Absorption In Biological Tissues Research Articles

Quantitative photoacoustic measurement of tissue optical absorption spectrum aided by an optical contrast agent

In photoacoustic imaging, the intensity of photoacoustic signal induced by optical absorption in biological tissue is proportional to light energy deposition, which is the product of the absorption coefficient and the local light fluence. Because tissue optical properties are highly dependent on the wavelength, the spectrum of the local light fluence at a target tissue beneath the sample surface is different than the spectrum of the incident light fluence. Therefore, quantifying the tissue optical absorption spectrum by using a photoacoustic technique is not feasible without the knowledge of the local light fluence. In this work, a highly accurate photoacoustic measurement of the subsurface tissue optical absorption spectrum has been achieved for the first time by introducing an extrinsic optical contrast agent with known optical properties. From the photoacoustic measurements with and without the contrast agent, a quantified measurement of the chromophore absorption spectrum can be realized in a strongly scattering medium. Experiments on micro-flow vessels containing fresh canine blood buried in phantoms and chicken breast tissues were carried out in a wavelength range from 680 nm to 950 nm. Spectroscopic photoacoustic measurements of both oxygenated and deoxygenated blood specimens presented an improved match with the references when employing this technique.

Ultrasound absorption and entropy production in biological tissue: a novel approach to anticancer therapy

The entropy production of tumorous cells is higher than that of normal cells, and entropy flow is therefore directed from tumorous toward healthy cells. This results in information concerning the cancer propagating into the surrounding normal tissue. However, ultrasound absorption results in additional entropy production in tissues. The entropy mechanism possibly provides a basis for a novel approach to anticancer therapy through the use of ultrasound irradiation.Through the calculation of ultrasound-induced entropy production and comparison of the theoretical results with the experimental data on ultrasound absorption in biological tissues, we have demonstrated that ultrasound absorption will increase the entropy in normal tissue more efficiently than in tumorous tissue due to the more acidic nature of the latter. Consequently, the direction of entropy flow between these two kinds of cells may be reversed on exposure to ultrasound.The higher entropy accumulation of normal cells during ultrasound irradiation may possibly lead to a change in the original direction of entropy flow and avoid the propagation of information on the cancer into the normal tissues. We suggest that low-intensity, low-frequency ultrasound irradiation may be an efficient tool for the therapy of solid tumors.

Nonlinear absorption in biological tissue for high intensity focused ultrasound

In recent years the propagation of the high intensity focused ultrasound (HIFU) in biological tissue is an interesting area due to its potential applications in non-invasive treatment of disease. The base principle of these applications is the heat effect generated by ultrasound absorption. In order to control therapeutic efficiency, it is important to evaluate the heat generation in biological tissue irradiated by ultrasound. In his paper, based on the Khokhlov–Zabolotkaya–Kuznetsov (KZK) equation in frequency-domain, the numerical simulations of nonlinear absorption in biological tissues for high intensity focused ultrasound are performed. We find that ultrasound thermal transfer effect will be enhanced with the increasing of initial acoustic intensity due to the high harmonic generation. The concept of extra absorption factor is introduced to describe nonlinear absorption in biological tissue for HIFU. The theoretical results show that the heat deposition induced by the nonlinear theory can be nearly two times as large as that predicated by linear theory. Then, the influence of the diffraction effect on the position of the focus in HIFU is investigated. It is shown that the sound focus moves toward the transducer compared with the geometry focus because of the diffraction of the sound wave. The position of the maximum heat deposition is shifted to the geometry focus with the increase of initial acoustic intensity because the high harmonics are less diffraction. Finally, the temperature in the porcine fat tissue changing with the time is predicated by Pennes’ equation and the experimental results verify the nonlinear theoretical prediction.

Generalized Transmission-Line Model forEstimation of Cellular Handset Power Absorption in Biological Tissues

Evaluation of cellular handset power absorption in biological tissues has recently received due public attention. Generally, the solution of even simple cellular phone-human head configurations, involves massive and time consuming excitation of numerical algorithms. Furthermore, an explicit dependence of numerical solution on the physical parameters as well as on the configuration geometry is usually difficult to achieve. Herein, we focus on a generalized one-dimensional transmission-line model, which is capable of establishing tight bounds and estimates on the actual power absorption and radiation for many realistic configurations. The solution is given by explicit closed-form expressions, which depend continuously on the physical and geometrical parameters of the problem and, thus, can be readily physically interpreted. The potential promise of our simplified model is numerically verified via alternative finite-difference time-domain and moment method data for cellular handsets closely coupled to human head.

Bounds and estimates for power absorption in two-dimensional highly lossy configurations

Electromagnetic power absorption in biological tissues has recently received due scientific and public attention, particularly, in the areas of cellular communication and hyperthermic treatments. While efficient numerical algorithms, such as the finite difference time domain technique and the method of moments, have been developed as to obtain accurate power distributions in complicated configurations, their physical interpretation and explicit dependence on problem’s parameters are still difficult to achieve. In attempt to gain a clear insight into the electromagnetic power absorption mechanism as well as its estimation and relation to the Specific Absorption Rate (SAR), we have recently proposed an infinite-extent current-sheet model. Herein, the model is further extended by incorporating finite-extent sources, i.e., electric and magnetic line-sources, exciting a highly lossy semi-infinite half-space. This modification results in deeper insight and understanding of the crucially important parameters, commonly involved in realistic configurations, namely, bounds and estimates on the power absorption and radiation efficiencies, local and total SAR coupling coefficients, and effective absorption dimensions.

Plane-wave model for electromagnetic power absorption in biological tissues

The phenomenon of electromagnetic power absorption in biological tissues has recently become of increased scientific and public interest, particularly in the areas of cellular communication and hyperthermia systems. Electromagnetic power absorption in biological tissues is a well-known phenomenon. Its evaluation requires, in general, a solution of the three-dimensional frequency-dependent wave equation in complex configurations, which may necessitate quite massive analytical and numerical efforts. Herein, we focus on an elementary plane-wave model. The model establishes a tight estimate on the optimal (maximal/minimal) power absorption in realistic microwave configurations, in particular, cellular communications safety assessments. Furthermore, the absorption efficiency as well as the source impedance are obtained via explicit closed-form expressions, leading to an explicit maximal power absorption criterion for highly lossy tissues. The results depend continuously and explicitly on the physical parameters of biological tissues as well as on the plane-wave incidence angle and excitation source location. They are shown to be closely related to electromagnetic specific absorption rate estimations in biological tissues. In view of the well-known analogy between plane waves and rectangular waveguide modes, our results can be applied to optimization schemes of microwave heating and waveguide based therapeutic hyperthermia systems.

Photoacoustic tomography of biological tissues with high cross-section resolution: reconstruction and experiment.

A modified back-projection approach deduced from an exact reconstruction solution was applied to our photoacoustic tomography of the optical absorption in biological tissues. Pulses from a Ti:sapphire laser (4.7 ns FWHM at 789.2 nm) were employed to generate a distribution of photoacoustic sources in a sample. The sources were detected by a wide-band nonfocused ultrasonic transducer at different positions around the imaging cross section perpendicular to the axis of the laser irradiation. Reconstructed images of phantoms made from chicken breast tissue agreed well with the structures of the samples. The resolution in the imaging cross section was experimentally demonstrated to be better than 60 microm when a 10 MHz transducer (140% bandwidth at -60 dB) was employed, which was nearly diffraction limited by the detectable photoacoustic waves of the highest frequency.

Experimental in vivo fenestration of guinea pig cochlea using 2.79 Μm laser radiation

Erbium-YSGG laser systems are promising tools in ear, nose and throat (ENT) surgery. The high absorption in biological tissues, resulting in precise tissue ablation with minimal thermal tissue damage, and the possibility to guide the radiation through optical fibres make the 2.79 Μm wavelength a favourite for microsurgery. In order to simulate the fenestration of the human stapes foot plate required for prosthesis implantation when treating otosclerosis, five guinea pig cochleae were irradiated in vivo until perforation was achieved. The laser-induced temperature rise and pressure transients evoke activity in the inner hair cells that was investigated by micro-iontophoresis. Perforation of the cochlea bone (hole diameter of 350 Μm) can be performed with a few laser pulses and high precision with a thermal damage zone of<100 Μm. The bone ablation rate is 10 ± 2 Μm pulse-1 at a radiant exposure of 12 J cm-2. The functionality of the afferent inner hair cells in the guinea pig cochlea was verified before and after laser treatment using glutamate receptor agonists AMPA and NMDA. For the above selected laser parameters, the induced 15-min enhanced activity was blockable with the specific reversible AMPA and NMDA antagonists CNQX and AP-7. Micro-iontophoresis confirms the reversibility of cochlea functionality after its perforation with Er-YSGG laser pulses. A limit of radiant exposure around 12 J cm-2 is found for safe fenestration. It is demonstrated that the Er-YSGG laser is a precise and safe instrument whilst still using adequate laser parameters. On the other hand, this study demonstrates the potential of uncontrollable and unintended induced damage, resulting from vapour channel formation in the perilymph, if a high laser radiant exposure is applied.

Nonlinear Acoustic Behavior in Focused Ultrasonic Fields: Observations of Intensity Dependent Absorption in Biological Tissue

Nonlinear Acoustic Behavior in Focused Ultrasonic Fields: Observations of Intensity Dependent Absorption in Biological Tissue

Apparatus for investigation of the dynamics of liquid absorption in biological tissues

Apparatus for investigation of the dynamics of liquid absorption in biological tissues

A photographic personnel dosimeter for x-radiation in the range from 30 kev to beyond 1 MEV.

Introduction Biological Considerations: When used for x-ray dosimetry, photographic film is at best a rough, secondary instrument. It has to be calibrated against primary standards, processed under controlled conditions, and, if possible, placed in a special holder designed to produce a suitable film response as a function of radiation energy. Ideally, the response of a radiation dosimeter should parallel closely the radiation damage to biological tissue. For the tactical radiation dosimeters used by the Military, the biological damage criterion usually selected is the lethal effect of the radiation on mammals. In the case of x-rays, the lethal exposure as measured in roentgens in free air was found to increase sharply below about 80 key (1). A sharp drop of dosimeter response below this energy is therefore sometimes thought to be desirable for tactical x-ray dosimetry. As most of the film dosimeters presently in use employ filters of high atomic number over at least a portion of the sensitive area (2, 3), they display this cut-off. In civilian applications, biological criteria other than lethality apply, and damage to superficially located biological structures must be considered. It is now believed that, for most types of biological action, the effect of radiation is proportional to the amount of energy imparted to tissue along unit track length of the secondary ionizing particles (linear energy transfer) (4); also, it has been shown (5) that the linear energy transfer of electrons rises sharply as their energy decreases from 100 key to 1 kev. If one assumes that for equal energy absorption per gram of tissue the relative biological effectiveness of x-rays below 100 kev does not decrease as the x-ray energy decreases, one may con conelude that a response cut-off of a radiation dosimeter below 80 kev is undesirable for most civilian applications. A ims and A ccomplishments of Present Study: Groups concerned with personnel monitoring have frequently expressed a demand for a film dosimeter whose response to x-radiation of energy below 100 kev parallels more closely the energy absorption in biological tissue, or at least that in air (i.e., the exposure in roentgens). The instrument described in this paper is, in part, an answer to this demand. Its response to x-radiation between 30 kev and 1 MEV lies within ±20 per cent of that of air for exposures ranging from roughly 250 mr or less to about 3 r, and within ±30 per cent for exposures ranging from about 3 r to 6 r. It is useful also for radiation energies higher than 1 MEV, although with slightly decreased accuracy, and its exposure range can be extended up to 600 r for high-energy emergency work. Principle of Film-Stack Dosimeter Basic Idea: The idea for the dosimeter here referred to as the "film-stack dosimeter" was first conceived by Allisy (6).