No description available.

Radiofrequency ablation (RFA) is an established treatment option for patients with inoperable liver tumours and is now being investigated for the treatment of lung and other solid tumours. The aim of this thesis was to investigate the use RFA to decrease blood loss during liver resection, for the treatment of the liver resection edge and to investigate the safety and efficacy of brain RFA. Blood loss is an important factor affecting both the morbidity and mortality following liver resection. The use of a novel in line RF probe to ablate the transection plane prior to liver resection resulted in decreased blood loss with easier resection. This has potential in the treatment of liver tumors in cirrhotic livers and also in other vascular organs. The other important prognostic factor affecting long-term survival in patients undergoing liver resection for liver tumors is the surgical margins. Positive margins which cannot be treated with repeat resection may be treated with cryotherapy. The use of a novel probe to ablate the resection edge with RFA was found to be equally effective as cryotherapy and superior to argon beam coagulation or diathermy in an ex-vivo model. The radiofrequency ablation of the brain was found to be safe with no hemorrhage or damage to the surrounding brain parenchyma. There was no rise in intra-cranial pressure in the animals treated with RFA. The brain RFA was found to be effective and has potential for the treatment of brain tumours. Dispersive pad site burns was a significant problem in patients treated with radiofrequency ablation for lung and liver tumours occurring in 5% of patients. Pad tissue temperature of 45oC was found to be the threshold temperature above which burns occurred. Monitoring of pad-tissue temperatures with thermocouples and application of ice packs in addition to increasing the number of pads may help decrease this complication.

No description available.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1959. / Vita. Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 122-124).

Thesis (M.S. in Electrical Engineering and Electrical Engineer) Naval Postgraduate School, June 1997. / Thesis advisors, Randy L. Borchardt, Rudlof Panholzer. Includes bibliographical references (p. 99). Also available online.

The present work describes a theoretical and experimental investigation of the stimulated Raman effect excited by the focused output of a slow, Q-switched ruby laser in the self-focusing liquids benzene, nitrobenzene, chlorobenzene, and carbon disulphide. Time relationships between the exciting pulse, the transmitted laser pulse, and the time resolved stimulated Raman spectra have been studied using a high speed streak camera in conjunction with fast photodiodes. The spontaneous Raman spectra of these liquids have been investigated using a photoelectric Raman spectrometer and a method is outlined for measuring the relative values of the stimulated Raman gain coefficients. It is experimentally shown that, on a nanosecond time scale, stimulated Raman lines are not generated simultaneously but in the sequence Stokes, Anti-Stokes, and second harmonic Stokes. Further, the time delay between the start of first and second harmonic Stokes is shown to be dependent on the rate of rise of the exciting pulse. It was found that during stimulated Raman generation the laser pulse transmitted through the liquid was heavily distorted and that each liquid produced its own characteristic pulse distortion. No distortion was found in the absence of stimulated Raman generation. Time correlations were found between the duration of features of the pulse distortion and the duration of first Stokes and second harmonic Stokes. These correlations show that forward stimulated Raman generation is controlled by the transmitted laser pulse not the exciting pulse. The threshold for the onset of pulse distortion is shown to be dependent on the rate of rise of the exciting pulse whilst, in all the liquids, apart from carbon disulphide, the 'cut-off' threshold is dependent on the peak power of the incident pulse. Investigation of the pulse distortion thresholds for the range of liquids produced relative values which did not agree with those predicted from either the optical Kerr coefficient or the calculated stimulated Raman gain coefficients. A theoretical model of the self-focusing of a focused beam in a medium for which both electrostriction and the optical Kerr effect are significant is presented and has been used to explain the anomalous threshold results. Within the experimental scatter of the results obtained, this model appears to explain the observed threshold effects. Since the forward stimulated Raman generation was weak in comparison to the transmitted laser pulse and followed this distorted pulse rather than the exciting pulse, it is concluded that stimulated Raman is not the dominant mechanism in the interaction. A brief review is presented of the theory and predictions of steady and non-steady state Brillouin scattering. Although the phonon lifetimes for the other liquids appear to be too short to be of significance, the results are similar in form to those of carbon disulphide. An explanation based on multiphoton absorption is suggested to explain the anomalous behaviour of these liquids. It is concluded that the observed effects in the forward stimulated Raman process depend upon the development in time of the non-linear field dependent self-focusing of the exciting beam and the strong backward scattering process.

No description available.

Deep brain stimulation (DBS) improves the quality of life for patients suffering from neurological disorders such as Parkinson’s disease and, more recently, psychiatric/cognitive disorders such as depression and addiction. This treatment option involves the implantation of an implantable pulse generator (or neurostimulator) and leads (or electrodes) implanted deep within the human brain. Magnetic resonance imaging (MRI) is a powerful diagnostic tool that offers superior soft tissue contrast and is routinely used in clinics for neuroimaging applications. MRI is advantageous in DBS pre-surgical planning as precise lead placement within the brain is essential for optimal treatment outcomes. DBS patients can also benefit from post-surgery MRI, and studies have shown that DBS patients are more likely to require MRI within 5-10 years post-surgery. However, imaging DBS patients is restricted by substantial safety concerns that arise from localized electric charge accumulation along the implanted device during resonant radiofrequency (RF) excitation, which can potentially lead to tissue heating and bodily damage. With the technological advancement of ultra-high field (UHF) MRI systems and a growing DBS patient population, DBS MRI safety will become increasingly problematic in the future and needs to be addressed. Parallel RF transmission (pTx) is a promising technology that utilizes multiple transmit channels to generate a desired electromagnetic profile during MRI RF excitation. Several proof-of-concept studies successfully demonstrated its efficacy in creating a "safe mode" of imaging that minimizes the localized RF heating effects. However, pTx MRI systems are not easily accessible and are often custom-built and integrated onto existing MRI systems. Consequently, it adds system characterization and verification complexity to the DBS MRI safety problem. System channel count is also an important consideration as implementation costs can be very high, and the impact of system transmit channel count remains unexplored. Furthermore, in practice, DBS patients with motor-related disorders will impact the pTx MRI system’s ability to precisely generate these safe mode electromagnetic profiles. Commercial DBS devices (i.e., the neurostimulator and leads) are manufactured with fixed dimensions, and the caring surgeon typically manages the surgical orientation of the implanted DBS device and leads. Therefore, lead trajectories can vary hospital-to-hospital. As a result, standard phantoms, i.e., the ASTM International Standard, used in safety verification experiments may not be suitable for DBS MRI applications. To advance DBS patient safety in MRI, this thesis studied the implant heating effects of pTx system uncertainty, system channel count, patient motion on a novel pTx MRI research platform and its associated safe mode of imaging. It developed a new anthropomorphic heterogeneous phantom to improve safety verification experiments. / Dissertation / Doctor of Philosophy (PhD)

No description available.

Multiple-mouse MRI (MMMRI) accelerates biomedical research by imaging multiple mice simultaneously. To date, MMMRI has been explored in three ways: shielded transmit-receive coils, shielded transmits coil with separate unshielded receive coils; and finally shielded transmit-receive coils with independent gradient coils. However alternative transmit coil configurations and possible benefits of eliminating shielding have not yet been explored. The goal of this thesis is to test possible radiofrequency configurations with and without shielding for the purpose of improving image quality for MMMRI. Results demonstrate that using an unshielded transmit-receive coil array provided a 20% improvement over an identical shielded coil. A new unshielded 7-coil MMMRI array is presented, minimizing the ghosting between image overlap using mutual inductance minimization and a sensitivity encoding (SENSE) reconstruction. The final array provided high resolution images (90µm) of up to seven live mice simultaneously with appropriate signal-to-noise for automated analysis.