Thermal Properties of Tissue

Duck, Francis

doi:10.1016/b978-0-12-222800-1.50006-1

Cited by 441 publications

(388 citation statements)

References 55 publications

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“…This decrease is consistent with compositional analysis data showing lower blood and water content for fat versus glandular tissue (27). Scatter power also declines with age after age 50 years.…”

Section: Quantities Versus Agesupporting

confidence: 89%

Sources of Absorption and Scattering Contrast for Near-Infrared Optical Mammography

et al. 2001

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Rationale and Objectives. Near-infrared (NIR) diffuse optical spectroscopy and imaging may enhance existing technologies for breast cancer screening, diagnosis, and treatment. NIR techniques are based on sensitive, quantitative measurements of functional contrast between healthy and diseased tissue. In this study, the authors quantified the origins of this contrast in healthy breasts. Materials and Methods.A seven-wavelength frequency-domain photon migration probe was used to perform noninvasive NIR measurements in the breasts of 28 healthy women, both pre-and postmenopausal, aged 18 -64 years. A diffusive model of light transport quantified oxygenated and deoxygenated hemoglobin, water, and lipid by their absorption signatures. Changes in the measured light-scattering spectra were quantified by means of a "scatter power" parameter.Results. Substantial quantitative differences were observed in both absorption and scattering spectra of breast as a function of subject age. These physiologic changes were consistent with long-term hormone-dependent transformations that occur in breast. Instrument response was not adversely affected by subject age or menopausal status. Conclusion.These measurements provide new insight into endogenous optical absorption and scattering contrast mechanisms and have important implications for the development of optical mammography. NIR spectroscopy yields quantitative functional information that cannot be obtained with other noninvasive radiologic techniques.

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Section: Quantities Versus Agesupporting

confidence: 89%

Sources of Absorption and Scattering Contrast for Near-Infrared Optical Mammography

et al. 2001

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“…Segmentation was performed manually with reference to textbooks on anatomy and with assistance from two practicing radiologists. At each frequency, appropriate values from the literature for tissue mass density (7)(8)(9)(10), water content by percent mass (11), and electrical permittivity and conductivity (12) were assigned to each tissue. Tissue mass density information was used in calculation of SAR, and water content was used to weight signal from different tissues differently in calculation of simulated images.…”

Section: Head Modelmentioning

confidence: 99%

Signal‐to‐noise ratio and absorbed power as functions of main magnetic field strength, and definition of “90°” RF pulse for the head in the birdcage coil

Collins

Smith

2001

Magnetic Resonance in Med

246

267

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Calculations of the RF magnetic (B 1 ) field as a function of frequency between 64 and 345 MHz were performed for a head model in an idealized birdcage coil. Absorbed power (P abs ) and SNR were calculated at each frequency with three different methods of defining excitation pulse amplitude: maintaining 90°fl ip angle at the coil center (center ␣ Predictions of trends in signal-to-noise ratio (SNR) and specific energy absorption rate (SAR) with increasing static magnetic field (B 0 ) strength based on MR theory, the principle of reciprocity, and analytical RF magnetic field (B 1 ) calculations have been shown to be reasonably accurate at frequencies up to 64 MHz in head-and body-sized samples (1,2). MRI experiments are currently performed at static magnetic field (B 0 ) strengths as high as 8.0 Tesla, where the frequency of the RF magnetic field (B 1 ) for imaging with 1 H is about 340 MHz. At these frequencies, significant interaction between the applied B 1 field and human tissues is expected. The effects of this interaction on SNR and the total absorbed power are complicated, and are dependent on the experiment being performed, RF coil type and performance, and even on the specific subject geometry and position in the coil (2,3).‫؍‬In this study we performed calculations of SAR in the head, the total absorbed power (P abs ) in the head and shoulders, and SNR on an axial plane of the head at several B 1 frequencies between 64 and 345 MHz for an anatomically-accurate model in an idealized birdcage coil. The head position and orientation, and the coil behavior are kept constant so that B 1 frequency and definition of the excitation pulse are the only variables. Electrical properties of all tissues are set appropriately at each frequency. The excitation pulse amplitude is defined with three different methods at each frequency.Since our interest was primarily in the effects of the high-frequency RF fields on the imaging experiment, we chose to ignore several factors that complicated both the calculation and interpretation of the results. We chose to consider signal from protons in water only, and to ignore T 1 and T 2 relaxation effects in this work. This simplifies the presentation of results, making them independent of TE and TR, but it also removes some realism from the simulation. We also neglected many other experimental effects, such as those of B 0 inhomogeneity, inevitable variation in sample and coil geometry, signal filtering, and signal amplifier integrity and performance (4). Thus, the findings concerning signal in the images, FID amplitude, and SNR presented here should be considered predictions of the types of phenomena that may be seen at high frequency due to behavior of the RF fields. Manifestation of these phenomena in experiment should not be expected to occur exactly as in these calculations. METHODSThe finite difference time domain (FDTD) numerical method for electromagnetics was used to calculate all electrical and magnetic fields throughout a head model in an idealized birdcage coil. This me...

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“…In large arteries, red blood cell concentrations can reach 45% by volume, compared to around 4.5% in small vessels, such as the arterioles of the skin (Bonner and Nossal 1990). The penetration depths achieved at wavelengths of 500nm and 1000nm are, 50grn and 400ýtrn for the larger vessels and 500ýLrn and 250ORm for the smaller vessels (Duck 1990). These figures are based on an oxygen saturation of 100% and increase slightly at reduced oxygenation levels.…”

Section: Optical Properties Of the Skin And Bloodmentioning

confidence: 99%

“…The concentration of the two pigments is determined by exposure to sunlight and varies around the world. Absorption by skin pigments occurs mainly below 600nm, above this wavelength scattering processes dominate (Duck 1990). …”

Section: Optical Properties Of the Skin And Bloodmentioning

confidence: 99%

“…The direction of propagation of a scattered wave depends on the shape of the scattering particle. For non-spherical particles, including red blood cells, the scattering direction can be estimated using the (Duck 1990). If the wavelength of the source is greater than about 600nm, absorption by chromophores in the tissue is relatively low, and scattering processes will dominate.…”

Section: Optical Properties Of the Skin And Bloodmentioning

confidence: 99%

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An in-shoe laser Doppler sensor for assessing plantar blood flow in the diabetic foot

Cobb¹,

Claremont²

2001

Medical Engineering & Physics

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An in-shoe laser Doppler sensor for assessing plantar blood flow in the diabetic foot. Jonathan Edwin CobbPlantar ulceration is a complication of the diabetic foot prevalent in adults with type 11 diabetes mellitus. Although neuropathy, microvascular disease and biornechanical factors are all implicated, the mechanism by which the tissue becomes pre-disposed to damage remains unclear. Recent theories suggest that the nutritional supply to the tissue is compromised, either by increased flow through the arteriovenous anastomoses ('capillary steal' theory) or through changes in the micro vascu I ature (haemodynamic hypothesis). Clinical data to support these ideas has been limited to assessment of the unclad foot under rest conditions. A limitation of previous studies has been the exclusion of static and dynamic tissue loading, despite extensive evidence that these biornechanical factors are essential in the development of plantar ulceration. The present study has overcome these problems by allowing assessment of plantar blood flow, in-shoe, during standing and walking.The system comprises a laser Doppler blood flux sensor operating at 780nm, load sensor, measurement shoe, instrumentation, and analysis software. In-vitro calibration was performed using standard techniques. An in-vivo study of a small group of diabetic subjects indicated differences in the blood flux response between diabetic neuropaths, diabetics with vascular complications and a control group. For example, following a loading period of 120s, relative increases in response from rest to peak were: Control (150% to 259%), Vascular (-70% to 242%), Neuropathic (109%-174%) and recovery times to 50% of the peak response were: Control (33s to 45s), Vascular (43s to >120s), Neuropathic (>120s). Dynamic re-perfusion rates (arbitrary units per millisecond) obtained for the swing phase of gait were: Control (6.1 a. u/ms to 7.9 a. u/ms), Vascular (4 a. u/ms to 6.2 a. u/ms), Neuropathic (2.3 a. u/ms to 4.5 a. u/ms).

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Thermal Properties of Tissue

Cited by 441 publications

References 55 publications

Sources of Absorption and Scattering Contrast for Near-Infrared Optical Mammography

Sources of Absorption and Scattering Contrast for Near-Infrared Optical Mammography

Signal‐to‐noise ratio and absorbed power as functions of main magnetic field strength, and definition of “90°” RF pulse for the head in the birdcage coil

An in-shoe laser Doppler sensor for assessing plantar blood flow in the diabetic foot

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