From SPECT/CT towards absolute quantification? - the case of unilateral condylar hyperplasia of the mandible

• Published in: EJNMMI physics Vol. 11; no. 1; pp. 74 - 16
• Main Authors: De Schepper, Stijn, Gnanasegaran, Gopinath, De Vos, Wouter, Van de Casteele, Elke, Dickson, John C., Van den Wyngaert, Tim
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 23.08.2024; Springer Nature B.V; SpringerOpen
• Subjects: 3D printing; Anthropomorphism; Applied and Technical Physics; Attenuation; Computational Mathematics and Numerical Analysis; Computed tomography; Engineering; Hyperplasia; Image reconstruction; Imaging; Inserts; Mandible; Medicine; Medicine & Public Health; Modelling; Nuclear Medicine; Original Research; Phantom; Quantitative SPECT/CT; Radiology; Recovery; Recovery coefficient; Scattering; Skewed distributions; Three dimensional printing; Unilateral condylar hyperplasia; Phantom; Recovery coefficient; Mandible; Unilateral condylar hyperplasia; Quantitative SPECT/CT; 3D printing
• ISSN: 2197-7364; 2197-7364
• DOI: 10.1186/s40658-024-00676-6

Background Unilateral condylar hyperplasia (UCH) of the mandible is a rare condition characterized by asymmetric growth of the mandibular condyles. Bone scintigraphy with SPECT(/CT) is commonly used to diagnose UCH and guide treatment. Still, varying results have been reported using the traditional threshold of 55%:45% in relative tracer uptake. While absolute quantification of uptake on SPECT/CT could improve results, optimal correction and reconstruction settings are currently unknown. Methods Three anthropomorphic phantoms representing UCH were developed from patient CT volumes and produced using 3D printing technology. Fillable spherical inserts of different sizes (Ø: 8–15 mm) were placed in the condylar positions representing symmetrical and asymmetrical distributions. Recovery coefficients were determined for SPECT/CT using various reconstruction corrections, including attenuation and scatter correction (ACSC), resolution modeling (RM), and partial volume correction (PVC) using phantom measurements. Uptake ratios between condyles and condyle to clivus were evaluated. Finally, the impact of these correction techniques on absolute activity and diagnostic accuracy was assessed in a retrospective patient cohort for the diagnostic threshold of 55%:45%. Results The activity was only partially recovered in all spherical inserts (range: 22.5–64.9%). However, RM improved relative recovery by 20.2–62.3% compared to ACSC. In the symmetric phantoms, the 95% confidence interval (CI) of condyle ratios included the diagnostic threshold (57.6%:42.4%) for UCH when using ACSC potentially leading to false positives, but not for ACSCRM datasets. Partial volume corrections coefficients from the NEMA IQ phantom was positionally dependent, with improvements seen performing PVC using coefficients derived from anthropomorphic phantoms. Retrospective application in a patient cohort showed only a weak linear correlation (R²: 0.25–0.67) and large limits of agreement (9.6–12.5%) between different reconstructions. Up to 44% of patients were reclassified using the 55%:45% threshold. Using clinical outcome data, ACSCRM had highest sensitivity (91%; 95% CI 59–100%) and specificity (66%; 95% CI 47–81%), significantly improving specificity ( P  = 0.038). Conclusions Anthropomorphic phantoms were shown to be essential in determining optimal settings for acquisition, reconstruction, and analysis. SPECT/CT reconstructions with attenuation and scatter correction and resolution modeling are recommended and could improve specificity when using the 55%:45% threshold to assess condylar growth.