18F-Fluorodeoxyglucose positron emission tomography/CT scanning in diagnosing vascular prosthetic graft infection

Utility of multimodal molecular imaging in the diagnosis and decision-making in arterial diseases

Arterial diseases are prevalent in the general population, particularly in the elderly, and they are among the main causes of morbidity and mortality worldwide. Nuclear imaging is a useful tool in diagnosis and follow-up in different areas of medicine, and over the last 2 decades, these study modalities have become more relevant in the field of angiology and vascular surgery due to their potential benefit in the interpretation of pathophysiological mechanisms associated with the natural history and severity of diseases that affect the circulation such as vasculitis, degenerative aortic aneurysms (AA), peripheral arterial disease (PAD), and complications following reconstructive procedures such as graft infections. The literature has shown evidence of an important number of radiotracers for specific molecules involved in the activity of these entities and their utility as predictors during surveillance and possible therapeutic targets. The present narrative review aims to describe the use of nuclear medicine, imaging methods, and radiotracers that have been applied in arterial diseases, as well as the advantages and considerations, their importance in the diagnosis and follow-up of these complex groups of patients, and future perspectives.

Variability of [18F]FDG-PET/LDCT reporting in vascular graft and endograft infection

PURPOSE

18F-fluoro-D-deoxyglucose positron emission tomography with low dose and/or contrast enhanced computed tomography ([18F]FDG-PET/CT) scan reveals high sensitivity for the diagnosis of vascular graft and endograft infection (VGEI), but lower specificity. Reporting [18F]FDG-PET/CT scans of suspected VGEI is challenging, reader dependent, and reporting standards are lacking. The aim of this study was to evaluate variability of [18F]FDG-PET/low dose CT (LDCT) reporting of suspected VGEI using a proposed standard reporting format.

METHODS

A retrospective cohort study was conducted including all patients with a suspected VGEI (according to the MAGIC criteria) without need for urgent surgical treatment who underwent an additional [18F]FDG-PET/LDCT scan between 2006 and 2022 at a tertiary referral centre. All [18F]FDG-PET/LDCT reports were scored following pre-selected criteria that were formulated based on literature and experts in the field. The aim was to investigate the completeness of [18F]FDG-PET/LDCT reports for diagnosing VGEI (proven according to the MAGIC criteria) and to evaluate if incompleteness of reports influenced the diagnostic accuracy.

RESULTS

Hundred-fifty-two patients were included. Median diagnostic interval from the index vascular surgical procedure until [18F]FDG-PET/LDCT scan was 35.5 (7.3-73.3) months. Grafts were in 65.1% located centrally and 34.9% peripherally. Based on the pre-selected reporting criteria, 45.7% of the reports included all items. The least frequently assessed criterion was FDG-uptake pattern (40.6%). Overall, [18F]FDG-PET/LDCT showed a sensitivity of 91%, a specificity of 72%, and an accuracy of 88% when compared to the gold standard (diagnosed VGEI). Lower sensitivity and specificity in reports including ≤ 8 criteria compared to completely evaluated reports were found (83% and 50% vs. 92% and 77%, respectively).

CONCLUSION

Less than half of the [18F]FDG-PET/LDCT reports of suspected VGEI met all pre-selected criteria. Incompleteness of reports led to lower sensitivity and specificity. Implementing a recommendation with specific criteria for VGEI reporting is needed in the VGEI-guideline update. This study provides a first recommendation for a concise and complete [18F]FDG-PET/LDCT report in patients with suspected VGEI.

Diagnosis and treatment of vascular graft and endograft infections: a structured clinical approach

A vascular graft or endograft infection (VGEI) is a severe complication that can occur after vascular graft or endograft surgery and is associated with high morbidity and mortality rates. A multidisciplinary approach, consisting of a team of vascular surgeons, infectious diseases specialists, medical microbiologists, radiologists, nuclear medicine specialists, and hospital pharmacists, is needed to adequately diagnose and treat VGEI. A structured diagnostic, antibiotic, and surgical treatment algorithm helps clinical decision making and ultimately aims to improve the clinical outcome of patients with a VGEI.

FDG PET/CT in abdominal aortic graft infection: A case report and literature review

This case report follows a 47-year-old man who had multiple grafts undergoing FDG PET/CT (positron emission tomography/computed tomography) scan to evaluate for graft infection. Initial CT showed enhancing soft tissue and fluid collection around the graft, and the subsequent FDG PET/CT showed findings concerning for graft infection. This case exemplifies that FDG PET/CT is a synergistic tool in diagnosing aortic graft infections, a rare and often fatal complication of aortic grafts.

Evidence-based guideline of the European Association of Nuclear Medicine (EANM) on imaging infection in vascular grafts

Purpose

Consensus on optimal imaging procedure for vascular graft/endograft infection (VGEI) is still lacking and the choice of a diagnostic test is often based on the experience of single centres. This document provides evidence-based recommendations aiming at defining which imaging modality may be preferred in different clinical settings and post-surgical time window.

Methods

This working group includes 6 nuclear medicine physicians appointed by the European Association of Nuclear Medicine, 4 vascular surgeons, and 2 radiologists. Vascular surgeons formulated 5 clinical questions that were converted into 10 statements and addressed through a systematic analysis of available literature by using PICOs (Population/problem–Intervention/Indicator–Comparator–Outcome) strategy. Each consensus statement was scored for level of evidence and for recommendation grade, according to the Oxford Centre for Evidence-based Medicine criteria.

Results

Sixty-six articles, published from January 2000 up to December 2021, were analysed and used for evidence-based recommendations.

Conclusion

Computed tomography angiography (CTA) is the first-line imaging modality in suspected VGEI but nuclear medicine modalities are often needed to confirm or exclude the infection. Positron emission tomography/computed tomography (PET/CT) with 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) has very high negative predictive value but it should be performed preferably at least 4 months after surgery to avoid false positive results. Radiolabelled white blood cell (WBC) scintigraphy, given its high diagnostic accuracy, can be performed at any time after surgery.

Preamble

The European Association of Nuclear Medicine (EANM) is a professional no-profit medical association that facilitates communication worldwide between individuals pursuing clinical and research excellence in nuclear medicine. The EANM was founded in 1985. EANM members are physicians, technologists, and scientists specializing in the research and practice of nuclear medicine. The EANM will periodically define new guidelines for nuclear medicine practice to help advance the science of nuclear medicine and to improve the quality of service to patients throughout the world. Existing practice guidelines will be reviewed for revision or renewal, as appropriate, on their fifth anniversary or sooner, if indicated. Each practice guideline, representing a policy statement by the EANM, has undergone a thorough consensus process in which it has been subjected to extensive review. The EANM recognizes that the safe and effective use of diagnostic nuclear medicine imaging requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guideline by those entities not providing these services is not authorized. These guidelines are an educational tool designed to assist practitioners in providing appropriate care for patients. They are not inflexible rules or requirements of practice and are not intended, nor should they be used, to establish a legal standard of care. For these reasons and those set forth below, the EANM suggests caution against the use of the current consensus document in litigation in which the clinical decisions of a practitioner are called into question. The ultimate judgement regarding the propriety of any specific procedure or course of action must be made by the physician or medical physicist in the light of all the circumstances presented. Thus, there is no implication that an approach differing from the consensus document, standing alone, is below the standard of care. To the contrary, a conscientious practitioner may responsibly adopt a course of action different from that set forth in the consensus document when, in the reasonable judgement of the practitioner, such course of action is indicated by the condition of the patient, limitations of available resources, or advances in knowledge or technology subsequent to publication of the consensus document. The practice of medicine includes both the art and the science of the prevention, diagnosis, alleviation, and treatment of disease. The variety and complexity of human conditions make it impossible to always reach the most appropriate diagnosis or to predict with certainty a particular response to treatment. Therefore, it should be recognized that adherence to this consensus document will not ensure an accurate diagnosis or a successful outcome. All that should be expected is that the practitioner will follow a reasonable course of action based on current knowledge, available resources, and the needs of the patient, to deliver effective and safe medical care. The sole purpose of this consensus document is to assist practitioners in achieving this objective.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-022-05769-x.

Difficult diagnosis and management of a complicated Nellix graft infection

An 81-year-old man, with a complex vascular surgical history, presents with sepsis from an infected Nellix stent-graft. He required an urgent laparotomy, explantation of the graft, and extra-anatomical repair. Although now widely used for this indication, the preoperative 18F-fluorodeoxyglucose positron emission tomography/computed tomography was nondiagnostic for his stent-graft infection. We describe our management of a complicated Nellix graft infection and discuss the utility of positron emission tomography/computed tomography for stent-graft infections.

PET/CT Imaging for Personalized Management of Infectious Diseases

Positron emission tomography combined with computed tomography (PET/CT) is a nuclear imaging technique which is increasingly being used in infectious diseases. Because infection foci often consume more glucose than surrounding tissue, most infections can be diagnosed with PET/CT using 2-deoxy-2-[18F]fluoro-D-glucose (FDG), an analogue of glucose labeled with Fluorine-18. In this review, we discuss common infectious diseases in which FDG-PET/CT is currently applied including bloodstream infection of unknown origin, infective endocarditis, vascular graft infection, spondylodiscitis, and cyst infections. Next, we highlight the latest developments within the field of PET/CT, including total body PET/CT, use of novel PET radiotracers, and potential future applications of PET/CT that will likely lead to increased capabilities for patient-tailored treatment of infectious diseases.

PET/CT with 18F-Fluordesoxyglucose in patients with suspected endovascular prosthesis infection

OBJECTIVE

Infection of large vessel prostheses is a rare but critical complication. The aim of this work is to assess the impact of PET/CT with 18F-Fluordesoxyglucose (PET-FDG) on the diagnosis of infection in our environment.

MATERIAL AND METHODS

Thirty-five patients (38 scans) were evaluated for suspected prosthetic infection. A qualitative analysis was performed taking into account the distribution of the radiopharmaceutical, categorizing the studies as positive or negative for infection. Those with focal or multifocal deposits along the vascular prosthesis were considered positive, and negative if a homogeneous and diffuse distribution over the whole prosthesis was observed, or a total absence of uptake. A semi-quantitative analysis was performed using SUVmax and average SUV values, and a metabolic index was calculated (SUVmax of the graft / average SUV of the normal vascular pool).

RESULTS

The PET-FDG study was positive in 20 patients, with a diagnostic accuracy of 84%. The 38 PET-FDG scans performed showed positive capture patterns (focal in 6, multifocal in 15, diffuse in 4) and negative pattern in the remaining 13. The sensitivity, specificity, positive and negative predictive values obtained for the PET-FDG were 95%, 89%, 90% and 94%, and for the AngioTC study 50%, 73%, 73% and 50%, respectively. The area values under the ROC curve were as follows: for the AngioTC 0.642 (not significant), and for the SUVmax values of 0.925 (p<0.005), average SUV of 0.922 (p<0.005) and for the metabolic index of 0.917 (p<0.005).

CONCLUSIONS

The PET-FDG proves to be a tool with high diagnostic accuracy in the infection of vascular prosthesis, both visual analysis according to patterns and semi-quantitative.

Physiological Appearance of Hybrid FDG-Positron Emission Tomography/Computed Tomography Imaging Following Uncomplicated Endovascular Aneurysm Sealing Using the Nellix Endoprosthesis

Purpose: To investigate the physiological uptake of hybrid fluorine-18-fluorodeoxyglucose (FDG)-positron emission tomography/computed tomography (PET/CT) before and after an uncomplicated endovascular aneurysm sealing (EVAS) procedure as a possible tool to diagnose EVAS graft infection and differentiate from postimplantation syndrome. Materials and Methods: Eight consecutive male patients (median age 78 years) scheduled for elective EVAS were included in the prospective study (ClinicalTrials.gov identifier NCT02349100). FDG-PET/CT scans were performed in all patients before the procedure and 6 weeks after EVAS. The abdominal aorta was analyzed in 4 regions: suprarenal, infrarenal neck, aneurysm sac, and iliac. The following parameters were obtained for each region: standard uptake value (SUV), tissue to background ratio (TBR), and visual examination of FDG uptake to ascertain its distribution. Demographic data were obtained from medical files and scored based on reporting standards. Results: Visual examination showed no difference between pre- and postprocedure FDG uptake, which was homogenous. In the suprarenal region no significant pre- and postprocedure differences were observed for the SUV and TBR parameters. The infrarenal neck region showed a significant decrease in the SUV and no significant decrease in the TBR. The aneurysm sac and iliac regions both showed a significant decrease in SUV and TBR between the pre- and postprocedure scans. Conclusion: Physiological FDG uptake after EVAS was stable or decreased with regard to the preprocedure measurements. Future research is needed to assess the applicability and cutoff values of FDG-PET/CT scanning to detect endograft infection after EVAS.

PET/MRI reveals ongoing metabolic activity in ACL grafts one year post-ACL reconstruction

Purpose

To use serial PET/MRI imaging to radiographically evaluate the metabolic activity of the ACL graft over the first post-operative year.

Methods

Six patients undergoing primary ACL reconstruction were recruited in this prospective study in an inpatient university hospital. All patients underwent femoral and tibial suspensory cortical fixation with quadrupled semitendinosus autograft hamstring ACL reconstruction by an orthopaedic surgeon. Simultaneous ¹⁸F-FDG PET and MRI of both the operative and non-operative knee was performed at three, six, and 12 months post-operatively. Quantification of the mean standardized uptake value (SUV) within the whole-knee, as well as tibial tunnel, femoral tunnel, and intra-articular graft regions of interest (ROIs).

Results

PET whole-knee activity was increased at all time-points post-operatively compared to the control, non-operative knee. Activity decreased over time, yet considerable generalized activity remained 1 year post-operatively, with relative intensity 34% percent higher than control. When the operative knee was divided into three whole-regions, there was greater activity in the tibia at three than 12 months, the femur at six than 12 months, and in the tibia compared to the intra-articular region at 3 months. When they were separated into sub-regions, results demonstrated greater activity closer to the joint surface.

Conclusions

PET/MRI evaluation of ACL graft reconstructions demonstrates evolving biologic activity within the graft and both tunnels. Focal areas of increased activity within the tunnels may indicate of ligamento-osseous morphologic changes. These data suggest that graft incorporation continues well beyond 1 year post-operatively.

Level of evidence

Level IV.

Diagnostic yield of 18F-FDG PET/CT in suspected diagnosis of vascular graft infection: A prospective cohort study

BACKGROUND

Prosthetic vascular graft infection (PVGI) is a severe complication associated with high morbidity and mortality. Clinical diagnosis is complex, requiring image testing such as CT angiography or leukocyte scintigraphy, which has considerable limitations. The aim of this study was to know the diagnostic yield of PET/CT with 18F-Fluorodeoxyglucose (18F-FDG) in patients with suspected PVGI.

METHODS

We performed a prospective cohort study including 49 patients with suspected PVGI, median age of 62 ± 14 years. Three uptake patterns were defined following published recommendations: (i) focal, (ii) patched (PVGI criteria), and (iii) diffuse (no PVGI criterion).

RESULTS

Sensitivity, specificity, and positive and negative predictive values for 18F-FDG-PET/CT were 88%, 79%, 67%, and 93%, respectively. 18F-FDG-PET/CT identified 14/16 cases of PVGI showing a focal (n = 10) or patched pattern (n = 4), being true negative in 26/33 cases with either a diffuse pattern (n = 16) or without uptake (n = 10). Five of the seven false-positive cases (71%) showed a patched pattern and all coincided with the application of adhesives for PVG placement.

CONCLUSIONS

18F-FDG-PET/CT is a useful technique for the diagnosis of PVGI. A patched pattern on PET/CT in patients in whom adhesives were applied for prosthetic vascular graft placement does not indicate infection.

Mimics of Complications in the Postsurgical Aorta at CT

Various surgical techniques of the aorta result in expected imaging appearances on CT images that resemble complications such as pseudoaneurysm, perigraft abscess, and dissection. Awareness of these techniques, understanding the clinical situation in which they are performed, and familiarity with the typical appearances and locations of these mimics are essential for accurate interpretation. CT imaging techniques such as electrocardiographic gating and inclusion of a precontrast series can help distinguish an expected postsurgical finding from a complication. Information in the medical record, particularly the operative note, can clarify challenging cases with unusual imaging features. This review article provides examples of expected postsurgical findings at CT mimicking complications. © RSNA, 2019.

How to recognize stent graft infection after endovascular aortic repair: the utility of 18F-FDG PET/CT in an infrequent but serious clinical setting

OBJECTIVE

To evaluate the diagnostic performance of ¹⁸F-FDG PET/CT in the detection of stent graft infection (SGI).

METHODS

In a retrospective study, two nuclear medicine physicians have independently analyzed 17 ¹⁸F-FDG PET/CT examinations performed for clinical suspicion of SGI. The images were evaluated for the uptake pattern and intensity, and by the maximum standard uptake value (SUV_max), the target-to-background ratio with blood pool (TBR_BP) and liver uptake (TBR_hep) as a reference. The SGI was defined as the presence of focal hyperactivity with an intensity exceeding hepatic uptake. CT images were independently assessed for signs of SGI. Clinical review of all further patients' data served as the standard of reference.

RESULTS

Nine cases were established as SGI by the clinical review. PET/CT correctly diagnosed SGI in eight and yielded a sensitivity of 89% and specificity of 100%. The mean SUV_max, TBR_BP, and TBR_hep values were 9.8 ± 4.0, 6.9 ± 2.6, and 4.6 ± 1.7 in the group of patients with true SGI, and 4.0 ± 1.1, 2.5 ± 0.4 (p < 0.001) and 1.9 ± 0.2 (p < 0.001) in true negative cases, respectively. CT alone showed a sensitivity of 78% and specificity of 100% and was concordant with PET/CT in 14 cases. The best performing threshold values of SUV_max, TBR_BP, and TBR_hep were 5.6, 3.5, and 2.2, respectively.

CONCLUSION

¹⁸F-FDG PET/CT with expert evaluation, semiquantitative and quantitative image analysis with the proposed threshold values for SUV_max, TBR_BP, and TBR_hep has good diagnostic accuracy in the detection of SGI. We propose that visual grading scale for SGI should use hepatic uptake as a visual reference.

Retrospective Study Comparing WBC scan and 18F-FDG PET/CT in Patients with Suspected Prosthetic Vascular Graft Infection

OBJECTIVES

Prosthetic vascular graft infections (PVGIs) are associated with high mortality rates. To improve treatment outcome, an early and definite diagnosis is critical, and current diagnostic criteria are often insufficient. The accuracy of 2-deoxy-2-[fluorine-18]-fluoro-d-glucose positron emission tomography integrated with computed tomography (¹⁸F-FDG PET/CT) and white blood cell (WBC) scan for the diagnosis of PVGI were compared.

METHODS

A retrospective single centre study was conducted on patients undergoing WBC scan and ¹⁸F-FDG PET/CT for a suspected PVGI between April 2013 and June 2016 at the Bordeaux University Hospital, France. The diagnostic value of both imaging tests was assessed for all grafts, using receiver operating characteristic (ROC) curve analysis. Images were independently interpreted by two nuclear medicine physicians blinded to the patients' clinical and other imaging data.

RESULTS

Thirty-nine patients were included, of whom 15 had PVGI. Antibiotic treatment was started before nuclear imaging for 16 patients, including nine patients with a PVGI. The 96 grafts of these patients were analysed, and 19 were infected. The diagnostic value of the WBC scan was significantly higher than ¹⁸F-FDG PET/CT (ROC AUC = 0.902, 95% CI 0.824-0.980, and 0.759, CI 95% (0.659-0.858), respectively, p = .0071). Interobserver agreement was good for ¹⁸F-FDG PET/CT and excellent for WBC scan (kappa value of 0.76, 95% CI 0.62-0.9, and 0.97, 95% CI 0.92-1, respectively). Only one patient had a false negative ¹⁸F-FDG PET/CT result under antibiotic therapy.

CONCLUSION

The WBC scan has a better diagnostic value than ¹⁸F-FDG PET/CT for PVGI diagnosis.

A systematic review and meta-analysis of 18F-fluorodeoxyglucose positron emission tomography or positron emission tomography/computed tomography for detection of infected prosthetic vascular grafts

OBJECTIVE

The purpose of this investigation was to evaluate the diagnostic accuracy of ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET) or PET/computed tomography (PET/CT) for the detection of vascular prosthetic graft infection (VPGI) using a diagnostic accuracy test.

METHODS

The MEDLINE/PubMed and Embase databases, from the earliest available date of indexing through March 31, 2018, were searched for results investigating the diagnostic accuracy of ¹⁸F-FDG PET or PET/CT for the detection of VPGI. We calculated the pooled sensitivities and specificities of included studies, calculated positive and negative likelihood ratios, and obtained summary receiver operating characteristic curves.

RESULTS

Across 10 studies (286 patients), the pooled sensitivity was 0.96 (95% confidence interval [CI], 0.89-0.98) without heterogeneity (I² = 40.2; 95% CI, 0.0-84.4; P = .09), and pooled specificity was 0.74 (95% CI, 0.67-0.81) without heterogeneity (I² = 39.9; 95% CI, 0.0-84.3; P = .09). Likelihood ratio syntheses showed an overall positive likelihood ratio of 3.7 (95% CI, 2.9-4.9) and negative likelihood ratio of 0.06 (95% CI, 0.02-0.15). The pooled diagnostic odds ratio was 63 (95% CI, 23-173). The hierarchical summary receiver operating characteristic curve showed the area under the curve to be 0.87 (95% CI, 0.83-0.89).

CONCLUSIONS

This study showed the high sensitivity and moderate specificity of ¹⁸F-FDG PET or PET/CT for the detection of VPGI. The clinical usefulness of ¹⁸F-FDG PET or PET/CT for detection of VPGI should be validated through further large multicenter studies.

Endovascular Aneurysm Repair Complicated with Type Ia Endoleak and Presumable Infection Treated with a Fenestrated Endograft

An 81-year-old patient presented to the emergency room 5 years after infrarenal endovascular aneurysm repair, with a Type Ia endoleak and a presumable infection of the graft material with Listeria monocytogenes . He was treated with a custom-made fenestrated endograft to seal the endoleak and lifelong antibiotic therapy to suppress the infection. Full explantation of graft material is not always preferable, and endovascular treatment combined with antibiotic suppressive therapy is in some cases an appropriate alternative.

Textural features of 18F-fluorodeoxyglucose positron emission tomography scanning in diagnosing aortic prosthetic graft infection

BACKGROUND

The clinical problem in suspected aortoiliac graft infection (AGI) is to obtain proof of infection. Although ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography scanning (PET) has been suggested to play a pivotal role, an evidence-based interpretation is lacking. The objective of this retrospective study was to examine the feasibility and utility of ¹⁸F-FDG uptake heterogeneity characterized by textural features to diagnose AGI.

METHODS

Thirty patients with a history of aortic graft reconstruction who underwent ¹⁸F-FDG PET/CT scanning were included. Sixteen patients were suspected to have an AGI (group I). AGI was considered proven only in the case of a positive bacterial culture. Positive cultures were found in 10 of the 16 patients (group Ia), and in the other six patients, cultures remained negative (group Ib). A control group was formed of 14 patients undergoing ¹⁸F-FDG PET for other reasons (group II). PET images were assessed using conventional maximal standardized uptake value (SUVmax), tissue-to-background ratio (TBR), and visual grading scale (VGS). Additionally, 64 different ¹⁸F-FDG PET based textural features were applied to characterize ¹⁸F-FDG uptake heterogeneity. To select candidate predictors, univariable logistic regression analysis was performed (α = 0.16). The accuracy was satisfactory in case of an AUC > 0.8.

RESULTS

The feature selection process yielded the textural features named variance (AUC = 0.88), high grey level zone emphasis (AUC = 0.87), small zone low grey level emphasis (AUC = 0.80), and small zone high grey level emphasis (AUC = 0.81) most optimal for distinguishing between groups I and II. SUVmax, TBR, and VGS were also able to distinguish between these groups with AUCs of 0.87, 0.78, and 0.90, respectively. The textural feature named short run high grey level emphasis was able to distinguish group Ia from Ib (AUC = 0.83), while for the same task the TBR and VGS were not found to be predictive. SUVmax was found predictive in distinguishing these groups, but showed an unsatisfactory accuracy (AUC = 0.75).

CONCLUSION

Textural analysis to characterize ¹⁸F-FDG uptake heterogeneity is feasible and shows promising results in diagnosing AGI, but requires additional external validation and refinement before it can be implemented in the clinical decision-making process.

Cross-sectional imaging of aortic infections

Aortic infections are uncommon clinical entities, but are associated with high rates of morbidity and mortality. In this review, we focus on the cross-sectional imaging appearance of aortic infections, including aortic valve endocarditis, pyogenic aortitis, mycotic aneurysm and aortic graft infections, with an emphasis on CT, MRI and PET/CT appearance. Teaching Points • Aortic infections are associated with high morbidity and mortality. • CT, MRI and FDG PET/CT play complementary roles in aortic infection imaging. • Radiologists should be vigilant for aortic infection manifestations to ensure timely diagnosis.

Differential FDG-PET Uptake Patterns in Uninfected and Infected Central Prosthetic Vascular Grafts

OBJECTIVE

(18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) scanning has been suggested as a means to detect vascular graft infections. However, little is known about the typical FDG uptake patterns associated with synthetic vascular graft implantation. The aim of the present study was to compare uninfected and infected central vascular grafts in terms of various parameters used to interpret PET images.

METHODS

From 2007 through 2013, patients in whom a FDG-PET scan was performed for any indication after open or endovascular central arterial prosthetic reconstruction were identified. Graft infection was defined as the presence of clinical or biochemical signs of graft infection with positive cultures or based on a combination of clinical, biochemical, and imaging parameters (other than PET scan data). All other grafts were deemed uninfected. PET images were analyzed using maximum systemic uptake value (SUVmax), tissue to background ratio (TBR), visual grading scale (VGS), and focality of FDG uptake (focal or homogenous).

RESULTS

Twenty-seven uninfected and 32 infected grafts were identified. Median SUVmax was 3.3 (interquartile range [IQR] 2.0-4.2) for the uninfected grafts and 5.7 for the infected grafts (IQR 2.2-7.8). Mean TBR was 2.0 (IQR 1.4-2.5) and 3.2 (IQR 1.5-3.5), respectively. On VGS, 44% of the uninfected and 72% of the infected grafts were judged as a high probability for infection. Homogenous FDG uptake was noted in 74% of the uninfected and 31% of the infected grafts. Uptake patterns of uninfected and infected grafts showed a large overlap for all parameters.

CONCLUSION

The patterns of FDG uptake for uninfected vascular grafts largely overlap with those of infected vascular grafts. This questions the value of these individual FDG-PET-CT parameters in identifying infected grafts.