الفهرس 
PULMONARY VASCULATUREOnly 14 pages are availabe for public view
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Abstract
PE is a common and potentially fatal disorder for which treatment is effective and improves the chance of survival. PE is the third most common acute cardiovascular disease, after myocardial infarction and stroke, and it leads to thousands of deaths each year because it often goes undetected. Post mortum studies have indicated that 65% of hospitalized patients have PE. It has been estimated that 7% of hospital patients die as a result of PE as the sole cause.
However, the accurate diagnosis of acute pulmonary embolism can be difficult because of unreliable clinical and laboratory findings.
Diagnosis of pulmonary embolism depends on clinical suspicious. PE is often under diagnosed due to the non specific nature of its signs and symptoms, which frequently seen in other cardiac and pulmonary conditions.
The presence of predisposing factors that increase the risk for DVT should raise the suspicion for the presence of pulmonary embolism; unfortunately, these conditions are non sensitive and non specific and are frequently present in patients who did not have pulmonary embolism. So, Objective testing for pulmonary embolism is crucial, because clinical assessment alone is unreliable and the consequences of misdiagnosis are serious.
The advent of chest CT scanning for the diagnosis of pulmonary embolism was hailed as an improvement, even before recent studies were undertaken. By 2001, CT scanning was being used more often than lung scanning to investigate suspected pulmonary embolism.
There are now multiple generations of CT scanners, but even first generation machines delivered images that were dramatic in clarity, rapidly acquired, and accurate in delineating the proximal pulmonary arterial tree. This noninvasive technology has evolved rapidly.
A 16-slice multi-detector-row CT scanner can image the entire chest with sub-millimeter resolution and requires a breath-hold of less than 10 seconds.
MDCT pulmonary angiography and venography for suspected venous thrombo-embolism are safe, readily available, and increasingly being used. Recent advances in technology allow faster scanning, thinner images, and more reproducible interpretations.
The most important advantage of CT over other imaging modalities is that both mediastinal and parenchymal structures are evaluated, and thrombus is directly visualized. Studies have shown that up to two thirds of patients with an initial suspicion of PE receive another diagnosis, some with potentially life-threatening diseases, such as aortic dissection, pneumonia, lung cancer, and pneumothorax. Most of these diagnoses are amenable to CT visualization, so that in many cases a specific etiology for the patients’ symptoms and important additional diagnoses can be established.
Use of high resolution multi-detector-CT protocols was shown to improve visualization of pulmonary arteries and the detection of small subsegmental emboli and such small peripheral clots that might have gone unnoticed in the past are now frequently detected, often in patients with minor symptoms.
In suspected PE, establishing an unequivocal diagnosis as to the presence or absence of emboli or other disease based on a high-quality multidetector- row CT examination may reduce the overall radiation burden of patients, since further work-up with other tests that involve ionizing radiation may be less frequently required.
As compared with single-detector row scanning, pulmonary angiography with multi-detector row CT significantly improves vessel visualization in the middle and peripheral lung zones.
And comparing MSCT with V/Q scintigraphy which is still considered as one of the most important tools of PE diagnosis, MSCT proved to have better specificity as well as its ability to detect the embolus itself not its consequences unlike V/Q scan.
Multiplanar reconstructions improve the ability to identify the origin of middle and peripheral vessels and connect them with their central arteries of origin. Narrower collimation improves the quality of the transverse and multiplanar images, and faster acquisition times make the examination better tolerated and improve contrast and spatial resolution, which may improve detection of peripheral pulmonary emboli.