Feasibility Study of a PET Detector with a Wavelength-Shifting Fiber Readout

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript describes a simulation study of a novel detector design for applications in positron emission tomography devices. The design is based on monolithic LYSO scintillator with orthogonally positioned strips of wave length shifting fibers, subsequently read out by silicon photomultipliers. The main feature of the design is the potential to significantly reduce the number of readout channels. The results suggest that acceptable resolutions may be achieved based on the design. 

The manuscript is well organized and mostly well presented, however in my view these comments need to be addressed: 

Major issues:

(1) L125 and Figure 2 - I am concerned about modeling the SiPM. First, you need to specify which S13360 was used, there are 25 um, 50 um and 75 um pitch models and they have different fill factors and different PDE curves. Moreover, the PDE curve shown in the manuscript does not match any of the curves  described by the manufacturer, please have a look at:https://www.hamamatsu.com/content/dam/hamamatsu-photonics/sites/documents/99_SALES_LIBRARY/ssd/s13360_series_kapd1052e.pdf

Since the simulated PDE has important implications on the final result, this must be clarified.

 

(2) Timing resolution - throughout the manuscript you are not discussing the timing resolution of the detector. Please include in the manuscript discussion on what is the expected impact of the proposed design on timing resolution and how you are going to address the potential issues. Compare with previous designs using WLS readout.  One may expect that using indirect readout with WLS will reduce the number of photons reaching the SiPMs with potentially a crucial impact on timing resolution. If this is the case, the claim in Lines 243-245 of enhanced sensitivity and improved image may not be supported or would have to be modified. 

 

Minor issues:

L40 Reference [1] is not appropriate here. The sentence is generally introducing the concept of the line-of-response, so I don't see a connection to the cited reference. 

L55-57 Please add relevant references that show the claims - improvement of spatial resolution, sensitivity, timing with monolithic over pixelated crystals. These claims must be supported.

L67 remove "the" before "uniformity"

L72-85 (Section2)

Please make clear that this is the concept which is being simulated and not an actually assembled detector.

L74 a base size -> a volume, not a base  (area) is descirbed in the next line, so correct accordingly

Figure 1 - add more details: mark the positions of the SiPMs, ESR. Also you have to add a legend describing all the layers and elements. 

L120 - optical grease. Why optical grease? It is know that in practice the grease penetrates between the elements, so it may spread between the WLS which may cause light sharing. Have you considered another optical material? Could you comment?

Figure 4 - the magenta curve is hardly visible. Try using another color.

L168-172. Some parts of sentences are repeating. Please rewrite more concisely.

Figure 5 - The caption contains a wrong descritpion "photoelectric absorption" instead of Compton scattering. Also Write the full description of panels (c) and (d), do not just refer to Figure 4.

L177 You say that (x,y)=(15mm,15mm) in Figure 6, but the Figure's captions says (20mm, 15mm) - so which one is it? Please check these numbers throughout the paper thoroughly.

L188 Again the sentence does not match the caption of Figure 8.

I am guessing that Figure 8 is a 3D plot of either Figure 9 or Figure 10. It would be more instructive to keep all these figures on the same page. 

L199 You mention thickness "c", but the equation (1) uses L for the thickness. Please use the labels consistently.

Figure 11(b) and L212 - The Figure is nice, but one cannot deduce the measure of uniformity of the detector response. Please write explicitly what is the detector sensitivity (number of detected photons) variation with the position. This may lead to local variations of energy calibration and may worsen the overall energy resolution. Also write explicitly what is the variation of the spatial resolution across the detector to support the claim in lines 212-213.

Figure 12 -panel labels (a), (b), (c) are misaligned. In caption you say that the sigma of the Gaussian is the energy resolution. Usually it is FWHM which is sigma*2.35.

L229. It is not completely clear what you refer to and the reference [36] does not seem to be relevant to support that claim. Different SiPMs are used in commercial systems typically from 3x3 mm2 to 6x6 mm2.

References:

14. - missing the relevant bibliographic data

25. I do not find this reference. Please check it

Check all the references from proper formatting and relevant data. 

 

 

 

 

 

Author Response

For research article
Feasibility Study of a PET Detector with Wavelength-Shifting Fiber Readout

Response to Reviewer 1 Comments

1. Summary        
Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files. 

2. Questions for General Evaluation    Reviewer’s Evaluation    Response and Revisions
Does the introduction provide sufficient background and include all relevant references?    Yes/Can be improved/Must be improved/Not applicable    
Are all the cited references relevant to the research?    Yes/Can be improved/Must be improved/Not applicable    
Is the research design appropriate?    Yes/Can be improved/Must be improved/Not applicable    
Are the methods adequately described?    Yes/Can be improved/Must be improved/Not applicable    
Are the results clearly presented?    Yes/Can be improved/Must be improved/Not applicable    
Are the conclusions supported by the results?    Yes/Can be improved/Must be improved/Not applicable    
3. Point-by-point response to Comments and Suggestions for Authors
Comments 1: Major issues:
(1) L125 and Figure 2 - I am concerned about modeling the SiPM. First, you need to specify which S13360 was used, there are 25 um, 50 um and 75 um pitch models and they have different fill factors and different PDE curves. Moreover, the PDE curve shown in the manuscript does not match any of the curves described by the manufacturer, please have a look at:https://www.hamamatsu.com/content/dam/hamamatsu-photonics/sites/documents/99_SALES_LIBRARY/ssd/s13360_series_kapd1052e.pdf
Since the simulated PDE has important implications on the final result, this must be clarified.
Thank you for pointing this out. I agree with this comment. Therefore, I have
Response 1: This research is evaluation study and PDE was similar to Hamamatsu S13360 but not matches exactly. I have implemented into GEANT4 model PDE spectrum of S13360 75CS as demonstrated on figure below and run simulations to verify impact of this discrepancy. It was found that there is no impact on position resolution between simplified PDE build on several point and detailed spectrum of S13360 75CS PDE. Now in model I am using detailed PDE of S13360 75CS SiPM. The figure 2 was updated.
 
Demonstration of old PDE and implemented PDE of Hamamatsu S13360 75CS (red dashed line). 

Comments 2: Timing resolution - throughout the manuscript you are not discussing the timing resolution of the detector. Please include in the manuscript discussion on what is the expected impact of the proposed design on timing resolution and how you are going to address the potential issues. Compare with previous designs using WLS readout.  One may expect that using indirect readout with WLS will reduce the number of photons reaching the SiPMs with potentially a crucial impact on timing resolution. If this is the case, the claim in Lines 243-245 of enhanced sensitivity and improved image may not be supported or would have to be modified. 

Response 2: Agree. Timing resolution was indeed not previously discussed, and I have filled in this gap. I have added figures that demonstrate the time spectrum of a typical signal from 511 keV detection in LYSO. I observed that there is a delay of approximately 10 nanoseconds due to the decay time of the BCF-91A WLS fiber. To address this, I have implemented the material properties table for BCF-92 WLS fiber into the GEANT4 model. According to simulation results, the number of detected photons by SiPMs is about 10% lower compared to the BCF-91A WLS fiber. Nevertheless, simulations using the BCF-92 WLS fiber demonstrate practically the same spatial resolution. The simulated Time spectra are added to manuscript. 

                                               
Time spectrum of LYSO with BCF-91a WLS fiber.              Time spectrum of LYSO with BCF-92 WLS fiber.

Comments 3:
Minor issues:
L40 Reference [1] is not appropriate here. The sentence is generally introducing the concept of the line-of-response, so I don't see a connection to the cited reference. 
RESPONSE 3: Reference [1] removed.

Comments 4:
L55-57 Please add relevant references that show the claims - improvement of spatial resolution, sensitivity, timing with monolithic over pixelated crystals. These claims must be supported.
RESPONSE 4: relevant references added

Comments 5:
L67 remove "the" before "uniformity"
RESPONSE 5: "the" removed

Comments 6:
L72-85 (Section2)
Please make clear that this is the concept which is being simulated and not an actually assembled detector.
RESPONSE 6: Section title was corrected 

Comments 7
L74 a base size -> a volume, not a base (area) is described in the next line, so correct accordingly
Figure 1 - add more details: mark the positions of the SiPMs, ESR. Also, you have to add a legend describing all the layers and elements. 
RESPONSE 7: Changed with “a base size” ->to with dimensions.
 Figure 1 - added more details and a legend describing elements.

Comments 8
L120 - optical grease. Why optical grease? It is known that in practice the grease penetrates between the elements, so it may spread between the WLS which may cause light sharing. Have you considered another optical material? Could you comment?
RESPONSE 8: I have tested both optical grease (n=1.46) and Meltmount158 adhesive (n=1.58). Both acting similarly just not been less then 1.42. I agree, optical grease has a technological constrain therefor I replaced in text grease to glue (adhesive)

Comments 9:
Figure 4 - the magenta curve is hardly visible. Try using another color.
RESPONSE 9: magenta color changed to green 

Comments 10:
L168-172. Some parts of sentences are repeating. Please rewrite more concisely.
Figure 5 - The caption contains a wrong description "photoelectric absorption" instead of Compton scattering. Also Write the full description of panels (c) and (d), do not just refer to Figure 4.
RESPONSE 10: Some sentences are edited to remove repeating text. Figure 5 corrected - In caption a wrong description "photoelectric absorption" replaced to “Compton scattering”. Full description of panels (c) and (d) is written.

Comments 11:
L177 You say that (x,y)=(15mm,15mm) in Figure 6, but the Figure's captions says (20mm, 15mm) - so which one is it? Please check these numbers throughout the paper thoroughly.
RESPONSE 11: Following changes made: positions (x, y) = (20 mm, 20 mm) and (x, y) = (15 mm, 15 mm)

Comments 12:
L188 Again the sentence does not match the caption of Figure 8.
I am guessing that Figure 8 is a 3D plot of either Figure 9 or Figure 10. It would be more instructive to keep all these figures on the same page. 
RESPONSE 12: corrected. Figure 8 combined with Figure 9 or Figure 10 to avoid misunderstanding. 

Comments 13:
L199 You mention thickness "c", but the equation (1) uses L for the thickness. Please use the labels consistently.
RESPONSE 13: perlaced"c" - > L

Comments 14:
Figure 11(b) and L212 - The Figure is nice, but one cannot deduce the measure of uniformity of the detector response. Please write explicitly what is the detector sensitivity (number of detected photons) variation with the position. This may lead to local variations of energy calibration and may worsen the overall energy resolution. Also write explicitly what is the variation of the spatial resolution across the detector to support the claim in lines 212-213.
RESPONSE 14: Figure 11(b) is added with histograms of the average number of detected photons demonstrating uniformly of energy resolution across detector sensitive area

Comments 15:
Figure 12 -panel labels (a), (b), (c) are misaligned. In caption you say that the sigma of the Gaussian is the energy resolution. Usually it is FWHM which is sigma*2.35.
RESPONSE 15: corrected, added formula to figure caption.

Comments 16:
L229. It is not completely clear what you refer to and the reference [36] does not seem to be relevant to support that claim. Different SiPMs are used in commercial systems typically from 3x3 mm2 to 6x6 mm2.
RESPONSE 16: reference corrected

Comments 17:
References:
14. - missing the relevant bibliographic data
25. I do not find this reference. Please check it
RESPONSE 17: bibliographic data added, Reference 25 removed 

Check all the references from proper formatting and relevant data. 

4. Response to Comments on the Quality of English Language
Point 1:
Response 1:    (in red)
5. Additional clarifications

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Review for the manuscript:

Entitled: " Feasibility Study of a PET Detector with Wavelength-Shifting Fiber

Readout"

 

for Instruments.

 

With ID: instruments-3389501

  

General comments

 

Comments for the Author

 

The manuscript under consideration is well fitted with the aim and scope of Instruments Journal and it may be of interest to most of its readers. It is well written, except from some points that need better writing. It shows an introductory background material sufficient for someone not an expert in this area to understand the context and significance of this work, however with few references to follow. It is a simulation study and as every simulation study in order to be valid it should provide direct comparisons, for at least some basic aspects of the research with published experimental data.

Turnitin showed a similarity index of less than 22% (AI detection score was not provided).

 

For all the above, and the specific comments below, I have opted to recommend a Major revision for the current form of this work.

 

Specific comments

 

Abstract

P1, L1: ‘We designed and evaluated performance’, P2, L58 ‘In this paper, we are exploring’ as well all the other instances of using ‘We’. However, I see only one author in the manuscript. No one else contributed in this study?

 

Introduction

P1, L19-34: Please provide appropriate references for the various statement in these two paragraphs.

 

P2, L72: Paragraph: ‘2. The WLS-PET detector configuration’ refers to experimental procedures or a simulation setup? Please specify.

 

P3, L87: ‘GEANT4’ Please specify the version and provide appropriate reference.

 

P3, L104: ‘LYSO has a high effective atomic number’ Please justify the choice of LYSO. Why for example not Gd₃Al₂Ga₃O₁₂:Ce or LaBr₃:Ce with LY reaching 6000 ph/MeV, CdWO₄ etc.? Please specify and possible provide a table with the characteristics of LYSO in comparison with other scintillator, in order to justify the selection.

 

P4, Fig.2 Please correct ‘Wavelenght’

 

P4, L129-132: ‘A GEANT4 model, as described in [28], was created, and parameters were adjusted until agreement was achieved with the energy resolution data presented in the publication. The simulation parameters for WLS fibers were adjusted in [30].’ I do not understand the meaning of ‘adjusted’ Please specify. Furthermore, every simulation study in order to be valid should do direct comparisons with experimental data.  

 

Results

 

P5, L154: ‘using a functions’ Please revise.

 

P6, L174: ‘In future work, we plan to incorporate Compton kinematic reconstruction to include Compton scattering events in the analysis.’

 

However, in P3, L87 author states that: ‘In the GEANT4 simulation for this study, all relevant physical processes have been included to ensure accurate modeling of photon interactions within the PET detector. The following electromagnetic processes, such as ionization, bremsstrahlung, multiple scattering, pair production, Compton scattering’

 

Please clarify.

 

P6, L181: ‘It can be seen that FWTM is larger increased with increase of crystal thickness then FWHM.’ This is common knowledge. What does it contribute in the results section?

 

P7, Fig.8. Please revise these figures. The axes are overlapping.

 

Discussion

 

P9, L216: ‘with pixel size 4x4 mm²’ This is the only available commercial arrangement? Please specify and provide appropriate reference.

Author Response

For research article

Feasibility Study of a PET Detector with Wavelength-Shifting Fiber Readout

 

 

Response to Reviewer 2 Comments
1. Summary
Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.
2. Questions for General Evaluation	Reviewer’s Evaluation	Response and Revisions
Does the introduction provide sufficient background and include all relevant references?	Yes/Can be improved/Must be improved/Not applicable
Are all the cited references relevant to the research?	Yes/Can be improved/Must be improved/Not applicable
Is the research design appropriate?	Yes/Can be improved/Must be improved/Not applicable
Are the methods adequately described?	Yes/Can be improved/Must be improved/Not applicable
Are the results clearly presented?	Yes/Can be improved/Must be improved/Not applicable
Are the conclusions supported by the results?	Yes/Can be improved/Must be improved/Not applicable
3. Point-by-point response to Comments and Suggestions for Authors
Comments 1: Abstract P1, L1: ‘We designed and evaluated performance’, P2, L58 ‘In this paper, we are exploring’ as well all the other instances of using ‘We’. However, I see only one author in the manuscript. No one else contributed in this study?
Response 1: The phrase "We designed" was replaced with the more neutral "This paper presents" to align with formal and objective academic writing style, making the statement more suitable for a broader audience, such as journal readers or reviewers. Thank you for pointing this out.
Comments 2: Introduction P1, L19-34: Please provide appropriate references for the various statement in these two paragraphs.
Response 2: Agree. References provided    Comments 3:  P2, L72: Paragraph: ‘2. The WLS-PET detector configuration’ refers to experimental procedures or a simulation setup? Please specify. Response 3: I agree- changed to – “Detector design and simulation setup”   Comments 4:  P3, L87: ‘GEANT4’ Please specify the version and provide appropriate reference. Response 4: GEANT4 version specified   Comments 5:  P3, L104: ‘LYSO has a high effective atomic number’ Please justify the choice of LYSO. Why for example not Gd₃Al₂Ga₃O₁₂:Ce or LaBr3:Ce with LY reaching 6000 ph/MeV, CdWO4 etc.? Please specify and possible provide a table with the characteristics of LYSO in comparison with other scintillator, in order to justify the selection.   Response 5:  Paragraph was added arguing selection of LYSO and table was added with some crystal scintillators relevant to PET detectors   Comments 6:   P4, Fig.2 Please correct ‘Wavelenght’  Response 6:   corrected Wavelenght - > Wavelength   Comments 7:  P4, L129-132: ‘A GEANT4 model, as described in [28], was created, and parameters were adjusted until agreement was achieved with the energy resolution data presented in the publication. The simulation parameters for WLS fibers were adjusted in [30].’ I do not understand the meaning of ‘adjusted’ Please specify. Furthermore, every simulation study in order to be valid should do direct comparisons with experimental data.   Response 7:   As the exact optical characteristics are unknown, the variation of some parameters were performed to find the best agreement with the experimental measurement of spectroscopic response of LYSO from [28]. The energy resolution in this experimental data was ~10.8%. To match the experimental energy resolution pulse height centroid. The all surfaces were considered to be ground with a polish value was varied from 0.5 to 0.95 in steps of 0.1 until agreement for simulated energy resolution pulse height centroid with data [28] was obtained.     Figures from [28].   Simulation of the setup from [28].                                                 Simulation of WLS-plastic set up from [30].     Comments 8:  P5, L154: ‘using a functions’ Please revise. Response 8:  revised.      Comments 9:  P6, L174: ‘In future work, we plan to incorporate Compton kinematic reconstruction to include Compton scattering events in the analysis.’ However, in P3, L87 author states that: ‘In the GEANT4 simulation for this study, all relevant physical processes have been included to ensure accurate modeling of photon interactions within the PET detector. The following electromagnetic processes, such as ionization, bremsstrahlung, multiple scattering, pair production, Compton scattering’  Please clarify.  Response 9:    In the GEANT4 simulation, Compton scattering events are fully processed. When the interaction position determination algorithm is applied to the detected light distributions, events with complex light distributions—such as those showing multiple peaks, as illustrated in Figure 5—are excluded. This exclusion occurs because it is challenging to determine which peak corresponds to the first interaction position. Furthermore, there is a possibility that the actual first interaction may result in a weak peak that is either misidentified or not detected at all. As a result, such events are omitted from the analysis to maintain the accuracy of interaction position determination. To avoid misunderstandings, I removed from the manuscript the sentence: “In further work we plan…”   Comments 10:  P6, L181: ‘It can be seen that FWTM is larger increased with increase of crystal thickness then FWHM.’ This is common knowledge. What does it contribute in the results section?  Response 10:   The paragraph was added to Conclusion section which consider impact of crystal thickness and possible improvement of proposed design.   Comments 11:  P7, Fig.8. Please revise these figures. The axes are overlapping. Response 11:  The figure 8 were revised.   Discussion   Comments 12:  P9, L216: ‘with pixel size 4x4 mm2’ This is the only available commercial arrangement? Please specify and provide appropriate reference. Response12:  This statement is incorrect, there is wide range of crystal dimensions which form the array, therefor this statement corrected.
4. Response to Comments on the Quality of English Language
Point 1:
Response 1:    (in red)
5. Additional clarifications
[Here, mention any other clarifications you would like to provide to the journal editor/reviewer.]

 

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Referee report on the paper Instruments 3389501 “Feasibility Study of a PET Detector with Wavelength-Shifting Fiber Readout” by A.Sh. Georgadze

The paper reports a feasibility study of a detector optimized for PET using LYSO modules, WLS LG and SiPM. For this purpose the response of the detector was simulating in different configuration. While the argument has its own interest and it can be published, the style of the paper is not ready for publication.

There is a big confusion about the figures:

- fig. 2 is not cited in the text
- fig. 7 is not cited in the text
- lines 176-178 the description of fig. 6 does not correspond to the figure caption
- lines 188-194 the description of fig. 8 does not correspond to the figure caption
- why has a single event two peaks in fig. 8? Is it due to Compton scatterings?
- line 205 12b —> 12c
- fig 11b does not show any quantitative info. Thus, it should be removed
- fig. 12 the labels a,b,c are bad positioned

Moreover, other possible improvements are:

- line 81 explain ESR Enhanced Specular Reflector mirror
- line 84 there is written that 66 fibers are totally, however in fig. 1 it seems that they are 64
- line 102 and before. "For each surface, the appropriate optical boundary processes and reflectivity were specified." At the end of these sentences it is necessary to explain how.

Finally, the paper must be thoroughly revised for English language accuracy. A lot of definite articles must be included.

Some possible language improvements: line 1 the performance; line 69; line 108 the refractive index … is set, the light … is set….; line 140 The generated optical…; Caption of fig. 4 the simulated results; line 235, and more

Comments on the Quality of English Language

see before

Author Response

For research article

Feasibility Study of a PET Detector with Wavelength-Shifting Fiber Readout

 

 

Response to Reviewer 2 Comments
1. Summary
Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.
2. Questions for General Evaluation	Reviewer’s Evaluation	Response and Revisions
Does the introduction provide sufficient background and include all relevant references?	Yes/Can be improved/Must be improved/Not applicable
Are all the cited references relevant to the research?	Yes/Can be improved/Must be improved/Not applicable
Is the research design appropriate?	Yes/Can be improved/Must be improved/Not applicable
Are the methods adequately described?	Yes/Can be improved/Must be improved/Not applicable
Are the results clearly presented?	Yes/Can be improved/Must be improved/Not applicable
Are the conclusions supported by the results?	Yes/Can be improved/Must be improved/Not applicable
3. Point-by-point response to Comments and Suggestions for Authors
Comments 1: There is a big confusion about the figures: - fig. 2 is not cited in the text
Response 1: Thank you for pointing this out.
Fig. 2 is cited   Comments 2: - fig. 7 is not cited in the text Response 2:: fig. 7 is cited in the text   Comments 3: - lines 176-178 the description of fig. 6 does not correspond to the figure caption Response 3: description of fig. 6 is modified according to figure caption   Comments 4: - lines 188-194 the description of fig. 8 does not correspond to the figure caption Response 4: description of fig. 8 corrected   Comments 5: - why has a single event two peaks in fig. 8? Is it due to Compton scatterings? RESPONSE 5: No, fig. 8 was just a 3d representation of the same distribution as on fig. 9. To avoid misunderstanding I have combined both fig.8 and fig. 9 into one figure.   Comments 6: - line 205 12b —> 12c RESPONSE 6: corrected   Comments 7: - fig 11b does not show any quantitative info. Thus, it should be removed RESPONSE 7: Figure 11b illustrates that the spatial response of the detector remains uniform, despite the detector being an assembly of 16 monolithic scintillators. One of the reviewers expressed interest in this figure and requested further explanation. Given its relevance and the reviewer's inquiry, I suggest keeping this figure in the paper to provide additional clarity and insight into the uniformity of the spatial response across the detector.   Comments 8: - fig. 12 the labels a,b,c are bad positioned RESPONSE 8: corrected   Comments 9: Moreover, other possible improvements are: - line 81 explain ESR Enhanced Specular Reflector mirror RESPONSE 9:  ESR is added description Comments 10: - line 84 there is written that 66 fibers are totally, however in fig. 1 it seems that they are 64 RESPONSE 10:  Fig. 1 is not a CAD model but a sketch figure of the detector, which contains some approximations in order to make fibers more visibly separated. The actual detector model has 66 fibers on each side.   Comments 11: - line 102 and before. "For each surface, the appropriate optical boundary processes and reflectivity were specified." At the end of these sentences it is necessary to explain how. RESPONSE 11:   added specification of optical surfaces between volumes Finally, the paper must be thoroughly revised for English language accuracy. A lot of definite articles must be included.   Comments 12: Some possible language improvements: line 1 the performance; line 69; line 108 the refractive index … is set, the light … is set….; line 140 The generated optical…; Caption of fig. 4 the simulated results; line 235, and more RESPONSE 12: language improvements were implemented   Comments on the Quality of English Language see before
4. Response to Comments on the Quality of English Language
Point 1:
Response 1:    (in red)
5. Additional clarifications

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear author, 

thank you for submitting the corrected and a more complete version of the manuscript. I find the following issues remain to be resolved:

I. major issue: L257-268. You added a details about the simulated time response of the WLS-PET plates. However, there is no result about the resolution (CTR), since one cannot make a straightforward conclusion about the CTR from the WLS decay spectrum. Can you show the CTR and compare it to  comercial PET scanners (CTR in the range of 200-500 ps FWHM). If you cannot show it, please state in the discussion/conclusion that the CTR yet needs to be evaluated to for the design to be fully comparable with standards PET detectors.

II. minor issues:

- throughout the manuscript: you are the only author, so you may consider writing the manuscript in the 1st person singular ("I" instead of "we")

L79 "Detector design and simulation setup" - you don't mention the simulation in this section, so please revise the title accordingly

L80-85 words and phrases appearing twice in a row - check the wording

Reference 35 - misses the standard bibliographical information, please correct

Figure 4 and 5 caption: blue curve -> blue histogram, green curve - hardly visible

Figure 6: panels (b) and (c) should be swapped to match the description

Figure 6 caption: missing description of panels (c) and (d). Also the data in the caption does not match the text L214

Figure 7 and 8 caption: the description does not match the text L229-231. Please check carefully for consistency and state clearly what is presented.

L243 "Figure 11(b)" should probably say Figure 10(b)

L251 "Figure 10(a)" should probably say Figure 11(a)

L252 around 3-4 mm. Can you express it in terms of mean+- std?

L296-301 You are discussing the benefits of reconstructing the Compton events, but you did not show it in the manuscript. Either show the results or remove this part of the discussion.

Author Response

Reviewer 1

 

Round 2

 

Dear reviewer,

Thank you very much for your patience while reviewing the article. Your  comments  on   manuscript allowed me  to  improve the  paper.   Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.

 

268. major issue: L257-268. You added a details about the simulated time response of the WLS-PET plates. However, there is no result about the resolution (CTR), since one cannot make a straightforward conclusion about the CTR from the WLS decay spectrum. Can you show the CTR and compare it to commercial PET scanners (CTR in the range of 200-500 ps FWHM). If you cannot show it, please state in the discussion/conclusion that the CTR yet needs to be evaluated to for the design to be fully comparable with standards PET detectors.

Response: Unfortunately, this study is not funded and is based on a mid-range computer with a GPU integrated into the CPU, while the development of the GEANT4 geometry for a full ring PET system, including the implementation of all WLS fibers, is computationally intensive and requires high-performance computing resources, in particular a high-performance GPU. Therefore, I cannot estimate the coincidence timing resolution in this work. I have added a statement in the discussion section that the CTR still needs to be estimated for the full PET design to be fully comparable with standard PET scanners.

1. minor issues:

- throughout the manuscript: you are the only author, so you may consider writing the manuscript in the 1st person singular ("I" instead of "we")

Response: I follow the example of other publication (DOI 10.1088/0031-9155/54/21/004) and prefer to use "we".

L79 "Detector design and simulation setup" - you don't mention the simulation in this section, so please revise the title accordingly

Response: revised to: Detector design

L80-85 words and phrases appearing twice in a row - check the wording

Response: repetition of words removed

Reference 35 - misses the standard bibliographical information, please correct

Response: Reference 35 corrected

Figure 4 and 5 caption: blue curve -> blue histogram, green curve - hardly visible

Response: corected green curve thickness increased for better visibility

Figure 6: panels (b) and (c) should be swapped to match the description. Figure 6 caption: missing description of panels (c) and (d). Also the data in the caption does not match the text L214

Response: Figure 6 is updated to demonstrate reconstruction for 7mm and 15 mm crystal thicknesses. The text and figure caption are updated.

Figure 7 and 8 caption: the description does not match the text L229-231. Please check carefully for consistency and state clearly what is presented.

Response: the text L229-231 is updated to match captions of Figure 7 and 8

L243 "Figure 11(b)" should probably say Figure 10(b)

Response: corrected

L251 "Figure 10(a)" should probably say Figure 11(a)

Response: corrected

L252 around 3-4 mm. Can you express it in terms of mean+- std?

Response: corrected

L296-301 You are discussing the benefits of reconstructing the Compton events, but you did not show it in the manuscript. Either show the results or remove this part of the discussion.

Response: L296-301 removed

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Review for the manuscript:

Entitled: " Feasibility Study of a PET Detector with Wavelength-Shifting Fiber

Readout"

 

for Instruments.

 

With ID: instruments-3389501.R1

  

General comments

My previous remarks were addressed; thus, the manuscript can be published.

 

Best regards

Author Response

Dear reviewer,

Thank you very much for your patience while reviewing the article. Your comments on manuscript allowed me to improve the  paper.   

Reviewer 3 Report

Comments and Suggestions for Authors

Referee report on the revised version of the paper Instruments 3389501 “Feasibility Study of a PET Detector with Wavelength-Shifting
Fiber Readout” by A.Sh. Georgadze

Unfortunately, it appears that the author has not adhered to the requirements outlined in my previous report. There is still significant confusion regarding the figures. While some improvements have been made, not all of the necessary changes have been implemented.

There are 13 figures in total, some of which contain multiple panels. It is essential that all figures are cited in the correct order and adequately described in the text, as this is a fundamental requirement for any manuscript.

Currently, I have found only the following citation order: 1, 2, 3, 4, 5, 6, 8, 11b, 11a, 12c, 9, 13. However, figures 7, 9, 10, 12a, and 12b are not cited at all. Additionally, figure 9 is referenced too late in the manuscript.

Until these issues are addressed, I am unable to proceed with a full review of the paper.

Author Response

Reviewer 3:

 

Round 2

 

Dear reviewer,

thank you very much for your patience while reviewing the article. Due to the need for additional modeling, not all the shortcomings were corrected in time.

Now all the figures are arranged in the order of references in the text.

Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.

 

Referee report on the revised version of the paper Instruments 3389501 “Feasibility Study of a PET Detector with Wavelength-Shifting Fiber Readout” by A.Sh. Georgadze

 

Unfortunately, it appears that the author has not adhered to the requirements outlined in my previous report. There is still significant confusion regarding the figures. While some improvements have been made, not all of the necessary changes have been implemented.

 
There are 13 figures in total, some of which contain multiple panels. It is essential that all figures are cited in the correct order and adequately described in the text, as this is a fundamental requirement for any manuscript.

Response: The figures have been rearranged, links to all figures have been added, figure captions and text have been corrected.

Currently, I have found only the following citation order: 1, 2, 3, 4, 5, 6, 8, 11b, 11a, 12c, 9, 13. However, figures 7, 9, 10, 12a, and 12b are not cited at all. Additionally, figure 9 is referenced too late in the manuscript.

Response: The figures have been rearranged, links to all figures have been added, figure captions and text have been corrected.

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

Dear author, I believe that my objections have been met and that the manuscript is now of a good quality and of interest to the community.

Author Response

Dear Reviewer,

Thank you very much for your careful reading and for your comments on the manuscript, they certainly allowed me to improve it.

Kind regards,

Anzori Georgadze, PhD,

Institute of Physics, University of Tartu
Institute for Nuclear Research of the National Academy of Sciences of Ukraine (KINR), Kyiv, Ukraine.

Reviewer 3 Report

Comments and Suggestions for Authors

Referee report on the revised version of the paper Instruments 3389501 “Feasibility Study of a PET Detector with Wavelength-Shifting Fiber Readout” by A.Sh. Georgadze

After two avoidable passages, the structure of the paper is now correct.I have a few minor comments left, and then it can be accepted.

- Table 1 the decay time of NaI(Tl) is not 630 ns but 240 ns. Please, revise all this table

- Line 235ff. Fig. 9 shows two different cases; however, without a fit it is difficult to evaluate possible differences. In the text it is written some, but a fit in the figure should help the reader.

- line 309 there is a typo

Comments on the Quality of English Language

There are typos and missing articles.

Author Response

Dear Reviewer, 
Thank  you  very  much  for  your  comments  on  manuscript.  They  certainly allowed  me  to  improve the  paper.  

 

Comment1.  Table 1 the decay time of NaI(Tl) is not 630 ns but 240 ns. Please, revise all this table

Response: Table 1 was revised and changes were made correct the decay time of NaI(Tl). 

Comment2. Line 235ff. Fig. 9 shows two different cases; however, without a fit it is difficult to evaluate possible differences. In the text it is written some, but a fit in the figure should help the reader.

Response:  Your suggestion to show the response time fit of the data is really helpful for visualizing scintillation decay and effectively comparing the performance of different fibers. Since fitting the time distribution of individual detected photon events is not practical due to large statistical fluctuations, I averaged the time distribution of detected photons over 2000 events that can be reliably fitted with an exponential function. This required adding Figure 9c, which shows the results of fitting with an exponential function.

Comment3.  line 309 there is a typo

Response: line 309 typo was corrected. 

Kind regards,

Anzori Georgadze