Andrew Todd-pokropek
University College London, Medical Physics, Faculty Member
Currently, various data formats are widely used for medical imags, eg DICOM for exchange through network and storage media, and INTERFILE for image exchange in nuclear medicine. These formats are only able partly to solve problems arising... more
Currently, various data formats are widely used for medical imags, eg DICOM for exchange through network and storage media, and INTERFILE for image exchange in nuclear medicine. These formats are only able partly to solve problems arising in accessing and handling imags. ...
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Simultaneous imaging of Tc-99m and I-123 has important applications for brain imaging but is hindered by crosstalk between the two radionuclides. Monte Carlo simulations of 15 different dual-isotope studies were performed using a digital... more
Simultaneous imaging of Tc-99m and I-123 has important applications for brain imaging but is hindered by crosstalk between the two radionuclides. Monte Carlo simulations of 15 different dual-isotope studies were performed using a digital brain phantom. Several physiologic Tc-99m and I-123 uptake patterns were modeled in the brain structures. Spectral factor analysis (SFA) using constraints on the primary spectra was
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Research Interests: Computer Science, Image Processing, Medical Imaging, Decision Making, Medical Image Processing, and 15 moreImaging, Evaluation, Image Analysis, Algorithm, Information Processing, Decision support system, Information, Decision Support, Differential Diagnosis, Support, Knowledge base, Clinical Decision Support System, Data Logging, Digital Image, and Medical
To demonstrate CD36 expression with quantum dots (QDs) 525 and/or 605 on human monocytic U937 cells and atherosclerotic tissue sections by means of flow cytometry (FCM) and/or confocal laser scanning microscopy (CLSM). U937 cells and... more
To demonstrate CD36 expression with quantum dots (QDs) 525 and/or 605 on human monocytic U937 cells and atherosclerotic tissue sections by means of flow cytometry (FCM) and/or confocal laser scanning microscopy (CLSM). U937 cells and tissue sections were analyzed by means of FCM and/or CLSM. FCM was performed, using different ultraviolet (UV) and visible (488/532 nm) excitation modes. In the visible mode, fluorescence intensities of QDs, phycoerythrin (PE) and fluorescein isothiocyanate (FITC) were compared. Three-dimensional (3-D) sequences of images were obtained by spectral analysis in a CLSM and analyzed by the factor analysis of medical image sequences (FAMIS) algorithm, providing factor curves and images. Factor images are the result of the FAMIS image processing method, which differentiates emission spectra from 3D sequences of images. In CLSM analysis, preparations are screened in a UV excitation mode to optimize the possibilities of QDs and have the benefit of 4',6-diam...
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To analyze multilamellar cytoplasmic structures by confocal laser scanning microscopy (CLSM) combined with factor analysis of biomedical image sequences (FAMIS). After treatment of U937 cells with 7-ketocholesterol (7-keto), cytoplasmic... more
To analyze multilamellar cytoplasmic structures by confocal laser scanning microscopy (CLSM) combined with factor analysis of biomedical image sequences (FAMIS). After treatment of U937 cells with 7-ketocholesterol (7-keto), cytoplasmic alterations were assessed with monodansylcadaverine (MDC). By ultraviolet excitation of a confocal laser scanning microscope (UV-CLSM), spectral sequences were performed to characterize 7-keto and MDC distribution inside cells. FAMIS was used to transform the image sequences in factor curves and images. By UV-CLSM, 7-keto fluorescence was detected together with MDC, which revealed morphologic cytoplasmic changes in cells. The factor images obtained from confocal image sequences emphasized the view of these results. These data are in agreement with biochemical characterizations of MDC-positive structures. The combined use of confocal microscopy and FAMIS allowed us to detect MDC-positive cytoplasmic structures in 7-keto-treated cells and to colocalize...
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To analyze functional and morphologic alterations that occur at the mitochondrial level by flow cytometry and laser scanning confocal microscopy (CLSM) combined with factor analysis of biomedical image sequences (FAMIS). Under treatment... more
To analyze functional and morphologic alterations that occur at the mitochondrial level by flow cytometry and laser scanning confocal microscopy (CLSM) combined with factor analysis of biomedical image sequences (FAMIS). Under treatment of U937 cells with 7-ketocholesterol, functional alterations that occur at the mitochondrial level (especially loss of transmembrane mitochondrial potential [delta psi m]) were assessed with 3,3'-dihexyloxacarbocyanine iodide (DiOC6(3)) and mitotracker red (CMXRos), whereas morphologic changes were analyzed with nonyl acridine orange (NAO). By flow cytometry, these different dyes were excited at 488 nm, whereas on CLSM, excitation of NAO and CMXRos was performed by lines of an argon laser. By CLSM, spectral sequences were performed to characterize NAO and CMXRos. FAMIS was used to transform the image sequences in factor images. By flow cytometry, rapid loss of delta psi m induced by 7-ketocholesterol was detected with both DiOC6(3) and CMXRos, wh...
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The use of H(2)(15)O PET scans for the measurement of myocardial perfusion reserve (MPR) has been validated in both animal models and humans. Nevertheless, this protocol requires cumbersome acquisitions such as C(15)O inhalation or... more
The use of H(2)(15)O PET scans for the measurement of myocardial perfusion reserve (MPR) has been validated in both animal models and humans. Nevertheless, this protocol requires cumbersome acquisitions such as C(15)O inhalation or (18)F-FDG injection to obtain images suitable for determining myocardial regions of interest. Regularized factor analysis is an alternative method proposed to define myocardial contours directly from H(2)(15)O studies without any C(15)O or FDG scan. The study validates this method by comparing the MPR obtained by the regularized factor analysis with the coronary flow reserve (CFR) obtained by intracoronary Doppler as well as with the MPR obtained by an FDG acquisition. Ten healthy volunteers and 10 patients with ischemic cardiopathy or idiopathic dilated cardiomyopathy were investigated. The CFR of patients was measured sonographically using a Doppler catheter tip placed into the proximal left anterior descending artery. The mean velocity was recorded at ...
Research Interests: Nuclear medicine, Medicine, Nuclear, Factor analysis, Humans, and 15 moreFemale, Male, Heart, Perfusion, Dilated cardiomyopathy, Clinical Sciences, Middle Aged, Single Photon Emission Computed Tomography, Analysis of Variance, Coronary Circulation, Radiopharmaceuticals, Myocardial Perfusion Imaging, Coronary Artery Disease, Case Control Studies, and Coronary Flow Reserve
CADMIUM II is a system for the interpretation of mammograms. A novel aspect of the system is that it combines symbolic reasoning with image processing, in contrast with most other approaches, which use only image processing and rely on... more
CADMIUM II is a system for the interpretation of mammograms. A novel aspect of the system is that it combines symbolic reasoning with image processing, in contrast with most other approaches, which use only image processing and rely on artificial neural networks (ANNs) to classify mammograms. A problem of ANNs is that the advice they give cannot be traced back to communicable diagnostic inferences. Our approach is to provide advice based on explicit knowledge about the diagnostic process. To this end, we have conducted a knowledge elicitation study which looked at the descriptors used by expert radiologists when making diagnostic decisions about mammograms. The analysis of the radiologists' reports yielded a set of salient diagnostic features. These were used to inform the advice provided by the symbolic decision making component of CADMIUM II.
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A method for estimation of organ volume is proposed, based on analysis of individual slices obtained from SPET images. In a phantom simulating clinical circumstances, the data show that the level a threshold at 46% of the maximum activity... more
A method for estimation of organ volume is proposed, based on analysis of individual slices obtained from SPET images. In a phantom simulating clinical circumstances, the data show that the level a threshold at 46% of the maximum activity predicts most closely the true volume over a wide range above one liter. The level at 45% predicted better volumes of less than one liter. For phantoms of 839 ml or less, the error was 6.3 ml (one standard error of estimation). This level seems to be independent of the plane or position of the phantom and also independent of the amount of scattering material around it. Nonradioactive voids ("holes") within a phantom may be included or excluded at will when their edges are not tangent to the edge of the phantom. In such cases, their edges are not distinguishable from the edge of the phantom and their volumes are excluded. Knowledge of organ volumes has both diagnostic and therapeutic importance and could lead to a more precisely quantitate...
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ABSTRACT The clinical use of image analysis requires on the one hand a knowledge of pathology, physiology and other medical fields, and on the other hand expertise in image processing techniques. Because of the increasing complexity,... more
ABSTRACT The clinical use of image analysis requires on the one hand a knowledge of pathology, physiology and other medical fields, and on the other hand expertise in image processing techniques. Because of the increasing complexity, these techniques are not often employed by clinical users, who want to focus on interpreting results rather than focusing on the choice of a specific package, the way it operates and the underlying processes. Thus it is of prime importance to clinical users to have at their disposal a system which can accept their clinical knowledge as input, then convert it into an appropriate mathematical language, process it, and finally return the results to them in a clinically intelligible fashion. The concept of an 'intelligent system' interface between medical users and applications has been developed, which we have termed an Interactive Quantitation Support System (IQSS). Such a system translates clinical knowledge into symbolic descriptions and transmits them to the software application. IQSS manages the dialogue between user and application, as well as error handling. A prototype of the user interface has been developed based on a client/server architecture and a data-oriented environment. Early in its development, this IQSS has been tested in prototype form to perform a three-dimensional registration of multimodality images.
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Research Interests: Computer Science, Biomedical Engineering, Pattern Recognition, Image Analysis, Multiscale Modeling, and 15 moreImage segmentation, Image Registration, Complex System, Motion estimation, Data Science, Interdisciplinary, Calibration, Proteins, Computer Graphic, Integrated Approach, Formal Model, Challenges, Biocomplexity, Electrical And Electronic Engineering, and Physiological mechanisms
Research Interests: Computer Science, Artificial Intelligence, Computer Vision, Magnetic Resonance Imaging, Temporal Resolution, and 15 moreMedicine, Multidisciplinary, Image Registration, Clinical Practice, Software, Humans, Perfusion, Contrast-Enhanced Ultrasound, Medical Image, Theoretical Models, Myocardium, Clinical Data, Right Ventricle, Myocardial Perfusion Imaging, and Left Ventricle
Research Interests: Engineering, Computer Science, Magnetic Resonance Imaging, Medicine, Image Registration, and 14 moreHumans, Female, Feasibility Studies, Male, Physical sciences, Heart, Perfusion, Aged, Middle Aged, Magnetic, Coronary Circulation, Myocardial Perfusion Imaging, Coronary Arteries, and Medical and Health Sciences
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Research Interests: Computer Science, Andrology, Ultrasound, Medicine, Humans, and 15 moreUltrasonography, Feasibility Studies, Male, Penis, Real Time, Clinical Sciences, Vagina, Three Dimensional, Volume of Interest, Sexual Activity, Penile Erection, Coitus, Equipment and Supplies, Paediatrics and reproductive medicine, and three-dimensions
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Research Interests: Computer Science, Algorithms, Artificial Intelligence, Geriatrics, Biomedical Engineering, and 15 moreFuzzy Logic, Fuzzy set theory, Image segmentation, Biomedical, Fuzzy Clustering, Clinical Practice, Humans, Back Pain, Cluster Analysis, Intervertebral disc, Degeneration, Bayes Theorem, Electrical And Electronic Engineering, Computer Aided Diagnosis, and Fuzzy C mean
Research Interests: Physics, Carbon Dioxide, Positron Emission Tomography, Medicine, Brain, and 11 moreHumans, Calibration, Clinical Sciences, Single Photon Emission Computed Tomography, Physical Performance, Positron, Attenuation, Oxygen Consumption, Cerebrovascular Disorders, Elementary Particles, and Physical Phenomena
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Abstract. Manual segmentation of liver tissue from computerised tomography (CT) datasets can provide useful information to clinicians, such as an estimation of the volume of the liver and the quantification of abnormalities. However,... more
Abstract. Manual segmentation of liver tissue from computerised tomography (CT) datasets can provide useful information to clinicians, such as an estimation of the volume of the liver and the quantification of abnormalities. However, manual segmentation is a slow, laborious ...
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A 3D image processing method to increase reproducibility in the handling of PET myocardial perfusion studies is proposed. It is basedon the 3D regularization of factor volumes, which are estimated by FAMIS (Factor Analysis of Medical... more
A 3D image processing method to increase reproducibility in the handling of PET myocardial perfusion studies is proposed. It is basedon the 3D regularization of factor volumes, which are estimated by FAMIS (Factor Analysis of Medical Image Sequences). The resulting ...
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Research Interests: Monte Carlo Simulation, Radiation Protection, Nuclear medicine, Image Quality, Quality Control, and 12 moreNuclear, Structural equation models, Statistical Significance, Clinical Sciences, Single Photon Emission Computed Tomography, Computerized tomography, Spatial resolution, Signal - to - noise ratio, Experimental Measurement, Signal to Noise Ratio, Monte Carlo Method, and Structural model
A computer program using Monte-Carlo techniques has been developed to simulate gamma camera collimator performance. Input data include hole length, septum thickness, hole size and shape, collimator material, source characteristics, source... more
A computer program using Monte-Carlo techniques has been developed to simulate gamma camera collimator performance. Input data include hole length, septum thickness, hole size and shape, collimator material, source characteristics, source to collimator distance and medium, radiation energy, total events number. Agreement between Monte-Carlo simulations and experimental measurements was found for commercial hexagonal parallel hole collimators in terms of septal
Research Interests: Image Processing, Monte Carlo Simulation, Nuclear medicine, Performance Evaluation, Process Simulation, and 9 moreTransfer Function, Computer Program, Hot Spot, Single Photon Emission Computed Tomography, Computerized tomography, Experimental Measurement, High Sensitivity, Monte Carlo Method, and Performance Test
Research Interests: Monte Carlo Simulation, Radiation Protection, Nuclear medicine, Image Quality, Quality Control, and 12 moreNuclear, Structural equation models, Statistical Significance, Clinical Sciences, Single Photon Emission Computed Tomography, Computerized tomography, Spatial resolution, Signal - to - noise ratio, Experimental Measurement, Signal to Noise Ratio, Monte Carlo Method, and Structural model
This study demonstrates the difficulties which arise in statistical analysis derived from data of observations in post-treatment healing and recurrence of periodontal disease. Ten individuals received an initial phase of treatment... more
This study demonstrates the difficulties which arise in statistical analysis derived from data of observations in post-treatment healing and recurrence of periodontal disease. Ten individuals received an initial phase of treatment followed by surgical pocket elimination utilizing replaced flap surgery. Clinical measurements of recession and pocketing were taken pre-operatively and 6 monthly thereafter for a period of four years after treatment. The results have shown that surgical treatment is least benefit in cases of mild pocketing, and of most benefit in cases of severe pocketing. A tendency for reduction in recession levels after two years was observed. Pocketing and attachment levels showed a tendency toward relapse as early as 6 months postoperatively. However, this simple observation masks a complex pattern of tissue remodeling in which some sites remain stable, others improve, while others relapse with time. Improvement may occur concurrently in different sites. Continued improvement in the clinical parameters of pocketing and attachment levels was observable in some sites for up to 2 years after surgery, after which the tendency for recurrent disease became more noticeable. Analyses of changes in attachment levels may be misleading, because they may mask the divergent or convergent trends of recession and pocketing, which may be occurring simultaneously. As bursts of healing as well as bursts of destruction could be observed concurrently over the period of 4 years after treatment, it is suggested that a state of "dynamic equilibrium" is established, in which continued tissue remodeling over a protracted period of time, may give rise to the clinical misconception that little or no changes are occurring in the majority of sites with time.
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As part of the evaluation of the display requirements needed in PACS, an ROC curve study was performed in order to assess clinical performance and compare two different display workstations using the results from the original films as a... more
As part of the evaluation of the display requirements needed in PACS, an ROC curve study was performed in order to assess clinical performance and compare two different display workstations using the results from the original films as a reference. It was found that in both cases the ROC curves obtained from the displays were significantly worse than obtained from the original film. It is therefore suggested that considerable care needs to be paid to the performance of such displays for them to fulfil the requirements of a clinically viable PACS system.
An important aim in SPECT, for example in the measurement of cerebral function using labelled amines such as IMP and HIPDM is to quantitate regional uptake in terms of activity concentration. However a major requirement for such systems... more
An important aim in SPECT, for example in the measurement of cerebral function using labelled amines such as IMP and HIPDM is to quantitate regional uptake in terms of activity concentration. However a major requirement for such systems is to be able to perform an accurate attenuation correction independent of object activity distribution. This is clearly not the case with
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Page 1. Abstract We propose a novel approach to improve further the quality of recovered images from standard super-resolution reconstruction, using Lewitt's Kaiser-Bessel window functions (blobs) as the basis functions instead of... more
Page 1. Abstract We propose a novel approach to improve further the quality of recovered images from standard super-resolution reconstruction, using Lewitt's Kaiser-Bessel window functions (blobs) as the basis functions instead of normal pixels or voxels. ...
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Dual isotope-imaging has a high clinical potential in the assessment of brain perfusion (HMPAO-Tc-99m) and neurotransmission (IBZM-I-123) but is affected by cross-talk between the two radionuclides. We developed a new cross-talk... more
Dual isotope-imaging has a high clinical potential in the assessment of brain perfusion (HMPAO-Tc-99m) and neurotransmission (IBZM-I-123) but is affected by cross-talk between the two radionuclides. We developed a new cross-talk correction method based on artificial neural networks (ANN). The ANN learning phase was performed using a Monte Carlo (MC) simulation of a geometrical phantom. The ANN correction was evaluated
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In radiotherapy treatment, the calculation of radiation dose distribution in target volume lead to an optimum set of planning parameters. This worked has been aimed to compare two photon beam dose calculation algorithms in the Oncentra... more
In radiotherapy treatment, the calculation of radiation dose distribution in target volume lead to an optimum set of planning parameters. This worked has been aimed to compare two photon beam dose calculation algorithms in the Oncentra Treatment Planning system for Varian Linear Accelerator, to assure the quality of treatment planning. Monitor Units to be delivered on normalization depth in patient has been calculated using the pencil beam and collapsed cone algorithms for two photon energies 6 and 10 MV. The percentage depth dose and beam profiles for 21 treatment fields, for both the calculation systems have been compared for both photon energies. The percentage depth doses and beam profiles for both calculation systems are comparable in large field sizes as well as central axis field settings. The doses normalization depth deviate for some field settings, but in central axis large field sizes the difference within tolerance limits. Both calculation algorithms are in close agreeme...
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The DynamicSpatial Reconstructor (DSR) is a 14 x-ray source video imaging system which operates on the computerized tomography scanning principle. It scans a cylindrical volume 18. 5 cm in axial height with equal resolution in the... more
The DynamicSpatial Reconstructor (DSR) is a 14 x-ray source video imaging system which operates on the computerized tomography scanning principle. It scans a cylindrical volume 18. 5 cm in axial height with equal resolution in the transverse and axial directions and repeats this volume scan (of up to 240 0. 7 mm thick parallel slices) at 16. 67 ms intervals. The output of each of the 14 video imaging systems is A/D converted shading corrected and stored in 64 megabytes of memory. The memory is used efficiently because the shading correction reduces the gray scale information of the pixels from 12 to 10 bits and because we need record only a selectable region of interest within the full video image. 1_. THE DSR SCANNER SYSTEM The DSR imaging system (Figure 1) consists of 14 rotating-anodeS x-ray sources which sequentially irradiate the object of study during the first 10. 5 ms of each 16. 67 ms sequence. '' Figure 1 - Photograph of the DSR scanner. Note several of the x-ray t...
In the early stages of articular cartilage disease, the most prevalent of which is osteoarthritis (OA), changes occur in the cartilage matrix, where a loss of proteoglycans and changes to the network of collagen fibrils in the... more
In the early stages of articular cartilage disease, the most prevalent of which is osteoarthritis (OA), changes occur in the cartilage matrix, where a loss of proteoglycans and changes to the network of collagen fibrils in the extracellular matrix are observed (1). This occurs before any morphological changes to the cartilage, and therefore both thickness and volume measurements are insensitive to the initial stages of disease progression. The current clinical standard for evaluating the progression of OA involves examining the joint space width from x-ray images, and is therefore insensitive to early stage disease. In order to clinically monitor early stage disease and potential treatments, methods to determine changes to the cartilage matrix need to be developed. MRI techniques have shown promise in evaluating the constituents of the cartilage matrix. The mechanical properties of articular cartilage are determined by contributions from both the collagen fibrils and the proteoglyca...
Renal transplant recipients (RTRs) have a high incidence of erectile dysfunction (ED). Differentiation of penile vasculogenic impotence from other causes is important for treatment. Conventional 2-D color Doppler assessment after... more
Renal transplant recipients (RTRs) have a high incidence of erectile dysfunction (ED). Differentiation of penile vasculogenic impotence from other causes is important for treatment. Conventional 2-D color Doppler assessment after intracavernosal stimulant injection often fails to produce reliable results because of limited views by the cross-sectional imaging and the painful procedure. In comparison to the findings in three healthy volunteers, we determined cavernosal vascular hemodynamics in eight RTRs with ED before and after oral sildenafil by using live 3-D ultrasound and dynamic 3-D color Doppler. Results showed that, before sildenafil, penile arterial flow signals could only be reliably detected in one patient. After sildenafil, all had reliably detectable flow with grades II to III erection. Our data suggest that 3-D volumetric changes of the penis and its vasculature during erection can be studied by this technique and that this method could be useful for the evaluation of n...