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The standardized uptake value (SUV) is often used in positron emission tomography (PET) imaging for a (semi)quantitative analysis. Its use is particularly common in the analysis of ()fluorodeoxyglucose (()FDG) images of cancer patients. It can also be used with other PET agents especially when no arterial input function is available for more detailed pharmacokinetic modeling. Otherwise measures like the fractional uptake rate (''FUR'') or parameters from more advanced pharmacokinetic modeling may be preferable. The ''SUV'' is the ratio of the image derived radioactivity concentration ''cimg'' and the whole body concentration of the injected radioactivity ''cinj'', While this equation looks simple, there are a number of details that need to be discussed, such as (1) the origin of ''cimg'' data, (2) the origin of ''cinj'' data, (3) time, and (4) units. The ''cimg'' data may be the pixel intensities of a calibrated PET image. Calculated ''SUV'' data can then be visualized as parametric ''SUV'' image. Alternatively, groups of such pixels may be selected e.g. by manually drawing or otherwise segmenting a region of interest (ROI) on the PET image. Then e.g. the average intensity of that ROI may be used as ''cimg'' input to calculate ''SUV''s. The ''cinj'' value is calculated as ratio of two independent measurements: the injected radioactivity (injected dose, ID) and the body weight (BW) of the subject. The ID can be estimated e.g. as difference in the radioactivity of the syringe before and after injection, if deemed necessary with correction for physical decay between each of those measurements and the time of injection. Conventionally the time of injection is ''t''=0. This reference concentration represents the hypothetical case of an even distribution of the injected radioactivity across the whole body. SUV values thus quantify the measured deviation from this even radioactivity distribution. The injection of radioactivity is often followed by a waiting time interval and then a time span during which the PET image data are acquired. After image reconstruction, the image ''cimg (t)'' data need to be decay corrected to the injection time point ''t''=0. The time point ''t'' may be the image acquisition start time, or in case of a long acquisition duration e.g. the midpoint of the PET image acquisition may be more appropriate. This decay correction needs to be done for each image in case of a series of images acquired after a single injection ("dynamic imaging"). The unit of ''cimg'' is MBq/mL or equivalent, based on (a) the pixel intensity calibrated with a radioactive source ("phantom") itself of known radioactivity and volume, and (b) the pixel volume or ROI volume. The unit of ''cinj'' is MBq/g or equivalent, based on the measured radioactivity and the subject's body weight. This would give ''SUV'' in units of g/mL or equivalent. However, ''SUV'' is typically presented as a unitless parameter. The reason is that the ROI is usually defined over soft tissue which has a mass density of approximately 1 g/mL. Thus the image derived intensities are implicitly converted by dividing by 1 g/mL to yield ''cimg'' in the same units as ''cinj''. This results in a unitless ''SUV'' parameter. In summary this gives the following equation to calculate ''SUV'' at time ''t'' post injection, The ''SUV'' concept has been only begun to be tested in connection with other radiotracers like ()fluorothymidine (()FLT) and conclusions on its usefulness and robustness in these cases might be premature. In summary, ''SUV''s are a convenient measure for the evaluation of ()FDG PET images within a subject to study e.g. therapy monitoring/therapy response, and also for comparison between subjects. However, care has to be taken with respect to its pitfalls and with respect to the interpretation of the results. == See also == * Functional imaging * Medical imaging * Positron emission tomography * Fluorodeoxyglucose * Multi-compartment model * Patlak plot * Pharmacokinetics * Physiologically-based pharmacokinetic modelling 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Standardized uptake value」の詳細全文を読む スポンサード リンク
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