Bone age assessment by a quantitative sonometer Short title€¦ · Rachmiel et al, Bone age by ultrasound 3. Introduction Skeletal maturity assessment, defined also as ‘bone age’

Rachmiel et al, Bone age by ultrasound

1

Bone age assessment by a quantitative sonometer

Short title: Bone age by ultrasound

Marianna Rachmiel, MD 1,2

, Larisa Naugolni, MD 1, Kineret Mazor-Aronovitch, MD

2,3, Amnon

Levin 4, Nira Koren-Morag, PhD

5, Tzvi Bistritzer, MD

1,2. Ze’ev Hochberg, MD PhD

6

1Pediatric Endocrinology Clinic, Assaf Haroffeh Medical Center, Zerifin Israel,

2Sackler School

of Medicine, Tel Aviv University, Tel Aviv, Israel,3Pediatric Endocrinology Unit, Shebba

Medical Center, Israel, 4SonicBone Medical Company, Rishon Lezion, Israel ,

5 Department of

Epidemiology and Preventive Medicine, Sackler Faculty of Medicine, Tel-Aviv University

6 Pediatric Endocrinology, the Technion – Israel Institute of Technology, School of Medicine,

Haifa. Israel

Corresponding author: Marianna Rachmiel, Pediatric Diabetes Service, Division of pediatrics,

Assaf-Harofeh Medical Center, Zerifin, 70300, Israel.

Tel: 972-8-9542007, Fax: 972-8-9779156, E.mail:[email protected]

Key terms: short children, skeletal maturation, x-ray, bone age assessment, ultrasound,

SonicBone, sonometer

Conflict of Interest:

The study was funded by SonicBone (Rishon Lezion, Israel).

AL is an employee of SonicBone and ZH is an independent consultant

Words count: 2109


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Abstract

Objective: Bone maturation is currently assessed by repeated radiography using eye-balling

subjective readings, or automated comparison of the characteristics of hand and wrist bones. The

aim of the study was to evaluate the concordance and reproducibility of a new portable device

(SonicBone's BAUSTM

) that utilizes quantitative ultrasonographic (US) technology measuring

the speed of sound (SOS) of US waves propagating along measured bone, and to compare it to

the current irradiating methods of bone age (BA) assessment (Greulich and Pyle (GP), Tanner-

Whitehouse 3 (TW3)).

Methods: The study population included 150 participants, 76 males, age 10.63.3 years,

attending an endocrine clinic. X-ray scans were evaluated independently by 4 observers.

Separate readings for wrist, carpal and phalanx were averaged for child's BA assessment. Data

from 100 subjects were utilized to assess the correlation between the speed-of-sound (SOS) and

attenuation (ATN) parameters against the manual BA by GP method, and to establish a

conversion equation for BA assessment by SonicBone. Fifty participants were assigned to assess

validity. BA assessment by SonicBone was correlated for manual GP, automated GP and TW3

methods.

Results: The coefficient of determination, R2 ,for the conversion equation including gender, SOS

and ATN was 0.80 for manual GP, 0.81 for automated GP and 0.82 for automated TW3

(p<0.001 for all). Pearson correlation between Sonographic BA and manual GP, automated GP

and automated TW3 demonstrated significant validity, r=0.89, r=0.91, r=0.91 (p<0.001 for all),

respectively.

Conclusion: BA assessment by SonicBone is comparable to the assessment by all three X-ray

based methods: manual GP, automated GP and TW3


3

.

Introduction

Skeletal maturity assessment, defined also as ‘bone age’ (BA), is frequently used for evaluating

growth and puberty in children and adolescents. It is recommended as part of the routine clinical

care workup of a child with short or tall stature, precocious and delayed puberty, and more 1, 2

.

Repeated BA assessments are an important clinical tool utilized during the follow-up of such

patients, especially when treated by growth and puberty-related interventions1, 2

. BA is currently

assessed by radiography of the hand, using eye-balling or automated comparison of the shape

and size of the wrist and hand bones to a standard series of representative radiographic films of

hands according to the 1959 Radiographic Atlas of Skeletal Development by Greulich and Pyle

(GP) 1, 3

, or to the scoring method by Tanner and Whitehouse, currently in its 2001 third edition

TW3 1, 4, 5

.

To address the disadvantage of repeated irradiation, the need for specialized radiation centers,

heavy equipment and subjective reading1, 6-8

a new device, SonicBone (SB) (Rishon Lezion,

Israel) was developed. SB utilizes a quantitative ultrasonographic (QUS) technology of

ultrasonic (US) waves, propagating along a measured bone distance9, 10

.

Here, we report the validity and reproducibility of BA by SB, as compared to eye-balling BA by

the GP method and an automated reading by both the GP and TW3 methods.

Patients and Methods:

Study design: This was a cross sectional study. The study subjects (n=150, 76 males) were

recruited consecutively in a pediatric endocrine clinic. All BAs performed by X-ray scans and

QUS were conducted prior to data analysis. The participants were then randomized to an

’Analysis group’ (n=100, 40 males) and a 'Validation group’ (n=50, 27 males). Analysis


4

performed on data obtained from the ’Analysis group’ enabled to establish a conversion equation

for BA assessment by SonicBone. Analysis performed on data obtained from the ‘Validation

group’ assessed the relationship between QUS against the manual GP method, automated GP

method, and automated TW3 method.

The study protocol was approved by the institutional review board and by the Helsinki

Committee of the Israeli Ministry of Health, and registered at www.clinicaltrials.gov

(NCT01346618). Written informed consent was obtained from each legal guardian, and the

participant assented for the study.

Study population: Patients ranging between 4-17 years of age were recruited from the Pediatric

Endocrinology Clinic at Assaf Haroffeh Medical Center, Israel. Inclusion criteria included all

patients who performed hand x-ray scan as part of their clinical care. Exclusion criteria included

children with bone diseases or those who within the last year took medications which might

change bone metabolism or mineralization (such as: high dose steroids, biphosphonates, high

dose Vitamin D, calcitriol).

BA assessment by the manual GP method: Hand x-ray scans were reviewed and assessed

independently by four pediatric endocrinologists being blinded to each other’s findings. They

assigned a separate BA to the long bones (Radius and Ulna, the carpalsand the short bones, and

the mean of the three readings was defined as the child’s BA , as previously described 11, 12

. The

mean of four observers was defined as the child’s BA by GP.

Automated BA assessment: The images were analyzed using the BoneXpert version 2.1

automated method for BA determination (Visiana, Denmark), which determines both GP and

TW3 BA 13, 14


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Ultrasonic BA assessment: The SonicBone (SB) device (Rishon Lezion, Israel) is a small (50cm

X 25cm X 25cm), portable, bone sonometer (Figure 1), which measures two parameters: a)

speed of propagation through bone (speed-of-sound, SOS, m/sec) of inaudible high frequency

waves of a short ultrasound pulse; and b) attenuation (ATN; the decay rate) of the sound wave by

the bone as a function of the distance it travels between a transmitter probe and a receiver

probe15

. The hand was measured by (Figure 1): 1- wrist (W), measuring SOS and ATN at the

distal radius and ulna secondary ossification centers of the epiphyses; 2-metacarpals (MC),

measuring SOS and ATN at the distal metacarpal epiphyses; and 3- phalange (P), measuring

SOS and ATN along the bent proximal third phalanx shaft, growth plate and epiphysis. The

average of those 3 readings was defined as the child’s BA by SB. All ultrasonic examinations

were conducted at the Pediatric Endocrinology Clinic, by trained personnel. The examiners were

blinded to the clinical background and to the BA by GP or TW3. Each subject underwent two

readings by two observers. Eight additional repeated readings were performed for 10 subjects, 5

boys and 5 girls, aged 6-16 to ensure reproducibility and precision positioning assessment.

Statistical Analysis: Data was analyzed with SPSS software version 21.0 (SPSS Inc. Chicago, Il,

USA). The estimation of within subject repeatability was calculated by a one way analysis of

variance (ANOVA) model. The outcome measures of the study included the correlation and

hypothesis testing of equality of BA by SB and BA by manual GP, automated GP and automated

TW3. The immediate side effects were also examined, by counting the numbers of incidents, the

nature of inconveniencies and other complaints. The first phase analysis, performed on all study

population (n=150), using Pearson correlation coefficient, demonstrated, the linear relationship

between BA by GP and measurements of SB, SOS and ATN parameters. The second phase

analysis of 100 subjects (‘Analysis group’) established a conversion equation for estimating BA

by SB out of the multivariate linear regression coefficients involving gender and the SB

parameters. These equations provided the best R² result .


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The third phase analysis was performed on data collected from the ‘Validation Group’ (n=50)

using the equations generated at phase 2 .The correlation between BA by X-ray and by SB was

analyzed by the Pearson correlation coefficient. Comparison of the differences between the BA

by SB and by X-ray based methods was conducted by the paired t test and further presented by

95% confidence intervals.

Results

The study population included 150 subjects (76 males), mean age 10.63.3 years (4.1-17.4

years), recruited between June 2011 and March 2012. At the time of research investigation they

were diagnosed with short stature and failure to thrive (46%), growth hormone deficiency (9%),

precocious or early puberty (23%) overweight and obesity (8%), normal and healthy (14%). The

clinical, demographic and body composition characteristics of the analysis and validation groups

were similar (Table 1).

According to measurements conducted independently in the same environment by two

examiners, the performance analysis of SB revealed high reproducibility and repeatability

Upon performing 10 repeated readings, on 10 subjects, the percent of relative standard deviation

(%RSD) for SOS were smaller than 0.73% for all the children, with a maximum standard

deviation of 13.7%. The %RSD for ATN was less than 3.5% for all the children with a

maximum standard deviation of 1.4%.

The distribution of SOS and ATN measurements according to skeletal area (W, MC, P) in the

study population (n=150) is presented in Figure 2. The SOS measurements ranged from 1604 -

2647 m/sec and the ATN surrogate distance ranged from 29.5 - 82.7 mm.

In the first phase analysis we correlated between BA by manual and automated GP and

automated TW3 against SOS and ATN from SonicBone in all study population (n=150). A


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significant correlation for both SOS ( r2=0.68, 0.68, 0.69 for manual GP, automated GP and

automated TW3, respectively) and ATN (r2=0.88, 0.88, 0.89 for e manual GP, automated GP and

the automated TW3, respectively) was found.

In phase 2, multiple linear regression analysis was utilized in order to estimate the BA by the

three methods using gender, SOS and ATN. The linear regression coefficients are presented in

Table 2. For all three methods, both SOS and ATA were significantly strong predictors for BA.

SOS was an important and significant predictor for BA above and beyond the ATN; the

coefficient of determination R2 significantly increased using SOS. As much as 82% of the total

variation in BA is explained by ATN and SOS. Table 2 also shows the un-standardized

coefficient b that are used for predicting future outcomes, and the standardized coefficients beta

that were used to evaluate the relative strength of the relationship to BA.

In the third phase analysis, the only data from the ‘Validation group’ was compared to the

assessment of BA, as delivered by the device according to the conversion equation performed in

the second phase (BA by SB), to the three hand X-ray based methods. The results demonstrate a

significant correlation between BA by SB and the BA by manual GP (r=0.89, P<0.001),

automated GP (r=0.91, P<0.001) and automated TW3 (r=0.91, P<0.001). There were no clinical

or statistical significance differences between methods, using paired comparisons (P=0.887;

Table 3).

Discussion

In the dialectics of human anthropology and auxology, ‘BA is an expression of the skeletal

maturity of a child. Inferring from bone maturity, the clinician contemplate diagnostic

considerations and evaluate height prediction, and would recommend sport activity and dancing,


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or the timing for orthodontic procedures and orthopedic surgery. This is accomplished in a

variety of methods, all of which utilize X-ray technology and compare a given film to various

standards, followed by designation of a BA. The problematical utilization of repeated X-ray

evaluations is well-appreciated. Here, we present the applicability of radiation-free BA

assessment by QUS and its concordance with currently employed BA valuation by X-ray-based

methods.

This is not the first attempt to apply QUS technology for BA assessment; other attempts failed to

enter clinical practice. Castriota-Scanderbeg et al17, 18

attempted to assess skeletal maturation by

quantifying the cartilage overlying layer of the femoral head. They demonstrated a decrease in

cartilage thickness with age. Yet, a comparison with the BA by GP showed poor agreement18

.

Shimura et al,14

and Khan et al,19, 20

assessed skeletal maturation by SOS through a single site at

the head of the ulna (similar to W site in the current study), that often differs from other bones,

not testing the sites available by SB device.

2, 11, 12

.

The SB device provides three independent measurements of the Radius and Ulna epiphyses, of

metacarpals and of phalanges, similar to clinical practice assessments of hand x-ray scans. While

the sites assessed by SB and by the X-ray methods are not identical, we demonstrate a significant

correlation between BA by SB and BA by GP and TW3 methods at each site separately and by

the mean BA 11

.

The BA by SB result was generated by the equation for BA assessment by QUS, which was

integrated in the device, according to the data retrieved from the analysis of 100 subjects,

including SOS, ATN and the manual reading by the GP method. It was then validated in 50

subjects against both manual and automated GP reading as well as the automated TW3 methods

showing a high performance of reliability and significant concordance.


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The ultrasound technique used by SonicBone is the "through transmission technique", as

described in Figure 1. An ultrasound wave is propagated perpendicularly through a medium

containing soft tissue and bone, from transmitter to receiver. Two parameters are used in this

method: The primary parameter is SOS (time of flight) of the US wave over the distance from

transmitter to receiver. SOS correlates strongly with the structure and density of the bone.

However, bone is attenuative and dispersive. The attenuation is seen in the change in amplitude

of a travelling wave and in the values of the reflection coefficients. The dispersion contributes to

the distortion of the wave, and we therefore included in the equation the attenuation – the decay

rate of a wave as it propagates through bone. We use the distance between transmitter and

receiver as an ‘Attenuation factor - ATN’.

In the current study, the new technique was compared with manual reading by the GP method

and with automated reading using both PG and TW3 methods. The latter gave the best regression

against BA by SB; as much as 82% of the total variation in BA, is explained by ATN and SOS.

For all three methods, the ATN showed important contribution to the regression, yet, in all three

the SOS was important and significant predictor for bone age above and beyond the ATN.

Thus, the measurements of SB device are all hand-area inclusive (W, MC, P), objective, and of

physiological agreement to the goal of bone maturation assessment (SOS, ATN), offering a

possible alternative to the present radiation based mostly subjective GP, and TW3 methods. As

BA is an essential measurement procedure for pediatric Endocrinology physicians and quite

often must be repeated over time, the SonicBone offers an important advantage over the current

methods, with no side effects and with objective readings by a system accessible at the clinician

office. The current report does not provide reference or standard for BA by chronological age for

the QUS method. This is currently under development using a normal population distribution for

all ages according to gender.


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In summary, the radiation-free assessment of BA by the SonicBone device in pediatric

population attending endocrinology clinics was found to be highly reproducible and comparable

to the BA assessed by hand X-rays based methods, both subjective and objective methods.

Author Contribution:

MR, LN, KMA, AL, NKM, TB and ZH, made substantial contributions to conception and

design, or acquisition of data, or analysis and interpretation of data, took part in drafting the

article or revising it critically for important intellectual content, and gave their final approval of

the version to be published.

MR, ZB, LN, NKM and ZH take responsibility for the integrity of the work as a whole, from

inception to published article.

References

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Cameron, N., Caliebe, J., Hertel, T., Kiepe, D., Albertsson-Wikland, K., Thodberg, H.H.,

Binder, G. & Ranke, M.B. (2011) The use of bone age in clinical practice - part 1. Horm

Res Paediatr 76, 1-9.


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The use of bone age in clinical practice - part 2. Horm Res Paediatr 76, 10-16.

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for automated determination of skeletal maturity. IEEE Trans Med Imaging 28, 52-66.

14 Martin, D.D., Deusch, D., Schweizer, R., Binder, G., Thodberg, H.H. & Ranke, M.B.

(2009) Clinical application of automated Greulich-Pyle bone age determination in

children with short stature. Pediatr Radiol 39, 598-607.

15 Hosokawa, A. & Otani, T. (1997) Ultrasonic wave propagation in bovine cancellous

bone. The Journal of the Acoustical Society of America 101, 558-562.

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17 Castriota-Scanderbeg, A. & De Micheli, V. (1995) Ultrasound of femoral head cartilage:

a new method of assessing bone age. Skeletal Radiol 24, 197-200.

18 Castriota-Scanderbeg, A., Sacco, M.C., Emberti-Gialloreti, L. & Fraracci, L. (1998)

Skeletal age assessment in children and young adults: comparison between a newly

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of ultrasound for bone age estimation in clinical practice. J Pediatr 154, 243-247.

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Table 1: Demographic, clinical and body composition parameters of study population, randomly

divided into the analysis and the validation groups

All ‘Analysis

Group’

‘Validation

Group’

P

value

Number 150 100 50

Gender (f) 74 51 (51%) 23 (46%) 0.34

Pre-puberty* 46 39 (39%) 17 (34%) 0.33

BMI SDS 0.21.4 0.31.3 -0.11.5 0.09

Age (years) 10.63.3 10.53.2 10.93.4 0. 85

Mean BA by GP - W (years) 10.03.4 10.13.2 10.03.8 0.20

Mean BA by GP - CMC (years) 10.13.5 10.13.3 10.03.8 0.26

Mean BA by GP - P (years) 10.33.4 10.33.2 10.33.7 0.47

Mean BA by GP (all sites ) 10.1 3.3 10.1 3.1 9.9 3.6 0.77

*Data is based on n=148, FTT- failure to thrive, GHD – growth hormone deficiency.


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Table 2: The regression coefficients, used in the conversion equation from the Analaysis Group

Site

Parameter

Coef.b

SE

Beta

t

P value

R2

BA-Manual GP

Constant -28.68 4.87 -5.88 <0.001

0.80

Gender 0.187 0.310 0.030 0.602 0.548

SOS *(cm/sec) 1.09 0.293 0.230 3.73 <0.001

ATN **(mm) 0.330 0.029 0.724 11.39 <0.001

BA-Automated GP

Constant -30.77 4.88 -6.30 <0.001

0.81

Gender 0.345 0.31 0.053 1.11 0.268

SOS *(cm/sec) 1.160 0.293 0.236 3.96 <0.001

ATN **(mm) 0.341 0.029 0.722 11.75 <0.001

BA- Automated TW3

Constant -29.55 4.55 -6.49 <0.001

0.82

Gender 0.411 0.289 0.067 1.42 0.159

SOS *(cm/sec) 1.133 0.274 0.241 4.14 <0.001

ATN **(mm) 0.323 0.027 0.718 11.94 <0.001

SE= standard error, t=statistics value. *SOS- speed of sound, measurements ranges from 1,604

m/sec to 2,647 m/sec. ***ATN- attenuation, measurements ranges from 29.5 mm to 82.7 mm.


15

Table3: Comparison of BA by SonicBone to the BA by the three X-ray methods (in the

validation group of subjects).

Mean

difference

S.E.

95% C.I.

P

SB - manual GP

-0.034

0.237

-0.51-0.44

0.887

SB - automated GP

0.036

0.207

-0.38-0.45

0.861

SB -automated TW3

0.219

0.198

-0.18-0.62

0.274


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Figure legends:

Figure 1: Bone age assessment by SonicBone bone sonometer at the third proximal phalange

(A), the metacarpal (B) and the wrist (C). The device measures two parameters (D): the speed of

propagation of inaudible high frequency waves of a short ultrasound pulse through bone; and the

Attenuation/distance between a transmitter probe (T) and a receiver probe (R), located at the

edges of the measured bone area for assessment of the attenuation factor.

Figure 2: Quartiles distribution of SonicBone parameters of SOS and ATN according to the

measured areas of the left hand, wrist (W), carpal (MC) and phalanx (P), in the whole study

population (n=150). 1a. Speed of sound in m/sec (SOS). 1b. Attenuation/distance in mm (ATN).

Lines within boxes indicate median; limits of boxes indicate 25th and 75th percentiles; circles

represent outliers.


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Figure 1

A

A

B

B

C

C

D


18

Figure 2a Figure 2b

Documents

Bone age assessment by a quantitative sonometer Short title€¦ · Rachmiel et al, Bone age by ultrasound 3. Introduction Skeletal maturity assessment, defined also as ‘bone age’