Effect of Reconstruction Parameters in High-Definition PET/CT on Assessment of Lymph Node Metastases in Head and Neck Squamous Cell Carcinoma

Abstract

Therapy outcome and overall survival in patients with head and neck squamous cell carcinoma (HNSCC) is influenced by precise localization of the primary tumor and detection of lymph node metastasis involvement at the time of initial diagnosis. Only accurate preoperative staging can improve primary tumor response and avoid early locoregional recurrence with lymph node metastases. The purpose of this study was the optimization of reconstruction parameters in high-definition PET/CT for the improved diagnostic assessment of lymph node metastases. Methods: In the experimental study, image contrast and signal-to-noise ratio were evaluated using a Jaszczak phantom. In the clinical study, 54 patients underwent head and neck imaging on a PET/CT scanner. Diagnostic findings were correlated with postoperative histopathology. For the 54 patients, 123 lymph nodes were evaluated on PET and histologically correlated with the neck dissection specimen. Forty-one lymph nodes were benign, and 82 findings were confirmed as being malignant. Both experimental and clinical studies were reconstructed into a 200 · 200 matrix using a 3-dimensional iterative reconstruction algorithm (ordered-subset expectation maximization [OSEM], 3 iterative steps, 24 subsets). Postfiltering with a 3-dimensional gaussian filter was applied. To study the effect of smoothing filter strength on the diagnostic accuracy of lymph node metastasis detection, 3 different cutoffs-1, 3, and 6 mm in full width at half maximum-were used to perform reconstructions. Results: Phantom studies showed that images reconstructed with 3-mm gaussian postfiltering gained a higher image quality and signal-to-noise ratio. Overall sensitivities for correctly diagnosed lymph nodes were best in 3-mm postfiltered images. Best results for true-positive lymph node findings were achieved with 3-mm postfiltering. With 1-mm postfiltering, accurate lesion detection was not improved, because increasing sensitivity (95% true-positive) correlated with decreasing specificity (12% false-positive). Conclusion: For lymph node assessment on a high-resolution PET/CT scanner, we consider the OSEM algorithm with 3 iterations and 24 subsets, combined with 3-dimensional 3-mm gaussian postfiltering, to be optimal. The continuous application of presently established PET protocols in patients with HNSCC will prove whether current acquisition and reconstruction methods are valuable and should be maintained.

¹⁸F-Fluorodeoxyglucose Uptake Level-Based Lymph Node Staging in Oropharyngeal Squamous Cell Cancer - Role of Molecular Marker Expression on Diagnostic Outcome

“…Assessment of the SUVmax has been feasible in many tumor entities, and its value is in agreement with several studies [11,17,19]. Some authors assume that the SUVmax is not a valuable parameter for outcome prediction [17,20].…”

“…PET/CT scanner technology, dedicated imaging protocols, and high-quality postprocessing software are improving the diagnostic output in lymph node staging [6,17]. Still, the ‘N0 neck' continues to be a challenge despite increased diagnostic accuracy of up to 95%, by combining high-resolution PET with contrast-enhanced CT [18].…”

Effect of Time-of-Flight Technique on the Diagnostic Performance of 18F-FDG PET/CT for Assessment of Lymph Node Metastases in Head and Neck Squamous Cell Carcinoma

“…The imaging protocol, established by us for dedicated head and neck imaging, was similar to that in a recent study published by our group (16). Patients were imaged on a Biograph mCT PET/CT scanner (Siemens Healthcare) with a high-counting-rate lutetium oxyorthosilicate detector and a 64-slice CT scanner.…”

“…The TOF PET sequences (reconstructed using the TOF method) and highdefinition (HD) PET sequences (reconstructed using the standard TrueX method [Siemens Healthcare]) were reconstructed with 2 different matrices: 200 · 200 and 400 · 400. HD PET sequences used 3 iterations and 24 subsets combined with 3-dimensional gaussian postfiltering at 3 mm in full width at half maximum, which renders high diagnostic output for HNSCC lymph node staging (16). For TOF PET sequences, 3 iterations and 21 subsets were recommended by the manufacturer for clinical routine imaging of the head and neck region.…”

“…Initially, the effect of high-definition PET/CT reconstruction parameters on accuracy in the detection of HNSCC lymph node metastases was analyzed (16). The purpose of the current clinical study was to investigate the effect of TOF PET on 18 F-FDG PET/CT in the preoperative detection of HNSCC lymph node metastases.…”