Biomedical subjects

Elizabeth Berry

Publications and source records attributed to Elizabeth Berry.

7 recordsLinked to original sources

PubMed2006

Visualizing three-dimensional facial soft tissue changes following orthognathic surgery.

Laser scanning can be used to visualize the face in three dimensions. These scans can then be processed to enable assessment of facial changes. The aim of this single-centre, prospective, longitudinal, cohort study was to investigate whether four different visualization methods correctly represented facial changes occurring as a result of orthognathic surgery. Twenty-six consecutive orthognathic patients (13 female mandibular advancement and 13 male bimaxillary Class III) were included as well as a control group of 12 non-growing adults (6 males and 6 females). Pre- and post-operative facial laser scans were superimposed and four different visualization methods applied: correspondences with sensitivity to movement, normals, radial, and closest point. A group of 10 'blinded' observers determined the surgical procedure (if any) that had been performed by applying a specific colour scale to each facial image. The sensitivities and specificities for each visualization method applied to each subject group were determined. The intraobserver repeatability was investigated using Cohen's kappa (k). The radial method was found to be superior for identifying mandibular advancement patients (sensitivity/specificity 58.5/92.4 per cent), the normals method for visualization of bimaxillary Class III cases (26.2/99.6 per cent), while the control group was best represented using the closest point (60.0/80.8 per cent). Overall, intraobserver repeatability was good (k = 0.61). A good level of repeatability was demonstrated in the separate subject groups (mandibular advancement 0.70, bimaxillary Class III 0.70, and controls 0.62). There was no significant difference in the abilities of the four visualization methods to represent facial changes. Each method allowed correct identification of different proportions of the subject groups.

Adolescent↗

PubMed2004

Materials for phantoms for terahertz pulsed imaging.

Phantoms are commonly used in medical imaging for quality assurance, calibration, research and teaching. They may include test patterns or simulations of organs, but in either case a tissue substitute medium is an important component of the phantom. The aim of this work was to identify materials suitable for use as tissue substitutes for the relatively new medical imaging modality terahertz pulsed imaging. Samples of different concentrations of the candidate materials TX151 and napthol green dye were prepared, and measurements made of the frequency-dependent absorption coefficient (0.5 to 1.5 THz) and refractive index (0.5 to 1.0 THz). These results were compared qualitatively with measurements made in a similar way on samples of excised human tissue (skin, adipose tissue and striated muscle). Both materials would be suitable for phantoms where the dominant mechanism to be simulated is absorption (approximately 100 cm(-1) at 1 THz) and where simulation of the strength of reflections from boundaries is not important; for example, test patterns for spatial resolution measurements. Only TX151 had a frequency-dependent refractive index close to that of tissue, and could therefore be used to simulate the layered structure of skin, the complexity of microvasculature or to investigate frequency-dependent interference effects that have been noted in terahertz images.

Coloring Agents↗

PubMed2004

Abnormalities on magnetic resonance imaging seen acutely following mild traumatic brain injury: correlation with neuropsychological tests and delayed recovery.

Mild traumatic brain injury (MTBI) is a common reason for hospital attendance and is associated with significant delayed morbidity. We studied a series of 80 persons with MTBI. Magnetic resonance imaging (MRI) and neuropsychological testing were used in the acute phase and a questionnaire for post-concussion syndrome (PCS) and return to work status at 6 months. In 26 subjects abnormalities were seen on MRI, of which 5 were definitely traumatic. There was weak correlation with abnormal neuropsychological tests for attention in the acute period. There was no significant correlation with a questionnaire for PCS and return to work status. Although non-specific abnormalities are frequently seen, standard MRI techniques are not helpful in identifying patients with MTBI who are likely to have delayed recovery.

Adult↗

PubMed2004

Modelling the propagation of terahertz radiation through a tissue simulating phantom.

Terahertz (THz) frequency radiation, 0.1 THz to 20 THz, is being investigated for biomedical imaging applications following the introduction of pulsed THz sources that produce picosecond pulses and function at room temperature. Owing to the broadband nature of the radiation, spectral and temporal information is available from radiation that has interacted with a sample; this information is exploited in the development of biomedical imaging tools and sensors. In this work, models to aid interpretation of broadband THz spectra were developed and evaluated. THz radiation lies on the boundary between regions best considered using a deterministic electromagnetic approach and those better analysed using a stochastic approach incorporating quantum mechanical effects, so two computational models to simulate the propagation of THz radiation in an absorbing medium were compared. The first was a thin film analysis and the second a stochastic Monte Carlo model. The Cole-Cole model was used to predict the variation with frequency of the physical properties of the sample and scattering was neglected. The two models were compared with measurements from a highly absorbing water-based phantom. The Monte Carlo model gave a prediction closer to experiment over 0.1 to 3 THz. Knowledge of the frequency-dependent physical properties, including the scattering characteristics, of the absorbing media is necessary. The thin film model is computationally simple to implement but is restricted by the geometry of the sample it can describe. The Monte Carlo framework, despite being initially more complex, provides greater flexibility to investigate more complicated sample geometries.

Diagnostic Imaging↗

PubMed2004

Multispectral classification techniques for terahertz pulsed imaging: an example in histopathology.

Terahertz pulsed imaging is a spectroscopic imaging modality using pulses of electromagnetic radiation (100 GHz-10 THz), and there has been recent interest in studying biomedical specimens. It is usual to display parametric images derived from the measured pulses. In this work, classification was achieved by applying multispectral clustering techniques to sets of parametric images. It was hypothesised that adequate information for clustering was carried in a small number of parametric images, providing these were weighted by complementary physical properties. Materials prepared for histopathological examination were chosen because their condition remained stable during long imaging periods and because their dehydrated state led to greater penetration of the radiation. Two specimens were examined in this pilot study, one of basal cell carcinoma and one of melanoma. Unsupervised ISODATA classification using three selected parametric terahertz pulsed images was compared qualitatively with k-means classification using the shape of the whole time series, and with conventional stained microscope slides. There was good qualitative agreement between the classifications. Classifications were consistent with the morphological appearances expected, but further work is required to determine if tumour discrimination is possible. The results have implications for the future development of the technique as the need for only a small number of features could lead to considerably reduced acquisition times.

Algorithms↗

PubMed2002

Use of magnetic resonance angiography to select candidates with recently symptomatic carotid stenosis for surgery: systematic review.

OBJECTIVE: To determine if sufficient evidence exists to support the use of magnetic resonance angiography as a means of selecting patients with recently symptomatic high grade carotid stenosis for surgery. DESIGN: Systematic review of published research on the diagnostic performance of magnetic resonance angiography, 1990-9. MAIN OUTCOME MEASURES: Performance characteristics of diagnostic test. RESULTS: 126 potentially relevant articles were identified, but many articles failed to examine the performance of magnetic resonance angiography as a diagnostic test at the surgical decision thresholds used in major clinical trials on endarterectomy. 26 articles were included in a meta-analysis that showed a maximal joint sensitivity and specificity of 99% (95% confidence interval 98% to 100%) for identifying 70-99% stenosis and 90% (81% to 99%) for identifying 50-99% stenosis. Only four articles evaluated contrast enhanced magnetic resonance angiography. CONCLUSIONS: Magnetic resonance angiography is accurate for selecting patients for carotid endarterectomy at the surgical decision thresholds established in the major endarterectomy trials, but the evidence is not very robust because of the heterogeneity of the studies included. Research is needed to determine the diagnostic performance of the most recent developments in magnetic resonance angiography, including contrast enhanced techniques, as well as to assess the impact of magnetic resonance angiography on surgical decision making and outcomes.

Carotid Stenosis↗

PubMed2002

How to undertake a clinically relevant systematic review in a rapidly evolving field. Magnetic resonance angiography.

OBJECTIVES: The aim was to determine which generations of the evolving technology of magnetic resonance angiography (MRA) are currently of clinical relevance in two clinical applications. Our purpose was to plan a systematic review that would be valuable both to purchasers driven by cost-effectiveness and to practicing clinicians. METHODS: Information was gathered from a search of major bibliographic databases, from a short questionnaire sent to 500 U.K. vascular radiologists and vascular surgeons, and from local clinical experts. We asked which of the MRA techniques were currently used and, assuming availability, what would be their technique of choice. RESULTS: There were 206 published articles that satisfied preliminary inclusion criteria: 69 discussed 2D time of flight (TOF); 47, 3D TOF; and 38, contrast-enhanced techniques. There were 162 questionnaires returned (60 radiologists, 102 surgeons). Of the total respondents, 77/162 (48%) used MRA in the assessment of carotid artery stenosis; 47/77 (61%) used 2D TOF; 32/77 (42%), 3D TOF; and 26/77 (34%), contrast-enhanced techniques. Thirty-five of 162 (22%) respondents used MRA in the assessment of peripheral vascular disease (PVD); 15/35 (43%) used 2D TOF, 4/35 (11%) used 3D TOF, and 22/35 (63%) used contrast-enhanced techniques. For those wishing to use MRA, contrast-enhanced techniques were the method of choice. CONCLUSIONS: The TOF methods that represent earlier generations of the technology remain clinically relevant, and will therefore be included in our systematic review. To ensure complete and relevant coverage in reviews of other evolving technologies, it would be advisable to obtain data for guidance in a similar way.

Humans↗