Accuracy of motion quantification in dynamic CT images of the wrist joint across multiple CT vendors: A phantom study.

backgroundFour-dimensional computed tomography (4D CT) allows dynamic assessment of wrist kinematics and offers a non-invasive alternative for evaluating ligament instability. However, insufficient temporal resolution and differences in acquisition or reconstruction protocols may introduce motion-related artifacts that affect quantitative analysis. As these artifacts can mimic pathological carpal motion, measurement error must be quantified to distinguish true pathology from methodological error. Therefore, systematic evaluation of motion quantification across different CT systems and acquisition protocols is required. PURPOSE: To evaluate the errors in motion quantification across acquisition and reconstruction protocols of different CT systems in 4D CT imaging of wrist bones.

methodsA rotating wrist phantom with three 3D-printed bones (scaphoid, lunate, capitate) was scanned on five CT systems from three manufacturers (Aquilion ONE PRISM and ONE Vision, Canon Medical; Revolution Apex, GE HealthCare; single-source and dual-source SOMATOM Force, Siemens Healthcare). One static 3D scan and multiple 4D scans were acquired at different phantom rotation speeds, each lasting 10 s. Single-source covered 0.050-0.300 phantom rotations per second (rps), and dual-source 0.100-0.600 rps. Dose dependence was evaluated on two systems (80 kV/40 mA and 120 kV/100 mA). Images were reconstructed in full and partial modes, segmented, and registered using point-to-image registration. Motion quantification error was calculated for translation and rotation of the scaphoid and capitate relative to the lunate, referenced to the static scan, and reported per rotation cycle. Motion quantification error was additionally expressed as a function of normalized motion per reconstructed frame to relate the error to the amount of motion occurring during image acquisition. Effects of CT system, bone type, reconstruction method, and rotation speed were analyzed using a linear mixed model. Statistical significance was defined as p < 0.05.

resultsThe motion quantification error was hardly affected by dose. For 0.100 rps, the errors of the best single-source system were median 0.29 mm (interquartile range: 0.21-0.36 mm) and 1.37° (0.82°-2.18°) for full and 0.21 mm (0.16-0.25 mm) and 0.70° (0.52°-0.95°) for partial reconstructions for the capitate; the dual-source system showed the lowest errors (0.14 mm (0.12-0.17 mm) and 0.48° (0.39°-0.62°)). Motion quantification error scaled approximately linearly with normalized motion per reconstructed frame, corresponding to approximately 15% of the motion occurring during one reconstructed frame.

conclusionsMotion quantification errors were largely determined by phantom rotation speed and temporal resolution. The reported values provide a basis for defining the detection threshold for quantitative wrist kinematics, supporting differentiation between true kinematics and apparent displacement caused by motion artifacts.