Positron emission tomography-computed tomography standardized uptake values in clinical practice and assessing response to therapy

Abstract

The use of standardized uptake values (SUVs) is now common place in clinical 2-deoxy-2-[(18)F] fluoro-D-glucose (FDG) position emission tomography-computed tomography oncology imaging and has a specific role in assessing patient response to cancer therapy. Ideally, the use of SUVs removes variability introduced by differences in patient size and the amount of injected FDG. However, in practice there are several sources of bias and variance that are introduced in the measurement of FDG uptake in tumors and also in the conversion of the image count data to SUVs. In this article the overall imaging process is reviewed and estimates of the magnitude of errors, where known, are given. Recommendations are provided for best practices in improving SUV accuracy.

Fig 1

Roles of SUVs in Quantitative Imaging with PET/CT.

Fig 2

Error dependency for PET/CT SUVs.

Fig 3

Left: Transverse PET and CT images of a modified NEMA image quality phantom containing six spheres with diameters from 10 to 37 mm. There is a 4:1 sphere:background ratio of FDG concentration in each sphere. Right: Recovery coefficient (ratio of measured/true SUV) as a function of object size for the six spheres. Error bars are based on 20 repeated 5 min scans at typical clinical tissue activity values. (Reprinted with permission from.)

Fig 4

Average breast cancer tumor SUV values versus time from injection for 20 patients. (Reprinted with permission from.)

Fig 5

Injected dose and post-injection residual activity for 250 patients. Data courtesy of Dr Osama Mawlawi, MD Anderson Cancer Center.

Fig 6

Timing of measurement and injection steps needed for accurate decay injection steps.

Fig 7

Effect of increased smoothing on SUV quantitation. S1 and S2 are 1 cm diameter spheres with a true SUV of 4.0 in a torso phantom. Increased smoothing increases the bias of the measured SUV of the small spheres and reduces noise.

Fig 8

Steps in establishing scanner calibration factor.

Fig 9

Steps in generating SUV images showing the dependency on patient weight, decay corrected net injected dose, and scanner calibration factor.

Fig 10

Impact of incorrect scanner calibration on patient SUV values for a large lung lesion (box). Both images are scaled to their maximum values.

Fig 11

Scanner calibration factors measured over a 3.6 year period using standard procedures with ¹⁸F-FDG and with fixed ⁶⁸Ge/⁶⁸Ga source.

Fig 12

Left: Image of a simulated 33 cm diameter cylindrical phantom containing two cylindrical lesions of 2 and 5 cm diameter. The SUVs of the background and lesions are 1.0 and 2.0. Right: Profile is from a reconstructed image including the spatial volume errors and reconstruction smoothing effects. The amount of signal loss in the measured SUV depends on lesion size and position within the lesion.

Fig 13

Use of SUVmax versus SUV mean (and other approaches in scientific publications. Data from Wahl et al. (Reprinted with permission from.)