Beyond the acoustic diffraction limit: superresolution localization optoacoustic tomography (LOT)

11Ysciescopu

Toward functional ultrasound-modulated optical tomography: a phantom study

We present the feasibility of functional ultrasound-modulated optical tomography (UOT) in tissue phantoms with two optical wavelengths. By using intense acoustic bursts and a CCD camera-based speckle contrast detection technique, we observe variations of UOT signal at different optical absorptions. In addition, the results from Monte Carlo simulations highly correlate with the experimental outcomes. By irradiating the sample at two optical wavelengths, we quantitatively estimate the total concentration and the concentration ratio of double dyes in inclusions inside tissue phantoms. Therefore, UOT is potentially able to supply functional imaging of the total concentration and oxygen saturation of hemoglobin non-invasively in biological tissues

Multimodal photoacoustic imaging: systems, applications, and agents

없음11Yscopuskc

In Vivo Photoacoustic Tomography of Chemicals: High-Resolution Functional and Molecular Optical Imaging at New Depths

High-resolution volumetric optical imaging modalities, such as confocal microscopy, two-photon microscopy, and optical coherence tomography, have become increasingly important in the biomedical imaging field. However, due to strong light scattering, the penetration depths of these imaging modalities are limited to the optical transport mean free path in biological tissues, for example, ∼1 mm in the skin. Photoacoustic tomography (PAT), an emerging hybrid imaging modality that can provide strong endogenous and exogenous optical absorption contrasts with high ultrasonic spatial resolution using the photoacoustic (PA) effect, has overcome the fundamental depth limitation. The image resolution is scalable with the ultrasonic frequency. The imaging depth is limited to the reach of photons and up to a few centimeters deep in biological tissues. This Review will focus on the following aspects of PAT described in works published from 2003 to 2009: (1) multiscale PAT systems, (2) morphological and functional PAT using intrinsic contrasts (hemoglobin or melanin), and (3) functional and molecular PAT using exogenous contrast agents (organic dyes, nanoparticles, reporter genes, or fluorescence proteins)

Nonionizing photoacoustic cystography in vivo

We demonstrate the feasibility of a novel and nonionizing process for bladder imaging in vivo, called photoacoustic cystography (PAC). Using a photoacoustic imaging system, we have successfully imaged a rat bladder filled with clinically used Methylene Blue (MB) dye. An image contrast of ~8 was achieved. Further, spectroscopic PAC confirmed the accumulation of MB in the bladder. Using a laser pulse energy of less than 1 mJ/cm^2 (1/20 of the ANSI safety limit), a deeply (1.2 cm) positioned bladder in biological tissues was clearly visible in the PA image. Our results suggest that PAC can potentially provide a nonionizing, relatively cheap, and portable tool for bladder mapping. Among our clinical interests, nonionizing PAC with an injection of MB can potentially monitor vesicoureteral reflux in children

Real-time delay-multiply-and-sum beamforming with coherence factor for in vivo clinical photoacoustic imaging of humans

In the clinical photoacoustic (PA) imaging, ultrasound (US) array transducers are typically used to provide B-mode images in real-time. To form a B-mode image, delay-and-sum (DAS) beamforming algorithm is the most commonly used algorithm because of its ease of implementation. However, this algorithm suffers from low image resolution and low contrast drawbacks. To address this issue, delay-multiply-and-sum (DMAS) beamforming algorithm has been developed to provide enhanced image quality with higher contrast, and narrower main lobe compared but has limitations on the imaging speed for clinical applications. In this paper, we present an enhanced real-time DMAS algorithm with modified coherence factor (CF) for clinical PA imaging of humans in vivo. Our algorithm improves the lateral resolution and signal-to-noise ratio (SNR) of original DMAS beam-former by suppressing the background noise and side lobes using the coherence of received signals. We optimized the computations of the proposed DMAS with CF (DMAS-CF) to achieve real-time frame rate imaging on a graphics processing unit (GPU). To evaluate the proposed algorithm, we implemented DAS and DMAS with/without CF on a clinical US/PA imaging system and quantitatively assessed their processing speed and image quality. The processing time to reconstruct one B-mode image using DAS, DAS with CF (DAS-CF), DMAS, and DMAS-CF algorithms was 7.5, 7.6, 11.1, and 11.3 ms, respectively, all achieving the real-time imaging frame rate. In terms of the image quality, the proposed DMAS-CF algorithm improved the lateral resolution and SNR by 55.4% and 93.6 dB, respectively, compared to the DAS algorithm in the phantom imaging experiments. We believe the proposed DMAS-CF algorithm and its real-time implementation contributes significantly to the improvement of imaging quality of clinical US/PA imaging system.11Ysciescopu

Towards nonionizing photoacoustic cystography

Normally, urine flows down from kidneys to bladders. Vesicoureteral reflux (VUR) is the abnormal flow of urine from bladders back to kidneys. VUR commonly follows urinary tract infection and leads to renal infection. Fluoroscopic voiding cystourethrography and direct radionuclide voiding cystography have been clinical gold standards for VUR imaging, but these methods are ionizing. Here, we demonstrate the feasibility of a novel and nonionizing process for VUR mapping in vivo, called photoacoustic cystography (PAC). Using a photoacoustic (PA) imaging system, we have successfully imaged a rat bladder filled with clinically being used methylene blue dye. An image contrast of ~8 was achieved. Further, spectroscopic PAC confirmed the accumulation of methylene blue in the bladder. Using a laser pulse energy of less than 1 mJ/cm2, bladder was clearly visible in the PA image. Our results suggest that this technology would be a useful clinical tool, allowing clinicians to identify bladder noninvasively in vivo

Real-time Near-infrared Virtual Intraoperative Surgical Photoacoustic Microscopy

AbstractWe developed a near infrared (NIR) virtual intraoperative surgical photoacoustic microscopy (NIR-VISPAM) system that combines a conventional surgical microscope and an NIR light photoacoustic microscopy (PAM) system. NIR-VISPAM can simultaneously visualize PA B-scan images at a maximum display rate of 45Hz and display enlarged microscopic images on a surgeon's view plane through the ocular lenses of the surgical microscope as augmented reality. The use of the invisible NIR light eliminated the disturbance to the surgeon's vision caused by the visible PAM excitation laser in a previous report. Further, the maximum permissible laser pulse energy at this wavelength is approximately 5 times more than that at the visible spectral range. The use of a needle-type ultrasound transducer without any water bath for acoustic coupling can enhance convenience in an intraoperative environment. We successfully guided needle and injected carbon particles in biological tissues ex vivo and in melanoma-bearing mice in vivo

Ultrasound-modulated optical tomography with intense acoustic bursts

Ultrasound-modulated optical tomography (UOT) detects ultrasonically modulated light to spatially localize multiply scattered photons in turbid media with the ultimate goal of imaging the optical properties in living subjects. A principal challenge of the technique is weak modulated signal strength. We discuss ways to push the limits of signal enhancement with intense acoustic bursts while conforming to optical and ultrasonic safety standards. A CCD-based speckle-contrast detection scheme is used to detect acoustically modulated light by measuring changes in speckle statistics between ultrasound-on and ultrasound-off states. The CCD image capture is synchronized with the ultrasound burst pulse sequence. Transient acoustic radiation force, a consequence of bursts, is seen to produce slight signal enhancement over pure ultrasonic-modulation mechanisms for bursts and CCD exposure times of the order of milliseconds. However, acoustic radiation-force-induced shear waves are launched away from the acoustic sample volume, which degrade UOT spatial resolution. By time gating the CCD camera to capture modulated light before radiation force has an opportunity to accumulate significant tissue displacement, we reduce the effects of shear-wave image degradation, while enabling very high signal-to-noise ratios. Additionally, we maintain high-resolution images representative of optical and not mechanical contrast. Signal-to-noise levels are sufficiently high so as to enable acquisition of 2D images of phantoms with one acoustic burst per pixel