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Biomedical subjects

J C Bamber

Publications and source records attributed to J C Bamber.

At least 19 recordsLinked to original sources
PubMed2000

Differentiation of common benign pigmented skin lesions from melanoma by high-resolution ultrasound.

BACKGROUND: There are potential clinical benefits if non-invasive methods can be used to diagnose or exclude melanoma. OBJECTIVES: We investigated high-resolution ultrasound (HRU) as a potential non-invasive diagnostic aid for pigmented skin lesions. METHODS: Using a 20-MHz ultrasound B-scan imaging system interfaced to a computer, we assessed acoustic shadowing and entry echo line enhancement (EEE) for 29 basal cell papillomas (BCPs) and 25 melanomas. Acoustic shadowing was estimated by the dermal echogenicity ratio (DER), comparing mean echogenicity below the lesion with that of adjacent dermis. Histological features were scored independently. RESULTS: DER < 3 correctly distinguished melanoma from BCP with 100% sensitivity and 79% specificity. Specificity increased to 93% if the presence of EEE was included as a discriminator. Shadowing correlated most significantly with histological extent of hyperkeratosis (P < 0.0001). Consequently, this method falsely identified non-keratotic acanthotic BCP (n = 3) as melanoma. Highly significant differences between benign naevi (n = 15) and melanomas (n = 24) were found. The SD of retrolesional echogenicity was higher for naevi than melanomas (P < 0.0001), but such an analysis was poorly specific for the diagnosis of melanoma (30%). CONCLUSIONS: Overall, HRU has considerable potential as a high-performance screening tool to assist in the discrimination between BCP, but not benign naevi, and melanoma. In particular, it may be possible to exclude melanoma with 100% certainty in the differentiation of BCP from melanoma.

Diagnosis, Differential↗
PubMed2000

Classification of reflectance spectra from pigmented skin lesions, a comparison of multivariate discriminant analysis and artificial neural networks.

Successful treatment of skin cancer, especially melanoma, depends on early detection, but diagnostic accuracy, even by experts, can be as low as 56% so there is an urgent need for a simple, accurate, non-invasive diagnostic tool. In this paper we have compared the performance of an artificial neural network (ANN) and multivariate discriminant analysis (MDA) for the classification of optical reflectance spectra (320 to 1100 nm) from malignant melanoma and benign naevi. The ANN was significantly better than MDA, especially when a larger data set was used, where the classification accuracy was 86.7% for ANN and 72.0% for MDA (p < 0.001). ANN was better at learning new cases than MDA for this particular classification task. This study has confirmed that the convenience of ANNs could lead to the medical community and patients benefiting from the improved diagnostic performance which can be achieved by objective measurement of pigmented skin lesions using spectrophotometry.

Algorithms↗
PubMed2000

Spectrophotometric assessment of pigmented skin lesions: methods and feature selection for evaluation of diagnostic performance.

This study documents the optical reflectance characteristics of pigmented skin lesions and evaluates their potential for improving the differential diagnosis of malignant melanoma from benign pigmented skin lesions. Optical reflectance spectra in the wavelength range 320-1100 nm were obtained from 121 lesions already selected by expert dermatologists as suspicious of malignancy. Characteristic differences in spectra from benign and malignant lesions were studied. Feature extraction showed significant differences between lesion groups classified by histology. Seven of the most relevant features were used in the discriminant analysis of reflectance spectra from 15 melanoma and 32 compound naevi which resulted in a sensitivity of 100% and specificity of 84.4% when compared with histology. This simple objective technique appears to perform as well as the expert dermatologist and may improve the diagnostic accuracy of non-specialists such as trainees and GPs. Further prospective clinical study of reflectance spectrophotometry in a larger patient group is now required.

Adolescent↗
PubMed2000

Evaluation of an iterative reconstruction method for quantitative elastography.

This paper describes an inverse reconstruction technique based on a modified Newton Raphson iterative scheme and the finite element method, which has been developed for computing the spatial distribution of Young's modulus from within soft tissues. Computer simulations were conducted to determine the relative merits of reconstructing tissue elasticity using knowledge of (a) known displacement boundary conditions (DBC), and (b) known stress boundary conditions (SBC). The results demonstrated that computing Young's modulus using knowledge of SBC allows accurate quantification of Young's modulus. However, the quality of the images produced using this reconstruction approach was dependent on the Young's modulus distribution assumed at the start of the reconstruction procedure. Computing Young's modulus from known DBC provided relative estimates of tissue elasticity which, despite the disadvantage of not being able to accurately quantify Young's modulus, formed images that were generally superior in quality to those produced using the known SBC, and were not affected by the trial solution. The results of preliminary experiments on phantoms demonstrated that this reconstruction technique is capable in practice of improving the fidelity of tissue elasticity images, reducing the artefacts otherwise present in strain images, and recovering Young's modulus images that possess excellent spatial and contrast resolution.

Computer Simulation↗
PubMed2000

Thresholds for visual detection of Young's modulus contrast in simulated ultrasound image movies.

Elasticity imaging (EI) is being developed to allow the evaluation of the mechanical properties of soft tissue, but these properties are already assessed in routine ultrasound breast examination using a method that involves the subjective interpretation of tissue motion seen in real-time B-mode image movies during palpation. We refer to this method as relative motion assessment (RMA). The purpose of this study was to begin a process of learning about the usefulness and limitations of RMA relative to the emerging method of elasticity imaging. Perception experiments were performed to measure Young's modulus contrast thresholds for positive contrast lesions under controlled conditions that could subsequently be repeated to evaluate elasticity imaging for the same task. Observer ability to grade relative lesion contrast using RMA was also assessed. Simulated sequences of B-scans of tissue moving in response to an applied force were generated and used in a two-alternative forced-choice (2-AFC) experiment to measure contrast thresholds for the detection of disc-shaped elastic lesions by RMA in the absence of ultrasound echo contrast. Results were obtained for four observers at a lesion area of about 77 speckle cells and for five observers at lesion areas of about 42 and 139 speckle cells. Young's modulus contrast thresholds were found to decrease with increasing lesion size and were well within the range of contrast values that have been measured for breast tumours in vitro. It was also found that observers were quite skilled at using RMA to grade the relative strain contrast of lesions. The nonlinear relationship between the object contrast (Young's modulus contrast) and the image contrast (strain contrast) prevented observers from detecting very small lesions with 100% accuracy, no matter how high the object contrast. A preliminary comparison of the results for RMA with published thresholds for elastography indicated that elastography is likely to offer great benefit in reducing modulus contrast thresholds, but further study is required to confirm this.

Algorithms↗
PubMed1999

Evaluation of soft-tissue masses using segmented color Doppler velocity images: preliminary observations.

OBJECTIVE: We report our initial experience with segmented color Doppler velocity-based estimates of tumor vascularity for various histogically proven soft-tissue masses. SUBJECTS AND METHODS: Color Doppler sonography of 23 histologically proven masses in 22 patients was performed. Digital color Doppler images were acquired directly off the scanner output or from video recordings and stored on a personal computer as 24-bit gray-scale and color composite images. A color Doppler velocity segmentation and analysis algorithm was applied to the digital images, from which we calculated the normalized percentage of color Doppler area. Normalization was determined by expressing color Doppler area as a percentage of the area enclosed by a preselected region of interest. We also calculated mean percentage, SD, and cumulative distribution of color Doppler area, relative to a fixed threshold, for the acquired image data sets. RESULTS: Estimates of mean percentage of color Doppler area showed a dynamic range of at least two or three orders of magnitude between lowest and highest values obtained. A scatterplot of mean percentage of color Doppler area versus SD of percentage of color Doppler area showed a linear monotonic relationship (r2 = .92), illustrating increasing vascular heterogeneity with mean vascularity. Preliminary data also suggest the presence of at least two distinct groups of masses (p < .0001) based on these vascularity estimates. One group corresponds to high-grade lesions in which tumor angiogenesis is expected to be important in predicting biologic behavior. The second group appeared to have little or no relationship to tumor vascularity or was of an intermediate (or lower) histologic grade. CONCLUSION: Quantitative color Doppler estimates of tumor vascularity can be obtained over a wide dynamic range. Such estimates provide a mechanism to assess vascular heterogeneity of soft-tissue tumors. Preliminary data suggest that two biologically distinct groups of masses may be separable on the basis of quantitative velocity-based estimates of tumor vascularity as obtained from color Doppler sonography.

Adolescent↗
PubMed1996

Microbubble contrast agent for color Doppler US: effect on breast masses. Work in progress.

PURPOSE: To evaluate the effects of a new microbubble contrast agent for ultrasound (US) on breast masses. MATERIALS AND METHODS: Thirty-four patients underwent color Doppler US before and after intravenous injection of a "contrast agent" containing microbubbles. The authors subjectively evaluated the increase in intensity of the Doppler signals, the changes in the vascular patterns, and the timing of the transit of the microbubble bolus. The diagnostic confidence was assessed before and after administration of contrast material. RESULTS: After contrast material injection, there was greater and longer signal enhancement in the cancers than in the benign lesions. The cancers displayed characteristic vascular morphologic features, with more additional vessels visualized in relation to the lesion and a greater increase in vascular tortuousity. Shunts between vessels were demonstrated in all cancers but were not seen in any benign lesion. The diagnostic confidence increased with use of the contrast agent. The appearance at contrast-enhanced US led to a change in the US diagnosis in four patients. This increased both sensitivity and specificity to 100%. CONCLUSION: Injection of a microbubble agent enabled accurate differentiation of benign masses from carcinomas.

Adult↗
PubMed1995

Segmentation and analysis of colour Doppler images of tumour vasculature.

A technique has been developed to segment (separate), from a digitized colour Doppler video image, the colour and greyscale information and then to estimate from the colour information the original mean Doppler frequency shift data from which the image was created. The remapped velocity image is then analysed to extract numerical features of the tumour vasculature. The present version of the software is set-up to work for an Acuson 128 colour Doppler system using the V4 colour scale, although it should work well with any system which modulates only two colours for each flow direction and displays a colour calibration scale at the side of the image. Accuracy of classification of greyscale, colour and flow direction was estimated as being in the region of 95% for typical breast tumour images. The degree of agreement between the remapped colour velocity values and those stated by the scanner at the same image locations was evaluated in terms of the linearity of the relationship (> 99%), precision (better than +/- 5%) and accuracy (better than 7.6%). We investigated the value, for diagnosis and assessment of response of, a variety of characteristics of the displayed vascularity. At present, the software calculates the following vascular image features within any region of interest defined by the operator: mean displayed velocity, maximum displayed velocity, standard deviation of displayed velocity, total area occupied by colour signal, percentage area occupied by colour signal, area integral of displayed velocity and the total displayed velocity per unit area.

Algorithms↗
PubMed1995

Ultrasonic propagation properties of excised human skin.

Eight human skin samples were excised postmortem from the upper and lower back, chest and abdomen from two cadavers. The acoustical speed, attenuation and backscatter were measured as a function of frequency (20 to 30 MHz) at 100 positions on a uniform grid over a cross-sectional slice through each sample with the sound incident in a direction parallel to the skin surface. Measurements were made at 24 +/- 0.5 degrees C. Samples were then frozen, cut and stained for histological examination and quantification of fibrous proteins and fat content. The mean attenuation coefficients obtained for whole skin agreed well with previously published results. Employing the model alpha = alpha 1f" where alpha is the attenuation coefficient in decibels per centimeter, alpha 1 is the value of the attenuation coefficient at 1 MHz and f is frequency raised to the power n, mean values (+/- 1 standard deviation) for epidermis were alpha 1 = 0.44 +/- 0.26 and n = 1.55 +/- 0.12, and for dermis alpha 1 = 0.264 +/- 0.17 dB cm-1 and n = 1.69 +/- 0.084. Using a similar model the mean backscatter coefficient was defined by mu 1 = (5.01 +/- 25.76) x 10(-8) Sr-1 cm-1, n = 3.77 +/- 1.5 for the epidermis, and mu 1 = (1.79 +/- 19.5) x 10(-6) and n = 2.76 +/- 1.4 for the dermis. The speed of sound values fell within the range to be found in the literature with a mean value in the epidermis of 1645 m s-1 and in the dermis of 1595 m s-1. Significant, strong correlation existed between the spatially averaged fibrous protein content in the epidermis and dermis and the spatially averaged integrated attenuation measurements. Likewise, strong correlation existed between integrated backscatter and fibrous protein content in the epidermis but not in the dermis. Further research is required to confirm these preliminary findings and to evaluate the role of collagen fibre orientation as a source of variation in the backscattering coefficient of dermis.

Abdomen↗
PubMed1995

Colour DOPPLER image analysis for tissue vascularity and perfusion: a preliminary clinical evaluation.

An automated system for measuring features of colour Doppler (CD) images has been examined for its ability to measure tissue perfusion in vivo under conditions of diffuse vascularity. Seven statistical features were extracted from CD images of human calf muscle and compared with the arterial input measured by plethysmography. It was found that, when appropriate scanning procedures are employed, good correlation is achieved with arterial input (r = 0.96 to 0.99). Ultrasound beam angle was important, even for the assessment of "colour area." A sensitive velocity scale was ideal for "percentage colour" (r = 0.979). "Mean colour velocity" correlates well with arterial input (r = 0.979) when the volocity scale was optimised for each CD scan. "Integrated colour velocity per unit area" was more responsive when using a variable velocity scale (r = 0.99) than a fixed velocity scale (r = 0.98), but was less responsive to low flow. Automated CD analysis speeds up the process of quantitative assessment of tissue vasculature and perfusion. It is therefore essential for the analysis of dynamic studies of ultrasound contrast agents and serial examinations when monitoring response to therapy.

Arteries↗
PubMed1995

Automated quantification of color Doppler signals: a preliminary study in breast tumors.

PURPOSE: To quantify color Doppler (CD) signals reflected by breast lesions to improve differential diagnosis and serial comparisons. MATERIALS AND METHODS: Frame-grabbed color-capture scans were remapped to original velocities on a pixel-by-pixel basis for statistical analysis. Total CD area and its percentage, peak and mean velocities, standard deviation of velocity, and integral CD velocity and its percentage were calculated. These indexes were applied to scans of 44 cancers, 16 fibroadenomas, and 14 benign breast changes in 74 patients. RESULTS: With the region of interest confined to the lesion and a 5-mm margin, no CD signals were reflected by the benign breast changes. All carcinomas and 12 fibroadenomas (those that were vascular) reflected CD signals, and, except for mean and peak velocity, all scores for cancers were significantly higher than for fibroadenomas (P < .0001). Integral CD velocity was the best discriminator, with no overlap between carcinomas (range, 1,128-50,228 cm3/sec) and fibroadenomas (range, 0-1,027 cm3/sec). CONCLUSION: Automatic CD quantification improved differential diagnosis of breast masses.

Adult↗
PubMed1995

Adaptive speckle reduction for improving the differential diagnosis of breast lesions.

Adaptive speckle reduction could mask diagnostic features and adversely affect diagnosis of focal breast lesions. Four radiologists assessed focal breast lesions (29 malignant and 31 benign) by blind review of representative static B-mode scans before and after adaptive speckle reduction processing, scoring 14 diagnostic features for breast cancer and recording their opinions on the diagnosis and on how adaptive speckle reduction affected interpretation of each feature. No adverse affect on diagnosis of malignant (P = 0.756) or benign (P = 1.000) breast lesions was found, despite some differences in scoring of the diagnostic features after adaptive speckle reduction. Observer recognition of most diagnostic features was easier after adaptive speckle reduction (e.g., edge definition [50% of cases], edge regularity [40%], lesion texture [44%], and lesion echogenicity [35%]).

Adult↗
PubMed1994

Breast carcinoma: measurement of tumor response to primary medical therapy with color Doppler flow imaging.

PURPOSE: To assess the ability of color Doppler flow imaging to help evaluate the response of breast cancer to medical therapy. MATERIALS AND METHODS: Thirty-four patients with large or centrally located breast carcinomas were studied. All tumors had been treated medically. Tumor size was assessed at clinical examination, volume at B-mode ultrasound (US), and vascularity at color Doppler flow imaging. The changes seen during the treatment course were cross compared and correlated with final tumor response. RESULTS: In 97 of the 126 treatment cycles (77%), changes in vascularity were concordant with changes in the size of the tumors (reduction in the vascularity with response to therapy and an increase in tumor size with lack of response or progression). Changes seen at color Doppler flow imaging occurred at least 4 weeks before those seen at clinical and B-mode US examination in 40% and 38% of cases, respectively. Changes in vascularity could be assessed in every patient. CONCLUSION: Color Doppler flow imaging can help assessed and predict the response of breast cancer to medical treatment.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1993

Acoustic properties of lesions generated with an ultrasound therapy system.

Methods for quantitative imaging of ultrasound propagation properties were applied to the examination of the acoustic appearance of lesions generated by high intensity focused ultrasound in excised pig livers. Single lesions, about 10 mm maximum diameter by 30 mm long, were created in each of six liver specimens. Two dimensional images (32 by 32 points) of sound speed, mean attenuation coefficient (as a function of frequency in the range 3 to 8.5 MHz) and mean backscattering coefficient (5 to 8 MHz) were obtained in 7 mm thick sections of tissue, cut to include a cross-section through the lesion. Images of these properties, presented alongside surface photographs of the samples, provided a qualitative demonstration that attenuation coefficient was the most useful and backscattering coefficient was the least useful acoustic parameter for visualizing such lesions. Quantitatively the data demonstrated significant increases in attenuation coefficient and sound speed in lesioned liver relative to normal, whereas backscattering was shown not to change in a significant manner except when undissolved gas is the mechanism for increased acoustic scattering. Samples where gas was not fully removed following lesion production gave significant increases in backscattering at the lesion centre, but the shape and size of regions of high backscattering coefficient corresponded poorly with the shape and size of the lesions, unlike attenuation and sound speed for which such correspondence was good.

Acoustics↗
PubMed1993

Compensation for the signal processing characteristics of ultrasound B-mode scanners in adaptive speckle reduction.

A systematic method to compensate for nonlinear amplification of individual ultrasound B-scanners has been investigated in order to optimise performance of an adaptive speckle reduction (ASR) filter for a wide range of clinical ultrasonic imaging equipment. Three potential methods have been investigated: (1) a method involving an appropriate selection of the speckle recognition feature was successful when the scanner signal processing executes simple logarithmic compressions; (2) an inverse transform (decompression) of the B-mode image was effective in correcting for the measured characteristics of image data compression when the algorithm was implemented in full floating point arithmetic; (3) characterising the behaviour of the statistical speckle recognition feature under conditions of speckle noise was found to be the method of choice for implementation of the adaptive speckle reduction algorithm in limited precision integer arithmetic. In this example, the statistical features of variance and mean were investigated. The third method may be implemented on commercially available fast image processing hardware and is also better suited for transfer into dedicated hardware to facilitate real-time adaptive speckle reduction. A systematic method is described for obtaining ASR calibration data from B-mode images of a speckle producing phantom.

Algorithms↗