Volume 31, Issue 7, July 2004
Index of content:
- PH. D. THESES ABSTRACTS
Fiber-optic, real-time dosimeter based on optically stimulated luminescence of and KBr:Eu for potential use in the radiotherapy of cancer31(2004); http://dx.doi.org/10.1118/1.1758349View Description Hide Description
This thesis describes a single-fiber dosimetrysystem based on optically stimulated luminescence(OSL) of artificially grown single crystals of and KBr:Eu, with potential application in the medical field, especially in radio oncology. Small fiber-shaped dosimeters with dimensions (diameter/length) on the order of 500 μm/5 mm are attached to one end of an optical fiber, resulting in fiber probes with diameters of less than 1 mm and lengths of up to 15 m. The opposite end of the fiber is connected to an OSL reader that contains a stimulation light source (laser) and a photomultiplier tube that is used for luminescence detection. During irradiation, an optomechanical shutter periodically allows laser light to be transmitted down the optical fiber, to stimulate the luminescence response from the dosimeter being irradiated at a remote location. The luminescence measured during each interval of laser stimulation is indicative of the radiationdose absorbed in the dosimeter since the previous stimulation. The integral absorbed dose is obtained via a summation procedure from the measured dose fractions. Several operating procedures and data processing algorithms were developed in order to increase the speed and accuracy of the measurements, and integrated into the software that controls automated operation of the OSL readers. Periodic modulation of the stimulation also allows the OSL signal to be discriminated from background fluorescence, and thus yields measurements that are unaffected by Čerenkov light (the so-called “stem effect”). Depending on the type of material used, the speed of the measurements, expressed as the time required to estimate an individual dose fraction, can be as short as 67 ms. Integral dose estimates from real-time OSL of and KBr:Eu were obtained for water-phantom irradiations performed with medical teletherapy sources, and were found to agree within 3.7% and 2.8%, respectively, with reference measurements from ionization chambers. We also investigated the possibility of using the fiber OSL readers for other purposes, such as two-dimensional mapping of dose distributions on compacted layers of grains, and detection of low-level doses, for possible application in Homeland Security projects.
31(2004); http://dx.doi.org/10.1118/1.1763412View Description Hide Description
Diffuse optical techniques were used to measurehemodynamics of tissues noninvasively. Spectroscopy and tomography of the brain,muscle, and implanted tumors were carried out in animal models and humans. Two qualitatively different methods, diffuse optical tomography and diffuse correlation tomography, were hybridized permitting simultaneous measurement of total hemoglobin concentration, blood oxygen saturation, and blood flow. This combination of information was processed further to derive estimates of oxygen metabolism (e.g., in tissue. The diffuse correlation measurements of blood flow were demonstrated in human tissues, for the first time, demonstrating continous noninvasive imaging of oxygen metabolism in large tissue volumes several centimeters below the tissue surface. The bulk of these investigations focussed on cerebral hemodynamics. Extensive validation of this methodology was carried out in in vivo rat brain models. Three-dimensional images of deep tissuehemodynamics in middle cerebral artery occlusion and cortical spreading depression (CSD) were obtained. CSD hemodynamics were found to depend strongly on partial pressure of carbon dioxide. The technique was then adapted for measurement of human brain. All optical spectroscopic measurements of during functional activation were obtained through intact human skull noninvasively. Finally, a high spatiotemporal resolution measurement of cerebral blood flow due to somatosensory cortex activation following electrical forepaw stimulation in rats was carried out with laser speckle flowmetry. New analysis methods were introduced for laser speckle flowmetry. In other organs, deep tissuehemodynamics were measured on human calf muscle during exercise and cuff-ischemia and were shown to have some clinical utility for peripheral vascular disease. In mice tumor models, the measuredhemodynamics were shown to be predictive of photodynamic therapy efficacy, again suggesting the promise of clinical utility. In total, the research has pioneered the development of diffuse optical measurements of blood flow, oxygenation, and oxygen metabolism in a large range of research and clinical applications.