Hand-Held Optoacoustic System for the Localization of Mid-Depth Blood Vessels

Round 1

Reviewer 1 Report

The manuscript by Zohar Or and other co-authors has described the study for optoacoustic imaging system targeting mid depth blood vessels. The study introduced and used the unfocused, wide linear US probe to image the blood vessels for the strength of the probe. The main idea of the study is development of the hand-held probe and OAT imaging system specialized for the parallel blood vessel. However, the manuscript needs more information about the imaging system and explanation of results. And, it is hard to decide that the images of blood vessels shows better. Overall, the study may be required more results with details.

1.       In the Introduction, the sentence. ‘ Doppler ultrasound is limited to ….’, is not correct. Doppler is limited to small vessels and slow flow as the reference 4.

2.        In the manuscript, the author said the disadvantage of the design. But, the advantage is too weak. What situation can be required for the system?

3.       In Fig3. Three signals are displayed as -2, 0, 2 mm. What is it?

4.       Fig.6 and 7 are located in wrong positions.

5.       Fig. 7, 8 and 9 need x and y scales and intensity.

6.       Does Fig.9 show the three images from 3 different probes? Or different angles?

Author Response

Thanks for your comments. please see attachment for a point by point response.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors have submitted a well-written manuscript about a home-made optoacoustic imaging system. The manuscript is well written and has merit. However, I do have some criticism, which I divide below into major and minor parts: 

Minor: 

- The abstract claims that the probe enables a depth-independent response up to 1cm. However, lines 170-172 seem to indicate the opposite. Perhaps the authors can be more specific about what 'response' is depth-independent, or revisit this claim. 

- In line 42, the authors state that the main source on optoacoustic contrast in the NIR I region is from blood. This is likely not true for a large part of the global population, particular from melanin in individuals with a skin tone darker than Fitzpatrick IV. It is recommended that the authors reconsider this claim. 

- There are minor typographical errors (e.g. line 12, 'in/at the focal plane'; line 252, in with). 

- The captions for figures 3, 6 and 9 were truncated in the version for review. This should be checked and edited. 

Major: 

- Lines 45-52 provide a summary of pre-existing implementations of handheld optoacoustic imaging systems. Noticeably absent is the linear array developed by Seno Medical which is both (the only) FDA and also CE certified as a medical device. As such, this detector cannot/should not be overlooked, particularly when in the next paragraph the authors frame their new type of array as linear. The authors should distinguish which part of their design is novel in the context at least of this particular medical device. The Seno array has a single fiber bundle, whereas they have two. The frequency is similar. Thus, it would be helpful for the authors to describe in detail the novelty in this context. 

- Line 189 indicates the laser energy used for imaging, and provides a safety reference. This reference is inadequate / indirect because it references a research manuscript and not the primary standard (note: the reference does make its own reference the actual standard). Of note, the reference in question performs imaging at a different wavelength and in some cases at a different laser frame rate of 10Hz. As the authors must know, the maximum permissible energy depends on the wavelength, pulse duration and pulse repetition. In fact, the point of the reference paper is that by using 1064nm, they can operate their laser at a much higher energy. Thus, the reference in question is not relevant to the current work. The authors state that the applied energy 'corresponds to 8.5mJ/cm2 at the output of the fiber bundle, well below the ANSI maximum permissible exposure of 30mJ/cm2.' To be confirmed, but I believe for a nanosecond laser at 808nm at 50Hz, the MPE is in this case is closer to 6mJ/cm2. If that calculation is accurate, then the authors have used their laser in an unsafe manner which should not be repeated by others in the field. This is the major sticking point for this paper. Because the initial reference was not relevant, and because of the different understanding from the reviewer, it is suggested that the authors check the primary standard and perform and justify in the manuscript their own calculation of the safety of the applied laser energy. If the energy can be justified in the context of the standard, then the experiments as conducted are reasonable and only the methods / reference should be updated. However, if the applied energy was unsafe, then the experiments should be repeated at a safe energy, and the figures / text updated. 

Author Response

Thanks for your comments. please see the attachment for a point by point response.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

With the revision, the manuscript are enough to be published. I recommend the editor to consider the study published in Photonics. Thank you.

Reviewer 2 Report

Thank you for addressing the suggested changes.