Performance Evaluation of the Current Birmingham PEPT Cameras

Round 1

Reviewer 1 Report

I would like to congratulate the authors for their work, it is an interesting article.  The authors performed several laboratory measurements for comparison of PEPT cameras in view of their performance. I consider the paper very well written with clear description of methods applied. The only and minor remark is that the presented article is basically a teaser before the full report on the performance of new detectors (as promised in lines 159-160). Nevertheless I recommend the paper to be published.

Author Response

We thank the reviewer for their kind comments, and note that they have not asked for any changes.

Reviewer 2 Report

Dear Authors,

 

thank you for your manuscript on the “Performance evaluation of the current Birmingham PEPT cameras”. It presents a very interesting comparison of several PEPT devices developed in the recent years providing valuable information for the community. 

 

The manuscript has a clear structure and reads well. First three chapters clearly present the topic of the research and explain all  performance parameters discussed in the second part of the article, where three PEPT cameras are being compared.

 

I recommend the paper for publication in “Applied Sciences” after taking into accounts the following comments, mainly of a cosmetic nature.

 

1. Introduction

• I am missing references to other instruments of this kind, outside Birmingham.

 

2. Simple characterisation of PEPT systems 

• 61-64 requires some typesetting as sometimes formulas are part of the sentence, sometimes are put in a separate line. First three formulas could be put in separate lines and enumerated. Those in line 63 (Delta-T and uncertainty) are later referred to in section 5.
• 91-92 please consider writing fractions using a slash “/“ symbol. 
• 92 countrate —> count rate

 

3. Development of positron cameras at Birmingham 

• 122-126 you introduce word “buckets” twice

 

5. Results

 

• Both sections 5 and 6 are written differently wrt. the first 4 sections. This includes style but also fonts, symbols, etc. (e.g. <~ instead of $\lesssim$, F-18 instead of $^{18}F$ as in the previous section). Please unify!
• Figures 5-7: please consider using different symbols for different data sets (prompt, delayed, trues) and don’t change colours of those in between the plots as it is hard to compare between Fig. 5-7. This way you can still differentiate different camera measurements in the summary figure 8. 
• Figures 5-7: Trues were actually not clearly introduced in the text. Please add a sentence. 
• 233-234: it is not clear why exactly 15 MBq is chosen as the maximum desirable activity to be used with ADAC Forte. In 237-238 you refer to some “low activity” and in 244-245 7.5 MBq activity is discussed. However, you do not refer to 15 MBq anymore. Shouldn’t the 7.5 MBq be considered as a max desirable then?
  Please elaborate.
• 239-243: This whole paragraph doesn’t need to be put in parenthesis. Please remove []. 
• Can you compile the results obtained with different cameras in a form of a table? You can also add most important design parameters there, if necessary.
• You mention the intrinsic resolution of the ADAC Forte modules. Can you also provide the respective values for SuperPEPT and MicroPEPT detectors?

 

6. Discussion

• The section number is wrong (4).
• 312: For PEPT —> For MicroPEPT
• 313 no need to bold w
• Following comment to the 1. Introduction, can you compare your results with other instruments of this type?

 

General editorial comments

• Put a blank (space) between a value and its unit, e.g. 40 cm not 40cm
• Giving area values, please use $\times$ instead of letter “x”. Also, put blanks around $\times$.

Author Response

We thank the reviewer for their very detailed and constructive comments.

We are not aware of any other instruments designed specifically to perform PEPT.  Some groups use scanners designed for medical PET to perform PEPT measurements but these are not necessarily characterised using the approach of this paper.  For these reasons we have not added any such comparison.

In terms of the maximum useful activity for the Forte, we consider 15 MBq an appropriate value (though only a rough guide).  Subsequent results are quoted for a 7.5 MBq source as this was what was used for the measurements.  

The intrinsic resolution of the detectors used in SuperPEPT and MicroPEPT is of course linked to the size of the crystal elements (whose dimensions are quoted in section 3) but a direct comparison with the intrinsic resolution of the large area detectors of the Forte would require measurements which we have not made.

Otherwise, we believe we have made all the changes requested:

With regard to the comment about trues not being adequately introduced, we have expanded the discussion of this point in section 4 (lines 206-210 of the revised paper).

 

Reviewer 3 Report

 

The article describes quite clearly the use of the two gamma's emitted back-to-back after positron annihilation in artificial additives in moving or flowing material. This is an obvious application of this nuclear radiation process, enabling the determination of the source positions, even in complex mechanical enclosres. While the positron emission camera is widely used in medical applications, now achieving precision on the sub-mm-scale, the reviewer was not aware of the specific apparatus which has been evaluated in this work.

The results described here by the Birmingham team serve as a good introduction for the non-specialist reader. Probably, specialists in the field of PET can see immediate possibilities for further improvements of this tracking method, both in precision and in rate capability. However, R&D resources needed for progress in this field can be quite substantial, and beyond the means of teams at Universities.

Author Response

We thank the reviewer for their supportive comments and note that they have not requested any changes to the manuscript.