Clinical Usefulness of ¹⁸F-FDG PET/CT for the Detection of Infections of Unknown Origin in Patients Undergoing Maintenance Hemodialysis

Correlation between Kidney Uptake at [18F]FDG PET/CT and Renal Function

Different insights into the connection between kidney [18F]fluorodesoxyglucose ([18F]FDG) uptake at positron emission tomography/computed tomography (PET/CT) and renal function have been proposed in the past. The aim of this study was therefore to assess the presence of a correlation between these two parameters. Kidney uptakes were assessed and compared to the creatinine (Cr) values and estimated glomerular filtration rate (EGFR) among different classes of renal functional impairment or kidney status. A total of 339 patients and 385 different PET/CT scans were included in this study. Significant correlations between kidney uptakes and renal function parameters were reported in most of the groups studied, with the exception of patients with Cr < 1.2 mg/dL and subjects with a kidney transplantation. Strong concordance in the assessment of renal parenchymal uptakes between the different readers was reported. To conclude, strong correlations for renal [18F]FDG uptake with Cr levels and the EGFR were reported, with the exception of the group of patients with a Cr value < 1.2 mg/dL and for the group with a kidney transplantation.

Non-invasive molecular imaging of kidney diseases

In nephrology, differential diagnosis or assessment of disease activity largely relies on the analysis of glomerular filtration rate, urinary sediment, proteinuria and tissue obtained through invasive kidney biopsies. However, currently available non-invasive functional parameters, and most serum and urine biomarkers, cannot capture intrarenal molecular disease processes specifically. Moreover, although histopathological analyses of kidney biopsy samples enable the visualization of pathological morphological and molecular alterations, they only provide information about a small part of the kidney and do not allow longitudinal monitoring. These limitations not only hinder understanding of the dynamics of specific disease processes in the kidney, but also limit the targeting of treatments to active phases of disease and the development of novel targeted therapies. Molecular imaging enables non-invasive and quantitative assessment of physiological or pathological processes by combining imaging technologies with specific molecular probes. Here, we discuss current preclinical and clinical molecular imaging approaches in nephrology. Non-invasive visualization of the kidneys through molecular imaging can be used to detect and longitudinally monitor disease activity and can therefore provide companion diagnostics to guide clinical trials, as well as the safe and effective use of drugs.

Diagnostic Role of 18F-Fluorodeoxyglucose Positron Emission Tomography for the Evaluation of Patients With Inflammation of Unknown Origin

BACKGROUND

Sometimes, the underlying causes of inflammation cannot be established despite meticulous investigation, including medical history, physical examination, laboratory tests, and radiologic procedures. Rheumatologists are often faced with patients whose condition is known as inflammation of unknown origin (IUO). Differential diagnosis of IUO is diverse, and investigation of these cases is challenging and time-consuming.

OBJECTIVE

The study aimed to assess the diagnostic role of positron emission tomography/computed tomography (PET/CT) in the evaluation of patients with IUO.

METHODS

The study sample consisted of 97 adult patients with IUO who have not been previously diagnosed with an infectious, inflammatory, or malignant disease. The necessary data were collected from January 2015 to June 2018 with a 6-month follow-up period. The patients were screened using PET/CT after a specific diagnosis could not be established with detailed laboratory and radiologic evaluations.

RESULTS

A final diagnosis was established at follow-up, and 47 (54%) of the 97 patients had inflammatory diseases, 30 (34.4%) had malignancies, and 10 (11.4%) had infections. Despite meticulous investigation, 10 patients were left undiagnosed in the follow-up. PET/CT aided diagnosis in 59 patients (60.8%), but it was not helpful in 38 patients (39.2%). PET/CT was positive in 30 (63%) of the 47 patients with inflammatory diseases, whose final diagnosis was inflammatory rheumatic disease, as follows: large-vessel vasculitis in 19 patients, polymyalgia rheumatica in 7 patients, and seronegative arthritis or other rare miscellaneous diseases in 4 patients. The sensitivity of PET/CT was 67% with a specificity and diagnostic accuracy of 100% and 71%, respectively.

CONCLUSIONS

Investigation of the underlying etiology of IUO is time-consuming and challenging. PET/CT may help identify the final diagnosis more quickly by locating an obscure inflammatory site; thus, it may reduce the number of unnecessary biopsies, diagnostic time, anxiety, work loss, morbidity, and mortality.

Imaging a Fever-Redefining the Role of 2-deoxy-2-[18F]Fluoro-D-Glucose-Positron Emission Tomography/Computed Tomography in Fever of Unknown Origin Investigations

Growing evidence suggests that 2-deoxy-2-[18F]fluoro-D-glucose (18FDG)-positron emission tomography/computed tomography (PET/CT) is a useful imaging technique for the evaluation of fever of unknown origin (FUO). This imaging technique allows for accurate localization of foci of hypermetabolism based on 18FDG uptake in glycolytically active cells that may represent inflammation, infection, or neoplasia. The presence of abnormal uptake can help direct further investigation that may yield a final diagnosis. A lack of abnormal uptake can be reasonably reassuring that these conditions are not present, thereby avoiding unnecessary additional testing. Insurers have not routinely covered outpatient 18FDG-PET/CT for the indication of FUO in the United States. However, data published since 2007 suggest early use in FUO diagnostic evaluations improves diagnostic efficiency and reduces costs. Clinicians and insurers should consider 18FDG-PET/CT as a useful tool when preliminary studies are unrevealing.

Improving the Diagnostic Performance of 18F-Fluorodeoxyglucose Positron-Emission Tomography/Computed Tomography in Prosthetic Heart Valve Endocarditis

BACKGROUND

¹⁸F-Fluorodeoxyglucose (FDG) positron-emission tomography/computed tomography (PET/CT) was recently introduced as a new tool for the diagnosis of prosthetic heart valve endocarditis (PVE). Previous studies reporting a modest diagnostic accuracy may have been hampered by unstandardized image acquisition and assessment, and several confounders, as well. The aim of this study was to improve the diagnostic performance of FDG PET/CT in patients in whom PVE was suspected by identifying and excluding possible confounders, using both visual and standardized quantitative assessments.

METHODS

In this multicenter study, 160 patients with a prosthetic heart valve (median age, 62 years [43-73]; 68% male; 82 mechanical valves; 62 biological; 9 transcatheter aortic valve replacements; 7 other) who underwent FDG PET/CT for suspicion of PVE, and 77 patients with a PV (median age, 73 years [65-77]; 71% male; 26 mechanical valves; 45 biological; 6 transcatheter aortic valve replacements) who underwent FDG PET/CT for other indications (negative control group), were retrospectively included. Their scans were reassessed by 2 independent observers blinded to all clinical data, both visually and quantitatively on available European Association of Nuclear Medicine Research Ltd-standardized reconstructions. Confounders were identified by use of a logistic regression model and subsequently excluded.

RESULTS

Visual assessment of FDG PET/CT had a sensitivity/specificity/positive predictive value/negative predictive value for PVE of 74%/91%/89%/78%, respectively. Low inflammatory activity (C-reactive protein <40 mg/L) at the time of imaging and use of surgical adhesives during prosthetic heart valve implantation were significant confounders, whereas recent valve implantation was not. After the exclusion of patients with significant confounders, diagnostic performance values of the visual assessment increased to 91%/95%/95%/91%. As a semiquantitative measure of FDG uptake, a European Association of Nuclear Medicine Research Ltd-standardized uptake value ratio of ≥2.0 was a 100% sensitive and 91% specific predictor of PVE.

CONCLUSIONS

Both visual and quantitative assessments of FDG PET/CT have a high diagnostic accuracy in patients in whom PVE is suspected. FDG PET/CT should be implemented early in the diagnostic workup to prevent the negative confounding effects of low inflammatory activity (eg, attributable to prolonged antibiotic therapy). Recent valve implantation was not a significant predictor of false-positive interpretations, but surgical adhesives used during implantation were.

Increase Trichomonas vaginalis detection based on urine routine analysis through a machine learning approach

Trichomonas vaginalis (T. vaginalis) detection remains an unsolved problem in using of automated instruments for urinalysis. The study proposes a machine learning (ML)-based strategy to increase the detection rate of T. vaginalis in urine. On the basis of urinalysis data from a teaching hospital during 2009–2013, individuals underwent at least one urinalysis test were included. Logistic regression, support vector machine, and random forest, were used to select specimens with a high risk of T. vaginalis infection for confirmation through microscopic examinations. A total of 410,952 and 428,203 specimens from men and women were tested, of which 91 (0.02%) and 517 (0.12%) T. vaginalis-positive specimens were reported, respectively. The prediction models of T. vaginalis infection attained an area under the receiver operating characteristic curve of more than 0.87 for women and 0.83 for men. The Lift values of the top 5% risky specimens were above eight. While the most risky vigintile was picked out by the models and confirmed by microscopic examination, the incremental cost-effectiveness ratios for T. vaginalis detection in men and women were USD$170.1 and USD$29.7, respectively. On the basis of urinalysis, the proposed strategy can significantly increase the detection rate of T. vaginalis in a cost-effective manner.

Contribution of 18F-FDG PET/CT in a case-mix of fever of unknown origin and inflammation of unknown origin: a meta-analysis

BACKGROUND

Fever of unknown origin (FUO) and inflammation of unknown origin (IUO) are challenging medical problems. Previous studies have shown that 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) plays an important role in the diagnosis of FUO, but few studies have explored this diagnostic technique in relation to IUO.

PURPOSE

To systematically review and perform a meta-analysis of published data on the diagnostic performance of PET/CT in the diagnosis of FUO and IUO.

MATERIAL AND METHODS

A comprehensive literature search was performed in accordance with the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) guidelines published in March 2018. Meta-analysis of diagnostic performance was performed using STATA 12.0 software. Subgroup analysis was performed by stratification based on study design, number of patients, geographic area, and final diagnosis based on 18F-FDG PET/CT. Meta-regression analyses were performed to recognize heterogeneity.

RESULTS

Our meta-analysis included 23 studies, comprising a total sample size of 1927 patients. The pooled diagnosis performance was calculated with a per-patient-based analysis: sensitivity = 0.84 (95% confidence interval [CI] = 0.79-0.89), specificity = 0.63 (95% CI = 0.49-0.75), positive likelihood ratio = 2.3 (95% CI = 1.5-3.4), negative likelihood ratio = 0.25 (95% CI = 0.16-0.38), diagnostic odds ratio = 9 (95% CI = 4.0-20), and AUC = 0.84 (95% CI = 0.81-0.87).

CONCLUSION

In patients with non-specific symptoms and signs, 18F-FDG PET/CT is very helpful for recognizing and excluding diseases, directing further diagnostic decisions, and avoiding unnecessary invasive examinations. We recommend that 18F-FDG PET/CT should be considered among the first-line diagnostic tools for patients with FUO and IUO.

Potential usefulness of 68Ga-citrate PET/CT in detecting infected lower limb prostheses

Background

Prosthetic joint infections may lead to failures of total joint arthroplasty. Radionuclide imaging can play a diagnostic role in identifying such infections, which require two-stage exchange arthroplasty (instead of simple revision surgery performed in non-infected cases). Although ¹⁸F-FDG PET/CT has emerged as a novel diagnostic tool in this setting, the clinical usefulness of ⁶⁸Ga-citrate PET/CT has not been previously investigated. This single-center prospective study was designed to address this issue.

Methods

Between January 2016 and October 2017, we examined 34 patients with clinically proven or suspected prosthetic hip/knee joint infections scheduled to undergo surgery. All patients underwent ⁶⁸Ga-citrate PET/CT scans and sequential ¹⁸F-FDG PET/CT imaging for comparative purposes. Intraoperative findings and the results of microbiological analyses of surgical specimens served as gold standard. The diagnostic results were examined according to (1) image interpretation based on radiotracer uptake patterns and (2) quantitative analysis using volumes of interest (VOIs) to calculate standard uptake values (SUVs) and metabolic volumes (MVs).

Results

A total of 26 (76%) patients were diagnosed as having infections. Based on radiotracer uptake pattern criteria, the sensitivity, specificity, and accuracy of ⁶⁸Ga-citrate PET/CT and ¹⁸F-FDG PET/CT were 92%, 88%, and 91% and 100%, 38%, and 85%, respectively. MV was significantly higher in the infected group when ⁶⁸Ga-citrate PET/CT was used (422.45 vs. 303.65 cm³, p = 0.027), whereas no significant differences were observed on ¹⁸F-FDG PET/CT. According to receiver operating characteristic (ROC) curve analysis, a cut-off value of 370.86 for MV resulted in a sensitivity of 61.5% and a specificity of 87.5% (area under curve: 0.75, 95% confidence interval: 0.57–0.88, p = 0.035).

Conclusions

Subject to future confirmation, our data provide preliminary evidence that ⁶⁸Ga-citrate PET/CT may have a complimentary role to ¹⁸F-FDG PET/CT in detecting prosthetic joint infections, being characterized by a higher specificity and the possibility to discriminate between an infectious condition and sterile inflammation.

Trial registration

This prospective study was registered at clinicaltrials.gov (registration number: NCT02855190).

C-reactive protein levels can predict positive 18F-FDG PET/CT findings that lead to management changes in patients with bacteremia

BACKGROUND/PURPOSE

Bacteremia portends high rates of morbidity and mortality. Although ¹⁸F-fluorodeoxyglucose positron emission tomography and computed tomography (¹⁸F-FDG PET/CT) imaging has clinical value in assessing fever of unknown origin, its usefulness in bacteremia has not been entirely elucidated. We therefore designed the current single-center retrospective study to investigate 1) the clinical value of ¹⁸F-FDG PET/CT imaging in assessing bacteremia and 2) the association between laboratory data and imaging findings.

METHODS

We examined 102 patients with bacteremia who had undergone ¹⁸F-FDG PET/CT imaging. The patients' clinical and laboratory data were reviewed and analyzed in relation to ¹⁸F-FDG PET/CT findings. Patients showing positive results underwent quantitative measurements of ¹⁸F-FDG uptake.

RESULTS

Positive ¹⁸F-FDG PET/CT findings were identified in 74 (72.5%) patients, and 40 (54.1%) underwent modified treatment or management because of the imaging results (p = 0.003). Positive ¹⁸F-FDG PET/CT findings were significantly associated with higher white blood cell (WBC) counts and C-reactive protein (CRP) levels (p = 0.012 and < 0.001, respectively). Notably, CRP levels accurately predicted (area under curve = 0.752; p < 0.001) positive ¹⁸F-FDG PET/CT findings (optimal cut-off point: 54.025 mg/L).

CONCLUSION

A majority (54.1%, n = 40) of the patients with positive ¹⁸F-FDG PET/CT results underwent treatment modifications; they accounted for most cases (87%) of management changes in our cohort. Leukocytosis and increased CRP levels are significantly associated with positive ¹⁸F-FDG PET/CT findings in patients with bacteremia. CRP levels >54.025 mg/L were accurate predictors of positive ¹⁸F-FDG PET/CT results.

Clinical utility of FDG PET/CT in acute complicated pyelonephritis-results from an observational study

BACKGROUND

Acute complicated pyelonephritis (ACP) is an upper urinary tract infection associated with coexisting urinary tract abnormalities or medical conditions that could predispose to serious outcomes or treatment failures. Although CT and magnetic resonance imaging (MRI) are frequently used in patients with ACP, the clinical value of ¹⁸F-fluorodeoxyglucose positron emission tomography and computed tomography (FDG PET/CT) has not been systematically investigated. This single-center retrospective study was designed to evaluate the potential usefulness of FDG PET/CT in patients with ACP.

METHODS

Thirty-one adult patients with ACP who underwent FDG PET/CT were examined. FDG PET/CT imaging characteristics, including tracer uptake patterns, kidney volumes, and extrarenal imaging findings, were reviewed in combination with clinical data and conventional imaging results.

RESULTS

Of the 31 patients, 19 (61%) showed focal FDG uptake. The remaining 12 study participants showed a diffuse FDG uptake pattern. After volumetric approximation, the affected kidneys were found to be significantly enlarged. Patients who showed a focal uptake pattern had a higher frequency of abscess formation requiring drainage. ACP patients showing diffuse tracer uptake patterns had a more benign clinical course. Seven patients had suspected extrarenal coinfections, and FDG PET/CT successfully confirmed the clinical suspicion in five cases. FDG PET/CT was as sensitive as CT in identifying the six patients (19%) who developed abscesses. Notably, FDG PET/CT findings caused a modification to the initial antibiotic regimen in nine patients (29%).

CONCLUSIONS

FDG PET/CT may be clinically useful in the assessment of patients with ACP who have a progressive disease course.