Tumor quantification in clinical positron emission tomography

Abstract

Positron emission tomography (PET) is used extensively in clinical oncology for tumor detection, staging and therapy response assessment. Quantitative measurements of tumor uptake, usually in the form of standardized uptake values (SUVs), have enhanced or replaced qualitative interpretation. In this paper we review the current status of tumor quantification methods and their applications to clinical oncology. Factors that impede quantitative assessment and limit its accuracy and reproducibility are summarized, with special emphasis on SUV analysis. We describe current efforts to improve the accuracy of tumor uptake measurements, characterize overall metabolic tumor burden and heterogeneity of tumor uptake, and account for the effects of image noise. We also summarize recent developments in PET instrumentation and image reconstruction and their impact on tumor quantification. Finally, we offer our assessment of the current development needs in PET tumor quantification, including practical techniques for fully quantitative, pharmacokinetic measurements.

Keywords: Positron emission tomography; tumor quantification.

Fig 1

PET tumor quantification improves prediction of patient survival. Kaplan-Meier plots for estimating probability of event free survival (EFS) according to PET status at mid therapy. (A) Survival curves based on visual analysis. (B) Survival curves based on percentages of SUV_max reduction. Reprinted by permission of the Society of Nuclear Medicine from Lin et al.

Fig 2

Effect of uptake time on measured changes in ¹⁸F-FDG SUV between pre-therapy baseline and intra-therapy follow-up scans. Data were taken from 60 min dynamic ¹⁸F-FDG PET studies. Each symbol and line represents data from a single subject. (A) Tracer uptake times were equal in response and baseline studies. (B) 10-min mismatch in uptake time between response and baseline studies. In B, baseline uptake period was set at 48 min, and response uptake time was set at 38 min or 58 min. When the uptake times differed by 10 min, there were significant differences in observed responses (paired t test, P<0.0001). Reprinted by permission of the Society of Nuclear Medicine from Boellaard et al.

Fig 3

Repeatability of SUV_max and SUV_mean(MVBT). Threshold for SUV_mean = 50% of SUV_max. Estimated study-specific SD (colored dashed lines; study as a fixed effect) and overall SD (black solid lines; study as a random effect) of SUV_max (A) and SUV_mean (D). Test and retest scan values of SUV_max (B) and SUV_mean (E) plotted on original scale. Solid line is coefficient of repeatability (CR95). Relationship between CR95, expressed as percentage change, and level of SUV_max (C) and SUV_mean (F). Reprinted by permission of the Society of Nuclear Medicine from de Langen et al.

Fig 4

Image reconstruction-based (OSEM-NM, OSEM-M) vs. image deconvolution-based (ΔLR) and GTM (Mask-based) partial volume correction. Shown are recovery coefficients for six hot spheres positioned in the NEMA NU2 image quality phantom. Reprinted with permission from Hoetjes et al.

Fig 5

Quantification of intra-tumoral uptake heterogeneity. Cumulative SUV-volume histograms for a diagnostic lung tumor study (a) and lung tumor response study (b). VOIs of response scans were either defined on the baseline scan (VOI^BL) or on the response scan (VOI^R). Reprinted with permission from van Velden et al.