Hans Henrik Thodberg

The BoneXpert Method for Automated Determination of Skeletal Maturity

Bone age rating is associated with a considerable variability from the human interpretation, and this is the motivation for presenting a new method for automated determination of bone age (skeletal maturity). The method, called BoneXpert, reconstructs, from radiographs of the hand, the borders of 15 bones automatically and then computes ldquointrinsicrdquo bone ages for each of 13 bones (radius, ulna, and 11 short bones). Finally, it transforms the intrinsic bone ages into Greulich Pyle (GP) or Tanner Whitehouse (TW) bone age. The bone reconstruction method automatically rejects images with abnormal bone morphology or very poor image quality. From the methodological point of view, BoneXpert contains the following innovations: 1) a generative model (active appearance model) for the bone reconstruction; 2) the prediction of bone age from shape, intensity, and texture scores derived from principal component analysis; 3) the consensus bone age concept that defines bone age of each bone as the best estimate of the bone age of the other bones in the hand; 4) a common bone age model for males and females; and 5) the unified modelling of TW and GP bone age. BoneXpert is developed on 1559 images. It is validated on the Greulich Pyle atlas in the age range 2-17 years yielding an SD of 0.42 years [0.37; 0.47] 95% conf, and on 84 clinical TW-rated images yielding an SD of 0.80 years [0.68; 0.93] 95% conf. The precision of the GP bone age determination (its ability to yield the same result on a repeated radiograph) is inferred under suitable assumptions from six longitudinal series of radiographs. The result is an SD on a single determination of 0.17 years [0.13; 0.21] 95% conf.

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.

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.

The Use of Bone Age in Clinical Practice – Part 2

If height-limiting treatment is being considered for a child with tall stature, skeletal maturity is invaluable in the selection of appropriate patients for treatment, determining appropriate age of treatment commencement, monitoring progress of treatment, and determining the expected treatment effect on adult height. In precocious puberty, bone maturation can be usefully assessed at initial diagnosis and start of treatment and at regular intervals thereafter during treatment monitoring. Together with height, bone maturation is an essential parameter for long-term treatment monitoring in congenital adrenal hyperplasia. Bone age (BA) determination in children with skeletal dysplasia is only feasible in a few disorders and estimations should be treated with caution. Radiographs of the left hand and wrist are, however, essential in the diagnosis of many skeletal disorders. Bone mineralization and measures of bone lengths, width, thickness and cortical thickness should always be evaluated in relation to a child’s height and BA, especially around puberty. The use of skeletal maturity, assessed on a radiograph alone to estimate chronological age for immigration authorities or criminal courts is not recommended.

A paediatric bone index derived by automated radiogrammetry

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

Validation of a new method for automated determination of bone age in Japanese children.

A = \pi {\text{ }}T{\text{ }}W\left( {{\text{1}} - T/W} \right)

Validation of automatic bone age rating in children with precocious and early puberty

, where T is the cortical thickness and W the bone width. The indices are the metacarpal index A/W2, 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/(WaLb), 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.ResultsThe preferred index is A/(W1.33L0.33), which is named the Paediatric Bone Index, PBI. It has mean relative SD 7.5% and precision 1.42%.ConclusionsAs 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.

Automation of Bone Age Reading and a New Prediction Model Improve Adult Height Prediction in Children with Short Stature

Background/Aims: A more advanced bone age (BA) has been reported for the left hand relative to the right hand, while another study has found no such effect. The aim was to study the average difference of automated BoneXpert BA determination (left- vs. right-hand) for normal children, examine the precision of automatic BA and provide a BA reference for normal Caucasian children. Methods: Radiographs of both hands (age range: 2–20 years) were digitised and analysed automatically to determine Greulich-Pyle BA, producing analysis results for 3,374 left-hand and 2,752 right-hand images. Results: Comparison of left- and right-hand BA showed no average difference (<0.07 years, 95% confidence). The SD of the differences between left and right sides was 0.25 years for boys as well as girls, implying the precision of automated Greulich-Pyle BA determination was 0.18 years or better. Greulich-Pyle BA for boys and girls were on average 0.10 and 0.21 years below the chronological age. Conclusion: The left and right hand give the same BA on average and the SD between the sides is 0.25 years, indicating an excellent precision of the automated method.