A-posteriori symbol probabilities and log-likelihood ratios for coherently detected π/4-DE-QPSK

In this letter, coherent detection of p/4-DE-QPSK is considered, but our analysis also holds for common DE-QPSK. It is shown that maximum a-posteriori (MAP) sequence detection can be regarded as an approximation, based on selecting dominant exponentials, of MAP symbol detection. A better approximation, relying on piecewise-linear fitting of the logarithm of the hyperbolic cosine, is proposed. This approximation results in a performance very close to optimal symbol detection. For the case where the symbols are produced by convolutional encoding and Gray mapping, the log-likelihood ratios are investigated. Again a simple approximation based on selecting dominant exponentials and an improved approximation relying on piecewise-linear fits, are discussed. As in the uncoded case the improved approximation gives a performance quite close to ideal. While the particular examples considered show modest gains in performance, this letter provides a way of improving performance when needed

Is there an indication for computed tomography and magnetic resonance imaging in the evaluation of coronary artery bypass grafts?

This meta-analysis evaluates the diagnostic accuracy of multidetector computed tomography (MDCT) and magnetic resonance imaging (MRI) for bypass graft occlusion and stenosis detection compared with coronary angiography in post-coronary artery bypass graft patients. The indication for noninvasive imaging in post-coronary artery bypass graft patients with these techniques is discussed. Overall, MRI had significantly lower sensitivity (81%) and specificity (91%) for occlusion detection than MDCT (96% and 98%, respectively). Only 2 studies assessed the accuracy of stenosis detection with MRI. Stenosis detection with MDCT had a pooled sensitivity of 89% and specificity of 97%. Multidetector computed tomography is therefore superior to MRI for the noninvasive detection of coronary bypass graft occlusion and stenosis. For stenosis detection, the accuracy of MDCT is, however, not sufficient to warrant a wide clinical use. The remaining indication for MRI-guided bypass graft assessment is in combination with myocardial evaluation such as magnetic resonance perfusion, wall motion, and stress test as a "one-stop-shop" procedur

Dynamic contact area ratio in shoulder instability: an innovative diagnostic technique measuring interplay of bony lesions

Purpose: The hypothesis of this study is that Dynamic Contact Area Ratio of the humerus and glenoid, measured with CT scans, is significantly reduced in patients with anterior shoulder instability compared to the Dynamic Contact Area Ratio in a control group of people without shoulder instability. Methods: Preoperative CT scans of patients who underwent surgery for anterior shoulder instability were collected. Additionally, the radiologic database was searched for control subjects. Using a validated software tool (Articulis) the CT scans were converted into 3-dimensional models and the amount the joint contact surface during simulated motion was calculated. Results: CT scans of 18 patients and 21 controls were available. The mean Dynamic Contact Area Ratio of patients was 25.2 \ub1 6.7 compared to 30.1 \ub1 5.1 in healthy subjects (p = 0.014). Conclusion: Dynamic Contact Area Ratio was significantly lower in patients with anterior shoulder instability compared to controls, confirming the hypothesis of the study. The findings of this study indicate that calculating the Dynamic Contact Area Ratio based on CT scan images may help surgeons in diagnosing anterior shoulder instability. Level of evidence: III