Catálogo de publicaciones - libros

Non-invasive CT angiography of the coronary arteries is a challenging and rapidly advancing technique. Electron beam tomography initially permitted the non-invasive visualization of coronary arteries and detection of stenoses. Multidetector CT provides very high spatial resolution and allows for excellent visualization of the coronary arteries. Hemodynamically significant stenoses can be detected and excluded with high accuracy. Current limitations of CT angiography include gantry rotation speed, arrhythmias, and the presence of severe coronary calcification. Continued technical progress is expected to overcome some of these limitations. The most likely beneficial clinical application for the use of CT coronary angiography will be to rule out the presence of relevant coronary artery stenoses in symptomatic patients with a low-to-intermediate likelihood of coronary artery stenoses. Sufficiently large outcome studies will ultimately have to define the most beneficial applications of CT coronary angiography and compare CTA to traditional diagnostic methods.

This paper investigates the applicability of high-level semantic features for video retrieval using the benchmarked data from TRECVID 2003 and 2004, addressing the contributions of features like outdoor, face, and animal in retrieval, and if users can correctly decide on which features to apply for a given need. Pooled truth data gives evidence that some topics would benefit from features. A study with 12 subjects found that people often disagree on the relevance of a feature to a particular topic, including disagreement within the 8% of positive feature-topic associations strongly supported by truth data. When subjects concur, their judgments are correct, and for those 51 topic-feature pairings identified as significant we conduct an investigation into the best interactive search submissions showing that for 29 pairs, topic performance would have improved had users had access to ideal classifiers for those features. The benefits derive from generic features applied to generic topics (27 pairs), and in one case a specific feature applied to a specific topic. Re-ranking submitted shots based on features shows promise for automatic search runs, but not for interactive runs where a person already took care to rank shots well.

Two-dimensional images are the basis for interpretation of all CT imaging, including CT angiography. Understanding the anatomy, being able to track the structures on consecutive slices, and ultimately diagnosing these studies accurately will be dependent on the CT user’s understanding of the axial images and corresponding anatomy. This is probably the most important skill to learn, as virtually all diagnoses can be made based solely on the original axial image set. Analysis of the 2-D images has been shown to be as accurate for the diagnosis of obstructive CAD as 3-D imaging, and superior to some reconstruction methods (see Chapter 4).

During the past decade, we have been witness to a tremendous development in the field of CT imaging. CTA has gained remarkably by improvements in scan time and image quality, replacing diagnostic angiography in many cases of peripheral, carotid, and renal angiography. These vascular beds do not suffer from motion artifacts, so imaging with CT is ideal. CTA is less expensive, less invasive, and allows simultaneous visualization of large anatomic areas from multiple angles using 3-D display. Nevertheless, along with exciting advances, MDCT also carries some emerging and important issues such as increased patient radiation exposure and continued exposure to iodinated contrast.

There have been extensive validations using EBCT for virtually all cardiac size, shape, and functional measures and these were established long before such measures were attempted by MRI. Recent improvements in spiral/helical CT have also accorded this validity to MDCT. CT then becomes a very robust method to define the heart and its detailed anatomy in health and in disease. Furthermore, these types of measures can be accomplished during postprocessing of images intended to define coronary artery anatomy, generally without the need for additional imaging. The disadvantage is that additional sets of cardiac data are required at various portions of the cardiac cycle (nominally at end-diastole and end-systole) and this then obligates concomitant increases in radiation exposure to the patient. That said, CT is a very robust method that can function as both a primary method and a complementary method (such as to echocardiography, contrast ventriculography, radionuclide angiography, and MRI) to quantitate details of cardiac anatomy and function.

The validation of CAC scanning as a risk assessment tool may well represent one of the most significant advances in the history of preventive medicine. It offers the possibility of accurately identifying the vast majority of patients destined to suffer acute cardiac events, and in so doing, will allow for substantial reduction of cardiovascular mortality and morbidity by increasingly effective pharmacologic therapy of the underlying disease process.

The data presented in this chapter provide evidence that non-invasive CT imaging can be used to monitor the effectiveness of medical therapy by following changes in burden of calcified plaque. Nonetheless, there are some limitations inherent with the technology currently available. There is a strong need to standardize the scoring methods and assess the equivalence of the existing CT equipment. Additionally, the rigid application of a density threshold of 130 HU to define the presence of vascular or valvular calcification in all patients limits our ability to identify more recent, less densely calcified and therefore softer plaques. Though further prospective studies will be necessary to confirm the clinical significance of the findings herein summarized, it is quite evident that the effectiveness of anti-atherosclerotic therapy can be gauged with sequential CT imaging. The application of this technology will greatly facilitate primary and secondary prevention studies by allowing a great reduction in the number of patients needed to show effectiveness of therapy. Simultaneously, a physician’s effort to implement preventive measures could be gratified by the ability to measure the effectiveness of the applied remedies. Interventions directed at modifying risk factors associated with atherosclerosis besides LDL such as small-density LDL, Lp(a), low HDL, elevated homocysteine levels, and use of anti-viral and anti-bacterial agents will likely be the focus of future research.

With continued improvements in CT technology and expanded clinical experience, it is hoped that the role of coronary calcium in primary and secondary prevention will be further defined and become more readily accepted by a wider circle of physician users.

Two-dimensional images are the basis for interpretation of all CT imaging, including CT angiography. Understanding the anatomy, being able to track the structures on consecutive slices, and ultimately diagnosing these studies accurately will be dependent on the CT user’s understanding of the axial images and corresponding anatomy. This is probably the most important skill to learn, as virtually all diagnoses can be made based solely on the original axial image set. Analysis of the 2-D images has been shown to be as accurate for the diagnosis of obstructive CAD as 3-D imaging, and superior to some reconstruction methods (see Chapter 4).

Non-invasive CT angiography of the coronary arteries is a challenging and rapidly advancing technique. Electron beam tomography initially permitted the non-invasive visualization of coronary arteries and detection of stenoses. Multidetector CT provides very high spatial resolution and allows for excellent visualization of the coronary arteries. Hemodynamically significant stenoses can be detected and excluded with high accuracy. Current limitations of CT angiography include gantry rotation speed, arrhythmias, and the presence of severe coronary calcification. Continued technical progress is expected to overcome some of these limitations. The most likely beneficial clinical application for the use of CT coronary angiography will be to rule out the presence of relevant coronary artery stenoses in symptomatic patients with a low-to-intermediate likelihood of coronary artery stenoses. Sufficiently large outcome studies will ultimately have to define the most beneficial applications of CT coronary angiography and compare CTA to traditional diagnostic methods.

During the past decade, we have been witness to a tremendous development in the field of CT imaging. CTA has gained remarkably by improvements in scan time and image quality, replacing diagnostic angiography in many cases of peripheral, carotid, and renal angiography. These vascular beds do not suffer from motion artifacts, so imaging with CT is ideal. CTA is less expensive, less invasive, and allows simultaneous visualization of large anatomic areas from multiple angles using 3-D display. Nevertheless, along with exciting advances, MDCT also carries some emerging and important issues such as increased patient radiation exposure and continued exposure to iodinated contrast.