PURPOSE: The potential for improving the diagnostic performance of static positron imaging tomography (PET) by judiciously choosing optimum post-injection imaging times is investigated. PROCEDURES: Dynamic and whole-body scan data, from 2-deoxy-2-[18F]fluoro-D-glucose (FDG) oncological studies, are analyzed for changing standardized uptake value (SUV) behavior with increasing post-injection times at either single- or multiple-bed positions. Model-based interpretations address d(SUV)/dt, shown to correlate with SUV, and the contrast ratio for a tumor and its surroundings. A method for correcting measurements to a standardized time is given. RESULTS: Both data and model-based equations suggest that starting data acquisition later than the average 55 +/- 15 (SD) minutes post-injection reported in the FDG literature can improve contrast ratios. Considerations for choosing an optimum time from a clinical standpoint are listed. CONCLUSIONS: It is concluded that the appropriate time for each particular protocol can be found with the aid of the information presented here. True optimization, however, remains a complex issue.

Journal Article↗

PubMedDate not supplied

2-deoxy-2-[F-18]fluoro-D-glucose-positron emission tomography sensitivity to serum glucose: a survey and diagnostic applications.

OBJECTIVE: The positron emission tomography (PET) clinical utility of the sensitivity (gamma) of uptake (Q) to a change in plasma glucose concentration (C) is investigated. METHODS: Gamma is obtained from data as [ln(Q (2)/Q (1))] / [ln(C(2)/C(1))], using previously published intrapatient studies varying C within a single patient and some interpatient ones. It can be theoretically related to the half-saturation constant in the Michaelis-Menten quantification of competitive uptake. One of its uses is making uptake corrections for desired vs. actual C using Q(2) = Q(1) (C(2)/C(1))(gamma). RESULTS: Intrapatient studies proved to be preferable to interpatient ones, and a 2-deoxy-2-[F-18]fluoro-D-glucose (FDG)-PET survey with analyses for gamma yielded the following result: usually the gamma values of tumors and brain tissues were near -1, whereas those of other noncerebral tissues were near 0. Regarding correcting uptakes for C, instead of a universally assumed and applied gamma = -1, corrections should be for a single tissue using its known gamma. An advantageous use of gamma is predicting how C affects image contrast, including where glucose loading is sometimes preferable to fasting. CONCLUSIONS: A potentially useful quantifier of uptake sensitivity to plasma glucose has been defined and values obtained. Correcting uptakes to some standard C requires special care. gamma can help PET clinicians select fasting or loading to achieve glucose levels for optimum contrast.

Blood Glucose↗

PubMedDate not supplied

A weight index for the standardized uptake value in 2-deoxy-2-[F-18]fluoro-D-glucose-positron emission tomography.

INTRODUCTION: Known errors in the standardized uptake value (SUV) caused by variations in subject weights W encountered can be corrected by lean body mass or body surface area (bsa) algorithms replacing W in calculations. However this is infrequently done. The aims of the work here are: quantify sensitivity to W, encourage SUV correction with an approach minimally differing from tradition, and show what improvements in the SUV coefficient of variation (cv) for a population can be expected. METHODS: Selected for analyses were 2-deoxy-2-[F-18]fluoro-D-glucose (FDG) SUV data from positron emission tomography (PET) and PET/computed tomography (CT) scans at the University of Tennessee as well as from the literature. A weight sensitivity index was defined as -n=slope of ln(SUV/W) vs. lnW. The portion of the SUV variability due to this trend is removed by using the defined [formula: see text], or a virtually equal SUVm using [formula: see text], with Q and ID being tissue specific-activity and injected dose. [formula: see text] measures performance. Adapting to animal studies' tradition, [formula: see text] is preferred over the conventional [formula: see text]. RESULTS: For FDG in adults [formula: see text] from averaging over most tissues. In children, however, [formula: see text]. Tissues have the same index if their influx constants are independent of W. Suggested, therefore, is a very simplified [formula: see text], which is dimensionless and keeps the same population averages as traditional SUVs. It achieves [formula: see text]. Hence, for cv's of SUVs below approximately 1/3 improvements over tradition are possible, leading to F's<0.95. Accounting additionally for height, as in SUVbsa, gives very little improvement over the simplified approach here and gives essentially the same F's as SUVm. CONCLUSIONS: Introduced here is a weight index useful in reducing variability and further understanding the SUV. Addressing weight sensitivity is appropriate where the cv of the SUVs is below about 1/3. Proposed is the very simple approach of using an average of an adult patient's weight and approximately 70 kg for FDG SUV calculations. Unlike other approaches the dimensionless population average of SUVms is unchanged from tradition.

Adult↗

PubMedDate not supplied

Degree of fractal behavior as a diagnostic aid in quantitative image analyses.

PURPOSE: Multiple strategies in diagnoses of different diseases from images can include their histogram analyses. Any fractal behavior in the latter is to be quantified as to extent here, with a view toward contributing to a diagnostic process. PROCEDURE: One tool in quantitative image analyses is the fractal dimension D of the pixel histogram, a measure of self-similarity over various scales in a fitted power-law behavior of pixel intensity cumulative probability distribution. Proposed and developed here as diagnostic markers are features of its determination process that indicate to what extent there is fractal behavior. One of these is the curvature c that exists in log-log plots used for extracting the fractal exponent D of power-law behavior. RESULTS: Specific implementations are given both for a general lognormal pixel intensity distribution and for lung images. Both Ds and cs are determined for: normals, pulmonary embolism, cystic fibrosis, as well as a theoretical lognormal distribution. It is shown that D and heterogeneity described by a standard deviation are reciprocally related and not typically independent markers. The added independent information from c has possibilities of assisting in discrimination of normal and pathologic conditions, such as in lung diseases. CONCLUSION: In addition to a histogram's fractal dimension itself, there are indications that measures of the degree of fractal behavior may also hold promise in image diagnoses.

Animals↗