Ultrasound Volume Projection Imaging for Assessment of Scoliosis

Significance of recumbent curvature in prediction of in-orthosis correction for adolescent idiopathic scoliosis

BACKGROUND:

Prediction of in-orthosis curvature at pre-orthosis stage is valuable for the treatment planning for adolescent idiopathic scoliosis, while the position of spinal curvature assessment that is effective for this prediction is still unknown.

OBJECTIVES:

To compare the spinal curvatures in different body positions for predicting the spinal curvature rendered by orthosis.

STUDY DESIGN:

A prospective cohort study.

METHODS:

Twenty-two patients with adolescent idiopathic scoliosis (mean Cobb angle: 28.1°± 7.3°) underwent ultrasound assessment of spinal curvature in five positions (standing, supine, prone, sitting bending, prone bending positions) and that within orthosis. Differences and correlations were analyzed between the spinal curvatures in the five positions and that within orthosis.

RESULTS:

The mean in-orthosis curvature was 11.2° while the mean curvatures in five studied positions were 18.7° (standing), 10.7° (supine), 10.7° (prone), -3.5° (prone bending), and -6.5° (sitting bending). The correlation coefficients of the in-orthosis curvature and that in five studied positions were r = 0.65 (standing), r = 0.76 (supine), r = 0.87 (prone), r = 0.41 (prone bending), and r = 0.36 (sitting bending).

CONCLUSION:

The curvature in recumbent positions (supine and prone) is highly correlated to the initial in-orthosis curvature without significant difference. Thus, the initial effect of spinal orthosis could be predicted by the curvature in the recumbent positions (especially prone position) at the pre-orthosis stage.

CLINICAL RELEVANCE

Prediction of in-orthosis correction at pre-orthosis stage is valuable for spinal orthosis design. This study suggests assessing the spinal curvature in recumbent position (especially prone position) to predict the initial in-orthosis correction for optimizing the orthosis design.

Non-ionizing method of screening adolescent idiopathic scoliosis in schoolchildren

Adolescent idiopathic scoliosis (AIS) affects 2% to 4% of young people in Brazil. Repeated exposures to radiation used in the monitoring of the deformity can be harmful to the health. This study aimed to present a photogrammetry protocol as a non-ionizing method to quantify scoliosis and relate it to the Cobb radiological method. Sixteen individuals with idiopathic scoliosis (age: 21.4 ± 6.1 years, body mass index: 19.8 ± 0.2 kg/m2) underwent standing posteroanterior X-ray examination of the trunk. Additionally, markers were placed on the spinal processes of the C7 to L5 vertebrae, and posterior trunk photographs were taken. All images were sent for independent analysis by two examiners who were trained in the quantification of scoliosis. The average of the thoracic curvature evaluated through the photogrammetry and Cobb methods were 36.43° and 36.14°, respectively. With an average difference of 4.1°, the methods were not statistically different (p < 0.05). As a non-ionizing method that is low cost and portable, photogrammetry may represent a suitable alternative to the radiological method. Further studies are needed for the improvement of non-ionizing techniques in AIS screening.

Patterns of coronal curve changes in forward bending posture: a 3D ultrasound study of adolescent idiopathic scoliosis patients

PURPOSE

The Adam's forward bending test is the most commonly used approach to assess the spine deformity in adolescent idiopathic scoliosis (AIS) patients. However, there are noticeable differences in the hump appearance from standing to forward bending. This phenomenon has yet to be understood due to limitations of conventional radiographs. This study aimed to investigate effects of postural change in the spine deformity in the coronal plane of AIS patients using a 3D ultrasound imaging system.

METHODS

This was a prospective study that recruited 72 AIS patients at a single institute. All patients were scanned twice in the sitting and sitting forward bending postures. A coronal ultrasound image showing the spinal curvature was generated after each scan and the spinous process angle (SPA) representing the deformity was manually measured from it. Correlation of SPAs under sitting and sitting forward bending postures was analyzed.

RESULTS

In the comparison test, it was noted that there were three types of spine profile alternation after the postural change. In types I and II, the SPA angle numbers were the same before and after forward bending and only SPA values changed. In type III, the two curvatures were changed to one curvature in the forward bending posture. Moderate correlation was observed between the angles obtained in the two postures (r = 0.55, p < 0.001).

CONCLUSIONS

Spine deformities of AIS patients vary with different postures. The patterns of changes in sitting and sitting forward bending postures are highly subject dependent. These slides can be retrieved under Electronic Supplementary Material.

Factors influencing spinal curvature measurements on ultrasound images for children with adolescent idiopathic scoliosis (AIS)

The measurements of spinal curvatures using the ultrasound (US) imaging method on children with scoliosis have been comparable with radiography. However, factors influencing the reliability and accuracy of US measurement have not been studied. The purpose of this study is to investigate the effects of curve features and patients' demographics on US measurements and to determine which factors influence the reliability and accuracy. Two hundred children with scoliosis were recruited and scanned with US by one experienced operator and three trainees. One experienced rater measured the proxy Cobb angles from US images twice one week apart and compared the results with clinical radiographic records. The correlation and accuracy between the US and radiographic measurements were subdivided by different curve severities, curve types, subjects' weight status and US acquisition experiences. A total of 326 and 313 curves were recognized from radiographs and US images, respectively. The mean Cobb angles of the 13 missing curves were 17.4±7.4° and 11 at the thoracic region. Among the 16 curves showing large discrepancy (≥6°) between US and radiographic measurements, 7 were main thoracic and 6 were lumbar curves. Twelve had axial vertebral rotation (AVR) greater than 8°. The US scans performed by the experienced operator showed fewer large discrepancy curves, smaller difference and higher correlation than the scans from the trainees (3%, 1.7±1.5°, 0.95 vs 6%, 2.4±1.8°, 0.90). Only 4% missing and 5% large discrepancy curves were demonstrated for US measurements in comparison to radiography. The missing curves were mainly caused by small severity and in the upper spinal region. There was a higher chance of the large discrepancy curves in the main thoracic and lumbar regions with AVR>8°. A skilled operator acquired better US images and led to more accurate measurements especially for those subjects with larger curvatures, AVR and body mass index (BMI).

A reliability and validity study for different coronal angles using ultrasound imaging in adolescent idiopathic scoliosis

BACKGROUND CONTEXT

Radiation exposure remains a big concern in adolescent idiopathic scoliosis (AIS). Ultrasound imaging of the spine could significantly reduce or possibly even eliminate this radiation hazard. The spinous processes (SPs) and transverse processes (TPs) were used to measure the coronal deformity. Both landmarks provided reliable information on the severity of the curve as related to the traditional Cobb angle. However, it remained unclear which coronal ultrasound angle is the most appropriate method to measure the curve severity.

PURPOSE

The objective of this study was to test the reliability and the validity of several ultrasound angle measurements in the coronal plane as compared with the radiographic coronal Cobb angle in patients with AIS.

STUDY DESIGN/SETTING

This is a cross-sectional study.

PATIENT SAMPLE

The study included 33 patients with AIS, both male and female (Cobb angle range: 3°-90°, primary and secondary curves), who underwent posterior-anterior radiography of the spine.

OUTCOME MEASURES

The outcome measures were the reliability (intraclass correlation coefficients [ICCs] for the intra- and interobserver variabilities) and the validity (linear regression analysis and Bland-Altman method, including the mean absolute difference [MAD]) of different ultrasound measurements.

MATERIALS AND METHODS

The patients were scanned using a dedicated ultrasound machine (Scolioscan, Telefield Medical Imaging Ltd, Hong Kong). The reliability and the validity were tested for three coronal ultrasound angles: an automatic and manual SP angle and a manual TP angle as compared with the radiographic coronal main thoracic or (thoraco)lumbar Cobb angles.

RESULTS

The ICC showed very reliable measurements of all ultrasound methods (ICC ≥0.84). The ultrasound angles were 15%-37% smaller as compared with the Cobb angles; however, excellent linear correlations were seen between all ultrasound angles and the Cobb angle (thoracic: R²≥0.987 and (thoraco)lumbar R²≥0.970), and the Bland-Altman plot showed a good agreement between all ultrasound angles and the Cobb angle. The MADs of the ultrasound angles, corrected using the linear regression equation, and the Cobb angles showed no significant difference between the different ultrasound angles (MAD: automatic SP angle 4.9°±3.2°, manual SP angle 4.5°±3.1°, and manual TP angle 4.7°±3.6°; p≥.388).

CONCLUSIONS

Coronal ultrasound angles are based on different landmarks than the traditional Cobb angle measurement and cannot represent the same angle values. In this study, we found excellent correlations between the ultrasound and Cobb measurements, without differences in the reliability and validity between the ultrasound angles based on the SPs and TPs. Therefore, the severity of the deformity in patients with AIS can be assessed by ultrasound imaging, avoiding hazardous ionizing radiation and enabling more individualized patient care. It also opens possibilities for screening.

2.5-D Extended Field-of-View Ultrasound

Recently, the growing emphasis on medical ultrasound (US) has led to a rapid development of US extended field-of-view (EFOV) techniques. US EFOV techniques can be classified into three categories: 2-D US EFOV, 3-D US, and 3-D US EFOV. In this paper, we propose a novel EFOV method called 2.5-D US EFOV that combines both the advantages of the 2-D US EFOV and the 3-D US by generating a panorama on a curved image plane guided by a curved scanning trajectory of the US probe. In 2.5-D US EFOV, the real-time position and orientation of the US image plane can be recorded via an electromagnetic spatial sensor attached to the probe. The scanning direction is not necessarily straight and can be curved according to the regions of interest (ROI). To form the curved panorama, an image cutting method is proposed. Finally, the curved panorama is rendered in a 3-D space using a surface rendering based on a texture mapping technique. This allows 3-D measurements of lines and angles. Phantom experiments demonstrated that 2.5-D US EFOV images could show anatomical structures of ROI accurately and rapidly. The overall average errors for the distance and angle measurements are -0.097 ± 0.128 cm (-1% ± 1.2%) and 1.50° ± 1.60° (1.9% ± 2%), respectively. A typical extended US image can be reconstructed from 321 B-scans images within 3 s. The satisfying quantitative result on the spinal tissues of a scoliosis subject demonstrates that our system has potential applications in the assessment of musculoskeletal issues.

Automatic Measurement of Spine Curvature on 3-D Ultrasound Volume Projection Image With Phase Features

This paper presents an automated measurement of spine curvature by using prior knowledge on vertebral anatomical structures in ultrasound volume projection imaging (VPI). This method can be used in scoliosis assessment with free-hand 3-D ultrasound imaging. It is based on the extraction of bony features from VPI images using a newly proposed two-fold thresholding strategy, with information of the symmetric and asymmetric measures obtained from phase congruency. The spinous column profile is detected from the segmented bony regions, and it is further used to extract a curve representing spine profile. The spine curvature is then automatically calculated according to the inflection points along the curve. The algorithm was evaluated on volunteers with the different severity of scoliosis. The results obtained using the newly developed method had a good linear correlation with those by the manual method (r ≥ 0.90, p <; 0.001) and X-ray Cobb's method (r = 0.83, p <; 0.001). The bigger variations observed in the manual measurement also implied that the automatic method is more reliable. The proposed method can be a promising approach for facilitating the applications of 3-D ultrasound imaging in the diagnosis, treatment, and screening of scoliosis.

A reliability and validity study for Scolioscan: a radiation-free scoliosis assessment system using 3D ultrasound imaging

BACKGROUND

Radiographic evaluation for patients with scoliosis using Cobb method is the current gold standard, but radiography has radiation hazards. Several groups have recently demonstrated the feasibility of using 3D ultrasound for the evaluation of scoliosis. Ultrasound imaging is radiation-free, comparatively more accessible, and inexpensive. However, a reliable and valid 3D ultrasound system ready for clinical scoliosis assessment has not yet been reported. Scolioscan is a newly developed system targeted for scoliosis assessment in clinics by using coronal images of spine generated by a 3D ultrasound volume projection imaging method. The aim of this study is to test the reliability of spine deformity measurement of Scolioscan and its validity compared to the gold standard Cobb angle measurements from radiography in adolescent idiopathic scoliosis (AIS) patients.

METHODS

Prospective study divided into two stages: 1) Investigation of intra- and inter- reliability between two operators for acquiring images using Scolioscan and among three raters for measuring spinal curves from those images; 2) Correlation between the Cobb angle obtained from radiography by a medical doctor and the spine curve angle obtained using Scolioscan (Scolioscan angle). The raters for ultrasound images and the doctors for evaluating radiographic images were mutually blinded. The two stages of tests involved 20 (80 % females, total of 26 angles, age of 16.4 ± 2.7 years, and Cobb angle of 27.6 ± 11.8°) and 49 (69 % female, 73 angles, 15.8 ± 2.7 years and 24.8 ± 9.7°) AIS patients, respectively. Intra-class correlation coefficients (ICC) and Bland-Altman plots and root-mean-square differences (RMS) were employed to determine correlations, which interpreted based on defined criteria.

RESULTS

We demonstrated a very good intra-rater and intra-operator reliability for Scolioscan angle measurement with ICC larger than 0.94 and 0.88, respectively. Very good inter-rater and inter-operator reliability was also demonstrated, with both ICC larger than 0.87. For the thoracic deformity measurement, the RMS were 2.5 and 3.3° in the intra- and inter-operator tests, and 1.5 and 3.6° in the intra- and inter-rater tests, respectively. The RMS differences were 3.1, 3.1, 1.6, 3.7° in the intra- and inter-operator and intra- and inter-rater tests, respectively, for the lumbar angle measurement. Moderate to strong correlations (R(2) > 0.72) were observed between the Scolioscan angles and Cobb angles for both the thoracic and lumbar regions. It was noted that the Scolioscan angle slightly underestimated the spinal deformity in comparison with Cobb angle, and an overall regression equation y = 1.1797x (R(2) = 0.76) could be used to translate the Scolioscan angle (x) to Cobb angle (y) for this group of patients. The RMS difference between Scolioscan angle and Cobb angle was 4.7 and 6.2°, with and without the correlation using the overall regression equation.

CONCLUSIONS

We showed that Scolioscan is reliable for measuring coronal deformity for patients with AIS and appears promising in screening large numbers of patients, for progress monitoring, and evaluation of treatment outcomes. Due to it being radiation-free and relatively low-cost, Scolioscan has potential to be widely implemented and may contribute to reducing radiation dose during serial monitoring.

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.

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°.

Freehand three-dimensional ultrasound system for assessment of scoliosis

Background/Objective

Standing radiograph with Cobb's method is routinely used to diagnose scoliosis, a medical condition defined as a lateral spine curvature > 10° with concordant vertebral rotation. However, radiation hazard and two-dimensional (2-D) viewing of 3-D anatomy restrict the application of radiograph in scoliosis examination.

Methods

In this study, a freehand 3-D ultrasound system was developed for the radiation-free assessment of scoliosis. Bony landmarks of the spine were manually extracted from a series of ultrasound images with their spatial information recorded to form a 3-D spine model for measuring its curvature. To validate its feasibility, in vivo measurements were conducted in 28 volunteers (age: 28.0 ± 13.0 years, 9 males and 19 females). A significant linear correlation (R² = 0.86; p < 0.001) was found between the spine curvatures as measured by Cobb's method and the 3-D ultrasound imaging with transverse process and superior articular process as landmarks. The intra- and interobserver tests indicated that the proposed method is repeatable.

Results

The 3-D ultrasound method using bony landmarks tended to underestimate the deformity, and a proper scaling is required. Nevertheless, this study demonstrated the feasibility of the freehand 3-D ultrasound system to assess scoliosis in the standing posture with the proposed methods and 3-D spine profile.

Conclusion

Further studies are required to understand the variations that exist between the ultrasound and radiograph results with a larger number of volunteers, and to demonstrate its potential clinical applications for monitoring of scoliosis patients. Through further clinical trials and development, the reported 3-D ultrasound imaging system can potentially be used for scoliosis mass screening and frequent monitoring of progress and treatment outcome because of its radiation-free and easy accessibility feature.