Multiphoton Tomography in Cosmetic Research

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this paper, entitled "Multiphoton Tomography in Cosmetic Research", the authors conduct a literature review on the topic. The focus is on the principles, historical development and main applications of multiphoton tomography in cosmetic research. The article is well written and easy to read with a good level of theoretical detail.

 

Section 3.2 Line 170-172 I feel that the last sentence of this paragraph should be supported by a reference.

 

I suggest adding a paragraph on the limitations of multiphoton tomography, such as imaging depth (inability to visualise deep dermis and subcutaneous fat), limited field of view requiring multiple scans to cover larger areas of skin, and risks of photodamage as a consequence of repeated or prolonged exposure to the laser.

Author Response

Reviewer 1: Section 3.2 Line 170-172 I feel that the last sentence of this paragraph should be supported by a reference. I suggest adding a paragraph on the limitations of multiphoton tomography, such as imaging depth (inability to visualise deep dermis and subcutaneous fat), limited field of view requiring multiple scans to cover larger areas of skin, and risks of photodamage as a consequence of repeated or prolonged exposure to the laser.

Comment: We thank the reviewer andd added ref 15 to section 3.2. and added the paragraph:

Limitations of the current MT technology includes the limited imaging depth of 0.2 mm which corresponds to the working distance of the high NA focusing optics. In fact, the high numerical aperture of 1.3 provides not only the superior resolution but is also a key element in the safety concept of the medical device. The high divergence of the laser beam beneath 0.2 mm tissue depth avoids any tissue damage including ocular damage.

Repeated scans and prolonged beam dwell time per pixel should be avoided. The aquisition time of a 512x512 pixels frame should be 6 seconds or less.  

Currently, the prices of tunable laser are still higher than 100,000 dollars. The costs for the femtosecond fiber laser are less. The price for the multiphoton tomograph is high but less compared with a commercial two-photon microscope provider. A limitation is the complexity, in particular, when using the two-photon FLIM module. In future, image processing should become simpler and should include AI.

An interesting approach is the combination of MPT with other non-invasive label-free skin imaging methods such as OCT, ultrasound, and photoacoustics. In particular, ultrasound and photoacoustics provide imaging depth in the range of millimeters. The effects of cosmetic treatments can be studied on multiple skin layers including deep dermis and fat layers. 

Reviewer 2: 1. The paper should explicitly state its inclusion/exclusion criteria for reviewed studies. 2. Please address limitations. The authors should dedicate a section to discussing MPT’s weaknesses, such as limited imaging depth and high costs, challenges in widespread adoption, operational complexity, and training requirements. And propose solutions or ongoing research addressing these issues. 3. One area that could further enhance the discussion is the potential synergy of MPT with other non-invasive imaging modalities, such as ultrasound.Ultrasound is widely recognized for its ability to assess deeper tissue structures, which complements MPT's high-resolution imaging of superficial skin layers. A discussion on how these two modalities could be combined-for instance, to achieve multi-scale imaging of both cellular and subcutaneous structures-would add valuable insight. Such a combination could broaden the applicability of MPT in cosmetic research, particularly for studying the effects of treatments on multiple skin layers. Please see this paper: Beiu, C.; Popa, L.G.; Bălăceanu-Gurău, B.; Iliescu, C.A.; Racoviță, A.; Popescu, M.N.; Mihai, M.M. Personalization of Minimally-Invasive Aesthetic Procedures with the Use of Ultrasound Compared to Alternative Imaging Modalities. Diagnostics 2023, 13, 3512. https://doi.org/10.3390/diagnostics13233512

Comment: We modified the paper regarding points 2 and 3 and added the paragraph:

Limitations of the current MT technology includes the limited imaging depth of 0.2 mm which corresponds to the working distance of the high NA focusing optics. In fact, the high numerical aperture of 1.3 provides not only the superior resolution but is also a key element in the safety concept of the medical device. The high divergence of the laser beam beneath 0.2 mm tissue depth avoids any tissue damage including ocular damage.

Repeated scans and prolonged beam dwell time per pixel should be avoided. The aquisition time of a 512x512 pixels frame should be 6 seconds or less.  

Currently, the prices of tunable laser are still higher than 100,000 dollars. The costs for the femtosecond fiber laser are less. The price for the multiphoton tomograph is high but less compared with a commercial two-photon microscope provider. A limitation is the complexity, in particular, when using the two-photon FLIM module. In future, image processing should become simpler and should include AI.

An interesting approach is the combination of MPT with other non-invasive label-free skin imaging methods such as OCT, ultrasound, and photoacoustics. In particular, ultrasound and photoacoustics provide imaging depth in the range of millimeters. The effects of cosmetic treatments can be studied on multiple skin layers including deep dermis and subcutaneous fat layers. 

We also added the cited reference.

Regarding point 1 we can state that we inlcuded all MPT studies in cosmetics we are aware of and did not exclude any study.

 

Reviewer 2 Report

Comments and Suggestions for Authors

 

            This paper offers a good foundation for understanding MPT’s applications in cosmetic research. While it effectively highlights the technology’s strengths, incorporating the recommendations below would make it a more balanced and comprehensive review:

 

1.     The paper should explicitly state its inclusion/exclusion criteria for reviewed studies.

 

2.     Please address limitations. The authors should dedicate a section to discussing MPT’s weaknesses, such as limited imaging depth and high costs, challenges in widespread adoption, operational complexity, and training requirements. And propose solutions or ongoing research addressing these issues.

 

3.     One area that could further enhance the discussion is the potential synergy of MPT with other non-invasive imaging modalities, such as ultrasound.Ultrasound is widely recognized for its ability to assess deeper tissue structures, which complements MPT's high-resolution imaging of superficial skin layers. A discussion on how these two modalities could be combined-for instance, to achieve multi-scale imaging of both cellular and subcutaneous structures-would add valuable insight. Such a combination could broaden the applicability of MPT in cosmetic research, particularly for studying the effects of treatments on multiple skin layers.

Please see this paper: Beiu, C.; Popa, L.G.; Bălăceanu-Gurău, B.; Iliescu, C.A.; Racoviță, A.; Popescu, M.N.; Mihai, M.M. Personalization of Minimally-Invasive Aesthetic Procedures with the Use of Ultrasound Compared to Alternative Imaging Modalities. Diagnostics 2023, 13, 3512. https://doi.org/10.3390/diagnostics13233512

Author Response

1. The paper should explicitly state its inclusion/exclusion criteria for reviewed studies.

 

2. Please address limitations. The authors should dedicate a section to discussing MPT’s weaknesses, such as limited imaging depth and high costs, challenges in widespread adoption, operational complexity, and training requirements. And propose solutions or ongoing research addressing these issues.

 

3. One area that could further enhance the discussion is the potential synergy of MPT with other non-invasive imaging modalities, such as ultrasound.Ultrasound is widely recognized for its ability to assess deeper tissue structures, which complements MPT's high-resolution imaging of superficial skin layers. A discussion on how these two modalities could be combined-for instance, to achieve multi-scale imaging of both cellular and subcutaneous structures-would add valuable insight. Such a combination could broaden the applicability of MPT in cosmetic research, particularly for studying the effects of treatments on multiple skin layers.

Please see this paper: Beiu, C.; Popa, L.G.; Bălăceanu-Gurău, B.; Iliescu, C.A.; Racoviță, A.; Popescu, M.N.; Mihai, M.M. Personalization of Minimally-Invasive Aesthetic Procedures with the Use of Ultrasound Compared to Alternative Imaging Modalities. Diagnostics 2023, 13, 3512. https://doi.org/10.3390/diagnostics13233512

comment: we added the paragraph and the cited reference:

Limitations of the current MT technology includes the limited imaging depth of 0.2 mm which corresponds to the working distance of the high NA focusing optics. In fact, the high numerical aperture of 1.3 provides not only the superior resolution but is also a key element in the safety concept of the medical device. The high divergence of the laser beam beneath 0.2 mm tissue depth avoids any tissue damage including ocular damage.

In our review we mentioned all MPT studies in cosmetics that we are aware of and did not exclude any study.  

Repeated scans and prolonged beam dwell time per pixel should be avoided. The aquisition time of a 512x512 pixels frame should be 6 seconds or less.  

Currently, the prices of tunable laser are still higher than 100,000 dollars. The costs for the femtosecond fiber laser are less. The price for the multiphoton tomograph is high but less compared with a commercial two-photon microscope provider. A limitation is the complexity, in particular, when using the two-photon FLIM module. In future, image processing should become simpler and should include AI.

An interesting approach is the combination of MPT with other non-invasive label-free skin imaging methods such as OCT, ultrasound, and photoacoustics. In particular, ultrasound and photoacoustics provide imaging depth in the range of millimeters. The effects of cosmetic treatments can be studied on multiple skin layers including deep dermis and subcutaneous fat layers.