Assessment of the scatter fraction evaluation methodology using Monte Carlo simulation techniques

To evaluate scatter fraction and scatter pair spatial distribution, experimental methods are generally used. These methods make use of a line source, placed along the FOV axis, inserted in a cylindrical phantom filled with air or water. The accuracy of these experimental methodologies can be tested by the use of a Monte Carlo method. In fact, the simulation allows the shape of the scatter event projection and the scatter fraction to be defined. An example of this application is the simulation package PETSI (PET SImulation). In this paper the comparison between the predicted scatter fraction and the experimentally evaluated one, obtained using an ECAT III PT 911/02 double ring whole body scanner are presented. PETSI permits additional data to be obtained: a) the true and scatter component of the energy spectrum; b) the spatial distribution, in the FOV plane, of the detected scatter events at different energy thresholds; c) the scatter to total detected events ratio; d) the predicted scatter fraction at both energy thresholds and FOV diameters. This information is very useful for optimizing both energy threshold and FOV size and to improve the accuracy of the currently used methods for the scatter fraction evaluation. Preliminary results of the predicted scatter fraction in a uniform phantom are presented.This article was presented at the 1st EEC workshop on accuracy determination in PET, January 19–20th. 1989 Pisa, Italy (COMAC-BME Concerted Project Characterization and Standardization of PET Instrumentation)     

Changes in tissue optical properties due to radio-frequency ablation of myocardium

The optical properties of pig heart tissue were measured after in vivo ablation therapy had been performed during open-heart surgery. In vitro samples of normal and ablated tissue were subjected to measurements with an optically integrating sphere set-up in the region 470–900 nm. Three independent measurements were made: total transmittance, total reflectance and collimated transmittance, which made it possible to extract the absorption and scattering coefficients and the scattering anisotropy factor g, using an inverse Monte Carlo model. Between 470 and 700 nm, only the reduced scattering coefficient and absorption could be evaluated. The absorption spectra were fitted to known tissue chromophore spectra, so that the concentrations of haemoglobin and myoglobin could be estimated. The reduced scattering coefficient was compared with Mie computations to provide Mie equivalent average radii. Most of the absorption was from myoglobin, whereas haemoglobin absorption was negligible. Metmyoglobin was formed in the ablated tissue, which could yield a spectral signature to distinguish the ablated tissue with a simple optical probe to monitor the ablation therapy. The reduced scattering coefficient increased by, on average, 50% in the ablated tissue, which corresponded to a slight decrease in the Mie equivalent radius.     

Laser tomography of heterogeneous scattering media using spatial and temporal resolution

Time-resolved tomography is performed in transillumination by using 527 nm picosecond pulses from a passively mode-locked doubled Nd/glass laser and a streak camera to select photons according to their flight time. This work reports on the increase in contrast of a time-resolved profile of a 2 mm radius opaque object embedded in a scattering medium, constituted of diluted milk in a 30 mm thick cell. For spatial analysis, the emerging photons are detected through a 6 mm slit at the outlet face of the cell. Transmission profiles obtained as a function of time show that the contrast is enhanced for the shortest flight times, while the ‘shadow’ of the object is no longer detected after about 100 ps. Moreover, improvements in contrast are studied for different configurations of the model, to analyse separately the role of collimated and scattered photons. It is expected that such a tomographic method based on time-resolved absorption could be applied to imaging for more complex biological structures in the red and near-infra-red range.     

Cell refractive index: Models,insights, applications and future perspectives

Cell refractive index (RI) is an intrinsic optical parameter that governs the propagation of light (i.e., scattering and absorption) in the cell matrix. The RI of cell is sensitively correlated with its mass distribution and thereby has the capability to provide important insights for diverse biological models. Herein, we review the cell refractive index and the fundamental models for measurement of cell RI, summarize the published RI data of cell and cell organelles and discuss the associated insights. Illustrative applications of cell RI in cell biology are also outlined. Finally, future research trends and applications of cell RI, including novel imaging techniques, reshaping flow cytometry and microfluidic platforms for single cell manipulation are discussed. The rapid technological advances in optical imaging integrated with microfluidic regime seems to enable deeper understanding of subcellular dynamics with high spatio-temporal resolution in real time.     

Frequency and pressure dependent attenuation and scattering by microbubbles

The aim of this study was to evaluate experimentally the degree of pressure dependence of attenuation and scattering by microbubbles at low acoustic pressures with an empirical nonlinear model. In addition, the pressure dependency over a range of frequencies (1 to 5 MHz) has been studied. A series of transmission and scattering measurements were made with the microbubble SonoVue, using an automated system. Results show that, within the pressure range studied, attenuation as a result of the microbubble is pressure-dependent, whereas no such dependence of scattering was detectable. The pressure dependence of attenuation for SonoVue was found to be most significant at 1.5 MHz. The scattering is shown to be the highest at the lowest insonation frequency, around 1 approximately 1.25 MHz, and then decreases with frequency.     

数字人体微观研究:量子人体的散射理论模型

散射理论模型是量子人体信息机理研究的主要内容.本文主要讨论了量子人体的相互作用表象,量子人体态随时间演化的算符和量子人体的微扰论展开;阐述了量子人体的散射矩阵,量子人体S矩阵的微扰论的展开,量子人体的散射截面和量子人体的分波法;最后,从七个方面对全文进行了结语概括;为量子人体散射机理研究提供理论模型.     

Carbon fiber reinforced vs titanium implants for fixation in spinal metastases: A comparative clinical study about safety and effectiveness of the new “carbon-strategy”

In spinal oncology traditional titanium implants could significantly impair evaluation of postoperative imaging because of artifacts, potentially affecting proper planning and execution of radiotherapy and adequate radiological follow-up to rule out progression of the disease. This is why carbon fiber reinforced (CFR)-PEEK implants have been developed for spinal fixation. The advantages of this system include fewer artifacts on imaging, potentially improving the execution and quality of radiotherapy, with also a reduced scattering effect to neighboring tissues.A comparative clinical and radiological study between new CFR-PEEK and standard titanium implants is described. Data recorded for each case included patient demographics, clinical, radiological and surgical data, intra- and postoperative complications, follow-up information. The goal of this study was to verify the safety and effectiveness of CFR-PEEK devices compared to standard titanium implants.A total number of 78 patients were reviewed. 36 patients underwent CFR-PEEK fixation, while titanium implants were used for 42 patients. Functional recovery was obtained in both groups and registered at last follow-up in terms of axial pain and neurological status. No significative differences were found between the two groups in terms of post-operative clinical complications and hardware-related complications.CFR-PEEK implants constitute a feasible and effective way to restore stability in metastatic spine tumors. This study found a non inferior favorable profile in terms of intraoperative and postoperative complications and functional recovery, compared to titanium. Further prospective studies are needed to clarify the potential oncological advantage of their radiolucency.     

A Multi-Method Approach to Assess the Self-Interaction Behavior of Infliximab

Attractive self-interaction processes in antibody formulations increase the risk of aggregation and extraordinarily elevated viscosity at high protein concentrations. These challenges affect manufacturing and application. This study aimed to understand the self-interaction process of Infliximab as a model system with pronounced attractive self-interaction. The association mechanism was studied by a multi-method approach comprising analytical ultracentrifugation, dynamic light scattering, small angle X-ray scattering, self-interaction bio-layer interferometry and hydrogen-deuterium exchange mass spectrometry. Based on our results, both Fab and Fc regions of Infliximab are involved in self-interaction. We hypothesize a mechanism based on electrostatic interactions of polar and charged residues within the identified areas of the heavy and the light chain of the mAb. The combination of fast and reliable screening methods and low throughput but high resolution methods can contribute to detailed characterization and deeper understanding of specific self-interaction processes.     

胃腺癌组织与非肿瘤胃壁组织的吸收和散射特性的差异

目的：探讨人胃腺癌组织与非肿瘤胃壁组织的吸收和散射光谱的差异。方法：测定26例人胃腺癌标本的肿瘤及非肿瘤区域的组织的吸收系数光谱和散射系数光谱。结果：人胃腺癌组织吸收系数光谱、散射系数与非肿瘤胃壁组织光谱明显不同，胃腺癌组织吸收系数在300～720nm光谱范围内明显低于非肿瘤胃壁组织，散射系数在480～1100nm光谱范围内也明显低于非肿瘤胃壁组织。结论：胃腺癌组织和非肿瘤胃壁组织的吸收系数光谱和散射系数光谱比较差异均有统计学意义。     

Distortions of ultrasonic field introduced by the rib cage in echocardiography

In ultrasonic examination of the heart, the anatomy and motion of heart structures can be observed by placing the ultrasonic transducer over an intercostal window adjacent to the sternum. The ultrasonic beam may be reflected, refracted, or scattered from its path by the ribs and soft tissues before reaching the target of interest. This interaction between the tissues and ultrasound beam, which introduces significant changes in ultrasonic beam characteristics, may result in considerable degradation of the lateral resolution of the ultrasonic system, determined largely by the beam width. In this paper, the effect of rib cage on the beam characteristics is examined. It is shown that the rib cage can produce severe distortions of the ultrasonic beam, namely, asymmetry in beam cross-section, alteration in beam diameter, and deflection of the beam from its central path. It is also demonstrated that this distortion is dependent upon transducer diameter, width of the intercostal window, and transducer angulation relative to the breast plate.