Fractal analysis of radiographs: assessment of trabecular bone structure and prediction of elastic modulus and strength

Comparing lateral plantar process trabecular structure to other regions of the human calcaneus

Investigating skeletal adaptations to bipedalism informs our understanding of form-function relationships. The calcaneus is an important skeletal element to study because it is a weight-bearing bone with a critical locomotor role. Although other calcaneal regions have been well studied, we lack a clear understanding of the functional role of the lateral plantar process (LPP). The LPP is a bony protuberance on the inferolateral portion of the calcaneus thought to aid the tuberosity in transmission of ground reaction forces during heel-strike. Here, we analyze LPP internal trabecular structure relative to other calcaneal regions to investigate its potential functional affinities. Human calcanei (n = 20) were micro-CT scanned, and weighted spherical harmonic analysis outputs were used to position 251 volumes of interest (VOI) within each bone. Trabecular thickness (Tb.Th), spacing (Tb.Sp), degree of anisotropy (DA), and bone volume fraction (BV/TV) were calculated for each VOI. Similarities in BV/TV and DA (p = 0.2741) between the LPP and inferior tuberosity support suggestions that the LPP is a weight-bearing structure that may transmit forces in a similar direction. The LPP significantly differs from the inferior tuberosity in Tb.Th and Tb.Sp (p < 0.05). Relatively thinner, more closely spaced trabeculae in the LPP may serve to increase internal surface area to compensate for its relatively small size compared to the tuberosity. Significant differences in all parameters between LPP and joint articular surfaces indicate that trabecular morphology is differently adapted for the transmission of forces associated with body mass through joints.

Type II collagen scaffolds repair critical-sized osteochondral defects under induced conditions of osteoarthritis in rat knee joints via inhibiting TGF-β-Smad1/5/8 signaling pathway

The bidirectional relationship between osteochondral defects (OCD) and osteoarthritis (OA), with each condition exacerbating the other, makes OCD regeneration in the presence of OA challenging. Type II collagen (Col2) is important in OCD regeneration and the management of OA, but its potential applications in cartilage tissue engineering are significantly limited. This study investigated the regeneration capacity of Col2 scaffolds in critical-sized OCDs under surgically induced OA conditions and explored the underlying mechanisms that promoted OCD regeneration. Furthermore, the repair potential of Col2 scaffolds was validated in over critical-sized OCD models. After 90 days or 150 days since scaffold implantation, complete healing was observed histologically in critical-sized OCD, evidenced by the excellent integration with surrounding native tissues. The newly formed tissue biochemically resembled adjacent natural tissue and exhibited comparable biomechanical properties. The regenerated OA tissue demonstrated lower expression of genes associated with cartilage degradation than native OA tissue but comparable expression of genes related to osteochondral anabolism compared with normal tissue. Additionally, transcriptome and proteome analysis revealed the hindrance of TGF-β-Smad1/5/8 in regenerated OA tissue. In conclusion, the engrafting of Col2 scaffolds led to the successful regeneration of critical-sized OCDs under surgically induced OA conditions by inhibiting the TGF-β-Smad1/5/8 signaling pathway.

Assessment of bone quality of apical periodontitis treated with MTA plug and regenerative endodontic techniques

Fractal analysis (FA) is a quantitative, objective and non-invasive method that facilitates the characterisation of the tissue architecture. This study aims to compare the periapical healing at 1-year follow-up by evaluating newly generated trabecular bone with FA after Mineral trioxide aggregate (MTA) plug and regenerative endodontic treatment (RET). A total of 55 asymptomatic teeth with a single-canal, open apex and periapical lesion, treated with MTA plug or RET, were evaluated retrospectively. After considering the inclusion/exclusion criteria, FA was conducted on 30 periapical images using the box-counting method. In both groups, a significant decrease was observed in the periapical lesion size at 1-year follow-up (p < 0.01). However, there was no significant difference between the MTA plug and RET (p > 0.01). Significantly higher fractal dimension values were detected at 1-year follow-up in both MTA plug and RET cases (p < 0.01). However, the difference was not significant between the groups (p > 0.01). Both procedures seem to improve periapical healing with a new resistant bone of similar density and complexity.

Fractal Perspective on the Rapid Maxillary Expansion Treatment; Evaluation of the Relationship Between Midpalatal Suture Opening and Dental Effects

OBJECTIVE

This retrospective study investigates the relationship between the midpalatal suture opening and the dental effects of Rapid Maxillary Expansion (RME) treatment using fractal analysis.

METHODS

The participants of this study were selected from the patients who underwent Cone Beam Computed Tomography(CBCT) scans in 2019 and were treated with banded type Maxillary Expander. This study included 20 participants (with a mean age of 10.64±10.64, ranging from 8 to 13 years): 12 males and 8 females. Patients went through CBCT scan and images taken were analyzed using the ImageJ program. The following parameters were measured and analyzed before and after RME treatment: fractal dimensional value of Midpalatal suture(MPS), Distobuccal(DB), Mesiobuccal(MB), Palatal(P), Total distance, Cortical bone and linear values of External maxilla, Internal maxilla, Palatal roots, distance of Central fosses and angular values of Tipping value of 16 and 26. We used Spearman's nonparametric test for non-normal variables to investigate the correlation between changes in MPS and other variables.

RESULTS

The results showed a strong positive correlation between the MPS and Right MB (0.34, p<0.05) and Left MB (0.59, p<0.05) variables and a strong negative correlation between the MPS and the External maxillary variables (-0.53, p<0.05).

CONCLUSION

The results of the study have shown a strong correlation between right and left MB and External Maxilla. RME caused a reduction in buccal alveolar bone thickness and a slight reduction in MPS thickness in growing patients. Therefore, we suggest that fractal analysis can be used to evaluate the skeletal and dental effects of RME in patients.

Interest of Bone Histomorphometry in Bone Pathophysiology Investigation: Foundation, Present, and Future

Despite the development of non-invasive methods, bone histomorphometry remains the only method to analyze bone at the tissue and cell levels. Quantitative analysis of transiliac bone sections requires strict methodologic conditions but since its foundation more 60 years ago, this methodology has progressed. Our purpose was to review the evolution of bone histomorphometry over the years and its contribution to the knowledge of bone tissue metabolism under normal and pathological conditions and the understanding of the action mechanisms of therapeutic drugs in humans. The two main applications of bone histomorphometry are the diagnosis of bone diseases and research. It is warranted for the diagnosis of mineralization defects as in osteomalacia, of other causes of osteoporosis as bone mastocytosis, or the classification of renal osteodystrophy. Bone biopsies are required in clinical trials to evaluate the safety and mechanism of action of new therapeutic agents and were applied to anti-osteoporotic agents such as bisphosphonates and denosumab, an anti-RANKL, which induces a marked reduction of the bone turnover with a consequent elongation of the mineralization period. In contrast, an increased bone turnover with an extension of the formation site is observed with teriparatide. Romosozumab, an anti-sclerostin, has a dual effect with an early increased formation and reduced resorption. Bone histomorphometric studies allow us to understand the mechanism of coupling between formation and resorption and to evaluate the respective role of bone modeling and remodeling. The adaptation of new image analysis techniques will help bone biopsy analysis in the future.

Differentiation of osteosarcoma from osteomyelitis using microarchitectural analysis on panoramic radiographs

Diagnosing osteosarcoma (OS) is very challenging and OS is often misdiagnosed as osteomyelitis (OM) due to the nonspecificity of its symptoms upon initial presentation. This study investigated the possibility of detecting OS-induced trabecular bone changes on panoramic radiographs and differentiating OS from OM by analyzing fractal dimensions (FDs) and degrees of anisotropy (DAs). Panoramic radiographs of patients with histopathologically proven OS and OM of the jaw were obtained. A total of 23 patients with OS and 40 patients with OM were enrolled. To investigate whether there was a microarchitectural difference between OS lesions and normal trabecular areas in each patient, two regions of interest (ROIs) were located on the CT images. Three microarchitectural parameters (box-counting FD, fast Fourier transform-based FD, and DA) were calculated. For both OS and OM, significant differences were found for all three microarchitectural parameters. Compared to normal trabecular bone, trabecular bone affected by OS and OM became isotropic and more complex. When comparing OS and OM, a statistically significant difference was found only in DA. Trabecular bones affected by OS became more isotropic than those affected by OM. Microarchitectural analysis, especially DA, could be useful for detecting OS-induced trabecular alterations and differentiating OS from OM.

Evaluation of architectural changes in mandibular trabecular and cortical bone pattern after functional treatment

Purpose:

To assess the changes in mandibular trabecular and cortical bone following functional appliance treatment through fractal dimension (FD) and cortical thickness (CorT) measurements.

Material and methods

The study was performed on 45 mandibular retrognathia cases. While the treatment group (T) comprised 30 patients treated using a functional appliance for one year during puberty, the control group (C) consisted of 15 patients who did not receive any orthodontic treatment due to insufficient oral hygiene. FD and CorT analyses were bilaterally evaluated for each mandible. FD measurements were performed on the condylar process, the antegonial notch, and ramus regions on panoramic radiographs. A paired t-test was applied for group analysis, before (T1) and after treatment (T2) and, correspondingly, before (C1) and after (C2) controls. In addition, an independent t-test was used to determine differences between the treatment (∆T = T2−T1) and the control group (∆C = C2−C1).

Results

Statistically significant differences were found in the treatment group between the initial and post-treatment FD values of the right (p < 0.05) and left condyles (p < 0.05), and the CorT measurements on the right (p < 0.01) and the left sides (p < 0.05). There was no statistically significant difference in FD parameters in the control group and a significant difference was only found in the left CorT (p < 0.05). A comparison of the treatment and control groups revealed that the changes in FD and CorT measurements were not statistically significantly different between the groups (p > 0.05).

Conclusion:

Mandibular protraction appliances do not produce trabecular bone alteration in the mandibular condyles, the antegonial notch and ramus over a 12-month time period.

Density and mechanical properties of vertebral trabecular bone-A review

Being able to predict the mechanical properties of vertebrae in patients with osteoporosis and other relevant pathologies is essential to prevent fractures and to develop the most favorable fracture treatments. Furthermore, a reliable prediction is important for developing more patient- and pathology-specific biomaterials. A plethora of studies correlating bone density to mechanical properties has been reported; however, the results are variable, due to a variety of factors, including anatomical site and methodological differences. The aim of this study was to provide a comprehensive literature review on density and mechanical properties of human vertebral trabecular bone as well as relationships found between these properties. A literature search was performed to include studies, which investigated mechanical properties and bone density of trabecular bone. Only studies on vertebral trabecular bone tissue, reporting bone density or mechanical properties, were kept. A large variation in reported vertebral trabecular bone densities, mechanical properties, and relationships between the two was found, as exemplified by values varying between 0.09 and 0.35 g/cm3 for the wet apparent density and from 0.1 to 976 MPa for the elastic modulus. The differences were found to reflect variations in experimental and analytical processes that had been used, including testing protocol and specimen geometry. The variability in the data decreased in studies where bone tissue testing occurred in a standardized manner (eg, the reported differences in average elastic modulus decreased from 400% to 10%). It is important to take this variability into account when analyzing the predictions found in the literature, for example, to calculate fracture risk, and it is recommended to use the models suggested in the present review to reduce data variability.

Comparison of anterior and posterior trabecular bone microstructure of human mandible using cone-beam CT and micro CT

Background

The aim of this study was to compare the trabecular bone microstructures of anterior and posterior edentulous regions of human mandible using cone-beam computed tomography (CBCT) and micro computed tomography (µCT).

Methods

Twenty volumes of interests consisting of six anterior and fourteen posterior edentulous regions were obtained from human mandibular cadavers. A CBCT system with a resolution of 80 µm (3D Accuitomo 170, J. Morita, Kyoto, Japan) and a µCT system with a resolution of 35 µm (SkyScan 1173, Kontich, Belgium) were used to scan the mandibles. Three structural parameters namely, trabecular number (Tb.N), trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp) were analysed using CTAn software (v 1.11, SkyScan, Kontich, Belgium). For each system, the measurements obtained from anterior and posterior regions were tested using independent sample t-test. Subsequently, all measurements between systems were tested using paired t-test.

Results

In CBCT, all parameters of the anterior and posterior mandible showed no significant differences (p > 0.05). However, µCT showed a significant different of Tb.Th (p = 0.023) between anterior and posterior region. Regardless of regions, the measurements obtained using both imaging systems were significantly different (p ≤ 0.021) for Tb.Th and Tb.N.

Conclusions

The current study demonstrated that only the variation of Tb.Th between anterior and posterior edentulous region of mandible can be detected using µCT. In addition, CBCT is less feasible than µCT in assessing trabecular bone microstructures at both regions.

Is there any predictive bone parameter for implant stability in 2-dimensional and 3-dimensional radiologic images?

OBJECTIVES

This ex vivo study aimed to compare radiomorphometric parameters between 2-dimensional (2-D) and 3-dimensional (3-D) radiographs and evaluate the influence of preoperative radiologic bone parameters on the clinical outcomes of implant stability.

STUDY DESIGN

Implant recipient sites in fresh bovine blocks were evaluated on panoramic radiographs for gray value (GV), fractal dimension (FD), number of connected trabeculae (Co), and density of connected trabeculae (CoD). Cone beam computed tomography (CBCT) scans were evaluated for trabecular thickness (TbTh), cortical thickness (CTh), degree of anisotropy (DA), FD, and Co. Insertion torque (IT) and implant stability quotient (ISQ) were measured.

RESULTS

GV was significantly correlated with all parameters in 2-D and 3-D images except FD in 2-D and Co in 3-D, and with all surgical parameters (P ≤ .029). Co and CoD values on panoramic radiographs had significant correlation with TbTh, CTh, and DA values on CBCT images (P < .001). All 2-D parameters and TbTh and CTh in the CBCT data were significantly correlated with IT only (P ≤ .047). Only GV was correlated with ISQ measurements (P ≤ .029).

CONCLUSIONS

GV, Co, and CoD values on panoramic radiographs reflect the architecture of trabecular bone and the thickness of cortical bone, and might help predict implant stability in clinical situations.

Fractal dimension in CBCT images as predictor for MRONJ: a retrospective cohort study

Objective

To estimate boxcounting fractal dimension in a standardized approach in CBCT images of the mandible and maxilla in a group of patients with MRONJ in comparison to a healthy control group.

Material and methods

From our records, a study group consisting of 80 maxillary and mandibular CBCTs in 77 cases of patients having MRONJ was collected. The control group consisted of 84 mandibular and maxillary CBCTs in a total of 78 patients. Using the boxcounting method, fractal dimension (FD) was estimated in a standardized fashion either cranially to the apex of the canine (maxilla) or beneath the tooth apices of the lower molars in the bone area above the mandibular canal (mandible). Intra-observer reproducibility of the FD-measurements was assessed by 6 repeated measurements in 10 individuals. FD values were correlated to age and sex of the individuals as well as to region of interest (ROI) sizes.

Results

FD in the study group (1.684 ± 0.051) was roughly 3.5 % lower than in the control group (1.745 ± 0.026, p < 0.0001). Sex and age had a significant (p < 0.001) influence on FD values in the study group, yet not in the control group. FD values increased with age (study group, spearman-rho: 0.2895, p < 0.05) and also ROI size (both groups, p < 0.0001). Reproducibility was good (intra-class correlation coefficient (ICC): 0.87).

Conclusions

Fractal dimension as assessed by boxcounting seems to be a good descriptor for MRONJ in jaw bones. Influence of age and sex on the outcome values needs to be further investigated in future studies.

Clinical relevance

CBCTs could be assessed with respect to FD to obtain an overview of the disease status of MRONJ patients.

Carbon Nanostructures for Actuators: An Overview of Recent Developments

In recent decades, micro and nanoscale technologies have become cutting-edge frontiers in material science and device developments. This worldwide trend has induced further improvements in actuator production with enhanced performance. A main role has been played by nanostructured carbon-based materials, i.e., carbon nanotubes and graphene, due to their intrinsic properties and easy functionalization. Moreover, the nanoscale decoration of these materials has led to the design of doped and decorated carbon-based devices effectively used as actuators incorporating metals and metal-based structures. This review provides an overview and discussion of the overall process for producing AC actuators using nanostructured, doped, and decorated carbon materials. It highlights the differences and common aspects that make carbon materials one of the most promising resources in the field of actuators.

Thermoacoustic elastography: recovery of bulk elastic modulus of heterogeneous media using tomographically measured thermoacoustic measurements

Background

Tissue mechanical parameters such as elasticity are of great significance for the assessment of biological histopathological and physiological characteristics. Here, we propose a new approach called thermoacoustic elastography (TAE) for imaging tissue elastic modulus.

Methods

Central to TAE is an image reconstruction algorithm that allows the recovery of both microwave energy loss and elastic modulus distributions. The algorithm is first evaluated using simulated data under various practical scenarios, including a varied range of microwave energy loss and elastic modulus between the heterogeneity and background region, different noise levels, and multiple targets. The feasibility of the proposed TAE was then validated by imaging the elastic modulus distribution of agar phantoms with various elastic modulus and microwave energy loss.

Results

The results from both the simulated and phantom experiments show that the recovered elastic modulus by TAE agree well with the exact values, having an average error of less than 12.74%.

Conclusions

The findings from this study suggest that TAE provides a new addition to the family of elasticity imaging and may have broad application prospects, such as cirrhosis and atherosclerosis detection.

Standardizing compression testing for measuring the stiffness of human bone

Objectives

The ability to determine human bone stiffness is of clinical relevance in many fields, including bone quality assessment and orthopaedic prosthesis design. Stiffness can be measured using compression testing, an experimental technique commonly used to test bone specimens in vitro. This systematic review aims to determine how best to perform compression testing of human bone.

Methods

A keyword search of all English language articles up until December 2017 of compression testing of bone was undertaken in Medline, Embase, PubMed, and Scopus databases. Studies using bulk tissue, animal tissue, whole bone, or testing techniques other than compression testing were excluded.

Results

A total of 4712 abstracts were retrieved, with 177 papers included in the analysis; 20 studies directly analyzed the compression testing technique to improve the accuracy of testing. Several influencing factors should be considered when testing bone samples in compression. These include the method of data analysis, specimen storage, specimen preparation, testing configuration, and loading protocol.

Conclusion

Compression testing is a widely used technique for measuring the stiffness of bone but there is a great deal of inter-study variation in experimental techniques across the literature. Based on best evidence from the literature, suggestions for bone compression testing are made in this review, although further studies are needed to establish standardized bone testing techniques in order to increase the comparability and reliability of bone stiffness studies.

Cite this article: S. Zhao, M. Arnold, S. Ma, R. L. Abel, J. P. Cobb, U. Hansen, O. Boughton. Standardizing compression testing for measuring the stiffness of human bone. Bone Joint Res 2018;7:524–538. DOI: 10.1302/2046-3758.78.BJR-2018-0025.R1.

Cortical Fractal Analysis and Collagen Crosslinks Content in Femoral Neck After Osteoporotic Fracture in Postmenopausal Women: Comparison with Osteoarthritis

The femoral neck (FN) has been previously characterized by thinner cortices in osteoporotic fracture (HF) when compared to hip osteoarthritis (HOA). The purposes of this study were to complete the previous investigations on FNs from HF and HOA by analyzing the complexity of the cortical structure and to approach the intrinsic properties of cortical bone by assessing the collagen crosslink contents. FN samples were obtained during arthroplasty in 35 postmenopausal women (HF; n = 17; mean age 79 ± 2 years; HOA; n = 18; mean age 66 ± 2 years). The cortical fractal dimension (Ct.FD) and lacunarity (Ct.Lac) derived from high-resolution peripheral quantitative tomography (isotropic voxel size: 82 μm) images of FN by using Ctan software and Fraclac running in ImageJ were analyzed. The collagen crosslinks content [pyridinoline, deoxypyridinoline, pentosidine (PEN)] were assessed in cortical bone. Ct.FD was significantly lower (p < 0.0001) in HF than HOA reflecting a decreased complexity and was correlated to the age and BMD. In two sub-groups, BMD- and age-matched, respectively, Ct.FD remained significantly lower in HF than HOA (p < 0.001). Ct.Lac was not different between HF and HOA. PEN content was two times higher in HF than HOA (p < 0.0001) independently of age. In conclusion, FN with HF was characterized by a less complex cortical texture and higher PEN content than HOA. In addition to the decreased bone mass and BMD previously reported, these modifications contribute to the lower bone quality in HF than HOA in postmenopausal women.

The computed tomography-based fractal analysis of trabecular bone structure may help in detecting decreased quality of bone before urgent spinal procedures

BACKGROUND CONTEXT

To date, no reliable method is available to determine the parameters of bone density based on the routine spinal computed tomography (CT) in the emergency setup. We propose the use of fractal analysis to detect patients with poor quality of bone before urgent or semi-urgent spinal procedures.

PURPOSE

This study aimed to validate the hypothesis that the CT-based fractal analysis of the trabecular bone structure may help in detecting patients with poor quality of bone before urgent spinal procedures.

STUDY DESIGN

This is a retrospective analysis of prospectively collected data.

METHODS

Patients in whom the dual-energy x-ray absorptiometry (DEXA) scan and lumbar spine CT were performed at an interval of no more than 3 months were randomly selected from a prospectively collected database. Diagnostic axial CT scans of L2, L3, and L4 vertebrae were processed to determine the fractal dimension (FD) of the trabecular structure of each spinal level. Box-count method and ImageJ 1.49 software were used. The FD was compared with the results of the DEXA scan: bone mineral density (BMD) and T-score by mean of correlation coefficients. Receiver operating characteristic curve analysis was later performed to determine the cutoff value of FD.

RESULTS

A total of 102 vertebral levels obtained from 35 patients (mean age 60±18 years; 29 female) were analyzed. The FD was significantly higher in the group of patients with decreased bone density (DBD) (T-score<-1.0) (1.67 vs. 1.43; p<.0001) and negatively correlated with BMD (R Spearman, -0.53; p<.0001) and T-score (-0.49; p<.0001). Receiver operating characteristic curve analysis revealed that a cutoff value of FD>1.53 indicates DBD (p<.0001; area under the ROC curve [AUC], 0.84; 95% confidence interval [CI], 0.76-0.91).

CONCLUSIONS

This study shows that fractal analysis of the lumbar spine CT images may be used to determine bone density before spinal instrumentation (eg, metastatic or traumatic cord compression). Further prospective studies comparing results of the fractal analysis of CT scans with quantitative CT (qCT) are warranted.

Assessment of the trabecular structure of mandibular condyles in patients with temporomandibular disorders using fractal analysis

OBJECTIVES

The aim of this study was to evaluate changes in the trabecular structure of the mandibular condyle in patients with temporomandibular disorders (TMDs) using fractal analysis.

STUDY DESIGN

A total of 100 patients ages 18 to 73 years were clinically assessed using the Diagnostic Criteria for Temporomandibular Disorders. The control group was age- and sex-matched with the patient group. Panoramic radiographs were obtained using a Kodak 8000 digital device with 73 kVp and 5 mA fixed parameters. The degree of degeneration in the mandibular condyles was calculated. Regions of interest (84 × 84 pixels) were selected within the cortical boundary of the mandibular condyle, and the fractal dimension (FD) was calculated using ImageJ version 1.48.

RESULTS

Radiographic degenerative changes were more frequently present and more severe in the patient group (P < .001). The mean value of FD was 1.22 ± 0.06 in the patient group and 1.25 ± 0.06 in the control group (P = .001). A significant decrease in FD was observed (P = .001) in the left temporomandibular joints of the patient group, whereas a nonsignificant decrease in FD was observed in the right temporomandibular joints (P = .073) as degenerative changes increased.

CONCLUSIONS

Lower FD values were associated with more severe degenerative changes in the patient group. The trabecular structure of condyles in patients with TMD exhibited decreased complexity when erosive and sclerotic changes were evident. As a result, fractal analysis enhanced the use of panoramic radiography in detecting degenerative changes in patients with TMD.

Quantitative evaluation of midpalatal suture maturation via fractal analysis

Objective

The purpose of this study was to determine whether the results of fractal analysis can be used as criteria for midpalatal suture maturation evaluation.

Methods

The study included 131 subjects aged over 18 years of age (range 18.1–53.4 years) who underwent cone-beam computed tomography. Skeletonized images of the midpalatal suture were obtained via image processing software and used to calculate fractal dimensions. Correlations between maturation stage and fractal dimensions were calculated using Spearman's correlation coefficient. Optimal fractal dimension cut-off values were determined using a receiver operating characteristic curve.

Results

The distribution of maturation stages of the midpalatal suture according to the cervical vertebrae maturation index was highly variable, and there was a strong negative correlation between maturation stage and fractal dimension (−0.623, p < 0.001). Fractal dimension was a statistically significant indicator of dichotomous results with regard to maturation stage (area under curve = 0.794, p < 0.001). A test in which fractal dimension was used to predict the resulting variable that splits maturation stages into ABC and D or E yielded an optimal fractal dimension cut-off value of 1.0235.

Conclusions

There was a strong negative correlation between fractal dimension and midpalatal suture maturation. Fractal analysis is an objective quantitative method, and therefore we suggest that it may be useful for the evaluation of midpalatal suture maturation.

Qualitative and quantitative ultrashort-TE MRI of cortical bone

Osteoporosis causes over 1.5 million fractures per year, costing about $15 billion annually in the USA. Current guidelines utilize bone mineral density (BMD) to assess fracture risk; however, BMD alone only accounts for 30-50% of fractures. The other two major components of bone, organic matrix and water, contribute significantly to bone mechanical properties, but cannot be assessed with conventional imaging techniques in spite of the fact that they make up about 57% of cortical bone by volume. Conventional clinical MRI usually detects signals from water in tissues without difficulty, but cannot detect the water bound to the organic matrix, or the free water in the microscopic pores of the Haversian and the lacunar-canalicular system of cortical bone, because of their very short apparent transverse relaxation times (T2 *). In recent years, a new class of sequences, ultrashort-TE (UTE) sequences, with nominal TEs of less than 100 µs, which are much shorter than the TEs available with conventional sequences, have received increasing interest. These sequences can detect water signals from within cortical bone and provide an opportunity to study disease of this tissue in a new way. This review summarizes the recent developments in qualitative UTE imaging (techniques and contrast mechanisms to produce bone images with high contrast) and quantitative UTE imaging (techniques to quantify the MR properties, including T1 , T2 * and the magnetization transfer ratio, and tissue properties, including bone perfusion, as well as total, bound and free water content) of cortical bone in vitro and in vivo. The limitations of the current techniques for clinical applications and future directions are also discussed.

Prospective assessment of bone texture parameters at the hand in rheumatoid arthritis

OBJECTIVE

Fractal bone analysis (Hmean) is a texture parameter reflecting bone microarchitecture. The BMA device (D3A™ Medical Systems, Orléans, France) is a high-resolution X-ray device that allows assessment of bone texture analysis. We aimed to measure Hmean in rheumatoid arthritis patients at the second and third metacarpal bones, at baseline and after 1 year of follow-up, and to assess the relationship of Hmean and rheumatoid arthritis disease parameters.

METHODS

Patients with rheumatoid arthritis according to ACR criteria were included. They were assessed over 1 year, in the context of a prospective study conducted in Maastricht. For this substudy, activity of the disease was assessed by erythrocyte sedimentation rate, C-reactive protein and Disease Activity Score 28 performed at each visit. Radiographic bone damage was assessed using hand and feet radiographs at baseline and on a 1-year basis. The bone texture parameters were evaluated on the second and third metacarpal heads of the left hand using BMA device.

RESULTS

One hundred and sixty-five rheumatoid arthritis patients were included in this study. At baseline, Hmean was negatively correlated with age [r=-0.22 (P=0.013)] and erythrocyte sedimentation rate [r=-0.16 (P=0.039)]. No significant correlation was found between Hmean and Disease Activity Score, disease activity Visual Analog Scale, daily corticosteroid dose and C-reactive protein. There was a significant increase in Hmean of second and third metacarpal bones over 1 year (1.6% and 1.3%, P<0.01) except in patients with local second and third metacarpal bones erosion.

CONCLUSION

The bone texture parameter Hmean is influenced by age, inflammation and local erosions in rheumatoid arthritis.

Assessment of hand trabecular bone texture with high resolution direct digital radiograph in rheumatoid arthritis: a case control study

OBJECTIVES

Rheumatoid arthritis is characterized by an early inflammatory related periarticular osteopenia. A new high resolution direct digital X-ray device has been recently developed to provide bone texture analysis which is designed to assess changes in trabecular bone architecture. For the first time, we have evaluated trabecular bone texture impairment in rheumatoid arthritis patients compared to healthy controls.

METHODS

In this cross-sectional study, the reproducibility was assessed by three separate digital X-rays of the right hand, with repositioning in 14 late rheumatoid arthritis patients and 14 healthy subjects. Then, trabecular bone texture of the MCP2 and MCP3 from patients enrolled in a prospective cohort of 78 rheumatoid arthritis patients was compared with that of 50 healthy subjects, using three texture parameters: Hmean, co-occurrence and run-length.

RESULTS

The coefficients of variation of the high resolution direct digital X-ray measurements ranged from 0.5 to 1.8%. Only the Hmean parameter was significantly decreased in rheumatoid arthritis patients compared to healthy subjects at MCP2 (0.637±0.040 vs. 0.654±0.032, P<0.05) and at MCP3 (0.646±0.044 vs. 0.665±0.037, P<0.05). This reduction was significantly correlated to disease activity.

CONCLUSIONS

This study demonstrated both the good reproducibility of the high resolution digital X-ray measurements and the trabecular bone texture impairment at MCP joints in rheumatoid arthritis patients. In addition to provide a high resolution hand radiograph, this technique may represent an interesting tool to easily quantify periarticular osteopenia with a low radiation dose.

Fractal analysis of mandibular trabecular bone: optimal tile sizes for the tile counting method

Purpose

This study was performed to determine the optimal tile size for the fractal dimension of the mandibular trabecular bone using a tile counting method.

Materials and Methods

Digital intraoral radiographic images were obtained at the mandibular angle, molar, premolar, and incisor regions of 29 human dry mandibles. After preprocessing, the parameters representing morphometric characteristics of the trabecular bone were calculated. The fractal dimensions of the processed images were analyzed in various tile sizes by the tile counting method.

Results

The optimal range of tile size was 0.132 mm to 0.396 mm for the fractal dimension using the tile counting method. The sizes were closely related to the morphometric parameters.

Conclusion

The fractal dimension of mandibular trabecular bone, as calculated with the tile counting method, can be best characterized with a range of tile sizes from 0.132 to 0.396 mm.

Development of a parametric finite element model of the proximal femur using statistical shape and density modelling

Skeletal fractures associated with bone mass loss are a major clinical problem and economic burden, and lead to significant morbidity and mortality in the ageing population. Clinical image-based measures of bone mass show only moderate correlative strength with bone strength. However, engineering models derived from clinical image data predict bone strength with significantly greater accuracy. Currently, image-based finite element (FE) models are time consuming to construct and are non-parametric. The goal of this study was to develop a parametric proximal femur FE model based on a statistical shape and density model (SSDM) derived from clinical image data. A small number of independent SSDM parameters described the shape and bone density distribution of a set of cadaver femurs and captured the variability affecting proximal femur FE strength predictions. Finally, a three-dimensional FE model of an 'unknown' femur was reconstructed from the SSDM with an average spatial error of 0.016 mm and an average bone density error of 0.037 g/cm(3).

Peri-implant bone tissue assessment by comparing the outcome of intra-oral radiograph and cone beam computed tomography analyses to the histological standard

OBJECTIVES

The present study aims to identify radiographic methods revealing data that are most representative for the true peri-implant bone as assessed by histology.

MATERIALS AND METHODS

Eighty implants were placed in 10 minipigs. To assess matching between different image modalities, measurements conducted on intra-oral digital radiographs (IO), cone beam computer tomography (CBCT) and histological images were correlated using Spearman's correlation. Paired tests (Wilcoxon test) were used to determine changes in the bone parameters after 2 and 3 months of healing.

RESULTS

Significant correlations between bone defect depth on IO and histological slices (r= + 0.7, P<0.01), as well as on CBCT images and histological slices (r= + 0.61, P<0.01), were found. CBCT and IO images deviate, respectively, 1.20 and 1.17 mm from the histology regarding bone defects. No significant correlations were detected between fractal analysis on CBCT, intra-oral radiography and histology. For bone density assessment, significant but weaker correlations (r= + 0.5, P<0.01) were found for intra-oral radiography vs. histology. Significant marginal bone-level changes could be observed after 3 months of healing using intra-oral radiography.

CONCLUSIONS

This study allowed linking radiographic bone defect depth to the histological observations of the peri-implant bone. Minute bone changes during a short-term period can be followed up using digital intra-oral radiography. Radiographic fractal analysis did not seem to match histological fractal analysis. CBCT was not found to be reliable for bone density measures, but might hold potential with regard to the structural analysis of the trabecular bone.

The Founder's Lecture 2009: advances in imaging of osteoporosis and osteoarthritis

The objective of this review article is to provide an update on new developments in imaging of osteoporosis and osteoarthritis over the past three decades. A literature review is presented that summarizes the highlights in the development of bone mineral density measurements, bone structure imaging, and vertebral fracture assessment in osteoporosis as well as MR-based semiquantitative assessment of osteoarthritis and quantitative cartilage matrix imaging. This review focuses on techniques that have impacted patient management and therapeutic decision making or that potentially will affect patient care in the near future. Results of pertinent studies are presented and used for illustration. In summary, novel developments have significantly impacted imaging of osteoporosis and osteoarthritis over the past three decades.

Trabecular bone analysis in CT and X-ray images of the proximal femur for the assessment of local bone quality

Currently, conventional X-ray and CT images as well as invasive methods performed during the surgical intervention are used to judge the local quality of a fractured proximal femur. However, these approaches are either dependent on the surgeon's experience or cannot assist diagnostic and planning tasks preoperatively. Therefore, in this work a method for the individual analysis of local bone quality in the proximal femur based on model-based analysis of CT- and X-ray images of femur specimen will be proposed. A combined representation of shape and spatial intensity distribution of an object and different statistical approaches for dimensionality reduction are used to create a statistical appearance model in order to assess the local bone quality in CT and X-ray images. The developed algorithms are tested and evaluated on 28 femur specimen. It will be shown that the tools and algorithms presented herein are highly adequate to automatically and objectively predict bone mineral density values as well as a biomechanical parameter of the bone that can be measured intraoperatively.

Advances in osteoporosis imaging

In the assessment of osteoporosis, the measurement of bone mineral density (BMD(a)) obtained from dual energy X-ray absorptiometry (DXA; g/cm(2)) is the most widely used parameter. However, bone strength and fracture risk are also influenced by parameters of bone quality such as micro-architecture and tissue properties. This article reviews the radiological techniques currently available for imaging and quantifying bone structure, as well as advanced techniques to image bone quality. With the recent developments in magnetic resonance (MR) techniques, including the availability of clinical 3T scanners, and advances in computed tomography (CT) technology (e.g. clinical Micro-CT), in-vivo imaging of the trabecular bone architecture is becoming more feasible. Several in-vitro studies have demonstrated that bone architecture, measured by MR or CT, was a BMD-independent determinant of bone strength. In-vivo studies showed that patients with, and without, osteoporotic fractures could better be separated with parameters of bone architecture than with BMD. Parameters of trabecular architecture were more sensitive to treatment effects than BMD. Besides the 3D tomographic techniques, projection radiography has been used in the peripheral skeleton as an additional tool to better predict fracture risk than BMD alone. The quantification of the trabecular architecture included parameters of scale, shape, anisotropy and connectivity. Finite element analyses required highest resolution, but best predicted the biomechanical properties of the bone. MR diffusion and perfusion imaging and MR spectroscopy may provide measures of bone quality beyond trabecular micro-architecture.

Anniversary paper: History and status of CAD and quantitative image analysis: the role of Medical Physics and AAPM

The roles of physicists in medical imaging have expanded over the years, from the study of imaging systems (sources and detectors) and dose to the assessment of image quality and perception, the development of image processing techniques, and the development of image analysis methods to assist in detection and diagnosis. The latter is a natural extension of medical physicists' goals in developing imaging techniques to help physicians acquire diagnostic information and improve clinical decisions. Studies indicate that radiologists do not detect all abnormalities on images that are visible on retrospective review, and they do not always correctly characterize abnormalities that are found. Since the 1950s, the potential use of computers had been considered for analysis of radiographic abnormalities. In the mid-1980s, however, medical physicists and radiologists began major research efforts for computer-aided detection or computer-aided diagnosis (CAD), that is, using the computer output as an aid to radiologists-as opposed to a completely automatic computer interpretation-focusing initially on methods for the detection of lesions on chest radiographs and mammograms. Since then, extensive investigations of computerized image analysis for detection or diagnosis of abnormalities in a variety of 2D and 3D medical images have been conducted. The growth of CAD over the past 20 years has been tremendous-from the early days of time-consuming film digitization and CPU-intensive computations on a limited number of cases to its current status in which developed CAD approaches are evaluated rigorously on large clinically relevant databases. CAD research by medical physicists includes many aspects-collecting relevant normal and pathological cases; developing computer algorithms appropriate for the medical interpretation task including those for segmentation, feature extraction, and classifier design; developing methodology for assessing CAD performance; validating the algorithms using appropriate cases to measure performance and robustness; conducting observer studies with which to evaluate radiologists in the diagnostic task without and with the use of the computer aid; and ultimately assessing performance with a clinical trial. Medical physicists also have an important role in quantitative imaging, by validating the quantitative integrity of scanners and developing imaging techniques, and image analysis tools that extract quantitative data in a more accurate and automated fashion. As imaging systems become more complex and the need for better quantitative information from images grows, the future includes the combined research efforts from physicists working in CAD with those working on quantitative imaging systems to readily yield information on morphology, function, molecular structure, and more-from animal imaging research to clinical patient care. A historical review of CAD and a discussion of challenges for the future are presented here, along with the extension to quantitative image analysis.

Classification of trabecular bone texture from MRI and CT scan images by multi resolution analysis

Although bone mineral density measurements constitute one of the main clinical indicators of osteoporosis, we know that bone fragility risk is also related to deteriorations of osseous architecture. Medical imaging constitutes one means to appreciate in vivo bone screen, what is particularly important in the follow up of the osteoporosis. This paper presents a method of bone textural MRI and CT scan classification, based on the use of multifractal analysis by the WTMM-2d method, we propose the choice of three features to realize these images classification: the Hölder exponents average at the peaks of Legendre spectrums, the wavelet transform skeletons density by pixel, and variance of directions of gradients. The preliminary results of 40 images directly resulting from two medical imaging (MRI and CT scan), prove to be interesting since 90% of cases are well estimated, and two classes instantaneous clustering of the results (one healthy patient class and one osteoporotic patient class) quite separate.

Direct measurement of trabecular bone anisotropy using directional fractal dimension and principal axes of inertia

OBJECTIVE

Precise in vivo measurement of the trabecular bone's mechanical properties is very important for endosseous dental implant treatment and design in clinical practice. The fractal structure of trabecular bone shows directional anisotropy of the architecture, as is shown in most biological fractals. To analyze the anisotropy of the trabecular bone, the fractal geometry technique was applied to 2-dimensional plain radiographs.

STUDY DESIGN

The power spectrum was used to calculate the fractal dimensions (FD) of the trabecular bone. The FDs calculated as a function of orientation yielded the fractal information reflecting the spatial characteristics of the trabecular bone in each direction. A polar plot of directional FDs was defined as an ellipse of inertia. The principal loading direction in a local region of the trabecular bone was determined from the minimum moment of inertia for the ellipse of FDs. The anisotropy was calculated directly as the ratio of the 2 principal moments of inertia from the ellipse.

RESULTS

The anisotropies were measured for radiographs from the angle and incisor region of 21 human mandibles based on the principal axes of inertia and the best-fitting ellipse. The anisotropy of the angle region was significantly greater than that of the incisor region of the mandibles.

CONCLUSION

The method using directional FDs as determined by the principal axis of inertia measures the anisotropy directly, using 2-dimensional plain radiographs. It can quantify the anisotropy of trabecular bone in vivo. The investigation can be applied to the analysis of the relationships between in vivo 2-dimensional parameters and 3-dimensional mechanical properties, which enables us to predict the bone mechanical properties such as strength in vivo in various regions of the mandible.

Comparison of trabecular bone anisotropies based on fractal dimensions and mean intercept length determined by principal axes of inertia

The mechanical quality of trabecular bone depends on both its stiffness and its strength characteristics, which can be predicted indirectly by the combination of bone volume fraction and architectural anisotropy. To analyze the directional anisotropy of the trabecular bone, we applied the fractal geometry technique to plain radiographs. The anisotropy of the bone was quantified from an ellipse, based on the directional fractal dimensions (FD), by the principal axes of inertia. The anisotropies based on the FD were compared with those determined using the common method of mean intercept length (MIL). The directional FD gave the fractal information obtained from a projection along the MIL orientation. For this reason, the spatial variations associated with the bone length in any direction were manifested in a related frequency band of the power spectrum determined along the direction. The directional FD and MIL plots were highly correlated, although they originated from quite different geometries. Of the angle, premolar, and incisor regions of the human mandible, the anisotropies calculated using both FD and MIL showed the highest correlation in the trabecular bone of the angle region. The method using directional FDs as determined by the principal axis of inertia measures the anisotropy directly, using two-dimensional plain radiographs. This kind of method will be a useful to provide better estimates of bone quality in vivo compared with the density measurements alone, especially for the indirect diagnosis of jawbone quality in dental clinics.

Comparative assessment of bone mass and structure using texture-based and histomorphometric analyses

The purpose of this study was to develop a methodology for quantitatively assessing bone quantity and anisotropy based on texture analysis using Gabor wavelets. The wavelet approach has the capability to simultaneously examine the images at low and high resolutions to gain information on both global and detailed local features of the bone image. The program that implemented the texture analysis gave measures of density (M(Density)) and anisotropy (M(Anisotropy)). It also allowed us to examine the texture energy at four orientations (0 degrees , 45 degrees , 90 degrees , 135 degrees) to gain insight about the details of the anisotropy. Analysis of templates of four simulated patterns, which had same number of dots but with differing orientations, demonstrated how the texture-based analysis differentiated between these templates. The measures of M(Anisotropy) discriminated between the four simulated patterns. The M(Density) measures were similar across all patterns. These outcomes matched the design intent of the simulated patterns. We also compared the trabecular bone images obtained from a previous study, in which the right forelimbs of normal female retired breeder beagle dogs (5-7 years old) were cast for 12 months to induce bone loss, using both histomorphometry and texture analysis. Both histomorphometry and the texture analysis detected significant differences in the trabecular bone of the distal metatarsal between the control and disuse groups. Percent trabecular bone (Tb.Ar/T.Ar) and the textural density parameter (M(Density)) were highly correlated (r=0.962). M(Anisotropy) was decreased (3.9%) after the 12-month disuse protocol, but was not significantly different from normal. However, the texture energy values at all orientations (0 degrees , 45 degrees , 90 degrees and 135 degrees) were significantly decreased in the disuse group. Therefore, texture analysis was able to assess anisotropy, which could not be extracted from histomorphometric parameters. We conclude that texture analysis is an effective tool for assessing 2D bone images that yields information regarding the quantity of bone as well as the orientation of the trabecular structure that can augment our ability to discriminate between normal and pathological bone tissue.

Bone texture analysis on direct digital radiographic images: precision study and relationship with bone mineral density at the os calcis

Assessment of bone microarchitecture in complement to bone mineral density (BMD) exam could improve prediction of osteoporotic fractures. A high-resolution X-ray prototype was developed to assess microarchitecture quality. Images were obtained on os calcis; then, three texture parameters were calculated on the same region of interest (ROI): a fractal parameter, a run-length parameter, and a co-occurrence parameter. This work describes the reproducibility of this method. We also examine the relationship between texture parameters and BMD at a site-matched ROI. Measurements on the left heel were performed on 30 healthy women, on the same day, with repositioning for short-term precision error. An additional measurement was done at 1 week to evaluate mid-term precision error on 14 subjects. Os calcis images from 10 healthy women were used to evaluate both intra- and interobserver reproducibility. Thirty other healthy patients were measured successively on two similar devices for interprototype comparison. BMD and texture analyses of the left heel were obtained from 57 women. Short-term precision errors ranged 1.16-1.24% according to the texture parameter. Mid-term precision error was slightly higher than short-term precision for the mean Hurst exponent parameter. Comparisons of texture parameters and BMD at a site-matched ROI on the os calcis showed no significant relationships. The results also show that the use of this high-resolution digital X-ray device improves the reproducibility of parameter measurement compared to the indirect digitization of radiologic films previously used.

Relevance of 2D radiographic texture analysis for the assessment of 3D bone micro-architecture

Although the diagnosis of osteoporosis is mainly based on dual x-ray absorptiometry, it has been shown that trabecular bone micro-architecture is also an important factor in regard to fracture risk. In vivo, techniques based on high-resolution x-ray radiography associated to texture analysis have been proposed to investigate bone micro-architecture, but their relevance for giving pertinent 3D information is unclear. Thirty-three calcaneus and femoral neck bone samples including the cortical shells (diameter: 14 mm, height: 30-40 mm) were imaged using 3D-synchrotron x-ray micro-CT at the ESRF. The 3D reconstructed images with a cubic voxel size of 15 microm were further used for two purposes: (1) quantification of three-dimensional trabecular bone micro-architecture, (2) simulation of realistic x-ray radiographs under different acquisition conditions. The simulated x-ray radiographs were then analyzed using a large variety of texture analysis methods (co-occurrence, spectral density, fractal, morphology, etc.). The range of micro-architecture parameters was in agreement with previous studies and rather large, suggesting that the population was representative. More than 350 texture parameters were tested. A small number of them were selected based on their correlation to micro-architectural morphometric parameters. Using this subset of texture parameters, multiple regression allowed one to predict up to 93% of the variance of micro-architecture parameters using three texture features. 2D texture features predicting 3D micro-architecture parameters other than BV/TV were identified. The methodology proposed for evaluating the relationships between 3D micro-architecture and 2D texture parameters may also be used for optimizing the conditions for radiographic imaging. Further work will include the application of the method to physical radiographs. In the future, this approach could be used in combination with DXA to refine osteoporosis diagnosis.

Influence of bone quality on the strength of internal and external fixation of tibial plateau fractures

We studied the influence of different parameters of bone quality on the fixation strength of bicondylar tibial plateau fractures and examined the relationship between these parameters. Bone quality was measured in the plateau of 16 cadaveric tibias using three modalities: dual-energy X-ray absorptiometry (DXA), peripheral quantitative computer tomography (pQCT), and spectral analysis of digitized radiographs (SADR). The tibias were divided into two groups by the median bone mineral density (BMD) and randomized to receive either dual plating or external fixator for the stabilization of a standardized bicondylar tibial fracture. The fixed fractures were subjected to axial compression until failure. DXA BMD correlated most significantly with the failure load (r>or=0.79, p<0.001), followed by the pQCT parameters of cancellous bone (0.52>or=r>or=0.73, p<0.01). Similar strong correlations were also evident in both fixation methods. For parameters derived from SADR, only those including both longitudinal and transverse trabecular orientations had modest correlation with the fixation strength (0.53>or=r>or=0.71, p<0.01). The failure loads of the two fixation techniques were not significantly different (mean+/-SD=3522+/-1386 N and 3710+/-1356 N, respectively, p=0.78). However, BMD in the dual-plating group influenced the failure load significantly (p=0.03), whereas in the external fixation group this was less evident (p=0.100). The majority of bone quality parameters that correlated with fixation strength were also strongly correlated with each other, particularly the BMDs measured by DXA and pQCT. This is the first study that relates fixation strength of bicondylar tibial plateau fractures to bone quality assessed at the same anatomical site. BMD around the fracture site had the best correlation with the failure load regardless of the fixation technique. The two fixation methods tested performed equally well, and the choice between them depends on the soft tissue condition and surgeon preference.

Relationship between two-dimensional and three-dimensional bone architecture in predicting the mechanical strength of the pig mandible

OBJECTIVES

To investigate the relationship between two-dimensional (2D) and three-dimensional (3D) bone imaging parameters.

STUDY DESIGN

Bone specimens were obtained from the mandibles of five male pigs weighing around 110 kg each. A total of 111 samples were measured two-dimensionally with using solid state digital intraoral radiography. Of these 111 samples, 43 were selected for 3D analysis and measured by microcomputed tomography. Through destructive mechanical testing, strength parameters were obtained.

RESULTS

Correlations between the 2D and 3D parameters were rare; however, both 2D and 3D parameters separately showed significant correlations with strength. Multiple linear regression analyses using both 2D and 3D parameters together showed greater predictability than those using only 2D or only 3D parameters.

CONCLUSION

Architectural parameters in 2D and 3D independently affect trabecular strength; the combination of the two can be used to improve bone strength predictability.

Three-dimensional texture analysis of cancellous bone cores evaluated at clinical CT resolutions

The objective of this study was to determine if three-dimensional (3D) Haralick co-occurrence texture measures calculated from low-resolution CT images of trabecular bone correlate with 3D structural indices measured from high-resolution CT images. Thirty-three cubical regions of trabecular bone from human calcanei were analyzed using images obtained from a micro-computed tomography (micro-CT) scanner. 3D measures of bone architecture were calculated. The original images were then subsampled by factors of 5, 10, 15, and 20, and 3D texture features were calculated for each set of subsampled images. Linear regression models showed that co-occurrence texture features were significantly correlated with structural indices. Over 90% of the variation in three different structural indices was explained in two-variable regression models using texture features as predictors when the voxel side length was reduced by a factor of 10. Texture features calculated from clinical images may increase our ability to obtain trabecular bone architectural information when high-resolution images are unobtainable.

Bone shape, structure, and density as determinants of osteoporotic hip fracture: a pilot study investigating the combination of risk factors

OBJECTIVES

This article compares and combines methods for examining the external shape and the internal structure of the proximal femur with bone mineral density (BMD) to provide a classifier for hip fracture.

MATERIALS AND METHODS

Fifty standard pelvic radiographs were available from age-matched fracture and control groups of postmenopausal women. Femoral shape was measured using an active shape model, the trabecular structure by means of a Fourier transform.

RESULTS

Both the shape and various structure measures were independent of BMD (P=0.16 and >0.50, respectively). Calculating the area under the receiver operator characteristic (ROC) curve (Az), each of shape (Az=0.81), the best structure measure (Az=0.79-0.93), and BMD (Az=0.79), could partially classify the fracture and control groups. However, the combination achieved almost perfect separation (Az=0.99).

CONCLUSIONS

This pilot study shows how bone shape and structure can complement BMD measurements for investigations of fracture risk.

Fractal analysis of bone architecture at distal radius

Bone strength depends on bone quality (architecture, turnover, damage accumulation, and mineralization) as well as bone mass. In this study, human bone architecture was analyzed using fractal image analysis, and the clinical relevance of this method was evaluated. The subjects were 12 healthy female controls and 16 female patients suspected of having osteoporosis (age range, 22-70 years; mean age, 49.1 years). High-resolution CT images of the distal radius were acquired and analyzed using a peripheral quantitative computed tomography (pQCT) system. On the same day, bone mineral densities of the lumbar spine (L-BMD), proximal femur (F-BMD), and distal radius (R-BMD) were measured by dual-energy X-ray absorptiometry (DXA). We examined the correlation between the fractal dimension and six bone mass indices. Subjects diagnosed with osteopenia or osteoporosis were divided into two groups (with and without vertebral fracture), and we compared measured values between these two groups. The fractal dimension correlated most closely with L-BMD (r=0.744). The coefficient of correlation between the fractal dimension and L-BMD was very similar to the coefficient of correlation between L-BMD and F-BMD (r=0.783) and the coefficient of correlation between L-BMD and R-BMD (r=0.742). The fractal dimension was the only measured value that differed significantly between both the osteopenic and the osteoporotic subjects with and without vertebral fracture. The present results suggest that the fractal dimension of the distal radius can be reliably used as a bone strength index that reflects bone architecture as well as bone mass.

Bisphosphonate therapy improves the outcome of conventional periodontal treatment: results of a 12-month, randomized, placebo-controlled study

BACKGROUND

Bone loss in periodontitis results from inflammatory reactions that stimulate osteoclastic bone resorption. Bisphosphonates inhibit bone resorption and increase bone mass. This study evaluated the effect of bisphosphonate therapy as an adjunct to non-surgical periodontal treatment in patients with moderate to severe chronic periodontitis.

METHODS

Patients were randomized (2:1) to one of two bisphosphonate therapies or placebo for 1 year. All patients received non-surgical periodontal treatment (scaling, root planing) and periodontal maintenance therapy every 3 months. Clinical assessments at baseline and 6 and 12 months included clinical attachment level (CAL), probing depth (PD), and bleeding on probing (BOP). Periodontal bone mass was assessed by dental radiographs at baseline and 12 months using fractal analysis and digital subtraction radiography (DSR).

RESULTS

Seventy patients were randomized, 43 to the bisphosphonate group and 27 to the placebo group. Bisphosphonate therapy significantly improved CAL, PD, and BOP relative to the placebo group during the 6- to 12-month period (CAL, P = 0.0002; PD, P = 0.0156; BOP, P = 0.0079). There was no difference in the change in periodontal bone mass between the bisphosphonate and placebo groups as measured by fractal analysis and DSR.

CONCLUSION

These data suggest that bisphosphonate treatment improves the clinical outcome of non-surgical periodontal therapy and may be an appropriate adjunctive treatment to preserve periodontal bone mass.

Fractal analysis of trabecular bone in knee osteoarthritis (OA) is a more sensitive marker of disease status than bone mineral density (BMD)

The purpose of this study was to determine whether fractal analysis (FSA) of macroradiographs or bone mineral density (BMD) is more sensitive in detecting disease-related cancellous bone alterations in knee osteoarthritis (OA). Differences in BMD between 11 OA (6 females) and 11 non-OA reference (7 females) tibiae were compared with differences in trabecular organization measured by computerized method of fractal signature analysis (FSA) of digitized macroradiographs (x3.5 to x5). OA knees had anatomic and radiographic evidence of medial compartment disease. FSA measured cancellous bone organization at 4 regions of interest (ROI): medial and lateral subchondral (Sc) and subarticular (Sa) sites, dual X-ray absorptiometry (DXA) measured BMD at the same ROIs. Compared to non-OA, OA tibiae had significant increased (P < 0.05) in FSA of vertical trabeculae in the medial Sa region (trabecular size range: 0.42-0.54; 0.90-1.98 mm) and significant decrease (P < 0.05) in FSA for some horizontal trabeculae in the Sc region (trabecular size range: medial side 0.12-0.18 mm; lateral side 0.12-0.24 mm). Compared to non-OA, BMD of OA tibiae was not significantly different at any ROI. BMD was not sensitive to changes in trabecular organization detected by FSA. The increase in FSA of vertical trabeculae in the medial Sa region was consistent with trabecular fenestration and thinning, which may have been detected as decreased BMD in a larger sample. For studies involving small sample sizes, quantifying changes in trabecular organization is more sensitive than BMD for detecting bone alterations in knee OA.

Identification of hip fracture patients from radiographs using Fourier analysis of the trabecular structure: a cross-sectional study

BACKGROUND: This study presents an analysis of trabecular bone structure in standard radiographs using Fourier transforms and principal components analysis (PCA) to identify contributions to hip fracture risk. METHODS: Radiographs were obtained from 26 hip fracture patients and 24 controls. They were digitised and five regions of interest (ROI) were identified from the femoral head and neck for analysis. The power spectrum was obtained from the Fourier transform of each region and three profiles were produced; a circular profile and profiles parallel and perpendicular to the preferred orientation of the trabeculae. PCA was used to generate a score from each profile, which we hypothesised could be used to discriminate between the fracture and control groups. The fractal dimension was also calculated for comparison. The area under the receiver operating characteristic curve (Az) discriminating the hip fracture cases from controls was calculated for each analysis. RESULTS: Texture analysis of standard radiographs using the fast Fourier transform yielded variables that were significantly associated with fracture and not significantly correlated with age, body mass index or femoral neck bone mineral density. The anisotropy of the trabecular structure was important; both the perpendicular and circular profiles were significantly better than the parallel-profile (P < 0.05). No significant differences resulted from using the various ROI within the proximal femur. For the best three groupings of profile (circular, parallel or perpendicular), method (PCA or fractal) and ROI (Az = 0.84 - 0.93), there were no significant correlations with femoral neck bone mineral density, age, or body mass index. PCA analysis was found to perform better than fractal analysis (P = 0.019). CONCLUSIONS: Both PCA and fractal analysis of the FFT data could discriminate successfully between the fracture and control groups, although PCA was significantly stronger than fractal dimension. This method appears to provide a powerful tool for the assessment of bone structure in vivo with advantages over standard fractal methods.

Current diagnostic techniques in the evaluation of bone architecture

Bone quality, which encompasses trabecular bone and cortical bone architecture, bone mineralization, turnover, and microdamage, is an essential component of bone strength. Therefore, bone quality, bone density, and total content are the most important parameters in the diagnosis of osteoporosis. Noninvasive assessment of bone quality has recently received considerable attention because bone density alone is not a surrogate for fracture prevalence and occurrence, and does not completely explain the therapeutic efficacy of emerging treatments. This paper will focus on the noninvasive assessment of trabecular bone architecture, one of the factors that governs bone strength and may be categorized as a contributor to bone quality. The methodologies described will include magnetic resonance imaging, clinical multislice spiral computed tomography, and micro-computed tomography, along with computerized analysis of radiographic patterns of trabecular bone.