The BoneXpert method for automated determination of skeletal maturity

Metacarpal thickness, width, length and medullary diameter in children--reference curves from the First Zürich Longitudinal Study

SUMMARY

Metacarpal thickness (T), width (W), length (L) and medullary diameter (M) were measured in 3,121 X-rays from 231 healthy Caucasian children aged 3 to 19 years and analysed for bone age, age, height, weight and gender-related characteristics, showing highly differentiated growth patterns with prepubertal dips. Reference data for the four metacarpal measures are presented.

INTRODUCTION

The aim of the study was to create and explore a reference database for metacarpal T, W, L and M in children.

METHODS

Three thousand one hundred twenty-one left-hand X-rays (1,661 from boys) from 231 healthy Caucasian subjects (119 boys) aged 3 to 19 years were analysed by BoneXpert, a programme for automatic analysis of hand X-rays and bone age (BA; in years).

RESULTS

In boys, growth of T, W and L shows a prepubertal decrease from BA 7 to 13 and then accelerates again. In girls, the same is seen only for T starting from BA 8 to 11, whereas W and L grow at a declining rate. M shows steady growth until BA 10.5 in girls and BA 13.5 in boys and then grows smaller in both. W is greater in boys from BA 6 onwards, while L is greater in girls from BA 9 to 13 and T from BA 11 to 14. BA is reflected best by L until start of puberty and by T and L thereafter.

CONCLUSION

T, W, L and M show highly differentiated growth patterns. These reference data provide a basis for further research into skeletal development and the management of hormone therapies in children.

Validation and reference values of automated bone age determination for four ethnicities

RATIONALE AND OBJECTIVES

Bone age (BA) rating is associated with a considerable rater variability, which would be eliminated with an automated computerized method. The aim of the study was to validate the BoneXpert method, an automated determination of BA, in American children of four ethnicities.

MATERIALS AND METHODS

The study is based on a publicly available database of hand x-rays of healthy children, established in a previous, National Institutes of Health-funded study. Radiographs of the left hand were recorded between 1993 and 2006 in Los Angeles, including 1100 images with two independent manual BA ratings and 280 additional images for which the manual ratings were not used. Images were evenly split between Caucasian, African American, Hispanic, and Asian children, and the age range was 0-18.99 years.

RESULTS

The automated method analyzed all images with BA >2.5 years for boys and >2 years for girls. The root-mean-square (RMS) error between the two manual ratings was 0.63 years, whereas the RMS deviation between the automated BA and the average of the two manual ratings was 0.61 years. The mean BA minus age was computed versus age for each sex and ethnicity. The largest deviation from zero was seen for Hispanic and Asian children older than 12 years, who were about 1 year advanced relative to the Greulich and Pyle standard.

CONCLUSION

The automated method can analyze images of all ethnicities within a BA range of 2.5-17 years for boys and 2-15 years for girls, and can therefore eliminate the problem with rater variability in BA rating.

Insulin sensitivity and lipid profiles in girls with central precocious puberty before and during gonadal suppression

CONTEXT

Early menarche is associated with increased risk of cardiovascular disease in adulthood. It is unknown whether metabolic risk factors are adversely affected in girls with central precocious puberty (CPP) already at time of diagnosis.

OBJECTIVE

The objective of the study was to evaluate metabolic profiles in girls with early normal puberty (EP) and CPP.

DESIGN AND SETTING

This was a combined cross-sectional and longitudinal study at a tertiary center of pediatric endocrinology.

PATIENTS AND INTERVENTION

Twenty-three girls with EP or CPP and 115 controls with normal pubertal timing were evaluated by oral glucose tolerance test, dual-energy x-ray absorptiometry scan, and fasting blood samples. Fifteen girls (13 CPP) were treated with GnRH agonists (GnRHa) and reevaluated after 12 and 52 wk of treatment.

MAIN OUTCOME MEASURES

Insulin and glucose levels during oral glucose tolerance test and fasting lipid levels were measured.

RESULTS

At the time of diagnosis, girls with CPP had higher fasting insulin, triglyceride, and low-density lipoprotein-cholesterol levels as well as lower insulin sensitivity and high-density lipoprotein/total cholesterol ratios (all P<0.05) compared with controls after adjustment for pubertal stage and body fat percentage. Age at pubertal onset positively predicted insulin sensitivity for a given pubertal stage (P=0.04) in girls with EP and CPP. Insulin sensitivity decreased significantly during 1 yr of GnRHa treatment (P=0.04).

CONCLUSIONS

Girls with CPP had adverse metabolic profiles at the time of diagnosis compared with puberty-matched controls. In addition, those with the earliest onset of puberty had the most adverse metabolic profiles. Surprisingly, metabolic profiles deteriorated even further after withdrawal of sex steroids by GnRHa treatment.

A paediatric bone index derived by automated radiogrammetry

SUMMARY

Hand radiographs are obtained routinely to determine bone age of children. This paper presents a method that determines a Paediatric Bone Index automatically from such radiographs. The Paediatric Bone Index is designed to have minimal relative standard deviation (7.5%), and the precision is determined to be 1.42%.

INTRODUCTION

We present a computerised method to determine bone mass of children based on hand radiographs, including a reference database for normal Caucasian children.

METHODS

Normal Danish subjects (1,867), of ages 7-17, and 531 normal Dutch subjects of ages 5-19 were included. Historically, three different indices of bone mass have been used in radiogrammetry all based on A = piTW(1 - T/W), where T is the cortical thickness and W the bone width. The indices are the metacarpal index A/W(2), DXR-BMD = A/W, and Exton-Smith's index A/(WL), where L is the length of the bone. These indices are compared with new indices of the form A/(W(a) L(b)), and it is argued that the preferred index has minimal SD relative to the mean value at each bone age and sex. Finally, longitudinal series of X-rays of 20 Japanese children are used to derive the precision of the measurements.

RESULTS

The preferred index is A/(W(1.33) L(0.33)), which is named the Paediatric Bone Index, PBI. It has mean relative SD 7.5% and precision 1.42%.

CONCLUSIONS

As part of the BoneXpert method for automated bone age determination, our method facilitates retrospective research studies involving validation of the proposed index against fracture incidence and adult bone mineral density.

A fuzzy-based growth model with principle component analysis selection for carpal bone-age assessment

There are two well-known methods to assess bone age, the Greulich-Pyle method and the Tanner-Whitehouse method, which both utilize the hand radiogram to make bone-age assessment to assist medical doctors to identify the growth status of children. Basically, the morphology of bones could be evaluated to quantitatively describe the maturity. The study extracted the morphology of carpal bones and applied the fuzzy theory with principle component analysis to estimate the maturity of skeleton. Five geometric features of the carpals were extracted including the bone area, the area ratio, and the bone contour of the carpals. In order to analyze these features, the principle component analysis and the statistical correlation combined with three different types of procedure were used to construct a growth model of carpals. Eventually, the results of the three types of procedure with fuzzy rules can construct a bone-age assessment system to identify the maturity of children. The study shows that the proposed model based on fuzzy rule has an accuracy rate above 89% in Type-I and II, and above 87% in Type-III within a tolerance of 1.5 years.

Prediction of adult height based on automated determination of bone age

CONTEXT

Adult height prediction is a common procedure in pediatric endocrinology, but it is associated with a considerable variability and bias from the bone age rating.

OBJECTIVE

A new method for adult height prediction is presented, based on automated bone age determination.

METHOD

The method predicts the fraction of height left to grow from age and BoneXpert bone age. This is refined by drawing the prediction toward the population mean, or alternatively toward the height predicted from the parents' heights. Boys' body mass index and girls' height at menarche can be included optionally as predictors.

PARTICIPANTS

A total of 231 normal children from the First Zurich Longitudinal Study (1ZLS) were followed from age 5 until cessation of growth with annual x-rays of the left hand. A total of 198 normal children from the Third Zurich Longitudinal Study were used for validation.

RESULTS

The root mean square error of adult height prediction (Tanner-Whitehouse 3 method in parentheses considered as standard for accuracy) on the 1ZLS was 3.3 cm (3.5 cm) for boys aged 10-15 yr and 2.7 cm (3.1 cm; P < 0.005 for difference to Tanner-Whitehouse 3) for girls aged 8-13 yr. High body mass index before puberty negatively affected adult height of boys, independent of bone age.

CONCLUSIONS

With the new method, adult height prediction has become objective because the dependence on manual bone age rating is eliminated. The method is well-suited to analyze large studies and provide a consistent body of evidence regarding the relation between maturation, body mass, and growth across populations, conditions, and ethnicities.

Computational radiology in skeletal radiography

Recent years have brought rapid developments in computational image analysis in musculo-skeletal radiology. Meanwhile the algorithms have reached a maturity that makes initial clinical use feasible. Applications range from joint space measurement to erosion quantification, and from fracture detection to the assessment of alignment angles. Current results of computational image analysis in radiography are very promising, but some fundamental issues remain to be clarified, among which the definition of the optimal trade off between automatization and operator-dependency, the integration of these tools into clinical work flow and last not least the proof of incremental clinical benefit of these methods.

Clinical review: An automated method for determination of bone age

CONTEXT

Bone age rating is associated with a considerable rater variability, which limits its usefulness in modern pediatric endocrinology. An automated computerized method would theoretically solve this problem but has been surprisingly difficult to establish.

EVIDENCE ACQUISITION

We review the development of automated bone age assessment and describe how the conceptual understanding of bone age rating shifted from a rule-based theory to a more intuitive and experience-based approach. The role of the CASAS system from 1992 is described. The BoneXpert system from 2008 employs deformable models of each bone to locate the bones and extracts the component of the bone appearance related to maturity in a holistic, statistical manner. Two clinical studies have been published on its accuracy, defined as the root mean square deviation from manual rating. Other studies addressed the precision of the method, defined as its ability to give the same result on a repeated x-ray, expressed as the sd on a single measurement.

EVIDENCE SYNTHESIS

The accuracy of the automated bone age determination was 0.71-0.72 yr, and the precision was 0.17-0.18 yr. More than 98.6% of the images could be analyzed. The system was validated on children with various diagnoses of short stature in the bone age range 2.5-17 yr for boys and 2-15 yr for girls.

CONCLUSION

The reviewed validation studies suggest that this automated bone age determination system has adequate accuracy, precision, and efficiency to be clinically useful.

Automatic determination of Greulich and Pyle bone age in healthy Dutch children

BACKGROUND

Bone age (BA) assessment is a routine procedure in paediatric radiology, for which the Greulich and Pyle (GP) atlas is mostly used. There is rater variability, but the advent of automatic BA determination eliminates this.

OBJECTIVE

To validate the BoneXpert method for automatic determination of skeletal maturity of healthy children against manual GP BA ratings.

MATERIALS AND METHODS

Two observers determined GP BA with knowledge of the chronological age (CA). A total of 226 boys with a BA of 3-17 years and 179 girls with a BA of 3-15 years were included in the study. BoneXpert's estimate of GP BA was calibrated to agree on average with the manual ratings based on several studies, including the present study.

RESULTS

Seven subjects showed a deviation between manual and automatic BA in excess of 1.9 years. They were re-rated blindly by two raters. After correcting these seven ratings, the root mean square error between manual and automatic rating in the 405 subjects was 0.71 years (range 0.66-0.76 years, 95% CI). BoneXpert's GP BA is on average 0.28 and 0.20 years behind the CA for boys and girls, respectively.

CONCLUSION

BoneXpert is a robust method for automatic determination of BA.

Clinical application of automated Greulich-Pyle bone age determination in children with short stature

BACKGROUND

Bone age (BA) rating is time consuming and highly rater dependent.

OBJECTIVE

To adjust the fully automated BoneXpert method to agree with the manual Greulich and Pyle BA (GP BA) ratings of five raters and to validate the accuracy for short children.

MATERIALS AND METHODS

A total of 1,097 left hand radiographs from 188 children with short stature, including growth hormone deficiency (44%) and Turner syndrome (29%) were evaluated.

RESULTS

BoneXpert rejected 14 of the 1,097 radiographs, and deviated by more than 1.9 years from the operator BA for 27 radiographs. These were rerated blindly by four operators. Of the 27 new ratings, 26 were within 1.9 years of the automatic BA values. The root mean square deviation between manual and automatic rating was 0.72 years (95% CI 0.69-0.75).

CONCLUSION

BoneXpert's ability to process 99% of images automatically without errors, and to obtain good agreement with an operator suggests that the method is efficient and reliable for short children.