Intensity of 18F-FDG PET Uptake in Culture-Negative and Culture-Positive Cases of Chronic Osteomyelitis

Diagnostic value of hybrid FDG-PET/MR imaging of chronic osteomyelitis

Background

Magnetic resonance imaging (MRI) and 2-[¹⁸F]-fluoro-2-deoxy-d-glucose (¹⁸F-FDG) Positron Emission Tomography, paired with Computed Tomography (PET/CT) are commonly used modalities in the complicated diagnostic work-up of osteomyelitis. PET/MRI is a relatively novel hybrid modality with suggested applications in bone infection imaging, based on expert opinion and previous qualitative research. ¹⁸F-FDG PET/MRI has the advantages of reduced radiation dose, more soft tissue information, and is deemed more valuable for surgical planning compared to ¹⁸F-FDG PET/CT. The goal of this study is to quantitatively assess the diagnostic value of hybrid ¹⁸F-FDG PET/MRI for chronic osteomyelitis.

Methods

A retrospective analysis was performed by a nuclear medicine physician and radiologist on 36 patients with ¹⁸F-FDG PET/MRI scans for suspected osteomyelitis. Sensitivity, specificity, and accuracy were determined with the clinical assessment by the orthopaedic surgeon (based on subsequent intraoperative microbiology or long-term follow-up) as the ground truth. Standardized uptake values (SUV) were measured and analysed by means of receiver operating characteristics (ROC).

Results

This first study to quantitatively report the diagnostic value of ¹⁸F-FDG PET/MRI yielded a sensitivity, specificity, and accuracy of 78%, 100%, and 86% respectively. Area under the ROC curve was .736, .755, and .769 for the SUVmax, target to background ratio, and SUVmax_ratio respectively. These results are in the same range and not statistically different compared to diagnostic value for ¹⁸F-FDG PET/CT imaging of osteomyelitis in literature.

Conclusions

Based on the aforementioned advantages of ¹⁸F-FDG PET/MRI and the diagnostic value reported here, the authors propose ¹⁸F-FDG PET/MRI as an alternative to ¹⁸F-FDG PET/CT in osteomyelitis diagnosis, if available.

Radiological evaluation of postoperative osteomyelitis in long bones: Which is the best tool?

Currently, definitive diagnosis of osteomyelitis involves a combination of clinical signs, symptoms, laboratory tests, imaging modalities and cultures from blood, joint or body fluid. Imaging plays a critical role in the osteomyelitis diagnosis. Each of these tests incurs an additional cost to the patient or healthcare system and their use varies according to the preference of the healthcare professional and the healthcare setup. Imaging plays a critical role in the diagnosis and management of postoperative long bone osteomyelitis, with the aim of reducing long-term complications such as non-union, amputation and pathological fractures. In this review, we discuss the key findings on different radiological modalities and correlate them with disease pathophysiology. Currently, magnetic resonance imaging is the best available imaging modality due to its sensitivity in detecting early signs of long bone osteomyelitis and high soft tissue resolution. Other modalities such as radio-nuclear medicine, computed tomography and ultrasound have been proved to be useful in different clinical scenarios as described in this narrative review.

MRI nomenclature for musculoskeletal infection

The Society of Skeletal Radiology (SSR) Practice Guidelines and Technical Standards Committee identified musculoskeletal infection as a White Paper topic, and selected a Committee, tasked with developing a consensus on nomenclature for MRI of musculoskeletal infection outside the spine. The objective of the White Paper was to critically assess the literature and propose standardized terminology for imaging findings of infection on MRI, in order to improve both communication with clinical colleagues and patient care.A definition was proposed for each term; debate followed, and the committee reached consensus. Potential controversies were raised, with formulated recommendations. The committee arrived at consensus definitions for cellulitis, soft tissue abscess, and necrotizing infection, while discouraging the nonspecific term phlegmon. For bone infection, the term osteitis is not useful; the panel recommends using terms that describe the likelihood of osteomyelitis in cases where definitive signal changes are lacking. The work was presented virtually to SSR members, who had the opportunity for review and modification prior to submission for publication.

Real-world experience of the role of 18F FDG PET-computed tomography in chronic spinal implant infection

OBJECTIVES

The presence of postinstrumentation back pain in patients after undergoing spinal surgery is a well established phenomenon. So too is the presence of infection, both overt and subclinical which can be a source of pain. The accurate assessment of infection in patients with spinal implants in situ and no overt radiological or biochemical abnormalities frequently presents a diagnostic challenge. We present our experience spanning 5 years of using 2-deoxy-2-[18F]fluoro-D-glucose positron emission tomography (18F FDG PET)-computed tomography (CT) scans to aid the diagnostic process in treating presumed low-grade chronic implant infection.

METHODS

We undertook a retrospective analysis of all patients with spinal implants in place who were referred for 18F FDG PET-CT imaging over a 5-year period. All available images, case notes and laboratory results were reviewed.

RESULTS

Data pertaining to 49 patients were analysed, with infection diagnosed on 18F FDG PET-CT in 24 (45%) of those sent for scanning. Fifteen patients in the cohort underwent revision surgery, and 11 of whom had been diagnosed as infected on PET-CT. Confirmation of infection with positive microbiological sampling occurred in 8/11 giving a positive predictive value of 0.72 in our series.

CONCLUSION

We present a real-world experience of using 18F FDG PET-CT as a diagnostic tool in the evaluation of patients with chronic pain after undergoing spinal implantation. We have found PET-CT to be a promising modality and would recommend multicentre collaboration to ensure reproducibility across more centres.

Hybrid FDG-PET/MR imaging of chronic osteomyelitis: a prospective case series

Background

Magnetic resonance imaging (MRI) and 2-[18F]-fluoro-2-deoxy-D-glucose (FDG) positron emission tomography paired with computed tomography (PET/CT) are two commonly used imaging modalities in the complicated diagnostic workup of osteomyelitis. Diagnosis using these modalities relies on, respectively, anatomical (MRI) and metabolic (PET) signs. With hybrid PET/MRI being recently available, our goal is to qualitatively compare hybrid FDG PET/MRI to FDG PET/CT in the diagnosis and operative planning of chronic osteomyelitis.

Methods

Five patients with suspected chronic osteomyelitis in an extremity underwent an ¹⁸F-FDG single-injection/dual-imaging protocol with hybrid PET/CT and hybrid PET/MR. Images and clinical features were evaluated using a standardized assessment method. Standardized uptake value (SUV) measurements were performed on all images. Concordant and discordant findings between PET/MRI and PET/CT were analysed.

Results

The consensus diagnoses based on PET/MRI and PET/CT images were identical for all five patients. One discrepancy between PET/MRI and PET/CT was found in the assessment of the features in one patient. PET signal intensities and target-to-background ratios were on average highest for PET/MRI. On PET/MRI, the location of infection based on FDG uptake could clearly be correlated with certain soft tissue structures (oedema, fluid collection, or muscle), which is paramount for surgical planning.

Conclusions

In the presented cases, FDG PET/MRI led to the same diagnosis and provided at least the same diagnostic information as PET/CT. PET/MRI was able to provide additional soft-tissue information for the physician planning treatment. Because of this, we suggest that PET/MRI could be used for osteomyelitis diagnosis and treatment planning.

The diagnostic accuracy of 18F-FDG PET/CT in diagnosing fracture-related infections

Purpose

¹⁸F-Fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET/CT) is frequently used to diagnose fracture-related infections (FRIs), but its diagnostic performance in this field is still unknown. The aims of this study were: (1) to assess the diagnostic performance of qualitative assessment of ¹⁸F-FDG PET/CT scans in diagnosing FRI, (2) to establish the diagnostic performance of standardized uptake values (SUVs) extracted from ¹⁸F-FDG PET/CT scans and to determine their associated optimal cut-off values, and (3) to identify variables that predict a false-positive (FP) or false-negative (FN) ¹⁸F-FDG PET/CT result.

Methods

This retrospective cohort study included all patients with suspected FRI undergoing ¹⁸F-FDG PET/CT between 2011 and 2017 in two level-1 trauma centres. Two nuclear medicine physicians independently reassessed all ¹⁸F-FDG PET/CT scans. The reference standard consisted of the result of at least two deep, representative microbiological cultures or the presence/absence of clinical confirmatory signs of FRI (AO/EBJIS consensus definition) during a follow-up of at least 6 months. Diagnostic performance in terms of sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) was calculated. Additionally, SUVs were measured on ¹⁸F-FDG PET/CT scans. Volumes of interest were drawn around the suspected and corresponding contralateral areas to obtain absolute values and ratios between suspected and contralateral areas. A multivariable logistic regression analysis was also performed to identify the most important predictor(s) of FP or FN ¹⁸F-FDG PET/CT results.

Results

The study included 156 ¹⁸F-FDG PET/CT scans in 135 patients. Qualitative assessment of ¹⁸F-FDG PET/CT scans showed a sensitivity of 0.89, specificity of 0.80, PPV of 0.74, NPV of 0.91 and diagnostic accuracy of 0.83. SUVs on their own resulted in lower diagnostic performance, but combining them with qualitative assessments yielded an AUC of 0.89 compared to an AUC of 0.84 when considering only the qualitative assessment results (p = 0.007). ¹⁸F-FDG PET/CT performed <1 month after surgery was found to be the independent variable with the highest predictive value for a false test result, with an absolute risk of 46% (95% CI 27–66%), compared with 7% (95% CI 4–12%) in patients with ¹⁸F-FDG PET/CT performed 1–6 months after surgery.

Conclusion

Qualitative assessment of ¹⁸F-FDG PET/CT scans had a diagnostic accuracy of 0.83 and an excellent NPV of 0.91 in diagnosing FRI. Adding SUV measurements to qualitative assessment provided additional accuracy in comparison to qualitative assessment alone. An interval between surgery and ¹⁸F-FDG PET/CT of <1 month was associated with a sharp increase in false test results.