published_or_final_version / Surgery / Master / Master of Medical Sciences

Diss. Stockholm : Karol. inst.

Thesis (Ph. D.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains xi, 140 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 117-128).

Thesis (doctoral)--Københavns Universitet.

Thesis (doctoral)--Københavns Universitet.

Head trauma patients are susceptible to secondary injuries where afflicted tissues can propagate towards dysfunction after the initial injury is treated. Monitoring blood oxygenation (SpO2) below the skull is crucial for the early detection of secondary head injury such as hematoma. To obtain such information in a point-of-care setting, photoacoustic (PA) imaging can be used to differentiate optical contrast between hemoglobin (Hb) species by measuring resultant ultrasonic waves emitted by optically irradiated tissue. Given the ratio of Red:NIR light absorption, information regarding SpO2 can be determined in vivo. In this project, computer simulations involving PA imaging of tissue models have been performed and techniques tested using an optic fiber/transducer PA imaging system. In simulated and physical PA scans, Red:NIR ratio values are computed for various tissue models to evaluate optical contrast in target absorbers. Images reconstructed from simulations showed the ability to visualize differences in SpO2 across a layer of skull tissue using multi-spectral optical irradiation. Red:NIR ratios were calculated using PA signals produced by 750 nm light and 850 nm light. Physical image reconstructions were conducted using a 5 ns pulsed laser and near-infrared (NIR) optical parametric oscillator (OPO). The pulse energy used during physical PA raster scans reached up to 5.3 mJ/pulse. Tissue phantoms scanned consisted of optical absorbers surrounded by various tissue-mimicking materials. Images from physical acquisitions were acquired using a 2D CNC-controlled moving stage, but free-hand tracking using inertial and optical sensors have been investigated. At 5.3 mJ/pulse, images reconstructed from physical scans could not resolve optical absorbers positioned beneath a layer of skull-mimicking tissue. A limiting factor contributing to low signal-to-noise ratio (SNR) from inferior absorbers was the percentage of power lost during beam focusing. However, simulation results encourage future work to improve pulse energy output before simulation results can be validated. / Thesis / Master of Applied Science (MASc)

No description available.

BACKGROUND: Pre-term delivery is known to cause developmental problems due to the fragile nature of the premature brain. In particular, ventriculomegaly is a commonly observed phenomenon due to the hemorrhaging of the germinal matrix, and may cause alterations in the volumes of gray matter, white matter and cerebrospinal fluid in growing pre-term children. METHODS: The volume and symmetry of a sample population of ELGAN (Extremely Low Gestational Age Newborns) and normal-term population obtained from the NIH Study of Normal Brain Development was evaluated. The ELGAN group consisted of 88 subjects from age group 9 to 11 and the normal-term group consisted of 68 subjects from age group 7 to 11. Magnetic resonance images were taken from both samples and the intracranial matter was measured and segmented. RESULTS: Histograms of the obtained volumes showed a normal distribution and statistical analysis for each sample group and gender. The ELGAN group had higher intracranial volumes and showed statistically significant asymmetry that was not present in the normal term population with a larger right brain than left brain. Discussion: Results indicate that preterm delivery may alter processes that allow for symmetrical brain development and heavily favor the relative higher expansion of the right side of the brain. CONCLUSION: Further analysis of the concentration and location of the white matter and gray matter in both preterm and normal term children is necessary in order to understand the adaptive mechanisms that may be activated in order to offset the damage done to the premature brain.

No description available.

Thesis (Ph.D.)--George Mason University, 2008. / Vita: p. 83. Thesis director: Juan R. Cebral. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Computational Sciences and Informatics. Title from PDF t.p. (viewed Aug. 27, 2008). Includes bibliographical references (p. 78-82). Also issued in print.