MRI of the lung (3/3)-current applications and future perspectives

BACKGROUND: MRI of the lung is recommended in a number of clinical indications. Having a non-radiation alternative is particularly attractive in children and young subjects, or pregnant women. METHODS: Provided there is sufficient expertise, magnetic resonance imaging (MRI) may be considered as the preferential modality in specific clinical conditions such as cystic fibrosis and acute pulmonary embolism, since additional functional information on respiratory mechanics and regional lung perfusion is provided. In other cases, such as tumours and pneumonia in children, lung MRI may be considered an alternative or adjunct to other modalities with at least similar diagnostic value. RESULTS: In interstitial lung disease, the clinical utility of MRI remains to be proven, but it could provide additional information that will be beneficial in research, or at some stage in clinical practice. Customised protocols for chest imaging combine fast breath-hold acquisitions from a "buffet" of sequences. Having introduced details of imaging protocols in previous articles, the aim of this manuscript is to discuss the advantages and limitations of lung MRI in current clinical practice. CONCLUSION: New developments and future perspectives such as motion-compensated imaging with self-navigated sequences or fast Fourier decomposition MRI for non-contrast enhanced ventilation- and perfusion-weighted imaging of the lung are discussed. Main Messages • MRI evolves as a third lung imaging modality, combining morphological and functional information. • It may be considered first choice in cystic fibrosis and pulmonary embolism of young and pregnant patients. • In other cases (tumours, pneumonia in children), it is an alternative or adjunct to X-ray and CT. • In interstitial lung disease, it serves for research, but the clinical value remains to be proven. • New users are advised to make themselves familiar with the particular advantages and limitations

An optimized b-value distribution for triexponential intravoxel incoherent motion (IVIM) in the liver.

Purpose To find an optimized b-value distribution for reproducible triexponential intravoxel incoherent motion (IVIM) exams in the liver.Methods A numeric optimization of b-value distributions was performed using the triexponential IVIM equation and 27 different IVIM parameter sets. Starting with an initially optimized distribution of 6 b-values, the number of b-values was increased stepwise. Each new b-value was chosen from a set of 64 predefined b-values based on the computed summed relative mean error of the fitted triexponential IVIM parameters. This process was repeated for up to 100 b-values. In simulations and in vivo measurements, optimized b-value distributions were compared to 4 representative distributions found in literature.Results The first 16 optimized b-values were 0, 0.3, 0.3, 70, 200, 800, 70, 1, 3.5, 5, 70, 1.2, 6, 45, 1.5, and 60 in units of s/mm2 . Low b-values were much more frequent than high b-values. The optimized b-value distribution resulted in a higher fit stability compared to distributions used in literature in both, simulation and in vivo measurements. Using more than 6 b-values, ideally 16 or more, increased the fit stability considerably.Conclusion Using optimized b-values, the fit uncertainty in triexponential IVIM can be largely reduced. Ideally, 16 or more b-values should be acquired

Echo time dependence of biexponential and triexponential intravoxel incoherent motion parameters in the liver.

Purpose Intravoxel incoherent motion (IVIM) studies are performed with different acquisition protocols. Comparing them requires knowledge of echo time (TE) dependencies. The TE-dependence of the biexponential perfusion fraction f is well-documented, unlike that of its triexponential counterparts f 1 and f 2 and the biexponential and triexponential pseudodiffusion coefficients D * , D1∗ , and D2∗ . The purpose was to investigate the TE-dependence of these parameters and to check whether the triexponential pseudodiffusion compartments are associated with arterial and venous blood. Methods Fifteen healthy volunteers (19-58 y; mean: 24.7 y) underwent diffusion-weighted imaging of the abdomen with 24 b-values (0.2-800 s/mm 2 ) at TEs of 45, 60, 75, and 90 ms. Regions of interest (ROIs) were manually drawn in the liver. One set of bi- and triexponential IVIM parameters per volunteer and TE was determined. The TE-dependence was assessed with the Kruskal-Wallis test. Results TE-dependence was observed for f (P < .001), f 1 (P = .001), and f 2 (P < .001). Their median values at the four measured TEs were: f: 0.198/0.240/0.274/0.359, f 1 : 0.113/0.139/0.146/0.205, f 2 : 0.115/0.155/0.182/0.194. D, D * , D1∗ , and D2∗ showed no significant TE-dependence. Their values were: diffusion coefficient D (10 -4 mm 2 /s): 9.45/9.63/9.75/9.41, biexponential D * (10 -2 mm 2 /s): 5.26/5.52/6.13/5.82, triexponential D1∗ (10 -2 mm 2 /s): 1.73/2.91/2.25/2.51, triexponential D2∗ (mm 2 /s): 0.478/1.385/0.616/0.846. Conclusion f 1 and f 2 show similar TE-dependence as f, ie, increase with rising TE; an effect that must be accounted for when comparing different studies. The diffusion and pseudodiffusion coefficients might be compared without TE correction. Because of the similar TE-dependence of f 1 and f 2 , the triexponential pseudodiffusion compartments are most probably not associated to venous and arterial blood

Biomarker prediction of complex coronary revascularization procedures in the FOURIER trial

Background Biomarkers are known to predict major adverse cardiovascular events. However, the association of biomarkers with complex coronary revascularization procedures or high-risk coronary anatomy at the time of revascularization is not understood. Objectives We examined the associations between baseline biomarkers and major coronary events (MCE) and complex revascularization procedures. Methods FOURIER was a randomized trial of the proprotein convertase subtilisin–kexin type 9 inhibitor evolocumab vs placebo in 27,564 patients with stable atherosclerosis. We analyzed adjusted associations among the biomarkers, MCE (coronary death, myocardial infarction, or revascularization), and complex revascularization (coronary artery bypass graft or complex percutaneous coronary intervention) using a multimarker score with 1 point assigned for each elevated biomarker (high-sensitivity C-reactive protein ≥2 mg/L; N-terminal pro–B-type natriuretic peptide ≥450 pg/mL; high-sensitivity troponin I ≥6 ng/L; growth-differentiation factor-15 ≥1,800 pg/mL). Results When patients were grouped by the number of elevated biomarkers (0 biomarkers, n = 6,444; 1-2 biomarkers, n = 12,439; ≥3 biomarkers, n = 2,761), there was a significant graded association between biomarker score and the risk of MCE (intermediate score: HRadj: 1.57 [95% CI: 1.38-1.78]; high score: HRadj: 2.90 [95% CI: 2.47-3.40]), and for complex revascularization (intermediate: HRadj: 1.33 [95% CI: 1.06-1.67]; high score: HRadj: 2.07 [95% CI: 1.52-2.83]) and its components (Ptrend <0.05 for each). The number of elevated biomarkers also correlated with the presence of left main disease, multivessel disease, or chronic total occlusion at the time of revascularization (P < 0.05 for each). Conclusions A biomarker-based strategy identifies stable patients at risk for coronary events, including coronary artery bypass graft surgery and complex percutaneous coronary intervention, and predicts high-risk coronary anatomy at the time of revascularization. These findings provide insight into the relationships between cardiovascular biomarkers, coronary anatomical complexity, and incident clinical events. (Further Cardiovascular Outcomes Research With PCSK9 Inhibition in Subjects With Elevated Risk [FOURIER]; NCT01764633