Name: hand-held clinical photoacoustic imaging system for real-time non-invasive small animal imaging
Uploaded: 2017-10-16T15:00:00
Description: Watch this Scientific Journal Video about Hand-held Clinical Photoacoustic Imaging System for Real-time Non-invasive Small Animal Imaging at JoVE.com

The authors would like to acknowledge the financial support from the Tier 1 research grant funded by the Ministry of Education in Singapore (RG48/16: M4011617) and Tier 2 research grant funded by Ministry of Education in Singapore (ARC2/15: M4020238). The authors would like to acknowledge Dr. Rhonnie Austria Dienzo for his help with animal handling.

All animal experiments were performed according to the approved guidelines and regulations by the institutional Animal Care and Use committee of Nanyang Technological University, Singapore (Animal Protocol Number ARF-SBS/NIE-A0263).
1. Handheld Real-time Clinical PA and US Imaging System
<ol>
	<li>The schematic of the handheld clinical PAI system33 is shown in Figure 1a. It consists of a optical parametric oscillator (OPO) laser pumped by...

<ol>
	<li>Yun, S. H., Kwok, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Light+in+diagnosis,+therapy+and+surgery.">Light in diagnosis, therapy and surgery.</a> Nat. Biomed. Eng. 1, 0008 (2017).</li><li>Tseng, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clinical+accuracy+of+preoperative+breast+MRI+for+breast+cancer.">Clinical accuracy of preoperative breast MRI for breast cancer.</a> J. Surg. Oncol. , (2017).</li><li>Baran, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimization+of+propagation-based+x-ray+phase-contrast+tomography+for+breast+cancer+imaging.">Optimization of propagation-based x-ray phase-contrast tomography for breast cancer imaging.</a> Phys. Med. Biol. 62 (6), 2315 (2017).</li><li>Huzarski, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Screening+with+magnetic+resonance+imaging,+mammography+and+ultrasound+in+women+at+average+and+intermediate+risk+of+breast+cancer.">Screening with magnetic resonance imaging, mammography and ultrasound in women at average and intermediate risk of breast cancer.</a> Hered. Cancer Clin. Pract. 15 (1), 4 (2017).</li><li>Upputuri, P. K., Pramanik, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+advances+toward+preclinical+and+clinical+translation+of+photoacoustic+tomography:+a+review.">Recent advances toward preclinical and clinical translation of photoacoustic tomography: a review.</a> J. Biomed. Opt. 22 (4), 041006 (2017).</li><li>Wang, L. V., Yao, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+practical+guide+to+photoacoustic+tomography+in+the+life+sciences.">A practical guide to photoacoustic tomography in the life sciences.</a> Nat. Methods. 13 (8), 627-638 (2016).</li><li>Wang, L. V., Gao, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photoacoustic+microscopy+and+computed+tomography:+from+bench+to+bedside.">Photoacoustic microscopy and computed tomography: from bench to bedside.</a> Annu Rev Biomed Eng. 16, 155-185 (2014).</li><li>Beard, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biomedical+photoacoustic+imaging.">Biomedical photoacoustic imaging.</a> Interface Focus. 1 (4), 602-631 (2011).</li><li>Yao, J., Wang, L. 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K., Moothanchery, M., Pramanik, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pulsed+laser+diode+photoacoustic+tomography+(PLD-PAT)+system+for+fast+in+vivo+imaging+of+small+animal+brain.">Pulsed laser diode photoacoustic tomography (PLD-PAT) system for fast in vivo imaging of small animal brain.</a> Proc Spie. , (2017).</li><li>Fakhrejahani, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clinical+report+on+the+first+prototype+of+a+photoacoustic+tomography+system+with+dual+illumination+for+breast+cancer+imaging.">Clinical report on the first prototype of a photoacoustic tomography system with dual illumination for breast cancer imaging.</a> PLoS One. 10 (10), e0139113 (2015).</li><li>Wang, L. 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D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Morbidity+after+sentinel+lymph+node+biopsy+in+primary+breast+cancer:+results+from+a+randomized+controlled+trial.">Morbidity after sentinel lymph node biopsy in primary breast cancer: results from a randomized controlled trial.</a> J. Clin. Oncol. 23 (19), 4312-4321 (2005).</li><li>Kim, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Handheld+array-based+photoacoustic+probe+for+guiding+needle+biopsy+of+sentinel+lymph+nodes.">Handheld array-based photoacoustic probe for guiding needle biopsy of sentinel lymph nodes.</a> J. Biomed. Opt. 15 (4), 046010 (2010).</li><li>Garcia-Uribe, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dual-Modality+Photoacoustic+and+Ultrasound+Imaging+System+for+Noninvasive+Sentinel+Lymph+Node+Detection+in+Patients+with+Breast+Cancer.">Dual-Modality Photoacoustic and Ultrasound Imaging System for Noninvasive Sentinel Lymph Node Detection in Patients with Breast Cancer.</a> Sci. Rep. 5, 15748 (2015).</li><li>Kim, C., Song, K. H., Gao, F., Wang, L. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sentinel+Lymph+Nodes+and+Lymphatic+Vessels:+Noninvasive+Dual-Modality+in+Vivo+Mapping+by+Using+Indocyanine+Green+in+Rats-Volumetric+Spectroscopic+Photoacoustic+Imaging+and+Planar+Fluorescence+Imaging.">Sentinel Lymph Nodes and Lymphatic Vessels: Noninvasive Dual-Modality in Vivo Mapping by Using Indocyanine Green in Rats-Volumetric Spectroscopic Photoacoustic Imaging and Planar Fluorescence Imaging.</a> Radiology. 255 (2), 442-450 (2010).</li><li>Pan, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Near+infrared+photoacoustic+detection+of+sentinel+lymph+nodes+with+gold+nanobeacons.">Near infrared photoacoustic detection of sentinel lymph nodes with gold nanobeacons.</a> Biomaterials. 31 (14), 4088-4093 (2010).</li><li>Song, K. H., Kim, C., Cobley, C. M., Xia, Y., Wang, L. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Near-infrared+gold+nanocages+as+a+new+class+of+tracers+for+photoacoustic+sentinel+lymph+node+mapping+on+a+rat+model.">Near-infrared gold nanocages as a new class of tracers for photoacoustic sentinel lymph node mapping on a rat model.</a> Nano Lett. 9 (1), 183-188 (2009).</li><li>Sivasubramanian, K., Periyasamy, V., Wen, K. K., Pramanik, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimizing+light+delivery+through+fiber+bundle+in+photoacoustic+imaging+with+clinical+ultrasound+system:+Monte+Carlo+simulation+and+experimental+validation.">Optimizing light delivery through fiber bundle in photoacoustic imaging with clinical ultrasound system: Monte Carlo simulation and experimental validation.</a> J. Biomed. 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Currently the cost of screening, diagnosis, and treatment of cancer is very high. There are different imaging modalities which are being used for cancer screening and diagnosis. However, a lot of these imaging techniques have limitations including bulky machine size, invasive diagnosis, unfriendliness to patients, too expensive, requirement of ionizing radiation, or use of radioactive contrast agents. Therefore, an efficient, cost effective, real-time imaging and guiding system is much needed. Combined US and PA imaging ...

For the detection and staging of cancer, different imaging techniques are available. Some of the widely used imaging modalities are magnetic resonance imaging (MRI), X-Ray computed tomography (CT), X-Ray, ultrasound (US), positron emission tomography (PET), fluorescence imaging, etc.1,2,3,4. But, some of the existing imaging techniques are either invasive, have harmful radiation, or are slow, expensive, bulky, or unfriendly to patients. Thus, there is a constant need to develop new, fast, and cost-effective imaging techniques for diagnostics and therapy5.
Photoacoustic imaging (PAI) is an emerging imaging technique, which combines rich optical contrast with high ultrasonic resolution at a deeper imaging depth5,6,7,8,9. In PAI, a short laser pulse is used for tissue irradiation. The light gets absorbed by the tissue which leads to a small temperature rise. Due to thermoelastic expansion, pressure waves (in the form of acoustic waves) are generated within the tissue. The generated acoustic waves (also known as photoacoustic (PA) waves) are acquired with a wideband ultrasound transducer (UST) outside the tissue boundary. These acquired PA signals can be used to reconstruct PA images, revealing the structural and functional information inside the tissue. PAI has a wide array of applications, including: blood vessel imaging, sentinel lymph node imaging, brain vasculature imaging, tumor imaging, molecular imaging, etc.10,11,12,13,14,15 PAI has numerous applications because of its advantages, namely: deeper penetration depth, good spatial resolution, and high soft tissue contrast. The contrast in PAI can be endogenous from blood, melanin, etc. When the endogenous contrast is not strong enough, exogenous contrast agents like organic dyes, nanoparticles, quantum dots, etc.16,17,18,19,20,21 can be used for improving the contrast.
Although PAI has numerous benefits relative to other imaging techniques, clinical translation is still a very big challenge. The main limitations are the bulky nature of the lasers being used, most of the USTs used for data acquisition are not compatible with clinical US systems, and the non-availability of commercially available clinical US imaging systems which give access to raw channel data. Only recently, commercial clinical US machines with access to raw data have become available22. In this work, we aim to demonstrate the feasibility of PAI with a handheld set-up using a clinical US platform. We aim to demonstrate this by showing non-invasive imaging of sentinel lymph nodes (SLNs) in a small animal model.
Invasive breast tumors are one of the leading causes of cancer death among women. Diagnosing and staging breast cancer early is vital for deciding treatment strategies, which play an important role in the prognosis of the patient. For breast cancer staging sentinel lymph node biopsies (SLNB) are usually used23,24. SLN is the primary lymph node where the possibility of finding cancer cells is the highest due to metastasis. SLNBs involve injecting a dye or a radioactive tracer, followed by cutting open the area with a small incision, and then locating the SLN visually in case of dyes or with the help of a Geiger counter, in case of a radioactive tracer. After identification, a few SLN are removed for histopathological studies24,25. Positive SLNB indicates that the tumor has metastasized to nearby lymph nodes and maybe to other organs. Negative SLNB indicates that the probability of metastasis is negligible26. SLNB has numerous complications associated with it like arm numbness, lymphedema, etc.27 To eliminate the SLNB associated complications, a non-invasive imaging technique is needed.
For SLN mapping in small animals and humans, PA imaging has been explored extensively with the help of different contrast agents15,28,29,30,31,32. However, the systems used currently cannot be used in a clinical scenario as pointed out earlier. Another concern to be addressed is the surgical procedure involved in SLNB28. Adapting minimally invasive procedures for fine needle aspiration biopsy (FNAB) was needed to reduce the recovery time and the side effects of the patients. In this work, a clinical US system was used for combined US and PA imaging was used. For ease of use in clinical setup, a custom made handheld holder for housing optical fiber and UST was designed. Methylene blue (MB) was used for identifying and mapping SLNs. Additionally, to eliminate the complications associated with the SLNB surgery, non-invasive real-time needle tracking is also demonstrated.

<table>
	<tbody>
		<tr>
			<td>Q-switched Nd:YAG laser</td>
			<td>Continuum</td>
			<td>Surelite</td>
			<td>Pump laser</td>
		</tr>
		<tr>
			<td>Optical parametric oscillator</td>
			<td>Continuum</td>
			<td></td>
			<td>OPO laser</td>
		</tr>
		<tr>
			<td>Clinical ultrasound imaging system</td>
			<td>Alpinion</td>
			<td>E-CUBE 12R</td>
			<td>Dual modal ultrasound and photoacoustic imaging system</td>
		</tr>
		<tr>
			<td>Linear array ultrasound transducer</td>
			<td>Alpinion</td>
			<td>L3-12</td>
			<td>128 element linear array transducer with centre frequency of 8.5 MHz, fractional bandwidth of 95%,</td>
		</tr>
		<tr>
			<td>Bifurcated optical fiber</td>
			<td>CeramOptec</td>
			<td>Custom made</td>
			<td>To couple the light from the laser to the handheld fiber holder</td>
		</tr>
		<tr>
			<td>Lens</td>
			<td>Thorlabs</td>
			<td>LB1869</td>
			<td>Focus light from the laser to the optical fiber</td>
		</tr>
		<tr>
			<td>Ultrasound gel</td>
			<td>Progress/parker acquasonic gel</td>
			<td>PA-GEL-CLEA-5000</td>
			<td>Acoustic coupling</td>
		</tr>
		<tr>
			<td>Image Processing software</td>
			<td>Mathworks</td>
			<td>Matlab</td>
			<td>Home made program using Matlab</td>
		</tr>
		<tr>
			<td>Anesthetic Machine</td>
			<td>medical plus pte ltd</td>
			<td>Non-Rebreathing Anaesthesia machine with oxygen concentrator.</td>
			<td>Supplies oxygen and isoflurane to animal</td>
		</tr>
		<tr>
			<td>Pulse Oxymeter portable</td>
			<td>Medtronic</td>
			<td>PM10N with veterinary sensor</td>
			<td>Monitors the pulse oxymetry of the animal</td>
		</tr>
		<tr>
			<td>Animal distributor</td>
			<td>In Vivos Pte Ltd, Singapore</td>
			<td></td>
			<td>Animal distributor that supplies small animals for research purpose.</td>
		</tr>
		<tr>
			<td>Breathing mask</td>
			<td>Custom made</td>
			<td></td>
			<td>Used along with animal holder to supply anesthesia mixture to the animal</td>
		</tr>
		<tr>
			<td>chicken breast tissue</td>
			<td>Pasar</td>
			<td></td>
			<td>Used to add depth to mimic human imaging scenario</td>
		</tr>
		<tr>
			<td>23G needle</td>
			<td>BD Precisionglide</td>
			<td>23G,1 and half inch</td>
			<td>Used for realtime needle guidance</td>
		</tr>
		<tr>
			<td>Holder for the fiber optic cable</td>
			<td>Custom made</td>
			<td></td>
			<td>To hold the input end of the bifurcated cable</td>
		</tr>
		<tr>
			<td>Handheld probe</td>
			<td>Custom made 3D printed</td>
			<td></td>
			<td>With two slots for the two output ends of the optical fiber and one slot for the ultrasound transducer</td>
		</tr>
		<tr>
			<td>Methylene blue (10 mg/mL)</td>
			<td>Sterop</td>
			<td></td>
			<td>Contrast agent for PA imaging</td>
		</tr>
		<tr>
			<td>Laser tuning software</td>
			<td>Surelite OPO PLUS</td>
			<td>SLOPO</td>
			<td>Software to tune the wavelength of OPO laser</td>
		</tr>
		<tr>
			<td>Photodiode</td>
			<td>Thorlabs</td>
			<td>SP05/M</td>
			<td>To detect the laser pulse to trigger the ultrasound system</td>
		</tr>
		<tr>
			<td>Photodiode bias module</td>
			<td>Thorlabs</td>
			<td>PBM42</td>
			<td>To amplify the photodiode signal to tigger ultrasound signal</td>
		</tr>
		<tr>
			<td>Depilatory cream</td>
			<td>Reckitt Benckiser</td>
			<td>Veet</td>
			<td>Used to remove hair from the imaging area</td>
		</tr>
		<tr>
			<td>Laser power meter</td>
			<td>Ophir</td>
			<td>Starlite, p/n: 7Z01565</td>
			<td>Used to measure the laser power</td>
		</tr>
	</tbody>
</table>

hand-held clinical photoacoustic imaging system for real-time non-invasive small animal imaging

Translation of photoacoustic imaging into the clinic is a major challenge. Handheld real-time clinical photoacoustic imaging systems are very rare. Here, we report a combined photoacoustic and clinical ultrasound imaging system by integrating an ultrasound probe with light delivery for small animal imaging. We demonstrate this by showing sentinel lymph node imaging in small animals along with minimally invasive real-time needle guidance. A clinical ultrasound platform with access to raw channel data allows the integration of photoacoustic imaging leading to a handheld real-time clinical photoacoustic imaging system. Methylene blue was used for sentinel lymph node imaging at 675 nm wavelength. Additionally, needle guidance with dual modal ultrasound and photoacoustic imaging was shown using the imaging system. Depth imaging of up to 1.5 cm was demonstrated with a 10 Hz laser at a photoacoustic imaging frame rate of 5 frames per second.

<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56649/56649fig1.jpg" /> 
Figure 1: System description. (a) Schematic representation of the PAI system with dual modal clinical US system. OPO - optical parametric oscillator, OF - optical fiber bundle, FH - fiber holder, USM- clinical US machine. The fiber holder integrates the UST and two output optical fiber bundle. The anesthesia machine supplying isoflurane and oxygen is used to keep the ...

Watch this Scientific Journal Video about Hand-held Clinical Photoacoustic Imaging System for Real-time Non-invasive Small Animal Imaging at JoVE.com

Hand-held Clinical Photoacoustic Imaging System for Real-time Non-invasive Small Animal Imaging

A clinical handheld photoacoustic imaging system will be demonstrated for real-time non-invasive small animal imaging.

Translation of photoacoustic imaging into the clinic is a major challenge. Handheld real-time clinical photoacoustic imaging systems are very rare. Here, ...

The overall goal of this procedure is to demonstrate non-invasive handheld photoacoustic imaging at the sentinel lymph node using a clinical ultrasound system and to illustrate real-time photoacoustic needle guidance. Photoacoustic imaging, hybrid imaging modality combining light and ultrasound provides high optical contrast, high resolution, deep tissue imaging in vivo. However, translating for the crystal imaging into clinical application is challenging.This work presents a hand-held, real time, photoacoustic imaging system by integrating light illumination with the clinical ultrasound platform. Demonstrating the procedure will be Kathyayini Sivasubramanian a PHD student and Vijitha Periyasamy a researcher from our laboratory. Turn on the laser by switching on the AC power and turning the key on the laser controller to the left.To set the Q-switch delay, press the select key until you see the delay value and increase it to 170 microseconds. Then, set the repetition rate to 10 hertz to ensure low laser energy and start the laser. Open the laser wavelength tuning software.Select the Go To menu, enter the wavelength at 675 nano meters and press the start button to set the wavelength to 675 nano meters. Then press the shutter button and turn the laser on using the switch. Use a one inch diameter planoconvex lens with a focal length of 15 millimeters to focus the laser beam to the fiber bundle so that all the light falls on the fiber input end.Once aligned, switch off the laser. Choose the appropriately angled probe holder based on the desired depth of imaging, the size of the object, the shape of the object, and the object's location. For this experiment, fit the bifurcated optical fiber into the side slot of the probe holder at a light illumination angle of 15 degrees.Loosen the screws on the side and adjust the distance between the transducer and the fiber's end to one centimeter. After adjusting it to the exact distance tighten the screws. Then, switch the laser back on and make sure to obtain a rectangular laser beam spot in front of the transducer.Once the rectangular beam can be seen in front of the transducer, increase the delay value to 210 microseconds. Next, turn on the clinical ultrasound system and open the imaging software provided by the manufacturer. From the touch screen, select the research button to Operate and Research mode, then click on the combined ultrasound and photoacoustic imaging script and click the run button for imaging in the combined mode.To begin, place a 23 gauge needle on top of a piece of raw chicken breast tissue. Apply ultrasound gel and then add a slice of chicken tissue on top of it. With the laser on, take photoacoustic images of the needle.Then, apply ultrasound gel on top of the breast tissue and add a second piece of tissue. Take another photoacoustic image and continue to apply the ultrasound gel and stack the breast tissue one-by-one up to three centimeters thick imaging every time chicken tissue layer is added. Ensure that the animal is anesthetized by checking for reflex following a toe pinch.Then, remove hair from the region of interest using a hair removal cream and apply an artificial tear ointment to prevent the eyes from dryness and accidental laser damage. Next, place a blue under pad on the table and position the animal sideways on it. Affix the nose cone to administer inhalation anesthesia and clip a pulse oximeter to the hind paw to maintain and monitor the animal during the experiments.Prior to imaging, apply one to two milliliters of ultrasound gel on the skin, using a syringe, and spread it well using an applicator. Then, place a 0.5 centimeter thick slice of chicken breast tissue on the imaging area and apply more u.s. gel on the chicken tissue to improve coupling.At this point, switch on the laser and place the hand held probe holder on top of the chicken tissue. Move the holder right to left in the combined ultrasound and photoacoustic modes. Press the freeze button on the ultrasound system and then press the export selected frames button to export the control images prior to injecting the contrast agent.Then, inject 0.2 milliliters of the methylene blue contrast agent into the fore paw of the animal and massage it well for two minutes to facilitate the move of the contrast agent to the lymph nodes through the lymph vessels. After, five minutes, scan the area again with the handheld probe along the chicken tissue to locate the sentinel lymph nodes with the help of the photoacoustic signal. Once identified, save the frames.Add two more layers of 0.5 centimeter thick chicken tissue slices on top of the animal one by one and locate and save the sentinel lymph node images up to 1.5 centimeters into the tissue. After imaging, switch off the laser, remove all of the chicken tissue slices and prepare the rat for photoacoustic spectroscopy. Place a 0.5 centimeter thick slab of chicken breast tissue onto the rat.Then, change the wavelength of the laser to 670 nanometers and switch on the laser. Scan with the probe along the chicken breast tissue to locate the sentinel lymph node with the help of the photoacoustic signal. Hold the probe stable after identifying the sentinel lymph node.In the laser tuning software, enter the wavelength as 800 nanometers, set the speed to 10 nanometers per second and click the start button. This will vary the wavelength from 670 nanometers to 800 nanometers at a speed of 10 nanometers per second. Observe the change in the photoacoustic signal from the sentinel lymph node on the monitor of the ultrasound system.To track needles in real time, set the wavelength to 675 nanometers then move the probe to locate and identify a sentinel lymph node on the screen. Inject a 23 gauge needle into the rat parallel to the ultrasound transducer. Guide it in real time as it passes through the chicken tissue and into the animal to reach the sentinel lymph node.Once finished, turn off the laser. Remove the chicken tissue and pulse oximeter from the animal and move the animal to the work bench. Then, clean the ultrasound gel from the rat with cotton wipes.Once clean, place the animal on its bedding. Monitor it until it regains consciousness and return it to it's cage after it's behavior is normal. Using the method shown in this video, the full width at half maximum was calculated from the needle images at various depths.The axial resolution was calculated to be 207 micrometers and the lateral resolution, limited by the ultrasound transducer, was 351 micrometers. Before adding the contrast agent, methylene blue, the sentinel lymph node blends in with the other tissue. Following injection, the sentinel lymph node can be very easily identified due to the strong photoacoustic signal from the accumulated methylene blue.Photoacoustic imaging is also useful for needle guidance as ultrasound alone provides poor contrast. With photoacoustic imaging, the contrast obtained from the needle is very high and can be easily monitored and tracked in vivo. Once the needle reaches the sentinel lymph node, a small portion of the lymph tissue can be taken out for further histological examination.The visibility of the photoacoustic needle guidance is demonstrated with the clinical ultrasound system. Once mastered, the technique of photoacoustic sentinel lymph node and needle imaging can be done within an hour if it performed properly. Laser light delivery integrated with clinical ultrasound system enables hand held photoacoustic imaging.This will help in the translation of photoacoustic imaging into the clinic. Potential applications of handheld photoacoustic imaging system incudes imaging of blood vessels, tumor, sentinel lymph node, urinary bladder, and circulating tumor cells.

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Research

JoVE Journal

Bioengineering

Three-dimensional Optical-resolution Photoacoustic Microscopy

Optical microscopy, providing valuable insights at the cellular and organelle levels, has been widely recognized as an enabling biomedical technology. As the mainstays of in vivo three-dimensional (3-D) optical microscopy, single-/multi-photon fluorescence microscopy and optical coherence tomography (OCT) have demonstrated their extraordinary sensitivities to fluorescence and optical scattering contrasts, respectively. However, the optical absorption contrast of biological tissues, which encodes essential physiological/pathological information, has not yet been assessable. 
The emergence of biomedical photoacoustics has led to a new branch of optical microscopy optical-resolution photoacoustic microscopy (OR-PAM)1, where the optical irradiation is focused to the diffraction limit to achieve cellular1 or even subcellular2 level lateral resolution. As a valuable complement to existing optical microscopy technologies, OR-PAM brings in at least two novelties. First and most importantly, OR-PAM detects optical absorption contrasts with extraordinary sensitivity (i.e., 100%). Combining OR-PAM with fluorescence microscopy3 or with optical-scattering-based OCT4 (or with both) provides comprehensive optical properties of biological tissues. Second, OR-PAM encodes optical absorption into acoustic waves, in contrast to the pure optical processes in fluorescence microscopy and OCT, and provides background-free detection. The acoustic detection in OR-PAM mitigates the impacts of optical scattering on signal degradation and naturally eliminates possible interferences (i.e., crosstalks) between excitation and detection, which is a common problem in fluorescence microscopy due to the overlap between the excitation and fluorescence spectra. 
Unique for optical absorption imaging, OR-PAM has demonstrated broad biomedical applications since its invention, including, but not limited to, neurology5, 6, ophthalmology7, 8, vascular biology9, and dermatology10. In this video, we teach the system configuration and alignment of OR-PAM as well as the experimental procedures for in vivo functional microvascular imaging.

Optical-resolution photoacoustic microscopy (OR-PAM) is an emerging technology capable of imaging optical absorption contrasts in vivo with cellular resolution and sensitivity. Here, we provide a visualized instruction on the experimental protocols of OR-PAM, including system configuration, system alignment, typical in vivo experimental procedures, and functional imaging schemes.

Optical microscopy, providing valuable insights at the cellular and organelle levels, has been widely recognized as an enabling biomedical technology. As ...

Photoacoustic Cystography

Conventional pediatric cystography, which is based on diagnostic X-ray using a radio-opaque dye, suffers from the use of harmful ionizing radiation. The risk of bladder cancers in children due to radiation exposure is more significant than many other cancers. Here we demonstrate the feasibility of nonionizing and noninvasive photoacoustic (PA) imaging of urinary bladders, referred to as photoacoustic cystography (PAC), using near-infrared (NIR) optical absorbents (i.e. methylene blue, plasmonic gold nanostructures, or single walled carbon nanotubes) as an optical-turbid tracer. We have successfully imaged a rat bladder filled with the optical absorbing agents using a dark-field confocal PAC system. After transurethral injection of the contrast agents, the rat's bladders were photoacoustically visualized by achieving significant PA signal enhancement. The accumulation was validated by spectroscopic PA imaging. Further, by using only a laser pulse energy of less than 1 mJ/cm2 (1/20 of the safety limit), our current imaging system could map the methylene-blue-filled-rat-bladder at the depth of beyond 1 cm in biological tissues in vivo. Both in vivo and ex vivo PA imaging results validate that the contrast agents were naturally excreted via urination. Thus, there is no concern regarding long-term toxic agent accumulation, which will facilitate clinical translation.

Photoacoustic cystography (PAC) has a great potential to map urinary bladders, a radiation sensitive internal organ in pediatric patients, without using any ionizing radiation or toxic contrast agent. Here we demonstrate the use of PAC for mapping urinary bladders with an injection of optical-opaque tracers in rats in vivo.

Conventional pediatric cystography, which is based on diagnostic X-ray using a radio-opaque dye, suffers from the use of harmful ionizing radiation. The ...

Universal Hand-held Three-dimensional Optoacoustic Imaging Probe for Deep Tissue Human Angiography and Functional Preclinical Studies in Real Time

The exclusive combination of high optical contrast and excellent spatial resolution makes optoacoustics (photoacoustics) ideal for simultaneously attaining anatomical, functional and molecular contrast in deep optically opaque tissues. While enormous potential has been recently demonstrated in the application of optoacoustics for small animal research, vast efforts have also been undertaken in translating this imaging technology into clinical practice. We present here a newly developed optoacoustic tomography approach capable of delivering high resolution and spectrally enriched volumetric images of tissue morphology and function in real time. A detailed description of the experimental protocol for operating with the imaging system in both hand-held and stationary modes is provided and showcased for different potential scenarios involving functional and molecular studies in murine models and humans. The possibility for real time visualization in three dimensions along with the versatile handheld design of the imaging probe make the newly developed approach unique among the pantheon of imaging modalities used in today&#8217;s preclinical research and clinical practice.

We provide herein a detailed description of the experimental protocol for imaging with a newly developed hand-held optoacoustic (photoacoustic) system for three-dimensional functional and molecular imaging in real time. The demonstrated powerful performance and versatility may define new application areas of the optoacoustic technology in preclinical research and clinical practice.

The exclusive combination of high optical contrast and excellent spatial resolution makes optoacoustics (photoacoustics) ideal for simultaneously ...

Using Cell-substrate Impedance and Live Cell Imaging to Measure Real-time Changes in Cellular Adhesion and De-adhesion Induced by Matrix Modification

Cell-matrix adhesion plays a key role in controlling cell morphology and signaling. Stimuli that disrupt cell-matrix adhesion (e.g., myeloperoxidase and other matrix-modifying oxidants/enzymes released during inflammation) are implicated in triggering pathological changes in cellular function, phenotype and viability in a number of diseases. Here, we describe how cell-substrate impedance and live cell imaging approaches can be readily employed to accurately quantify real-time changes in cell adhesion and de-adhesion induced by matrix modification (using endothelial cells and myeloperoxidase as a pathophysiological matrix-modifying stimulus) with high temporal resolution and in a non-invasive manner. The xCELLigence cell-substrate impedance system continuously quantifies the area of cell-matrix adhesion by measuring the electrical impedance at the cell-substrate interface in cells grown on gold microelectrode arrays. Image analysis of time-lapse differential interference contrast movies quantifies changes in the projected area of individual cells over time, representing changes in the area of cell-matrix contact. Both techniques accurately quantify rapid changes to cellular adhesion and de-adhesion processes. Cell-substrate impedance on microelectrode biosensor arrays provides a platform for robust, high-throughput measurements. Live cell imaging analyses provide additional detail regarding the nature and dynamics of the morphological changes quantified by cell-substrate impedance measurements. These complementary approaches provide valuable new insights into how myeloperoxidase-catalyzed oxidative modification of subcellular extracellular matrix components triggers rapid changes in cell adhesion, morphology and signaling in endothelial cells. These approaches are also applicable for studying cellular adhesion dynamics in response to other matrix-modifying stimuli and in related adherent cells (e.g., epithelial cells).

Here, we present a protocol to continuously quantify cell adhesion and de-adhesion processes with high temporal resolution in a non-invasive manner by cell-substrate impedance and live cell imaging analyses. These approaches reveal the dynamics of cell adhesion/de-adhesion processes triggered by matrix modification and their temporal relationship to adhesion-dependent signaling events.

Cell-matrix adhesion plays a key role in controlling cell morphology and signaling. Stimuli that disrupt cell-matrix adhesion (e.g., myeloperoxidase and ...

Real-time Monitoring of High Intensity Focused Ultrasound (HIFU) Ablation of In Vitro Canine Livers Using Harmonic Motion Imaging for Focused Ultrasound (HMIFU)

Harmonic Motion Imaging for Focused Ultrasound (HMIFU) is a technique that can perform and monitor high-intensity focused ultrasound (HIFU) ablation. An oscillatory motion is generated at the focus of a 93-element and 4.5 MHz center frequency HIFU transducer by applying a 25 Hz amplitude-modulated signal using a function generator. A 64-element and 2.5 MHz imaging transducer with 68kPa peak pressure is confocally placed at the center of the HIFU transducer to acquire the radio-frequency (RF) channel data. In this protocol, real-time monitoring of thermal ablation using HIFU with an acoustic power of 7 W on canine livers in vitro is described. HIFU treatment is applied on the tissue during 2 min and the ablated region is imaged in real-time using diverging or plane wave imaging up to 1,000 frames/second. The matrix of RF channel data is multiplied by a sparse matrix for image reconstruction. The reconstructed field of view is of 90&#176; for diverging wave and 20 mm for plane wave imaging and the data are sampled at 80 MHz. The reconstruction is performed on a Graphical Processing Unit (GPU) in order to image in real-time at a 4.5 display frame rate. 1-D normalized cross-correlation of the reconstructed RF data is used to estimate axial displacements in the focal region. The magnitude of the peak-to-peak displacement at the focal depth decreases during the thermal ablation which denotes stiffening of the tissue due to the formation of a lesion. The displacement signal-to-noise ratio (SNRd) at the focal area for plane wave was 1.4 times higher than for diverging wave showing that plane wave imaging appears to produce better displacement maps quality for HMIFU than diverging wave imaging.

Real-time Monitoring of High Intensity Focused Ultrasound HIFU Ablation of In Vitro Canine Livers Using Harmonic Motion Imaging for Focused Ultrasound HMIFU

This article describes real-time monitoring of HIFU ablation in canine liver with high frame rate ultrasound imaging using diverging and plane wave imaging. Harmonic Motion Imaging for Focused Ultrasound is used to image the decrease of acoustic radiation force induced displacement in the ablated region.

Harmonic Motion Imaging for Focused Ultrasound (HMIFU) is a technique that can perform and monitor high-intensity focused ultrasound (HIFU) ablation. An ...

Multimodal Imaging and Spectroscopy Fiber-bundle Microendoscopy Platform for Non-invasive, In Vivo Tissue Analysis

Recent fiber-bundle microendoscopy techniques enable non-invasive analysis of in vivo tissue using either imaging techniques or a combination of spectroscopy techniques. Combining imaging and spectroscopy techniques into a single optical probe may provide a more complete analysis of tissue health. In this article, two dissimilar modalities are combined, high-resolution fluorescence microendoscopy imaging and diffuse reflectance spectroscopy, into a single optical probe. High-resolution fluorescence microendoscopy imaging is a technique used to visualize apical tissue micro-architecture and, although mostly a qualitative technique, has demonstrated effective real-time differentiation between neoplastic and non-neoplastic tissue. Diffuse reflectance spectroscopy is a technique which can extract tissue physiological parameters including local hemoglobin concentration, melanin concentration, and oxygen saturation. This article describes the specifications required to construct the fiber-optic probe, how to build the instrumentation, and then demonstrates the technique on in vivo human skin. This work revealed that tissue micro-architecture, specifically apical skin keratinocytes, can be co-registered with its associated physiological parameters. The instrumentation and fiber-bundle probe presented here can be optimized as either a handheld or endoscopically-compatible device for use in a variety of organ systems. Additional clinical research is needed to test the viability of this technique for different epithelial disease states.

Multimodal Imaging and Spectroscopy Fiber-bundle Microendoscopy Platform for Non-invasive, In Vivo Tissue Analysis

The assembly and use of a multimodal microendoscope is described which can co-register superficial tissue image data with tissue physiological parameters including hemoglobin concentration, melanin concentration, and oxygen saturation. This technique can be useful for evaluating tissue structure and perfusion, and can be optimized for individual needs of the investigator.

Recent fiber-bundle microendoscopy techniques enable non-invasive analysis of in vivo tissue using either imaging techniques or a combination of ...

Switchable Acoustic and Optical Resolution Photoacoustic Microscopy for In Vivo Small-animal Blood Vasculature Imaging

Photoacoustic microscopy (PAM) is a fast-growing invivo imaging modality that combines both optics and ultrasound, providing penetration beyond the optical mean free path (~1 mm in skin) with high resolution. By combining optical absorption contrast with the high spatial resolution of ultrasound in a single modality, this technique can penetrate deep tissues. Photoacoustic microscopy systems can have either a low acoustic resolution and probe deeply or a high optical resolution and probe shallowly. It is challenging to achieve high spatial resolution and large depth penetration with a single system. This work presents an AR-OR-PAM system capable of both high-resolution imaging at shallow depths and low-resolution deep-tissue imaging of the same sample in vivo. A lateral resolution of 4 &#181;m with 1.4 mm imaging depth using optical focusing and a lateral resolution of 45 &#181;m with 7.8 mm imaging depth using acoustic focusing were successfully demonstrated using the combined system. Here,&#160;in vivo&#160;small-animal blood vasculature imaging is performed to demonstrate its biological imaging capability.

Switchable Acoustic and Optical Resolution Photoacoustic Microscopy for In Vivo Small-animal Blood Vasculature Imaging

Here a switchable acoustic resolution (AR) and optical resolution (OR) photoacoustic microscopy (AR-OR-PAM) system capable of both high resolution imaging at shallow depth and low resolution deep tissue imaging on the same sample in vivo is demonstrated.

Photoacoustic microscopy (PAM) is a fast-growing invivo imaging modality that combines both optics and ultrasound, providing penetration beyond the ...

A High-performance Compact Photoacoustic Tomography System for In Vivo Small-animal Brain Imaging

In vivo small-animal imaging has an important role to play in preclinical studies. Photoacoustic tomography (PAT) is an emerging hybrid imaging modality that shows great potential for both preclinical and clinical applications. Conventional optical parametric oscillator-based PAT (OPO-PAT) systems are bulky and expensive and cannot provide high-speed imaging. Recently, pulsed-laser diodes (PLDs) have been successfully demonstrated as an alternative excitation source for PAT. Pulsed-laser diode PAT (PLD-PAT) has been successfully demonstrated for high-speed imaging on photoacoustic phantoms and biological tissues. This work provides a visualized experimental protocol for in vivo brain imaging using PLD-PAT. The protocol includes the compact PLD-PAT system configuration and its description, animal preparation for brain imaging, and a typical experimental procedure for 2D cross-sectional rat brain imaging. The PLD-PAT system is compact and cost-effective and can provide high-speed, high-quality imaging. Brain images collected in vivo at various scan speeds are presented.

A High-performance Compact Photoacoustic Tomography System for In Vivo Small-animal Brain Imaging

A compact pulsed-laser diode-based photoacoustic tomography (PLD-PAT) system for high-speed in vivo brain imaging in small animals is demonstrated.

In vivo small-animal imaging has an important role to play in preclinical studies. Photoacoustic tomography (PAT) is an emerging hybrid imaging modality ...

A Protocol for Real-time 3D Single Particle Tracking

Real-time three-dimensional single particle tracking (RT-3D-SPT) has the potential to shed light on fast, 3D processes in cellular systems. Although various RT-3D-SPT methods have been put forward in recent years, tracking high speed 3D diffusing particles at low photon count rates remains a challenge. Moreover, RT-3D-SPT setups are generally complex and difficult to implement, limiting their widespread application to biological problems. This protocol presents a RT-3D-SPT system named 3D Dynamic Photon Localization Tracking (3D-DyPLoT), which can track particles with high diffusive speed (up to 20 &#181;m2/s) at low photon count rates (down to 10 kHz). 3D-DyPLoT employs a 2D electro-optic deflector (2D-EOD) and a tunable acoustic gradient (TAG) lens to drive a single focused laser spot dynamically in 3D. Combined with an optimized position estimation algorithm, 3D-DyPLoT can lock onto single particles with high tracking speed and high localization precision. Owing to the single excitation and single detection path layout, 3D-DyPLoT is robust and easy to set up. This protocol discusses how to build 3D-DyPLoT step by step. First, the optical layout is described. Next, the system is calibrated and optimized by raster scanning a 190 nm fluorescent bead with the piezoelectric nanopositioner. Finally, to demonstrate real-time 3D tracking ability, 110 nm fluorescent beads are tracked in water.

This protocol details the construction and operation of a real-time 3D single particle tracking microscope capable of tracking nanoscale fluorescent probes at high diffusive speeds and low photon count rates.

Real-time three-dimensional single particle tracking (RT-3D-SPT) has the potential to shed light on fast, 3D processes in cellular systems. Although ...

Targeting Neuronal Fiber Tracts for Deep Brain Stimulation Therapy Using Interactive, Patient-Specific Models

Deep brain stimulation (DBS), which involves insertion of an electrode to deliver stimulation to a localized brain region, is an established therapy for movement disorders and is being applied to a growing number of disorders. Computational modeling has been successfully used to predict the clinical effects of DBS; however, there is a need for novel modeling techniques to keep pace with the growing complexity of DBS devices. These models also need to generate predictions quickly and accurately. The goal of this project is to develop an image processing pipeline to incorporate structural magnetic resonance imaging (MRI) and diffusion weighted imaging (DWI) into an interactive, patient specific model to simulate the effects of DBS. A virtual DBS lead can be placed inside of the patient model, along with active contacts and stimulation settings, where changes in lead position or orientation generate a new finite element mesh and solution of the bioelectric field problem in near real-time, a timespan of approximately 10 seconds. This system also enables the simulation of multiple leads in close proximity to allow for current steering by varying anodes and cathodes on different leads. The techniques presented in this paper reduce the burden of generating and using computational models while providing meaningful feedback about the effects of electrode position, electrode design, and stimulation configurations to researchers or clinicians who may not be modeling experts.

The goal of this project is to develop an interactive, patient-specific modeling pipeline to simulate the effects of deep brain stimulation in near real-time and provide meaningful feedback as to how these devices influence neural activity in the brain.

Deep brain stimulation (DBS), which involves insertion of an electrode to deliver stimulation to a localized brain region, is an established therapy for ...