[Comparison of temporomandibular joint images with different fields of view in cone beam CT].

Abstract

Objective: To observe and compare the application of different scanning fields of view (FOV) in cone beam CT (CBCT) imaging of the temporomandibular joint (TMJ), and to explore the advantages and disadvantages of different CBCT scanning FOV for TMJ imaging. The aim is to provide a reference for the rational selection of CBCT scanning FOV for TMJ imaging in clinical practice. Methods: A total of 46 patients with temporomandibular disorders [22 males, 24 females; median age 24.5 years (range from 12 to 84 years)] were enrolled from the Department of Stomatology,the First Medical Centre, Chinese PLA General Hospital, between January 2023 and January 2025. All patients underwent CBCT scanning of the temporomandibular joints with both large and small fields of view using the same CBCT device, Newtom 5G (QR S.r.l, Italy), including small-field-of-view (sFOV 6 cm×6 cm, 46 cases, 92 sides) and large-field-of-view (lFOV 15 cm×12 cm for 26 cases with 52 sides or 18 cm×16 cm for 20 cases with 40 sides). A self-matched design was used to compare imaging parameters (scan time, exposure time, reconstruction voxel, radiation dose, data volume), image quality, and lesion detection efficacy (articular surface flattening, surface erosion, osteophyte, subcortical sclerosis, subcortical cyst, intra-articular calcification). Additionally, differences in joint spaces, condylar head height, and condylar height were analyzed. Results: In the sFOV group, scan time (72 s vs. 24 s) and exposure time (14.6 s vs. 4.8 s) were significantly longer than those in the lFOV group, with smaller reconstruction voxels (0.15 mm vs. 0.3 mm). Radiation dose in the sFOV group [(199.94±5.52) mGy·cm] was significantly higher than that in the lFOV 15 cm×12 cm subgroup [(96.20±25.34) mGy·cm, t=-20.29, P<0.001] and the 18 cm×16 cm subgroup [(101.73±13.49) mGy·cm, t=-31.34, P<0.001]. In terms of data volume, the sFOV group [(274.18±1.74) MB] was larger than the lFOV 15 cm×12 cm subgroup [(208.83±20.13) MB, t=-16.75, P<0.001], while the lFOV 18 cm×16 cm subgroup [(386.39±1.63) MB] was significantly larger than the sFOV group [(274.83±1.78) MB, t=214.49, P<0.001]. sFOV images showed clearer anatomical margins, distinguishable trabecular bone, and fewer artifacts. The detection rate of subcortical cyst in the sFOV group (50.0%, 46/92) was significantly higher than that in the lFOV group (36.96%, 34/92, χ²=5.61, P=0.018), with a moderate agreement Kappa coefficient of 0.48. Detection rates of articular surface flattening (80.43%, 74/92) and osteophyte (55.43%, 51/92) were identical between groups, with a perfect agreement Kappa coefficient of 1. Detection rates of subcortical sclerosis (69.57% vs. 68.48%) and intra-articular calcification (5.43% vs. 4.34%) were slightly higher in sFOV but without statistical significance (P>0.05), with high Kappa coefficients of 0.93 and 0.88, respectively. For subcortical erosion, sFOV detection rate (38.04%, 35/92) was higher than lFOV (26.09%, 24/92, Kappa=0.53, moderate agreement), with no significant difference in detection rate (χ²=2.97, P=0.085). There were no statistical differences in joint space or condylar head height measurements between groups (P>0.05), but condylar height measurements in the sFOV group were significantly greater than those in the lFOV group (t=4.52, P<0.001). Conclusions: Large FOV provides wide anatomical coverage, optimizes radiation dose and data processing efficiency, and is more convenient for quantitative TMJ measurements.Small FOV offers superior resolution for displaying subtle condylar structures and lesions.Clinically, the choice of scan field should be individualized based on examination objectives (large FOV for holistic assessment/quantitative analysis; small FOV for early bone lesion diagnosis), equipment performance, and patient characteristics.