The research is supported by the Tier 2 grant funded by the Ministry of Education in Singapore (ARC2/15: M4020238) and the Singapore Ministry of Health's National Medical Research Council (NMRC/OFIRG/0005/2016: M4062012). The authors would like to thank Mr. Chow Wai Hoong Bobby for the machine shop help.

All animal experiments were performed according to the guidelines and regulations approved by the Institutional Animal Care and Use Committee of Nanyang Technological University, Singapore (Animal Protocol Number ARF-SBS/NIE-A0263).
1. System Description
<ol>
	<li>Mount the PLD inside the circular scanner, as shown in Figure 1a. Connect the PLD to the laser driver unit (LDU). 
	NOTE: The PLD provides ~136-ns pulses at a wavelength of ~803 nm, with a maximum...

<ol>
	<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>Strohm, E. M., Moore, M. J., Kolios, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single+Cell+Photoacoustic+Microscopy:+A+Review.">Single Cell Photoacoustic Microscopy: A Review.</a> IEEE Sel Top Quantum Electron. 22 (3), 6801215 (2016).</li><li>Valluru, K. S., Willmann, J. 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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=Experimental+validation+of+tangential+resolution+improvement+in+photoacoustic+tomography+using+a+modified+delay-and-sum+reconstruction+algorithm.">Experimental validation of tangential resolution improvement in photoacoustic tomography using a modified delay-and-sum reconstruction algorithm.</a> J Biomed Opt. 21 (8), 086011 (2016).</li><li>Strohm, E. M., Moore, M. J., Kolios, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+resolution+ultrasound+and+photoacoustic+imaging+of+single+cells.">High resolution ultrasound and photoacoustic imaging of single cells.</a> Photoacoustics. 4 (1), 36-42 (2016).</li><li>Upputuri, P. K., Wen, Z. -. B., Wu, Z., 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=Super-resolution+photoacoustic+microscopy+using+photonic+nanojets:+a+simulation+study.">Super-resolution photoacoustic microscopy using photonic nanojets: a simulation study.</a> J Biomed Opt. 19 (11), 116003 (2014).</li><li>Zhou, Y., 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=A+Phosphorus+Phthalocyanine+Formulation+with+Intense+Absorbance+at+1000+nm+for+Deep+Optical+Imaging.">A Phosphorus Phthalocyanine Formulation with Intense Absorbance at 1000 nm for Deep Optical Imaging.</a> Theranostics. 6 (5), 688-697 (2016).</li><li>Upputuri, P. K., Wu, Z., Gong, L., Ong, C. 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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=Noninvasive+photoacoustic+computed+tomography+of+mouse+brain+metabolism+in+vivo.">Noninvasive photoacoustic computed tomography of mouse brain metabolism in vivo.</a> Neuroimage. 64 (1), 257-266 (2013).</li><li>Hu, S., 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=Neurovascular+photoacoustic+tomography.">Neurovascular photoacoustic tomography.</a> Front Neuroenergetics. 2, 10 (2010).</li><li>Upputuri, P. 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This work presents a protocol for performing in vivo brain imaging on rats using a PLD-PAT system. The protocol includes a detailed description of the imaging system and its alignment, as well as an illustration of brain imaging on rats. The existing OPO-based PAT systems are expensive and bulky and can provide one cross-sectional image in 5-10 min. The PLD-PAT system is compact, portable, and low-cost and can provide good-quality images in 3 s. The performance of the system was previously studied in phantoms an...

Photoacoustic tomography (PAT) is a hybrid imaging modality that has many applications in both clinical and preclinical studies1,2,3,4,5. In PAT, nanosecond laser pulses irradiate biological tissue. The absorption of incident light by the tissue chromophores leads to a local temperature rise, which then yields pressure waves emitted in the form of sound waves. An ultrasound detector collects the photoacoustic signals at various positions around the sample. The photoacoustic (PA) signals are reconstructed using various algorithms (such as a delay-and-sum algorithm)6 to generate the photoacoustic image.
This hybrid imaging modality offers high-resolution, deep-tissue imaging and high optical absorption contrast7,8. Recently, a ~12-cm imaging depth9 was achieved in chicken breast tissue with the aid of a longer wavelength (~1,064 nm) and an exogenous contrast agent calledphosphorus phthalocyanine. This depth sensitivity is much higher than the depth sensitivity of other optical methods, such as confocal fluorescence microscopy, two-photon fluorescence microscopy,10 optical coherence tomography, 11etc. Using more than one wavelength, PAT can demonstrate structural and functional changes in organs. For many human diseases, small-animal models have been well-established12,13,14,15. For the imaging of small animals, several modalities have been demonstrated. Out of all those approaches, PA imaging has gained attention rather quickly due to the advantages mentioned above. PAT has shown its potential for imaging blood vessels in the tissues and organs (i.e., heart, lungs, liver, eyes, spleen, brain, skin, spinal cord, kidney, etc.) of small animals4,16,17,18. PAT is a well-established modality for small-animal brain imaging. PA waves are produced due to the light absorption by the chromophores, so multiple-wavelength PAT allows for the mapping of total hemoglobin concentration (HbT) and oxygen saturation (SO2)19,20,21,22. Brain neurovascular imaging was achieved with the aid of exogenous contrast agents12,23,24. PA modality can help to give a better understanding of brain health by providing information at the molecular and genetic levels.
For small-animal imaging, Nd : YAG/OPO lasers are widely used as PAT excitation sources. These lasers deliver ~5 ns near-infrared pulses with energy (~100 mJ at the OPO output window) at a ~10-Hz repetition rate25. The PA system equipped with such lasers is costly and bulky and allows for low-speed imaging with single-element ultrasound transducers (UST) due to the low repetition rate of the laser source. A typical A-line acquisition time in such PA systems is ~5 min per cross-section25. An imaging system with such a lengthy measurement time is not ideal for small-animal imaging, because it is difficult to control the physiological parameters for full-body imaging, time-resolved functional imaging, etc. By adopting multiple single-element USTs, array-based USTs, or a high-repetition-rate laser, it is possible to increase the imaging speed of PA systems. Using only one single-element UST to collect all PA signals around the sample will limit the imaging speed of the system. Multiple single-element USTs arranged in circular or semi-circular geometry are demonstrated for high-speed, highly sensitive imaging techniques. Array-based USTs26, such as linear, semi-circular, circular, and volumetric arrays, have been successfully used for real-time imaging1. These array-based USTs will increase the imaging speed and reduce the measurement sensitivity, but they are expensive. However, the imaging speed of PA systems that use array-based USTs is still limited by the repetition rate of the laser.
Pulsed-laser technology advanced to make high-repetition-rate pulsed-laser diodes (PLDs). 7,000 frames/s B-scan photoacoustic imaging was demonstrated with PLDs using a clinical ultrasound platform27. Such PLDs can improve the imaging speed of the PAT system, even with single-element UST circular scanning geometry. Single-element USTs are less expensive and highly sensitive, unlike array-based USTs. Over the last decade, little research was reported on the use of high-repetition-rate PLDs as the excitation source for PA imaging. A fiber-based near-infrared PLD was demonstrated for PA imaging of phantoms28. The in vivo imaging of blood vessels at a ~1 mm depth below the human skin was demonstrated using low-energy PLDs29. A PLD-based optical resolution photoacoustic microscope (ORPAM) was reported. Using PLDs, ~1.5 cm deep imaging at a frame rate of 0.43 Hz was demonstrated30. Very recently, a PLD-PAT system was reported that provided images in as short as ~3 s and at a ~2 cm imaging depth in biological tissue25,31. This study proved that such a low-cost, compact system can provide high-quality images, even at high speeds. The PLD-PAT system can be used for high-frame-rate (7,000 fps) photoacoustic imaging, surficial blood vessel imaging, finger joint imaging, 2 cm-deep tissue imaging, small-animal brain imaging, etc. The single-wavelength and low-pulse-energy pulses from PLD limit its application to multi-spectral and deep-tissue imaging. Experiments have been carried out on small animals using the same PLD-PAT system used for pre-clinical applications. The purpose of this work is to provide the visualized experimental demonstration of the PLD-PAT system for in vivo 2D cross-sectional brain imaging of small animals.

<table border="0" cellpadding="0" cellspacing="0" width="1212">
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		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="63">
			<td height="63" style="height:63px;width:243px;">Pulsed laser diode</td>
			<td style="width:195px;">Quantel, France</td>
			<td style="width:327px;">QD-Q1910-SA-TEC</td>
			<td style="width:449px;">It is the excitation laser source with specifications 803 nm, 1.4mJ per pulse, 136 ns pulse, 7kHz maximum, dimentions : 11.0 x 6.0 x 3.6 cm, weight: ~150 gm</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Stepper motor with gearbox</td>
			<td style="width:195px;">LIN Engineering (Servo Dynamics)</td>
			<td style="width:327px;">Motor: CO-5718-01P, Gearbox: DPL64/1, I = 10 for NEMA 23; power supply PW100-48</td>
			<td style="width:449px;">To move the detector holder in a circular geometry. Torque: 2.08 N-m, Rotor inertia: 2.6 kg-cm2</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Ultrasonic pulser/receiver</td>
			<td>Olympus</td>
			<td>5072PR</td>
			<td style="width:449px;">To receive, filter and ampligy the PA signal from UST. Its bandwidth is 35MHz, and gain is &#177;59 dB.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Ultrasound Transducer</td>
			<td>Olympus</td>
			<td>V306-SU-NK-CF1.9IN/Q4200069</td>
			<td style="width:449px;">Ultrasonic sensors used for photoacoustic detection. Central freqency 2.25 MHz, 0.5 in, Cylindrical focus 1.9 inch</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">PCIe DAQ (Data acquisition) Card</td>
			<td>GaGe</td>
			<td>CSE4227/ A6000610/B0E00610</td>
			<td style="width:449px;">12 bit, 100 Ms/s, 2 channels, 1 Gs on board memory, PCIe x16 interface</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Rats</td>
			<td>In Vivos Pte Ltd, Singapore</td>
			<td style="width:327px;">NTac:SD, Sprague Dawley / SD</td>
			<td>Female, weight 100&#177;10g</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">Acrylic water tank </td>
			<td style="width:195px;">NTU workshop</td>
			<td style="width:327px;">Custom-made</td>
			<td style="width:449px;">It contains the water that acts as an acoustic coupling medium between brain and detector</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Circular Scanner </td>
			<td style="width:195px;">NTU workshop</td>
			<td style="width:327px;">Custom-made</td>
			<td>Scanner is made out of Alluminum </td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">Anesthetic Machine</td>
			<td>medical plus pte ltd</td>
			<td style="width:327px;">Non-Rebreathing Anaesthesia machine with oxygen concentrator.</td>
			<td>Supplies oxygen and isoflurane to animal</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Pulse Oxymeter portable</td>
			<td>Medtronic</td>
			<td style="width:327px;">PM10N with veterinary sensor</td>
			<td>Monitors the pulse oxymetry of the animal</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Ultrasound gel</td>
			<td style="width:195px;">Progress/parker acquasonic gel</td>
			<td>PA-GEL-CLEA-5000</td>
			<td>Clear ultrasound gel</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:243px;">Data acqusison software</td>
			<td style="width:195px;">National Instruments Corporation,Austin,TX,USA)</td>
			<td style="width:327px;">NI LabVIEW 2015 SP1</td>
			<td style="width:449px;">LabVIEW based program was developed in our laboratory for controlling the stepper motor and acquring the PA singnals from the detector</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">Data processing software</td>
			<td style="width:195px;">Matlab (Mathworks, Natick, MA, USA)</td>
			<td style="width:327px;">Matlab R2012b</td>
			<td style="width:449px;">Matlab code for reconstruction of PA images was developed in our lab</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Temperature controller </td>
			<td>LaridTech, MO,USA</td>
			<td>MTTC1410</td>
			<td>It will constantly control temperature of the PLD </td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">12 V power supply </td>
			<td>Voltcraft </td>
			<td style="width:327px;">PPS-11810</td>
			<td>To supply operating voltage for PLD</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Variable power supply </td>
			<td>BASETech</td>
			<td>BT-153</td>
			<td>To change the laser output power</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">Funtion generator </td>
			<td style="width:195px;">Funktionsgenerator</td>
			<td>FG250D</td>
			<td style="width:449px;">To change the repetetion rate of the PLD. It will provide TTL signal to synchronize the DAQ with the laser excitation.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Animal distributor</td>
			<td style="width:195px;">In Vivos Pte Ltd, Singapore</td>
			<td style="width:327px;"></td>
			<td>Animal distributor that supplies small animals for research purpose.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Animal holder</td>
			<td style="width:195px;">NTU workshop</td>
			<td style="width:327px;">Custom-made</td>
			<td>Used for holding the animal on its abdomen</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Breathing mask</td>
			<td style="width:195px;">NTU workshop</td>
			<td style="width:327px;">Custom-made</td>
			<td>Used along with animal holder to supply anesthesia mixture to the animal</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Pentobarbital sodium</td>
			<td style="width:195px;">Valabarb</td>
			<td style="width:327px;"></td>
			<td>Used for euthanizing the animal after the expeirment.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Optical diffuser</td>
			<td style="width:195px;">Thorlabs</td>
			<td style="width:327px;">DG10-1500</td>
			<td>Used to to make the laser beam homogeneous</td>
		</tr>
	</tbody>
</table>

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.

The in vivo brain imaging results that demonstrate the capabilities of the described PLD-PAT system are showcased in this section. To demonstrate the high-speed imaging capabilities of the PLD-PAT system, the in vivo brain imaging of two different healthy rats was performed. Figure 2 shows the brain images of a female rat (93 g) at various scan speeds. Figure 2a and b show the photographs of the rat brain before...

Watch this Scientific Journal Video about A High-performance Compact Photoacoustic Tomography System for In Vivo Small-animal Brain Imaging at JoVE.com

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.

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 ...

The overall goal of this procedure is to demonstrate the performance of a low-cost, compact photoacoustic system for in vivo brain imaging of small animals. Photoacoustic tomography or PAT is a hybrid imaging modality combining light and sound. PAT offers in vivo deep tissue imaging of organ to organelles with very high optical contrast.This work presents a compact, high speed pulsar laser diode based photoacoustic tomography system for in vivo cross-sectional brain imaging in rats. Demonstrating the procedure will be Dr.Paul Kumar Upputuri, a research fellow, Sandeep Kumar Kalva, a PhD student, and Vijitha Periyasamy, a project officer from our lab. To begin the system preparation, turn on the pulsed-laser diode mounted in the circular scanner assembly.Use the laser driver unit to set the repetition rate to 7, 000 Hertz. Set the laser power supply to 3.1 volts to achieve the pulse energy of 1.42 millijoules. Then connect a focused ultrasonic emersion transducer to a pulser-receiver unit.Mount the transducer in its holder under the circular scanning plate, with the transducer oriented towards the center of the plate. Place the scanning assembly in an acrylic tank, with a polyethylene imaging window in the bottom of the tank. Add water to the tank until the transducer is fully immersed.Verify that the photoacoustic signal is being detected by the pulser-receiver unit before proceeding to imaging. To begin the imaging procedure, obtain a healthy female rat. Following anesthesia, trim the fur on the scalp with a hair clipper.Gently apply depilatory cream to the trimmed area. After four to five minutes, remove the cream with a cotton swab. Apply sterile ocular ointment to the rat's eyes to prevent dryness and to block scattered laser beams.Fix a custom made imaging bed equipped with a breathing mask on a lab jack with surgical tape. Place the animal in a prone position on the imaging bed, with its nose and mouth in the mask. Secure the animal in the imaging bed with surgical tape.Position the imaging bed assembly on the optical table. Connect the breathing mask to an anesthesia machine, and begin delivering the inhaled anesthetic. Affix a pulse oximeter to the animal's tail or hind paw to monitor its physiological condition throughout the procedure.Apply a colorless ultrasound gel to the scalp of the animal. Ensure that the imaging bed assembly is securely positioned under the scanner, with the animal's scalp centered under the imaging window. Carefully raise the imaging bed until the ultrasound gel contacts the imaging window, taking care to minimize the pressure against the animal's head.Acquire test images and adjust the vertical position of the bed until the imaging cross-sectional plane of the brain is at the focus point of the ultrasonic transducer. Then, set the parameters for the experiment and start the scan. Monitor the animal during the imaging period.Use reconstruction software to obtain the cross-sectional brain image. Once imaging is complete, discontinue anesthesia and allow the animal to recover fully under observation. cross-sectional images of a healthy female rat brain were obtained with non-invasive PLD PAT imaging.Scan times ranged from five to 20 seconds. The transverse sinus, superior sagittal sinus, and cerebral veins were visible at all tested scan speeds. The same performance was observed when the procedure was repeated with a second healthy female rat.This compact photoacoustic system is used to acquire photoacousitc images of brain vasculature. The results promise that the system can provide high quality individual brain images in scanning time as low as five seconds. Future applications of the developed PAT system include brain tumor imaging, imaging organs in small animal, contrasts flowing in and out of the body, and other therapeutic applications.

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JoVE Journal

Bioengineering

10.3K Views.  Nanyang Technological University. The overall goal of this procedure is to demonstrate the performance of a low-cost, compact photoacoustic system for in vivo brain imaging of small animals. Photoacoustic tomography or PAT is a hybrid imaging modality combining light and sound. PAT offers in vivo deep tissue imaging of organ to organelles with very high optical contrast.This work presents a compact, high speed pulsar laser diode based photoacoustic tomography system for in vivo cross-sectional brain imaging in rats. De...