The use of tonebursts as an alternative to broadband signals in the measurement of speed of sound in human cancellous bone.

Speed of sound (SOS) measurements, typically made using 1 MHz broadband pulses, are increasingly used in the clinical diagnosis of bone disorders. Previous in vitro studies indicate that broadband ultrasound pulses are susceptible to distortion in cancellous bone, leading to imprecise arrival time and SOS measurements. We investigated the effect of bandwidth and frequency on SOS by comparing measurements made using 1 MHz broadband with 1 MHz and 300 kHz narrowband toneburst signals in 15 human proximal femur cancellous bone specimens. There was no significant difference in the value of SOS measured from the leading edge of 1 MHz broadband, 1 MHz toneburst and 300 kHz toneburst signals. Values of SOS in later regions of 1 MHz and 300 kHz tonebursts fell significantly (p < 0.001) when compared to earlier regions. This decrease in SOS levelled off by the third complete cycle of 300 kHz toneburst signals, reaching a plateau value of 1961 +/- 239 m s-1. No plateau SOS value was obtained in 1 MHz tonebursts. The reproducibility of SOS, as measured by the coefficient of variation, was higher for later regions of 300 kHz tonebursts than for the leading edge of 300 kHz toneburst and 1 MHz broadband signals (p < 0.005). The correlation between ultrasound measured modulus and compressive Young's modulus improved when 300 kHz tonebursts (r2 = 0.83) rather than 1 MHz broadband (r2 = 0.77) signals were used to calculate SOS. The improved SOS reproducibility of later regions 300 kHz tonebursts suggest that it may be beneficial to use such signals rather than 1 MHz broadband pulses in SOS measurement. Since no reliable SOS measurements could be obtained from any region of 1 MHz tonebursts, the use of high frequency toneburst signals in cancellous bone has little value.

The dependence of ultrasonic properties on orientation in human vertebral bone.

Speed of sound (SOS) and broad-band ultrasound attenuation (BUA) were measured in cubes of human trabecular bone from lumbar vertebrae, in the three major anatomical axes. There were significant differences in sos and in BUA when measured in the different axes, indicating a structural component to the ultrasonic measurement. Qualitatively different behaviour was observed in the cranio-caudal (CC) axis compared to the transverse directions: SOS was approximately 500 m s(-1) greater than in either the lateral (LT) or antero-posterior (AP) axes, and BUA was approximately 23 dB MHz(-1) cm(-1) greater. Small, but significant, differences existed between the AP and LT axes for both SOS and BUA. In the AP and LT directions, strong linear correlations existed between sos and apparent density (r = 0.90), and between BUA and apparent density (r = 0.96). In the cc axis, correlations with density were poorer. The anomalous behaviour in the cc axis was due to a transient travelling ahead of the main wavefront, and it is suggested that this represents propagation of ultrasound directly through the trabecular framework as a bar wave. This can only occur in the cc axis where the majority of trabeculae are orientated parallel to the direction of propagation. Measurements on cubes in air, as opposed to water, supported this hypothesis. Modifications to the experimental technique necessary to consistently detect this phenomenon are described.

Bone mineral density in healthy normal women and reproducibility of measurements in spine and hip using dual-energy X-ray absorptiometry.

Bone mineral density (BMD) using dual-energy X-ray absorptiometry (DEXA) has been measured in 394 healthy normal women. BMD is highest at the end of the 3rd decade and declines from 45 to 75 years by 0.0095 g/cm2/year in the lumbar spine and by 0.0052-0.0078 g/cm2/year in the upper femur depending on the site. BMD appears to increase in the 8th decade. Reproducibility (coefficient of variation (CV) of repeated measurements) was lowest in the lumbar spine (1.45%) and highest in Ward's triangle (4.29%). CV was not influenced by age at any site and by osteoporosis only in the femoral neck. BMD increased from L2 to L4 but the increase could not wholly be accounted for by the size of the vertebra, suggesting that the posterior elements were contributing to the observed increase of bone density.

Effect of Paget's disease of bone on areal lumbar spine bone mineral density measured by DXA, and density of cortical and trabecular bone measured by quantitative CT.

Although bone density may be increased in bone that is affected by Paget's disease, density changes in cortical and trabecular bone and the effect on bone that is apparently unaffected by Paget's disease are relatively unexplored. We have investigated 81 vertebrae (28 affected, 53 unaffected) in 27 patients with Paget's disease, by dual X-ray absorptiometry (DXA) and by quantitative CT (QCT) bone density measurements of trabecular and cortical bone. DXA bone density was high (mean z-score = 1.62, p < 0.001) in vertebrae affected by Paget's disease, but not significantly different from normal in unaffected vertebrae (mean z-score = 0.07, ns). Mean QCT z-score in Paget's vertebrae was 2.07 (p = 0.009) for cortical bone and 1.37 (p = 0.008) for trabecular bone. DXA correlated with QCT cortical values in affected and unaffected bone (r = 0.8 and 0.56, respectively), and with QCT trabecular values (r = 0.72 and 0.48, respectively). There was no significant difference in the slopes for the correlations in affected or unaffected bone. Cortical QCT values are underestimated in Paget's disease compared with physical measurements of density, owing to the computer algorithm used. High DXA values may alert to the possibility of Paget's disease, especially if the value deviates from the expected normal sequence in lumbar vertebrae. Osteoporotic vertebrae may be overlooked if the average value of bone mineral density is taken in the lumbar spine without reviewing each vertebra.

Influence of dose reduction recommendations on changes in chest radiography techniques.

A previous dosimetric study on chest radiography identified ways to reduce patient entrance surface dose (ESD). This present study was designed to monitor changes that had occurred in the use of applied potential and film-screen sensitivity, after a series of recommendations were issued. The study falls into two parts: (1) an assessment of the impact of the recommendations and (2) what factors were responsible for change. Where changes had occurred, exposure factors were collected for 30 patients per tube and the mean ESD was calculated for each tube. Intercomparison (r = 0.93, p < 0.001) was made between calculated and measured (TLDs) values of mean ESD for 10 X-ray units, to ensure that the calculated values provided accurate estimates of the new mean ESDs. 89% of units previously monitored for patient ESD now use average applied potentials greater than 90 kVp and 51% are using film-screen sensitivities of 400. The mean ESD has been reduced on average by 47%, from 0.15 mGy to 0.08 mGy. It has been estimated that the annual collective dose from diagnostic radiology procedures in 30 hospitals in the West Midlands has been reduced by a value in excess of 40 man Sv. Reasons for change could be attributed to some of the following factors: (a) a knowledge of dose levels in comparison with other centres; (b) personal contact with departments; (c) feedback in terms of results and dose savings and (d) positive encouragement to make changes.

Dose-area product readings for fluoroscopic and plain film examinations, including an analysis of the source of variation for barium enema examinations.

This paper contains the results of an investigation undertaken between 1994 and 1996 using dose-area product (DAP) meters for monitoring radiation doses from six types of simple examinations and seven types of complex examinations. Mean hospital DAP levels have been compared with National Reference Levels (NRL), with most departments producing levels lower than NRLs. DAP readings have allowed the proposal of provisional Reference Levels (RL) to be set for simple and complex examinations. The results were also compared with recently published data from the National Radiological Protection Board (NRPB), highlighting those hospitals which need to make changes in radiographic technique. The study of DAP reference doses also confirms that dose levels for complex investigations are clearly related to technique, in terms of screening time and number of films. Although the use of increased screening tube kilovoltage may be relevant, the overall effect is small. The results suggest that there is still a need to optimize the protocols for these examinations. The use of digital equipment has been shown to have a complex effect on dose, particularly in the case of investigations involving both films and fluoroscopy.

A computerized technique for vertebral morphometry.

A new technique for morphometric measurement of vertebral bodies has been described, in which a computerized image analysis system was used to digitize and measure standardized lateral radiographs of the thoracic and lumbar spine. The sources of error in the radiographic system and the image analysis system were assessed using vertebral phantoms and test images. Oblique projection in the radiographic image of a vertebra did not produce a significant error in the measured area. The radiographic magnification was approximately 35%. Optical non-uniformity was detected in the image analysis system, and was ascribed to the lens optics. The maximum intra-observer and inter-observer variations in vertebral area were 3.1% and 5.3% respectively for experienced observers. The technique is applicable to clinical studies of large populations, and has value in investigating vertebral deformity in the management of metabolic bone disease.

Fracture stiffness in callotasis determined by dual-energy X-ray absorptiometry scanning.

Assessing healing after distraction limb lengthening is essential to manage patients undergoing callotasis for leg lengthening or bone transport. Direct measurement of fracture stiffness can assess healing but the equipment may not be available. In addition, it requires removal of the fixator, which may be complicated for ring fixators. The present study investigates whether an equivalent measure of healing can be based on the mineral density pattern from dual-energy X-ray absorptiometry (DXA) scans. Nine consecutive patients undergoing callotasis were studied. Bending stiffness of the distraction segment was measured and DXA scans were performed regularly starting 6 weeks after completing distraction. In all, 23 simultaneous readings of bending stiffness and DXA scans were obtained. All density patterns showed a distinct minimum value of bone mineral density. We found a high and significant correlation between fracture bending stiffness and the square of the total mineral content at the location of minimum bone density (r2 = 0.77, P < 0.001). We conclude that DXA scans can be used reliably and effectively to determine fracture bending stiffness, valuable for determining both time of frame removal and delay in union.

Effect of age and gender on the number and distribution of sites in Paget's disease of bone.

Paget's disease of bone (PDB) is reportedly declining in prevalence and severity, with increasing numbers of monostotic cases. Some accounts suggest that these findings are more evident in women, and that monostotic disease is unexpectedly frequent at certain sites. We have studied whether birth date or gender is associated with the number of sites affected and with the distribution of sites in monostotic disease and, by reviewing 100 follow-up 99Tc(m) methylene diphosphonate (MDP) scans, whether additional sites appear after initial diagnosis. Scintigraphic scans from 171 male (age 40-91 years) and 179 female (44-88 years) consecutive referrals with PDB were reviewed. Patients were analysed by referral date (1982-1992 and 1993-2001), and by their median date of birth (before (PRE21) and after (POST21) 1921). Mean age of pre-1993 patients was 69 years and 75 years for referrals after 1993. Younger patients had more monostotic disease (POST21 vs PRE21 subjects (47% vs 28%)), with a more marked trend in females (52% vs 25%), and POST21 females had fewer polyostotic sites than males (p<0.05), whereas the number in PRE21 males and females was similar. Monostotic females, but not males, showed an excess of tibial involvement. The spine was less involved in monostotic disease. Follow-up scans in 100 patients revealed no new sites. The incidence of monostotic disease has doubled over the last 30 years, but diminishing site involvement appears to be more marked in females. The lesser involvement at the axial sites in monostotic disease may lead to overestimation of the decline in PDB based on abdominal radiographs.

Bone mineral content and density in healthy subjects and in osteogenesis imperfecta.

Lumbar spine bone mineral density in a cross sectional study of healthy subjects increased by 0.012 and 0.016 g/cm2/year in boys and girls respectively between 5 and 11 years of age. These rates increased five-fold in girls and threefold in boys between the ages of 11 and 13 years as a result of the bone mineral content increasing more rapidly than the coronal area at this age. By the age of 11 years the girls had 66% of the coronal area, 61% of the bone mineral density, and 41% of the bone mineral content of subjects aged 18-23 years. The ratio (lumbar spine bone mineral content/body weight) was constant in boys aged 6-13 years, but there were significant variations in girls. Femoral neck bone mineral density in both sexes changed little between 6 and 11 years and at 11 years was 69% of the adult values. Subjects with osteogenesis imperfecta had a low bone mineral density and bone mineral content for their age and weight. The z score of bone mineral density at the femoral neck was significantly lower than at the lumbar spine. In patients with recurrent fractures a low bone mineral density may help in identifying those with osteogenesis imperfecta and assist in their subsequent management.

Age-related changes in body composition, hydroxyproline, and creatinine excretion in normal women.

We have made a cross-sectional study of relationships among age, whole body bone mineral content (WBBMC), and non-bone lean body mass (NBLBM) measured by dual energy X-ray absorptiometry (DXA), and daily excretion of hydroxyproline (OHP) and creatinine (Cr) in a group of normal women. WBBMC fell with age from the 6th decade, whereas NBLBM was almost constant. Creatinine excretion fell with age from the 5th decade until the 9th, to a much greater degree than NBLBM, reaching a nadir in the 8th decade. Daily excretion of hydroxyproline showed a peak in the 6th decade and fell moderately thereafter. The greater fall of creatinine compared with hydroxyproline resulted in rising OHP/Cr ratios with advancing age, in contrast to the pattern of hydroxyproline excretion. The use of creatinine as a correction for urine dilution or for lean body mass (LBM) in assays for markers of bone turnover must therefore be viewed with caution.

Vertebral deformity, bone mineral density, back pain and height loss in unscreened women over 50 years.

Bone mineral density (BMD) was measured in the lumbar spine using dual-energy X-ray absorptiometry in 222 unscreened women (aged 50-82 years), and information on back pain and historic loss of standing height was obtained at interview. Vertebral morphometry was performed on lateral spinal radiographs. The shape of the vertebral body was quantified using appropriate vertebral shape indices (VSIs), and vertebral deformities were identified using thresholds defined in terms of the means (M) and standard deviations (SD) of these VSIs for the whole group. Severity of deformity was defined as either grade 1 (M+2SD < VSI < M+3SD), grade 2 (M+3SD < VSI < M+4SD or grade 3 (VSI > M+4SD). Subjects with grade 1 vertebral deformities were older than subjects without such deformities, but did not have a reduced age-related Z-score of BMD. Grade 2 wedge and concave deformities were associated with a reduced age-related Z-score of BMD, suggesting that the aetiology of such deformities is closest to conventional concepts of 'osteoporotic fracture'. Grade 3 deformities were associated with neither increased age nor decreased BMD. Stature decreased in these subjects with age. Subjects reporting historic height loss had a higher mean number of wedge deformities. Subjects with back pain did not have a higher incidence of vertebral deformity than subjects without, confirming that many deformities were asymptomatic. Neither back pain nor historic loss of height were found to be associated with low spinal BMD.

Vertebral morphometry in women aged 50-81 years.

Vertebral dimensions and vertebral shape indices (VSI) were investigated in T4-L4 in 926 females aged 50-81 years. The most consistent finding was the increase of inferior antero-posterior dimension with age. Wedging and concavity also increased with age but the changes were not significant at all vertebral levels. The value of VSIs also varied with level. Thus a particular degree of VSI, considered normal at one level or at one age, would be outside the reference range at a different level or age group. The number of subjects identified as osteoporotic by skewness (5.4%) or in excess of three standard deviations from the mean (6.5%) was much lower than in recent reports from North America. The number of subjects contributing to a skewed distribution increased with age from 0.5% at 55-59 years to 10.0% at 75-79 years. Change with age in the antero-posterior dimension could increase load-bearing area in older subjects, but the decline in bone density will be increased as a declining bone mineral content occupies a larger volume.

Does the thickness of the vertebral subchondral bone reflect the composition of the intervertebral disc?

Degeneration of the intervertebral disc, seen radiologically as loss of disc height, is often associated with apparent remodelling in the adjacent vertebral body. In contrast, maintenance or apparent increase in disc height is a common finding in osteoporosis, suggesting the properties of the intervertebral disc may be dependent on those of the vertebral body or vice versa. We have investigated this relationship by measuring the radiological thickness of the subchondral bone and comparing it to the chemical composition of the adjacent disc. Sagittal slabs were sampled from lumbar spines obtained at autopsy and X-rayed microfocally. The thickness of the subchondral bone was measured and correlated with the composition of the adjacent intervertebral disc. Eighty-three cadaveric endplates were studied from individuals aged 17-85 years. There was regional variation in thickness of the subchondral bone, being greater adjacent to the annulus than the nucleus, and the endplates cranial to the disc were thicker than those caudal. There was a positive correlation between the thickness of the subchondral bone and the proteoglycan content of the adjacent disc, particularly in the region of the nucleus. A weaker correlation was seen here between water content and thickness, whilst there was no significant correlation at the annulus or between the bone thickness and collagen content. The positive relationship between the radiographic thickness of vertebral subchondral bone and the proteoglycan content of the adjacent disc seen in human cadaveric material could be due to the bone responding to a greater hydrostatic pressure being exerted by discs with higher proteoglycan content than by those with less proteoglycan present. It is suggested that while this is true in "normal" specimens, the relationship becomes altered in disease states, possibly because of changes to the nutritional pathway of the disc, with resultant endplate-bone remodelling affecting the flow of solutes to and from the intervertebral disc.

The relative contribution of disc and vertebral morphometry to the angle of kyphosis in asymptomatic subjects.

In order to investigate the relative contributions of vertebra and inter-vertebral disk to kyphosis, a series of 100 asymptomatic healthy women (age range 39-91 years) were studied to evaluate lateral dorsal appearances and possible related parameters of bone loss. Subjects underwent lateral dorsal spine radiography and single photon absorptiometry of the radius. There was a significant decrease in physical height in relation to age (P < 0.001) and this was directly related to an increasing thoracic kyphosis (P < 0.005). The angle of kyphosis was better related to the average anterior disc height (P < 0.001) than to average anterior vertebral height. The vertebral body ratio, however (anterior/posterior height), was more strongly related to angle of kyphosis than was disk ratio. The results also showed a fall in the proximal and distal radial bone mineral content with age (P < 0.001). These findings suggest that dorsal kyphosis as part of the ageing process may be as closely related to the physical integrity of the disc as to the vertebral body. Hence, therapy for age related bone mineral loss may have limited effect on a kyphotic deformity of the dorsal spine in otherwise asymptomatic patients.

Ultrasound bone densitometry and dual energy X-ray absorptiometry in patients with spinal cord injury: a cross-sectional study.

Bone is lost following spinal cord injury (SCI) and in the long-term may become osteopenic and liable to fracture. Two non-invasive techniques, ultrasound bone densitometry (USBD) and dual energy X-ray absorptiometry (DXA), have been applied to monitor bone changes after spinal injury. 31 SCI patients were scanned using an ultrasound bone densitometer, to give measurements of speed of sound (SOS), broadband ultrasound attenuation (BUA) and "stiffness'. The time since injury of these patients ranged between 5 weeks to 36 years with a mean of 5.87 +/- 10.21 years. Ultrasonic properties at the calcaneus of these patients were significantly lower than the healthy reference population, and a rapid decline in ultrasound properties occurred in the first 3 months. The fall continued up to 54 months but at a slower rate. The normal linear relationship between SOS and BUA was not altered by SCI. Eighteen patients had DXA measurements at the lumbar spine and the right proximal femur. Bone mineral density (BMD) at the femoral neck was significantly lower than the normal reference population (P < 0.05). SOS and "stiffness' correlated significantly with BMD at the lumbar spine, Ward's triangle, the femoral neck, the greater trochanter and the intertrochanteric site (P < 0.05). BUA correlated significantly at all these sites with the exception of the trochanter. A negative correlation was found between the ultrasonic properties at the calcaneus and BMD at the lumbar spine which is in contrast to the positive relationship in normal subjects. There was a tendency for BMD to increase at the lumbar spine after the first 12 months after injury, although this trend was not significant overall. The "stiffness' at the calcaneus and BMD at the femoral neck were lower than the reference population following 12 months since injury. These results show that bone deficit at the calcaneus occurs rapidly and to a severe degree after SCI, and that ultrasound has an important role to play in the assessment of bone status in these patients.