Dissociation between global markers of bone formation and direct measurement of spinal bone formation in osteoporosis

Multimodal positron emission tomography (PET) imaging in non-oncologic musculoskeletal radiology

Musculoskeletal (MSK) disorders are associated with large impacts on patient's pain and quality of life. Conventional morphological imaging of tissue structure is limited in its ability to detect pain generators, early MSK disease, and rapidly assess treatment efficacy. Positron emission tomography (PET), which offers unique capabilities to evaluate molecular and metabolic processes, can provide novel information about early pathophysiologic changes that occur before structural or even microstructural changes can be detected. This sensitivity not only makes it a powerful tool for detection and characterization of disease, but also a tool able to rapidly assess the efficacy of therapies. These benefits have garnered more attention to PET imaging of MSK disorders in recent years. In this narrative review, we discuss several applications of multimodal PET imaging in non-oncologic MSK diseases including arthritis, osteoporosis, and sources of pain and inflammation. We also describe technical considerations and recent advancements in technology and radiotracers as well as areas of emerging interest for future applications of multimodal PET imaging of MSK conditions. Overall, we present evidence that the incorporation of PET through multimodal imaging offers an exciting addition to the field of MSK radiology and will likely prove valuable in the transition to an era of precision medicine.

Imaging bone turnover assessment through volumetric density-adjusted standardized uptake value using quantitative bone SPECT/CT in osteoporosis

BACKGROUND

Serum bone turnover markers offer limited insight into metabolic activity at the individual vertebra level in osteoporosis. This study introduces a novel image-derived bone turnover marker for individual vertebrae to address this limitation, utilizing volumetric density-adjusted quantitative bone single-photon emission computed tomography/computed tomography (SPECT/CT) with [99mTc]Tc-DPD. This retrospective study included 177 lumbar vertebrae from 55 postmenopausal South Korean women. The mean standardized uptake value (SUVmean, g/cm3) and volumetric bone mineral density (vBMD, mg/cm3) were determined within a 2-cm³ volume of interest in the trabecular portion of each vertebra using quantitative SPECT and CT. The density-adjusted mean standardized uptake value (dSUVmean) was calculated by dividing the SUVmean by the vBMD and multiplying by 1,000.

RESULTS

SUVmean correlated positively with vBMD (r = 0.60, p < 0.001). Conversely, dSUVmean correlated negatively with vBMD (ρ = -0.66, p < 0.001), highlighting the inverse relationship between bone mass and turnover after density adjustment of SUVmean. Patients with major osteoporotic fractures had lower vBMD (62.5 ± 29.4 vs. 92.3 ± 27.4 mg/cm³, p = 0.001) but higher dSUVmean (100.8 ± 60.7 vs. 62.6 ± 17.5, p = 0.001) compared to those without fractures, reinforcing the association between fracture prevalence, low bone mass, and high bone turnover.

CONCLUSION

Volumetric density-adjusted quantitative bone SPECT/CT offers a novel image-derived bone turnover marker for assessing bone turnover in osteoporosis. This method provides a precise assessment of fragility at the individual vertebra level, which may enhance personalized osteoporosis management.

Total Body PET/CT: A Role in Musculoskeletal Diseases

Recent advancements in PET technology have culminated in the development of total-body PET (TB-PET) systems, which overcome many limitations of traditional scanners. These TB-PET scanners, while still becoming widely available, represent the forefront of clinical imaging across numerous medical institutions worldwide. Early clinical applications have demonstrated their enhanced image quality, precise lesion quantification, and overall superior performance relative to conventional scanners. The capabilities of TB-PET technology, including extended scan range, ultrahigh sensitivity, exceptional temporal resolution, and dynamic imaging, offer significant potential to tackle unresolved clinical challenges in medical imaging. In this discussion, we aim to explore the emerging applications, opportunities, and future perspectives of TB-PET/CT in musculoskeletal disorders (MSDs). Clinical applications for both oncologic and non-oncologic musculoskeletal diseases are discussed, including inflammatory arthritis, infections, osteoarthritis, osteoporosis, and skeletal muscle disorders. From the ability to visualize small musculoskeletal structures and the entire axial and appendicular skeleton, TB-PET shows significant potential in the diagnosis and management of MSD conditions as it becomes more widely available.

State of the Art Imaging of Osteoporosis

Osteoporosis is a common disease, particularly prevalent in geriatric populations, which causes significant worldwide morbidity due to increased bone fragility and fracture risk. Currently, the gold-standard modality for diagnosis and evaluation of osteoporosis progression and treatment relies on dual-energy x-ray absorptiometry (DXA), which measures bone mineral density (BMD) and calculates a score based upon standard deviation of measured BMD from the mean. However, other imaging modalities can also be used to evaluate osteoporosis. Here, we review historical as well as current research into development of new imaging modalities that can provide more nuanced or opportunistic analyses of bone quality, turnover, and density that can be helpful in triaging severity and determining treatment success in osteoporosis. We discuss the use of opportunistic computed tomography (CT) scans, as well as the use of quantitative CT to help determine fracture risk and perform more detailed bone quality analysis than would be allowed by DXA . Within magnetic resonance imaging (MRI), new developments include the use of advanced MRI techniques such as quantitative susceptibility mapping (QSM), magnetic resonance spectroscopy, and chemical shift encoding-based water-fat MRI (CSE-MRI) to enable clinicians improved assessment of nonmineralized bone compartments as well as a way to longitudinally assess bone quality without the repeated exposure to ionizing radiation. Within ultrasound, development of quantitative ultrasound shows promise particularly in future low-cost, broadly available screening tools. We focus primarily on historical and recent developments within radiotracer use as applicable to osteoporosis, particularly in the use of hybrid methods such as NaF-PET/CT, wherein patients with osteoporosis show reduced uptake of radiotracers such as NaF. Use of radiotracers may provide clinicians with even earlier detection windows for osteoporosis than would traditional biomarkers. Given the metabolic nature of this disease, current investigation into the role molecular imaging can play in the prediction of this disease as well as in replacing invasive diagnostic procedures shows particular promise.

Bone turnover change after randomized switch from tenofovir disoproxil to tenofovir alafenamide fumarate in men with HIV

OBJECTIVE

Bone loss in people with HIV (PWH) is poorly understood. Switching tenofovir disoproxil fumarate (TDF) to tenofovir alafenamide (TAF) has yielded bone mineral density (BMD) increases. PETRAM (NCT#:03405012) investigated whether BMD and bone turnover changes correlate.

DESIGN

Open-label, randomized controlled trial.

SETTING

Single-site, outpatient, secondary care.

PARTICIPANTS

Nonosteoporotic, virologically suppressed, cis-male PWH taking TDF/emtricitabine (FTC)/rilpivirine (RPV) for more than 24 weeks.

INTERVENTION

Continuing TDF/FTC/RPV versus switching to TAF/FTC/RPV (1 : 1 randomization).

MAIN OUTCOME MEASURES

:[ 18 F]NaF-PET/CT for bone turnover (standardized uptake values, SUV mean ) and dual-energy x-ray absorptiometry for lumbar spine and total hip BMD.

RESULTS

Thirty-two men, median age 51 years, 76% white, median duration TDF/FTC/RPV 49 months, were randomized between 31 August 2018 and 09 March 2020. Sixteen TAF:11 TDF were analyzed. Baseline-final scan range was 23-103 (median 55) weeks. LS-SUV mean decreased for both groups (TAF -7.9% [95% confidence interval -14.4, -1.5], TDF -5.3% [-12.1,1.5], P  = 0.57). TH-SUV mean showed minimal changes (TAF +0.3% [-12.2,12.8], TDF +2.9% [-11.1,16.9], P  = 0.77). LS-BMD changes were slightly more favorable with TAF but failed to reach significance (TAF +1.7% [0.3,3.1], TDF -0.3 [-1.8,1.2], P  = 0.06). Bone turnover markers decreased more with TAF ([CTX -35.3% [-45.7, -24.9], P1NP -17.6% [-26.2, -8.5]) than TDF (-11.6% [-28.8, +5.6] and -6.9% [-19.2, +5.4] respectively); statistical significance was only observed for CTX ( P  = 0.02, P1NP, P  = 0.17).

CONCLUSION

Contrary to our hypothesis, lumbar spine and total hip regional bone formation (SUV mean ) and BMD did not differ postswitch to TAF. However, improved LS-BMD and CTX echo other TAF-switch studies. The lack of difference in SUV mean may be due to inadequate power.

Peri-Implantitis: A New Definition Proposal Based on Unnatural Spatial Arrangement and Late Mechanical Coupling between Two Cortical Bone Layers during Osseointegration Phase Part II

To date, the term peri-implantitis has been mostly associated with bacterial or foreign body reaction as primary factors of its development. Because of this, researchers’ and clinicians’ attention regarding treatment possibilities were directed into the solutions on the basis of surface modifications, debridement, and antibiotics. After years of clinical observations and poor results in treatment of peri-implantitis, a new proposal of this condition is presented, shifting our way of thinking regarding bone and implant interactions. In the second part of the paper presenting a new definition of peri-implantitis, we focused on a biological explanation of the bone behavior at the bone–implant interface. The main conclusion is that PI is not an “infectious disease”, but rather the result of natural changes of the bone’s morphology in response to implant such as a decrease in convexity of the outer surface of the bone and subsequently a decrease in concavity of the inner bone.

[18F] Sodium Fluoride PET Kinetic Parameters in Bone Imaging

This report describes the significance of the kinetic parameters (k-values) obtained from the analysis of dynamic positron emission tomography (PET) scans using the Hawkins model describing the pharmacokinetics of sodium fluoride ([¹⁸F]NaF) to understand bone physiology. Dynamic [¹⁸F]NaF PET scans may be useful as an imaging biomarker in early phase clinical trials of novel drugs in development by permitting early detection of treatment-response signals that may help avoid late-stage attrition.

Applications of Artificial Intelligence in 18F-Sodium Fluoride Positron Emission Tomography/Computed Tomography:: Current State and Future Directions

This review discusses the current state of artificial intelligence (AI) in ¹⁸F-NaF-PET/CT imaging and the potential applications to come in diagnosis, prognostication, and improvement of care in patients with bone diseases, with emphasis on the role of AI algorithms in CT bone segmentation, relying on their prevalence in medical imaging and utility in the extraction of spatial information in combined PET/CT studies.

18F-Sodium Fluoride PET as a Diagnostic Modality for Metabolic, Autoimmune, and Osteogenic Bone Disorders: Cellular Mechanisms and Clinical Applications

In a healthy body, homeostatic actions of osteoclasts and osteoblasts maintain the integrity of the skeletal system. When cellular activities of osteoclasts and osteoblasts become abnormal, pathological bone conditions, such as osteoporosis, can occur. Traditional imaging modalities, such as radiographs, are insensitive to the early cellular changes that precede gross pathological findings, often leading to delayed disease diagnoses and suboptimal therapeutic strategies. ¹⁸F-sodium fluoride (¹⁸F-NaF)-positron emission tomography (PET) is an emerging imaging modality with the potential for early diagnosis and monitoring of bone diseases through the detection of subtle metabolic changes. Specifically, the dissociated ¹⁸F^- is incorporated into hydroxyapatite, and its uptake reflects osteoblastic activity and bone perfusion, allowing for the quantification of bone turnover. While ¹⁸F-NaF-PET has traditionally been used to detect metastatic bone disease, recent literature corroborates the use of ¹⁸F-NaF-PET in benign osseous conditions as well. In this review, we discuss the cellular mechanisms of ¹⁸F-NaF-PET and examine recent findings on its clinical application in diverse metabolic, autoimmune, and osteogenic bone disorders.

Novel Musculoskeletal and Orthopedic Applications of 18F-Sodium Fluoride PET

PET imaging with ¹⁸F-sodium fluoride (NaF), combined with computed tomography or magnetic resonance, is a sensitive method of assessing bone turnover. Although NaF-PET is gaining popularity in detecting prostate cancer metastases to bone marrow, osseous changes represent secondary effects of cancer cell growth. PET tracers more appropriate for assessing prostate cancer metastases directly portray malignant activity and include ¹⁸F-fluciclovine and prostatic specific membrane antigen ligands. Recent studies investigating NaF-PET suggest utility in the assessment of benign musculoskeletal disorders. Emerging applications in assessing traumatic injuries, joint disease, back pain, orthopedic complications, and metabolic bone disease are discussed.

Total-Body PET Imaging of Musculoskeletal Disorders

Imaging of musculoskeletal disorders, including arthritis, infection, osteoporosis, sarcopenia, and malignancies, is often limited when using conventional modalities such as radiography, computed tomography (CT), and MR imaging. As a result of recent advances in Positron Emission Tomography (PET) instrumentation, total-body PET/CT offers a longer axial field-of-view, higher geometric sensitivity, and higher spatial resolution compared with standard PET systems. This article discusses the potential applications of total-body PET/CT imaging in the assessment of musculoskeletal disorders.

Bone biomarkers in koalas: validation of assays and preliminary analyses

Traumatic injury, including bone fracture, is, to date, one of the leading causes of koala mortality in the South East Queensland region of Australia. Further, the specialist diet of koalas, which is restricted to certain Eucalyptus spp., may impact their normal bone physiology. Considering the dramatic koala population decline and high incidence of trauma, a greater understanding of koala bone physiology may support conservation. We retrieved from GenBank the protein sequences of parathyroid hormone (PTH), osteocalcin (OCN), and tissue-nonspecific alkaline phosphatase (TNALP) in human, dog, cattle, horse, koala, and gray short-tailed opossum. After homology was determined, plasma samples from 13 koalas were analyzed with human PTH, OCN, and bone-specific ALP (BALP) assay kits. Although koala PTH exhibited relatively low sequence homology with placental mammals, high sequence homology between humans and koalas was observed for both OCN and TNALP, and successful cross-reactivity was achieved using human enzyme immunoassay kits for detection of OCN and BALP biomarkers in koala plasma. However, we identified no correlation between OCN and BALP concentrations of healthy and trauma-affected koalas (p = 0.66 and p = 0.79, respectively). Further analysis of OCN and BALP in healthy and diseased koalas will allow a better understanding of bone physiology in this unique marsupial.

Diagnosis and Monitoring of Osteoporosis with Total-Body 18F-Sodium Fluoride-PET/CT

In recent years, ¹⁸F-Sodium Fluoride (NaF)-PET/CT has seen its role in the detection and management of osteoporosis increase. This article reviews the extent of this application in the literature, its efficacy compared with other comparable imaging tools, and how total-body PET/CT combined with global disease assessment can revolutionize measurement of total osteoporotic disease activity. NaF-PET/CT eventually can be the modality of choice for metabolic bone disorders, especially with these advances in technology and computation.

Correlation between 18F-Sodium Fluoride positron emission tomography and bone histomorphometry in dialysis patients

BACKGROUND

The diagnosis of renal osteodystrophy is challenging. Bone biopsy is the gold standard, but it is invasive and limited to one site of the skeleton. The ability of biomarkers to estimate the underlying bone pathology is limited. ¹⁸F-Sodium Fluoride positron emission tomography (¹⁸F-NaF PET) is a noninvasive quantitative imaging technique that allows assessment of regional bone turnover at clinically relevant sites. The hypothesis of this study was, that ¹⁸F-NaF PET correlates with bone histomorphometry in dialysis patients and could act as a noninvasive diagnostic tool in this patient group.

METHODS

This was a cross-sectional diagnostic test study. 26 dialysis patients with biochemical abnormalities indicating mineral and bone disorder were included. All the participants underwent a ¹⁸F-NaF PET scan and a bone biopsy. Fluoride activity in the PET scan was measured in the lumbar spine and at the anterior iliac crest. Dynamic and static histomorphometric parameters of the bone biopsy were assessed. As histomorphometric markers for bone turnover we used bone formation rate per bone surface (BFR/BS) and activation frequency per year (Ac.f).

RESULTS

There was a statistically significant correlation between fluoride activity in the ¹⁸F-NaF PET scan and histomorphometric parameters such as bone formation rate, activation frequency and osteoclast and osteoblast surfaces and mineralized surfaces. ¹⁸F-NaF PET's sensitivity to recognize low turnover in respect to non-low turnover was 76% and specificity 78%. Because of the small number of patients with high turnover, we were unable to demonstrate significant predictive value in this group.

CONCLUSIONS

A clear correlation between histomorphometric parameters and fluoride activity in the ¹⁸F-NaF PET scan was established. ¹⁸F-NaF PET may possibly be a noninvasive diagnostic tool in dialysis patients with low turnover bone disease, but further research is needed.

Histological characteristics of advanced peri-implantitis bone defects in humans

BACKGROUND

Inflammatory osteolysis is the clinical hallmark of peri-implantitis. The morphology of the remaining peri-implant bone and the level of osseointegration, however, remain unknown. Our aim was to characterize advanced peri-implantitis bone defects in humans.

METHODS

Four patients (3 female and 1 male) were diagnosed with peri-implantitis. A total of 5 implants with machined surfaces and a mean loading time of 12 ± 6 years were removed due to advanced bone loss. The defect extension, the peri-implant bone density (bone area per tissue area in percentage), bone-to-implant contact (%), and the number of filled and empty osteocyte lacunae were calculated based on undecalcified histological specimens.

RESULTS

The defect extension was on average 4.2 mm (95% CI 0.8-3.4). Remaining peri-implant bone showed a high density of 85.5% (95% CI 79.1-91.3) and covered in total 74% (95% CI 70.5-77.5) of the implant surface. Filled and empty osteocyte lacunae density was on average 191 and 165/mm2 (95% CI 132-251; 103-225), respectively. Histology further revealed signs of ongoing bone formation and resorption.

CONCLUSION

There are signs that suggest that once the original cortical bone is lost due to peri-implantitis, the remaining apical trabecular bone is reinforced and transformed into cortical bone that might take over the functional load.

Bone metabolism of the jaw in response to bisphosphonate: a quantitative analysis of bone scintigraphy images

We examined the changes in the bone metabolism of the jaw in response to BP treatment, and we used bone SPECT-CT to analyze the site-specific bone metabolism between the jaw and other sites of bone. We compared the changes in the bone metabolism of each part of bone in response to BP treatment by performing a quantitative analysis of bone scintigraphy images between patients treated with low-dose BP for osteoporosis (LBP group; n = 17), those treated with high-dose BP for metastatic bone tumor (HBP group; n = 11), and patients with other oral disease who required bone scintigraphy, with no history of BP treatment (control group; n = 40). The study endpoint was the mean standardized uptake value (SUV) of the uptake of Tc-99 m methylene diphosphonate (MDP) in each group. The mean SUVs of the HBP group were significantly lower at the axial bone of the cervical vertebra, thoracic vertebra, sternum, and rib compared to those of the LBP and control groups. The LBP group's mean SUV was significantly higher at the temporal bone, the anodontia part of the alveolar bone in maxilla, the vital teeth part of alveolar bone in the mandible, and the temporomandibular joint. There was no significant difference among the three groups at the mandibular angle and mandibular ramus. Our analyses revealed that the bone metabolism of the jaw and temporal bone in the BP-treated patients was enhanced, and no suppression of bone remodeling in the jaw by BP was observed.

The influence of CT and dual-energy X-ray absorptiometry (DXA) bone density on quantitative [18F] sodium fluoride PET

Background

[¹⁸F] sodium fluoride PET/CT provides quantitative measures of bone metabolic activity expressed by the parameters standardised uptake value (SUV) and bone plasma clearance (K _i) that correlate with measurements of bone formation rate obtained by bone biopsy with double tetracycline labelling. Both SUV and K _i relate to the tracer uptake in each millilitre of tissue. In general, the bone region of interest (ROI) includes both mineralised bone {generally with a high concentration of [¹⁸F]NaF} and bone marrow (with a much lower concentration), suggesting that correcting SUV and K _i for volumetric bone mineral density (vBMD) and measuring them with respect to the tracer uptake in each gram of bone mineral might improve the correlation with the findings of bone biopsy. As a first test of this hypothesis, we looked for positive correlations between SUV and K _i values with CT and DXA bone mineral density (BMD) parameters measured in the same ROI.

Methods

A retrospective reanalysis was performed of 63 lumbar spine [¹⁸F]NaF PET/CT scans acquired in four earlier studies. The quantitative PET parameters SUV and K _i were measured in L1-L4 and Hounsfield units (HU) measured on the CT scans in the same ROI. Spine BMD data was also obtained from DXA scans in the form of areal BMD and used to derive the bone mineral apparent density (BMAD, an estimate of vBMD). Scatter plots were drawn of SUV and K _i against HU, BMAD and areal BMD and the Spearman rank correlation coefficients derived for each plot.

Results

All correlations were positive and statistically significant. Correlations were highest for HU (SUV: R_S =0.513, P<0.0001; K _i: R_S =0.429, P=0.0005) and lowest for areal BMD (SUV: R_S =0.353, P=0.005; K _i: R_S =0.274, P=0.03).

Conclusions

The results demonstrate significant positive correlations between SUV and K _i and vBMD measurements in the form of HU from CT or BMAD and areal BMD from DXA. These findings justify further exploration of the relationship between SUV and K _i [¹⁸F]NaF PET/CT measurements and CT or DXA measurements of vBMD to examine whether normalization for bone density might improve their correlation with bone metabolic activity as measured by bone biopsy.

Diagnosis and Monitoring of Osteoporosis With 18F-Sodium Fluoride PET: An Unavoidable Path for the Foreseeable Future

The prevalence of metabolic bone diseases particularly osteoporosis and its precursor, osteopenia, continue to grow as serious global health issues today. On a worldwide perspective, 200million people suffer from osteoporosis and in 2005, over 2million fracture incidents were estimated due to osteoporosis in the United States. Currently, osteoporosis and other metabolic bone diseases are evaluated primarily through dual energy X-ray absorptiometry, and rarely by bone biopsy with tetracycline labeling or Technetium-99m (^99mTc) based bone scintigraphy. Deficiencies in these methods have prompted the use of more precise methods of assessment. This review highlights the use of ¹⁸F-sodium fluoride (NaF) with PET (NaF-PET), NaF-PET/CT, or NaF-PET/MRI in the evaluation of osteoporosis and osteopenia in the lumbar spine and hip. This imaging modality provides a molecular perspective with respect to the underlying metabolic alterations that lead to osseous disorders by measuring bone turnover through standardized uptake values. Its sensitivity and ability to examine the entire skeletal system make it a more superior imaging modality compared to standard structural imaging techniques. Further research is needed to determine its accuracy in reflecting the efficacy of therapeutic interventions in metabolic bone diseases.

Acute myeloid leukemia transforms the bone marrow niche into a leukemia-permissive microenvironment through exosome secretion

Little is known about how leukemia cells alter the bone marrow (BM) niche to facilitate their own growth and evade chemotherapy. Here, we provide evidence that acute myeloid leukemia (AML) blasts remodel the BM niche into a leukemia growth-permissive and normal hematopoiesis-suppressive microenvironment through exosome secretion. Either engrafted AML cells or AML-derived exosomes increased mesenchymal stromal progenitors and blocked osteolineage development and bone formation in vivo. Preconditioning with AML-derived exosomes ‘primed’ the animals for accelerated AML growth. Conversely, disruption of exosome secretion in AML cells through targeting Rab27a, an important regulator involved in exosome release, significantly delayed leukemia development. In BM stromal cells, AML-derived exosomes induced the expression of DKK1, a suppressor of normal hematopoiesis and osteogenesis, thereby contributing to osteoblast loss. Conversely, treatment with a DKK1 inhibitor delayed AML progression and prolonged survival in AML-engrafted mice. In addition, AML-derived exosomes induced a broad downregulation of hematopoietic stem cell-supporting factors (for example, CXCL12, KITL and IGF1) in BM stromal cells and reduced their ability to support normal hematopoiesis. Altogether, this study uncovers novel features of AML pathogenesis and unveils how AML cells create a self-strengthening leukemic niche that promotes leukemic cell proliferation and survival, while suppressing normal hematopoiesis through exosome secretion.

Serum Osteocalcin and Testosterone Concentrations in Adult Males with or without Primary Osteoporosis: A Meta-Analysis

Osteocalcin (Ocn) and testosterone play important roles in male skeleton. However, the concentrations of serum osteocalcin and testosterone have never been systematically compared between populations with and without primary male osteoporosis, a common skeletal disorder in adult males. We searched the PubMed, Embase, and Cochrane Library for relevant studies. A meta-analysis was performed to compare the serum osteocalcin and testosterone concentrations between primary osteoporotic males and age-matched nonosteoporotic (non-OP) males. Five case-control studies with 300 adult males were included. We found no significant difference between cases and controls in serum total osteocalcin (TOcn) [95% confidence interval (CI): −1.25, 1.31; p = 0.96] and total testosterone (TT) concentrations [95% CI: −0.88, 4.22; p = 0.20]. The level of evidence of this carefully performed meta-analysis is 3a according to Oxford (UK) CEBM Levels of Evidence. Future well-designed studies with larger sample size and better standardization of Ocn assay are awaited to confirm and update our current findings.

Use of dual-energy computed tomography to measure skeletal-wide marrow composition and cancellous bone mineral density

Temporal and spatial variations in bone marrow adipose tissue (MAT) can be indicative of several pathologies and confound current methods of assessing immediate changes in bone mineral remodeling. We present a novel dual-energy computed tomography (DECT) method to monitor MAT and marrow-corrected volumetric BMD (mcvBMD) throughout the body. Twenty-three cancellous skeletal sites in 20 adult female cadavers aged 40-80 years old were measured using DECT (80 and 140 kVp). vBMD was simultaneous recorded using QCT. MAT was further sampled using MRI. Thirteen lumbar vertebrae were then excised from the MRI-imaged donors and examined by microCT. After MAT correction throughout the skeleton, significant differences (p < 0.05) were found between QCT-derived vBMD and DECT-derived mcvBMD results. McvBMD was highly heterogeneous with a maximum at the posterior skull and minimum in the proximal humerus (574 and 0.7 mg/cc, respectively). BV/TV and BMC have a nearly significant correlation with mcvBMD (r = 0.545, p = 0.057 and r = 0.539, p = 0.061, respectively). MAT assessed by DECT showed a significant correlation with MRI MAT results (r = 0.881, p < 0.0001). Both DECT- and MRI-derived MAT had a significant influence on uncorrected vBMD (r = -0.86 and r = -0.818, p ≤ 0.0001, respectively). Conversely, mcvBMD had no correlation with DECT- or MRI-derived MAT (r = 0.261 and r = 0.067). DECT can be used to assess MAT while simultaneously collecting mcvBMD values at each skeletal site. MAT is heterogeneous throughout the skeleton, highly variable, and should be accounted for in longitudinal mcvBMD studies. McvBMD accurately reflects the calcified tissue in cancellous bone.

Quantitative imaging methods in osteoporosis

Osteoporosis is characterized by a decreased bone mass and quality resulting in an increased fracture risk. Quantitative imaging methods are critical in the diagnosis and follow-up of treatment effects in osteoporosis. Prior radiographic vertebral fractures and bone mineral density (BMD) as a quantitative parameter derived from dual-energy X-ray absorptiometry (DXA) are among the strongest known predictors of future osteoporotic fractures. Therefore, current clinical decision making relies heavily on accurate assessment of these imaging features. Further, novel quantitative techniques are being developed to appraise additional characteristics of osteoporosis including three-dimensional bone architecture with quantitative computed tomography (QCT). Dedicated high-resolution (HR) CT equipment is available to enhance image quality. At the other end of the spectrum, by utilizing post-processing techniques such as the trabecular bone score (TBS) information on three-dimensional architecture can be derived from DXA images. Further developments in magnetic resonance imaging (MRI) seem promising to not only capture bone micro-architecture but also characterize processes at the molecular level. This review provides an overview of various quantitative imaging techniques based on different radiological modalities utilized in clinical osteoporosis care and research.

Age-related differences in the activity of arterial mineral deposition and regional bone metabolism: a 18F-sodium fluoride positron emission tomography study

Functional (18)F-fluoride PET demonstrated an inverse relationship between the activity of arterial mineral deposition and regional bone metabolism. While bone metabolism decreases with age, the activity of arterial mineral deposition increases.

INTRODUCTION

The extent of arterial calcification increases with age, whereas bone mineral density decreases, evidencing a well-known inverse correlation on morphological basis. The aim of this study was to evaluate the functional relationship between the activity of arterial mineral deposition and regional bone metabolism as assessed by (18)F-sodium fluoride (NaF) PET/CT.

METHODS

Three hundred four subjects were examined by (18)F-NaF PET/CT. Tracer accumulation in the femoral arteries was analyzed both qualitatively and semiquantitatively by measuring the blood-pool-corrected standardized uptake value (target-to-background ratio). Uptake was compared with cardiovascular risk factors (RFs), calcified plaque burden, and regional bone metabolism as assessed by PET/CT.

RESULTS

The activity of arterial mineral deposition significantly increased with age (p < 0.001), whereas regional bone metabolism significantly decreased (p < 0.001). There was a significant inverse correlation between bone metabolism and arterial mineral deposition (unadjusted, p < 0.001); that association was not significant (p = 0.79) when controlled for age and other RFs. Both high activity of arterial mineral deposition and low bone metabolism were significantly associated with cardiovascular events and other RFs.

CONCLUSION

(18)F-NaF PET/CT provides a tool to visualize and quantify the activity of arterial mineral deposition and regional bone metabolism. In this study, we observed an inverse correlation between the activity of arterial mineral deposition and regional bone metabolism. While the activity of arterial mineral deposition significantly increases with age, regional bone metabolism decreases.

(18)F-fluoride positron emission tomography measurements of regional bone formation in hemodialysis patients with suspected adynamic bone disease

(18)F-fluoride positron emission tomography ((18)F-PET) allows the assessment of regional bone formation and could have a role in the diagnosis of adynamic bone disease (ABD) in patients with chronic kidney disease (CKD). The purpose of this study was to examine bone formation at multiple sites of the skeleton in hemodialysis patients (CKD5D) and assess the correlation with bone biopsy. Seven CKD5D patients with suspected ABD and 12 osteoporotic postmenopausal women underwent an (18)F-PET scan, and bone plasma clearance, K i, was measured at ten skeletal regions of interest (ROI). Fifteen subjects had a transiliac bone biopsy following double tetracycline labeling. Two CKD5D patients had ABD confirmed by biopsy. There was significant heterogeneity in K i between skeletal sites, ranging from 0.008 at the forearm to 0.028 mL/min/mL at the spine in the CKD5D group. There were no significant differences in K i between the two study groups or between the two subjects with ABD and the other CKD5D subjects at any skeletal ROI. Five biopsies from the CKD5D patients had single tetracycline labels only, including the two with ABD. Using an imputed value of 0.3 μm/day for mineral apposition rate (MAR) for biopsies with single labels, no significant correlations were observed between lumbar spine K i corrected for BMAD (K i/BMAD) and bone formation rate (BFR/BS), or MAR. When biopsies with single labels were excluded, a significant correlation was observed between K i/BMAD and MAR (r = 0.81, p = 0.008) but not BFR/BS. Further studies are required to establish the sensitivity of (18)F-PET as a diagnostic tool for identifying CKD patients with ABD.

What can we learn about valvular heart disease from PET/CT?

Valvular heart disease is a major cause of morbidity and mortality, and with an aging population, its prevalence is increasing. Here, we review the evolving use of positron emission tomography/computed tomography in valvular heart disease, with particular focus on calcific aortic stenosis and infective endocarditis. In principle, the activity of any pathological process can be studied, as long as an appropriate radiotracer can be developed. We will review some of the early data using established tracers in the above and other conditions, providing discussion as to the future research and clinical roles of these techniques. Furthermore, we will discuss the potential impact of novel tracers that are currently under development or testing in preclinical models. It is hoped that such advanced imaging might improve the diagnosis, treatment and outlook for patients with valvular heart disease.

¹⁸F-fluoride PET as a noninvasive imaging biomarker for determining treatment efficacy of bone active agents at the hip: a prospective, randomized, controlled clinical study

The functional imaging technique of ¹⁸F-fluoride positron emission tomography (¹⁸F-PET) allows the noninvasive quantitative assessment of regional bone formation at any skeletal site, including the spine and hip. The aim of this study was to determine if ¹⁸F-PET can be used as an early biomarker of treatment efficacy at the hip. Twenty-seven treatment-naive postmenopausal women with osteopenia were randomized to receive teriparatide and calcium and vitamin D (TPT group, n = 13) or calcium and vitamin D only (control group, n = 14). Subjects in the TPT group were treated with 20 µg/day teriparatide for 12 weeks. ¹⁸F-PET scans of the proximal femur, pelvis, and lumbar spine were performed at baseline and 12 weeks. The plasma clearance of ¹⁸F-fluoride to bone, K(i), a validated measurement of bone formation, was measured at four regions of the hip, lumbar spine, and pelvis. A significant increase in K(i) was observed at all regions of interest (ROIs), including the total hip (+27%, p = 0.002), femoral neck (+25%, p = 0.040), hip trabecular ROI (+21%, p = 0.017), and hip cortical ROI (+51%, p = 0.001) in the TPT group. Significant increases in K(i) in response to TPT were also observed at the lumbar spine (+18%, p = 0.001) and pelvis (+42%, p = 0.001). No significant changes in K(i) were observed for the control group. Changes in BMD and bone turnover markers were consistent with previous trials of teriparatide. In conclusion, this is the first study to our knowledge to demonstrate that ¹⁸F-PET can be used as an imaging biomarker for determining treatment efficacy at the hip as early as 12 weeks after initiation of therapy.

Imaging technologies for assessment of skeletal health in men

Conventional radiography can detect most fractures, evaluate their healing, and visualize characteristic skeletal abnormalities for some metabolic bone diseases. Dual-energy X-ray absorptiometry (DXA) is used to measure areal bone mineral density (BMD) in order to diagnose osteoporosis, estimate fracture risk, and monitor changes in BMD over time. Vertebral fracture assessment by DXA can diagnose vertebral fractures with less ionizing radiation, greater patient convenience, and lower cost than conventional radiography. Quantitative computed tomography (QCT) measures volumetric BMD separately in cortical and trabecular bone compartments. High resolution peripheral QCT and high resolution magnetic resonance imaging are noninvasive research tools that assess the microarchitecture of bone. The use of these technologies and others has been associated with special challenges in men compared with women, provided insights into differences in the pathogenesis of osteoporosis in men and women, and enhanced understanding of the mechanisms of action of osteoporosis treatments.

Regional bone metabolism at the lumbar spine and hip following discontinuation of alendronate and risedronate treatment in postmenopausal women

The aim of this study was to examine the effects of bisphosphonate discontinuation on bone metabolism at the spine and hip measured using (18) F-fluoride PET. Bone metabolism at the spine remained stable following discontinuation of alendronate and risedronate at 1 year but increased in the hip in the alendronate group only.

INTRODUCTION

Bisphosphonates such as alendronate (ALN) or risedronate (RIS) have persistent effects on spine BMD following discontinuation.

METHODS

Positron emission tomography (PET) was used to examine regional bone metabolism in 20 postmenopausal women treated with ALN (n = 11) or RIS (n = 9) for a minimum of 3 years at screening (range 3-9 years, mean 5 years for both groups). Subjects underwent a dynamic scan of the lumbar spine and a static scan of both hips at baseline and 6 and 12 months following treatment discontinuation. (18) F-fluoride plasma clearance (K(i)) at the spine was calculated using a three-compartment model. Standardised uptake values (SUV) were calculated for the spine, total hip, femoral neck and femoral shaft. Measurements of BMD and biochemical markers of bone turnover were also performed.

RESULTS

With the exception of a significant decrease in spine BMD in the ALN group, BMD remained stable. Bone turnover markers increased significantly from baseline by 12 months for both study groups. Measurements of K(i) and SUV at the spine and femoral neck did not change significantly in either group. SUV at the femoral shaft and total hip increased significantly but in the ALN group only, increasing by 33.8% (p = 0.028) and 24.0% (p = 0.013), respectively.

CONCLUSIONS

Bone metabolism at the spine remained suppressed following treatment discontinuation. A significant increase in SUV at the femoral shaft and total hip after 12 months was observed but for the ALN group only. This study was small, and further clinical studies are required to fully evaluate the persistence of BP treatment.

Can PET-CT imaging and radiokinetic analyses provide useful clinical information on atypical femoral shaft fracture in osteoporotic patients?

Atypical femoral shaft fractures are associated with the extended usage of nitrogen-containing bisphosphonates as therapy for osteoporosis. For such fractures, the positron emission tomography (PET) procedure, coupled with computerized tomography (CT), provides a potential imaging modality for defining aspects of the pathogenesis, site specificity, and possible prodromal abnormalities prior to fracture. PET-CT may assess the radiokinetic variables K1 (a putative marker for skeletal blood flow) and Ki (a putative marker for skeletal bone formation), and when combined with PET imaging modalities and CT skeletal site localization, may define the site of such radiokinetic findings. Further studies into the clinical usage of PET-CT in patients with atypical femoral shaft fractures are warranted.

Kinetic analysis of 18F-fluoride PET images of breast cancer bone metastases

The most common site of metastasis for breast cancer is bone. Quantitative (18)F-fluoride PET can estimate the kinetics of fluoride incorporation into bone as a measure of fluoride transport, bone formation, and turnover. The purpose of this analysis was to evaluate the accuracy and precision of (18)F-fluoride model parameter estimates for characterizing regional kinetics in metastases and normal bone in breast cancer patients.

METHODS

Twenty metastatic breast cancer patients underwent dynamic (18)F-fluoride PET. Mean activity concentrations were measured from serial blood samples and regions of interest placed over bone metastases, normal vertebrae, and cardiac blood pools. This study examined parameter identifiability, model sensitivity, error, and accuracy using parametric values from the patient cohort.

RESULTS

Representative time-activity curves and model parameter ranges were obtained from the patient cohort. Model behavior analyses of these data indicated (18)F-fluoride transport and flux (K(1) and Ki, respectively) into metastatic and normal osseous tissue could be independently estimated with a reasonable bias of 9% or less and reasonable precision (coefficients of variation <or= 16%). Average (18)F-fluoride transport and flux into metastases from 20 patients (K(1) = 0.17 +/- 0.08 mL x cm(-3) x min(-1) and Ki = 0.10 +/- 0.05 mL x cm(-3) x min(-1)) were both significantly higher than for normal bone (K(1) = 0.09 +/- 0.03 mL x cm(-3) x min(-1) and Ki = 0.05 +/- 0.02 mL x cm(-3) x min(-1), P < 0.001).

CONCLUSION

Fluoride transport and flux can be accurately and independently estimated for bone metastases and normal vertebrae. Reasonable bias and precision for estimates of K(1) and Ki from simulations and significant differences in values from patient modeling results in metastases and normal bone suggest that (18)F-fluoride PET images may be useful for assessing changes in bone turnover in response to therapy. Future studies will examine the correlation of parameters to biologic features of bone metastases and to response to therapy.

Differences in regional bone perfusion and turnover between lumbar spine and distal humerus: (18)F-fluoride PET study of treatment-naïve and treated postmenopausal women

The functional imaging technique of (18)F-fluoride positron emission tomography ((18)F-PET) allows the non-invasive assessment of regional bone blood perfusion and turnover. Bone perfusion and turnover measured using (18)F-PET correlate closely with those obtained experimentally and so they can be readily applied in clinical research studies. The aim of this study was to compare bone perfusion and turnover between the lumbar spine and humerus in both treatment naïve postmenopausal women (n=11) and those on stable antiresorptive therapy (n=12). All women had a BMD T-score of less than -2 at the spine and/or hip. Each woman had a dynamic PET scan of the lumbar spine and distal humerus after injection of 90 MBq (18)F-fluoride. Using a three-compartmental model bone perfusion (K(1)), the net plasma clearance of tracer to bone mineral (K(i)) reflecting regional bone turnover and the rate constants k(2)-k(4) describing the transport of fluoride between plasma, an extravascular bone compartment and bone mineral compartment were calculated. Mean bone perfusion (K(1)) and bone turnover (K(i)) were significantly higher at the lumbar spine compared to the humerus for both treatment-naïve and antiresorptive groups. K(1) values were on average 3 times greater while K(i) was approximately 50% greater at the lumbar spine. The rate constant k(2), the reverse transport of fluoride from the extravascular compartment to plasma, was significantly lower at the humerus compared to the lumbar spine in both groups. The ratio K(i)/K(1) describing the unidirectional extraction efficiency to bone mineral was significantly greater at the humerus compared to the lumbar spine for both study groups. No significant differences between skeletal sites were observed for k(3) or k(4). In conclusion a significant skeletal heterogeneity was observed in terms of bone perfusion and turnover between the lumbar spine and humerus. (18)F-PET may aid in our understanding of the importance of bone perfusion in osteoporosis and differences in regional bone turnover with disease and in response to therapy.

Long-term precision of 18F-fluoride PET skeletal kinetic studies in the assessment of bone metabolism

(18)F-Fluoride PET allows noninvasive evaluation of regional bone metabolism and has the potential to become a useful tool for assessing patients with metabolic bone disease and evaluating novel drugs being developed for these diseases. The main PET parameter of interest, termed K(i), reflects regional bone metabolism. The aim of this study was to compare the long-term precision of (18)F-fluoride PET with that of biochemical markers of bone turnover assessed over 6 mo.

METHODS

Sixteen postmenopausal women with osteoporosis or significant osteopenia and a mean age of 64 y underwent (18)F-fluoride PET of the lumbar spine and measurements of biochemical markers of bone formation (bone-specific alkaline phosphatase and osteocalcin) and bone resorption (urinary deoxypyridinoline) at baseline and 6 mo later. Four different methods for analyzing the (18)F-fluoride PET data were compared: a 4k 3-compartmental model using nonlinear regression analysis (K(i-4k)), a 3k 3-compartmental model using nonlinear regression analysis (K(i-3k)), Patlak analysis (K(i-PAT)), and standardized uptake values.

RESULTS

With the exception of a small but significant decrease in K(i-3k) at 6 mo, there were no significant differences between the baseline and 6-mo values for the PET parameters or biochemical markers. The long-term precision, expressed as the coefficient of variation (with 95% confidence interval in parentheses), was 12.2% (9%-19%), 13.8% (10%-22%), 14.4% (11%-22%), and 26.6% (19%-40%) for K(i-3k), K(i-PAT), mean standardized uptake value, and K(i-4k), respectively. For comparison, the precision of the biochemical markers was 10% (7%-15%), 18% (13%-27%), and 14% (10%-21%) for bone-specific alkaline phosphatase, osteocalcin, and urinary deoxypyridinoline, respectively. Intraclass correlation between the baseline and 6-mo values ranged from 0.44 for K(i-4k) to 0.85 for K(i-3k). No significant correlation was found between the repeated mean standardized uptake value measurements.

CONCLUSION

The precision and intraclass correlation observed for K(i-3k) and K(i-PAT) was equivalent to that observed for biochemical markers. This study provided initial data on the long-term precision of (18)F-fluoride PET measured at the lumbar spine, which will aid in the accurate interpretation of changes in regional bone metabolism in response to treatment.