李林参与了该研究的构思、进行实验、分析数据并撰写手稿。 , Wanyi Chen, Junhui Shi 和 Lihong V .
LIST OF ILLUSTRATIONS AND/OR TABLES
7.6%), measured with a spectrophotometer before and after the photoacoustic experiment. 63 Figure 27. Experimental setup and a representative PA image of the phantom. -d) Line scan images of the parent vessel (c) and one daughter vessel (d) before and after the occlusion, showing blood flow slowing in the parent vessel and reversing in the daughter vessel.76 Figure 33.
LIST OF FREQUENTLY USED ABBREVIATIONS
INTRODUCTIONINTRODUCTION
Here, the solid angle of the entire sensing surface with respect to a given source is Ω0 𝑆 point. Accordingly, if the impulse response of the ultrasonic transducer has a Gaussian envelope, the axial resolution can be estimated as 0.88𝑣𝑠/𝐵, where the bandwidth of the ultrasonic transducer is approximately 𝐵. proportional to the center frequency.
PACT OF RAT BRAIN
The origin of the z-axis was aligned with the plane 3 mm above the fiber tip. We measured and compared the spontaneous hemodynamic responses between contralateral regions of the rat brain.
PACT OF HUMAN BREAST CANCER
Representations of the SBH-PACT system. a) Perspective cut away view of the system with data acquisition components removed. Simulation of the optical flow in breast tissue at 2 cm depth, produced by. the lighting beam is donut shaped. In comparison, SBH-PACT clearly revealed the tumors not easily seen in mammograms, despite the high radiographic density of the breast.
-PACT of breast cancer. a) X-ray mammograms of the affected breasts of seven breast cancer patients. To automatically segment tumors, we extracted the vascular skeleton and created a map of the vascular density of the breast (local vessel number/local area). -PACT elastography of a breast-mimicking phantom. a) Cross-sectional image of the phantom obtained by SBH-PACT.
In this pilot study, SBH-PACT identified eight of the nine biopsy-verified tumors by assessing blood vessel density. The fluctuation of the pixel values in the artery indicated the changes associated with arterial pulse propagation (Fig. 9f). To segment tumors automatically, we extracted the vasculature and produced a vessel density map (number of vessels/area) over the breast.
No obvious differences were observed in the concentration of the hair fiber between the balls and the phantom base. The chest wall pressed the breast against the agar cushion, causing a distortion of the breast in the coronal plane.
3D PACT OF HUMAN BRAIN
The system has 4 arc ultrasonic transducer arrays (1024 parallel channels) with per-element ultra-low-noise amplification and DAQ for high-speed, 3D, and spectroscopic PACT of human brain in vivo. This design ensures that the laser beam is unaffected by the rotation of the array, which is important to avoid PA signal fluctuations due to laser illumination so that small functional neural signals can be eradicated. The optical flow on the skin surface meets the ANSI safety standards [20]. a) Photograph of the 3D-PACT system.
To create a point source that emits strong PA waves, a point absorber (~100 µm) was attached to a tip of the optical fiber so that most of the light coupled into the fiber was absorbed. Here are the number of sources and point elements, respectively; 𝑀 𝑁 (𝑥𝑚,𝑦𝑚,𝑧𝑚) indicate the location of the -th point source; (𝑚 ( 𝑡𝑚,𝑛 is the acoustic propagation time from the -th point source to 𝑚. We have initial estimates of the unknown parameters from the water temperature measurement, 𝑐 (𝑥𝑚,𝑦𝑚,𝑧𝑚) from the reconstructed images and (𝑥𝑛 ,𝑦𝑛,𝑧𝑛) from the specific output.
We define radial calibration factor to limit the geometric error along the radial 𝛼𝑛 axis. where can be solved directly from the quadratic Eq. After optimizing the system with phantoms, we first performed in vivo tests by imaging a healthy human breast. MAP images of a healthy human breast obtained by 3D-PACT within a single breath of 10 seconds. 3D-PACT of a healthy human head. a) Photograph of a healthy subject being imaged.
MICROWAVE-BASED THERMOACOUSTIC TOMOGRAPHY
It was found that a uniform distribution of the electric field can be obtained within a plane 4.5 cm above the horn antenna (Fig. 21b). The dimension of the mesh holes was smaller than the microwave wavelength but larger than the ultrasonic wavelength. To image cross sections of the rat, we scanned the transducer circularly around the rat's trunk with 720 steps (0.5° step angle) and averaged signals 20 times at each scan step.
The thickness of the skull was inhomogeneous and ranged from 7 mm (temporal region) to 11 mm (frontal region). Due to near-field microwave illumination, SAR analysis within the head model is required to confirm compliance with the electromagnetic radiation exposure safety standard. A transverse TAT image of the rat trunk matches well with the corresponding photograph (Figure 24a).
Due to the deep penetration, we imaged up to 7 cm into the rat's body, where the ribs of the rat are shown. Due to the long microwave wavelength, objects are usually located in the near field of the antenna. Therefore, the positions and orientations of the antennas must be configured to evenly distribute the microwave energy in the tissue.
MULTI-CONTRAST PACT―MYOGLOBIN
In muscle tissue, the main absorbers in the visible and NIR spectral regions are oxygenated myoglobin (MbO2), oxygenated myoglobin (Mb), HbO2 and Hb. Figure 26a shows the optical absorption spectra of the major chromophores found in muscle. A standard spectrophotometer measured the absorbance, which was the product of the molar extinction coefficient, the molar concentration, and the path length of the cuvette. We derived the molar concentrations from the known molar extinction coefficients at different wavelengths and the path length of the cuvette.
The agar phantom was immersed ~5/6 in water and fixed in the center of the transducer array. After the light beam passed through a ground glass, it was turned off and delivered to the top of the phantom. In the table, the actual concentration fractions were calculated using the molar extinction coefficient of each chromophore and the spectrophotometer measurements of the mixture, for example Fig.
The estimated effective attenuation coefficients of the three. optical flow at the image plane was different for each sample. We used 780 nm light with full-ring illumination to obtain a cross-sectional image of the mouse at the kidney level, shown in Fig. We neglected the change in optical attenuation in tissue due to variations in sO2, mainly due to the high scattering and low volume fraction of blood in the skin.
HIGH-SPEED OR-PAM OF CORTICAL HEMODYNAMICS
-rate OR-PAM of ischemic mini-stroke dynamics in mouse brain. a) OR-PAM image of a 1 mm by 1 mm cortical area, where spontaneous hemorrhage was observed in the boxed area. In contrast, blood flow velocity in the intact daughter vessel was increased by ~100%, due to the maintenance of volumetric blood flow. Furthermore, the signal amplitude in the intact daughter vessel increased significantly, reflecting increased red blood cell (RBC) density (Fig. 31d).
The escalated blood flow rate and RBC density increased the risk of further bleeding in the remaining vessels [99]. The dynamic imaging revealed a dramatic decrease in uterine blood flow after occlusion (Fig. 32c). -d) Line scan images of the mother vessel (c) and a daughter vessel (d) before and after the occlusion, showing that blood flow decreases in the mother vessel and returns in the daughter vessel.
Amoeboid structures (indicated by arrows) were observed in the damaged areas after hemorrhage and vessel occlusion. For comparison, we also imaged the vasoactive effect of phenylephrine on the blood vessels in the mouse ear, where the vascular autoregulation system is much less developed (Fig. 34f). CA plays another important role in maintaining adequate and stable blood flow in the brain.
HANDHELD OR-PAM
Similar to the bench-OR-PAM in Chapter VII, the focused laser beam is reflected by the MEMS mirror plate onto the surface of the object to be imaged. Schematic of the OR-PAM hand probe. a) 2-D sketch of the optical and acoustic beams in the probe. To characterize the lateral resolution of the handheld OR-PAM system, the edge of a sharp.
The axial resolution of the system is determined by the bandwidth of the ultrasound transducer and was estimated to be 26 μm. To demonstrate the rapid imaging capability of the hand-held OR-PAM system, the vessels in a mouse ear were continuously scanned after a tail vein injection of 0.6 ml of 0.9%. To characterize the changes in the signal from the vessels quantitatively, we averaged the pixel amplitude over the area indicated by the dashed box.
The background signal was calculated by averaging an area of the same size, but without ships in it. To demonstrate the flexibility of the wearable probe in clinical applications, we tested the system by imaging human skin. 38(a), the vessels beneath the cuticle are clearly visible, with an SNR of 26 dB. OR-PAM of human skin through the portable probe. a) OR-PAM uptake from capillaries in a cuticle.
CONCLUSIONS AND OUTLOOK
BIBLIOGRAPHY
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