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Biomedical subjects

P F Sharp

Publications and source records attributed to P F Sharp.

At least 19 recordsLinked to original sources
PubMed1992

Automated detection and quantification of microaneurysms in fluorescein angiograms.

Fluorescein angiograms from diabetics were digitised for analysis using digital image-processing techniques. Computer algorithms were written to detect and count microaneurysms present in the images. The accuracy, speed and reproducibility of the technique were assessed and compared with those of manual counts made by clinicians from both digitised and analogue images. Free-response ROC (receiver operating characteristic) curves were used to assess the performance of both the clinicians and the computer by comparing the results with "gold standards" compiled from prints of the original fluorescein angiograms. The computer performed as well as the clinicians when the latter were analysing the digitised images (512 x 512 pixel resolution), but only when one image was acquired at 4 times this resolution did the computer's performance match that of the clinicians analysing the analogue image. The automated technique was more reproducible than the manual method.

Algorithms↗
PubMed1991

Detection and quantification of hyperfluorescent leakage by computer analysis of fundus fluorescein angiograms.

Digital imaging systems can be used for direct acquisition of images of the ocular fundus or for their indirect acquisition from fundus photographs or transparencies. Computerised image processing techniques can then be used to manipulate and quantify features of interest. We describe a method for the detection and quantification of macular leakage in fluorescein angiograms. The rate of change in fluorescence over time is examined on a pixel-by-pixel basis and used to provide a gradient threshold that discriminates pixels displaying leakage from normal pixels. A region-growing technique is then used to enhance the detection of leakage missed by gradient thresholding alone. This report discusses the potential applications of the technique and highlights the methodology required to obtain reproducible results.

Fluorescein↗
PubMed1991

Quantification of diabetic maculopathy by digital imaging of the fundus.

Measurement of the extent of diabetic retinopathy is an essential part of assessing the efficacy of local or systemic treatment regimens. Current clinical studies use empirical grading of retinopathy which is performed by a trained observer using standard photographs. This method is relatively arbitrary, as well as time consuming and vulnerable to observer error. We have developed a digital fundus imaging system and image processing programs which provide objective, quantitative measures of macular oedema, retinal exudates, and microaneurysms in diabetic retinopathy. Using fluorescein angiograms, the degree of macular oedema is quantified both in terms of area of fundus involved and severity of oedema by analysis of the temporal changes in intensity of fluorescence. Fluorescein angiograms are also used for the detection and counting of microaneurysms, by a combination of shade correction, matched filtering, and shape algorithms. For detection and measurement of retinal exudates, a colour transparency projected through a red free filter is analysed using a combination of shade correction and thresholding techniques. The system described is in clinical use, and has potential for a wide variety of applications. With further development, digital analysis of fundus images should supercede the currently used manual semi-quantitative methods, providing faster, more accurate, objective quantitative results.

Aneurysm↗
PubMed1990

Quantifying image quality.

The measurement of image quality is an essential stage in the evaluation of imaging techniques. Yet there is no accepted way of quantitatively assessing image quality. Current theories suggest that the quality of the raw data acquired by the device can be assessed independently from that of the displayed image. In this paper the various experimental techniques suitable for making psychometric measurements of displayed image quality are discussed.

Diagnostic Imaging↗
PubMed1990

Use of temporal information to quantify vascular leakage in fluorescein angiography of the retina.

Vascular leakage causing macular oedema is an important cause of visual loss in retinal vascular disorders such as diabetic retinopathy and retinal vein occlusion. By digitising selected frames from fundus fluorescein angiographic sequences we have developed a technique which uses the observed rate of change of fluorescence to detect and quantify areas of leakage. Reproducibility studies yielded a coefficient of variation of less than 6% for large areas of leakage, and 27% for very small areas of leakage. We believe this technique is sufficiently sensitive and robust for clinical use, and should find a significant role in the management of retinal vascular disorders.

Fluorescein Angiography↗
PubMed1990

Multimodal imaging in Alzheimer's disease. The relationship between MRI, SPECT, cognitive and pathological changes.

Patients with a clinical diagnosis of Alzheimer's disease were studied using MRI, SPECT, and psychometric tests. Significant correlations between focal perfusion deficits and focal cognitive deficits were found. Significant correlations between regional relaxation time of white matter and psychometric tests of diffuse and focal categories were also found. Pathological examination confirmed Alzheimer's disease as the only diagnosis.

Aged↗
PubMed1990

Regional cerebral blood flow imaging: a quantitative comparison of technetium-99m-HMPAO SPECT with C15O2 PET.

The aim of this study was to compare technetium-99m-hexamethylpropyleneamineoxime (99mTc-HMPAO) single-photon emission computed tomography (SPECT) with regional cerebral blood flow (rCBF) imaging using positron emission tomography (PET). As investigation of dementia is likely to be one of the main uses of routine rCBF imaging, 18 demented patients were imaged with both techniques. The PET data were compared quantitatively with three versions of the SPECT data. These were, first, data normalized to the SPECT cerebellar uptake, second, data linearly corrected using the PET cerebellar value and, finally, data Lassen corrected for washout from the high flow areas. Both the linearly-corrected (r = 0.81) and the Lassen-corrected (r = 0.79) HMPAO SPECT data showed good correlation with the PET rCBF data. The relationship between the normalized HMPAO SPECT data and the PET data was nonlinear. It is not yet possible to obtain rCBF values in absolute units from HMPAO SPECT without knowledge of the true rCBF in one reference region for each patient.

Aged↗
PubMed1989

Principles and appraisal of combined images in NMR.

The interpretation of NMR images at Aberdeen is most often performed by the individual study of the proton density, difference, inversion recovery and T1 image. This report investigates the usefulness of presenting the information from a pair of images, in this instance the T1 and proton density images, in a single composite image. Information from the two images is combined such that the values from one image are represented by a change in hue (colour), and the values from the other by a change in luminance (intensity). To test the advantages of such combined images, a trial was run using a selection of prediagnosed abnormal brain scans. The information perceived as hue and luminance in the combined images was compared with that from separate conventional monochrome proton density and T1 images. Medical and nonmedical users were told the final diagnosis and were asked whether it was possible to see more, less, or the same information with regard to clinically relevant details in the structure of the abnormality and the image as whole. The results have revealed that for the majority of cases the combined image format can effectively represent the information normally contained in both the monochrome proton density and T1 images--thus speeding up the image viewing process.

Biomedical Engineering↗
PubMed1989

Grey level linearising circuit for computer-interfaced display devices.

An earlier paper by the authors on the linearisation of computer-interfaced display devices has described a radiometric procedure for quantifying device non-linearity and a software technique for using the data to linearise screen luminance with respect to display grey level. As the display non-linearity varies with the particular settings of the brightness and contrast controls, any change in these settings requires that the data used with the software also be modified. While it is possible to store data for a number of selected control settings, it would be more convenient if linearisation could be performed using hardware for all relevant settings of these controls. The electronic circuit described in this paper makes use of the same non-linearity data to achieve device linearity with the added advantage of increased flexibility of use. The circuit is suitable for connection immediately following the digital-to-analogue converter or video processor and provides two useful new controls. One of these determines the amount of non-linearity correction to be applied to the video signal, while the second enables screen contrast to be varied without affecting the linearity achieved. The standard brightness and contrast controls of the display device are left as initially preset and require no subsequent adjustment.

Amplifiers, Electronic↗
PubMed1988

A comparison of Tc-99m HM-PAO and I-123 IMP cerebral SPECT images in Alzheimer's disease and multi-infarct dementia.

SPECT images of the brain can be obtained using either 123I labelled amines or 99mTc-hexamethylpropyleneamineoxime (HM-PAO). Both materials produce images which are blood flow dominated and so appear similar in normal subjects, although the respective mechanisms of uptake are not yet finally established. It seems likely, however, that the different mechanisms of uptake are responsible for recent reports of some differences seen in images obtained with the two types of agent in patients with cerebral pathology, mainly cerebrovascular disease. In this study, 12 demented patients, 6 with dementia of the Alzheimer type (DAT) and 6 with multi infarct dementia (MID), were imaged with 123I-isopropylamphetamine (IMP) and 99mTc-HM-PAO and the images compared. Significantly more lesions were seen with IMP than HM-PAO (P less than 0.02); out of a possible 120 sites, 41 lesions were seen with IMP compared to 28 with HM-PAO, 23 being seen with both agents. However, it is concluded that either agent can be used for the differential diagnosis of dementia, a task for which the new cerebral blood flow agents seem well suited.

Aged↗
PubMed1988

The use of technetium-99m-HM-PAO in the assessment of patients with dementia and other neuropsychiatric conditions.

One hundred fourteen patients suffering from neuropsychiatric conditions have been studied using 99mTc-labeled hexamethylpropyleneamine oxime (HM-PAO) and single photon emission computed tomography (SPECT). Ninety-one patients had a firm clinical diagnosis while 23 were examined without knowledge of the clinical diagnosis. Of the 91 patients, 51 were suffering from dementia, 25 multi-infarct type and 26 Alzheimer's disease. In 19 of the Alzheimer's patients, a characteristic pattern of decreased perfusion in the parieto-occipital regions was demonstrated while those with multi-infarct type showed varying degrees of irregular uptake in the cerebral cortex. These appearances are similar to those shown with positron emission tomography (PET) and we believe that HM-PAO will provide a widely available method for identifying patients with Alzheimer's disease. Twenty-nine patients were suffering from diseases involving the basal ganglia. Fifteen patients with Parkinson's disease showed no significant abnormality in basal ganglia uptake, while 7 or 8 patients with Huntington's disease who had full examinations showed decreased uptake in the caudate nuclei. Similarly, four of six patients with other basal ganglia diseases showed impaired uptake by basal ganglia, and it is concluded that HM-PAO may be useful for the diagnosis and management of this type of patient. Twenty-three patients received HM-PAO imaging as part of their diagnostic work-up; in 19 of them, detailed follow-up was obtained, which indicated that in 7 cases the result of the HM-PAO scan altered the clinical diagnosis and in 9 cases resulted in a change in management. In the remaining 13 cases, the study was found to be helpful in confirming the diagnosis.

Adult↗