Measuring the alveolar bone level in adolescents: A comparison between ultrasound and cone beam computed tomography.

BACKGROUND: Cone beam computed tomography (CBCT) is an imaging modality, which is used routinely in orthodontic diagnosis and treatment planning but delivers much higher radiation than conventional dental radiographs. Ultrasound is a noninvasive imaging method that creates an image without ionizing radiation. AIM: To investigate the reliability of ultrasound and the agreement between ultrasound and CBCT in measuring the alveolar bone level (ABL) on the buccal/labial side of the incisors in adolescent orthodontic patients. DESIGN: One hundred and eighteen incisors from 30 orthodontic adolescent patients were scanned by CBCT with 0.3-mm voxel size and ultrasound at 20 MHz frequency. The ABL, distance from the cementoenamel junction (CEJ) to the alveolar bone crest (ABC), was measured twice to evaluate the agreement between ultrasound and CBCT. In addition, the intra- and inter-rater reliabilities in measuring the ABL by four raters were compared. RESULTS: The mean difference (MD) in the ABL between ultrasound and CBCT was -0.07 mm with 95% limit of agreement (LoA) from -0.47 to 0.32 mm for all teeth. For each jaw, the MDs between the ultrasound and CBCT were -0.18 mm (for mandible with 95% LoA from -0.53 to 0.18 mm) and 0.03 mm (for maxilla with 95% LoA from -0.28 to 0.35 mm). In comparison, ultrasound had higher intra-rater (ICC = 0.83-0.90) and inter-rater reliabilities (ICC = 0.97) in ABL measurement than CBCT (ICC = 0.56-0.78 for intra-rater and ICC = 0.69 for inter-rater reliabilities). CONCLUSION: CBCT parameters used in orthodontic diagnosis and treatment planning in adolescents may not be a reliable tool to assess the ABL for the mandibular incisors. On the contrary, ultrasound imaging, an ionizing radiation-free, inexpensive, and portable diagnostic tool, has potential to be a reliable diagnostic tool in assessing the ABL in adolescent patients.

Ultrasound Imaging of the Periodontium Complex: A Reliability Study.

Background: Ultrasonography is a noninvasive, low-cost diagnostic tool widely used in medicine. Recent studies have demonstrated that ultrasound imaging might have the potential to be used intraorally to assess periodontal biomarkers. Objectives: To evaluate the reliability of interlandmark distance measurements on intraoral ultrasound images of the periodontal tissues. Materials and Methods: Sixty-four patients from the graduate periodontics (n = 33) and orthodontics (n = 31) clinics were recruited. A 20 MHz handheld intraoral ultrasound transducer was used to scan maxillary and mandibular incisors, canines, and premolars. Distances between the alveolar bone crest and cementoenamel junction (ABC-CEJ), gingival thickness (GT), and alveolar bone thickness (ABT) were measured by 3 raters. The intercorrelation coefficient (ICC) and mean absolute deviation (MAD) were calculated among and between the raters. Raters also scored images according to quality. Results: The ICC scores for intrarater reliability were 0.940 (0.932-0.947), 0.953 (0.945-0.961), and 0.859 (0.841-0.876) for ABC-CEJ, GT, and ABT, respectively. The intrarater MAD values were 0.023 (±0.019) mm, 0.014 (±0.005) mm, and 0.005 (±0.003) mm, respectively. The ICC scores for interrater reliability were 0.872 (95% CI: 0.836-0.901), 0.958 (95% CI: 0.946-0.968), and 0.836 (95% CI: 0.789-0.873) for ABC-CEJ, GT, and ABT, respectively. The interrater MAD values were 0.063 (±0.029) mm, 0.023 (±0.018) mm, and 0.027 (±0.012) mm, respectively. Conclusions: The present study showed the high reliability of ultrasound in both intrarater and interrater assessments. Results suggest there might be a potential use of intraoral ultrasound to assess periodontium.

Estimating Crestal Thickness of Alveolar Bones on Intra-oral Ultrasonograms.

OBJECTIVE: Alveolar crestal bone thickness and level provide important diagnostic and prognostic information for orthodontic treatment, periodontal disease management and dental implants. Ionizing radiation-free ultrasound has emerged as a promising clinical tool in imaging oral tissues. However, the ultrasound image is distorted when the wave speed of the tissue of interest is different from the mapping speed of the scanner and, therefore, the subsequent dimension measurements are not accurate. This study was aimed at deriving a correction factor that can be applied to the measurements to correct for discrepancy caused by speed variation. METHODS: The factor is a function of the speed ratio and the acute angle that the segment of interest makes with the beam axis perpendicular to the transducer. The phantom and cadaver experiments were designed to validate the method. DISCUSSION: The comparisons agree well with absolute errors not more than 4.9%. Dimension measurements on ultrasonographs can be properly corrected by applying the correction factor without recourse to the raw signals. CONCLUSION: The correction factor has reduced the measurement discrepancy on the acquired ultrasonographs for the tissue whose speed is different from the scanner's mapping speed.

Localization of cementoenamel junction in intraoral ultrasonographs with machine learning.

OBJECTIVE: Our goal was to automatically identify the cementoenamel junction (CEJ) location in ultrasound images using deep convolution neural networks (CNNs). METHODS: Three CNNs were evaluated using 1400 images and data augmentation. The training and validation were performed by an experienced nonclinical rater with 1000 and 200 images, respectively. Four clinical raters with different levels of experience with ultrasound tested the networks using the other 200 images. In addition to the comparison of the best approach with each rater, we also employed the simultaneous truth and performance level estimation (STAPLE) algorithm to estimate a ground truth based on all labelings by four clinical raters. The final CEJ location estimate was obtained by taking the first moment of the posterior probability computed using the STAPLE algorithm. The study also computed the machine learning-measured CEJ-alveolar bone crest distance. RESULTS: Quantitative evaluations of the 200 images showed that the comparison of the best approach with the STAPLE-estimate yielded a mean difference (MD) of 0.26 mm, which is close to the comparison with the most experienced nonclinical rater (MD=0.25 mm) but far better than the comparison with clinical raters (MD=0.27-0.33 mm). The machine learning-measured CEJ-alveolar bone crest distances correlated strongly (R = 0.933, p < 0.001) with the manual clinical labeling and the measurements were in good agreement with the 95% Bland-Altman's lines of agreement between -0.68 and 0.57 mm. CONCLUSIONS: The study demonstrated the feasible use of machine learning methodology to localize CEJ in ultrasound images with clinically acceptable accuracy and reliability. Likelihood-weighted ground truth by combining multiple labels by the clinical experts compared favorably with the predictions by the best deep CNN approach. CLINICAL SIGNIFICANCE: Identification of CEJ and its distance from the alveolar bone crest play an important role in the evaluation of periodontal status. Machine learning algorithms can learn from complex features in ultrasound images and have potential to provide a reliable and accurate identification in subsecond. This will greatly assist dental practitioners to provide better point-of-care to patients and enhance the throughput of dental care.

Fully Automated Segmentation of Alveolar Bone Using Deep Convolutional Neural Networks from Intraoral Ultrasound Images.

Delineation of alveolar bone aids the diagnosis and treatment of periodontal diseases. In current practice, conventional 2D radiography and 3D cone-beam computed tomography (CBCT) imaging are used as the non-invasive approaches to image and delineate alveolar bone structures. Recently, high-frequency ultrasound imaging is proposed as an alternative to conventional imaging methods to prevent the harmful effects of ionizing radiation. However, the manual delineation of alveolar bone from ultrasound imaging is time-consuming and subject to inter and intraobserver variability. This study proposes to use a convolutional neural network-based machine learning framework to automatically segment the alveolar bone from ultrasound images. The proposed method consists of a homomorphic filtering based noise reduction and a u-net machine learning framework for automated delineation. The proposed method was evaluated over 15 ultrasound images of tooth acquired from procine specimens. The comparisons against manual ground truth delineations performed by three experts in terms of mean Dice score and Hausdorff distance values demonstrate that the proposed method yielded an improved performance over a recent state of the art graph cuts based method.

Intra- and inter-rater reliability of spinal flexibility measurements using ultrasonic (US) images for non-surgical candidates with adolescent idiopathic scoliosis: a pilot study.

PURPOSE: This study aimed to determine the intra- and inter-rater reliabilities of spinal flexibility measurements using ultrasound imaging on non-surgical candidates with adolescent idiopathic scoliosis (AIS). METHODS: Twenty-eight consecutive consented AIS subjects (25 F; 3 M) were recruited; 24 subjects' data were used for analysis. This study explored curve magnitude differences between standing, prone and voluntary maximum side-bending postures to assess the reliability of spinal flexibility (SF). Two raters were included in this study. Four flexibility indices, PRSI, BRPI, B-PRSI, BRSI, based on the postural changes from standing to prone and from prone to bending position were defined. The reliability analysis was evaluated using the intra-class correlation coefficient (ICC) [1, 2] and the standard error of measurements (SEM). RESULTS: The ICC [1, 2] values of the intra-rater (R2 only) and inter-rater (R1 vs R2) reliabilities of the measurements (PRSI, BRPI, B-PRSI, BRSI) were (0.82, 0.64, 0.78, 0.91) and (0.78, 0.76, 0.84, 0.94), respectively. Among the four indices, the BRPI had the highest SEM values 1.42, and 0.73 for intra- and inter-raters results, respectively, while BRSI had the lowest SEM 0.04 and 0.02 for intra- and inter-rater, respectively. CONCLUSIONS: The BRPI, BRSI and B-PRSI could be measured reliably on US images when the Cobb angle at prone position was not close to zero. Using these three indices, information may provide more comprehensive information about the SF. Validity of spinal flexibility measurements still needed to be confirmed with a clinical study with more subjects. These slides can be retrieved under Electronic Supplementary Material.

Whether Orthotic Management and Exercise are Equally Effective to the Patients With Adolescent Idiopathic Scoliosis in Mainland China?: A Randomized Controlled Trial Study.

STUDY DESIGN: A prospective randomized controlled trial. OBJECTIVE: The aim of this study was to investigate the effectiveness of orthotic management versus exercise on spinal curvature, body symmetry, and quality of life. SUMMARY OF BACKGROUND DATA: A number of well-designed studies comparing conservative treatment of adolescent idiopathic scoliosis (AIS) have been conducted and the evidence becomes stronger. However, there is a lack of the information on the effectiveness of orthotic management versus exercise. METHODS: The inclusion criteria recommended by the Scoliosis Research Society (SRS) and the international Society on Scoliosis Orthopedic and Rehabilitation Treatment (SOSORT) were used during enrollment. Eligible patients were randomly assigned to either bracing group or exercise group. Patients in the bracing group were prescribed with a rigid thoracolumbosacral orthosis and requested to wear 23 h/day, while patients in the exercise group were treated with the protocol of the Scientific Exercise Approach to Scoliosis. Data regarding angle of trunk inclination, Cobb angle, shoulder balance, body image, and quality of life (QoL) were collected every 6 months. RESULTS: Twenty-four patients in the bracing group and 29 patients in the exercise group participated in this study. For the intergroup comparison, the bracing group showed better results about the correction of spinal curvature (Cobb angle at the first 12 months of intervention, P = 0.039), scores concerning QoL, especially function (P < 0.001), mental health (P < 0.001), and total score (P < 0.001), were higher than that of the exercise group. The results of body symmetry evaluation did not differ significantly between the two groups. For the intragroup comparison, parameters of spinal curvature (baseline vs. 12-month, P < 0.03 in the exercise group and P < 0.001 in the bracing group), QoL (baseline vs. 12-month, P < 0.001), and TAPS (baseline vs. 12-month, P < 0.033) significantly improved over the studied period. Shoulder balance (baseline vs. 12-month, P < 0.005) showed significant improvement only in the bracing group. CONCLUSION: Both interventions of bracing and exercise showed significant treatment effectiveness on the patients with AIS. Bracing was superior to capture corrections in parameters of spinal curvature and body symmetry, while the QoL, especially in aspect of the functional and psychological status, was significantly better in the exercise group. LEVEL OF EVIDENCE: 1.

Validity Study of Vertebral Rotation Measurement Using 3-D Ultrasound in Adolescent Idiopathic Scoliosis.

This study aimed to assess the validity of 3-D ultrasound measurements on the vertebral rotation of adolescent idiopathic scoliosis (AIS) under clinical settings. Thirty curves (mean Cobb angle: 21.7° ± 15.9°) from 16 patients with AIS were recruited. 3-D ultrasound and magnetic resonance imaging scans were performed at the supine position. Each of the two raters measured the apical vertebral rotation using the center of laminae (COL) method in the 3-D ultrasound images and the Aaro-Dahlborn method in the magnetic resonance images. The intra- and inter-reliability of the COL method was demonstrated by the intra-class correlation coefficient (ICC) (both [2, K] >0.9, p < 0.05). The COL method showed no significant difference (p < 0.05) compared with the Aaro-Dahlborn method. Furthermore, the agreement between these two methods was demonstrated by the Bland-Altman method, and high correlation was found (r > 0.9, p < 0.05). These results validated the proposed 3-D ultrasound method in the measurements of vertebral rotation in the patients with AIS.

Reliability of the axial vertebral rotation measurements of adolescent idiopathic scoliosis using the center of lamina method on ultrasound images: in vitro and in vivo study.

PURPOSE: This study aimed to investigate the intra- and inter-observer reliability of the axial vertebral rotation (AVR) measurements of adolescent idiopathic scoliosis (AIS) using the center of lamina (COL) method on ultrasound transverse images. METHODS: Three cadaver vertebrae were scanned with 42 AVR configurations by both ultrasound and radiograph. In this in vitro study, four observers measured the AVR using the COL method on ultrasound transverse images and three observers measured the AVR using the Stokes' method on radiographs. In the in vivo study, 13 AIS subjects were recruited. Eighteen spinal curvatures were identified and 48 vertebrae were selected for the AVR measurements. Two observers performed the AVR measurements on both the ultrasound images and radiographs. All measurements were performed twice with 1 week interval apart to reduce memory bias. The intraclass correlation coefficient (ICC), mean absolute differences (MAD), and standard deviation (SD) were used to analyze the intra- and inter-observer reliability of the AVR measurements. The Bland-Altman plot was used to analyze the 95 % limit of the differences between the two methods. RESULTS: The proposed COL method had high intra- and inter-observer reliability on both the in vitro and in vivo studies (ICCs > 0.91, MADs < 1.4°) and agreed well with the experimental setup (ICCs > 0.96, MADs < 2.3°). The COL method showed good agreement with the Stokes' method for the in vitro study (ICC 0.84-0.85, MAD 4.5°-5.0°), while poor agreement for the in vivo study (ICC 0.49-0.54, MAD 2.7°-3.5°). CONCLUSIONS: The pilot study indicated the proposed COL method was a simple and reliable method to evaluate the AVR on ultrasound images. Standardization of the posture during ultrasound scan and taking radiograph is important.

How quantity and quality of brace wear affect the brace treatment outcomes for AIS.

PURPOSE: To determine the reliability of a prognostic curve progression model and the role of the quantity and quality of brace wear for adolescent idiopathic scoliosis (AIS) brace treatment. METHODS: To develop a curve progression model for full-time AIS brace treatment, 20 AIS subjects (Group 1) prescribed full-time thoracolumbar sacral orthosis (TLSO) were monitored and followed for 2 years beyond maturity. The developed curve progression model was: curve progression (in degrees) = 33 + 0.11 × Peterson risk (%) - 0.07 in-brace correction (%) - 0.45 × quality (%) - 0.48 × quantity (%) + 0.0062 × quantity × quality. To validate the model, 40 new (test) subjects (Group 2) who met the same inclusion criteria and used the same type of monitors, were monitored and followed for 2 years after bracing. RESULTS: For the 40 test subjects (Group 2), the average in-brace correction was 40 ± 22 %. The average quantity and quality of the brace wear were 56 ± 19 and 55 ± 17 %, respectively. Twelve subjects (30 %) progressed of which 10 subjects (25 %) required surgery and 28 subjects (70 %) showed no progression. The accuracy of the model to determine which patients would progress was 88 % (35/40) which was better than the Peterson's risk model (68 %; 26/40) alone. Patients who had the combined quantity times the quality over a threshold 43 % had a success treatment rate of 95 %. CONCLUSIONS: This study showed the prognostic model of brace treatment outcome on AIS patients treated with full-time TLSO was reliable. Both the quantity and quality of the brace wear were important factors in achieving successful brace treatment.

Reliability and Validity Study of Clinical Ultrasound Imaging on Lateral Curvature of Adolescent Idiopathic Scoliosis.

BACKGROUND: Non-ionizing radiation imaging assessment has been advocated for the patients with adolescent idiopathic scoliosis (AIS). As one of the radiation-free methods, ultrasound imaging has gained growing attention in scoliosis assessment over the past decade. The center of laminae (COL) method has been proposed to measure the spinal curvature in the coronal plane of ultrasound image. However, the reliability and validity of this ultrasound method have not been validated in the clinical setting. OBJECTIVES: To evaluate the reliability and validity of clinical ultrasound imaging on lateral curvature measurements of AIS with their corresponding magnetic resonance imaging (MRI) measurements. METHODS: Thirty curves (ranged 10.2°-68.2°) from sixteen patients with AIS were eligible for this study. The ultrasound scan was performed using a 3-D ultrasound unit within the same morning of MRI examination. Two researchers were involved in data collection of these two examinations. The COL method was used to measure the coronal curvature in ultrasound image, compared with the Cobb method in MRI. The intra- and inter-rater reliability of the COL method was evaluated by intra-class correlation coefficient (ICC). The validity of this method was analyzed by paired Student's t-test, Bland-Altman statistics and Pearson correlation coefficient. The level of significance was set as 0.05. RESULTS: The COL method showed high intra- and inter-rater reliabilities (both with ICC (2, K) >0.9, p<0.05) to measure the coronal curvature. Compared with Cobb method, COL method showed no significant difference (p<0.05) when measuring coronal curvature. Furthermore, Bland-Altman method demonstrated an agreement between these two methods, and Pearson's correlation coefficient (r) was high (r>0.9, p<0.05). CONCLUSION: The ultrasound imaging could provide a reliable and valid measurement of spinal curvature in the coronal plane using the COL method. Further research is needed to validate the proposed ultrasound measurement in larger clinical trial and to optimize the ultrasound scanning and measuring procedure.

Predicting success or failure of brace treatment for adolescents with idiopathic scoliosis.

Adolescent idiopathic scoliosis (AIS) is a three-dimensional spinal deformity. Brace treatment is a common non-surgical treatment, intended to prevent progression (worsening) of the condition during adolescence. Estimating a braced patient's risk of progression is an essential part of planning treatment, so method for predicting this risk would be a useful decision support tool for practitioners. This work attempts to discover whether failure of brace treatment (progression) can be predicted at the start of treatment. Records were obtained for 62 AIS patients who had completed brace treatment. Subjects were labeled as "progressive" if their condition had progressed despite brace treatment and "non-progressive" otherwise. Wrapper-based feature selection selected two useful predictor variables from a list of 14 clinical measurements taken from the records. A logistic regression model was trained to classify patients as "progressive" or "non-progressive" using these two variables. The logistic regression model's simplicity and interpretability should facilitate its clinical acceptance. The model was tested on data from an additional 28 patients and found to be 75 % accurate. This accuracy is sufficient to make the predictions clinically useful. It can be used online: http://www.ece.ualberta.ca/~dchalmer/SimpleBracePredictor.html .

Validation of 3D surface reconstruction of vertebrae and spinal column using 3D ultrasound data--a pilot study.

Adolescent idiopathic scoliosis (AIS) is a three-dimensional deformity of spine associated with vertebra rotation. The Cobb angle and axial vertebral rotation are important parameters to assess the severity of scoliosis. However, the vertebral rotation is seldom measured from radiographs due to time consuming. Different techniques have been developed to extract 3D spinal information. Among many techniques, ultrasound imaging is a promising method. This pilot study reported an image processing method to reconstruct the posterior surface of vertebrae from 3D ultrasound data. Three cadaver vertebrae, a Sawbones spine phantom, and a spine from a child with AIS were used to validate the development. The in-vitro result showed the surface of the reconstructed image was visually similar to the original objects. The dimension measurement error was <5 mm and the Pearson correlation was >0.99. The results also showed a high accuracy in vertebral rotation with errors of 0.8 ± 0.3°, 2.8 ± 0.3° and 3.6 ± 0.5° for the rotation values of 0°, 15° and 30°, respectively. Meanwhile, the difference in the Cobb angle between the phantom and the image was 4° and the vertebral rotation at the apex was 2°. The Cobb angle measured from the in-vivo ultrasound image was 4° different from the radiograph.

Correlation between Cobb angle, spinous process angle (SPA) and apical vertebrae rotation (AVR) on posteroanterior radiographs in adolescent idiopathic scoliosis (AIS).

PURPOSE: To investigate the accuracy and reliability of the Cobb angle, the spinous process angle (SPA), and apical vertebral rotation (AVR) for measuring adolescent idiopathic scoliosis (AIS), and to evaluate the correlations between these measurements. METHODS: A retrospective study of two sets of standing posteroanterior radiographs of patients with AIS was performed. The first set was 59 consecutive patients with AIS with Cobb angles <45° and the second set was 25 patients with Cobb angles >45°. The Cobb angle, SPA and AVR of each curve was measured twice by three observers with varying measurement experience. The mean absolute difference, standard deviation, and intra- and inter-rater reliability coefficients for each measurement were examined. The Pearson correlation coefficients between any two parameters were reported. The association of the Cobb angle with the SPA and AVR was examined using a multiple regression model. RESULTS: The average intra- and inter-observer reliabilities (ICC [2, 1]) of the Cobb angle, SPA, and AVR were 0.99, 0.95, 0.92 and 0.98, 0.88, 0.83, respectively. The correlation coefficients (r) between Cobb angle and SPA, Cobb angle and AVR, and SPA and AVR were 0.93, 0.68, and 0.60, respectively. Using multiple regression, the association between the Cobb angle and SPA combined with AVR was R (2) = 0.90. The resulting regression model was: [Formula: see text]. CONCLUSION: The SPA has high correlation with the Cobb angle. Including the AVR as an additional factor in multiple regression improves the prediction of the Cobb angle.

3D ultrasound imaging method to assess the true spinal deformity.

Spinal deformity is a three-dimensional (3D) spinal disorder with a lateral deviation and coupled with axial vertebral rotation (AVR). The current clinical practice only measures its severity on postero-anterior (PA) radiographs, which may underestimate the deformity. The actual severity should be obtained on the plane of maximal curvature (PMC), which requires a 3D spinal image. There are many approaches to reconstruct 3D spinal images; however, ultrasound is one of the promising techniques with its non-ionizing characteristic. This study proposed an image processing method using the voxel-based bilinear interpolation to reconstruct a 3D spinal image from ultrasound data, from which the AVR was measured and the spinal curvature on the PMC was determined. In-vitro and in-vivo experiments were performed to determine the accuracy of the measurements from the ultrasound method. The results showed that the 3D ultrasound spinal image could be reconstructed. The curvature angle on the PA and the PMC planes could also be determined. The tilt angle of each individual vertebra in in-vitro study showed high accuracy and correlation (MAD <; 0.9° ± 0.2° and r(2) > 0.87) when comparing the measurements from CT with ultrasound. In in-vivo study, the curvature angles measured on the PA radiographs and ultrasound images yielded a small difference (MAD 3.4° ± 1.0°) and a strong correlation (r(2) = 0.63) within a clinical accepted error of 5°.

Multichannel filtering and reconstruction of ultrasonic guided wave fields using time intercept-slowness transform.

Multichannel ultrasonic axial-transmission data are multimodal by nature. As guided waves are commonly used in nondestructive material testing, wave field filtering becomes important because the analysis is usually limited to a few lower-order modes and requires their extraction. An application of the Radon transform to enhance signal-to-noise ratio and separate wave fields in ultrasonic records is presented. The method considers guided wave fields as superpositions of plane waves defined by ray parameters (p) and time intercepts (τ) and stacks the amplitudes along linear trajectories, mapping time-offset (t - x) data to a τ - p or Radon panel. The transform is implemented using a least-squares strategy with Cauchy-norm regularization that serves to enhance the focusing power. The method was verified using simulated data and applied to an uneven spatially sampled bovine-bone-plate data set. The results demonstrate the Radon panels show isolated amplitude clusters and the Cauchy-norm constraint provides a more focused Radon image than the damped least-squares regularization. Wave field separation can be achieved by selectively windowing the τ - p signals and inverse transformation, which is illustrated by the successful extraction of the A0 mode in bone plate. In addition, the method effectively attenuates noise, enhances the coherency of the guided wave modes, and reconstructs the missing records. The proposed transform presents a powerful signal-enhancement tool to process guided waves for further analysis and inversion.

Excitation of ultrasonic Lamb waves using a phased array system with two array probes: phantom and in vitro bone studies.

Long bones are good waveguides to support the propagation of ultrasonic guided waves. The low-order guided waves have been consistently observed in quantitative ultrasound bone studies. Selective excitation of these low-order guided modes requires oblique incidence of the ultrasound beam using a transducer-wedge system. It is generally assumed that an angle of incidence, θi, generates a specific phase velocity of interest, co, via Snell's law, θi=sin(-1)(vw/co) where vw is the velocity of the coupling medium. In this study, we investigated the excitation of guided waves within a 6.3-mm thick brass plate and a 6.5-mm thick bovine bone plate using an ultrasound phased array system with two 0.75-mm-pitch array probes. Arranging five elements as a group, the first group of a 16-element probe was used as a transmitter and a 64-element probe was a receiver array. The beam was steered for six angles (0°, 20°, 30°, 40°, 50°, and 60°) with a 1.6-MHz source signal. An adjoint Radon transform algorithm mapped the time-offset matrix into the frequency-phase velocity dispersion panels. The imaged Lamb plate modes were identified by the theoretical dispersion curves. The results show that the 0° excitation generated many modes with no modal discrimination and the oblique beam excited a spectrum of phase velocities spread asymmetrically about co. The width of the excitation region decreased as the steering angle increased, rendering modal selectivity at large angles. The phenomena were well predicted by the excitation function of the source influence theory. The low-order modes were better imaged at steering angle ⩾30° for both plates. The study has also demonstrated the feasibility of using the two-probe phased array system for future in vivo study.

Intra- and Interobserver Reliability of the Cobb Angle-Vertebral Rotation Angle-Spinous Process Angle for Adolescent Idiopathic Scoliosis.

STUDY DESIGN: A reliability analysis of Cobb angle, vertebral rotation (VR), and spinous process angle (SPA) measurements in adolescent idiopathic scoliosis. OBJECTIVE: To determine the intra- and interobserver reliability of semi-automated digital radiograph measurements. SUMMARY OF BACKGROUND DATA: Cobb angle measurements on posteroanterior radiographs are commonly used to determine the severity of scoliosis. Vertebral rotation helps assess scoliosis 3-dimensionally and has a role in predicting curve progression. Recent studies have shown that the spinous process angle is a useful parameter in assessing scoliosis when using ultrasound imaging. Because the reliability of SPA measurements on radiographs has yet to be determined, it is important to compare the reliability of these 3 parameters (Cobb angle, VR, and SPA) using a computer assisted semi-automated method. METHODS: Sixty posteroanterior radiographs of patients with adolescent idiopathic scoliosis were obtained and measured twice by 3 observers who were blinded to their previous measurements, using an in-house developed program. Measurements were obtained using a semi-automated method to minimize variability resulting from observer reliability. The intra- and interobserver reliabilities were analyzed using intra-class correlation coefficients (ICCs) as well as Bland-Altman's bias and limits of agreement. RESULTS: Over 350 (intra) and 90 (inter) sets of curves with an average Cobb angle of 26° ± 9° (range, 10° to 44°) were compared for each parameter. Intra-observer reliabilities for each parameter were excellent (ICC[2,1], .82; 1.00), with mean absolute differences under 3° between most measurements. Interobserver reliability (ICC[2,1], .72; .95) was mostly good to excellent, with mean absolute differences ranging from 2.0° to 5.6°. CONCLUSIONS: Both the intra- and interobserver assessment of the Cobb, VR, and SPA from the semi-automated measurements had clinically acceptable reliability ranges and may be considered for clinical implementation. Additional studies will be conducted to determine the accuracy and sensitivity to change of these scoliosis severity measurements.