Carotid magnetic resonance imaging for monitoring atherosclerotic plaque progression: a multicenter reproducibility study.

This study sought to determine the multicenter reproducibility of magnetic resonance imaging (MRI) and the compatibility of different scanner platforms in assessing carotid plaque morphology and composition. A standardized multi-contrast MRI protocol was implemented at 16 imaging sites (GE: 8; Philips: 8). Sixty-eight subjects (61 ± 8 years; 52 males) were dispersedly recruited and scanned twice within 2 weeks on the same magnet. Images were reviewed centrally using a streamlined semiautomatic approach. Quantitative volumetric measurements on plaque morphology (lumen, wall, and outer wall) and plaque tissue composition [lipid-rich necrotic core (LRNC), calcification, and fibrous tissue] were obtained. Inter-scan reproducibility was summarized using the within-subject standard deviation, coefficient of variation (CV) and intraclass correlation coefficient (ICC). Good to excellent reproducibility was observed for both morphological (ICC range 0.98-0.99) and compositional (ICC range 0.88-0.96) measurements. Measurement precision was related to the size of structures (CV range 2.5-4.9 % for morphology, 36-44 % for LRNC and calcification). Comparable measurement variability was found between the two platforms on both plaque morphology and tissue composition. In conclusion, good to excellent inter-scan reproducibility of carotid MRI can be achieved in multicenter settings with comparable measurement precision between platforms, which may facilitate future multicenter endeavors that use serial MRI to monitor atherosclerotic plaque progression.

Characteristic time courses of cortical and medullary sodium signals measured by noninvasive (23) Na-MRI in rat kidney induced by furosemide.

BACKGROUND: To characterize regional kidney sodium response by MRI following NKCC2 inhibition. METHODS: Regional renal sodium signals were monitored noninvasively using (23) Na-MRI at 9.4T with a temporal resolution of 1.5 min in anesthetized rats (N = 14). A mild NKCC2 inhibition was induced using a slow intravenous furosemide infusion. Time course of sodium signal was modeled as an exponential transient with a single characteristic time constant. RESULTS: Under normal physiological conditions, the renal sodium signals in medullary and cortical regions were stable and found to respond differently to furosemide challenge. Furosemide infusion at 1.2 mg/kg/h (N = 7) increased sodium signal in the cortex by 40 ± 6% (P < 7 × 10(-5) ) whereas decreased in the medulla by 29 ± 2% (P < 3 × 10(-6) ) with different temporal kinetics. The characteristic time constants of the change were determined to be: 8 ± 2 and 70 ± 10 min for medulla and cortex. Also, the medullary change occurred 9(±3) times faster than cortical independent of furosemide infusion rate up to 35 mg/kg/h. CONCLUSION: The pharmacological effects in terms of regional kidney sodium signal changes induced by NKCC2 inhibition are region-specific and highly predictable. Using noninvasive sodium MRI, we obtained regional renal sodium kinetics data sets in response to a low dose furosemide infusion in normal rats.

Intensification of statin therapy results in a rapid reduction in atherosclerotic inflammation: results of a multicenter fluorodeoxyglucose-positron emission tomography/computed tomography feasibility study.

OBJECTIVES: The study sought to test whether high-dose statin treatment would result in greater reductions in plaque inflammation than low-dose statins, using fluorodeoxyglucose-positron emission tomography/computed tomographic imaging (FDG-PET/CT). BACKGROUND: Intensification of statin therapy reduces major cardiovascular events. METHODS: Adults with risk factors or with established atherosclerosis, who were not taking high-dose statins (n = 83), were randomized to atorvastatin 10 versus 80 mg in a double-blind, multicenter trial. FDG-PET/CT imaging of the ascending thoracic aorta and carotid arteries was performed at baseline, 4, and 12 weeks after randomization and target-to-background ratio (TBR) of FDG uptake within the artery wall was assessed while blinded to time points and treatment. RESULTS: Sixty-seven subjects completed the study, providing imaging data for analysis. At 12 weeks, inflammation (TBR) in the index vessel was significantly reduced from baseline with atorvastatin 80 mg (% reduction [95% confidence interval]: 14.42% [8.7% to 19.8%]; p < 0.001), but not atorvastatin 10 mg (% reduction: 4.2% [-2.3% to 10.4%]; p > 0.1). Atorvastatin 80 mg resulted in significant additional relative reductions in TBR versus atorvastatin 10 mg (10.6% [2.2% to 18.3%]; p = 0.01) at week 12. Reductions from baseline in TBR were seen as early as 4 weeks after randomization with atorvastatin 10 mg (6.4% reduction, p < 0.05) and 80 mg (12.5% reduction, p < 0.001). Changes in TBR did not correlate with lipid profile changes. CONCLUSIONS: Statin therapy produced significant rapid dose-dependent reductions in FDG uptake that may represent changes in atherosclerotic plaque inflammation. FDG-PET imaging may be useful in detecting early treatment effects in patients at risk or with established atherosclerosis.

Positron emission tomography and drug discovery: contributions to the understanding of pharmacokinetics, mechanism of action and disease state characterization.

As an imaging modality, positron emission tomography (PET) provides unique quantitative in vivo information of value to drug discovery studies. These non-invasive studies span the pharmacokinetic/pharmacodynamic evaluation of potential drug candidates, receptor occupancy as an important determinant of efficacy, the pharmacological characterization of potential mechanisms of action, and the biological characterization of disease with well-characterized PET ligands. PET techniques are also being applied to the assessment of gene-level activities and the longitudinal evaluation of disease progression and therapeutic intervention. As the availability of PET scanners, cyclotrons, and specific PET ligands grows, the techniques highlighted in this review will become central to target validation, drug candidate selection, pharmacokinetic characterization, and clinical evaluation.