What is the Standardized Uptake Value (SUV) in Positron Emission Tomography (PET) scans?

From the Guidelines

The Standardized Uptake Value (SUV) is a crucial semi-quantitative measurement in PET scans, representing the ratio of radioactivity concentration in a specific area to the injected dose of radiotracer distributed throughout the body, with higher values often indicating increased metabolic activity. When interpreting PET scans, particularly in the context of lymphoma, the SUV can be used to differentiate between benign and malignant findings, with a cutoff SUVmax of 2.5 potentially being used to exclude lymphoma, as demonstrated by Freudenberg et al 1. Key points to consider when using SUV in PET scan interpretation include:

• The need for a standardized approach to SUV determination to ensure comparability among different sites, including strict adherence to predefined reconstruction algorithms and timing of PET imaging after FDG injection 1.
• The importance of clinical context in interpreting SUV values, as both malignant and benign conditions can exhibit elevated values.
• The use of SUVmax and SUVmean to comprehensively characterize lesions.
• The potential for SUV to help monitor treatment response and detect residual or recurrent disease, although the validity of using absolute SUV or percent reduction in SUV from baseline for PET interpretation at the conclusion of therapy requires further evaluation in rigorous prospective trials 1.

From the Research

Definition of SUV

• The Standardized Uptake Value (SUV) is a semi-quantitative metric used to measure the uptake of a radiotracer in PET scans, such as FDG-PET/CT 2.
• SUV is calculated by dividing the amount of radiotracer taken up by a region of interest by the amount of radiotracer injected into the body, normalized by the patient's weight.

Types of SUV

• There are different types of SUV measures, including SUV(max), SUV(peak), SUV(mean), and SUV(total) 3.
• SUV(max) is the maximum SUV value within a region of interest, while SUV(peak) is the average SUV value within a small region around the maximum uptake.
• SUV(mean) is the average SUV value within a region of interest, and SUV(total) is the total amount of radiotracer taken up by the region.

Factors Affecting SUV

• SUV can be affected by various factors, including the type of radiotracer used, the uptake period, and the imaging protocol 4, 5.
• The uptake period, which is the time between injection of the radiotracer and imaging, can significantly affect SUV values, with longer uptake periods resulting in higher SUV values 4.
• Technical factors, such as scanner calibration and imaging physics, can also affect SUV values 5.

Comparison of SUV Measures

• Different SUV measures can result in varying assessments of treatment response, with SUV(max) and SUV(peak) being more robust to image noise than SUV(mean) and SUV(total) 2, 3.
• The choice of SUV measure can affect the classification of tumor response, with different measures resulting in conflicting categorizations of PET response 3.
• PET/MRI and PET/CT can also result in different SUV values, with PET/MRI systematically undermeasuring SUV compared to PET/CT 6.