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.

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).

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.

No description available.

F. Bitter. / "March 2, 1949." / Signal Corps Contract no. W36-039-sc-32037. Project no. 102B Dept. of the Army Project no. 3-99-10-022

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Surface coil; Receiver coil; RF; MRI; High Input Reflection Coefficient Preamplifier. Includes bibliographical references (p. 86-88).

No description available.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Magnetic Resonance Imaging; Radio Frequency Coil; Breast Cancer; Imaging Systems. Includes bibliographical references (leaves 118-123).

The increasing importance of narrow-band radiations is traced in the recent history of radio astronomy. The need for multi-channel spectrometers to observe these radiations is stressed. The theoretical basis of spectral analysis is given with particular emphasis on autocorrelation or interference methods. A twenty-channel radio-frequency spectrometer designed on interference principles has been constructed and found to perform in accordance with its theory of operation. When used in conjunction with a 25-metre telescope and a hydrogen receiver the spectrometer is capable of producing low-noise wideband spectra at high speed. The spectrometer output was recorded on punched cards, and subsequent data processing was by digital methods. A large area including the position of the spiral galaxy M31 was surveyed with the help of the spectrometer. One hundred and forty-three independent spectra of the 21-cm radiation of atomic hydrogen were obtained and are analyzed in terms of area, velocity, and shape. The major axis of the nebula is found to extend about 2.5° either side of the centre, in agreement with the work of van de Hulst, Raimond, and van Woerden (1957). The length of the minor axis, after correction for the effect of the antenna beamwidth, is only 40', a result which indicates a reduction in the inclination (of the plane of the galaxy to the line of sight) from 14.5° to 8.2°. This lower value leads to an upward revision of the optical axial ratio (of galactic thickness to galactic diameter) to 0.2, while maintaining a low ratio (0.07, Schmidt, 1957) for the distribution of atomic hydrogen. A high axial ratio would clear the way for a reinterpretation of the optical velocities of emission nebulae in M31 (Mayall, 1950), which have so far appeared to be in violent contradiction to the radio velocities (van de Hulst et al, 1957). It is suggested that many of these emission objects may lie some distance from the plane of the galaxy. The position angle of M31, as revealed by the spectrometer observations is distinctly less than the 38° established optically. A new value of 33° is proposed and it is suggested that the former value can be accounted for in terms of an increased axial ratio and the observed asymmetries in the light distribution. The velocity of the centre of gravity of M31 has been obtained by summation of all 143 spectra. The result, -295.6±0.4 km/sec with respect to the local standard of rest, is in complete agreement with that found by van de Hulst (ibid). Radial motions of a few km/sec are possible in the outer parts of M31 but their presence has not been established. Many of the spectra have multiple peaks, which may be interpreted in terms of spiral structure. The velocities of certain concentrations of atomic hydrogen are measurable but their positions are not resolved by the antenna beam. / Science, Faculty of / Physics and Astronomy, Department of / Graduate