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Biomedical subjects

L S Wilson

Publications and source records attributed to L S Wilson.

At least 19 recordsLinked to original sources
PubMed2002

Modelling the cost-effectiveness of sentinel lymph node mapping and adjuvant interferon treatment for stage II melanoma.

Clinical studies have demonstrated that high dose adjuvant interferon therapy improves disease-free and overall survival among high risk (stage IIb and III) melanoma patients. Sentinel lymph node mapping (SLM) has been shown to accurately detect micrometastasis and may be used to identify higher risk stage II patients, who might benefit most from adjuvant interferon therapy. We modelled the cost-effectiveness of first testing with SLM and then treating with adjuvant interferon (IFN) therapy for stage II melanoma. We used a decision analytical model to compare four strategies for stage II patients after surgical excision of their melanoma: (1) treat all with low dose IFN; (2) test first with SLM and then treat only those with positive micrometastasis with high dose IFN; (3) test first with SLM and treat positives with high dose IFN and negatives with low dose IFN (test and treat appropriately); and (4) surgery only. Treatment, toxicity, follow-up and relapse costs were included over a 5 year time period. The primary outcome was cost per quality-adjusted relapse-free life year saved. Our analysis shows that, compared with the current surgery-only strategy, all three treatment strategies provide incremental benefits. The test and treat appropriately strategy is the most effective, with an incremental improvement of 0.64 quality-adjusted life-years (QALY). The cost-effectiveness of test and treat some with high dose IFN compared with the surgery-only strategy is $18,700/QALY. The test and treat appropriately strategy is also cost-effective compared with test and treat some at $31,100/QALY. In conclusion appropriate dosing of IFN therapy based on the results of SLM is a cost-effective strategy for stage II melanoma patients.

Adjuvants, Immunologic↗
PubMed2001

Model of estimated rates of colorectal cancer from polyp growth by year of surveillance.

OBJECTIVE: Most studies show protective effects of non-steroidal anti-inflammatory drugs (NSAIDs) against polyps and colorectal cancers (CRCs) of up to 50%. Current models are unable to directly estimate changes in effects of chemoprevention on CRCs. The purpose is to develop a model to examine effects of changes in growth rates of polyps on surveillance intervals and risk of CRC. METHODS: The growth model simulates 500 people after polypectomy, estimating number and size of polyps annually over 10 years. Each polyp is assigned a random growth rate consistent with distributions of empirically observed growth assumed to follow a log linear model. Rates of CRC were calculated from largest polyps distributed to people. RESULTS: Simulated distributions of polyps and CRCs closely match empirical estimates which confirms the usefulness of the model. If polyp growth is 25% of normal, the number of cancers by year 10 after index colonoscopy decrease from 146 to only 57/100 000 for those in risk group 0 (no polyps at index colonoscopy) and from 840 to 124/100 000 for those of risk group 3 (4 or more polyps). CONCLUSIONS: This is the first model based on polyp growth rates. The CRC rates suggest that for those with no polyps on index colonoscopy, surveillance may be as for people of average risk (7-10 years), whereas those with one polyp or more need more surveillance (2-5 years). The use of the model is the indication that surveillance intervals could be increased by as much as 2-10 years if the growth rates of polyps are slowed.

Colonic Polyps↗
PubMed2001

Foot and ankle injuries in motor vehicle accidents.

BACKGROUND: We studied foot and ankle (F/A) injuries that occurred in motor vehicle accidents treated in a Level 1 trauma center. METHODS: The records of F/A injuries of 2248 consecutive orthopedic patients were reviewed to find foot and ankle injuries. RESULTS: Pilon fractures were common. Motor Vehicle Accident (MVA) occupants with F/A injuries had a higher injury Severity Score than those without (17.9 vs. 11.6, p <. 001). MVA F/A injury risk was higher without restraint [relative risk ratio (rrr) 1.68, p <. 0032] than with restraint except for air bagged drivers who were similar to unrestrained drivers (rrr 1.18, p > .05, NS). CONCLUSION: Patients with F/A injuries may have serious associated injuries. Air bags may not protect feet.

Accidents, Traffic↗
PubMed2000

Elastography--the movement begins.

The advent of real-time ultrasound in the 1970s, together with a growing interest in tissue characterization, led to a number of investigators using the nature of tissue motion to distinguish healthy from diseased tissue. Our group at the (then) Ultrasonics Institute demonstrated the use of phase methods for detecting very small tissue motions, using natural stimuli. The method could also be applied in the lag (autocorrelation) domain to directly measure the amount of deformation to high accuracy. This method was also applied to measuring the amount of dilatation of blood vessels using both conventional and intravascular ultrasound. A basic limitation of these techniques was the poor spatial resolution, and quasistatic methods soon replaced this method of measuring tissue deformation. However, a new way of assessing the health of tissues had been established.

Blood Vessels↗
PubMed2000

Building the Hospital Without Walls--a CSIRO home telecare initiative.

Aging populations and rising health costs have created the need to care for more patients in their own homes. Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO) is developing a project, Hospital Without Walls, which aims to provide continuous monitoring of patients in certain diagnostic categories. The key technology is a miniature, wearable, low-power radio that can transmit vital sign and activity information to a home computer, from which data may be sent by telephone line and the Internet to appropriate medical professionals. The initial clinical scenario for this work is monitoring of elderly patients who have presented to hospitals following repeated falls. Accelerometers built into the radio sets will monitor activity and detect and characterise falls. Simultaneous measurement of heart rate will provide information about abnormalities of cardiovascular physiology at the time of a fall. The system has been tested in laboratory conditions and is being adapted for initial clinical trials.

Accidental Falls↗
PubMed1999

Pancreatic cancer: total costs and utilization of health services.

BACKGROUND AND OBJECTIVES: Pancreatic cancer ranks 11th in incidence, and fifth in cancer deaths, with 29,000 affected annually. Accurate estimates of the cost of pancreatic cancer are unavailable; existing estimates are variable or not generalizable. This paper presents detailed cost estimates for pancreatic cancer by service, age, and gender. METHODS: Direct and indirect societal costs are determined using a prevalence-based, human capital approach. RESULTS: Total annual costs are $4.9 billion, (men: $3.0 billion, women: $1.9 billion). Total direct costs are $881 million, with 71% ($627.1 M/$881.3 M) for those over 65 years. Total hospital costs are 77% ($679.5 M/$881.3 M) of total direct costs. Total indirect costs are $4.0 billion, with 63% ($2,518.43 M/$4,018 M) for those 45 to 64 years. Mortality costs are $3.7 billion, 93% ($3,739 M/$4,018 M) of indirect costs. CONCLUSIONS: This paper presents cost estimates that are precise and generalizable to the general population. The surgical cost burden may be less than indicated previously, with most hospitalizations not including a major procedure, and average operating room costs accounting for only 9% ($1,045/$11,055) of hospital costs. Women have significantly less cancer-directed surgery than men.

Age Factors↗
PubMed1997

Method for segmenting chest CT image data using an anatomical model: preliminary results.

We present an automated, knowledge-based method for segmenting chest computed tomography (CT) datasets. Anatomical knowledge including expected volume, shape, relative position, and X-ray attenuation of organs provides feature constraints that guide the segmentation process. Knowledge is represented at a high level using an explicit anatomical model. The model is stored in a frame-based semantic network and anatomical variability is incorporated using fuzzy sets. A blackboard architecture permits the data representation and processing algorithms in the model domain to be independent of those in the image domain. Knowledge-constrained segmentation routines extract contiguous three-dimensional (3-D) sets of voxels, and their feature-space representations are posted on the blackboard. An inference engine uses fuzzy logic to match image to model objects based on the feature constraints. Strict separation of model and image domains allows for systematic extension of the knowledge base. In preliminary experiments, the method has been applied to a small number of thoracic CT datasets. Based on subjective visual assessment by experienced thoracic radiologists, basic anatomic structures such as the lungs, central tracheobronchial tree, chest wall, and mediastinum were successfully segmented. To demonstrate the extensibility of the system, knowledge was added to represent the more complex anatomy of lung lesions in contact with vessels or the chest wall. Visual inspection of these segmented lesions was also favorable. These preliminary results suggest that use of expert knowledge provides an increased level of automation compared with low-level segmentation techniques. Moreover, the knowledge-based approach may better discriminate between structures of similar attenuation and anatomic contiguity. Further validation is required.

Computer Simulation↗
PubMed1996

The effect of variations in transducer position and sound speed in intravascular ultrasound: a theoretical study.

The intravascular insonation of a blood vessel in the presence of an impedance interface between blood and the inner vessel wall is studied theoretically. The model, which uses a ray approximation, is three dimensional and allows consideration of arbitrary noncircular lumen shapes. Model results are presented for the image geometry, and the insonating intensity over the vessel wall. It is shown that the inner lumen can be imaged accurately with the transducer at any position within the lumen, and at any forward viewing angle, provided the point of origin of the beam is stationary. If it is not stationary but rotating with the same angular velocity as the beam itself, the inner vessel wall is not mapped accurately. A particular geometric distortion which has been observed in practice is predicted if the transducer is near vessel wall. Acoustic impedance interfaces will be encountered in vascular disease because the speed of sound in fatty plaque is less than in blood, whereas the speed of sound in fibrous and calcified plaque is greater than in blood. A simplified model representation of an atherosclerotic lumen in developed using a cardioid-like curve and a single impedance interface. Model results show that refraction at this interface leads to an intensity distribution which is not uniform around the lumen, and which depends on lumen shape and transducer position. The exception is the special case of a circular lumen with a centrally positioned transducer. Noncircular impedance interfaces encountered in vivo in vascular disease may cause considerable intensity distortion, particularly if the transducer is close to the wall in an irregularly shaped lumen.

Arteriosclerosis↗
PubMed1994

Spectral tissue strain: a new technique for imaging tissue strain using intravascular ultrasound.

Spectral tissue strain (STS) is a new technique for measuring and imaging tissue strain from a set of images using intravascular ultrasound. The technique is based on the Fourier scaling property and uses the chirp z-transform (CZT) to estimate strain within the vessel walls. Some preliminary results, both in vitro and in vivo, are described. A novel display technique has also been developed for encoding radial strain and displaying the resulting colour map as an overlay on the original image.

Angioplasty, Balloon↗
PubMed1994

Preliminary results from attenuation-slope mapping of plaque using intravascular ultrasound.

Excised femoral and iliac artery segments have been examined with 20 MHz intravascular ultrasound followed by histological assessment. During the ultrasound examinations, radio-frequency (RF) data were recorded digitally, and used for calculating local values of attenuation slope throughout the tissue, using a frequency-domain technique. The RF data were also reconstructed as conventional ultrasound images, and the attenuation-slope information presented as a threshold colour overlay. Areas identified as degenerative plaque in the histological assessments were usually found to correspond to areas of high attenuation slope, and were clearly identified from the pattern of colours on the combined image. Some examples are presented, illustrating the appearance of various pathologies imaged by this technique.

Algorithms↗
PubMed1993

Measurement of two-dimensional blood velocity vectors by the ultrasonic speckle projection technique.

A technique has been developed for measuring the two in-plane components of blood velocity using ultrasound. The principle is based on analyzing a time sequence of successive images of the speckle pattern, and forming spatial projections of the resulting three-dimensional data set. The mathematics may be understood in terms of sections through a three-dimensional Fourier transform of the original data. The technique has been tested with data from a computer-controlled scanner using a tissue-mimicking phantom, and with data from a commercial ultrasound scanner using images of flowing blood in a jugular vein. In both cases, velocity vectors with many different orientations were measured, demonstrating the feasibility of the method. A less restrictive real-time implementation is suggested.

Blood Flow Velocity↗
PubMed1991

Pulse-echo ultrasound speed measurements: progress and prospects.

The data on the relationship of sound speed to tissue condition, and the development of methods for measurement of sound speed in vivo, are outlined. The methods developed by the authors are discussed. These include methods which use the spatial shift in images of targets viewed from different directions, time-of-flight measurements along incrementally tracked beams and echo tracking during transaxial compression of tissue. The reported sound-speed values are discussed, discrepancies noted and suggestions made on the potential clinical applications of in vivo sound-speed estimation.

Humans↗
PubMed1991

Description of broad-band pulsed Doppler ultrasound processing using the two-dimensional Fourier transform.

Considering data from a Doppler sample volume as a two-dimensional function of depth and time, the properties of its two-dimensional fast Fourier transform (2DFFT) are discussed. It is shown that the 2DFFT of idealized Doppler data from moving scatterers is a line whose slope is the velocity of the scatterers. Aliasing, finite bandwidth effects, and spectral broadening due to transit time effects receive simple descriptions in this scheme. Existing processing schemes can be described graphically in this unifying description. Processing of broad band pulsed Doppler ultrasound can incorporate a correction for aliasing if based on the two-dimensional Fourier transform, and this has been tested using data from tissue-mimicking phantom in a tank-based experiment.

Fourier Analysis↗
PubMed1990

Automatic vessel tracking and measurement for Doppler studies.

In this initial report, an imaging technique is described for automatically recognising the walls of a blood vessel during Doppler measurements, and hence automatically adjusting the position of the sample volume. The method reduces the inherently two-dimensional edge detection problem to a one-dimensional one, and iterates over several imaging frames to optimise the information. The orientation and diameter of the vessel are also measured. The technique has been clinically tested off-line and is particularly applicable to Doppler volumetric flow studies.

Algorithms↗
PubMed1988

Ultrasonic characterization of splenic tissue in myelofibrosis: further evidence for reversal of fibrosis with chemotherapy.

Fibrosis in patients with myelofibrosis (MF) is seen not only in the bone marrow but also around the metaplastic foci in the spleen and liver. Following our observation of reversal of bone marrow fibrosis in MF patients treated with chemotherapy, we undertook ultrasonic splenic tissue characterization studies using sound speed measurements to assess the effect of such therapy on the splenic fibrosis. Single studies in 19 patients showed overlapping ranges among the three sub-groups classified according to the grade of bone marrow fibrosis, but the mean values in these sub-groups showed a trend towards decreasing sound speed with increasing marrow fibrosis. Sequential studies in 9 of these patients showed increased splenic sound speed with decreasing marrow fibrosis in 8 patients following treatment, with a reversal of this pattern seen in 1 patient 1-2 years post-treatment. These results suggest simultaneous reversal of fibrosis in the bone marrow and the spleen in MF patients receiving effective chemotherapy.

Bone Marrow↗
PubMed1987

Clinical sound speed measurement in liver and spleen in vivo.

The paper describes an implementation of clinical sound speed measurement using either a commercial water path scanner or a specially developed dual transducer real time scanner, each interfaced to a general purpose minicomputer for off-line analysis. It describes the examination technique to obtain suitable in vivo clinical data from the liver and the spleen. It develops signal processing methods to achieve clinical confidence in individual measurements. Forty-five liver patients and 46 spleen patients were examined. Sound speed was found to correlate closely with fibrosis content in both the liver and the spleen with an increase in fibrosis resulting in a decrease in sound speed. Sound speed in various pathological conditions are discussed. Clinical results of sequential examinations on patients under treatment are presented and successful monitoring of the disease status is demonstrated. The potential clinical role of sound speed measurement is suggested.

Acoustics↗