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S R Arridge

Publications and source records attributed to S R Arridge.

8 recordsLinked to original sources
PubMed1992

Experimentally measured optical pathlengths for the adult head, calf and forearm and the head of the newborn infant as a function of inter optode spacing.

The Differential Pathlength Factor (DPF) has been measured for several different tissues. The results showed that the DPF varied with the type of tissue studied, and in the case of the adult calf with sex. However, the DPF for all tissues studied was constant once the inter optode spacing exceeded 2.5 cm. Thus, measurements can be made by NIR spectroscopy at a range of inter optode spacings, and a single DPF used in the calculation of chromophore concentration. The results also showed that the major source of error in the DPF lay in the measurement of the inter optode spacing. To improve accuracy, two options are possible. Firstly, some means of continuous measurement of inter optode spacing could be incorporated in the NIR instrumentation. The better alternative would be an instrument incorporating a method of directly measuring the optical pathlength at each wavelength. This could be done either by time of flight measurement, or if it can be validated, by phase shift measurement.

Adult↗
PubMed1992

The theoretical basis for the determination of optical pathlengths in tissue: temporal and frequency analysis.

A concise theoretical treatment is developed for the calculation of mean time, differential pathlength, phase shift, modulation depth and integrated intensity of measurements of light intensity as a function of time on the surface of tissue, resulting from either the input of picosecond light pulses, or radio frequency-modulated light. The treatment uses the Green's function of the diffusion approximation to the radiative transfer equation, and develops this and its Fourier transform in a variety of geometries. Detailed comparisons are made of several of these parameters in several geometries, and their relation to experimentally measured clinical data. The limitations of the use of phase measurements is discussed.

Diagnostic Imaging↗
PubMed1988

A computer system for the interactive planning and prediction of maxillofacial surgery.

A computer system has been developed for the simulation of facial surgery with interactive three-dimensional graphic techniques and data derived from computed tomographic scans and a purpose-built laser scanning system. The simulation includes the surgery on the hard tissues, and modeling of the soft tissue for prediction of the postoperative facial appearance. The facilities available are described and an example of their use is given.

Computer Graphics↗
PubMedDate not supplied

Three-dimensional visualization of computerized tomography and laser scan data for the simulation of maxillo-facial surgery.

A system has been developed for the three-dimensional (3D) visualization of the face and skull using data obtained from a purpose-built no-contact laser scanning system and from a series of scans produced by X-ray computerized tomography. Features developed allow the simulation, planning and prediction of maxillo-facial surgery. Realistic skeletal and facial images with a solid 3D appearance are produced from these two datasets using computer graphics techniques. The images can be sectioned for diagnostic purposes or parts can be repositioned for the simulation of surgery. 3D measurements can be made on the images for pre- and post-surgical analysis. An example of the clinical use of the system in the planning of surgery and the prediction of post-surgical facial appearance is given.

Computer Graphics↗
PubMedDate not supplied

Using greyscale voxel databases for improved shading and segmentation.

Many different data representations are possible in computer graphics. Originally, in the medical field, simplified methods were used in order to reduce computation times on small computer systems. Currently a wider range of techniques is developing as costs of hardware continue to fall. In this paper we review a number of possible representations and explain the advantage of one that is greyscale, volumetric and random access. Different segmentation techniques can be used, as well as shading algorithms that give greatly improved appearances. A quantitative analysis of shading methods is derived in terms of the degree of sampling of the 'pseudo-normal' vectors that estimate the direction of the tangent to a surface. The application to a study of multiple sclerosis lesions in the brain using nuclear magnetic resonance data is shown.

Brain↗