The clinical value of quantitative cardiovascular molecular imaging: a step towards precision medicine

Cardiovascular diseases (CVD) are the leading cause of death worldwide and have an increasing impact on society. Precision medicine, in which optimal care is identified for an individual or a group of individuals rather than for the average population, might provide significant health benefits for this patient group and decrease CVD morbidity and mortality. Molecular imaging provides the opportunity to assess biological processes in individuals in addition to anatomical context provided by other imaging modalities and could prove to be essential in the implementation of precision medicine in CVD. New developments in single-photon emission computed tomography (SPECT) and positron emission tomography (PET) systems, combined with rapid innovations in promising and specific radiopharmaceuticals, provide an impressive improvement of diagnostic accuracy and therapy evaluation. This may result in improved health outcomes in CVD patients, thereby reducing societal impact. Furthermore, recent technical advances have led to new possibilities for accurate image quantification, dynamic imaging, and quantification of radiotracer kinetics. This potentially allows for better evaluation of disease activity over time and treatment response monitoring. However, the clinical implementation of these new methods has been slow. This review describes the recent advances in molecular imaging and the clinical value of quantitative PET and SPECT in various fields in cardiovascular molecular imaging, such as atherosclerosis, myocardial perfusion and ischemia, infiltrative cardiomyopathies, systemic vascular diseases, and infectious cardiovascular diseases. Moreover, the challenges that need to be overcome to achieve clinical translation are addressed, and future directions are provided.

Positron Emission Tomography Imaging in Vasculitis

Systemic vasculitides comprise a group of autoimmune diseases affecting blood vessels. [18F]-fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography (FDG-PET/CT) plays an important role in the diagnosis and therapeutic monitoring of vasculitides affecting large-sized and medium-sized vessels. FDG-PET/CT also provides complementary information to other vascular imaging tools. The resolution and sensitivity of newer generation scanners continues to increase, hereby improving the ability of FDG-PET/CT to accurately assess the full disease extent in patients with vasculitis. Novel tracers targeting specific immune cells will allow for more detailed detection of vascular infiltrates.

Extending the clinical capabilities of short- and long-lived positron-emitting radionuclides through high sensitivity PET/CT

This review describes the main benefits of using long axial field of view (LAFOV) PET in clinical applications. As LAFOV PET is the latest development in PET instrumentation, many studies are ongoing that explore the potentials of these systems, which are characterized by ultra-high sensitivity. This review not only provides an overview of the published clinical applications using LAFOV PET so far, but also provides insight in clinical applications that are currently under investigation. Apart from the straightforward reduction in acquisition times or administered amount of radiotracer, LAFOV PET also allows for other clinical applications that to date were mostly limited to research, e.g., dual tracer imaging, whole body dynamic PET imaging, omission of CT in serial PET acquisition for repeat imaging, and studying molecular interactions between organ systems. It is expected that this generation of PET systems will significantly advance the field of nuclear medicine and molecular imaging.

Studying Telmisartan Plasma Exposure, Kidney Distribution, Receptor Occupancy, and Response in Patients With Type 2 Diabetes Using [11 C]Telmisartan

The angiotensin receptor blocker telmisartan slows progression of kidney disease in patients with type 2 diabetes (T2D), yet many patients remain at high risk for progressive kidney function loss. The underlying mechanisms for this response variation might be attributed to differences in angiotensin-1 receptor occupancy (RO), resulting from individual variation in plasma drug exposure, tissue drug exposure, and receptor availability. Therefore, we first assessed the relationship between plasma telmisartan exposure and urinary-albumin-to-creatinine-ratio (UACR) in 10 patients with T2D and albuminuria (mean age 66 years, median UACR 297 mg/g) after 4 weeks treatment with 80 mg telmisartan once daily. Increasing telmisartan exposure associated with a larger reduction in UACR (Pearson correlation coefficient (PCC) = -0.64, P = 0.046, median change UACR: -40.1%, 95% confidence interval (CI): -22.9 to -77.4%, mean telmisartan area under the curve (AUC) = 2927.1 ng·hour/mL, 95% CI: 723.0 to 6501.6 ng·hour/mL). Subsequently, we assessed the relation among plasma telmisartan exposure, kidney distribution, and angiotensin-1 RO in five patients with T2D (mean age 60 years, median UACR 72 mg/g) in a separate positron emission tomography imaging study with [¹¹ C]Telmisartan. Individual plasma telmisartan exposure correlated with telmisartan distribution to the kidneys (PCC = 0.976, P = 0.024). A meaningful RO could be calculated in three patients receiving 120 mg oral telmisartan, and although high exposure seems related to higher RO, with AUC_0-last of 31, 840, and 274 ng·hour/mL and corresponding RO values 5.5%, 44%, and 59%, this was not significant (P = 0.64). Together these results indicate, for the first time, a relationship among interindividual differences in plasma exposure, kidney tissue distribution, RO, and ultimately UACR response after telmisartan administration.

Galectin-3 and Risk of Late Graft Failure in Kidney Transplant Recipients: A 10-year Prospective Cohort Study

BACKGROUND

Galectin-3 may play a causal role in kidney inflammation and fibrosis, which may also be involved in the development of kidney graft failure. With novel galectin-3-targeted pharmacological therapies increasingly coming available, we aimed to investigate whether galectin-3 is associated with risk of late graft failure in kidney transplant recipients (KTR).

METHODS

We studied adult KTR who participated in TransplantLines Insulin Resistance and Inflammation Biobank and Cohort Study, recruited in a university setting (2001-2003). Follow-up was performed for a median of 9.5 (interquartile range, 6.2-10.2) years. Overall and stratified (Pinteraction < 0.05) multivariable-adjusted Cox proportional-hazards regression analyses were performed to study the association of galectin-3 with risk of graft failure (restart of dialysis or retransplantation).

RESULTS

Among 561 KTR (age 52 ± 12 y; 54% males), baseline median galectin-3 was 21.1 (interquartile range, 17.0-27.2) ng/mL. During follow-up, 72 KTR developed graft failure (13, 18, and 44 events over increasing tertiles of galectin-3). Independent of adjustment for donor, recipient, and transplant characteristics, galectin-3-associated with increased risk of graft failure (hazard ratios [HR] per 1 SD change, 2.12; 95% confidence interval [CI], 1.63-2.75; P < 0.001), particularly among KTR with systolic blood pressure ≥140 mmHg (HR, 2.29; 95% CI, 1.80-2.92; P < 0.001; Pinteraction = 0.01) or smoking history (HR, 2.56; 95% CI, 1.95-3.37; P < 0.001; Pinteraction = 0.03). Similarly, patients in the highest tertile of galectin-3 were consistently at increased risk of graft failure.

CONCLUSIONS

Serum galectin-3 levels are elevated in KTR, and independently associated with increased risk of late graft failure. Whether galectin-3-targeted therapies may represent novel opportunities to decrease the long-standing high burden of late graft failure in stable KTR warrants further studies.

Comparison of White Blood Cell Scintigraphy, FDG PET/CT and MRI in Suspected Diabetic Foot Infection: Results of a Large Retrospective Multicenter Study

Diabetic foot infections (DFIs) represent one of the most frequent and disabling morbidities of longstanding diabetes; therefore, early diagnosis is mandatory. The aim of this multicenter retrospective study was to compare the diagnostic accuracy of white blood cell scintigraphy (WBC), ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography ((¹⁸F) FDG PET/CT), and Magnetic Resonance Imaging (MRI) in patients with suspected DFI. Images and clinical data from 251 patients enrolled by five centers were collected in order to calculate the sensitivity, specificity, and accuracy of WBC, FDG, and MRI in diagnosing osteomyelitis (OM), soft-tissue infection (STI), and Charcot osteoarthropathy. In OM, WBC acquired following the European Society of Nuclear Medicine (EANM) guidelines was more specific and accurate than MRI (91.9% vs. 70.7%, p < 0.0001 and 86.2% vs. 67.1%, p = 0.003, respectively). In STI, both FDG and WBC achieved a significantly higher specificity than MRI (97.9% and 95.7% vs. 83.6%, p = 0.04 and p = 0.018, respectively). In Charcot, both MRI and WBC demonstrated a significantly higher specificity and accuracy than FDG (88.2% and 89.3% vs. 62.5%, p = 0.0009; 80.3% and 87.9% vs. 62.1%, p < 0.02, respectively). Moreover, in Charcot, WBC was more specific than MRI (89.3% vs. 88.2% p < 0.0001). Given the limitations of a retrospective study, WBC using EANM guidelines was shown to be the most reliable imaging modality to differentiate between OM, STI, and Charcot in patients with suspected DFI.

Effects of rosuvastatin on coronary flow reserve and metabolic mismatch in patients with heart failure (from the CORONA Study)

In patients with heart failure (HF), statin treatment might improve myocardial perfusion, but could also have detrimental effects on myocardial metabolism. A predefined substudy of the Controlled Rosuvastatin Multinational Trial in Heart Failure (CORONA) trial sought to determine the effects of statin treatment on myocardial blood flow reserve and cardiac metabolism. Sixteen patients with HF (New York Heart Association class II or III) were randomized to rosuvastatin 10 mg/day (n = 8) or placebo treatment (n = 8). At baseline and after 6 months of treatment, nitrogen-13 ammonia at rest and after dipyridamole stress and 18-fluorodeoxyglucose positron emission tomography were performed. Rosuvastatin treatment significantly lowered total (-36%, p <0.01) and low-density lipoprotein (-47%, p <0.001) cholesterol and C-reactive protein levels (-36%, p <0.05). Myocardial perfusion reserve (ratio) changed from 1.64 +/- 0.90 to 1.30 +/- 0.37 in placebo-treated and from 1.51 +/- 0.18 to 1.55 +/- 0.34 in rosuvastatin-treated patients (p = NS). Metabolic mismatch changed from 4.25 +/- 2.37% to 4.38 +/- 3.81% in placebo-treated and from 5.13 +/- 2.75% to 3.50 +/- 2.73% in rosuvastatin-treated patients (p = NS). In conclusion, changes regarding myocardial perfusion and metabolic mismatch after 6 months of rosuvastatin treatment in patients with HF did not suggest any beneficial or adverse effects in this pilot study, although due to the small numbers of patients small effects might have been missed.