Iterative reconstruction in single source dual-energy CT pulmonary angiography: Is it sufficient to achieve a radiation dose as low as state-of-the-art single-energy CTPA?

OBJECTIVE: Dual-energy (DE) brings numerous significant improvements in pulmonary CT angiography (CTPA), but is associated with a 15-50% increase in radiation dose that prevents its widespread use. We hypothesize that thanks to iterative reconstruction (IR), single source DE-CTPA acquired at the same radiation dose that a single-energy examination will maintain an equivalent quantitative and qualitative image quality, allowing a more extensive use of the DE technique in the clinical routine. MATERIAL AND METHODS: Fifty patients (58% men, mean age 64.8yo ± 16.2, mean BMI 25.6 ± 4.5) were prospectively included and underwent single source DE-CTPA with acquisition parameters (275 mA fixed tube current, 50% IR) tweaked to target a radiation dose similar to a 100 kV single-energy CTPA (SE-CTPA), i.e., a DLP of 260 mGy cm. Thirty patients (47% men, 64.4yo ± 18.6, BMI 26.2 ± 4.6) from a previous prospective study on DE-CTPA (375 mA fixed tube current, reconstruction with filtered-back projection) were used as the reference group. Thirty-five consecutive patients (57% men, 65.8yo ± 15.5, BMI 25.7 ± 4.4) who underwent SE-CTPA on the same scanner (automated tube current modulation, 50% IR) served as a comparison. Subjective image quality was scored by two radiologists using a 5-level scale and compared with a Kruskal-Wallis nonparametric test. Density measurements on the 65 keV monochromatic reconstructions were used to calculate signal-to-noise (SNR) and contrast-to-noise (CNR) ratios that were compared using a Student's t test. Correlations between image quality, SNR, CNR and BMI were sought using a Pearson's test. p<0.05 was considered significant. RESULTS: All examinations were of diagnostic quality (score ≥ 3). In comparison with the reference DE-CTPA and the SE-CTPA protocols, the DE-IR group exhibited a non-inferior image quality (p=0.95 and p=0.21, respectively) and a significantly lower mean image noise (p<0.01 and p=0.01) thus slightly improving the SNR (p=0.09 and p=0.47) and the CNR (p=0.12 and p=0.51). There was a strong negative relationship between BMI and SNR/CNR (ρ=-0.59 and -0.55 respectively), but only a moderate negative relationship between BMI and image quality (ρ=-0.27). CONCLUSION: With iterative reconstruction, objective and subjective image quality of single source DE-CTPA are preserved even though the radiation dose is lowered to that of a single-energy examination, overcoming a major limitation of the DE technique and allowing a widespread use in the clinical routine.

Imaging before and after catheter ablation of atrial fibrillation.

Catheter ablation of arrhythmogenic triggers has been validated for the treatment of atrial fibrillation that is refractory to anti-arrhythmic medication. Imaging plays an important role in guiding the procedure as well as in planning and follow-up. The goal of pre-procedural imaging is to obtain a detailed anatomical description of the pulmonary veins, to eliminate a thrombus of the left atrium and to define the prognostic factors. MDCT angiography effectively and simply meets nearly all of these needs. Thus, a precise description of the left atrium anatomy before the procedure is a key factor to success and left atrium volume is a reliable prognostic factor of recurrence. Radiologists should be aware of early and late complications, sometimes severe such as pulmonary vein stenosis, cardiac tamponade or atrial-esophageal fistula, whose positive diagnosis is based on imaging.

Thoracic dual energy CT: acquisition protocols, current applications and future developments.

Thanks to a simultaneous acquisition at high and low kilovoltage, dual energy computed tomography (DECT) can achieve material-based decomposition (iodine, water, calcium, etc.) and reconstruct images at different energy levels (40 to 140keV). Post-processing uses this potential to maximise iodine detection, which elicits demonstrated added value for chest imaging in acute and chronic embolic diseases (increases the quality of the examination and identifies perfusion defects), follow-up of aortic endografts and detection of contrast uptake in oncology. In CT angiography, these unique features are taken advantage of to reduce the iodine load by more than half. This review article aims to set out the physical basis for the technology, the acquisition and post-processing protocols used, its proven advantages in chest pathologies, and to present future developments.

Impaired inhibition of P2Y(12) by clopidogrel is a major determinant of cardiac death in diabetes mellitus patients treated by percutaneous coronary intervention.

OBJECTIVES: We sought to determine whether low platelet response (LR) to the P2Y(12) receptor antagonist as assessed by vasodilator-stimulated phosphoprotein flow cytometry (VASP-FCT) differentially affects outcome in patients with or without diabetes mellitus undergoing percutaneous coronary intervention. BACKGROUND: While both DM and LR to clopidogrel are known to predict an unfavorable outcome after PCI, the deleterious effect of their association is less well established. The VASP-FCT is specific for the P2Y(12) ADP receptor pathway. In this test, platelet activation is expressed as the platelet reactivity index (PRI). METHODS: Patients were assigned to four different groups according to the presence or not of DM (DM, NDM) and LR to clopidogrel (LR, R). LR was defined as a PRI of >61%, a threshold previously identified as the optimal cut-off value to predict cardiac death following PCI. RESULTS: A total of 436 consecutive patients (163 DM, 273 NDM) were enrolled. The proportion of LR patients was higher in DM (47.9% vs. 35.2% p=0.011). At 9±2 months follow-up, the rates of total and cardiac mortality and possible and overall stent thrombosis were higher in DM-LR patients. Conversely, the cardiovascular outcome of DM-R patients was comparable to that of NDM (-LR or -R) patients. In DM, a multivariate analysis identified LR to clopidogrel (HR 6.09 [1.27-29.08], p=0.023) as the sole independent predictor of cardiac mortality. CONCLUSIONS: In DM patients undergoing PCI, LR to clopidogrel is an independent predictor of cardiac death.