Subjects

The fused SPECT/CT image of 34 mandibular condyles of the 17 patients (3 males and 14 females) who visited the Department of Oral and Maxillofacial Surgery, Hanyang University Hospital, was retrospectively collected. All the 17 patients were suspected to have osteoarthritis of mandibular condyle on plain radiography and clinical examination; therefore, facial CT and bone SPECT were taken for further evaluation. The age distribution ranged from 14 to 66 years, with a mean age of 34.3 years. The protocol for this study was reviewed and approved by the Institutional Review Board (IRB) of the Hanyang University Hospital (HYUH 2012–11-009–012). The requirement for patient consent was waived by the IRB committee.

Diagnostic criteria and image acquisition

Primary diagnosis was based on DC/TMD Axis I (clinical physical examination), the clinical findings (palpation, subjective pain report, any coarse crepitus sound, and pain during movement), and bony change on plain radiography (erosion, sclerosis of cortical bone, osteophyte formation).

And then facial CT and bone SPECT of the patients were acquired. Facial CT (Sensation 16, Siemens, Berlin, Germany) was taken with exposure parameters at 120 kV, tube current 80 mA s/slice, and 1-mm slice thickness. Facial CT scan time was 10 s covering 17 cm. The estimated CT radiation dose was 6.5 mGy to each patient.

The bone SPECT was acquired 4 h after the intravenous administration of 99mTc-MDP (740 ~ 1110 MBq). The SPECT was taken on a dual head gamma camera (ECAM, Siemens Medical System, Chicago, IL, USA) using a low-energy, ultrahigh resolution collimator in a 128 × 128 matrix in continuous mode for 64 views per detector over 180° for 20 s per view. The bone SPECT data were reconstructed using OncoFlash (Siemens, Erlangen, Germany).

Group of the patients

According to the clinical and radiographic examinations of plain radiography, 34 TMJs of the 17 patients were divided into 4 groups. Thirty-four condyles were identified as anonymized patient number (from 1 to 17), and the right and left condyles were indicated as R and L, respectively (Supplemental Table).

Normal group (group N) included the TMJs defined as no symptom except occasional clicking sound and normal feature on radiographic exam.

Internal derangement group (group ID) was defined as an abnormal relationship between the articular disc and the mandibular condyle, articular fossa, and the articular eminence. These group represented the symptom of joint noise during normal function, mouth opening limitations, temporary joint locking, and pain without any bony change on plain radiography. These TMJs belonged to the group II of DC/TMD Axis I.

Group osteoarthritis (group OA) and group osteoarthritis sequelae (group OAseq) were belong to the group III of DC/TMD Axis I. In these groups, bony change such as bone erosion, cortical thinning, sclerosis, osteophyte, and irregularity on condylar head was observed on radiographic exam. Group OA showed the symptom of arthralgia on TMJ, and group OAseq showed no clinical symptom except crepitus.

Single rater, who was profession of the Department of Oral and Maxillofacial Surgery, assessed the TMJs and performed grouping, and another rater performed the grouping separately. The result of grouping coincided with each other.

Image analysis of fused image of bone SPECT and facial CT

SPECT data and CT data for each patient were transferred and co-registered to yield fused SPECT/CT image in axial, coronal, and sagittal plan using 3D software (Xelis, INFINITT Healthcare, Seoul, Korea) (Fig. 1).

Fig. 1

Facial CT, Bone SPECT and co-registered fused image using Xelis program in the transverse, coronal, and sagittal planes, showing focal hyperactivity of the radiopharmaceutical in the left TMJ

To quantitate the 99mTc-MDP uptake level of the TMJ, a sphere shape region of interest (ROI) (3.0 × 3.0 × 3.0 pixel) was designated in the highest point for evaluation and the counts in both the condyles and clivus measured (Fig. 2). For the bilateral condyle regions, the uptake ratio was obtained using the clivus as a background measurement. The average values were used to calculate uptake ratio (TMJ uptake ratio = average count at condyle/average count at clivus). Single rater experienced nuclear medicine clinicians, evaluated the uptake level of 99mTc-MDP of TMJ through visual analysis, and after 2 weeks, same and another rater repeated the evaluation. Both inter- and intra-examiner reliability showed excellent agreement; the intraclass correlation coefficient value was 0.892 and 0.922, respectively.

Fig. 2

Region of interest (ROI) drawn over the right condyle to calculate the maximum, minimum, and average radiotracer uptake count on bone SPECT and facial CT-fused image. a Radiotracer count was calculated by ROI (3.0 × 3.0 × 3.0 pixel) on coronal image. b Radiotracer count was calculated by ROI (3.0 × 3.0 × 3.0 pixel) on 3 planes (axial, sagittal, coronal view). Right, left condyle, and clivus also calculated for the ratio in each subject

Statistical analysis

Statistical analyses were performed using the SAS software, version 9.2 (SAS Institute Inc., Cary, USA). Kruskal-Wallis test, and further multiple comparisons using Tukey test for the post hoc analysis, was conducted to evaluate differences between groups. Value of p < 0.05 was considered to be significant.