This work demonstrates a rapid platform that can determine the antimicrobial susceptibility testing (AST) in cation-adjusted Mueller-Hinton Broth medium, urine and blood by stimulated Raman scattering (SRS) imaging of deuterium oxide (D2O) incorporation at a single bacterium level. The total AST assay time with the value of the single-cell metabolism inactivation concentration (SC-MIC) obtained is less than 2.5 h from colony to results. The SC-MIC results of 37 sets of bacterial isolate samples were systematically validated by MIC determined by the Clinical and Laboratory Standards Institute criteria, with a category agreement of 94.6% and 5.4% minor error. Furthermore, SRS imaging of D2O metabolic incorporation can rapidly determine SC-MIC directly in clinical samples for urinary tract infection or septicemia blood infection.
The survival rate for renal cancer patients is closely related to the surgical margin status. Thus, accurate and rapid detection of renal cancer is needed. Here, we integrated photoacoustic tomography (PAT) with ultrasound imaging in a single system, which achieved tissue imaging depth about 3 mm and imaging speed about 3.5 cm2/min. We used the wavelength at 1064 nm and 1197 nm to map both blood and lipid distribution in 16 normal and 17 clear cell renal cell carcinoma (ccRCC) tissues, collected from nephrectomy. Our results indicated that the photoacoustic signal from lipids, but not blood, was significantly higher in ccRCC tissues than that in normal tissues. Moreover, based on the quantification of lipid area ratio, we were able to differentiate normal and ccRCC with 100% sensitivity, 80% specificity, and area under receiver operating characteristic curve of 0.95. Our findings show promise of using multimodal PAT for intraoperative ccRCC detection.
Breast-conserving surgery is a well-accepted breast cancer treatment. However, it is still challenging for the surgeon to accurately localize the tumor during the surgery. Also, the guidance provided by current methods is 1 dimensional distance information, which is indirect and not intuitive. Therefore, it creates problems on a large re-excision rate, and a prolonged surgical time. To solve these problems, we have developed a fiber-delivered optoacoustic guide (OG), which mimics the traditional localization guide wire and is preoperatively placed into tumor mass, and an augmented reality (AR) system to provide real-time visualization on the location of the tumor with sub-millimeter variance. By a nano-composite light diffusion sphere and light absorbing layer formed on the tip of an optical fiber, the OG creates an omnidirectional acoustic source inside tumor mass under pulsed laser excitation. The optoacoustic signal generated has a high dynamic range (~ 58dB) and spreads in a large apex angle of 320 degrees. Then, an acoustic radar with three ultrasound transducers is attached to the breast skin, and triangulates the location of the OG tip. With an AR system to sense the location of the acoustic radar, the relative position of the OG tip inside the tumor to the AR display is calculated and rendered. This provides direct visual feedback of the tumor location to surgeons, which will greatly ease the surgical planning during the operation and save surgical time. A proof-of-concept experiment using a tablet and a stereo-vision camera is demonstrated and 0.25 mm tracking variance is achieved.
KEYWORDS: Image resolution, In vivo imaging, Fiber optics, Ultrasonography, Mirrors, Imaging systems, Real time imaging, Photoacoustic imaging, Absorption, Image processing, High speed imaging
Intravascular photoacoustic-ultrasound (IVPA-US) imaging is an emerging hybrid modality for the detection of lipidladen plaques by providing simultaneous morphological and lipid-specific chemical information of an artery wall. The clinical utility of IVPA-US technology requires real-time imaging and display at speed of video-rate level. Here, we demonstrate a compact and portable IVPA-US system capable of imaging at up to 25 frames per second in real-time display mode. This unprecedented imaging speed was achieved by concurrent innovations in excitation laser source, rotary joint assembly, 1 mm IVPA-US catheter, differentiated A-line strategy, and real-time image processing and display algorithms. By imaging pulsatile motion at different imaging speeds, 16 frames per second was deemed to be adequate to suppress motion artifacts from cardiac pulsation for in vivo applications. Our lateral resolution results further verified the number of A-lines used for a cross-sectional IVPA image reconstruction. The translational capability of this system for the detection of lipid-laden plaques was validated by ex vivo imaging of an atherosclerotic human coronary artery at 16 frames per second, which showed strong correlation to gold-standard histopathology.
A hyperspectral image corresponds to a data cube with two spatial dimensions and one spectral dimension. Through linear un-mixing, hyperspectral images can be decomposed into spectral signatures of pure components as well as their concentration maps. Due to this distinct advantage on component identification, hyperspectral imaging becomes a rapidly emerging platform for engineering better medicine and expediting scientific discovery. Among various hyperspectral imaging techniques, hyperspectral stimulated Raman scattering (HSRS) microscopy acquires data in a pixel-by-pixel scanning manner. Nevertheless, current image acquisition speed for HSRS is insufficient to capture the dynamics of freely moving subjects. Instead of reducing the pixel dwell time to achieve speed-up, which would inevitably decrease signal-to-noise ratio (SNR), we propose to reduce the total number of sampled pixels. Location of sampled pixels are carefully engineered with triangular wave Lissajous trajectory. Followed by a model-based image in-painting algorithm, the complete data is recovered for linear unmixing. Simulation results show that by careful selection of trajectory, a fill rate as low as 10% is sufficient to generate accurate linear unmixing results. The proposed framework applies to any hyperspectral beam-scanning imaging platform which demands high acquisition speed.
Stimulated Raman scattering (SRS) microscopy is a promising technique for label-free imaging of living systems. We demonstrate microsecond-scale SRS spectral imaging by tuning two spectrally focused pulses temporally through a resonant delay-line. Our platform acquired an SRS spectrum within 42 microseconds and formed a spectral image composed of 40,000 pixels in real-time.
Lipid deposition inside the arterial wall is a hallmark of plaque vulnerability. Overtone absorption-based intravascular photoacoustic (IVPA) catheter is a promising technology for quantifying the amount of lipid and its spatial distribution inside the arterial wall. Thus far, the clinical translation of IVPA technology is limited by its slow imaging speed due to lack of a high-power and high-repetition-rate laser source for lipid-specific excitation at 1.7 μm. Here, we demonstrate a potassium titanyl phosphate-based optical parametric oscillator (OPO) with output pulse energy up to 2 mJ at a wavelength of 1724 nm and with a repetition rate of 500 Hz. This OPO enabled IVPA imaging at 1 frame per sec, which is about 50-fold faster than previously reported IVPA systems. The IVPA imaging system was characterized by a pencil lead and a lipid-mimicking phantom for its imaging resolution, sensitivity, and specificity, respectively. Its performance was further validated by ex vivo study of an atherosclerotic human femoral artery and comparison to gold standard histology.
Atherosclerotic plaque at the carotid bifurcation is the underlying cause of the majority of ischemic strokes. Noninvasive imaging and quantification of the compositional changes preceding gross anatomic changes within the arterial wall is essential for diagnosis of disease. Current imaging modalities such as duplex ultrasound, computed tomography, positron emission tomography are limited by the lack of compositional contrast and the detection of flow-limiting lesions. Although high-resolution magnetic resonance imaging has been developed to characterize atherosclerotic plaque composition, its accessibility for wide clinical use is limited. Here, we demonstrate a fiber-based multispectral photoacoustic tomography system for excitation of lipids and external acoustic detection of the generated ultrasound. Using sequential ultrasound imaging of ex vivo preparations we achieved ~2 cm imaging depth and chemical selectivity for assessment of human arterial plaques. A multivariate curve resolution alternating least squares analysis method was applied to resolve the major chemical components, including intravascular lipid, intramuscular fat, and blood. These results show the promise of detecting carotid plaque in vivo through esophageal fiber-optic excitation of lipids and external acoustic detection of the generated ultrasound. This imaging system has great potential for serving as a point-ofcare device for early diagnosis of carotid artery disease in the clinic.
Photoacoustic imaging employing molecular overtone vibration as a contrast mechanism opens a new avenue for bond-selective imaging of deep tissues. Broad use of this modality is, however, hampered by the extremely low conversion efficiency of optical parametric oscillators at the overtone transition wavelengths. To overcome such a barrier, we demonstrate the construction and use of a compact, barium nitrite crystal-based Raman laser for photoacoustic imaging of C–H overtone vibrations. Using a 5-ns Nd∶YAG laser as the pumping source, up to 21.4 mJ pulse energy at 1197 nm was generated, corresponding to a conversion efficiency of 34.8%. Using the 1197 nm pulses, three-dimensional photoacoustic imaging of intramuscular fat was demonstrated.
Photoacoustic imaging employing molecular overtone vibration as contrast mechanism opens a new avenue for deep tissue imaging with chemical bond selectivity. Here, we demonstrate vibration-based photoacoustic tomography with an imaging depth on the centimeter scale. To provide sufficient pulse energy at the overtone transition wavelengths, we constructed a compact, barium nitrite crystal-based Raman laser for excitation of 2nd overtone of C-H bond. Using a 5-ns Nd:YAG laser as pumping source, up to 105 mJ pulse energy at 1197 nm was generated. Vibrational photoacoutic spectroscopy and tomography of phantom (polyethylene tube) immersed in whole milk was performed. With a pulse energy of 47 mJ on the milk surface, up to 2.5 cm penetration depth was reached with a signal-to-noise ratio of 12.
Photoacoustic microscopy using vibrational overtone absorption as a contrast mechanism allows bond-selective imaging of deep tissues. Due to the spectral similarity of molecules in the region of overtone vibration, it is difficult to interrogate chemical components using photoacoustic signal at single excitation wavelength. Here we demonstrate that lipids and collagen, two critical markers for many kinds of diseases, can be distinguished by multispectral photoacoustic imaging of the first overtone of C-H bond. A phantom consisting of rat-tail tendon and fat was constructed to demonstrate this technique. Wavelengths between 1650 and 1850 nm were scanned to excite both the first overtone and combination bands of C-H bonds. B-scan multispectral photoacoustic images, in which each pixel contains a spectrum, were analyzed by a multivariate curve resolution-alternating least squares algorithm to recover the spatial distribution of collagen and lipids in the phantom.
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