to the Reviewer 2

We would like to thank reviewer 2 for appreciating the value of Nuclear Resonance Fluorescence-based computed tomography imaging with a quasi-monochromatic Laser Compton Scattering gamma-ray beam for its significant advancement in nuclear engineering by the non-destructive inspection of the hidden isotopic compositions of target materials and the isotope selectivity assessment. We appreciate his/her insightful suggestions and efforts toward enhancing our manuscript, as well as the supportive and positive reviews. We have integrated the suggestions into the manuscript to strengthen and clarify it. A comprehensive response to all comments is given below (reviewers' comment are in black, and our response is in red).

Sincerely,

Khaled Ali,

Heishun Zen,

Hideaki Ohgaki,

Toshiteru Kii,

Takehito Hayakawa,

Toshiyuki Shizuma,

Masahiro Katoh.

Yoshitaka Taira,

Masaki Fujimoto,

Hiroyuki Toyokawa.

 

 

Point 1: The only my remark is some disagreement in visibility of the Fe rod in the figures. While in figs 3-4 and 8 the Fe rod is invisible, in fig 7 it is clearly seen. I suggest to either improve the figures or to comment on this.

Response 1:

We agreed with your comments about the Fe rods' visibility in the 2D gamma-CT images. We double-checked the raw data from experiment and found a mistake in representing the gamma-CT images in 2D. Therefore, we corrected the data and re-plotted figures 3, 4 and 5. In addition, we update the related figures of figure 7, figure 8, figure 9, movie 1 and movie 2.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Thanks for sharing your work. The manuscript is well-written/organized and the results presented in this work are interesting. In general, the writing style is good with no major issues. To that front, I recommend following minor corrections:

• Abstract Line 3: Remove “which is a significant technique in nuclear engineering” This is already implied.
• Abstract: Statement “Since the NRF-CT…10 photons/s/eV” is too long to read/understand. Please break in two or more statement.
• In the statements “ Improving the NRF-CT…better pixel resolution”, the authors first use image “resolution” and then image “quality.” Was this intended? Else it will be better to be consistent in terminology.
• Abstract: Please define the acronym LCS prior to its usage.
• Section 1: Please define the acronym “UVSOR.” Also the authors may want to cite reference 19 here.
• Figure 1 caption: Many items in the caption are redundant (already mentioned in the text). I suggest avoiding reputation; perhaps this can be done for Figure 2 as well.
• Section 2.2, Page 4: Please specify the energy resolution of the LaBr₃
• Section 2.2, Page 4: The lanthanum halide scintillators including the LaBr3(Ce) possess intrinsic radioactivity. Was this an issue at all? Why wasn’t an alternative detector was used otherwise? A short discussion can be included in this section.
• Section 2.2: What is the advantage of using Bismuth? Why not any other element? Please comment.
• Section 3.1: “Measured by the LaBr₃(Ce) detector” is used several times. At many places the sentences can be shortened by avoiding redundancy.
• Movie-1: Is it possible to overlay text for the isotopes that are clearly distinguished here?
• “Quantification” has been used repetitively in the entire manuscript. I am not sure if this is the right keyword to use here—as I don’t see any assessment made on the “quantity” in this paper? I agree the technique “identifies” isotopes but not about the quantification as far as this work is concerned. May be “identification” is the right choice? Please comment.
  
  

Author Response

Response to the Reviewer 3

We would like to express our appreciation to reviewer 3 for taking the time to read our manuscript thoroughly, and for his/her appreciating to the value of Nuclear Resonance Fluorescence-based computed tomography imaging with a quasi-monochromatic Laser Compton Scattering gamma-ray beam for its significant advancement in nuclear engineering by the non-destructive inspection of the hidden isotopic compositions of target materials and the isotope selectivity assessment. He/she is generally concerned that our original manuscript's conclusion could be improved and presented more succinctly. We make every attempt to solve these issues. We hope the reviewer 3 approve of our responses to his/her feedback.

Sincerely,

Khaled Ali,

Heishun Zen,

Hideaki Ohgaki,

Toshiteru Kii,

Takehito Hayakawa,

Toshiyuki Shizuma,

Masahiro Katoh.

Yoshitaka Taira,

Masaki Fujimoto,

Hiroyuki Toyokawa.

Point 1: Abstract Line 3: Remove “which is a significant technique in nuclear engineering” This is already implied.

Response 1:

• Removed

Point 2: Abstract: Statement “Since the NRF-CT…10 photons/s/eV” is too long to read/understand. Please break in two or more statement.

Response 2:

• We break the old statement and combine it with the previous statement to be more read/understand to be as follows:

“We experimentally obtained a three-dimensional (3D) isotope-selective CT image based on the NRF transmission method (3D NRF-CT) for the enriched lead isotope distribution of ²⁰⁸Pb in a cylindrical holder in a previous study. The cylindrical holder's diameter and height are 25 mm and 20 mm, respectively. The NRF-CT imaging technique requires a considerable data accumulation time. It took 48 hours to obtain an image with a resolution of 4 mm/pixel in the horizontal plane and 8 mm/pixel in the vertical plane using a laser Compton scattering (LCS) gamma-ray beam with a beam size of 2 mm and a flux density of 10 photons/s/eV.”.

Point 3: In the statements “Improving the NRF-CT…better pixel resolution”, the authors first use image “resolution” and then image “quality.” Was this intended? Else it will be better to be consistent in terminology.

Response 3:

• We re-phrased the statement to be consistent in terminology by using only the term “resolution” in both positions.

Point 4: Abstract: Please define the acronym LCS prior to its usage.

Response 4:

• We defined the acronym LCS on the abstract. Please check the response to comment point 2.

Point 5: Section 1: Please define the acronym “UVSOR.” Also, the authors may want to cite reference 19 here.

Response 5:

• We defined the acronym “UVSOR” in section 1 as: “Ultraviolet synchrotron orbital radiation-III (UVSOR-III) synchrotron radiation facility at the Institute of Molecular Science at the National Institutes of Natural Sciences in Japan.”.
• We deleted the citation to reference [19].

Point 6: Figure 1 caption: Many items in the caption are redundant (already mentioned in the text). I suggest avoiding reputation; perhaps this can be done for Figure 2 as well.

Response 6:

• We domified the captions of figures 1 and 2 to be as follows:

The new caption of Figure 1:

“Figure 1. (a) The cylindrical CT sample holder’s geometry, with the arrangement of the rods within the holder. (b) Picture of the CT sample during the experiment.”

The new caption of Figure 2:

“Figure 2. Schematic diagram of the experimental setup to measure the 3D gamma-CT image at the beamline BL1U in the UVSOR-III synchrotron radiation facility”.

Point 6: Section 2.2, Page 4: Please specify the energy resolution of the LaBr₃.

Response 6:

• We specified the energy resolution of the LaBr₃(Ce) on page 4 of section 2.2 as 2.7% at 662 KeV.

Point 7: Section 2.2, Page 4: The lanthanum halide scintillators including the LaBr₃(Ce) possess intrinsic radioactivity. Was this an issue at all? Why wasn’t an alternative detector was used otherwise? A short discussion can be included in this section.

Response 7:

• We added an explanation in section 2.2 as follows:

“We chose the LaBr₃(Ce) scintillation detector due to a better energy resolution, 2.7% at 662 KeV, than the NaI(Tl) scintillation detector whose typical energy resolution is approximately 6% to 8% at 662 keV. In addition, the availability of a high counting rate of the LaBr₃(Ce) scintillation detector due to the short decay time is suitable for our measurement. The intrinsic radiation of the LaBr₃(Ce) scintillation detector contributes significantly to the background radiation in the region below 1.6 MeV [20], which is far below from our energy of interest (around 5.5 MeV).”.

Point 8: Section 2.2: What is the advantage of using Bismuth? Why not any other element? Please comment.

Response 8:

• We added an explanation in section 2.2 as follows:

“We used the bismuth as an absorber because of its high density. In addition, in the NRF-CT imaging technique, we measure the scattered NRF gamma rays from a witness target made from the isotope of interest such as the lead isotope ²⁰⁸Pb in our experiments. If we used lead material as an absorber, the NRF gamma rays would be contaminated by the scattered NRF gamma rays from the absorber material. Therefore, it is preferable to avoid using the isotope of interest material an absorber. Other high-density materials, such as tungsten, can be used as absorbers as well, however bismuth is less expensive than tungsten.”.

Point 9: Section 3.1: “Measured by the LaBr₃(Ce) detector” is used several times. At many places, the sentences can be shortened by avoiding redundancy.

Response 9:

• We deleted the repeated the sentence

Point 10: Movie-1: Is it possible to overlay text for the isotopes that are clearly distinguished here?

Response 10:

• We could easily overly text for the isotopes in the movie, and we could also use multiple colors to distinguish the different isotope rods, but we think it is better to leave the movie without change to demonstrate the inability of the gamma-CT imaging technique to distinguish between the different isotopes within a sample.

Point 11: “Quantification” has been used repetitively in the entire manuscript. I am not sure if this is the right keyword to use here—as I don’t see any assessment made on the “quantity” in this paper? I agree the technique “identifies” isotopes but not about the quantification as far as this work is concerned. May be “identification” is the right choice? Please comment.

Response 11:

• Although the current outcomes of the NRF-CT imaging technique demonstrate the isotopes identification, the expression “quantification” was mentioned within the manuscript in three positions as follows:

1. Section 3.2 (IV) page 12.

Since the overlapping process of the post-multiply FV method was performed by multiplying the intensity value at each pixel in the  images by a value of 1 in the ²⁰⁸Pb locations inside the rod’s edge or by a value of 0 in the surrounding regions, the method preserved the locations of the isotopes of interest and completely eliminated the surrounding distortion and background noise. Furthermore, it kept the intensity value at each pixel constant, making this approach useful for isotope quantification. So, we used the term "quantification" here to describe the anticipated outcome of utilizing our technique for isotope quantification (Future plan).

2. Section 3.2 (V) page 14.

We used the term "quantification" to describe that the post-multiply FV method (without 2D gamma-CT image segmentation) cannot be used for isotope quantification because the intensity at each pixel of the NRF-CT image was not conserved.

3. Section 3.2 (V) page 14.

We used the term "quantification" to describe that the post-sum FV method and that the obtained image shows the change in the intensity at each pixel, so this method is useless for isotope quantification.

Therefore, we think that using of the term quantification is proper for each position.

Author Response File: Author Response.pdf