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

Summary

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

Abstract

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.

Introduction

Photoacoustic tomography (PAT) is a hybrid imaging modality that has many applications in both clinical and preclinical studies^1,2,3,4,5. 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 us....

Protocol

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

1. 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 pulse energy of ~1.42 mJ and a repetition rate up to 7 kHz. The laser driving unit (LDU) includes: a temperature controller, a variable power supply, a....

Results

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.......

Discussion

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.......

Materials

List of materials used in this article

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