SUV (nuclear medicine)
The acronym SUV stands for ' s tandardized u ptake v alue' and is used in positron emission tomography used for physiological quantification of regional radioactivity concentrations. The SUV value describes the glucose metabolism of a tumor quantitatively , for example when using the tracer FDG . The SUV value is the ratio to the injected activity and is calculated as follows:
SUV = activity concentration [Bq / ml] * normalization value / applied activity [Bq].
The normalization value contains the physical device correction parameters (attenuation correction, scatter correction, dead time correction, etc.) as well as the following patient or examination-specific information: radionuclide used (because of the decay correction), patient weight, patient size, activity of the full syringe, activity of the empty syringe , Time of injection, time of examination and time of measurement of the empty syringe.
For an inter-individual comparison, the activity is standardized either on body weight (BW [g]), on lean body mass (LBM [kg]) or on body surface area (BSA [m²]). If the radioactivity is evenly distributed, the result is an SUV value of 1, values greater than one describe an enrichment, values less than one a depletion. Since a tracer is not evenly distributed in the body, values between 1 and 2 are usually present in healthy tissue - provided that there is no physiological accumulation there, e.g. B. in the brain, heart, kidney and bladder or hardly any FDG can be found such as in adipose tissue or in cysts (see figure). The SUV value helps to differentiate between malignant (malignant) and benign (benign) tissue; Values up to approx. 20 occur in tumors, but it is subject to a number of influencing factors:
- Lesion or ROI shape and size: Small lesions (<1 cm) show high measurement uncertainties due to partial volume artifacts of the scanner.
- Time of measurement: Although the radioactive decay is taken into account in the normalization value, the accumulation in the lesion is not constant over time due to its pharmacokinetics . If two measurements are to be comparable, it must be ensured that both measurements were taken at the same time after the tracer was injected.
- Patient's blood sugar level: When the blood sugar level is high, FDG accumulates less.
- Patient's weight and fat percentage.
- Scanner design: The quality of the physical correction of the measurement signals as well as the spatial resolution of clinical PET scanners differs (manufacturer, type and age of the device) and has a significant influence on the level and measurement uncertainty of the determined SUV value.
- Selected image reconstruction method ( FBP or iterative) and the parameters of the image reconstruction.
- Physiological movement of the lesion: A metastasis located in the base of the lungs or in the liver, for example, is sometimes moved several centimeters by the patient's breathing movement during the recording, as the recording time (1–3 minutes) exceeds the maximum possible breath-hold time. The measured uptake is therefore "smeared" in the image - comparable to blurring in photography. This can mean that a lesion can no longer be recognized as such. Some newer PET scanners have what is known as breath triggering, in which this disruptive influence can largely be eliminated.
For the reasons mentioned, the SUV value is primarily recommended to describe the course of therapy or the response to therapy. Some of the above-mentioned influencing parameters remain constant in the measurements or can be kept constant.
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- Bernd J. Krause, Andreas K. Buck, Markus Schwaiger: Nuclear Medical Oncology. In: ecomed Medizin (c) 2007, ISBN 978-3-609-76308-8 , p. 56 ff.
- Sally F. Barrington, Michael N. Maisey and Richard L. Wahl: Atlas of Clinical Positron Emission Tomography. Second edition. Hodder Arnold, 2006, ISBN 0-340-81693-7 , pp. 24 and 25.
- GE Advantage Workstation Operating Instructions, Version 4.4