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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    European journal of nuclear medicine 23 (1996), S. 1300-1308 
    ISSN: 1619-7089
    Keywords: Myocardial single-photon emission tomography ; Scatter correction ; 180° acquisition ; Quantification ; Transmission-based correction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Meaningful comparison of single-photon emission tomographic (SPET) reconstructions for data acquired over 180° or 360° can only be performed if both attenuation and scatter correction are applied. Convolution subtraction has appeal as a practical method for scatter correction; however, it is limited to data acquired over 360°. A new algorithm is proposed which can be applied equally well to data acquired over 180° or 360°. The method involves estimating scatter based on knowl edge of reconstructed transmission data in combination with a reconstructed estimate of the activity distribution, obtained using attenuation correction with broad beam attenuation coefficients. Processing is implemented for planes of activity parallel to the projection images for which a simplified model for the scatter distribution may be applied, based on the measured attenuation. The appropriate broad beam (effective) attenuation coefficients were determined by considering the scatter buildup equation. It was demonstrated that narrow beam attenuation coefficients should be scaled by 0.75 and 0.65 to provide broad beam attenuation coefficients for technetium-99m and thallium-201 respectively. Using a thorax phantom, quantitative accuracy of the new algorithm was compared with conventional transmission-based convolution subtraction (TDCS) for 360° data. Similar heart to lung contrasts were achieved and correction of 180° data yielded a 10.4% error for cardiac activity compared to 5.2% for TDCS. Contrast for myocardium to ventricular cavity was similarly good for scatter-corrected 180° and 360° data, in contrast to attenuation-corrected data, where contrast was significantly reduced. The new algorithm provides a practical method for correction of scatter applicable to 180° myocardial SPET.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1619-7089
    Keywords: Radionuclide gated heart pool scan ; Diastole ; Peak filling rate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Abnormal left ventricular diastolic function is being increasingly recognised in patients with clinical heart failure and normal systolic function. A simple routine radionuclide measure of diastolic function would therefore be useful. To establish this, the relationship of peak diastolic filling rate (normalized for either end diastolic volume, stroke volume, or peak systolic emptying rate), and heart rate, age, and left ventricular ejection fraction was studied in 64 subjects with normal cardiovascular systems using routine gated heart pool studies. The peak filling rate, when normalized to end diastolic volume, correlated significantly with heart rate, age and left ventricular ejection fraction, whereas normalization to stroke volume correlated significantly to heart rate and age but not to left ventricular ejection fraction. Peak filling rate normalized for peak systolic emptying rate correlated with age only. Multiple regression equations were determined for each of the normalized peak filling rates in order to establish normal ranges for each parameter. When using peak filling rate normalized for end diastolic volume or stroke volume, appropriate allowance must be made for heart rate, age and ejection fraction. Peak filling rate normalized to peak ejection rate is a heart rate independent parameter which allows the performance of the patient's ventricle in diastole to be compared with its systolic function. It may be used in patients with normal systolic function to serially follow diastolic function or if age corrected, to screen for diastolic dysfunction.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    European journal of nuclear medicine 25 (1998), S. 1658-1665 
    ISSN: 1619-7089
    Keywords: Key words: Single-photon emission tomography ; Scatter correction ; Maximum likelihood reconstruction ; Monte Carlo simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Definition of a simplified model of scatter which can be incorporated in maximum likelihood reconstruction for single-photon emission tomography (SPET) continues to be appealing; however, implementation must be efficient for it to be clinically applicable. In this paper an efficient algorithm for scatter estimation is described in which the spatial scatter distribution is implemented as a spatially invariant convolution for points of constant depth in tissue. The scatter estimate is weighted by a space-dependent build-up factor based on the measured attenuation in tissue. Monte Carlo simulation of a realistic thorax phantom was used to validate this approach. Further efficiency was introduced by estimating scatter once after a small number of iterations using the ordered subsets expectation maximisation (OSEM) reconstruction algorithm. The scatter estimate was incorporated as a constant term in subsequent iterations rather than modifying the scatter estimate each iteration. Monte Carlo simulation was used to demonstrate that the scatter estimate does not change significantly provided at least two iterations OSEM reconstruction, subset size 8, is used. Complete scatter-corrected reconstruction of 64 projections of 40×128 pixels was achieved in 38 min using a Sun Sparc20 computer.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    European journal of nuclear medicine 24 (1997), S. 797-808 
    ISSN: 1619-7089
    Keywords: Single-photon emission tomography ; Maximum likelihood reconstruction ; Fast image processing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Although the potential benefits of maximum likelihood reconstruction have been recognised for many years, the technique has only recently found widespread popularity in clinical practice. Factors which have contributed to the wider acceptance include improved models for the emission process, better understanding of the properties of the algorithm and, not least, the practicality of application with the development of acceleration schemes and the improved speed of computers. The objective in this article is to present a framework for applying maximum likelihood reconstruction for a wide range of clinically based problems. The article draws particularly on the experience of the three authors in applying an acceleration scheme involving use of ordered subsets to a range of applications. The potential advantages of statistical reconstruction techniques include: (a) the ability to better model the emission and detection process, in order to make the reconstruction converge to a quantitative image, (b) the inclusion of a statistical noise model which results in better noise characteristics, and (c) the possibility to incorporate prior knowledge about the distribution being imaged. The great flexibility in adapting the reconstruction for a specific model results in these techniques having wide applicability to problems in clinical nuclear medicine.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    European journal of nuclear medicine 24 (1997), S. 797-808 
    ISSN: 1619-7089
    Keywords: Key words: Single-photon emission tomography ; Maximum likelihood reconstruction ; Fast image processing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Although the potential benefits of maximum likelihood reconstruction have been recognised for many years, the technique has only recently found widespread popularity in clinical practice. Factors which have contributed to the wider acceptance include improved models for the emission process, better understanding of the properties of the algorithm and, not least, the practicality of application with the development of acceleration schemes and the improved speed of computers. The objective in this article is to present a framework for applying maximum likelihood reconstruction for a wide range of clinically based problems. The article draws particularly on the experience of the three authors in applying an acceleration scheme involving use of ordered subsets to a range of applications. The potential advantages of statistical reconstruction techniques include: (a) the ability to better model the emission and detection process, in order to make the reconstruction converge to a quantitative image, (b) the inclusion of a statistical noise model which results in better noise characteristics, and (c) the possibility to incorporate prior knowledge about the distribution being imaged. The great flexibility in adapting the reconstruction for a specific model results in these techniques having wide applicability to problems in clinical nuclear medicine.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    European journal of nuclear medicine 24 (1997), S. 713-715 
    ISSN: 1619-7089
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1619-7089
    Keywords: Ventricular stroke volume ; Radionuclide angiography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The relationship between radionuclide and thermodilution measurement of stroke volumes (SV) was investigated in 30 patients without valvular regurgitation or intracardiac shunt (group A) at rest and during exercise. Both attenuated radionuclide right ventricular (RV) and left ventricular (LV) SV measurements correlated well with the SV determined by the thermodilution method (r=0.87 and r=0.93, all P〈 0.001). The reliability of the radionuclide method to estimate SV was evaluated prospectively in two additional groups of patients. In 11 patients without valvular regurgitation or intracardiac shunt (group B) the radionuclide RVSV and LVSV closely approximated to thermodilution SV at rest and during exercise. In 15 patients with aortic regurgitation (group C) the radionuclide stroke volume ratio correlated well with the angiographic regurgitant fraction. Thus, both RVSV and LVSV and the severity of aortic regurgitation can be reliably measured with gated radionuclide ventriculography.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1619-7089
    Keywords: Gallium 67 scanning ; Lymphoma ; Hodgkin's disease ; Non-Hodgkin's ; Instrumentation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Gallium 67 scanning in the malignant lympho mas has been done, with variable success, for over 20 years. After initial enthusiasm, the technique fell into disrepute and it was not until the early 1980s that it enjoyed a revival. There have been many major contributions to the literature, both favourable and unfavourable. The reasons for the latter include: poor instrumentation (only single-pulse height analysis), low gallium 67 doses, impatient and careless scanning techniques, timing of the study after treatment (chemotherapy, radiation) and insensitive methods of confirmation of the presence or absence of disease (“truth”). Anatomical diagnostic techniques (computed tomography, plain X-radiography, magnetic resonance imaging and others) are incapable of distinguishing viable tumour in normal size lymph nodes or necrotic/fibrotic residual masses. With improvements in instrumentation (triple-pulse height analysis, gamma camera resolution and tomographic techniques) gallium 67 can detect active tumour in residual masses and in normal-size nodes. This is due to gallium 67's unique ability to localize in viable tumour cells. It has greater than 90% sensitivity, specificity, accuracy and positive predictive value in patients with lymphoma. Its major contributions are in: staging (changing management of mediastinal disease, obviating the need for a laparotomy and clearlyidentifying stage IV disease); detecting relapse or residual, progressive disease (it establishes true complete remission and is often the first and only evidence of relapse before clinical evidence); predicting response to therapy (failure to convert to a negative scan post-treatment signals a poor prognosis and alternative therapy is required); and predicting outcome — prognosis (it is the only diagnostic modality to predict outcome accurately).
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    European journal of nuclear medicine 24 (1997), S. 713-715 
    ISSN: 1619-7089
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    Location Call Number Limitation Availability
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