Biomedical subjects

S C Orphanoudakis

Publications and source records attributed to S C Orphanoudakis.

4 recordsLinked to original sources

PubMed1978

Small hemorrhages vs. small calcifications in brain tumors: difficulty in differentiation by computed tomography.

The difficulty in differentiating multiple small hemorrhages from multiple small calcifications in brain tumors by computed tomography (CT) is discussed. Illustrative CT scans are presented and the theoretical basis for this problem is elaborated. The difficulty is attributed to the relatively large size of the voxel and the ensuing partial volume effect, particularly with small intraparenchymal lesions of different sizes and attenuations.

Adult↗

PubMedDate not supplied

Bone mineral analysis using single-energy computed tomography.

We present a new method for evaluating in vivo changes in bone mineralization in the peripheral skeleton, using computed tomography (CT). A set of bone mineralization indices are generated from numerous CT images of the patient's distal radius. The cross-sectional anatomy displayed by the CT scan allows for separate evaluation of the cortical and trabecular bone. Correction for possible drift of the CT number scale (Hounsfield scale) is achieved by scanning standard solutions of dipotassium hydrogen phosphate simultaneously with the forearm. Preliminary data indicate that this is a precise method for evaluating in vivo changes in bone mineralization.

Adolescent↗

PubMedDate not supplied

Mathematical model of conventional tomography.

A Fourier decomposition approach is used to study the imaging properties of conventional tomography. Spatial frequency response curves (MTFs) are calculated for both linear and axial transverse tomography. These curves depend on the product of the spatial frequency of the sinusoidal density variations in thin layers parallel to the tomographic plane and the distance between such layers and the tomographic plane. Based on the spatial frequency response curves, a quantitative definition of tomographic layer thickness is given. Furthermore, the spatial frequency response curves suggest that unattenuated low-frequency information from outside the tomographic layer limits the resolution in conventional tomograms and that high-pass spatial filtering of the image may substantially improve the diagnostic quality of tomographic images, particularly in the identification of boundaries.

Mathematics↗

PubMedDate not supplied

Linearizing mechanisms in conventional tomographic imaging.

Implicit in the concept of conventional tomography and in any attempt to characterize the tomographic process by a modulation transfer function is the assumption that the tomographic process is linear. A Fourier decomposition approach and an analysis of nonlinear contributions to the integrated tomographic image intensity are used in this paper to establish the validity of this assumption and to determine the mechanisms by which the tomographic process is effectively linearized.

Energy Transfer↗