Multimodality Imaging in the Diagnosis of Prosthetic Valve Endocarditis: A Brief Review

Infective endocarditis is a common and treatable condition that carries a high mortality rate. Currently the workup of infective endocarditis relies on the integration of clinical, microbiological and echocardiographic data through the use of the modified Duke criteria (MDC). However, in cases of prosthetic valve endocarditis (PVE) echocardiography can be normal or non-diagnostic in a high proportion of cases leading to decreased sensitivity for the MDC. Evolving multimodality imaging techniques including leukocyte scintigraphy (white blood cell imaging), 18F-fluorodeoxyglucose positron emission tomography (FDG-PET), multidetector computed tomographic angiography (MDCTA), and cardiac magnetic resonance imaging (CMRI) may each augment the standard workup of PVE and increase diagnostic accuracy. While further studies are necessary to clarify the ideal role for each of these imaging techniques, nevertheless, these modalities hold promise in determining the diagnosis, prognosis, and care of PVE. We start by presenting a clinical vignette, then evidence supporting various modality strategies, balanced by limitations, and review of formal guidelines, when available. The article ends with the authors' summary of future directions and case conclusion.

Analysis of Cell Fraction of 99mTc-HMPAO Radiolabeled Leukocytes

Purpose: 99mTc-HMPAO radiolabeled autologous leukocyte scintigraphy is routinely used clinically for infection imaging. Leukocytes are mostly separated via sedimentation. It is unknown whether leukocytes are clearly separated by sedimentation or selectively labeled. Therefore, in this study, the blood cell numbers were investigated after leukocyte radiolabeling to identify the cells strongly radiolabeled by 99mTc-HMPAO. Methods: This study was performed with leftover blood samples of the patients who underwent 99mTc-HMPAO scintigraphy at Chonbuk National University Hospital (2018-2019). The blood of 22 patients was drawn for 99mTc-HMPAO scintigraphy. WBCs were separated via conventional sedimentation at our clinic and radiolabeled. The concentration of cell components was determined using an automatic hematology analyzer. The cells in the final sample injectate sample were separated using Histopaque and counted with a dose calibrator. Results: The average numbers of RBCs, WBCs, and PLTs in the final injection sample were 79 ± 33, 23.26 ± 11.95, and 229.5 ± 206.57 x 103/μL, respectively. The PLT number was almost 10-fold the number of WBCs. The number of RBCs was nearly 3-fold higher than WBCs [RBC/WBC ratio = 4.67 ± 3.58, and PLT/WBC ratio = 10.65 ± 12.46]. Following Histopaque separation, the activity of each layer showed 99mTc-HMPAO labeling of WBC > RBC > PLT in order. The total activity/cell numbers of WBCs, RBCs and PLTs were 0.016 ± 0.010, 0.005 ± 0.005 and 0.003 ± 0.002, respectively (p > 0.05). Conclusion: Although the numbers of RBCs and PLTs were highly increased after sedimentation, their individual cellular activity was lower than that of WBCs. 99mTc-HMPAO was more selective to WBCs than RBCs or PLTs. In conclusion, a higher number of WBCs were radiolabeled compared with RBCs and PLTs.

Nuclear Medicine for the Orthopedic Foot and Ankle Surgeon

Nuclear medicine has been widely applied as a diagnostic tool for orthopedic foot and ankle pathology. Although its indications have diminished with improvements in and the availability of magnetic resonance imaging, nuclear medicine still has a significant and valuable role. The present article offers a comprehensive and current review of the most common nuclear imaging modalities for the orthopedic foot and ankle surgeon. Methods discussed include bone scintigraphy, gallium citrate scintigraphy, labeled-leukocyte scintigraphy, and single-photon emission computed tomography (SPECT). We review the indications and utility of these techniques as they pertain to specific foot and ankle conditions, including osteomyelitis, stress fractures, talar osteochondral lesions, complex regional pain syndrome, oncology, plantar fasciitis, and the painful total ankle arthroplasty. We conclude with a discussion of our approach to nuclear medicine with illustrative cases. Level of Evidence: Level V, expert opinion.

P3362Added value of radiolabeled leukocyte scintigraphy to cardiac device-related infective endocarditis diagnostic criteria

Background Radiolabeled leukocyte scintigraphy – hybrid technique of single photon emission tomography and computed tomography with application of technetium99m-hexamethylpropyleneamine oxime-labeled autologous leukocytes (99mTc-HMPAO-SPECT/CT) is an emerging technique in patients with suspected cardiac device-related infective endocarditis (CDRIE). Purpose The aim of this prospective study was to assess 99mTc-HMPAO-SPECT/CT added value to modified Duke criteria (mDuke) in CDRIE diagnostic process. Methods During the period 2015–2018, we enrolled 103 consecutive patients with suspected CDRIE [70 males (68%), mean age: 61±18 years, mean left ventricle ejection fraction value: 44±17%)]. All patients underwent clinical, microbiologic, echocardiographic evaluation according to ESC guidelines and additionally 99mTc-HMPAO-SPECT/CT (370–740 MBq). Scans were classified as positive in the presence of abnormal tracer uptake involving cardiac and intravascular sections of device electrodes. In the analysis, we added positive 99mTc-HMPAO-SPECT/CT result as an additional major criterion to mDuke classification. Additionally, we compared the diagnostic value of the mDuke classification including 99mTc-HMPAO-SPECT/CT (mDuke-SPET/CT) with the original mDuke classification. The sensitivity and specificity of those two scales were compared with McNemar's test. Diagnostic accuracy was calculated based on final clinical CDRIE diagnosis, including microbiology, echocardiography and 6 month-long follow-up with subsequent outpatient visit. Results Overall 58% patients had pacemakers, 25% had implantable cardioverter defibrillators, 16% had resynchronization therapy and 1% had an epicardial lead. Mean time from device implantation was 3.4±3.8 years. Final CDRIE diagnosis was established in 31 (30%) patients. The most common pathogens causing CDRIE were Enterococci (39%) and Staphylococci (35%). According to the original mDuke classification 16.5% patients had definite CDRIE, 49.5% had possible and in 34% CDRIE was excluded. Overall, 34% of 99mTc-HMPAO-SPECT/CT scans were positive for CDRIE. After reclassification, according to mDuke-SPET/CT the proportion of patients with definite CDRIE increased to 34%, whereas in 37% patients CDRIE was possible and in 29% cases CDRIE was excluded. Overall, mDuke was characterized with 83% accuracy, 0.52 Cohen's kappa coefficient, 48% sensitivity, 97% specificity, 81% negative predictive value (NPV), 88% positive predictive value (PPV). Whereas mDuke-SPET/CT had 88% accuracy, 0.73 Cohen's kappa coefficient, 87% sensitivity, 89% specificity, 94% NPV, 77% PPV. Compared to mDuke, mDuke-SPET/CT had significantly higher sensitivity (p<0.001). Conclusions In patients with suspected CDRIE inclusion of positive radiolabeled leukocyte scintigraphy into modified Duke diagnostic criteria yields significantly higher sensitivity, as well as modest reduction of possible CDRIE diagnoses. Acknowledgement/Funding Grant from the Jagiellonian University Medical College (K/DSC/004383)