Biomedical subjects

O Nalcioglu

Publications and source records attributed to O Nalcioglu.

60 records · Page 4Linked to original sources

PubMedDate not supplied

Applications of magnetic resonance in model systems: cancer therapeutics.

The lack of information regarding the metabolism and pathophysiology of individual tumors limits, in part, both the development of new anti-cancer therapies and the optimal implementation of currently available treatments. Magnetic resonance [MR, including magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), and electron paramagnetic resonance (EPR)] provides a powerful tool to assess many aspects of tumor metabolism and pathophysiology. Moreover, since this information can be obtained nondestructively, pre-clinical results from cellular or animal models are often easily translated into the clinic. This review presents selected examples of how MR has been used to identify metabolic changes associated with apoptosis, detect therapeutic response prior to a change in tumor volume, optimize the combination of metabolic inhibitors with chemotherapy and/or radiation, characterize and exploit the influence of tumor pH on the effectiveness of chemotherapy, characterize tumor reoxygenation and the effects of modifiers of tumor oxygenation in individual tumors, image transgene expression and assess the efficacy of gene therapy. These examples provide an overview of several of the areas in which cellular and animal model studies using MR have contributed to our understanding of the effects of treatment on tumor metabolism and pathophysiology and the importance of tumor metabolism and pathophysiology as determinants of therapeutic response.

Animals↗

PubMedDate not supplied

Normalization (division) versus subtraction of digitized images.

The propagation of noise in digitized images arrived at by algebraic manipulation of two images has been investigated. The algebraic manipulations investigated were logarithmic subtraction, linear subtraction, and division of the two images. The two images were identical except for the presence of a contrast-adding component in one of them. The two extreme cases of video-fluoroscope system behavior, gray level proportional to incident photon flux and gray level proportional to the product of thickness and linear attenuation coefficient, were investigated. The ratio of signal to noise was calculated for each of these cases and a figure of merit established for the ratio of signal to noise of the division process versus each of the subtraction processes for each of the two fluoroscopic system behaviors. In all cases, this figure of merit is greater than unity. Values of these figures of merit for iodine concentrations of 5, 20, and 300 mg/cm3 are given in the paper. The process of division appears to be advantageous as a signal-to-noise enhancer for all applications not requiring a quantitative relationship between image contrast and photon flux.

Fluoroscopy↗

PubMedDate not supplied

Characterization of the veiling glare PSF in x-ray image intensified fluoroscopy.

A theoretical derivation for the point spread function (PSF) which describes the veiling glare in x-ray image intensifiers (II) is presented. The PSF is dependent on two parameters which can be determined experimentally for a given II. An experimental investigation of the linearity of veiling glare phenomenon is undertaken. The experimental results indicate that veiling glare could be described as a linear process to a high degree of accuracy.

Fluoroscopy↗

PubMedDate not supplied

Removal of image intensifier veiling glare by mathematical deconvolution techniques.

X-ray images acquired with an image intensifier detector system suffer from veiling glare, a low-frequency degradation described by a point spread function (PSF). The PSF has two experimentally determined parameters unique to a given image intensifier. This information is utilized to deconvolve the degradation from digitally acquired images. Results demonstrate a significant increase in contrast ratio of high-contrast objects after deconvolution and image restoration.

Animals↗

PubMedDate not supplied

An improved nuclear magnetic resonance diffusion coefficient imaging method using an optimized pulse sequence.

Two-dimensional diffusion coefficient maps (images) of a carefully controlled diffusion phantom have been measured by a new diffusion imaging sequence using a 0.6-T whole-body nuclear magnetic resonance (NMR) scanner having a gradient field strength of 2.5 mT/m. The free induction decay (FID) data for the diffusion coefficient images were collected by varying the duration of the readout gradient in the conventional two-dimensional Fourier imaging sequence. The experimental results obtained by the proposed NMR diffusion measurement technique indicate a close agreement with other previous measurements. The selection of optimum spin-echo time for maximum signal-to-noise ratio (SNR) in diffusion imaging is studied and also experimentally confirmed. Finally, a preclinical study with human volunteers has been performed and results are presented.

Humans↗

PubMedDate not supplied

The effects of random directional distributed flow in nuclear magnetic resonance imaging.

Capillary flow or microscopic random directional coherent flow as a model of perfusion is investigated both theoretically and experimentally. In the model, we assumed that molecular motion within a finite resolvable volume element (voxel) is a superposition of flow of randomly oriented small capillaries. In such a case, the observed signal from the capillary flow within a voxel will be attenuated in signal amplitude without any change in phase. Although this attenuation effect is similar to the diffusion phenomenon, it differs basically in the following aspects: since the motion in each capillary segment is coherent, phase cancellation occurs at even echoes due to spin rephasing, while the diffusion phenomenon is a purely random Brownian motion of the thermally agitated molecules, changing both in direction and speed during the measurement period. Because of the random character of diffusion, even-echo rephasing cannot be observed. Thus capillary flow or perfusionlike microscopic flow can be measured based on the above distinct flow characteristics, i.e., signal restoration at even echoes versus signal amplitude attenuation at odd echoes. By applying a suitable mathematical algorithm, information on the capillary flow alone can be extracted from the two separate distinct measurements, i.e., one with a single echo and the other with a double echo. Both a theoretical calculation of the capillary flow, as well as the experimental results with a human volunteer by a 0.6-T nuclear magnetic resonance imager, are presented.

Algorithms↗