Enhancement of photoacoustic tomography in the tissue with speed-of-sound variance using ultrasound computed tomography

The speed-of-sound variance will decrease the imaging quality of photoacoustic tomography in acoustically inhomo- geneous tissue. In this study, ultrasound computed tomography is combined with photoacoustic tomography to enhance the photoacoustic tomography in this situation. The speed-of-sound information is recovered by ultrasound computed to- mography. Then, an improved delay-and-sum method is used to reconstruct the image from the photoacoustic signals. The simulation results validate that the proposed method can obtain a better photoacoustic tomography than the conventional method when the speed-of-sound variance is increased. In addition, the influences of the speed-of-sound variance and the fan-angle on the image quality are quantitatively explored to optimize the image scheme. The proposed method has a good performance even when the speed-of-sound variance reaches 14.2%. Furthermore, an optimized fan angle is revealed, which can keep the good image quality with a low cost of hardware. This study has a potential value in extending the biomedical application of photoacoustic tomography.

Combating acoustic heterogeneity in photoacoustic computed tomography:A review

Based on the energy conversion of light into sound,photoacoustic computed tomography(PACT)is an emerging biomedical imaging modality and has unique applications in a range of biomedical fields.In PACT,image formation relies on a process called acoustic inversion from received photoacoustic signals.While most PACT systems perform this inversion with a basic assumption that biological tissues are acoustically homogeneous,the community gradually rea-lizes that the intrinsic acoustic heterogeneity of tissues could pose distortions and artifacts to finally formed images.This paper surveys the most recent research progress on acoustic het-erogeneity correction in PACT.Four major strategies are reviewed in detail,including half-time or partial-time reconstruction,autofocus reconstruction by optimizing sound speed maps,joint reconstruction of optical absorption and sound speed maps,and ultrasound computed tomog-raphy(USCT)enhanced reconstruction.The correction of acoustic heterogeneity helps improve the imaging performance of PACT.

Adaptive optimization on ultrasonic transmission tomography-based temperature image for biomedical treatment

Hyperthermia has proven to be beneficial to treating superficial malignancies, particularly chest wall recurrences of breast cancer. During hyperthermia, monitoring the time–temperature profiles in the target and surrounding areas is of great significance for the effect of therapy. An ultrasound-based temperature imaging method has advantages over other approaches. When the temperature around the tumor is calculated by using the propagation speed of ultrasound, there always exist overshoot artifacts along the boundary between different tissues. In this paper, we present a new method combined with empirical mode decomposition（EDM）, similarity constraint, and continuity constraint to optimize the temperature images. Simulation and phantom experiment results compared with those from our previously proposed method prove that the EMD-based method can build a better temperature field image, which can adaptively yield better temperature images with less computation for assistant medical treatment control.

Simulation study on ultrasonic tomography for grouted reinforced concrete by finite element

A finite element reconstruction algorithm for ultrasound tomography based on the Helmholtz equation in frequency domain is presented to monitor the grouting defects in reinforced concrete structures.In this algorithm,a hybrid regularizations-based iterative Newton method is implemented to provide stable inverse solutions.Furthermore,a dual mesh scheme and an adjoint method are adopted to reduce the computation cost and improve the efficiency of reconstruction.Simultaneous reconstruction of both acoustic velocity and attenuation coefficient for a reinforced concrete model is achieved with multiple frequency data.The algorithm is evaluated with numerical simulation under various practical scenarios including varied transmission/receiving modes,different noise levels,different source/detector numbers,and different contrast levels between the heterogeneity and background region.Results obtained suggest that the algorithm is insensitive to noise,and the reconstructions are quantitatively accurate in terms of the location,size and acoustic properties of the target over a range of contrast levels.

Spectrum of mucin-producing neoplastic conditions of the abdomen and pelvis:Cross-sectional imaging evaluation

Various mucin-producing neoplasms originate in different abdominal and pelvic organs.Mucinous neoplasms differ from non-mucinous neoplasms because of the differences in clinical outcome and imaging appearance.Mucinous carcinoma,in which at least 50%of the tumor is composed of large pools of extracellular mucin and columns of malignant cells,is associated with a worse prognosis.Signet ring cell carcinoma is characterized by large intracytoplasmic mucin vacuoles that expand in the malignant cells with the nucleus displaced to the periphery.Its prognosis is also generally poor.In contrast,intraductal papillary mucinous neoplasm of the bile duct and pancreas,which is characterized by proliferation of ductal epithelium and variable mucin production,has a better prognosis than other malignancies in the pancreaticobiliary tree.Imaging modalities play a critical role in differentiating mucinous from non-mucinous neoplasms.Due to high water content,mucin has a similar appearance to water on ultrasound(US) ,computed tomography(CT) ,and magnetic resonance imaging,except when thick and proteinaceous,and then it tends to be hypoechoic with fine internal echoes or have complex echogenicity on US,hyperdense on CT,and hyperintense on T1and hypointense on T2-weighted images,compared to water.Therefore,knowledge of characteristic mucin imaging features is helpful to diagnose various mucinproducing neoplastic conditions and to facilitate appropriate treatment.

Compressed sensing in synthetic aperture photoacoustic tomography based on a linear-array ultrasound transducer

Photoacoustic tomography（PAT） has the unique capability of visualizing optical absorption inside several centimeters-deep biological tissue with a high spatial resolution. However, single linear-array transducer-based PAT suffers from the limited-view challenge, and thus the synthetic aperture configuration is designed that still requires multichannel data acquisition hardware. Herein, a feasible synthetic aperture PAT based on compressed sensing reconstruction is proposed. Both the simulation and experimental results tested the theoretical model and validated that this approach can improve the image resolution and address the limited-view problem while preserving the target information with a fewer number of measurements.

Asymptomatic pancreatic lesions: New insights and clinical implications

Despite great efforts in experimental and clinical research, the prognosis of pancreatic cancer (PC) has not changed significantly for decades. Detection of pre-invasive lesions or early-stage PC with small resectable cancers in asymptomatic individuals remains one of the most promising approaches to substantially improve the overall outcome of PC. Therefore, screening programs have been proposed to identify curable lesions especially in individuals with a familial or genetic predisposition for PC. In this regard, Canto et al recently contributed an important article comparing computed tomography, magnetic resonance imaging, and endoscopic ultrasound for the screening of 216 asymptomatic high-risk individuals (HRI). Pancreatic lesions were detected in 92 of 216 asymptomatic HRI (42.6%). The high diagnostic yield in this study raises several questions that need to be answered of which two will be discussed in detail in this commentary: First: which imaging test should be performed? Second and most importantly: what are we doing with incidentally detected pancreatic lesions? Which ones can be observed and which ones need to be resected?

Optimal morphometric and functional assessment of intermediate coronary lesions

Coronary lesions of intermediate severity, defined as 50%-70% luminal diameter narrowing by visualestimation at angiography, are frequently encountered in patients with stable or unstable coronary artery disease. Clinical decision making for patients with intermediate coronary stenosis is still challenging, but may be facilitated by assessing the morphology and physiological significance of these lesions.1 It is clear that angiographic stenosis is a highly unreliable surrogate for myocardial ischemia, as a significant proportion of anatomically high-grade lesions do not cause ischemia. Conversely, even for anatomically mild coronary lesions, a non-negligible rate of myocardial ischemia is consistently noted. Because the physiological significance of a lesion is mainly determined by both the severity of a stenosis and the amount of myocardium supplied, coronary angiography alone does not accurately predict the functional significance of intermediate coronary lesions.2,3