We report our initial clinical experience for image quality and diagnostic performance of a digital PET prototype scanner with time-of-flight (DigitalTF), compared with an analog PET scanner with time-of-flight (GeminiTF PET/CT). Methods: Twenty-one oncologic patients, mean age 58 y, first underwent clinical 18 F-FDG PET/CT on the GeminiTF. The scanner table was then withdrawn while the patient remained on the table, and the DigitalTF was inserted between the GeminiTF PET and CT scanner. The patients were scanned for a second time using the same PET field of view with CT from the GeminiTF for attenuation correction. Two interpreters reviewed the 2 sets of PET/CT images for overall image quality, lesion conspicuity, and sharpness. They counted the number of suggestive 18 F-FDG-avid lesions and provided the TNM staging for the 5 patients referred for initial staging. Standardized uptake values (SUVs) and SUV gradients as a measure of lesion sharpness were obtained. Results: The DigitalTF showed better image quality than the GeminiTF. In a side-by-side comparison using a 5-point scale, lesion conspicuity (4.3 ± 0.6), lesion sharpness (4.3 ± 0.6), and diagnostic confidence (3.4 ± 0.7) were better with DigitalTF than with GeminiTF (P , 0.01). In 52 representative lesions, the lesion maximum SUV was 36% higher with DigitalTF than with GeminiTF, lesion-toblood-pool SUV ratio was 59% higher, and SUV gradient was 51% higher, with good correlation between the 2 scanners. Lesions less than 1.5 cm showed a greater increase in SUV from GeminiTF to DigitalTF than those lesions 1.5 cm or greater. In 5 of 21 patients, DigitalTF showed an additional 8 suggestive lesions that were not seen using GeminiTF. In the 15 restaging patients, the true-negative rate was 100% and true-positive rate was 78% for both scanners. In the 5 patients for initial staging, DigitalTF led to upstaging in 2 patients and showed the same staging in the other 3 patients, compared with GeminiTF. Conclusion: DigitalTF provides better image quality, diagnostic confidence, and accuracy than GeminiTF. DigitalTF may be the most beneficial in detecting small tumor lesions and disease staging. PETcont inues to play a significant role in molecular imaging.Steady improvements in detector design and architecture as well as the implementation of time-of-flight (TOF) technology have created significant improvements in image quality and greater flexibility in reducing radiotracer dose and scanning time (1-4).The current trend in molecular imaging places emphasis on accurate, quantitative PET imaging for improved lesion characterization and treatment monitoring (5). A new type of scintillation detector, digital photon counters (DPC), was recently developed by Philips Healthcare (6-8). The key innovation of the new digital PET system is the replacement of conventional photomultipliers with high-performance digital detectors and the implementation of singlephoton avalanche photodiodes with low-voltage complementary metal-oxide semiconductor (CMOS) logic on the same silico...

The majority of aggressive lymphomas is characterized by an up regulated glycolytic activity, which enables the visualization by F-18 FDG-PET/CT. One-stop hybrid FDG-PET/CT combines the functional and morphologic information, outperforming both, CT and FDG-PET as separate imaging modalities. This has resulted in several recommendations using FDG-PET/CT for staging, restaging, monitoring during therapy, and assessment of treatment response as well as identification of malignant transformation. FDG-PET/CT may obviate the need for a bone marrow biopsy in patients with Hodgkin's lymphoma and diffuse large B-cell lymphoma. FDG-PET/CT response assessment is recommended for FDG-avid lymphomas, whereas CT-based response evaluation remains important in lymphomas with low or variable FDG avidity. The treatment induced change in metabolic activity allows for assessment of response after completion of therapy as well as prediction of outcome early during therapy. The five point scale Deauville Criteria allows the assessment of treatment response based on visual FDG-PET analysis. Although the use of FDG-PET/CT for prediction of therapeutic response is promising it should only be conducted in the context of clinical trials. Surveillance FDG-PET/CT after complete remission is discouraged due to the relative high number of false-positive findings, which in turn may result in further unnecessary investigations. Future directions include the use of new PET tracers such as F-18 fluorothymidine (FLT), a surrogate biomarker of cellular proliferation and Ga-68 CXCR4, a chemokine receptor imaging biomarker as well as innovative digital PET/CT and PET/MRI techniques.

Purpose The purpose of this study was to compare and correlate standardized uptake values (SUV) derived from magnetic resonance attenuation correction (MRAC) with those derived from computed tomography attenuation correction (CTAC) in an oncology patient population. Procedures The HIPAA-compliant study was approved by the Internal Review Board and all subjects gave written informed consent prior to inclusion in the study. Forty patients (mean age 61±15.1; 20 male) referred for clinically indicated 2-deoxy-2-[18F]fluoro-D-glucose (FDG) positron emission tomography/computed tomography (PET/CT) scans also underwent a PET/magnetic resonance imaging (MRI) examination. MRAC was performed using an automatic three-segment model. Regions of interest were drawn over eight normal structures in order to obtain SUVmax and SUVmean values. Spearman rank correlation coefficients (r) were calculated and two-tailed paired t tests were performed to compare the SUVmax and SUVmean values obtained from CTAC with those from MRAC. Results The mean time after FDG injection was 66±7 min for PET/CT and 117±15 min for PET/MRI examination. MRAC SUV values were significantly lower than the CTAC SUV values in mediastinal blood pool (p<0.001 for both SUVmax and SUVmean) and liver (p=0.01 for SUVmean). The MRAC SUV values were significantly higher in bone marrow (p<0.001 for both SUVmax and SUVmean), psoas major muscle (p<0.001 for SUVmax), and left ventricular myocardium (p<0.001 for SUVmax and p=0.01 for SUVmean). For the other normal structures, no significant difference was observed. When comparing SUV values generated from CTAC versus MRAC, high correlations between CTAC and MRAC were observed in myocardium (r=0.96/ 0.97 for SUVmax/mean), liver (r=0.68 for SUVmax), bone marrow (r=0.80/0.83 for SUVmax/mean), lung tissue (r=0.70 for SUVmax), and mediastinal blood pool (r=0.0.68/.069 for SUVmax/mean). Moderate correlations were found in lung tissue (r=0.67 for SUV mean), liver (r=0.66 for SUVmean), fat (r=0.48/0.53 for SUVmax/mean), psoas major muscle (r=0.54/0.58 for SUVmax/mean), and iliacus muscle (r=0.41 for SUVmax). Low correlation was found in iliacus muscle (r=0.32 for SUVmean). Conclusions Using the automatic three-segment model, our study showed high correlation for measurement of SUV values obtained from MRAC compared to those from CTAC, as the reference standard. Differences observed between MRAC and CTAC derived SUV values may be attributed to the time-delay between the PET/CT and PET/MRI scans or biologic clearance of radiotracer. Further studies are required to assess SUV measurements when performing different MR attenuation correction techniques.