J. M. James

Early diagnosis of cardiac implantable electronic device generator pocket infection using 18F-FDG-PET/CT.

Aims To examine the utility of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) in the early diagnosis of cardiac implantable electronic device (CIED) generator pocket infection. Methods and results A total of 86 patients with CIEDs were evaluated with 18F-FDG PET/CT imaging: 46 with suspected generator pocket infection and 40 without any history of infection. 18F-FDG activity in the region of the generator pocket was expressed as a semi-quantitative ratio (SQR)—defined as the maximum count rate around the CIED divided by the mean count rate between normal right and left lung parenchyma. All patients underwent standard clinical management, independent of the PET/CT result. Patients with suspected generator pocket infection that required CIED extraction (n = 32) had significantly higher 18F-FDG activity compared with those that did not (n = 14), and compared with controls (n = 40) [SQR: 4.80 (3.18–7.05) vs. 1.40 (0.88–1.73) vs. 1.10 (0.98–1.40), respectively; P < 0.001]. On receiver operator characteristic analysis, SQR had a high diagnostic accuracy (area under curve = 0.98) for the early identification of patients with confirmed infection (i.e. those ultimately needing extraction)—with an optimal SQR cut-off value of >2.0 (sensitivity = 97%; specificity = 98%). Conclusion This study highlights the potential benefits of evaluating patients with suspected CIED generator pocket infection using 18F-FDG PET/CT. In this study, 18F-FDG PET/CT had a high diagnostic accuracy in the early diagnosis of CIED generator pocket infection, even where initial clinical signs were underwhelming.

The performance of quantitation methods in the evaluation of cardiac implantable electronic device (CIED) infection: A technical review

BackgroundQuantitative assessment of [18F]-FDG PET/CT images has been shown to be useful in the diagnosis of cardiac implantable electronic device (CIED) infection. This study aimed to compare the accuracy of various quantitative methods, using the same patient cohort and to assess the utility of dual time point imaging.MethodsThe study comprised a retrospective review of 80 [18F]-FDG PET/CT studies. Of these, 41 were oncological patients with an asymptomatic CIED in situ (Group 1), and 39 were studies performed in patients with symptomatic devices. Of these, 14 were subsequently deemed on follow-up to be non-infected (Group 2), and 25 confirmed as infected post-device extraction (Group 3). Ratios of maximal uptake around the CIED in both the attenuation corrected and non-attenuation corrected images were calculated to regions of normal physiological uptake, along with the maximal standardized uptake value (SUVmax) alone. Receiver operating characteristic analysis was performed for all methods at both time points. Measurement reliability was assessed using the intraclass correlation coefficient (ICC).ResultsUsing Group 1 as a reference, all methods gave an area under the curve (AUC) greater than 0.93. Using Group 2 as reference, the accuracy varied greatly, with AUC values ranging from 0.71 to 0.97. The hepatic blood pool (HBP) ratio gave the highest AUC values. The calculated ICC values for each method showed the SUVmax and HBP measurement to have the greatest reliability, with values of 1.0 and 0.97, respectively.ConclusionsQuantitation of [18F] FDG uptake was found to have a high degree of accuracy in confirming the diagnosis of CIED infection. Normalization to HBP uptake was found to give the greatest AUC and demonstrated excellent reliability. Inconsistencies from published data indicate that individual imaging centers should only use published data for guidance.

The assessment of time-of-flight on image quality and quantification with reduced administered activity and scan times in 18F-FDG PET.

ObjectivesThe last decade has seen considerable technological innovations in PET detectors with the availability, among other advances, of time-of-flight (TOF). TOF has been shown to increase the signal-to-noise ratio (SNR), which should allow for a reduction in acquired counts while maintaining image quality. MethodsFifty-eight patients referred for routine 18F-flurodeoxyglucose (18F-FDG) oncology PET studies were included in this study. Patients with weight below or above 100 kg were prescribed 350 or 400 MBq of 18F-FDG, respectively. Listmode data were acquired for 2.5 min per bed position and reconstructed with ordered-subset expectation maximization (OSEM) reconstruction. TOF reconstruction was performed on reduced-count data, with two levels of reduction (−20 and −40% for patients <100 kg and −16 and −30% for patients >100 kg) achieved by clipping the listmode data. Liver SNR, mediastinum mean standardized uptake value (SUVmean), and lesion maximum standardized uptake value (SUVmax) were measured in all images. All images were visually assessed as adequate or suboptimal. ResultsNo significant difference was seen in mediastinum SUVmean or lesion SUVmax when comparing reduced-count TOF with full-count OSEM images. Compared with the original OSEM images, liver SNR was higher for TOF images using the more conservative −20% reduction of counts (P<0.001, Wilcoxon’s signed-rank test), whereas no significant statistical difference was seen with −40% reductions. ConclusionIncorporation of TOF allows for a reduction in acquired counts; this method has been implemented at our institution, with administered activity reduced for all patients to 280 MBq and a reduction in scan times for all but the largest patients. This has significantly reduced the patient radiation dose and improved scanner flexibility and throughput.

Metal artefact reduction algorithms prevent false positive results when assessing patients for cardiac implantable electronic device infection

Software-based metal artefact reduction (MAR) techniques are available to reduce artefacts from cardiac implantable electronic devices (CIED) in the CT data. The impact of disabling MAR techniques on quantification of 18F-FDG uptake around the CIED has not been examined. We consider the importance of enabling MAR in patients with suspected CIED infection to prevent inaccuracies in quantification of tissue tracer uptake on the attenuation-corrected PET images.

Pitfalls and Limitations of Radionuclide Renal Imaging in Adults

To understand pitfalls and limitations in adult renography, it is necessary to understand firstly the physiology of the kidney, especially the magnitude and control of renal blood flow, glomerular filtration rate and tubular fluid flow rate, and secondly the pharmacokinetics and renal handling of the three most often used tracers, Tc-99m-mercaptoacetyltriglycine (MAG3), Tc-99m-diethylene triamine pentaacetic acid (DTPA) and Tc-99m-dimercaptosuccinic acid (DMSA). The kidneys may be imaged dynamically with Tc-99m-MAG3 or Tc-99m-DTPA, with or without diuretic challenge, or by static imaging with Tc-99m-DMSA. Protocols are different according to whether the kidney is native or transplanted. Quantitative analysis of dynamic data includes measurement of renal vascularity (important for the transplanted kidney), absolute tracer clearance rates, differential renal function (DRF) and response to diuretic challenge. Static image reveals functional renal parenchymal damage, both focal and global, is useful in the clinical management of obstructive uropathy, renal stone disease and hypertension (under angiotensin converting enzyme inhibition), and is the preferred technique for determining DRF. Diagnosis based on morphological appearances is important in transplant management. Even though nuclear medicine is now in the era of hybrid imaging, renal imaging remains an important subspecialty in nuclear medicine and requires a sound basing in applied physiology, the classical supporting discipline of nuclear medicine.

Evaluation of carotid plaque inflammation in patients with active rheumatoid arthritis using 18F-fluorodeoxyglucose PET-CT and MRI: a pilot study

BACKGROUND Rheumatoid arthritis is associated with a 50% increased risk in cardiovascular mortality. Inflammation is thought to accelerate atherosclerosis and might also lead to an inflammatory rupture-prone plaque phenotype. We tested the hypothesis that patients with active rheumatoid arthritis also have carotid plaque inflammation and that plaque inflammation correlates with clinical and serological markers of inflammation. METHODS Patients with active rheumatoid arthritis, defined as the Disease Activity Score in 28 joints (DAS28) score of more than 3·2, were recruited to a single centre study in the UK. Patients with carotid plaque on ultrasound underwent carotid MRI followed by (18)F-fluorodeoxyglucose ((18)F-FDG) PET-CT. Scans were co-registered and analysed by a physicist, masked to clinical information. The maximum standardised uptake values (SUV(max)) were measured in the plaque area. The association of SUV with DAS28, C-reactive protein, and CD4+CD28- T-cell frequency was tested with non-parametric statistics. Ethics approval and informed consent were obtained. FINDINGS Scans were done in 13 patients, nine of whom were women. Median age was 60 years (IQR 57-65), disease duration was 11 years (6-25), and DAS28 score was 4·52 (4·32-5·13). None had a history or symptoms of clinical cardiovascular disease or took statins. All plaques caused less than 70% stenosis, and tracer uptake in plaque was seen on PET in all 13 patients. Median SUV(max) was 2·18 (IQR 2·00-2·65), and all cases had an SUV(max) greater than 1·6 (the threshold for defining carotid plaque inflammation). There was a significant association with SUV(max) and C-reactive protein (r=0·58, p=0·04) and quartiles of CD4+CD28- T-cell frequency (p=0·045), but not with low-density lipoprotein concentrations (r=-0·49, p=0·09) or DAS28 score (r=0·38, p=0·20). No association was found with age (r=0·13, p=0·69) or sex (p=0·64). INTERPRETATION In this small pilot study, plaque inflammation was seen in all patients and correlated with C-reactive protein. Whether this finding represents simultaneous joint and plaque inflammation, which might improve on treatment of joint disease, remains to be determined. CD4+CD28- T-cells are known to predict cardiovascular events in patients with angina. Their association with plaque inflammation in this study suggests a possible role in cardiovascular risk prediction in rheumatoid arthritis. Larger studies are warranted to investigate these findings further. FUNDING North West England MRC Clinical Pharmacology and Therapeutics Clinical Research Fellowship, National Institute for Health Research, AstraZeneca-University of Manchester Strategic Alliance Fund.

Contamination levels and doses to staff arising from the use of Technegas

The aim of this work was to assess the levels of airborne activity and contamination arising from Technegas ventilation scintigraphy and to estimate doses to staff. The maximum air concentration was below the 99Tcm-derived air concentration limit and considerably lower than reported levels for conventional radioaerosols. The level of contamination on staff gloves and aprons exceeded the body surface contamination limit in 63 and 9% of cases, respectively. Levels of contamination and air concentration were generally higher if the patient had difficulty with the administration procedure. Room surface contamination was very low. In 24% of cases activity was detectable on staff (either in the hair or nose) using gamma camera imaging. Annual skin doses from these sources are calculated to be below the limit for deterministic effects. Whole body effective doses are calculated to be similar to those received by staff performing other nuclear medicine studies. However, care should be exercised to keep exposure from both airborne and fixed sources to a minimum and a regular review of contamination levels is recommended. We recommend the wearing of gloves for all Technegas administrations and disposable hats and masks may be considered in certain cases.