Beyond the Focus of Hot Area Activity: Establishing ¹⁸F-FDG PET/CT as the Future Gold Standard in Diagnosing Vascular Graft Infections

INTRODUCTION

Vascular graft infections (VGIs) are potentially fatal complications of prosthetic vascular procedures. Their incidence ranges from 0.5% to 5% and is associated with high morbidity and mortality. The clinical presentation of these infections is often subtle and nonspecific, which can lead to delays in diagnosis and treatment.

Diagnosing VGIs remains challenging due to the often encountered vague symptomatology and the limited specificity of the established conventional imaging, such as CT and magnetic resonance imaging (MRI). This study investigates the clinical utility and diagnostic accuracy of ¹⁸F-fludeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in evaluating suspected VGIs and explores its role in treatment stratification. This manuscript aims to explore the utility of ¹⁸F-FDG PET/CT imaging in diagnosing VGIs, presenting statistical analyses of the data collected from a cohort of patients suspected of having VGIs.^[1]

MATERIAL AND METHODS

RESULTS

Diagnostic accuracy

Out of 39 patients:

• 30 demonstrated abnormal FDG uptake [Fig 1 and Tables 1-4].

• 16 were confirmed graft infections

• 14 had soft-tissue infections.

• 2 were false positives (infected hematomas)

• 1 false negative (low-grade chronic infection).

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Fig 1:

Maximum Intensity Projection [MIP images] image coronal section showing a high metabolic activity that is involving the graft and peri graft soft tissue in aorto iliac graft

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Table 1: Diagnostic contingency (2×2)

Variable	Infection present	Infection absent	Total
PET/CT positive	28 (TP)	2 (FP)	30
PET/CT negative	1 (FN)	8 (TN)	9
Total	29	10	39

Performance metrics: Sensitivity: 28/(28+1)=96.6%, Specificity: 8/(8+2) =80.0%, PPV: 28/(28+2)=93.3%, NPV: 8/(8+1)=88.9%, Accuracy: (28+8)/39=92.3%. PET: Positron emission tomography, CT: Computed tomography, TP: True positive, TN: True negative, FP: False positive, FN: False negative, NPV: Negative predictive value, PPV: Positive predictive value

Table 2: Standardized uptake value max threshold analysis

SUV max cut off	Sensitivity (%)	Specificity (%)	Youden index
>2.5	100	40	0.40
>3.5	96.6	60	0.566
>4.5	89.7	80	0.697
>5.5	76	85	0.61
>6.5	66	90	0.56

The average SUV max for infectious lesions was 5.9 (range: 3.4–9.1). ROC analysis suggested that SUV max >4.5 provided the best diagnostic trade-off. SUV: Standardized uptake value, ROC: Receiver operating characteristic, The calculations match the provided Youden index values, and the optimal cut-off value is indeed >4.5, which corresponds to the highest Youden index (0.697).

Table 3: Diagnostic accuracy of 18F-fludeoxyglucose positron emission tomography/computed tomography in suspected vascular graft infections

Metric	Value (%)	95% CI
Sensitivity	96.6	82.2-99.9
Specificity	80.0	44.4-97.5
PPV	93.3	77.9-99.2
NPV	88.9	51.7-99.7
Accuracy	92.3	79.1-98.4

Calculated from a cohort of 39 patients (TP=28, FP=2, FN=1, TN=8). Sensitivity, specificity, and predictive values were derived from a 2×2 table comparing PET/CT findings with surgical/histopathological confirmation in 39 patients. PET: Positron emission tomography, CT: Computed tomography, NPV: Negative predictive value, CI: Confidence interval, PPV: Positive predictive value

Table 4: Effect of varying standardized uptake value max cutoff thresholds on diagnostic performance

SUV max cutoff	Sensitivity (%)	Specificity (%)	Youden index (J)	Interpretation
>2.5	100	40	0.40	High sensitivity, many false positives
>3.5	96.6	60	0.566	Balanced, moderate, specificity
>4.5	89.7	80	0.697	Optimal diagnostic threshold
>5.5	76	85	0.61	Conservative threshold
>6.5	66	90	0.56	High specificity, risk of false negatives

Youden’s Index (J=Sensitivity + Specificity – 1) was used to identify the optimal SUV max threshold that maximizes both diagnostic sensitivity and specificity. SUV: Standardized uptake value, The calculations match the provided Youden index values, and the optimal cutoff value is indeed >4.5, which corresponds to the highest Youden index (0.697).

The case illustrations are presented in the [Fig 2 -6].

• Case 1: Aorto-bifemoral graft, standardized uptake value (SUV) max 8.5—confirmed infection; surgical debridement and antibiotic therapy successful

• Case 2: Femoro-popliteal graft, SUV max 4.8 – revision surgery confirmed diagnosis

• Case 3: Persistent discharge with SUV max 2.9 – confirmed as sterile hematoma; surgery avoided.

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Fig 2:

Aorto-bifemoral graft axial section shows high metabolic activity in graft and perigraft region at the proximal part of graft

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Fig 3:

Aorto-bifemoral graft axial section shows high metabolic activity in graft and perigraft region at the distal part of graft

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Fig 4:

Femoral-popliteal graft axial section shows high metabolic activity in graft and perigraft region at the proximal part of graft

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Fig 5:

Femoral-popliteal graft coronal section shows high metabolic activity in graft and perigraft region at the proximal part of graft

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Fig 6:

Aorto-uni femoral graft axial section shows sterile changes in graft and perigraft region

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DISCUSSION

This study demonstrates the high diagnostic performance of ¹⁸F-FDG PET/CT in VGIs, confirming its value as a complementary modality to conventional imaging. By combining metabolic and anatomical information, PET/CT provides accurate localization and disease mapping, which are often unattainable with CT or MRI alone. Our findings highlight both its high sensitivity and negative predictive value (NPV), which are crucial in complex postoperative patients where early differentiation between infection and sterile inflammation is paramount. Furthermore, our study reveals the extension of involved VGI that is of prime importance in deciding the further management. The proximal extension of infection up to the native blood vessels is crucial in deciding the surgery.

Early experiences with FDG PET/CT had mentioned its superiority over conventional modalities in detecting prosthetic VGIs.^[1] Keidar et al. showed that PET imaging could depict sites of VGI, even when CT findings were inconclusive.^[2] Later on the work by Spacek et al. reported sensitivity and specificity exceeding 90% for PET/CT, thus validating its diagnostic role.^[3] These pioneering studies showed the way for systematic evaluation of PET/CT in this area of interest.

A large systematic review and meta-analysis by Reinders Folmer et al. validated a pooled sensitivity of 96% and specificity of 74% for PET/CT in diagnosing VGIs, with focal uptake patterns being more reliable than diffuse uptake. [4] Similar study by Treglia et al. conducted a meta-analysis including over 400 patients and found sensitivity of 96% and specificity of 82%, underscoring the robust diagnostic value of modality across different patient cohorts.^[5]

Our findings are consistent with these data. SUV max thresholds have improved discrimination between infection and sterile postoperative changes as a semiquantitative analysis method.

Sah et al. introduced a standardized five-point visual grading scale and reported 100% sensitivity and 86% specificity, with SUV max ≥3.8 strongly associated with confirmed infection.^[6]

A recent literature, Bruggink et al. and Husmann et al., emphasized that focal or irregular FDG uptake with corresponding CT abnormalities such as peri-graft fluid, perigraft fat stranding, or gas, significantly increases specificity.^[7,8]

Chrapko et al. demonstrated that in some patients, FDG-avid abnormalities were the only indicator of infection when morphological CT changes were subtle or absent, highlighting FDG PET/CT’s sensitive role in early detection.^[9]

This aligns similarity with our study, where PET/CT provided diagnostic clarity in those cases where conventional imaging remained equivocal.

Similarly, Tokuda et al. reported that PET/CT impacted the management in nearly 30% of cases by ruling out infection or directing surgical exploration.^[10]

Strengths come with some limitations. False–positive FDG uptake due to inflammatory granulation tissue, suture material, hematoma, or foreign-body reaction remains a diagnostic challenge.^[11]

False positivity has also been associated with the use of surgical adhesives such as BioGlue, which can often produce heterogeneous FDG uptake and reduce specificity.^[12]

Careful correlation with surgical history, clinical signs and symptoms, biochemistry, inflammatory markers, and adjunct imaging is therefore essential for accurate interpretation.

Optimal timing of FDG-PET/CT is most important during clinical workup and technical protocols (posttracer injection). Furthermore, procedural standardization, patient preparation, scan acquisition, reconstruction, subsequent analysis, and clinical interpretation will finalize the imaging benefit.^[13]

The clinical implications of our study are noteworthy. The high NPV makes FDG PET/CT particularly valuable as a modality, reducing unnecessary invasive procedures and guiding a timely therapeutic strategies. Our findings align well with the results, particularly regarding SUV max-based thresholds, which enhance objectivity in clinical workflows. These comparisons underscore the clinical relevance of your study’s objective – to provide SUV max thresholds tailored to VGI detection.

Our results, like those of Spacek et al., emphasize the importance of combining visual and quantitative criteria for accurate PET/CT interpretation.^[3]

In our study, we observed similar false-positive instances due to healing tissue; careful correlation with surgical history and adjunct imaging is essential.

LIMITATIONS

Our single-center study, however, is limited by its modest sample size. Cost and limited availability of PET/CT can be crucial in resource-constrained healthcare systems. Nevertheless, the growing body of evidence suggests that 18F-FDG PET/CT should be considered an integral part of the diagnostic algorithm for VGIs, especially in patients with inconclusive or conflicting results from conventional imaging.

In summary, this study adds to existing evidence that ¹⁸F-FDG PET/CT provides a highly sensitive and specific tool for detecting VGIs. By integrating semi-quantitative SUV max analysis with established visual patterns, clinicians can improve diagnostic accuracy and confidence.

Future multicenter trials should focus on validating SUV thresholds, standardizing reporting criteria, and evaluating cost-effectiveness to facilitate broader adoption in clinical practice.

CONCLUSION

The complications associated with VGIs are serious and multifaceted, ranging from systemic issues like sepsis to localized problems such as abscess formation and limb loss.

Early recognition of these signs is critical in managing VGIs effectively. If any combination of these symptoms arises after surgery, it is essential for patients to seek immediate medical attention to prevent severe complications such as sepsis or limb loss. Early diagnosis often relies on clinical evaluation combined with imaging techniques such as PET/CT, which can help differentiate between infection and other postoperative changes.

While conventional imaging modalities have limitations in specificity and sensitivity, PET/CT demonstrates superior diagnostic capabilities due to its ability to combine metabolic and anatomical information.

Overall, ¹⁸F-FDG PET/CT is a powerful, noninvasive imaging tool for the detection of VGIs. Its superior sensitivity, specificity, and clinical utility support its role as a potential gold standard in diagnosing VGIs. It facilitates targeted therapy, minimizes unnecessary surgeries, and enhances patient outcomes.

Future multicenter studies should focus on standardizing imaging protocols, validating visual and semiquantitative scoring systems, and evaluating cost–benefit dynamics in diverse healthcare environments.