Dynamic Bone Imaging with 99mTc-Labeled Diphosphonates and 18F-NaF: Mechanisms and Applications

Assessing osteoporosis and bone mineral density through 18F-NaF uptake at lumbar spine

OBJECTIVES

The use of 18F-Sodium fluoride (NaF) PET/CT is established in the detection of metastatic bone disease, yet its utility in osteoporosis remains underexplored. This research aims to assess the variations in 18F-NaF uptake among individuals with differing bone mineral density (BMD) and to examine the relationship between 18F-NaF uptake and BMD.

METHODS

In this retrospective study, 199 patients (average age 56 ± 6, comprising 52 males and 147 females) with a history of cancer were analyzed. Each participant underwent both 18F-NaF PET/CT and lumbar dual-energy X-ray absorptiometry (DXA) scans within a span of 7 days. Based on DXA outcomes, patients and their lumbar vertebrae were categorized into normal BMD, osteopenia, and osteoporosis groups. The lumbar 18F-NaF uptake across these groups were compared, and to explore the association between lumbar standardized uptake values (SUV) values and BMD. The efficacy of 18F-NaF uptake in diagnosing osteoporosis or osteopenia was also evaluated. Analysis was conducted using Mann-Whitney U tests, Spearman regression, and receiver operating characteristic (ROC) curve analysis through GraphPad Prism 10.0.

RESULTS

A total of 796 lumbar vertebrae from 199 patients were measured. It was observed that osteoporotic patients had significantly lower 18F-NaF uptake than those with osteopenia and normal BMD across the L1-L4 lumbar vertebrae (P < 0.0001). In a vertebra-based analysis, normal BMD vertebrae exhibited the highest maximum SUV(SUVmax) compared to osteopenic (8.13 ± 1.28 vs. 6.61 ± 1.01, P < 0.0001) and osteoporotic vertebrae (8.13 ± 1.28 vs. 4.82 ± 1.01, P < 0.0001). There was a positive correlation between lumbar 18F-NaF uptake and BMD across all vertebrae, with correlation coefficients exceeding 0.5 (range: 0.57-0.8). The area under the ROC curve values were notably high, at 0.96 for osteoporosis and 0.83 for osteopenia diagnosis.

CONCLUSION

This study demonstrates distinct 18F-NaF uptake patterns among individuals with varying BMD levels, with a positive correlation between 18F-NaF uptake and BMD. These findings highlight the potential of 18F-NaF PET/CT as a supportive diagnostic method in the management of osteoporosis.

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.

Keeping Up With ChatGPT: Evaluating Its Recognition and Interpretation of Nuclear Medicine Images

PURPOSE

The latest iteration of GPT4 (generative pretrained transformer) is a large multimodal model that can integrate both text and image input, but its performance with medical images has not been systematically evaluated. We studied whether ChatGPT with GPT-4V(ision) can recognize images from common nuclear medicine examinations and interpret them.

PATIENTS AND METHODS

Fifteen representative images (scintigraphy, 11; PET, 4) were submitted to ChatGPT with GPT-4V(ision), both in its Default and "Advanced Data Analysis (beta)" version. ChatGPT was asked to name the type of examination and tracer, explain the findings and whether there are abnormalities. ChatGPT should also mark anatomical structures or pathological findings. The appropriateness of the responses was rated by 3 nuclear medicine physicians.

RESULTS

The Default version identified the examination and the tracer correctly in the majority of the 15 cases (60% or 53%) and gave an "appropriate" description of the findings or abnormalities in 47% or 33% of cases, respectively. The Default version cannot manipulate images. "Advanced Data Analysis (beta)" failed in all tasks in >90% of cases. A "major" or "incompatible" inconsistency between 3 trials of the same prompt was observed in 73% (Default version) or 87% of cases ("Advanced Data Analysis (beta)" version).

CONCLUSIONS

Although GPT-4V(ision) demonstrates preliminary capabilities in analyzing nuclear medicine images, it exhibits significant limitations, particularly in its reliability (ie, correctness, predictability, and consistency).

Opportunistic screening with multiphase contrast-enhanced dual-layer spectral CT for osteoblastic lesions in prostate cancer compared with bone scintigraphy

Our study aimed to compare bone scintigraphy and dual-layer detector spectral CT (DLCT) with multiphase contrast enhancement for the diagnosis of osteoblastic bone lesions in patients with prostate cancer. The patients with prostate cancer and osteoblastic bone lesions detected on DLCT were divided into positive bone scintigraphy group (pBS) and negative bone scintigraphy group (nBS) based on bone scintigraphy. A total of 106 patients (57 nBS and 49 pBS) was included. The parameters of each lesion were measured from DLCT including Hounsfield unit (HU), 40-140 keV monochromatic HU, effective nuclear numbers (Zeff), and Iodine no water (InW) value in non-contrast phase (N), the arterial phase (A), and venous phase (V). The slope of the spectral curve at 40 and 100 keV, the different values of the parameters between A and N phase (A-N), V and N phase (V-N), and hybrid prediction model with multiparameters were used to differentiate pBS from nBS. Receiver operating characteristic analysis was performed to compare the area under the curve (AUC) for differentiating the pBS group from the nBS group. The value of conventional HU values, slope, and InW in A-N and V-N, and hybrid model were significantly higher in the pBS group than in the nBS group. The hybrid model of all significant parameters had the highest AUC of 0.988, with 95.5% sensitivity and 94.6% specificity. DLCT with arterial contrast enhancement phase has the potential to serve as an opportunistic screening tool for detecting positive osteoblastic bone lesions, corresponding to those identified in bone scintigraphy.

SPECT/CT and PET/CT for the Evaluation of Persistent or Recurrent Pain After Spine Surgery: A Systematic Review and Case Series

OBJECTIVE

The differential diagnosis for postoperative back pain is broad, and conventional imaging modalities are not always conclusive. Therefore, we performed a systematic review of the literature and present case studies describing the use of single-photon emission CT (SPECT)/CT or positron emission tomography (PET)/CT in the diagnosis of back pain following spine surgery.

METHODS

A systematic review was conducted according to PRISMA guidelines across 5 databases. Relevant keywords included PET/CT, bone SPECT/CT, and pseudarthrosis. The studies were assessed for diagnostic accuracy of the imaging technologies.

RESULTS

A total of 2,444 studies were screened, 91 were selected for full-text review, and 21 were ultimately included. Six retrospective studies investigated the use of SPECT/CT with a total sample size of 309 patients. Two of these studies used SPECT/CT to predict screw loosening in over 50% of patients. Eight studies examined the use of 18-fluoride sodium fluoride (18F-NaF) PET/CT. Among these studies, measures of diagnostic accuracy varied but overall demonstrated the ability of 18F-NaF PET/CT to detect screw loosening and pseudarthrosis. Seven studies examined 18F-fluorodeoxyglucose (FDG) PET/CT and supported its utility in the diagnosis of postoperative infections in the spine.

CONCLUSIONS

PET/CT and SPECT/CT are useful in the evaluation of postoperative pain of the spine, especially in patients for whom conventional imaging modalities yield inconclusive results. More diagnostic accuracy studies with strong reference standards are needed to compare hybrid imaging to conventional imaging.

Nuclear medicine imaging for bone metastases assessment: what else besides bone scintigraphy in the era of personalized medicine?

Accurate detection and reliable assessment of therapeutic responses in bone metastases are imperative for guiding treatment decisions, preserving quality of life, and ultimately enhancing overall survival. Nuclear imaging has historically played a pivotal role in this realm, offering a diverse range of radiotracers and imaging modalities. While the conventional bone scan using 99mTc marked bisphosphonates has remained widely utilized, its diagnostic performance is hindered by certain limitations. Positron emission tomography, particularly when coupled with computed tomography, provides improved spatial resolution and diagnostic performance with various pathology-specific radiotracers. This review aims to evaluate the performance of different nuclear imaging modalities in clinical practice for detecting and monitoring the therapeutic responses in bone metastases of diverse origins, addressing their limitations and implications for image interpretation.

Extraosseous distribution of 99mTc-diphosphonates during bone scintigraphy: review of the literature with case series presentation

PURPOSE

Technetium-99m (99mTc)-diphosphonates represent the most common radiopharmaceutical used for bone scintigraphy. Even if the uptake in bone tissue has been widely explored, atypical uptake could be seen in soft tissue malignancies during bone scintigraphy. Increased vascularization and endothelium permeability represent front-row players in the biodistribution of the tracer, albeit other causes have been identified such as trauma, necrosis, the presence of calcification in metastasis, the pH of the tissue and consequently the type of ion concentration.

CONCLUSION

The aim of this paper is to summarize the state of art of atypical soft tissue uptake seen in cancer tissues. The research was conducted on PubMed. The analysis of the literature suggests that calcium metabolism and ionic saturation have a pivotal role in the biodistribution of bone tracers. This phenomenon ranks in a complex scenario that includes carcinogenesis and cancer environment aspects. We also report two cases in our Institution in which atypical uptake in cancer tissues was observed.

Platelet-Rich Fibrin-Enhanced Bone Healing Co-grafted With Either Hydroxyapatite and Beta Tricalcium Phosphate or Demineralized Freeze-Dried Bone in Small Maxillofacial Osseous Defects: A Clinical Comparison

INTRODUCTION

This study was conducted to clinically compare a commercially available combination of 70:30 nanocrystalline hydroxyapatite (HA) and beta tricalcium phosphate (βTCP) along with platelet-rich fibrin (PRF) with demineralized freeze-dried bone (DFDB) grafts along with PRF in small maxillofacial osseous defects.

MATERIALS AND METHODS

Thirty patients with one osseous defect were randomly distributed into two groups of 15 each: Group A and Group B. Group A patients received HA+βTCP+PRF while Group B received DFDB + PRF. Postoperative pain, swelling, wound dehiscence, and the presence or absence of infection were evaluated at various intervals up to seven postop days and compared between the two groups and within either group. A technetium 99m methylene diphosphonate (MDP 99mTc) scan was also done for a representative patient of either group at the end of three months to evaluate the fate of the graft.

RESULTS

We found no significant difference between the two groups for any of our parameters. Significant improvements were noted for pain and swelling within either group at various intervals. The MDP 99mTc scan showed increased tracer uptake for the representing patient of either group.

CONCLUSIONS

HA+βTCP is more inexpensive than DFDB and more readily available and has no host incompatibility or infection potential, resulting in similar clinical postoperative states as DFDB when either is used with PRF.

Imaging in metastatic breast cancer, CT, PET/CT, MRI, WB-DWI, CCA: review and new perspectives

BACKGROUND

Breast cancer is the most frequent cancer in women and remains the second leading cause of death in Western countries. It represents a heterogeneous group of diseases with diverse tumoral behaviour, treatment responsiveness and prognosis. While major progress in diagnosis and treatment has resulted in a decline in breast cancer-related mortality, some patients will relapse and prognosis in this cohort of patients remains poor. Treatment is determined according to tumor subtype; primarily hormone receptor status and HER2 expression. Menopausal status and site of disease relapse are also important considerations in treatment protocols.

MAIN BODY

Staging and repeated evaluation of patients with metastatic breast cancer are central to the accurate assessment of disease extent at diagnosis and during treatment; guiding ongoing clinical management. Advances have been made in the diagnostic and therapeutic fields, particularly with new targeted therapies. In parallel, oncological imaging has evolved exponentially with the development of functional and anatomical imaging techniques. Consistent, reproducible and validated methods of assessing response to therapy is critical in effectively managing patients with metastatic breast cancer.

CONCLUSION

Major progress has been made in oncological imaging over the last few decades. Accurate disease assessment at diagnosis and during treatment is important in the management of metastatic breast cancer. CT (and BS if appropriate) is generally widely available, relatively cheap and sufficient in many cases. However, several additional imaging modalities are emerging and can be used as adjuncts, particularly in pregnancy or other diagnostically challenging cases. Nevertheless, no single imaging technique is without limitation. The authors have evaluated the vast array of imaging techniques - individual, combined parametric and multimodal - that are available or that are emerging in the management of metastatic breast cancer. This includes WB DW-MRI, CCA, novel PET breast cancer-epitope specific radiotracers and radiogenomics.

99mTc-HDP Labeling-A Non-Destructive Method for Real-Time Surveillance of the Osteogenic Differentiation Potential of hMSC during Ongoing Cell Cultures

99-Metastabil Technetium (^99mTc) is a radiopharmaceutical widely used in skeletal scintigraphy. Recent publications show it can also be used to determine the osteogenic potential of human mesenchymal stem cells (hMSCs) by binding to hydroxyapatite formed during bone tissue engineering. This field lacks non-destructive methods to track live osteogenic differentiation of hMSCs. However, no data about the uptake kinetics of ^99mTc and its effect on osteogenesis of hMSCs have been published yet. We therefore evaluated the saturation time of ^99mTc by incubating hMSC cultures for different periods, and the saturation concentration by using different amounts of ^99mTc activity for incubation. The influence of ^99mTc on osteogenic potential of hMSCs was then evaluated by labeling a continuous hMSC culture three times over the course of 3 weeks, and comparing the findings to cultures labeled once. Our findings show that ^99mTc saturation time is less than 0.25 h, and saturation concentration is between 750 and 1000 MBq. Repeated exposure to γ-radiation emitted by ^99mTc had no negative effects on hMSC cultures. These new insights can be used to make this highly promising method broadly available to support researchers in the field of bone tissue engineering using this method to track and evaluate, in real-time, the osteogenic differentiation of hMSC, without any negative influence on the cell viability, or their osteogenic differentiation potential.

Quantitative [99mTc]Tc-MDP SPECT/CT correlated with [18F]NaF PET/CT for bone metastases in patients with prostate cancer

BACKGROUND

The purpose of the present study was to elucidate the correlation between standardized uptake value (SUV) and volume-based parameters measured by quantitative [^99mTc]Tc-methylene diphosphonate (MDP) single photon emission computed tomography (SPECT)/CT and [¹⁸F]-sodium fluoride ([¹⁸F]NaF) positron emission tomography (PET)/CT in the assessment of bone metastases in patients with prostate cancer.

METHODS

The study included 26 male prostate cancer patients with confirmed or suspected bone metastases who underwent both [^99mTc]Tc-MDP SPECT/CT and [¹⁸F]NaF PET/CT studies. Skeletal lesions visible on both SPECT/CT and PET/CT were classified as benign or metastases. The maximum SUV (SUVmax), peak SUV (SUVpeak), mean SUV (SUVmean), metabolic bone volume (MBV), and total bone uptake (TBU) were calculated for every lesion showing abnormal uptake.

RESULTS

A total of 202 skeletal lesions (147 benign and 55 metastases) were detected in the 26 patients. Strong significant correlations were noted between SPECT/CT and PET/CT for the SUV- and volume-based parameters (all P < 0.001). The SUVmax, SUVpeak, SUVmean, and TBU values obtained with SPECT/CT were significantly lower than the corresponding values obtained with PET/CT (all P < 0.001). The MBV in SPECT/CT was significantly higher than that in PET/CT (P < 0.001). All SUV- and volume-based parameters obtained with both SPECT/CT and PET/CT for metastatic lesions were significantly higher than the corresponding parameters for benign lesions (P values from 0.036 to < 0.001).

CONCLUSIONS

These preliminary results demonstrate that the SUV- and volume-based parameters for bone uptake obtained with quantitative SPECT/CT and PET/CT are strongly correlated in patients with prostate cancer. The SUV parameters obtained with SPECT/CT were significantly lower than those obtained with PET/CT, whereas the uptake volume obtained with SPECT/CT was significantly higher than that obtained with PET/CT.

Synthesis and evaluation of a multifunctional probe with a high affinity for prostate-specific membrane antigen (PSMA) and bone

Prostate cancer frequently metastasizes to the bone. Because patients with bone metastases suffer from skeletal-related events, the diagnosis and treatment of bone metastases in the early stage are important. In this study, to improve the sensitivity of detecting bone metastases in patients with prostate cancer, we designed, synthesized, and evaluated a multifunctional radiotracer, [⁶⁷Ga]Ga-D₁₁-PSMA-617 ([⁶⁷Ga]3), with an undeca-aspartic acid as a bone-seeking moiety between [⁶⁷Ga]Ga-DOTA and a prostate-specific membrane antigen (PSMA) ligand based on the lysine-urea-glutamate motif. [⁶⁷Ga]3 showed a high affinity for hydroxyapatite and high uptake in PSMA-positive LNCaP cells. Moreover, in biodistribution experiments using tumor-bearing mice, [⁶⁷Ga]3 exhibited high accumulation in the bone and PSMA-positive tumor although the accumulation of [⁶⁷Ga]3 in the PSMA-positive tumor was lower than that of [⁶⁷Ga]Ga-PSMA-617. This study provides valuable information for developing radiotheranostic probes combining multiple carriers with different mechanisms.

99mTc-polyphosphonate labelling - Enhancement of a novel method for the quantification of osteogenic differentiation of MSCs in vitro

Bone tissue engineering is a fast-growing field in regenerative medicine. Consequently, there is a high demand for new, fast and reliable methods to track and quantify the osteogenic differentiation of cells. Recently, a novel method was published to non-destructively quantify the hydroxyapatite content of monolayer and 3-dimensional mesenchymal stem cell cultures using the ability of ^99mTechnetium-methylene diphosphonate (MDP), a well-established tracer in clinical nuclear medicine, to bind to newly synthesized hydroxyapatite. In the present study, two other commonly used ^99mTechnetium tracers, 2,3-dicarboxypropane-1,1-diphosphonate (DPD) and hydroxydiphosphonate (HDP), were evaluated to see if they could also be used for the same purpose. Furthermore, we investigated if labelling at various timepoints influenced the effectiveness of the labelling. The results were analysed using one-factor ANOVA followed by Bonferroni post-hoc testing. This revealed a highly significant difference between the three osteogenic groups at each timepoint compared to their corresponding negative controls. However, there was no statistically significant difference between the three different tracers (MDP, DPD, HDP) in the osteogenic groups. Therefore all three tracers are of similar value when quantifying the extracellular hydroxylapatite content in osteogenic stem cells cultures.

[Update on non-unions 2022 : Imaging diagnostics, classification and treatment algorithms]

BACKGROUND

Fracture healing is a complex regenerative process. An unconsolidated fracture that will not heal without further surgical intervention is called non-union. The causes are multifactorial. Diagnostic imaging is a central pillar and provides insights into the morphology and biology of the fracture as a basis for optimal surgical treatment decisions.

AIM

Knowledge of fracture healing, targeted radiological and nuclear medical diagnostics, and interdisciplinary standardized classification are of high importance for optimal treatment.

METHODS

In this article, the proven and modern diagnostic procedures are presented, an overview of the currently used scoring and classification models is given and the optimal therapeutic approach based on the extended "diamond concept" is addressed. A possible diagnostic and therapeutic approach is shown using an algorithm.

CONCLUSION

For successful treatment of pseudarthrosis, targeted radiological and nuclear medical diagnostics with old established but also newest methods, such as dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and hybrid imaging, are necessary. An exact classification of non-unions using additional classification models makes it possible to determine and carry out the optimal surgical treatment at an early stage.

Reliability of Alkaline Phosphatase for Differentiating Flare Phenomenon from Disease Progression with Bone Scintigraphy

Simple Summary

Bone scintigraphy is the most widely used radionuclide technique to investigate bone metastasis, primarily due to its reasonable time and cost factor. However, it is important to recognize that bone scintigraphy to assess treatment response sometimes shows a “flare phenomenon”, which can be misinterpreted as disease progression. Distinction between flare phenomenon and disease progression could help in the decision to continue effective treatments in patients with flare phenomenon and to cease ineffective treatments and consider other salvage treatment plans in patients with disease progression. Despite many methods having been tried to answer this question, there was still no reliable way to differentiate between flare phenomenon and progression of bone metastases. Our results suggest that ALP is a useful serologic marker to differentiate flare phenomenon from disease progression on bone scintigraphy in breast or prostate cancer patients with bone metastasis.

Abstract

The flare phenomenon (FP) on bone scintigraphy after the initiation of systemic treatment seriously complicates evaluations of therapeutic response in patients with bone metastases. The aim of this study was to evaluate whether serum alkaline phosphatase (ALP) can differentiate FP from disease progression on bone scintigraphy in these patients. Breast or prostate cancer patients with bone metastases who newly underwent systemic therapy were reviewed. Pretreatment baseline and follow-up data, including age, pathologic factors, type of systemic therapy, radiologic and bone scintigraphy findings, and ALP levels, were obtained. Univariate and multivariate analyses of these factors were performed to predict FP. An increased extent and/or new lesions were found in 160 patients on follow-up bone scintigraphy after therapy. Among the 160 patients, 80 (50%) had an improvement on subsequent bone scintigraphy (BS), while subsequent scintigraphy also showed an increased uptake in 80 (50%, progression). Multiple regression analysis revealed that stable or decreased ALP was an independent predictor for FP (p < 0.0001). ALP was an independent predictor for FP on subgroup analysis for breast and prostate cancer (p = 0.001 and p = 0.0223, respectively). Results of the study suggest that ALP is a useful serologic marker to differentiate FP from disease progression on bone scintigraphy in patients with bone metastasis. Clinical interpretation for scintigraphic aggravation can be further improved by the ALP data and it may prevent fruitless changes of therapeutic modality by misdiagnosis of disease progression in cases of FP.

Review of imaging techniques for evaluating morphological and functional responses to the treatment of bone metastases in prostate and breast cancer

Bone metastases are very common complications associated with certain types of cancers that frequently negatively impact the quality of life and functional status of patients; thus, early detection is necessary for the implementation of immediate therapeutic measures to reduce the risk of skeletal complications and improve survival and quality of life. There is no consensus or universal standard approach for the detection of bone metastases in cancer patients based on imaging. Endorsed by the Spanish Society of Medical Oncology (SEOM), the Spanish Society of Medical Radiology (SERAM), and the Spanish Society of Nuclear Medicine and Molecular Imaging (SEMNIM) a group of experts met to discuss and provide an up-to-date review of our current understanding of the biological mechanisms through which tumors spread to the bone and describe the imaging methods available to diagnose bone metastasis and monitor their response to oncological treatment, focusing on patients with breast and prostate cancer. According to current available data, the use of next-generation imaging techniques, including whole-body diffusion-weighted MRI, PET/CT, and PET/MRI with novel radiopharmaceuticals, is recommended instead of the classical combination of CT and bone scan in detection, staging and response assessment of bone metastases from prostate and breast cancer.Clinical trial registration: Not applicable.

Multiplexed Molecular Imaging Strategy Integrated with RNA Sequencing in the Assessment of the Therapeutic Effect of Wharton's Jelly Mesenchymal Stem Cell-Derived Extracellular Vesicles for Osteoporosis

Introduction

Osteoporosis is a result of an imbalance in bone remodeling. Mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) have been considered as a potentially promising treatment for osteoporosis. However, the therapeutic effect, genetic alterations, and in vivo behavior of exogenous EVs for osteoporosis in mice models remain poorly understood.

Methods

A multiplexed molecular imaging strategy was constructed by micro-positron emission tomography (µPET)/computed tomography (CT), µCT, and optical imaging modality which reflected the osteoblastic activity, microstructure, and in vivo behavior of EVs, respectively. RNA sequencing was used to analyze the cargo of EVs, and the bone tissues of ovariectomized (OVX) mice post EV treatment.

Results

The result of [¹⁸F]NaF µPET showed an increase in osteoblastic activity in the distal femur of EV-treated mice, and the bone structural parameters derived from µCT were also improved. In terms of in vivo behavior of exogenous EVs, fluorescent dye-labeled EVs could target the distal femur of mice, whereas the uptakes of bone tissues were not significantly different between OVX mice and healthy mice. RNA sequencing demonstrated upregulation of ECM-related genes, which might associate with the PI3K/AKT signaling pathway, in line with the results of microRNA analysis showing that mir-21, mir-29, mir-221, and let-7a were enriched in Wharton’s jelly-MSC-EVs and correlated to the BMP and PI3K/AKT signaling pathways.

Conclusion

The therapeutic effect of exogenous WJ-MSC-EVs in the treatment of osteoporosis was successfully assessed by a multiplexed molecular imaging strategy. The RNA sequencing demonstrated the possible molecular targets in the regulation of bone remodeling. The results highlight the novelty of diagnostic and therapeutic strategies of EV-based treatment for osteoporosis.

SPECT/CT in the Evaluation of Suspected Skeletal Pathology

Dedicated multi-slice single-photon emission computed tomography/computed tomography (SPECT/CT) cameras have become widely available and are becoming a mainstay of clinical practice. The integration of SPECT and CT allow for precise anatomic location of scintigraphic findings. Fusion imaging with SPECT/CT can improve both sensitivity and specificity by reducing equivocal interpretation in comparison to planar scintigraphy or SPECT alone. This review article addresses the technique, basic science principles, and applications of integrated SPECT/CT in the evaluation of musculoskeletal pathology.

Biomaterials for Orthopaedic Diagnostics and Theranostics

Despite widespread use of conventional diagnostic methods in orthopaedic applications, limitations still exist in detection and diagnosing many pathologies especially at early stages when intervention is most critical. The use of biomaterials to develop diagnostics and theranostics, including nanoparticles and scaffolds for systemic or local applications, has significant promise to address these shortcomings and enable successful clinical translation. These developments in both modular and holistic design of diagnostic and theranostic biomaterials may improve patient treatments for myriad orthopaedic applications ranging from cancer to fractures to infection.

Quantitative bone single-photon emission CT/CT parameters reflect pain and functional status of symptomatic basal joint arthritis of the thumb

AIMS

The aim of this study was to assess arthritis of the basal joint of the thumb quantitatively using bone single-photon emission CT/CT (SPECT/CT) and evaluate its relationship with patients' pain and function.

METHODS

We retrospectively reviewed 30 patients (53 hands) with symptomatic basal joint arthritis of the thumb between April 2019 and March 2020. Visual analogue scale (VAS) scores for pain, grip strength, and pinch power of both hands and Patient-Rated Wrist/Hand Evaluation (PRWHE) scores were recorded for all patients. Basal joint arthritis was classified according to the modified Eaton-Glickel stage using routine radiographs and the CT scans of SPECT/CT, respectively. The maximum standardized uptake value (SUVmax) from SPECT/CT was measured in the four peritrapezial joints and the highest uptake was used for analysis.

RESULTS

According to Eaton-Glickel classification, 11, 17, 17, and eight hands were stage 0 to I, II, III, and IV, respectively. The interobserver reliability for determining the stage of arthritis was moderate for radiographs (k = 0.41) and substantial for CT scans (k = 0.67). In a binary categorical analysis using SUVmax, pain (p < 0.001) and PRWHE scores (p = 0.004) were significantly higher in hands with higher SUVmax. Using multivariate linear regression to estimate the pain VAS, only SUVmax (B 0.172 (95% confidence interval (CI) 0.065 to 0.279; p = 0.002) showed a significant association. Estimating the variation of PRWHE scores using the same model, only SUVmax (B 1.378 (95% CI, 0.082 to 2.674); p = 0.038) showed a significant association.

CONCLUSION

The CT scans of SPECT/CT provided better interobserver reliability than routine radiographs for evaluating the severity of arthritis. A higher SUVmax in SPECT/CT was associated with more pain and functional disabilities of basal joint arthritis of the thumb. This approach could be used to complement radiographs for the evaluation of patients with this condition. Cite this article: Bone Joint J 2021;103-B(8):1380-1385.

Computerized Tomography (CT) Updates and Challenges in Diagnosis of Bone Metastases During Prostate Cancer

Prostate cancer is one of the most common cancers in men. This cancer is often associated with indolent tumors with little or no lethal potential. Some of the patients with aggressive prostate cancer have increased morbidity and early deaths. A major complication in advanced prostate cancer is bone metastasis that mainly results in pain, pathological fractures, and compression of spinal nerves. These complications in turn cause severe pain radiating to the extremities and possibly sensory as well as motor disturbances. Further, in patients with a high risk of metastases, treatment is limited to palliative therapies. Therefore, accurate methods for the detection of bone metastases are essential. Technical advances such as single-photon emission computed tomography/ computed tomography (SPECT/CT) have emerged after the introduction of bone scans. These advanced methods allow tomographic image acquisition and help in attenuation correction with anatomical co-localization. The use of positron emission tomography/CT (PET/CT) scanners is also on the rise. These PET scanners are mainly utilized with 18F-sodium-fluoride (NaF), in order to visualize the skeleton and possible changes. Moreover, NaF PET/CT is associated with higher tracer uptake, increased target-to-background ratio and has a higher spatial resolution. However, these newer technologies have not been adopted in clinical guidelines due to lack of definite evidence in support of their use in bone metastases cases. The present review article is focused on current perspectives and challenges of computerized tomography (CT) applications in cases of bone metastases during prostate cancer.

Feasibility of dual-phase 99mTc-MDP SPECT/CT imaging in rheumatoid arthritis evaluation

Background

To prospectively demonstrate the feasibility of performing dual-phase SPECT/CT for the assessment of the small joints of the hands of rheumatoid arthritis (RA) patients, and to evaluate the reliability of the quantitative and qualitative measures derived from the resulting images.

Methods

A SPECT/CT imaging protocol was developed in this pilot study to scan both hands simultaneously in participants with RA, in two phases of ^99mTc-MDP radiotracer uptake, namely the soft-tissue blood pool phase (within 15 minutes after radiotracer injection) and osseous phase (after 3 hours). Joints were evaluated qualitatively (normal vs. abnormal uptake) and quantitatively [by measuring a newly developed metric, maximum corrected count ratio (MCCR)]. Qualitative and quantitative evaluations were repeated to assess reliability.

Results

Four participants completed seven studies (all four were imaged at baseline, and three of them at follow-up after 1-month of arthritis therapy). A total of 280 joints (20 per hand) were evaluated. The MCCR from soft-tissue phase scans was significantly higher for clinically abnormal joints compared to clinically normal ones; P<0.001, however the MCCR from the osseous phase scans were not different between the two joint groups. Intraclass Correlation Coefficient (ICC) for MCCR was excellent [0.9789, 95% confidence interval (CI): 0.9734-0.9833]. Intra-observer agreement for qualitative SPECT findings was substantial for both the soft-tissue phase (kappa =0.78, 95% CI: 0.72-0.83) and osseous-phase (kappa =0.70, 95% CI: 0.64-0.76) scans.

Conclusions

Extracting reliable quantitative and qualitative measures from dual-phase 99mTc-MDP SPECT/CT hand scans is feasible in RA patients. SPECT/CT may provide a unique means for assessing both synovitis and osseous involvement in RA joints using the same radiotracer injection.

Molecular and metabolic imaging of castration-resistant prostate cancer: state of art and future prospects

Prostate cancer (PCa) represents the most common tumor in male and one of the most relevant causes of death in Western countries. Androgen deprivation therapy (ADT) constitutes a widely used approach in advanced PCa. When PCa progresses in spite of ADT and castrate levels of testosterone, the severe clinical condition termed as metastatic castration-resistant prostate cancer (mCRPC) takes place. The only approach to mCRPC has been represented by chemotherapy with taxanes for many years. Nevertheless, recently introduced treatments such as 2nd generation antiandrogens (i.e. enzalutamide and abiraterone), cell immunotherapy with sipuleucel-T or targeted alpha therapy with 223Ra-dichloride, have dramatically changed mCRPC prognosis. These novel therapies call for an unmet need for imaging biomarkers suitable for patients' pre-treatment stratification and response assessment. In this scenario, nuclear medicine can provide several metabolic and molecular probes for investigating pathological processes at a cellular and sub-cellular level. The aim of this paper is to review the most relevant findings of the literature published to date on this topic, giving particular emphasis to the pros and cons of each tracer and also covering future prospects for defining personalized therapeutic approaches.

Bone tumor-targeted delivery of theranostic 195mPt-bisphosphonate complexes promotes killing of metastatic tumor cells

Platinum-based drugs such as cisplatin are very potent chemotherapeutics, whereas radioactive platinum (195mPt) is a rich source of low-energy Auger electrons, which kills tumor cells by damaging DNA. Auger electrons damage cells over a very short range. Consequently, 195mPt-based radiopharmaceuticals should be targeted toward ​tumors to maximize radiotherapeutic efficacy and minimize Pt-based systemic toxicity. Herein, we show that systemically administered radioactive bisphosphonate-functionalized platinum (195mPt-BP) complexes specifically accumulate in intratibial bone metastatic lesions in mice. The 195mPt-BP complexes accumulate 7.3-fold more effectively in bone 7 days after systemic delivery compared to 195mPt-cisplatin lacking bone-targeting bisphosphonate ligands. Therapeutically, 195mPt-BP treatment causes 4.5-fold more γ-H2AX formation, a biomarker for DNA damage in metastatic tumor cells compared to 195mPt-cisplatin. We show that systemically administered 195mPt-BP is radiotherapeutically active, as evidenced by an 11-fold increased DNA damage in metastatic tumor cells compared to non-radioactive Pt-BP controls. Moreover, apoptosis in metastatic tumor cells is enhanced more than 3.4-fold upon systemic administration of 195mPt-BP vs. radioactive 195mPt-cisplatin or non-radioactive Pt-BP controls. These results provide the first preclinical evidence for specific accumulation and strong radiotherapeutic activity of 195mPt-BP in bone metastatic lesions, which offers new avenues of research on radiotherapeutic killing of tumor cells in bone metastases by Auger electrons.

Development and validation of a kit formulation of [68Ga]Ga-P15-041 as a bone imaging agent

One of the commonly performed studies in nuclear medicine are bone scans with [^99mTc]Tc-methylene diphosphonate (MDP) for detecting various bone lesions, including cancer metastasis. The recent emergence of commercially available ⁶⁸Ge/⁶⁸Ga radionuclide generators makes it possible to provide ⁶⁸Ga-labelled bisphosphonates as positron emission tomography (PET) tracers for bone imaging. Preliminary human studies suggested that [⁶⁸Ga]Ga-HBED-CC-BP ([⁶⁸Ga]Ga-P15-041) in conjunction with PET/computed tomography (CT) showed accumulation in known bone lesions, fast clearance from blood and soft tissue, and an ability to provide high contrast images. A simple and efficient lyophilized P15-041 kit formulation for the rapid production of [⁶⁸Ga]Ga-P15-041 with excellent radiochemical purity (RCP) under ambient temperature without the need for purification is described. It is demonstrated that clinical doses of [⁶⁸Ga]Ga-P15-041 can be prepared manually within minutes with an excellent purity (> 90%) and readily meet the dose release criteria. When [⁶⁸Ga]Ga-P15-041 was evaluated in a patient with cancer, the imaging agent clearly showed accumulations in multiple lesions. In conclusion, [⁶⁸Ga]Ga-P15-041, prepared by a lyophilized kit, might be an excellent bone imaging agent for widespread clinical application.

18F-sodium fluoride bone deposition quantitation with PET in Mice: Variation with age, sex, and circadian rhythm

Aim The aim of this study was to establish a data base for normal 18F-sodium fluoride (18F-NaF) bone uptake as a function of age, sex and circadian rhythm in mice.

Methods In 12 female (F) and 12 male (M) C57BL/6N mice PET images were acquired 90 min after intravenous injection of 20 MBq 18F-NaF for 30 minutes. Each mouse was imaged in follow-up studies at 1, 3, 6, 13 and 21 months of age. In order to assess for physiologic changes related to circadian rhythm, animals were imaged during light (sleep phase) as well as during night conditions (awake phase). Bone uptake is described as the median percentage of the injected activity (%IA) and in relation to bone volume (%IA/ml).

Results A significant smaller bone volume was found in F (1.79 ml) compared to M (1.99 ml; p < 0.001). In sex-pooled data, highest bone uptake occurred at an age of 1 month (61.1 %IA, 44.5 %IA/ml) with a significant reduction (p < 0.001) at age 3 months (43.6 %IA, 23.6 %IA/ml), followed by an increase between 13 (47.3 %IA, 24.5 %IA/ml) and 21 months (52.2 %IA, 28.1 %IA/ml). F had a significantly higher total uptake (F 48.2 %IA, M 43.8 %IA; p = 0.026) as well as a higher uptake per ml bone tissue (F 27.0 %IA/ml; M 22.4 %IA/ml; p < 0.001). A significant impact of circadian rhythm was only found for F at ages of 3 and 6 months with a higher uptake during the sleep phase.

Conclusion Circadian rhythm had a significant impact on uptake only in F of 3 and 6 months. Regarding sex, F showed generally higher uptake rates than M. The highest uptake values were observed during bone growth at age 1 month in both sexes, a second uptake peak occurred in elderly F. Designing future bone uptake studies with M, attention must be paid to age only, while in F circadian rhythm and age must be taken into account.

Use of 55 PET radiotracers under approval of a Radioactive Drug Research Committee (RDRC)

BACKGROUND

In the US, EU and elsewhere, basic clinical research studies with positron emission tomography (PET) radiotracers that are generally recognized as safe and effective (GRASE) can often be conducted under institutional approval. For example, in the United States, such research is conducted under the oversight of a Radioactive Drug Research Committee (RDRC) as long as certain requirements are met. Firstly, the research must be for basic science and cannot be intended for immediate therapeutic or diagnostic purposes, or to determine the safety and effectiveness of the PET radiotracer. Secondly, the PET radiotracer must be generally recognized as safe and effective. Specifically, the mass dose to be administered must not cause any clinically detectable pharmacological effect in humans, and the radiation dose to be administered must be the smallest dose practical to perform the study and not exceed regulatory dose limits within a 1-year period. In our experience, the main barrier to using a PET radiotracer under RDRC approval is accessing the required information about mass and radioactive dosing.

RESULTS

The University of Michigan (UM) has a long history of using PET radiotracers in clinical research studies. Herein we provide dosing information for 55 radiotracers that will enable other PET Centers to use them under the approval of their own RDRC committees.

CONCLUSIONS

The data provided herein will streamline future RDRC approval, and facilitate further basic science investigation of 55 PET radiotracers that target functionally relevant biomarkers in high impact disease states.

Can Na18F PET/CT bone scans help when deciding if early intervention is needed in patients being treated with a TSF attached to the tibia: insights from 41 patients

Purpose

To demonstrate the usefulness of positron emission tomography (PET)/computed tomography (CT) bone scans for gaining insight into healing bone status earlier than CT or X-ray alone.

Methods

Forty-one prospective patients being treated with a Taylor Spatial Frame were recruited. We registered data obtained from successive static CT scans for each patient, to align the broken bone. Radionuclide uptake was calculated over a spherical volume of interest (VOI). For all voxels in the VOI, histograms and cumulative distribution functions of the CT and PET data were used to assess the type and progress of new bone growth and radionuclide uptake. The radionuclide uptake difference per day between the PET/CT scans was displayed in a scatter plot. Superimposing CT and PET slice data and observing the spatiotemporal uptake of ¹⁸F⁻ in the region of healing bone by a time-sequenced movie allowed qualitative evaluation.

Results

Numerical evaluation, particularly the shape and distribution of Hounsfield Units and radionuclide uptake in the graphs, combined with visual evaluation and the movies enabled the identification of six patients needing intervention as well as those not requiring intervention. Every revised patient proceeded to a successful treatment conclusion.

Conclusion

Numerical and visual evaluation based on all the voxels in the VOI may aid the orthopedic surgeon to assess a patient’s progression to recovery. By identifying slow or insufficient progress at an early stage and observing the uptake of ¹⁸F⁻ in specific regions of bone, it might be possible to shorten the recovery time and avoid unnecessary late complications.

Electronic supplementary material

The online version of this article (10.1007/s00590-020-02776-2) contains supplementary material, which is available to authorized users.

Hybrid PET- and MR-driven attenuation correction for enhanced 18F-NaF and 18F-FDG quantification in cardiovascular PET/MR imaging

BACKGROUND

The standard MR Dixon-based attenuation correction (AC) method in positron emission tomography/magnetic resonance (PET/MR) imaging segments only the air, lung, fat and soft-tissues (4-class), thus neglecting the highly attenuating bone tissues and affecting quantification in bones and adjacent vessels. We sought to address this limitation by utilizing the distinctively high bone uptake rate constant Ki expected from 18F-Sodium Fluoride (18F-NaF) to segment bones from PET data and support 5-class hybrid PET/MR-driven AC for 18F-NaF and 18F-Fluorodeoxyglucose (18F-FDG) PET/MR cardiovascular imaging.

METHODS

We introduce 5-class Ki/MR-AC for (i) 18F-NaF studies where the bones are segmented from Patlak Ki images and added as the 5th tissue class to the MR Dixon 4-class AC map. Furthermore, we propose two alternative dual-tracer protocols to permit 5-class Ki/MR-AC for (ii) 18F-FDG-only data, with a streamlined simultaneous administration of 18F-FDG and 18F-NaF at 4:1 ratio (R4:1), or (iii) for 18F-FDG-only or both 18F-FDG and 18F-NaF dual-tracer data, by administering 18F-NaF 90 minutes after an equal 18F-FDG dosage (R1:1). The Ki-driven bone segmentation was validated against computed tomography (CT)-based segmentation in rabbits, followed by PET/MR validation on 108 vertebral bone and carotid wall regions in 16 human volunteers with and without prior indication of carotid atherosclerosis disease (CAD).

RESULTS

In rabbits, we observed similar (< 1.2% mean difference) vertebral bone 18F-NaF SUVmean scores when applying 5-class AC with Ki-segmented bone (5-class Ki/CT-AC) vs CT-segmented bone (5-class CT-AC) tissue. Considering the PET data corrected with continuous CT-AC maps as gold-standard, the percentage SUVmean bias was reduced by 17.6% (18F-NaF) and 15.4% (R4:1) with 5-class Ki/CT-AC vs 4-class CT-AC. In humans without prior CAD indication, we reported 17.7% and 20% higher 18F-NaF target-to-background ratio (TBR) at carotid bifurcations wall and vertebral bones, respectively, with 5- vs 4-class AC. In the R4:1 human cohort, the mean 18F-FDG:18F-NaF TBR increased by 12.2% at carotid bifurcations wall and 19.9% at vertebral bones. For the R1:1 cohort of subjects without CAD indication, mean TBR increased by 15.3% (18F-FDG) and 15.5% (18F-NaF) at carotid bifurcations and 21.6% (18F-FDG) and 22.5% (18F-NaF) at vertebral bones. Similar TBR enhancements were observed when applying the proposed AC method to human subjects with prior CAD indication.

CONCLUSIONS

Ki-driven bone segmentation and 5-class hybrid PET/MR-driven AC is feasible and can significantly enhance 18F-NaF and 18F-FDG contrast and quantification in bone tissues and carotid walls.

A New [68Ga]Ga-HBED-CC-Bisphosphonate as a Bone Imaging Agent

Positron emission tomography (PET) imaging using ⁶⁸Ga-labeled bisphosphonates to target bone metastasis could be a valuable tool in cancer diagnosis and monitoring therapeutic treatment. A ⁶⁸Ga labeled ligand, N,N'-bis[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N'-diacetic acid (HBED-CC) containing one bisphosphonate group (HBED-CC-BP, 1) was prepared and evaluated. The new ligand, 1, reacted rapidly to form [⁶⁸Ga]Ga-1, via complexing with [⁶⁸Ga]GaCl₃ eluted from a commercially available ⁶⁸Ge/⁶⁸Ga generator (in a sodium acetate buffer at pH 4, reaching >95% labeling yield at room temperature in 5 min). The resulting [⁶⁸Ga]Ga-1 showed excellent stability in vitro and in vivo. [⁶⁸Ga]Ga-1 displayed high binding affinity to hydroxyapatite and good uptake in the tibia and femur bone of normal mice. Biodistribution and MicroPET imaging studies of [⁶⁸Ga]Ga-1 in normal mice and rats showed excellent bone uptake and retention comparable to that of Na[¹⁸F]F. The results suggested that [⁶⁸Ga]Ga-1 might be suitable as a bone imaging agent in humans and it could be useful as a convenient alternative to the current bone imaging PET agent, Na[¹⁸F]F, without the need of a near-by cyclotron. Also, an automated synthesis module was developed to produce clinical doses of [⁶⁸Ga]Ga-1 in a consistent and reproducible manner. Currently, the investigation new drug application (IND) for [⁶⁸Ga]Ga-HBED-CC-BP, [⁶⁸Ga]Ga-1, has received FDA approval, and it is currently under clinical trial (IND #129870).

Spatiotemporal characterization of microdamage accumulation and its targeted remodeling mechanisms in diabetic fatigued bone

The skeleton of type 1 diabetes mellitus (T1DM) has deteriorated mechanical integrity and increased fragility, whereas the mechanisms are not fully understood. Load-induced microdamage naturally occurs in bone matrix and can be removed by initiating endogenous targeted bone remodeling. However, the microdamage accumulation in diabetic skeleton and the corresponding bone remodeling mechanisms remain poorly understood. Herein, streptozotocin-induced T1DM rats and age-matched non-diabetic rats were subjected to daily uniaxial ulnar loading for 1, 4, 7, and 10 days, respectively. The SPECT/CT and basic fuchsin staining revealed significant higher-density spatial accumulation of linear and diffuse microdamage in diabetic ulnae than non-diabetic ulnae. Linear microcracks increased within 10-day loading in diabetic bone, whereas peaked at Day 7 in non-diabetic bone. Moreover, diabetic fatigued ulnae had more severe disruptions of osteocyte canaliculi around linear microcracks. Immunostaining results revealed that diabetes impaired targeted remodeling in fatigued bone at every key stage, including increased apoptosis of bystander osteocytes, decreased RANKL secretion, reduced osteoclast recruitment and bone resorption, and impaired osteoblast-mediated bone formation. This study characterizes microdamage accumulation and abnormal remodeling mechanisms in the diabetic skeleton, which advances our etiologic understanding of diabetic bone deterioration and increased fragility from the aspect of microdamage accumulation and bone remodeling.

99mTc-Methyl-Diphosphonate Binding to Mineral Deposits in Cultures of Marrow-Derived Mesenchymal Stem Cells in Osteogenic Medium

IMPACT STATEMENT

The work is notable for describing a highly sensitive, quantitative, and nondestructive method for evaluating the in vitro amount of mineral accompanying different types of osteogenic differentiation of mesenchymal stem cells in a monolayer cell culture. What is so unique and useful about the method is that it has the potential to be used to define the kinetics of the differentiation process, reflected in the mineralization, without destroying the monolayer. Therefore, it remains intact for further experiments.

A brief overview of metal complexes as nuclear imaging agents

Metallic radionuclides have been instrumental in the field of nuclear imaging for over half a century. While recent years have played witness to a dramatic rise in the use of radiometals as labels for chelator-bearing biomolecules, imaging agents based solely on coordination compounds of radiometals have long played a critical role in the discipline as well. In this work, we seek to provide a brief overview of metal complex-based radiopharmaceuticals for positron emission tomography (PET) and single photon emission computed tomography (SPECT). More specifically, we have focused on imaging agents in which the metal complex itself rather than a pendant biomolecule or targeting moiety is responsible for the in vivo behavior of the tracer. This family of compounds contains metal complexes based on an array of different nuclides as well as probes that have been used for the imaging of a variety of pathologies, including infection, inflammation, cancer, and heart disease. Indeed, two of the defining traits of transition metal complexes-modularity and redox chemistry-have both been creatively leveraged in the development of imaging agents. In light of our audience, particular attention is paid to structure and mechanism, though clinical data is addressed as well. Ultimately, it is our hope that this review will not only educate readers about some of the seminal work performed in this space over the last 30 years but also spur renewed interest in the creation of radiopharmaceuticals based on small metal complexes.

Spatiotemporal Distribution of Linear Microcracks and Diffuse Microdamage Following Daily Bouts of Fatigue Loading of Rat Ulnae

Microdamage accumulation contributes to impaired skeletal mechanical integrity. The bone can remove microdamage by initiating targeted bone remodeling. However, the spatiotemporal characteristics of microdamage initiation and propagation and their relationship with bone remodeling in response to fatigue loading, especially for more physiologically relevant daily bouts of compressive loading, remain poorly understood. The right forelimbs of 24 rats were cyclically loaded with a ramp waveform for 1,500 cycles/day, and contralateral ulnae were not loaded as the controls. The rats were divided into four equal groups and loaded for 1, 4, 7, and 10 days, respectively. We demonstrated that linear microcracking accumulation exhibited a non-linear time-varying process within 10 days of loading with peaked microcrack density at Day 7. Disrupted canaliculi surrounding linear microcracks showed high similarity with the temporal changes of linear microcracking accumulation. Observable intracortical resorption regions were found on Day 10. We found more linear microcracks accumulated in the tensile cortex, but longer cracks were observed in the compressive sides. Increased accumulation of diffuse microdamage was observed from Day 4, but no obvious peak was observed within the 10-day loading period. Diffuse damage first initiated in the compressive cortices but extended to tension from Day 7. The diffuse damage exhibited no impacts on the surrounding osteocyte integrity. Together, our findings revealed a time-dependent, bone remodeling-mediated varying process of linear microcracking accumulation following daily bouts of fatigue loading (with observable peak at Day 7 under our loading regime). Our study also identified distinct spatial accumulation of linear and diffuse microdamage in rat ulnae with tensile and compressive strains. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2112-2121, 2019.

In vivo imaging techniques for bone tissue engineering

Bone is a dynamic tissue that constantly undergoes modeling and remodeling. Bone tissue engineering relying on the development of novel implant scaffolds for the treatment of pre-clinical bone defects has been extensively evaluated by histological techniques. The study of bone remodeling, that takes place over several weeks, is limited by the requirement of a large number of animals and time-consuming and labor-intensive procedures. X-ray-based imaging methods that can non-invasively detect the newly formed bone tissue have therefore been extensively applied in pre-clinical research and in clinical practice. The use of other imaging techniques at a pre-clinical level that act as supportive tools is convenient. This review mainly focuses on nuclear imaging methods (single photon emission computed tomography and positron emission tomography), either alone or used in combination with computed tomography. It addresses their application to small animal models with bone defects, both untreated and filled with substitute materials, to boost the knowledge on bone regenerative processes.

Comparison of standardized uptake values between 99mTc-HDP SPECT/CT and 18F-NaF PET/CT in bone metastases of breast and prostate cancer

Background

Despite recent technological advances allowing for quantitative single-photon emission computed tomography (SPECT), quantitative SPECT has not been widely used in the clinical practice. The aim of this study is to evaluate the feasibility of quantitative SPECT for measuring metastatic bone uptake in breast and prostate cancer by comparing standard uptake values (SUVs) measured with ^99mTc-HDP SPECT/CT and ¹⁸F-NaF PET/CT.

Methods

Twenty-six breast and 27 prostate cancer patients at high risk of bone metastases underwent both ^99mTc-HDP SPECT/CT and ¹⁸F-NaF PET/CT within 14 days of each other. The SPECT and PET data were reconstructed using ordered-subset expectation-maximization algorithms achieving quantitative images. Metastatic and benign skeletal lesions visible in both data sets were identified, and their maximum, peak, and mean SUVs (SUV_max, SUV_peak, and SUV_mean) were determined. SUV ratios (SUVRs) between the lesions and adjacent normal appearing bone were also calculated. Linear regression was used to evaluate the correlations between the SUVs of SPECT and PET and Bland-Altman plots to evaluate the differences between the SUVs and SUVRs of SPECT and PET.

Results

A total of 231 skeletal lesions, 129 metastatic and 102 benign, were analyzed. All three SUV measures correlated very strongly between SPECT and PET (R² ≥ 0.80, p < 0.001) when all lesions were included, and the PET SUVs were significantly higher than SPECT SUVs (p < 0.001). The median differences were 21%, 12%, and 19% for SUV_max, SUV_peak, and SUV_mean, respectively. On the other hand, the SUVRs were similar between SPECT and PET with median differences of 2%, − 9%, and 2% for SUVR_max, SUVR_peak, and SUVR_mean, respectively.

Conclusion

The strong correlation between SUVs and similar SUVRs of ^99mTc-HDP SPECT/CT and ¹⁸F-NaF PET/CT demonstrate that SPECT is an applicable tool for clinical quantification of bone metabolism in osseous metastases in breast and prostate cancer patients.

BIOKINETIC AND DOSIMETRIC ASSESSMENT OF FLUORINE 18 IN HEALTHY VOLUNTEERS SUBJECTED TO 18F–NaF PET/CT BONE SCANS VIA COMPARTMENTAL/MATLAB MODELS AND IN-VIVO STUDY

Objective: This study quantified the time-dependent concentration of [Formula: see text]F–NaF in critical organs according to a simplified compartmental biokinetic model with clinical verification. Methods: The eleven volunteers were given [Formula: see text][Formula: see text]MBq [Formula: see text]F–NaF administration, then scanned (with 15[Formula: see text]min-collection, every 20[Formula: see text]min, for 200 consecutive min) with a Philips Gemini GXL PET/CT. The empirical data were collected and normalized as the input dataset for MATLAB program. A six-compartmental model was created as a set of time-dependent differential equations and analyzed by the MATLAB to optimize the correlation between the in vivo data and calculated results. The six compartments were: body fluid, bone, kidney, liver, remainder and excretion, while kidney and liver compartments were conventionally split into two subunits with different half-lives to fit properly the empirical data. Results: The average biological half-lives of body fluid, bone, kidney-1, kidney-2, liver-1, liver-2 and the remainder (rest of body) were assessed as [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text][Formula: see text]min, respectively. A dimensionless AT index of disagreement between the empirical data and MATLAB optimal solutions was proposed of validating the applied acquisition system and analytical method feasibility. The body fluid and bone AT values did not exceed 20%. The proposed refined equation yielded the internal dose from both gamma- and beta-rays ([Formula: see text] cSv as [Formula: see text] cSv/MBq), which exhibited good correlation with literature (0.00168–0.00270 cSv/MBq). Conclusion: The proposed MATLAB-based fitting of in-vivo data with the theoretical results was instrumental for assessing the radiation dose received by the PET/CT bone scan participants.

The diagnostic accuracy of imaging modalities to detect pseudarthrosis after spinal fusion-a systematic review and meta-analysis of the literature

OBJECTIVE

The aim of the study was to determine the diagnostic accuracy of imaging modalities to detect pseudarthrosis after thoracolumbar spinal fusion, with surgical exploration as reference standard.

MATERIALS AND METHODS

A systematic literature search for original studies was performed on the diagnostic accuracy of imaging as index test compared to surgical exploration as reference standard to diagnose pseudarthrosis after thoracolumbar spinal fusion. Diagnostic accuracy values were extracted and methodologic quality of studies was evaluated by the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool. Per modality, clinically comparable studies were included in subgroup meta-analysis and weighted odds ratios (ORs) were calculated using the random effects model.

RESULTS

Fifteen studies were included. Risk of bias was classified as high/unclear in 58% of the studies. Concerns of applicability was classified as high/unclear in 40% of the studies. Four scintigraphy studies including 93 patients in total were pooled to OR = 2.91 (95% confidence interval [CI]: 0.93-9.13). Five studies on plain radiography with 398 patients in total were pooled into OR = 7.07 (95% CI: 2.97-16.86). Two studies evaluating flexion-extension radiography of 75 patients in total were pooled into OR = 4.00 (95% CI: 0.15-105.96). Two studies of 68 patients in total were pooled for CT and yielded OR = 17.02 (95% CI: 6.42-45.10). A single study reporting on polytomography, OR = 10.15 (95% CI 5.49-18.78), was also considered to be an accurate study.

CONCLUSIONS

With a pooled OR of 17.02, CT can be considered the most accurate imaging modality for the detection of pseudarthrosis after thoracolumbar spinal fusion from this review.

11C-Choline Pharmacokinetics in Recurrent Prostate Cancer

The aim of this study was to investigate the value of pharmacokinetic modeling for quantifying 11C-choline uptake in patients with recurrent prostate cancer. Methods: In total, 194 patients with clinically suspected recurrence of prostate cancer underwent 11C-choline dynamic PET over the pelvic region (0-8 min), followed by a 6-min static acquisition at about 25 min after injection. Regions of interest were drawn over sites of disease identified by a radiologist with experience in nuclear medicine. 11C-choline uptake and pharmacokinetics were evaluated by SUV, graphical analysis (Patlak plot; KiP), and 1- and 2-compartment pharmacokinetic models (K1, K1/k2, k3, k4, and the macro parameter KiC). Twenty-four local recurrences, 65 metastatic lymph nodes, 19 osseous metastases, and 60 inflammatory lymph nodes were included in the analysis, which was subsequently repeated for regions of interest placed over the gluteus maximus muscle and adipose tissue as a control. Results: SUVmean and KiP were 3.60 ± 2.16 and 0.28 ± 0.22 min-1 in lesions, compared with 2.11 ± 1.33 and 0.15 ± 0.10 min-1 in muscle and 0.26 ± 0.07 and 0.02 ± 0.01 min-1 in adipose tissue. According to the Akaike information criterion, the 2-compartment irreversible model was most appropriate in 85% of lesions and resulted in a K1 of 0.79 ± 0.98 min-1 (range, 0.11-7.17 min-1), a K1/k2 of 2.92 ± 3.52 (range, 0.31-20.00), a k3 of 0.36 ± 0.30 min-1 (range, 0.00-1.00 min-1) and a KiC of 0.28 ± 0.22 min-1 (range, 0.00-1.33 min-1). The Spearman ρ between SUV and KiP, between SUV and KiC, and between KiP and KiC was 0.94, 0.91, and 0.97, respectively, and that between SUV and K1, between SUV and K1/k2, and between SUV and k3 was 0.70, 0.44, and 0.33, respectively. Malignant lymph nodes exhibited a higher SUV, KiP, and KiC than benign lymph nodes. Conclusion: Although 11C-choline pharmacokinetic modeling has potential to uncouple the contributions of different processes leading to intracellular entrapment of 11C-choline, the high correlation between SUV and both KiP and KiC supports the use of simpler SUV methods to evaluate changes in 11C-choline uptake and metabolism for treatment monitoring.

The utility of bone scintigraphy with SPECT/CT in the evaluation and management of frostbite injuries

OBJECTIVE:

Frostbite is a localized cold-thermal injury resulting from prolonged exposure of flesh to freezing and near freezing temperatures. The depth and extent of frostbite injuries are not easily assessed, from a clinical standpoint, at the time of injury making it challenging to plan appropriate management and treatment.

METHODS:

A review of the literature of management of cold-related injuries and retrospective case review of the imaging and clinical course of frostbite injury.

RESULTS:

Bone scintigraphy with single photon emission computed tomography (SPECT)/CT was performed in the acute and subacute course of frostbite injuries, subsequently leading to earlier definitive management and shorter hospital stay.

CONCLUSION:

Multiphase technetium-99m-methylenediphosphonate (⁹⁹mTc-MDP) bone scintigraphy with SPECT/CT can expedite clinical management of frostbite injuries by determining the extent of injury and can accurately predict the level of amputation if needed.

ADVANCES IN KNOWLEDGE:

 SPECT/CT is underutilized at many facilities but can have a profound and immediate impact on clinical management of patients with frostbite when used in combination with physiological bone scan imaging.

The clinical significance of incidental soft tissue uptake on whole body 18F-sodium fluoride bone PET-CT

¹⁸F-sodium fluoride (NaF) is a PET bone imaging agent and is commonly used in imaging patients with cancer; however, similar to technetium-99m medronic acid (^99mTc-MDP), it can be useful in the evaluation of benign bone and joint conditions. NaF is an excellent bone-seeking agent with high bone uptake due to rapid single-pass extraction. It has negligible plasma protein binding, rapid blood, renal clearance, high bone uptake and almost all NaF delivered is retained by bone after a single pass of blood; however, uptake of NaF can be observed in non-osseous structures such as the arterial vasculature, gastrointestinal tract, genitourinary tract, and viscera. In this article, we present a spectrum of clinical cases with non-osseous NaF uptake in patients referred for cancer staging.

Use of 18F-sodium fluoride bone PET for disability evaluation in ankle trauma: a pilot study

Background

There are no objective and accurate rating tools for permanent impairment of traumatized ankles. The purpose of this study is to assess the role of 18F-Sodium fluoride (18F-NaF) positron emission tomography-computed tomography (PET/CT) bone scans in evaluating patients with limited ankle range of motion (ROM) after trauma.

Methods

18F-NaF PET/CT was performed in 121 patients (75 men, 46 women; mean age: 45.8) who had ROM < 70% of normal after trauma affecting ankles. Metabolic target volume (MTV), the sum of voxels with standardized uptake value (SUV) > 2.5 was automatically obtained from the 3D volume that included the ankle joint. The maximum & mean SUV (SUVmax & SUVmean), and the total lesion activity (TLA) were measured.

Results

The median period from injury to performing 18F-NaF PET/CT was 290 days. The causes of injury were as follows: fracture (N = 95), Achilles tendon rupture (N = 12), and ligament injury (N = 12). Hot uptake in the ankle was seen in 113 of 121 patients. The fracture group had higher SUVmax, SUVmean, and TLA values than the non-fracture group. More limited ROM correlated with higher hot-uptake parameters (SUVmax, SUVmean, TLA). In subgroup analysis, the same correlations were present in the fracture, but not in the non-fracture group.

Conclusions

18F-NaF PET/CT can provide considerable information in impairment evaluations of limited ankle ROM, particularly in fracture around the ankle. Thus, 18F-NaF bone PET/CT may provide an additional option as an objective imaging tool in disability assessment after ankle injury.