**4. Dual E CT**

176 Pulmonary Embolism

Age > 80 y Age in years 1

History of cancer +30 1

 Pulse ≥110 beats/min +20 1 Systolic blood pressure <100 mmHg +30 1

SaO2 < 90% +20 1

a The total point score for each patient is calculated as the sum the patient's age in years and the points

Scores corresponding to risk classes include: 65 or less, class I; 66 to 85, class II; 86 to 105, class III; 106 to 125, class IV; and more than 125, class V. Patients in risk classes I and II are defined as being at low risk. bThe total point score for each patient is calculated as the sum of the points. Scores correspond to the

aorta were not indicators of mortality or severity of acute PE (Araoz et al., 2003; van der

Saddle PE is defined as a visible thromboembolus stradding the bifurcation of the main PA (Fig. 5). Saddle PE occurs at frequency of (5.2%) in all patients with PE (Pruszczyk et al., 2003). Such proximal thrombus may be regarded unstable, large clot burden in the PA, and "in-transit" embolus, which can fragment spontaneously or secondary to treatment and

Debate has been going on regarding the size of the clot and prognosis. Some studies suggest that simple distinction of saddle versus non-saddle PE by CT findings was associated with death within 1 year (OR 7.4, 95% CI 1.7-31.5) and may provide a straight forward method for risk stratification (Yusuf et al., 2010). Whereas other studies found that saddle PE was not associated with mortality rate and may not necessitate aggressive medical management (Ryu et al., 2007; Musani, 2010). Therefore the prognosis value of saddle PE is not well

following risk classes: 0, low risk; 1 or more, high risk. c The variables were combined into a single category of chronic cardiopulmonary disease.

Table 2. Original and simplified pulmonary embolism severity index (PESI)

obstruct multiple, distal pulmonary arteries (Pruszczyk et al., 2003).

Male sex +10

History of heart failure +10

History of chronic lung disease +10

 Respiratory rate ≥30 breaths/min +20 Temperature <36°C +20 Altered mental status +60

**Score**

**PESI a sPESI b**

1 c

**Variable** 

for each predictor when present.

**3.1.5 Saddle pulmonary embolism** 

Meer et al., 2005).

established.

Physiologic changes in patients with acute PE, such as RV overload, may be more closely related to the extent of the pulmonary perfusion defect than to the burden of intravascular emboli. Several studies have reported that the extent of the pulmonary perfusion defect, as assessed by perfusion scintigraphy or SPECT, is an important risk factor for recurrence of pulmonary embolism and RV dysfunction (Wolfe et al., 1994; Palla et al., 2010). However, CT angiography has shown better performance than perfusion scintigraphy or SPECT in the initial diagnosis of pulmonary embolism, since the former has several advantages, including high spatial resolution, rapid scanning time and easy availability.

Recent advances in CT technology have included dual-energy CT (DECT), using two tubes (dual-source CT) or a single tube with a rapid kVp switching technique. As iodine has unique spectral properties and X-ray absorption characteristics at higher and lower photon energies (e.g., 140-kVp and 80-kVp), iodine map images can be generated using DECT angiography (DECTA). These images may represent the regional perfusion status of lung parenchyma and showed good correlation with scintigraphic findings in patients with PE (Pontana et al., 2008; Thieme et al., 2008). Weighted-average 120-kVp equivalent CT angiography obtained from DECTA can be used for the direct visualization of a thromboembolism and for the evaluation of CT signs of RV dysfunction, similar to standard CT angiography. That is, information about regional lung perfusion status, as well as the burden of intravascular emboli and right-sided heart failure, can be evaluated by single scanning DECT.

RV dysfunction is predictive of a poor prognosis in patients with acute PE. On CT angiography images, RV/LV diameter ratio is a reliable marker of RV dysfunction, with higher RV/LV diameter ratios related to poor clinical outcomes (Quiroz et al., 2004; Schoepf et al., 2004; van der Meer et al., 2005). Furthermore, the extent of perfusion defect on DECTA has been correlated with RV/LV diameter ratio (Zhang et al., 2009; Chae et al., 2010; Bauer

Risk Stratification of Submassive Pulmonary Embolism:

(a) (b)

(c) (d)

Fig. 6. Pulmonary embolism without right ventricular dysfunction. (a) Dual-energy CT angiography (DECTA) shows filling defect in segmental branches of pulmonary arteries

(RV/LV ratio < 1). (c & d) Lung iodine images show wedge shaped pulmonary perfusion defect in right lower lobe lateral basal segment where emboli completely occludes

pulmonary artery. However, the posterior basal segment of right lower lobe shows normal perfusion status, because emboli partly occlude corresponding pulmonary artery. The relative volume of pulmonary perfusion defect was 8.3% and perfusion defect score was 10.

in right lower lobe. (b) DECTA shows normal ranged diameters of ventricles

link between diagnostic and risk stratification strategies in this setting.

The Role of Chest Computed Tomography as an Alternative to Echocardiography 179

diagnostic workup of patients with suspected PE. Thus, CT has the potential to become the

et al., 2011). A novel dual energy perfusion defect score has been proposed, in which the degree of lung perfusion in each segment is graded on a 3-point scale (0, normal perfusion; 1, moderately reduced perfusion, 2, profoundly reduced or absent perfusion), with the perfusion defect score calculated as ∑(n∙d)/40x100, where n is the number of segments and d is the degree of the perfusion defect (Chae et al., 2010). The perfusion defect score has shown good correlation with RV/LV diameter ratio (*r* = 0.69, *p* < 0.001). In addition, the numbers of lobes with pulmonary perfusion defects on iodine images of DECTA correlated well with RV/LV diameter ratio (*r* = 0.66, *p* < 0.05), whereas the number of lobes with PE on CT angiography did not (*p* > 0.05). Quantification of the area of pulmonary perfusion defect on iodine images showed that an pulmonary perfusion defect over 215.4 ml or a relative volume over 9.9% was related to an RV/LV diameter ratio > 1 (Bauer et al., 2011). These results therefore indicate that pulmonary perfusion defect size may be a surrogate marker for RV dysfunction (Fig. 6, Fig. 7). Readmission and death due to PE were observed only in patients with a relative perfusion defect size >5% of total lung volume, but not in any patient with a relative perfusion defect < 5% (Bauer, Frellesen et al. 2011). Patients with a relative perfusion defect >5% also showed lower median survival with increased relative hazard ratio for death than those with a relative perfusion defect <5%. These results indicate that pulmonary perfusion defect size may be prognostic in patients with PE.

The status of the pulmonary microvasculature is important in evaluating disease severity and prognosis in patients with PE. Although ventilation/perfusion scintigraphy was used to assess the pulmonary nomenclature, multi-detector CT angiography has replaced scintigraphy in the evaluation of these patients, since CT has higher spatial resolution and shorter acquisition time. Recently developed advanced CT techniques, including DECT, permits the evaluation of pulmonary perfusion status without significant additional radiation dose. Therefore, DECTA may become a leading imaging tool, both for detecting emboli and for risk stratification regarding of regional pulmonary perfusion status in patients with PE.

#### **5. The role of chest computed tomography as an alternative to echocardiography**

Retrospective studies have shown that multidetector chest CT and echocardiography yield similar prognostic data (Sanchez et al., 2008). While CT provides information on RV dilatation only, echocardiography also provides some information on contractility, e.g., septal or RV hypo- or dyskinesia. However, echocardiography is not always available in emergency settings and has limitations, including poor RV image quality and lack of a universal definition of RV dysfunction. Indeed, this method has limited sensitivity and negative findings on echocardiography do not exclude a diagnosis of PE (Miniati et al., 2001). In contrast, CT pulmonary angiography allows direct visualization of clots, as well as providing information on the status of the right heart and other adjacent organs. This tool is available around the clock at most institutions and has become the first-line test for patients suspected of having PE. PE may be diagnosed and its risk stratified at the same time. Of course, CT has several limitations, including an inability to assess RV function in real time and the lack of universally accepted criteria. Confirmation of these findings in further, prospective studies may make multidetector-row chest CT a reasonable alternative to echocardiography for diagnosing RV dysfunction. Imaging techniques are constantly being improved in the

et al., 2011). A novel dual energy perfusion defect score has been proposed, in which the degree of lung perfusion in each segment is graded on a 3-point scale (0, normal perfusion; 1, moderately reduced perfusion, 2, profoundly reduced or absent perfusion), with the perfusion defect score calculated as ∑(n∙d)/40x100, where n is the number of segments and d is the degree of the perfusion defect (Chae et al., 2010). The perfusion defect score has shown good correlation with RV/LV diameter ratio (*r* = 0.69, *p* < 0.001). In addition, the numbers of lobes with pulmonary perfusion defects on iodine images of DECTA correlated well with RV/LV diameter ratio (*r* = 0.66, *p* < 0.05), whereas the number of lobes with PE on CT angiography did not (*p* > 0.05). Quantification of the area of pulmonary perfusion defect on iodine images showed that an pulmonary perfusion defect over 215.4 ml or a relative volume over 9.9% was related to an RV/LV diameter ratio > 1 (Bauer et al., 2011). These results therefore indicate that pulmonary perfusion defect size may be a surrogate marker for RV dysfunction (Fig. 6, Fig. 7). Readmission and death due to PE were observed only in patients with a relative perfusion defect size >5% of total lung volume, but not in any patient with a relative perfusion defect < 5% (Bauer, Frellesen et al. 2011). Patients with a relative perfusion defect >5% also showed lower median survival with increased relative hazard ratio for death than those with a relative perfusion defect <5%. These results indicate

that pulmonary perfusion defect size may be prognostic in patients with PE.

**5. The role of chest computed tomography as an alternative to** 

patients with PE.

**echocardiography** 

The status of the pulmonary microvasculature is important in evaluating disease severity and prognosis in patients with PE. Although ventilation/perfusion scintigraphy was used to assess the pulmonary nomenclature, multi-detector CT angiography has replaced scintigraphy in the evaluation of these patients, since CT has higher spatial resolution and shorter acquisition time. Recently developed advanced CT techniques, including DECT, permits the evaluation of pulmonary perfusion status without significant additional radiation dose. Therefore, DECTA may become a leading imaging tool, both for detecting emboli and for risk stratification regarding of regional pulmonary perfusion status in

Retrospective studies have shown that multidetector chest CT and echocardiography yield similar prognostic data (Sanchez et al., 2008). While CT provides information on RV dilatation only, echocardiography also provides some information on contractility, e.g., septal or RV hypo- or dyskinesia. However, echocardiography is not always available in emergency settings and has limitations, including poor RV image quality and lack of a universal definition of RV dysfunction. Indeed, this method has limited sensitivity and negative findings on echocardiography do not exclude a diagnosis of PE (Miniati et al., 2001). In contrast, CT pulmonary angiography allows direct visualization of clots, as well as providing information on the status of the right heart and other adjacent organs. This tool is available around the clock at most institutions and has become the first-line test for patients suspected of having PE. PE may be diagnosed and its risk stratified at the same time. Of course, CT has several limitations, including an inability to assess RV function in real time and the lack of universally accepted criteria. Confirmation of these findings in further, prospective studies may make multidetector-row chest CT a reasonable alternative to echocardiography for diagnosing RV dysfunction. Imaging techniques are constantly being improved in the diagnostic workup of patients with suspected PE. Thus, CT has the potential to become the link between diagnostic and risk stratification strategies in this setting.

Fig. 6. Pulmonary embolism without right ventricular dysfunction. (a) Dual-energy CT angiography (DECTA) shows filling defect in segmental branches of pulmonary arteries in right lower lobe. (b) DECTA shows normal ranged diameters of ventricles (RV/LV ratio < 1). (c & d) Lung iodine images show wedge shaped pulmonary perfusion defect in right lower lobe lateral basal segment where emboli completely occludes pulmonary artery. However, the posterior basal segment of right lower lobe shows normal perfusion status, because emboli partly occlude corresponding pulmonary artery. The relative volume of pulmonary perfusion defect was 8.3% and perfusion defect score was 10.

Risk Stratification of Submassive Pulmonary Embolism:

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Fig. 7. Pulmonary embolism with right ventricular dysfunction. (a) Dual-energy CT angiography (DECTA) shows filling defect in right main pulmonary artery. (b) DECTA shows enlarged right ventricle (RV/LV ratio > 1). (c & d) Lung iodine images show perfusion defect in right lung except superior segment and posterior basal segment of right lower lobe. Multifocal wedge shaped perfusion defect in also noted in subpleural portion of left lung. The relative volume of pulmonary perfusion defect was 47.8% and perfusion defect score was 52.5.
