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 The scanner table was then withdrawn while the patient remained on the table, and the DigitalTF was inserted between the GeminiTF PET and CT scanner.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...
Purpose To evaluate the accuracy and consistency of a gradient-based PET segmentation method, GRADIENT, as compared to manual (MANUAL) and constant threshold (THRESHOLD) methods. Methods and Materials Contouring accuracy was evaluated with sphere phantoms and clinically realistic Monte Carlo PET phantoms of the thorax. The sphere phantoms were 10–37 mm in diameter and were acquired at 5 institutions emulating clinical conditions. One institution also acquired a sphere phantom with multiple source-to-background ratios (SBR) of 2:1, 5:1, 10:1, 20:1, and 70:1. One observer segmented (contoured) each sphere with GRADIENT and THRESHOLD from 25–50% at 5% increments. Subsequently, seven physicians segmented lessions (7–264ml) from 25 digital thorax phantoms using GRADIENT, THRESHOLD, and MANUAL. Results For spheres < 20 mm in diameter, GRADIENT was the most accurate with a mean absolute %error in diameter of 8.15% (10.2%SD) compared to 49.2% (51.1%SD) for 45% THRESHOLD (p < 0.005). For larger spheres the methods were statistically equivalent. For varying SBR, GRADIENT was the most accurate for spheres > 20 mm, (p < 0.065) and < 20 mm (p < 0.015). For digital thorax phantoms, GRADIENT was the most accurate, (p-value < 0.01), with a mean absolute %error in volume of 10.99% (11.9%SD) followed by 25% THRESHOLD at 17.5% (29.4%SD), and MANUAL, at 19.5% (17.2%SD). GRADIENT had the least systematic bias, 4 with a mean %error in volume of −0.05% (16.2%SD) compared with 25% THRESHOLD at - 2.1% (34.2%SD) and MANUAL at −16.3% (20.2%SD) (p-value < 0.01). Inter-observer variability was reduced using GRADIENT compared to both 25% THRESHOLD and MANUAL (p-value < 0.01, Levene's Test). Conclusion GRADIENT was the most accurate and consistent technique for target volume contouring. GRADIENT was also the most robust for varying imaging conditions. GRADIENT has the potential to play an important role for tumor delineation in radiation therapy planning and response assessment.
Cervical cancers have a high avidity for FDG. The use of PET-FDG scanning accurately predicts both the presence and absence of pelvic and para-aortic nodal metastatic disease.
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