Subcentimeter Tumor Lesion Delineation for High-Resolution 18F-FDG PET Images: Optimizing Correction for Partial-Volume Effects

Abstract

In PET, partial-volume effects cause errors in estimation of size and activity for small objects with radiopharmaceutical uptake. Recent methods for image reconstruction, compared with traditional reconstruction techniques, include algorithms for resolution recovery that result in images with higher resolution and enable quantification of size and activity of smaller objects. The purpose of this study was to evaluate a combination of 2 algorithms for volume delineation and partial-volume correction on uptake volumes smaller than 0.7 mL using image reconstruction algorithms with and without resolution recovery. Methods: Volumes of interests (VOIs) were delineated using a threshold intensity calculated as a weighted sum of tumor and background intensities. These VOIs were used for calculating correction factors by convolving a tumor mask with the system point-spread function. The methods algorithms were evaluated using a phantom constructed from 5 small different-sized balloons filled with 18 F-FDG in background activity. Six different backgrounds were used. Data were acquired using a PET/CT scanner, and the images were reconstructed using 2 iterative algorithms, one of which used a resolution recovery algorithm. Results: For the images reconstructed using the resolution recovery algorithm, the method for volume delineation resulted in VOI sizes that were correct within 1 SD for all balloons of a volume of 0.35 mL (equivalent diameter, 8.8 mm) and larger, in all backgrounds. For the images reconstructed without resolution recovery, the VOI sizes were background-dependent and generally less accurate. Correct volume delineations generally led to accurate activity estimates. Conclusion: The algorithms tested on the phantom developed for this study could, for this PET camera and these reconstruction algorithms, be used for accurate volume delineation and activity quantification of lesions 0.35 mL and larger. PETwi th 18 F-FDG is frequently used for diagnosis and staging of tumors and for therapy evaluation (1). Many methods for analyzing 18 F-FDG uptake in tumors are quantitative or semiquantitative (2), and a frequently used measure is the standardized uptake value (SUV) (3). SUV is subject to several factors affecting its reliability, such as motion artifacts, dependence on time between injection and image acquisition, and the method used for volume delineation (4). In addition to these, the relatively poor spatial resolution introduces biases, especially for small objects (5), such as small tumors and lymph nodes. This is called the partial-volume effect (PVE) (6). There is a demand for more complex algorithms for correct delineation also for larger tumors (7), and because SUV plays an important prognostic role in many cancer studies, such as non-small cell lung cancer imaging, there is a need for correct delineation and SUV calculations (8). Many studies have been performed on this subject (9-11) for varying objects and resolution. There are also extensive reviews on the subject (5,12).The spatial resolution of PE...

Positron range in PET imaging: non-conventional isotopes

“…PET scanners with "resolution-recovery" algorithms have become available. These algorithms usually account for all resolution-degrading effects and are typically based on measurements of pointlike sources for the determination of point-spread functions (Mourik et al 2010;Narayanan and Perkins 2013;Wallsten et al 2013). This is a simple and effective approach when only one isotope is to be used (e.g., 18 F) or when the contribution of the positron range is small compared to the other effects.…”

Accuracy and Precision of Partial-Volume Correction in Oncological PET/CT Studies

“…Clinical repeatability data consisted of an 18 F-FDG PET/CT study (28) on 11 patients with advanced non-small cell lung cancer and an 18 Ffluoromethylcholine PET/CT study (29) on 12 patients with metastatic prostate cancer. At the time the patients underwent PET, they received no treatment.…”

“…They fasted for 6 and 4 h before undergoing 18 F-FDG and 18 F-fluoromethylcholine PET, respectively. PET/CT scans were acquired at 60 and 40 min after injection of 185 MBq of 18 F-FDG and 200 MBq of 18 F-fluoromethylcholine, respectively. Images were reconstructed using ordered-subset time-of-flight iterative reconstruction with 3 iterations and 33 subsets, with and without resolution modeling.…”

“…However, each method has its limitations, and new methodology is still being developed. Some are adaptations of the recovery coefficient method (15,16), but others are more refined, such as resolution modeling (17,18), adaptations of iterative deconvolution (19)(20)(21), adaptations of the geometric transfer matrix (22,23), and background-adapted PVC algorithms (24).…”

“…In the present study, we investigated the effect of several combinations of PVC methods and VOI methods on the accuracy and precision of PET using phantoms and simulations. We also investigated the impact of PVC on the repeatability of 18 F-FDG and 18 F-fluoromethylcholine PET in patients with advanced non-small cell lung cancer and metastatic prostate cancer, respectively.…”