Noise Reduction in LED-Based Photoacoustic Imaging

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In my review report document, I mentioned in details.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

1. Sentence structures are often complex and there is excessive use of passive voice, which reduces clarity and directness. Some sentences also lack concision and could be more precisely worded. Transition between sections is not always smooth.

 

2. Check for the run-on sentences that could be more effectively split or restructured.

 

3. Technical terminology is generally well-used. However, some sentences require multiple readings to fully understand the intended meaning. Some technical jargons need sufficient contextual explanation.

 

4. Overall, while the document's language does not impede scientific understanding, it would benefit significantly from professional language editing to enhance readability and linguistic precision

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript titled “Noise Reduction in LED Light Source-based Photoacoustic Imaging” by Kono et al. was reviewed for potential publication in the MDPI Photonics journal.

The authors proposed a new noise-reduction technique for LED-based photoacoustic imaging by developing a jitter-compensated periodic unipolar M-sequence (PUM) algorithm. This method compensates for time delays and circuit jitters common in high-power LED systems, which negatively impact the signal-to-noise ratio (SNR) in photoacoustic imaging. Experimental results demonstrated that the proposed algorithm significantly enhanced SNR compared to conventional approaches, even under varying bit lengths. This advancement increases the feasibility of LED-based photoacoustic systems, making them safer, more cost-effective, and potentially suitable for clinical use. Future research will focus on in vivo testing to further evaluate the system's clinical applicability.

While the paper addresses an important and timely topic with potential significance for advancing photoacoustic technology in both preclinical and clinical domains, several shortcomings need to be addressed. The manuscript requires moderate to major revisions to improve its quality. The logic, scientific reasoning, and overall flow of the paper need significant refinement. In particular, the authors do not provide sufficient justification for how the proposed method addresses a technological gap or why it would outperform existing techniques. Additionally, the manuscript has numerous grammatical and structural issues, including awkward sentence construction, missing words, and unnecessary parentheses, which compromise its readability.

I recommend that the authors undertake a comprehensive revision to improve both the scientific content and writing quality before resubmission. These improvements will help strengthen the paper's clarity, coherence, and impact.

 Major Comments

1. Abstract: The statement that pulsed lasers come with stringent safety restrictions is inaccurate. ANSI safety limits regulate the energy levels for in vivo studies. Instead, the authors should highlight the cost and size limitations of commonly used tunable pulsed lasers such as Q-switched Nd:YAG or OPO lasers.
2. Introduction/Discussion: While LED-based photoacoustic (PA) systems offer certain advantages, they also have limitations, such as reduced penetration depth and limited wavelength options for spectroscopic applications. These constraints should be addressed in the manuscript.
3. Introduction: The rationale for choosing the periodic and unipolar M-sequence (PUM) is not explained. The authors need to provide justification for why this approach was selected for their study.
4. The manuscript lacks a strong innovative contribution. Both the PUM-based method and LED-based PA systems have been widely studied. The authors should clearly explain what sets this work apart and highlight any novel aspects.
5. Coded laser pulse excitation can compromise spatial resolution in imaging. This potential drawback should be clearly discussed in the manuscript.
6. The authors cite circuit jitters in LED drivers as a technological gap. It would strengthen the paper to reference prior studies that identify jitter as a source of artifacts in PA images. Additionally, much of the presented data focuses on PA signals rather than PA images, which should also be clarified.
7. The description of the proposed algorithm is incomplete. Further detail and explanation are needed.
8. The results presented in Figure 5 may be influenced by detection delay or jitter in the photodiode. This potential issue needs to be clarified.
9. The increased SNR with higher bit numbers is functionally similar to signal averaging in conventional PA, which also raises laser power and acquisition time. This should be clearly explained.
10. The discussion should incorporate similar algorithms that have been developed. The authors should explain why their work is relevant, what gap it fills, and how it compares to existing methods.

  Minor Comments

 

1. The manuscript requires thorough proofreading to correct language deficiencies and grammatical errors.
2. Figure captions are not descriptive enough and require major revision to clearly explain the content and context of each figure.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

1. The manuscript requires thorough proofreading to correct language deficiencies and grammatical errors.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In this manuscript, the author proposed a novel decoding algorithm that compensated for LED jitter in PUM-based photoacoustic imaging using LED illumination. The SNR improvement by the proposed method was demonstrated using a phantom experiment. Below are some comments for consideration.  

1.        The title can be more concise by emphasising the technical novelty and removing ‘light source’ as it is repetitive after ‘LED’.

2.        The last sentence in Line 100 -101 requires rephrasing for clarity.

3.        Singular value decomposition [1] and deep learning [2-3] have also been employed for improving SNR of LED-based photoacoustic imaging.

[1] Shi, M., Vercauteren, T., & Xia, W. (2022). Spatiotemporal singular value decomposition for denoising in photoacoustic imaging with a low-energy excitation light source. Biomedical Optics Express, 13(12), 6416-6430.

[2] Paul, A., & Mallidi, S. (2024). U‐Net enhanced real‐time LED‐based photoacoustic imaging. Journal of Biophotonics, e202300465.

[3] Anas, Emran Mohammad Abu, et al. "Enabling fast and high-quality LED photoacoustic imaging: a recurrent neural networks based approach." Biomedical optics express 9.8 (2018): 3852-3866.

4.        Section 2.2, the jitter issue associated with LED-based systems needs to be further explained. For example, why the time delays caused by the jitters can be random?

5.        In Eq. (2), the variables j, k was not explained. In Eq. (2) and (3), the convolution operator and deconvolution operator need explicit definitions.    

6.        The diagram in Figure 2 is difficult to follow. Suggestions for improvement include using the same color for a shift number and employing distinct arrow types for different annotations.

7.    Eq. (5), the proposed model should use . In addition,  was not explained here.

8.   The SNR calculation in Eq. (6) and (7) needs further clarification. Why  was not used? N’ was not defined in Eq. (6).

9.        Section 3.2: Key experimental parameters, such as the wavelength of the LEDs and their pulse repetition rate, should be provided.

10.  Figure 5, subfigure (a)-(b) can be combined to better illustrate the actual delay.

11.  Figure 7, why the trigger signals at 5 us were enhanced using the proposed jitter-compensated PUM?  

12.  Include p-values (t-test) alongside the SNR comparisons to demonstrate statistical significance.

13.  Discussion: Expand on the practicability and limitations of the proposed algorithm.

 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

can be improved by proofreading (esp. grammar and spelling check).

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

A must address and important point: The longer pulse width (500 ns) means that the authors may have experienced partial thermal diffusion which ultimately would have led to lower PA signal amplitude, broader PA frequency content, reducing spatial resolution. Hence, more dominant thermoelastic expansion will potentially lead to mixed PA and thermal signals. What they can do is to compare with a laser-induced PA signal to see differences. My suggestion will still be: Shorten the pulse width to ≤150 ns for better stress confinement. I would also suggest them to use any time-gated signal processing or a deconvolution process to filter out the thermal effects.

The authors have made reasonable efforts to address the concerns within the scope they defined for the paper. They have added experiments with a blood vessel model (tube with ink). They added statistical analysis with error bars and t-tests. Also, their experimental setup and filter selection are now better. Despite limitations, the paper demonstrates a working algorithm with experimental validation showing SNR improvement. The authors have acknowledged the paper's limited scope (algorithm demonstration rather than clinical validation) and have revised their manuscript.

However, their position is that they're demonstrating an algorithm rather than building a clinically viable system, which is a reasonable stance but should be made clearer in the manuscript.

I suggest them to be little bit more explicit about the technology readiness level of their approach. The quantitative analysis of jitter characteristics can also be another point for enhancement (Can refer to as a future aim). Add a bit more detailed discussion of the limitations inherent in their simplified experimental model. Also, mention what kind of t-test is performed.

Overall, The paper would benefit from more rigorous characterization of system parameters, especially those related to jitter behavior and LED emission characteristics under high-current operation. The clinical applicability claims should be significantly tempered unless more complex phantoms, ex vivo biological experiments are conducted. Even with the tube phantom addition, the experiments don't address the complexity of real biological tissues. The work is at an early stage of development rather than demonstrating a clinically viable solution. The limitations of the study should be structured in such a way so that the above concerns be addressed and become their future aims.

Comments on the Quality of English Language

Sentences are sometimes less fluid to go through. Please check the long sentences and make some researchers who are naive to this particular scientific field to validate once more.

Author Response

We appreciate your important comments about our paper. We have carefully considered your comments and have revised to improve the quality of the paper. 

As you pointed out, the current study has meaning of pilot study to test the application of M-sequence to photoacoustic signal imaging for possible system with LED. The development of LED based system is still a challenge with limited studies and so we believe that study like ours is necessary and important although the demonstration is limited to simple phantom samples. Therefore, the main modification was made to the explanations regarding the limitation.

Please see the attachment for details of our response to your comments.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have adequately addressed all my comments in the revised manuscript. I have no further comments. 

Author Response

Thank you very much for reviewing our paper.