Measuring temporal stability of positron emission tomography standardized uptake value bias using long-lived sources in a multicenter network

Abstract

Positron emission tomography (PET) is a quantitative imaging modality, but the computation of standardized uptake values (SUVs) requires several instruments to be correctly calibrated. Variability in the calibration process may lead to unreliable quantitation. Sealed source kits containing traceable amounts of [Formula: see text] were used to measure signal stability for 19 PET scanners at nine hospitals in the National Cancer Institute's Quantitative Imaging Network. Repeated measurements of the sources were performed on PET scanners and in dose calibrators. The measured scanner and dose calibrator signal biases were used to compute the bias in SUVs at multiple time points for each site over a 14-month period. Estimation of absolute SUV accuracy was confounded by bias from the solid phantoms' physical properties. On average, the intrascanner coefficient of variation for SUV measurements was 3.5%. Over the entire length of the study, single-scanner SUV values varied over a range of 11%. Dose calibrator bias was not correlated with scanner bias. Calibration factors from the image metadata were nearly as variable as scanner signal, and were correlated with signal for many scanners. SUVs often showed low intrascanner variability between successive measurements but were also prone to shifts in apparent bias, possibly in part due to scanner recalibrations that are part of regular scanner quality control. Biases of key factors in the computation of SUVs were not correlated and their temporal variations did not cancel out of the computation. Long-lived sources and image metadata may provide a check on the recalibration process.

Prospective Study of Serial 18F-FDG PET and 18F-Fluoride PET to Predict Time to Skeletal-Related Events, Time to Progression, and Survival in Patients with Bone-Dominant Metastatic Breast Cancer

“…Fasting was not required for 18 F-NaF PET studies, and patients underwent a 60-min dynamic scan before the torso survey. Scanners were calibrated using the manufacturer's recommended procedures and crosscalibrated regularly for quantitative comparisons (38,39). Most patients were imaged on the same scanner in serial studies for each tracer; however, because of the addition of a second GE Discovery STE PET/CT at our center, some patients underwent scan2 on the alternate scanner.…”

Simultaneous Estimation of Bias and Resolution in PET Images with a Long-Lived “Pocket” Phantom System

“…Currently, efforts to reduce variability in PET mainly consist of accreditation procedures ( 30 ) and consensus documents on best practices ( 31 – 33 ). Scanner accreditation often involves “cross calibration,” in which dose calibrator and scanner measurements are required to concur, but this process may not ensure biases are stable over time ( 13 ).…”

“…SUV bias due to this scale factor, or calibration bias, is unstable even when measurements are repeated at a single site ( 11 , 12 ). Further, biases of key factors in the computation of SUVs, from PET scanners and dose calibrators, are not correlated and thus do not cancel out ( 11 , 13 ).…”

Bias in PET Images of Solid Phantoms Due to CT-Based Attenuation Correction

“…It was made from the same epoxy as the above sources. We have previously reported on its signal properties and the bias between measured values and known tracer concentration (19, 20).…”

“…These phantoms' physical properties are well-matched to patient scans, to the extent that water-filled phantom scans are routinely used to measure the calibration factors used to convert clinical scans from a scanner's arbitrary units to true nuclide concentration. However, recent reports suggest that this calibration process may result in increased variability in PET signal, likely owing to difficulties in repeatedly refilling short-lived phantoms each time the phantom is used (19).…”