**7. References**

180 Pulmonary Embolism

(a) (b)

(c) (d)

defect score was 52.5.

**6. Conclusion** 

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

This chapter focused on the prognostic value of RV dysfunction as measured by chest CT in patients with hemodynamically stable PE. Although echocardiographic assessment of RV dysfunction is a generally accepted imaging modality, the lack of a clear echocardiographic definition of RV dysfunction, and the poor RV images, reduces its diagnostic capabilities. RV dysfunction assessed by CT, including RV enlargement, RV/LV ratio, interventricular septal bowing, pulmonary obstruction score, and pulmonary perfusion defect have been associated with poor patient outcomes. Risk stratification of patients with stable PE based on chest CT findings may comparable in results to echocardiography and may be useful.


Risk Stratification of Submassive Pulmonary Embolism:

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**9** 

*Sweden* 

**Quantitative Ventilation/Perfusion** 

**for Pulmonary Embolism Diagnosis** 

*Lund University and Skåne University Hospital, Lund* 

Marika Bajc and Jonas Jögi *Department of Clinical Physiology* 

**Tomography: The Foremost Technique** 

The value of perfusion scintigraphy in the detection of pulmonary embolism (PE) was demonstrated as early as 1964 by Wagner et al. PE causes perfusion defects that conform to the anatomical distribution of the pulmonary vascular bed. Perfusion defects in acute PE are therefore of sub-segmental, segmental or lobar character. Ventilation is normally preserved in these areas and the observed wedge shaped mismatch between ventilation and perfusion is typical for PE. Planar ventilation/perfusion scintigraphy (V/P scan) was until the 1990s the method of choice for studying patients with suspected PE. However, the large Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED I), showed a high number of non-diagnostic examinations (65%) with V/P scan and the probabilistic interpretation criteria were confusing to the clinicians (Gray et al., 1993; The PIOPED Investigators, 1990). Planar imaging has become obsolete, particularly when the issue is

identification and quantification of focal or regional aberration of organ function.

defects down to the sub-segmental level (Bajc et al., 2002b).

cardiopulmonary diseases.

The advantage of three dimensional tomography over planar imaging for PE detection had already been shown in 1983 in a study on dogs (Osborne et al., 1983). Furthermore, Magnussen et al. (1999) used a computerized model of PE to highlight the advantage of SPECT over planar imaging in the assessment of the size and location of perfusion defects. Using a dual head camera, Palmer et al. (2001), developed a fast and efficient method for ventilation/perfusion tomography (V/P SPECT ) for clinical practice with total acquisition time of only 20 minutes. Moreover, they developed an algorithm to calculate the quotient between ventilation and perfusion and to present it as V/Pquotient images. This facilitated PE diagnosis and the quantification of PE extension, which led to the use of the term quantitative V/P SPECT. Using a porcine model, Bajc et al. validated V/P SPECT for diagnosis of PE and confirmed the superior value of tomography over planar imaging with excellent interobserver agreement of

The objective of this chapter is to acquaint readers with the latest methodological approach of V/P SPECT in the diagnosis of PE, in accordance with the new guidelines of the European Association of Nuclear Medicine (Bajc et al., 2009a, b). In this chapter we also discuss the value of V/P SPECT in the follow up after acute PE and in the diagnosis of other

**1. Introduction** 

Zhang, L. J., Yang, G. F., Zhao, Y. E., Zhou, C. S., & Lu, G M. (2009). Detection of pulmonary embolism using dual-energy computed tomography and correlation with cardiovascular measurements: a preliminary study. *Acta Radiol* Vol. 50 (8): 892-901.
