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A Todd-Pokropek

Publications and source records attributed to A Todd-Pokropek.

At least 19 recordsLinked to original sources
PubMed1995

A new correction method for gamma camera non-uniformity due to energy response variability.

We present a new uniformity correction (Fourier energy correction) which is designed to correct for gamma camera non-uniformity caused by variations of the energy response function within a wide spectral range. A convolution model is used to describe the spatial distortions of the energy response function. The model is solved in Fourier space. A preliminary flood acquisition is required to obtain energy-dependent Fourier weights which are used to correct subsequent acquisitions. The influence of the parameters involved in the correction procedure is studied and the Fourier energy correction is compared to a conventional multiplicative energy correction for different acquisition geometries. The Fourier energy correction appears especially useful when the energy information associated with each detected photon is analysed using a fine sampling, or when windows different from the photopeak window are used.

Biophysical Phenomena↗
PubMed1995

Children with intractable focal epilepsy: ictal and interictal 99TcM HMPAO single photon emission computed tomography.

Fourteen children with intractable complex partial seizures underwent ictal and interictal 99TcM HMPAO single photon emission computed tomography (SPECT) scans. Abnormalities concordant with clinical and/or EEG localisation were present in 13 of 14 ictal and/or interictal scans. Focal hyperperfusion was seen at the seizure focus on ictal scans and focal hypoperfusion was seen on interictal scans. The timing of the injection in relation to the start of the seizure was crucial for reliable localisation. While recognisable patterns of regional cerebral blood flow (rCBF) were seen on either interictal or ictal scans, marked changes in the patterns of rCBF between the ictal study and interictal study provided the most reliable information about seizure localisation. Using both ictal and interictal studies, 99TcM HMPAO SPECT may provide data about both the seizure origin and its relationship to structurally abnormal regions of the brain.

Adolescent↗
PubMed1995

Comparative assessment of nine scatter correction methods based on spectral analysis using Monte Carlo simulations.

UNLABELLED: We compared nine scatter correction methods based on spectral analysis which process SPECT projections. METHODS: Monte Carlo simulation was used to generate histories of photons emitted from a realistic 99mTc phantom. A particular projection was considered. Information regarding the history, location and energy of the photons detected in this projection was analyzed to test the assumptions underlying each scatter correction method. Relative and absolute quantification and signal-to-noise ratio were assessed for each scatter corrected image. RESULTS: For the simulated data, two methods do not enable activity quantification. Among the methods requiring some parameters to be calibrated, the dual-energy window method shows the best compromise between accuracy and ease of implementation but introduces a bias in relative quantification. In this respect, a triple-energy window technique is more accurate than the dual-window method. A factor analysis approach results in more stable quantitative accuracy (error approximately 10%) for a wide range of activity but requires a more sophisticated acquisition mode (30 energy windows). CONCLUSION: These results show that a scatter correction method using spectral analysis can be used to substantially improve accurate quantification.

Humans↗
PubMed1994

Scatter correction in scintigraphy: the state of the art.

In scintigraphy, the detection of scattered photons degrades both visual image analysis and quantitative accuracy. Many methods have been proposed and are still under investigation to cope with scattered photons. The main features of the problem of scattering in radionuclide imaging are presented first, to provide a sound foundation for a critical review of the existing scatter correction techniques. These are described using a classification relating to their aims and principles. Their theoretical potentials are analysed, as well as the difficulties of their practical implementation. Finally, the problems of their evaluation and comparison are discussed.

Humans↗
PubMed1992

User requirements for information systems in nuclear medicine.

In the field of COST cooperation (COST = European Cooperation in the Field of Scientific and Technical Research) a project B2 for Quality Assurance in Nuclear Medicine Software has been established. In a memorandum of understanding setting up this project, user requirements were to be defined for the hardware and software used for data acquisition, processing and presentation. A subgroup of the management committee of COST B2 were interested in the Advanced Informatics in Medicine, AIM, task T-734 'Quality Assurance of Medical Software', and the AIM Project 'A 1034', coordinated by Dr K. Britton, was initiated. The initial drafts of this document were written in Helsinki during 1988-1990, and submitted for comment by the members of the management committee of COST B2. These comments were integrated in the text and this document was finalized by the UK group so as to make it available for international discussion. It is anticipated that, after appropriate international discussion, these User Requirements for Information Systems in Nuclear Medicine will be adopted by the management committee of COST B2 as a COST document. Towards these ends, a working group chaired by Dr Britton, including the British and Finnish teams and Ulrich Noelpp from Switzerland, was appointed by the management committee of COST B2 in April 1990. While writing it we have had the pleasure of working with referees from different European hospitals in many countries. We are happy to thank all of them for their valuable contributions.

Europe↗
PubMed1992

A file format for the exchange of nuclear medicine image data: a specification of Interfile version 3.3.

Working Group 1 of the European project COST-B2 on quality assurance of nuclear medicine software has been concerned with the development of an appropriate mechanism for the transfer of nuclear medicine image data files between computer systems from different vendors. To this end a protocol based upon Report No. 10 of the American Association of Physicists in Medicine (AAPM) [1] was adopted. A previous publication [2] gave a specification (V3.2) for an intermediate file format with a list of key-value pairs for the header data associated with nuclear medicine image data files. This paper presents a revised specification for the intermediate file format and associated keys, now called V3.3, which has evolved from the experience in using the earlier version. It is hoped that the modifications proposed will improve the definition and usability of the file format as given in the earlier version.

European Union↗
PubMed1991

Evaluation of a technique for the intraoperative detection of a radiolabelled monoclonal antibody against colorectal cancer.

Occult tumour deposits may be localised at operation with a radiation detecting probe following the administration of a radiolabelled monoclonal antibody (MoAb) recognising a tumour-associated antigen. We have recently evaluated the clinical usefulness of this technique in detecting primary colorectal tumours targetted with an indium-111 MoAb. In the present study the physical characteristics of the two detector systems used were investigated; a sodium iodide [NaI(Tl)] scintillation detector and a cadmium telluride (CdTe) semiconductor probe. Limitations of the technique in use have been examined by testing the statistical significance of tumour detection using an abdominal phantom based on the currently available clinical biodistribution data for tumour uptake of radiolabelled MoAbs. The effect of tumour volume, antibody uptake, collimation and counting conditions was examined. Results indicate that tumours of 10 ml volume may be detected with the NaI(Tl) probe at the lowest levels of radiolabelled antibody uptake currently reported in the literature but that at higher published levels, lesions as small as 1 ml may be identified with both detector systems. Detector sensitivity and limited antibody specificity restrict the usefulness of the technique, although moderate improvements in tumour uptake may allow the detection of tumour deposits not clinically apparent. The statistical significance criterion used for this study could be an accurate and reliable indicator for tumour detection in vivo.

Colorectal Neoplasms↗
PubMed1991

Measurement of haematological indices of chronic rheumatic disease with two newer generation automated systems, the H1 and H6000 (Technicon).

Two automated counters, the H1 (Technicon) and the H6000 (Technicon), which count 10,000 cells per sample, were compared and used to examine the clinical relevance of the additional haematological information now provided to the rheumatologist in three groups of patients--38 with rheumatoid arthritis (RA), 41 with ankylosing spondylitis (AS), and 35 with systemic lupus erythematosus (SLE). The two machines agreed in their estimations of the main indices (haemoglobin, red blood cell count, and white blood cell count), but estimations of platelet count and volume were significantly lower on the H6000 machine, as were mean cell haemoglobin and monocyte count, whereas packed cell volume and red cell distribution width were higher. As expected, both machines identified pancytopenia among the group with SLE, while low haemoglobin and high platelet count were found particularly among patients with RA and AS respectively. Additional information available from these counters showed marked variability in red cell size in SLE, and also of haemoglobin content, which is only measured on the newer H1 machine. Flags for microcythaemia, anisochromasis, and white cell noise (usually due to nucleated red cells) were all more common in SLE. Interpretation of results was complicated by the inevitable difference in age and sex distribution among the disease groups, and identification of active disease was also limited by the effect of drugs. In conclusion, the increasingly widespread use of automated counters as part of the routine haematological service may provide the rheumatologist with useful information, but, as always, care should be taken in the interpretation of indices in patients receiving non-steroidal or second line agents, and also in extrapolating results from one machine to another when they are updated or when patients are monitored at more than one centre.

Adolescent↗
PubMed1989

Clinical diagnosis from digital displays: preliminary findings of the St Mary's Evaluation Project.

Image quality is a fundamental issue in the introduction of picture archiving and communications systems (PACS), and one that has hitherto been eclipsed by other aspects of the considerable technological challenge facing scientists and manufacturers involved in its development. We conducted a formal evaluation of clinical radiological diagnosis from a commercially available PACS viewing station, using subperiosteal resorbtion in renal osteodystrophy as the test pathological diagnosis, with receiver operating characteristic (ROC) analysis of the results. We conclude that the displayed, digitised images were inferior to film using the apparatus tested and believe that careful, objective clinical evaluation of such systems is of paramount important.

Chronic Kidney Disease-Mineral and Bone Disorder↗
PubMed1988

Background in 99Tcm DTPA renography evaluated by the impact of its components on individual kidney glomerular filtration rate.

Following injection for renography, 99Tcm-labelled diethylenetriamine-pentacetic acid (DTPA) rapidly enters the extravascular space. Background therefore comprises two components, a falling intravascular signal and an extravascular signal which initially rises. We estimated the relative magnitudes of these two components in terms of their impact on the calculation of differential renal function and individual kidney glomerular filtration rate (IKGFR) from the second phase of the 99Tcm-labelled DTPA renogram in 56 paediatric kidneys. We expressed each of the two background signals as a GFR equivalent. The GFR equivalent of the intravascular signal recorded from a peri-renal background region of interest (ROI), scaled by a factor equal to the ratio of the pixel numbers in the renal and background ROIs, was -39 (S.D. 14) ml min-1. The GFR equivalent of the extravascular signal was smaller than this and opposite to it at 23 (S.D. 10) ml min-1, giving a median ratio for the two equivalents of -1.68. Because of the opposing effects of the two background components on the second phase of the renogram, techniques recently described for the quantification of IKGFR from the renogram, and which eliminate the intravascular component, offer no theoretical advantage over a method of analysis which uses 'direct' subtraction of the total background signal. In practice, however, these new techniques are superior in their handling of 'noisy' data, consistently giving a lower coefficient of variation in their estimation of IKGFR.

Child↗
PubMed1988

Appropriate selection of background for 99Tcm-DTPA renography.

Since 99Tcm-DTPA is diffusible and not significantly protein bound in plasma, it rapidly enters the extravascular space following injection. Therefore, during the first few minutes of the DTPA renogram, the period on which the measurements of individual kidney glomerular filtration rate and differential function are based, background activity comprises a rising extravascular signal and a falling intravascular signal. The aim of this study was to measure the ratio of these two signals in background present within the renal region of interest (ROI) and compare it with the ratio in a background ROI. An appropriate background ROI is one in which the ratio is equal to that in background in the renal ROI. To pursue this aim, we quantified the rates of change of the intravascular and extravascular activities in background and, by comparing them with the rate of increase of filtered activity, expressed them as GFR equivalents (the intravascular being negative). It is impossible, from a single renogram, to separate the rising extravascular signal from the signal due to filtered activity, and therefore impossible to quantify the extravascular GFR equivalent present in background within the renal ROI. We therefore studied six patients undergoing bone marrow transplantation before and after cyclosporin treatment. By comparing the dynamic renographic data between the two sequential studies, the substantial fall in GFR (from 107 +/- 12 S.D. to 49 +/- 7 ml min-1) permitted separate quantification of the extravascular GFR equivalent in the renal ROI in both studies. Three of the patients were studied on a third occasion after cyclosporin. In two, GFR remained low and these studies were paired with corresponding baseline studies, while in the other it increased and this was compared with the nephrotoxic study, giving a total of nine paired studies between which GFR changed. The ratio of intravascular to extravascular GFR equivalents in a background ROI placed above the kidney was considerably greater, and in a background ROI below the kidney considerably less, than that in the renal ROI. A background ROI which was the difference between the renal ROI and a perirenal ROI, 2 pixels outside the renal ROI along the horizontal and 1 pixel outside along the vertical, gave a ratio almost identical to that of the background within the renal ROI (renal ROI ratio:background ROI ratio = 1.09 +/- 0.17 S.D., n = 18).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1988

Disease activity in systemic lupus erythematosus related to a range of antibodies binding DNA and synthetic polynucleotides.

Antibodies to dDNA, nDNA, Z-DNA, poly(dT), poly(I), poly(dG.dC), poly(dA.dT), and total IgG and IgM were measured in five serial bleeds from 39 patients with systemic lupus erythematosus (SLE). The main findings were that those patients with renal disease form a distinct subset whose antibody levels correlate well with disease activity; anti-poly(dT) antibodies showed the best overall correlation with disease activity; and discriminant functional analysis demonstrated a major improvement in correlation of disease activity with combinations of antibodies to dDNA/nDNA/Z-DNA/poly(dT) (generally 50% or more were correctly classified) than with dDNA or nDNA alone (generally less than 25% correct). Serum IgG (but not IgM) correlated significantly (p less than 0.01) with six antibodies, suggesting that polyclonal activation plays a part in the development of these antibodies, though antibody cross reactivity is not excluded.

Antibodies↗
PubMed1988

Assessment and comparison of three scatter correction techniques in single photon emission computed tomography.

The detection of scattered radiation is recognized as one of the major sources of error in single photon emission computed tomography (SPECT). In this work three scatter correction techniques have been assessed and compared. Scatter coefficients and parameters characteristic of each technique have been calculated through Monte Carlo simulations and experimentally measured for various source geometries. Their dependence on the source/matter distribution and their spatial non-stationarity have been described. Each of the three scatter correction methods has then been tested on several SPECT phantom studies. The three methods provided comparable results. Following scatter compensation, both image quality and quantitative accuracy improved. In particular a slight improvement in spatial resolution and a statistically significant increase in cold lesion contrast, hot lesion recovery coefficient, and signal/noise ratio have been demonstrated with all methods.

Models, Structural↗
PubMed1987

99mTc DTPA scanning with diuretic washout. Is it useful in the investigation of obstruction in the presence of gross renal tract dilatation?

Diuretic-enhanced 99mTc DTPA renal scanning aims to determine whether or not a kidney is obstructed. In the presence of gross renal tract dilatation the validity of this technique is questioned. Twenty-eight patients (51 kidneys) with the prune belly syndrome, characterised by gross dilatation and tortuosity of the ureters, were studied. These patients underwent diuretic 99mTc DTPA scanning at the time of diagnosis and at yearly intervals thereafter. Long-term clinical follow-up (3 years) with serial serum creatinine was available in all children. In all cases renal function remained stable and on this basis urinary tract obstruction was excluded. Analysis of the first 99mTc DTPA scan included differential function, whole kidney mean transit time (WKMTT) and the time taken for tracer activity to fall to 75% of peak activity after diuretic stimulus (T75). Using the 99mTc DTPA scan, obstruction can be excluded if the WKMTT is less than 5 min or, in the presence of a prolonged WKMTT, if the diuretic stimulus results in a T75 of less than 5 min. A T75 of between 5 and 10 min is considered equivocal and a T75 exceeding 10 min means that obstruction cannot be excluded. 99mTc DTPA scanning, using these criteria for diagnosis, provided false positive information in 22 kidneys (43%). There were no false negatives. 99mTc DTPA scanning with diuretic washout, using WKMTT and T75 criteria, is not appropriate for the detection of renal tract obstruction in the presence of marked upper renal tract dilatation, since the false positive rate of 43% is unacceptably high.

Adolescent↗