الفهرس 
Anatomy of the lungsOnly 14 pages are availabe for public view
 |  | from | 126 |  |  |
| | | from | 126 | | |
Abstract
Pulmonary thrombo-embolism is a feared complication of deep venous thrombosis (DVT). The mortality rate in untreated cases is 25%–30%, whereas the mortality rate in treated cases decreases to 5%–8%. More than 90% of pulmonary emboli arise from deep veins of the legs and pelvis, and the primary risk factor for recurrent pulmonary embolism is the presence of residual proximal venous thrombosis (Loud et al., 2001).
CT is readily available at most institutions and is rapidly becoming the first-line imaging test for the assessment of patients with suspected PE (Quiroz et al., 2005).
With Spiral CT, thrombus is directly visualized, and both mediastinal and parenchymal structures are evaluated which may provide important alternative additional diagnoses ( Schoeopf et al., 2004).
However, conventional single-slice spiral CT has insufficient sensitivity for isolated peripheral PE (Quiroz et al., 2005).
The use of multi-detector row CT significantly improves pulmonary arterial visualization in the middle and the peripheral lung zones. 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 improves detection of peripheral pulmonary emboli (Raptopoulos & Boiselle, 2001).
Because deep vein thrombosis is a possible cause of pulmonary embolism, evaluation of the deep veins has been reported to increase the diagnostic accuracy and is performed at the time of CT pulmonary angiography in many institutions (Arakawa et al., 2007).
Relatively recently, CT venography (CTV) has been documented as offering a rapid and available alternative to venous sonography of the lower extremities in the evaluation for DVT, with sensitivity and specificity reported to be in the range of 89–100% and 94–100%, respectively. Indirect CT venography has several advantages over ultrasonography: It is not operator dependant and it can be used to diagnose clots in areas that are not accessible to ultrasound or difficult to evaluate. This includes the deep pelvic veins (a common source of thrombus that may embolize to the lungs) and the region around the adductor canal. Ultrasound can be of limited value in patients who are obese or who have had recent surgery (Pretorius & Solomon , 2006).
Indirect CTV coupled with CT pulmonary angiography provides a single examination capable of evaluating both the pulmonary arterial system and the pelvic and lower extremity venous system without the need for additional contrast injection (Cham et al., 2005).
It was found that the addition of indirect CT venography increases the gonadal radiation dose by 500- to 2000-fold compared with CT pulmonary angiography alone. Fortunately, this increase in gonadal dose is well below the thresholds for deterministic radiation effects provided in the International Commission on Radiological Protection. However some stochastic effects may occur .The use of discontinuous sections (5 mm sections) can reduce the integral dose by as much as 80 %( Cham et al., 2005).