Time of Flight (TOF) PET has great potential in whole-body oncological applications and recent work has demonstrated qualitatively in patient studies the improvement that can be achieved in lesion visibility. The aim of this work was to objectively quantify the improvement in lesion detectability that can be achieved in pulmonary and hepatic lesions with whole body FDG TOF-PET in a cohort of 100 patients as a function of patient body mass index (BMI), lesion location and contrast, and scanning time. Methods 100 patients with BMIs ranging from 16 to 45 were included in this study. Artificial 1-cm spherical lesions were imaged separately in air at variable locations of each patient’s lung and liver, appropriately attenuated and incorporated in the patient listmode data with four different lesion-to-background contrast ranges. The fused studies with artificial lesion present or absent were reconstructed using a listmode, un-relaxed OSEM with chronologically ordered subsets and a Gaussian TOF kernel for TOF reconstruction. Conditions were compared on the basis of performance of a 3-channel Hotelling observer (CHO-SNR) in detecting the presence of a sphere of unknown size on an anatomic background while modeling observer noise. Results TOF-PET yielded an improvement in lesion detection performance (ratio of CHO-SNR) over non-TOF PET of 8.3% in the liver and 15.1% in the lungs. The improvement in all lesions was 20.3, 12.0, 9.2 and 7.5% for mean contrast values of 2.0:1, 3.2:1, 4.4:1, and 5.7:1, respectively. Furthermore, this improvement was 9.8% in patients with BMI<30 and 11.1% in patients with BMI>30. Performance plateaued faster as a function of number of iterations with TOF than non-TOF. Conclusion TOF-PET yielded a significant improvement in lesion detection in oncologic studies over all contrasts and BMIs that was greater for lower lesion contrast. This improvement was achieved without compromising other aspects of PET imaging.

Objectives: Focal lesions in infants with congenital hyperinsulinism (HI) represent areas of adenomatosis that express a paternally derived ATP-sensitive potassium channel mutation due to embryonic loss of heterozygosity for the maternal 11p region. This study evaluated the accuracy of 18 F-fluoro-L-dihydroxyphenylalanine ([ 18 F]DOPA) positron emission tomography (PET) scans in diagnosing focal vs. diffuse disease and identifying the location of focal lesions.Design: A total of 50 infants with HI unresponsive to medical therapy were studied. Patients were injected iv with [18 F]DOPA, and PET scans were obtained for 50 -60 min. Images were coregistered with abdominal computed tomography scans. PET scan interpretations were compared with histological diagnoses. Results

Purpose:The variances and biases inherent in quantifying PET tracer uptake from instrumentation factors are needed to ascertain the significance of any measured differences such as in quantifying response to therapy. The authors studied the repeatability and reproducibility of serial PET measures of activity as a function of object size, acquisition, reconstruction, and analysis method on one scanner and at three PET centers using a single protocol with long half-life phantoms. Methods: The authors assessed standard deviations ͑SDs͒ and mean biases of consecutive measures of PET activity concentrations in a uniform phantom and a NEMA NU-2 image quality ͑IQ͒ phantom filled with 9 months half-life 68 Ge in an epoxy matrix. Activity measurements were normalized by dividing by a common decay corrected true value and reported as recovery coefficients ͑RCs͒. Each experimental set consisted of 20 consecutive PET scans of either a stationary phantom to evaluate repeatability or a repositioned phantom to assess reproducibility. One site conducted a comprehensive series of repeatability and reproducibility experiments, while two other sites repeated the reproducibility experiments using the same IQ phantom. An equation was derived to estimate the SD of a new PET measure from a known SD based on the ratios of available coincident counts between the two PET measures. Results: For stationary uniform phantom scans, the SDs of maximum RCs were three to five times less than predicted for uncorrelated pixels within circular regions of interest ͑ROIs͒ with diameters ranging from 1 to 15 cm. For stationary IQ phantom scans from 1 cm diameter ROIs, the average SDs of mean and maximum RCs ranged from 1.4% to 8.0%, depending on the methods of acquisition and reconstruction ͑coefficients of variation range 2.5% to 9.8%͒. Similar SDs were observed for both analytic and iterative reconstruction methods ͑p Ն 0.08͒. SDs of RCs for 2D acquisitions were significantly higher than for 3D acquisitions ͑p Յ 0.008͒ for same acquisition and processing parameters. SDs of maximum RCs were larger than corresponding mean values for stationary IQ phantom scans ͑p Յ 0.02͒, although the magnitude of difference is reduced due to noise correlations in the image. Increased smoothing decreased SDs ͑p Յ 0.045͒ and decreased maximum and mean RCs ͑p Յ 0.02͒. Reproducibility of GE DSTE, Philips Gemini TF, and Siemens Biograph Hi-REZ PET/CT scans of the same IQ phantom, with similar acquisition, reconstruction, and repositioning among 20 scans, were, in general, similar ͑mean and maximum RC SD range 2.5% to 4.8%͒. Conclusions: Short-term scanner variability is low compared to other sources of error. There are tradeoffs in noise and bias depending on acquisition, processing, and analysis methods. The SD of a new PET measure can be estimated from a known SD if the ratios of available coincident counts between the two PET scanner acquisitions are known and both employ the same ROI definition. Results suggest it is feasible to use PET/CTs from different vendors and...

The PET Core Laboratory of the American College of Radiology Imaging Network (ACRIN) qualifies sites to participate in multicenter research trials by quantitatively reviewing submitted PET scans of uniform cylinders to verify the accuracy of scanner standardized uptake value (SUV) calibration and qualitatively reviewing clinical PET images from each site. To date, cylinder and patient data from 169 PET scanners have been reviewed, and 146 have been qualified. Methods: Each site is required to submit data from 1 uniform cylinder and 2 patient test cases. Submitted phantom data are analyzed by drawing a circular region of interest that encompasses approximately 90% of the diameter of the interior of the phantom and then recording the mean SUV and SD of each transverse slice. In addition, average SUVs are measured in the liver of submitted patient scans. These data illustrate variations of SUVs across PET scanners and across institutions, and comparison of results with values submitted by the site indicate the level of experience of PET camera operators in calculating SUVs. Results: Of 101 scanner applications for which detailed records of the qualification process were available, 12 (12%) failed because of incorrect SUV or normalization calibrations. For sites to pass, the average cylinder SUV is required to be 1.0 6 0.1. The average SUVs for uniform cylinder images for the most common scanners evaluated-Siemens Biograph PET/CT (n 5 43), GE Discovery LS PET/CT (n 5 15), GE Discovery ST PET/CT (n 5 34), Philips Allegro PET (n 5 5), and Philips Gemini PET/CT (n 5 11)-were 0.99, 1.01, 1.00, 0.98, and 0.95, respectively, and the average liver SUVs for submitted test cases were 2.34, 2.13, 2.27, 1.73, and 1.92, respectively. Conclusion: Minimizing errors in SUV measurement is critical to achieving accurate quantification in clinical trials. The experience of the ACRIN PET Core Laboratory shows that many sites are unable to maintain accurate SUV calibrations without additional training or supervision. This raises concerns about using SUVs to quantify patient data without verification.