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Digital PET-CT in oncology: image quality optimization and diagnostic comparison with conventional PET

Winters, E.G. (2019) Digital PET-CT in oncology: image quality optimization and diagnostic comparison with conventional PET.

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Abstract:18F-FDG PET plays an important role in oncology for diagnosing, staging and therapy-response monitoring. Using 18F-labeled glucose, tissues with high glucose-metabolism are visualized, a common characteristic for tumors. Recently introduced PET-scanners using Silicon photomultipliers with digital readout have a better timing resolution and photon detection accuracy than conventional PET (cPET). The aims were to compare diagnostic outcome of digital PET (dPET) to cPET, secondly, to illustrate difficulties in the balance between sensitivity and specificity for cPET and dPET and lastly to determine an image reconstruction providing the best small lesion detectability without noise amplification for FDG-PET using dPET. We scanned 80 patients with proven cancer on dPET (Vereos, Philips) and cPET (Ingenuity, Philips) using high-resolution reconstructions to compare diagnostic outcome. We evaluated SUVmax, SUVmean, lesion-to-background ratio (LBratio) and metabolic tumor volume (MTV) in up to five lesions per patient and noise-levels in the liver. We determined ROC-curves, cut-off values and accuracy. TNM-staging was assessed by two NM-physicians. With dPET, uptake values and LBratio increased with 15% and 18% compared to cPET, MTV decreased with 7%. Malignant lesions showed higher SUVmax and LBratio than benign lesions (p<0.05). Moreover, we found higher AUCs, better characterization performance and TNM-upstaging in 4/26 patients with dPET. More research is necessary to assess the effect on different tumor types. For illustration of difficulties in the balance between sensitivity and specificity for cPET and dPET, we performed a case-study. We described a case of a 75-year old male. On cPET, esophageal cancer was found and a lesion in Th6 was marked as degenerative. He was treated curative for esophageal cancer. Several months later he had bone metastasis. By using dPET, it could have been that the Th6 lesion was reported as malignant, leading to a different treatment plan. For other patients, it is recommended to use both dPET and cPET, to obtain best possible diagnostics. For determination of an OSEM-based image reconstruction with the best small lesion detectability and acceptable noise level for FDG-PET using dPET, we performed a phantom study and a patient study. In the phantom study, highest noise was found for 51 updates without filtering, decreasing with 22% for 39 updates (p<0.01). In the patient study (n=24), noise-level decreased with 13% for 39 updates (p<0.01). For all lesions (n=80, size:0.1-8.1mL), SUVmean and SUVmax were similar between updates. Visual analysis showed no significant preference. Adequate image quality for a dPET-system using OSEM requires a selected number of updates. Lowest noise-level without impairing small-lesion detectability with acceptable image quality can be obtained using 2x2x2mm3 voxels with 3 iterations x 13 subsets (39 updates) without post-smoothing filter.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:44 medicine, 50 technical science in general
Programme:Technical Medicine MSc (60033)
Link to this item:http://purl.utwente.nl/essays/79906
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