First experience with early dynamic 18F-NaF-PET/CT in patients with chronic osteomyelitis

Validation of quantitative [18F]NaF PET uptake parameters in bone diseases: a systematic review

PURPOSE

[18F]NaF PET has become an increasingly important tool in clinical practice toward understanding and evaluating diseases and conditions in which bone metabolism is disrupted. Full kinetic analysis using nonlinear regression (NLR) with a two-tissue compartment model to determine the net rate of influx (Ki) of [18F]NaF is considered the gold standard for quantification of [18F]NaF uptake. However, dynamic scanning often is impractical in a clinical setting, leading to the development of simplified semi-quantitative parameters. This systematic review investigated which uptake parameters have been used to evaluate bone disorders and how they have been validated to measure disease activity.

METHODS

A literature search (in PubMed, Embase.com, and Clarivate Analytics/Web of Science Core Collection) was performed up to 28th November 2023, in collaboration with an information specialist. Each database was searched for relevant literature regarding the use of [18F]NAF PET/CT to measure disease activity in bone-related disorders. The main aim was to explore whether the reported semi-quantitative uptake values were validated against full kinetic analysis. A second aim was to investigate whether the chosen uptake parameter correlated with a disease-specific outcome or marker, validating its use as a clinical outcome or disease marker.

RESULTS

The initial search included 1636 articles leading to 92 studies spanning 29 different bone-related conditions in which [18F]NaF PET was used to quantify [18F]NaF uptake. In 12 bone-related disorders, kinetic analysis was performed and compared with simplified uptake parameters. SUVmean (standardized uptake value) and SUVmax were used most frequently, though normalization of these values varied greatly between studies. In some disorders, various studies were performed evaluating [18F]NaF uptake as a marker of bone metabolism, but unfortunately, not all studies used this same approach, making it difficult to compare results between those studies.

CONCLUSION

When using [18F]NaF PET to evaluate disease activity or treatment response in various bone-related disorders, it is essential to detail scanning protocols and analytical procedures. The most accurate outcome parameter can only be obtained through kinetic analysis and is better suited for research. Simplified uptake parameters are better suited for routine clinical practice and repeated measurements.

Application of Nuclear Medicine Techniques in Musculoskeletal Infection: Current Trends and Future Prospects

Nuclear medicine has become an indispensable discipline in the diagnosis and management of musculoskeletal infections. Radionuclide tests serve as a valuable diagnostic tool for patients suspected of having osteomyelitis, spondylodiscitis, or prosthetic joint infections. The choice of the most suitable imaging modality depends on various factors, including the affected area, potential extra osseous involvement, or the impact of previous bone/joint conditions. This review provides an update on the use of conventional radionuclide imaging tests and recent advancements in fusion imaging scans for the differential diagnosis of musculoskeletal infections. Furthermore, it examines the role of radionuclide scans in monitoring treatment responses and explores current trends in their application. We anticipate that this update will be of significant interest to internists, rheumatologists, radiologists, orthopedic surgeons, rehabilitation physicians, and other specialists involved in musculoskeletal pathology.

Imaging-Selected Host Responses in the Context of Infections

Recently developed molecular imaging approaches can be used to visualize specific host responses and pathology in a quest to image infections where few microbe-specific tracers have been developed and in recognition that host responses contribute to morbidity and mortality in their own right. Here we highlight several recent examples of these imaging approaches adapted for imaging infections. The early successes and new avenues described here encompass diverse imaging modalities and leverage diverse aspects of the host response to infection-including inflammation, tissue injury and healing, and key nutrients during host-pathogen interactions. Clearly, these approaches merit further preclinical and clinical study as they are complementary and orthogonal to the pathogen-focused imaging modalities currently under investigation.

Intraoperative assessment of bone viability through improved analysis and visualization of dynamic contrast-enhanced fluorescence imaging: technique report

Bone devitalization is believed to be a critical determinant of complications such as infection or nonunion. However, intraoperative assessment of bone devitalization, particularly in open fractures and infections, remains highly subjective resulting in variation in treatment. Optical imaging tools, particularly dynamic contrast-enhanced fluorescence imaging, can provide real-time, intraoperative assessment of bone and soft tissue perfusion, which informs the tissues' ability to heal and fight infection. We describe a novel technique to apply indocyanine green-based fluorescence imaging, using a device that is frequently used in the operating room to assess skin or flap perfusion in plastic surgery, to assess bone and deep tissue perfusion in three pertinent cases: (1) a chronic infection/nonunion after a Gustilo type 3A tibia fracture (patient 1), (2) an acute Gustilo type 3C tibia open fracture with extensive degloving/soft tissue stripping (patient 2), and (3) an atrophic nonunion of the humerus (patient 3). In all three cases, fluorescence imaging (both time-specific fluorescence and maximum fluorescence) and derived kinetic maps of time-to-peak, ingress slope, and egress slope demonstrated clear spatial variation in perfusion that corresponded to the patient pathogenesis. The impact of this information on patient outcome will need to be evaluated in future clinical trials; however, these cases demonstrate in principle that optical imaging information has the potential to inform surgical practice, reduce the variation in treatment, and improve outcomes observed in these challenging patients.

Clinical value of dual-phase F-18 sodium fluoride PET/CT for diagnosing bone metastasis in cancer patients with solitary bone lesion

Background

The present study aimed to investigate whether dual-phase F-18 sodium-fluoride (NaF) positron emission tomography/computed tomography (PET/CT) could improve the diagnostic accuracy of detecting bone metastasis in cancer patients with a solitary bone lesion compared to conventional F-18 NaF PET/CT.

Methods

We retrospectively enrolled 113 cancer patients who underwent dual-phase F-18 NaF PET/CT for the differential diagnosis of a solitary bone lesion seen on bone scintigraphy. According to the dual-phase PET/CT protocol, an early-phase scan was acquired immediately after radiotracer injection and a conventional F-18 NaF PET/CT scan was performed. The diagnostic abilities of the visual analysis of conventional and dual-phase PET/CT scans and two quantitative parameters (lesion-to-blood pool uptake ratio on early-phase scan and lesion-to-bone uptake ratio on conventional scan) for detecting bone metastasis were compared. The final diagnosis of bone metastasis was made by histopathological confirmation or follow-up imaging studies.

Results

A metastatic bone lesion was diagnosed in 28 patients (24.8%). The sensitivity, specificity, and accuracy were 100.0%, 70.6%, and 77.9%, respectively, for visual analysis of conventional F-18 NaF PET/CT, 92.9%, 42.4%, 54.9%, respectively, for lesion-to-bone uptake ratio, 96.4%, 88.2%, and 90.3%, respectively, for visual analysis of dual-phase PET/CT, and 92.9%, 81.2%, and 83.2%, respectively, for lesion-to-blood pool uptake ratio. Visual analysis of dual-phase PET/CT was shown to have the highest area under the receiver operating characteristic curve value (0.923; 95% CI, 0.858-0.965) among all parameters.

Conclusions

Dual-phase F-18 NaF PET/CT showed a high diagnostic ability for detecting bone metastasis with improved specificity and accuracy compared to conventional F-18 NaF PET/CT in cancer patients. Dual-phase F-18 NaF PET/CT might help diagnose bone metastasis in patients with malignancies who were shown to have a solitary bone lesion on bone scintigraphy.

Perspective on optical imaging for functional assessment in musculoskeletal extremity trauma surgery

SIGNIFICANCE

Extremity injury represents the leading cause of trauma hospitalizations among adults under the age of 65 years, and long-term impairments are often substantial. Restoring function depends, in large part, on bone and soft tissue healing. Thus, decisions around treatment strategy are based on assessment of the healing potential of injured bone and/or soft tissue. However, at the present, this assessment is based on subjective clinical clues and/or cadaveric studies without any objective measure. Optical imaging is an ideal method to solve several of these issues.

AIM

The aim is to highlight the current challenges in assessing bone and tissue perfusion/viability and the potentially high impact applications for optical imaging in orthopaedic surgery.

APPROACH

The prospective will review the current challenges faced by the orthopaedic surgeon and briefly discuss optical imaging tools that have been published. With this in mind, it will suggest key research areas that could be evolved to help make surgical assessments more objective and quantitative.

RESULTS

Orthopaedic surgical procedures should benefit from incorporation of methods to measure functional blood perfusion or tissue metabolism. The types of measurements though can vary in the depth of tissue sampled, with some being quite superficial and others sensing several millimeters into the tissue. Most of these intrasurgical imaging tools represent an ideal way to improve surgical treatment of orthopaedic injuries due to their inherent point-of-care use and their compatibility with real-time management.

CONCLUSION

While there are several optical measurements to directly measure bone function, the choice of tools can determine also the signal strength and depth of sampling. For orthopaedic surgery, real-time data regarding bone and tissue perfusion should lead to more effective patient-specific management of common orthopaedic conditions, requiring deeper penetrance commonly seen with indocyanine green imaging. This will lower morbidity and result in decreased variability associated with how these conditions are managed.

Endosteal and periosteal blood flow quantified with dynamic contrast-enhanced fluorescence to guide open orthopaedic surgery

Due to the lack of objectively measurable or quantifiable methods to assess the bone perfusion, the success of removing devitalized bone is based almost entirely on surgeon's experience and varies widely across surgeons and centers. In this study, an indocyanine green (ICG)-based dynamic contrast-enhanced fluorescence imaging (DCE-FI) has been developed to objectively assess bone perfusion and guide surgical debridement. A porcine trauma model (n = 6 pigs × 2 legs) with up to 5 conditions of severity in loss of flow in each, was imaged by a commercial fluorescence imaging system. By applying the bone-specific hybrid plug-compartment (HyPC) kinetic model to four-minute video sequences, the perfusion-related metrics, such as peak intensity, total bone blood flow (TBBF) and endosteal bone blood flow to TBBF fraction (EFF) were calculated. The results shown that the combination of TBBF and EFF can effectively differentiate injured from normal bone with the accuracy, sensitivity and specificity of 89%, 88% and 90%, respectively. Our subsequent first in human bone blood flow imaging study confirmed DCE-FI can be successfully translated into human orthopaedic trauma patients.

Clinical application of dual-phase F-18 sodium-fluoride bone PET/CT for diagnosing surgical site infection following orthopedic surgery

F-18 sodium-fluoride (NaF) bone positron emission tomography (PET/CT) has been used for diagnosing various bone and joint diseases, and, with using dual-phase scan protocol, it could give the same information obtained by the 3-phase bone scintigraphy. The present study aimed to evaluate the diagnostic ability of dual-phase F-18 NaF bone PET/CT in detecting surgical site infection after orthopedic surgery.Twenty-three patients who underwent dual-phase F-18 NaF bone PET/CT under clinical suspicion of surgical site infection of the bone following orthopedic surgery were enrolled in this study. Dual-phase bone PET/CT consisted of an early phase scan performed immediately after radiotracer injection and a conventional bone-phase scan. All dual-phase PET/CT images were visually assessed, and, for quantitative analysis, 6 parameters of dual-phase PET/CT (lesion-to-blood pool uptake ratio, lesion-to-bone uptake ratio, and lesion-to-muscle uptake ratio on both early phase and bone-phase scans) were measured.Surgical site infection was diagnosed in 14 patients of the 23 patients. The sensitivity, specificity, and accuracy of visual analysis of dual-phase F-18 NaF bone PET/CT for diagnosing surgical site infection of the bone were 92.9%, 100.0%, and 95.7%, respectively. Among the 6 parameters, the lesion-to-blood pool uptake ratio on early phase scan showed the highest area under the receiver operating characteristic curve value (0.857, 95% confidence interval, 0.649-0.966), with the cut-off value of 0.88 showing sensitivity, specificity, and accuracy of 85.7%, 88.9%, and 87.0%, respectively.Our study showed the high diagnostic ability of dual-phase F-18 NaF bone PET/CT for detecting surgical site infection following orthopedic surgery. Further studies are needed to compare the diagnostic ability of dual-phase bone PET/CT with other imaging modalities.

Presurgical localization of infected avascular bone segments in chronic complicated posttraumatic osteomyelitis in the lower extremity using dual-tracer PET/CT

Background

Localizing and removing the infected sequestrum in long-standing trauma-related chronic osteomyelitis remains a clinical challenge. PET/CT with 18F-fluorodeoxyglucose (FDG-PET) has a high sensitivity for chronic osteomyelitis and 18F-sodium-fluoride PET/CT (NaF-PET) has a high specificity for identifying non-viable bone. Combining both, high signal on FDG-PET in the bone without signal on NaF-PET could potentially guide surgery to become more precise with curative intent.

Eight patients with long-standing (average 22 years) posttraumatic (n = 7) or postoperative (n = 1) chronic osteomyelitis in the lower extremity and with multiple futile attempts for curative surgery were recruited in this prospective pilot study. FDG-PET and NaF-PET were performed within a week in between using standard scanning protocols. The most likely location of the culprit sequestrum was identified and was surgically removed. Based on perioperative tissue cultures, antibiotics were given for 6–8 months. Dual-tracer (FDG- and NaF-PET/CT) was performed again after 12 months to rule out persisting signs of infection.

Results

A likely culprit sequestrum could preoperatively be identified by dual-tracer PET in all eight cases and in four cases an additional sequestrum was identified at a location with no clinical sign of infection. The infected necrotic tissue was removed during surgery. Follow-up dual-tracer PET revealed no signs of persistent infection. All patients recovered with no clinical signs of recurrence for a follow-up of mean 4.5 (SD 1.3) years.

Conclusions

Dual-tracer PET/CT with FDG and NaF allows successful precise surgery with curative intent in patients with long-standing complicated posttraumatic chronic osteomyelitis with severely deranged anatomy.

Advanced Imaging Techniques in Skull Base Osteomyelitis Due to Malignant Otitis Externa

PURPOSE OF REVIEW

To give an up-to-date overview of the strengths and weaknesses of current imaging modalities in diagnosis and follow-up of skull base osteomyelitis (SBO).

RECENT FINDINGS

CT and MRI are both used for anatomical imaging, and nuclear techniques aid in functional process imaging. Hybrid techniques PET-CT and PET-MRI are the newest modalities which combine imaging strengths.

SUMMARY

No single modality is able to address the scope of SBO. A combination of functional and anatomical imaging is needed, in the case of newly suspected SBO we suggest the use of PET-MRI (T1, T2, T1-FS-GADO, DWI) and separate HRCT for diagnosis and follow-up.

Dual-phase hybrid 18 F-Fluoride Positron emission tomography/MRI in ankylosing spondylitis: Investigating the link between MRI bone changes, regional hyperaemia and increased osteoblastic activity

INTRODUCTION

Focal ¹⁸ F-Fluoride uptake on blood-pool phase PET represents regional hyperaemia, while it indicates osteoblastic activity on mineralization phase PET. This study investigates the link between regional hyperaemia and osteoblastic activity in inflammatory and chronic lesions of ankylosing spondylitis (AS) of the sacroiliac joints (SIJ) using dual-phase ¹⁸ F-Fluoride PET/MRI.

METHODS

Thirteen patients (six men, seven women, age: 37 ± 10 years) with active AS prospectively underwent dual-phase ¹⁸ F-Fluoride PET/MRI. Blood-pool phase PET was acquired 6 min and mineralization phase PET 40 min after injection of 158 ± 8 MBq ¹⁸ F-Fluoride. SIJ quadrants (SQ) were assessed regarding inflammatory lesions represented by bone marrow oedema (BME), chronic AS lesions such as erosion, fat deposition (FD), sclerosis and ankylosis on MRI, and regarding focal ¹⁸ F-Fluoride uptake on both PET datasets. Image quality (IQ) of both PET datasets and MRI was evaluated using a 4-point Likert scale.

RESULTS

Of 104 SQ, there were 63.4% SQ with FD, 42.3% SQ with BME, 26.9% SQ with erosions, 26% SQ with sclerosis and 10.6% SQ with ankylosis. BME alone was associated with focal ¹⁸ F-Fluoride uptake in 63.6% SQ on blood-pool phase and 90.9% SQ on mineralization phase ¹⁸ F-Fluoride PET/MRI. Instead, FD, erosion, sclerosis, ankylosis were not associated with focal ¹⁸ F-Fluoride uptake on either blood-pool or mineralization phase ¹⁸ F-Fluoride PET/MRI. SQ showing BME alone or a combination of BME and chronic AS lesions had a significantly higher percentage of focal ¹⁸ F-Fluoride uptake on blood-pool phase and mineralization phase PET/MRI than SQ showing AS lesions without BME (P < 0.001). Both ¹⁸ F-Fluoride PET datasets provided high IQ, albeit IQ of mineralization phase PET was superior to blood-pool phase PET (P < 0.001).

CONCLUSION

Dual-phase ¹⁸ F-Fluoride PET/MRI of the SIJ showed that inflammatory rather than chronic AS lesions are associated with regional hyperaemia and osteoblastic activity.

Spectrum of Benign Bone Conditions on NaF-PET

Fluoride imaging with ¹⁸F (NaF-PET), although not a new technique, is becoming increasingly utilized for evaluation of skeletal metastatic disease using PET/CT. As its use becomes more widespread, a variety of nonmalignant bone disorders will be encountered by the interpreting physician. It is important, therefore, to recognize these nonmalignant conditions to avoid errors in interpretation. Beyond this, there is increasing evidence in the literature that NaF-PET/CT imaging may provide valuable information for the primary diagnosis of these nonmalignant conditions, and furthermore may provide insight into the underlying biology leading to management decisions. In this article, we review a spectrum of benign bone conditions that can be visualized on NaF-PET.

Blood perfusion in osteomyelitis studied with [15O]water PET in a juvenile porcine model

Background

Osteomyelitis is a serious disease which can be difficult to treat despite properly instituted antibiotic therapy. This appears to be related at least partly to degraded vascularisation in the osteomyelitic (OM) lesions. Studies of perfusion in OM bones are, however, few and not quantitative. Quantitative assessment of perfusion could aid in the selection of therapy. A non-invasive, quantitative way to study perfusion is dynamic [¹⁵O]water positron emission tomography (PET). We aim to demonstrate that the method can be used for measuring perfusion in OM lesions and hypothesize that perfusion will be less elevated in OM lesions than in soft tissue (ST) infection. The study comprised 11 juvenile pigs with haematogenous osteomyelitis induced by injection of Staphylococcus aureus into the right femoral artery 1 week before scanning (in one pig, 2 weeks). The pigs were dynamically PET scanned with [¹⁵O]water to quantify blood perfusion. OM lesions (N = 17) in long bones were studied, using the left limb as reference. ST lesions (N = 8) were studied similarly.

Results

Perfusion was quantitatively determined. Perfusion was elevated by a factor 1.5 in OM lesions and by a factor 6 in ST lesions.

Conclusions

Blood perfusion was successfully determined in pathological subacute OM lesions; average perfusion was increased compared to that in a healthy bone, but as hypothesized, the increase was less than in ST lesions, indicating that the infected bone has less perfusion reserve than the infected soft tissue.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-016-0251-2) contains supplementary material, which is available to authorized users.

Recurrent surgical site infection of the spine diagnosed by dual (18)F-NaF-bone PET/CT with early-phase scan

We report a case of a 31-year-old man who showed recurrently elevated level of the serum inflammatory marker C-reactive protein (CRP) after spinal operation. He underwent (18)F-flurodeoxyglucose ((18)F-FDG) positron emission tomography/computed tomography (PET/CT) and dual (18)F-sodium-fluoride ((18)F-NaF) PET/CT with an additional early-phase scan to find a hidden inflammation focus. Only mildly increased (18)F-FDG was found at the surgical site of T11 spine on (18)F-FDG PET/CT. In contrast, dual (18)F-NaF bone PET/CT with early-phase scan demonstrated focal active inflammation at the surgical site of T11 spine. After a revision operation of the T11 spine, serum CRP level decreased to the normal range without any symptom or sign of inflammation. Inflammatory focus in the surgical site of the spine can be detected with using dual (18)F-NaF bone PET/CT scan with early-phase scan.

Using PET/CT Bone Scan Dynamic Data to Evaluate Tibia Remodeling When a Taylor Spatial Frame Is Used: Short and Longer Term Differences

Eighteen consecutive patients, treated with a Taylor Spatial Frame for complex tibia conditions, gave their informed consent to undergo Na¹⁸F⁻ PET/CT bone scans. We present a Patlak-like analysis utilizing an approximated blood time-activity curve eliminating the need for blood aliquots. Additionally, standardized uptake values (SUV) derived from dynamic acquisitions were compared to this Patlak-like approach. Spherical volumes of interest (VOIs) were drawn to include broken bone, other (normal) bone, and muscle. The SUV_m(t) (m = max, mean) and a series of slopes were computed as (SUV_m(t_i) − SUV_m(t_j))/(t_i − t_j), for pairs of time values t_i and t_j. A Patlak-like analysis was performed for the same time values by computing ((VOI_p(t_i)/VOI_e(t_i))−(VOI_p(t_j)/VOI_e(t_j)))/(t_i − t_j), where p = broken bone, other bone, and muscle and e = expected activity in a VOI. Paired comparisons between Patlak-like and SUV_m slopes showed good agreement by both linear regression and correlation coefficient analysis (r = 84%, r_s = 78%-SUV_max, r = 92%, and r_s = 91%-SUV_mean), suggesting static scans could substitute for dynamic studies. Patlak-like slope differences of 0.1 min⁻¹ or greater between examinations and SUV_max differences of ~5 usually indicated good remodeling progress, while negative Patlak-like slope differences of −0.06 min⁻¹ usually indicated poor remodeling progress in this cohort.

¹⁸F-fluoride PET and PET/CT in children and young adults

18F-fluoride PET/CT has been used for a wide variety of indications in children and young adults. Nearly all pediatric 18F-fluoride PET/CTs are performed to evaluate benign conditions. The most common indication is the evaluation of back pain in a wide variety of circumstances, including patients with sports injuries, scoliosis, trauma, and back pain after surgery. The high image quality of 18F-fluoride PET/CT can make it particularly useful for evaluating benign skeletal lesions such as osteoid osteoma and Langerhans cell histiocytosis. Quantitative assessment of bone turnover with 18F-fluoride PET/CT may make it useful for assessing the skeleton in patients with metabolic bone diseases, eating disorders, and avascular necrosis. There is little pediatric experience using 18F-fluoride PET/CT for evaluation of skeletal or soft tissue disease in childhood cancers.