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Biomedical subjects

T N Mills

Publications and source records attributed to T N Mills.

18 recordsLinked to original sources
PubMed2003

A system to monitor for fibre breakage during photodynamic therapy with diffuser fibres.

There is concern that the delicate fibres and cylindrical diffuser tips used for intraluminal PDT of blood vessels might break during the treatment. We have developed and tested a simple system to monitor for fibre breakage during PDT. Light from the laser is passed through a beam expander, then a beam splitter, and then is again contracted into the inlet of a diffuser fibre. Light reflected from the distal diffuser is also partially reflected by the beam splitter into a photodiode, which monitors changes in the intensity of the reflected light. The system was tested by simulating catastrophic failures in four fibres. In each case the output fell very significantly (DV=0.44-1.68 V, SD=0.01 V). Despite the small statistical sample, the average change in the reflected light intensity is still significant (p < 0.025, paired Student's t-test). Our conclusion was that this device can monitor the integrity of diffuser fibres during PDT.

Animals↗
PubMed2001

Electrical stimulation for propelling endoscopes.

BACKGROUND: Methods are needed for propulsion of endoscopes and wireless video capsules along the small intestine. This work aims to test the hypothesis that electrical stimulation could propel an endoscope by stimulating muscular contraction. METHODS: Prototype acrylic ovoid-shaped devices were constructed with 2 stainless steel electrodes mounted on the tapered section. Five devices 15 to 23 mm diameter with a taper of 28 degrees to 40 degrees (included angle) were tested. When these devices were in contact with the bowel wall, electrostimulation was applied causing circular muscle contraction, which when applied to the taper of the ovoid resulted in forward propulsion of the device. The method does not induce peristalsis but works by stimulating local contraction. The device was tested in the small intestine and esophagus of anesthetized pigs. RESULTS: Electrostimulation caused the ovoid to advance rapidly (6 mm/sec) up and down the esophagus by inducing circular esophageal muscle contraction. When stimulated at 15 Hz with 30-ms pulses, the threshold for movement in the small intestine was 12 mA; at 20 mA the device moved reliably in either direction in the small intestine at speeds of up to 4.5 mm/sec and negotiated tight curves. CONCLUSION: Electrostimulation can move endoscopes in the small intestine.

Animals↗
PubMed2001

Photothermal determination of optical coefficients of tissue phantoms using an optical fibre probe.

The absorption and reduced scattering coefficients of turbid tissue phantoms have been determined from photothermal measurements made using an optical fibre probe. The thermal sensor was a thin polymer film positioned at the end of a multimode optical fibre. The film was illuminated by the output of a continuous-wave diode laser and formed the cavity of a low-finesse Fabry-Perot interferometer. Low energy laser pulses, launched into the fibre and passed through the film, produced an abrupt temperature rise in the target tissue, which was placed in contact with the film. The subsequent conduction of heat into the film caused a change in its optical thickness and hence the reflected intensity. The absorption and reduced scattering coefficients of gelatine tissue phantoms of known optical properties were determined from the measurements using a numerical model of photothermal signal generation and maximum a posteriori estimation. The determined optical coefficients were in good agreement with the known values. The results showed that the probe can be used for the determination of optical coefficients provided the thermal coefficients of the target tissue are known with low uncertainty.

Gelatin↗
PubMed2000

The measurement of forces exerted during colonoscopy.

BACKGROUND: The widely varying forces used at colonoscopy have not been measured. An electronic device was designed to measure the forces exerted by the clinician on the endoscope during colonoscopy. METHODS: The device featured a handle designed in the shape of a hinged split cylinder that could be locked around the endoscope but readily moved up and down the insertion tube as the colonoscopy proceeded. This cylinder contained strain-gauges arranged so that the forces transmitted could be accurately measured. The device recorded the torque forces in addition to the push and pull forces exerted during diagnostic colonoscopy. RESULTS: In a series of 21 colonoscopies in 20 patients: peak pushing force = 4.4 kg, pulling force = -1.8 kg, anti-clockwise torque = 1.0 Newton meters, clockwise torque = 0.8 Newton meters. Percentage time force greater than 1 kg = 5%. Peak anal insertion force = 1.8 kg. CONCLUSIONS: These measurements represent the first accurate measurements of the forces exerted during colonoscopy. Reducing the force during colonoscopy is likely to diminish pain and reduce the risk of perforation. A knowledge of these forces may also help with the design of new instruments and models for teaching or research.

Adult↗
PubMed1999

Electrophysical factors influencing endoscopic sphincterotomy.

BACKGROUND: Analog computer techniques were used to measure electrosurgical power during sphincterotomy in experimental models and patients. METHODS: Total energy and transient changes in power were measured during sphincterotomy of bile ducts in the livers of pigs, ampullae of humans post mortem, and during clinical sphincterotomy. The effect of waveform on hemostasis was studied in experiments on canine mesenteric arteries. RESULTS: Electrosurgical waveforms (CUT, COAG, BLEND) were measured. Halving wire contact length halved energy needed to initiate cutting. The CUT waveform rarely initiated cutting at lower power settings than the BLEND waveform. With CUT, BLEND, and COAG waveforms, approximately the same energy initiated cutting. Efficiency of cutting increased linearly with power. The COAG waveform required higher power settings than BLEND or CUT to initiate cutting (p < 0.05). Force and wire diameter influenced cutting. BLEND was more effectively hemostatic than CUT (p < 0.05). COAG was significantly more hemostatic than BLEND and CUT. Cutting efficiency during clinical sphincterotomy was poor. CONCLUSIONS: This work has practical implications. Shortening wire contact length was effective in starting a cut at suboptimal settings, whereas changing from BLEND to CUT made little difference. Increasing power setting may help if cutting does not start. BLEND stops bleeding better than CUT. COAG stops bleeding better than BLEND but cuts poorly. Cutting during clinical sphincterotomy is inefficient and can be improved.

Analog-Digital Conversion↗
PubMed1998

Device for measuring the forces exerted on the shaft of an endoscope during colonoscopy.

Colonoscopy involves advancing a flexible endoscope into and along the entire length of the colon. The procedure can be painful and carries the risk of perforating the organ, yet very little is known of the forces involved. A device to measure the forces exerted on the endoscope during colonoscopy is described. The device features a handle designed in the shape of a hinged split cylinder that locks around the endoscope, gripping it tightly. The handle has two parts, an inner part that grips the endoscope, and an outer part that is gripped by the endoscopist. The two parts are joined together by members that transmit the forces through to the endoscope. One of the members incorporates strain gauges that measure the torque applied to the endoscope, as well as the push and pull forces. The handle can easily be unlocked and moved along the endoscope as the colonoscopy proceeds. The device is used to measure the forces applied to the endoscope during 11 routine colonoscopies, and summary results are presented. These are believed to be the first accurate measurements of the forces exerted during colonoscopy.

Colonoscopes↗
PubMed1997

Characterization of post mortem arterial tissue using time-resolved photoacoustic spectroscopy at 436, 461 and 532 nm.

Time-resolved photoacoustic spectroscopy has been used to characterize post mortem arterial tissue for the purpose of discriminating between normal and atheromatous areas of tissue. Ultrasonic thermoelastic waves were generated in post mortem human aorta by the absorption of nanosecond laser pulses at 436, 461 and 532 nm produced by a frequency doubled Q-switched Nd:YAG laser in conjunction with a gas filled Raman cell. A PVDF membrane hydrophone was used to detect the thermoelastic waves. At 436 nm, differences in the photoacoustic signatures of normal tissue and atherorma were found to be highly variable. At 461 nm, there was a clear and reproducible difference between the photacoustic response of atheroma and normal tissue as a result of increased optical attenuation in atheroma. At 532 nm, the generation of subsurface thermoelastic waves provided a means of determining the structure and thickness of the tissue sample. It is suggested that pulsed photoacoustic spectroscopy at 461 and 532 nm may find application in characterizing arterial tissue in situ by providing information about both the composition and thickness of the vessel wall.

Aorta↗
PubMed1987

The effect of wavelength, power and treatment pattern on the outcome of laser treatment of port-wine stains.

The argon laser was used to treat 220 patients with port-wine stains with moderate efficacy and few complications although perfect cosmetic results were rarely achieved. Primary failure of the argon laser to produce permanent blanching graded good or excellent was the most important factor limiting the final cosmetic results whilst severe scarring was rare (less than 2%). In order to improve the efficacy of this treatment, a randomized controlled study of different parameters of laser treatment was undertaken in test patches of port-wine stains in 50 patients. A treatment pattern with contiguous or overlapping laser spots was significantly superior to treatment with spots of 1 or 2 mm separation. Increasing the power level to twice the minimum blanching power did not improve efficacy or significantly increase scarring. A randomized study of selective absorption using a neodymium (Nd) YAG laser showed similar efficacy for the different wavelengths although scarring was greater with the Nd-YAG laser. This study has shown that laser treatment can offer a moderately effective treatment for port-wine stains. For best results spot separation needs to be carefully controlled, whilst wavelength and power level appear to be less important than previously reported.

Adolescent↗
PubMed1986

Nature of the bleeding vessel in recurrently bleeding gastric ulcers.

An unselected consecutive series of 826 patients admitted for acute upper gastrointestinal bleeding underwent urgent endoscopy. Peptic ulcers were found in 402 (49%). Of the 329 ulcer craters that could be fully examined, visible vessels were identified in 156 (47%), other stigmata of recent hemorrhage in 66, and no stigmata of recent hemorrhage in 107. One hundred twenty-nine patients with stigmata of recent hemorrhage (93 of whom had visible vessels) randomly allocated to no endoscopic treatment were observed for evidence of further bleeding. Fifty-four of the 93 patients (58%) with visible vessels rebled, compared with 2 of 36 (6%) with other stigmata of recent hemorrhage. No patient without stigmata of recent hemorrhage rebled. Twenty-seven patients in whom a visible vessel in a gastric ulcer was identified at endoscopy underwent urgent partial gastrectomy because of recurrent bleeding. The vessel identified at endoscopy was found in 26 of 27 resection specimens (96%). The arterial vessel wall protruded above the surface of the ulcer crater in 10 specimens, and clot in continuity with a breach in the vessel wall protruded in a further 10 specimens. Postoperative angiography, when technically possible, showed that the breached artery ran across the base of the ulcer in all of these specimens. Pathological changes were common in the bleeding artery and included arteritis in 24 of 29 (83%) eroded arteries found in these specimens, with aneurysmal dilatation in 14 of 27 (52%) bleeding points that could be fully examined. The ulcer had penetrated to serosa in 13 specimens (45%). The bleeding artery had a mean external diameter of 0.7 mm with a range of 0.1-1.8 mm. This study provides new information about the nature of the bleeding vessel in gastric ulcers, and some of this information is relevant in planning studies of endoscopic therapy for bleeding peptic ulcers. It validates the endoscopic identification of a visible vessel, and confirms that such identification has a high predictive value for the development of recurrent hemorrhage.

Arteries↗
PubMed1984

Which electrode? A comparison of four endoscopic methods of electrocoagulation in experimental bleeding ulcers.

Several inexpensive endoscopic methods of electrocoagulation have been advocated for treatment of gastrointestinal haemorrhage. We compared four types of electrode: dry monopolar - Cameron Miller (M), liquid monopolar - Storz (L), bipolar - Bicap ACMI (B), and heater probe - Seattle (H). The electrical and thermal properties of these probes were studied using computerised monitoring of energy deposition and their efficacy and safety was tested in a randomised study in 140 experimental canine gastric ulcers. At optimal pulse settings 20J (M), 70J (L), 17J (B), 15J (H), effective haemostasis was achieved in all ulcers, the mean number of pulses being M5, L6, H6 and B11, the first three requiring significantly (p less than 0.01) less pulse than B. Relative safety of the electrodes was assessed by comparing the incidence of full thickness damage at histology: B24%, H20%, L58% and M69%; B and H proving significantly (p less than 0.01) safer than L and M. Sticking was assessed as H greater than B greater than M much greater than L. Insensitivity to extreme angulation and force of application was assessed as L greater than B greater than M (H is preset). Of the two safer electrodes the heater probe was more effective than the bipolar probe. Despite its greater tendency to stick than the other devices, the heater probe appeared the most promising of the endoscopic electrodes tested.

Animals↗
PubMed1984

Comparative study of the safety and efficacy of liquid and dry monopolar electrocoagulation in experimental canine bleeding ulcers using computerized energy monitoring.

The drawbacks of monopolar electrocoagulation in the control of gastrointestinal bleeding include tissue adherence, unpredictable energy deposition, and a high incidence of tissue damage. Introduction of a conductive interfacial film of liquid between the monopolar electrode and the bleeding point during electrocoagulation may overcome these drawbacks. A prospective, controlled study was undertaken to evaluate the efficacy and safety of a monopolar electrode in liquid and dry modes when used to coagulate experimental canine bleeding ulcers. All experiments were done in open fashion via a gastrotomy with hand-held electrodes. An analog computer, which could be connected between a standard electrosurgical generator and the electrode, was designed and built to monitor and control the energy delivered to the tissue. Both liquid and dry electrodes were highly effective in stopping bleeding. The liquid electrode was found to be superior to the dry electrode in that tissue adherence was eliminated and energy deposition was more predictable, varying less with angle of incidence. The liquid electrode caused less macroscopic serosal damage and less full-thickness histologic damage if the total energy or number of pulses was limited; however, both caused microscopic full-thickness damage in one-half of the experimental ulcers treated, although no perforations occurred.

Animals↗
PubMed1983

Laser fragmentation of renal calculi.

Pulsed Nd YAG lasers will fragment all types of urinary calculi rapidly in air. The fragments are much smaller than with any other technique. Large stones can be split into a few discrete fragments which may prove to be an advantage in that the fragments could then be extracted without leaving multiple small fragments behind. Certain pulsed lasers can be transmitted through fine, flexible glass fibres which are small enough to pass through any sized instrument channel. There is therefore an immediate possibility of using this type of laser in the bladder with carbon dioxide instead of an irrigant. Further experiments are planned in order to investigate the possibility of using this mode of laser in the kidney percutaneously.

Endoscopy↗
PubMedDate not supplied

Knot tying at flexible endoscopy.

Four new knotting techniques were developed for use at flexible endoscopy: (1) half hitches tied with knot-pusher, (2) thread-locking device, (3) self-tightening slip-knot, and (4) externally releasable knot. Remoteness from site of action, access through small-diameter orifice, and difficulty in applying lateral traction to tighten knots are problems met in knot tying at endoscopy. All four knotting techniques were studied in experiments on postmortem human stomachs and used for radio-telemetry studies and anti-reflux operations in survival studies in dogs using endoscopic sewing techniques. Half hitches tied at endoscopy with a knot-pusher were also used in human studies to treat esophageal reflux and secure pH radio-telemetry capsules for long-term measurements. Externally releasable knots were used to secure nasogastric tubes to the stomach of five patients for long-term nutrition. Knot tying is feasible at flexible endoscopy by a variety of new techniques. Endoscopically tied knots can be as secure as surgically hand-tied knots and have been used successfully in man.

Animals↗