Image selection for computed tomography of the chest. A sampling approach

The cardiac autonomic nervous system: an introduction

In recent decades, numerous anatomical and physiological studies of the cardiac autonomic nervous system (ANS) have investigated the complex relationships between the brain and the heart. Autonomic activation not only alters heart rate, conduction, and hemodynamics, but also cellular and subcellular properties of individual myocytes. Moreover, the cardiac ANS plays an essential role in cardiac arrhythmogenesis. There is mounting evidence that neural modulation either by ablation or stimulation can effectively control a wide spectrum of cardiac arrhythmias. This article discusses anatomic aspects of the cardiac ANS, focusing on how autonomic activities influence cardiac electrophysiology. Specific autonomic triggers of various cardiac arrhythmias, in particular atrial fibrillation (AF) and ventricular arrhythmias, are also briefly discussed. Studies with heart-rate variability analysis indicate that, rather than being triggered by either vagal or sympathetic activity, the onset of AF can be associated with simultaneous discharge of both limbs, leading to an imbalance between these two arms of the cardiac ANS. At the same time, sudden cardiac death resulting from ventricular arrhythmias continues to be a significant health and societal burden. These nerve activities of the cardiac ANS can be targeted for the treatment for cardiac arrhythmias, in particular AF and ventricular tachyarrhythmias.

Accuracy of emphysema quantification performed with reduced numbers of CT sections

OBJECTIVE

The purpose of this study was to assess the accuracy of emphysema measurements obtained from systematic samples of evenly spaced CT images compared with measurements obtained from the entire scan.

MATERIALS AND METHODS

Evenly spaced transverse sections from the CT studies of 136 heavy smokers who underwent screening for lung cancer in the National Lung Screening Trial and of 112 subjects who underwent imaging before lung volume reduction surgery were sampled retrospectively. The samples were acquired both by selection of specific numbers of evenly spaced images and by selection of images at specific distance intervals. The percentage of lung pixels with attenuation below specific thresholds was used as an emphysema index. The image sample error was determined as the difference in emphysema index between the image samples and the entire scan.

RESULTS

The largest absolute image sample errors in the National Lung Screening Trial cohort with image sample sizes of five, 10, and 20 were 2.2, 0.8, and 0.5 index percentage points, respectively, at 1-mm section thickness (-960 HU threshold), and 2.6, 1.1, and 0.5 index percentage points at 5-mm section thickness (-930 HU threshold). The largest errors in the lung volume reduction surgery cohort for image sample sizes of five and 10 were 5.6 and 2.3 index percentage points at 8- to 10-mm section thickness (-900 HU threshold). Image sample errors were equivalent for the two sampling methods.

CONCLUSION

Systematic sampling resulted in very small errors in emphysema quantification and may be useful for decreasing radiation exposure in clinical research studies of emphysema.

High-Resolution CT in Diagnosis of Diffuse Infiltrative Lung Disease

The chest radiograph remains the first imaging modality for the approach to diffuse infiltrative lung disease (DILD), but, 23 years after its introduction, high-resolution CT (HRCT) is still considered the best imaging tool for the evaluation of the pulmonary interstitium and to diagnose and assess DILD. The introduction of multidetector computed tomography (MDCT) has provided the thoracic radiologist with a powerful tool with which to image the lung. Moreover MDCT has enabled radiologists to understand better the functional information contained within CT images of DILD. By focusing on the HRCT signs, patterns, and distributions of abnormalities, and mentioning the clinical aspects and the new recent advances in pulmonary imaging, in this article we provide an overview of a practical approach to the interpretation of the DILD.