**3.2 Diagnosis of pulmonary embolism**

In PE, an embolus blocks the blood flow, causing a perfusion defect, while ventilation remains normal because there is no corresponding blockage in the airway. To characterize the pattern of perfusion defects is crucial. Perfusion defects due to blockage of a pulmonary artery should reflect the branching of pulmonary circulation and its classical segmental anatomy. A segmental defect is wedge shaped with its base on the pleura.

On V/P SPECT images, it is relatively easy to identify segmental and sub-segmental patterns of perfusion defects. Figure 4a shows multiple perfusion defects in acute stage in a female patient with chest pains, who had fainted outside the hospital. Applying quantification on V/P SPECT images, extension of PE was estimated to be ca 60%. The patient was treated first with heparin for a week. However, Follow up showed limited regression (Fig 4b). As brain hemorrhage was excluded, thrombolysis was administered. The following day perfusion was normalized (Fig 4c).

Figure 2 shows sagittal slices of right lung of a patient studied for acute breathlessness. A segmental perfusion defect was well delineated, in perfusion and V/Pquotient images (Fig 2a). Moreover, it was possible to see broncho-constriction in the posterior part of the lung (blue arrow). The extension of perfusion defect was estimated at 10% and ventilation defect 25%. Three days later nearly complete resolution of the embolus was observed, as well as normalization of the ventilation (Fig 2b).

In planar images, the identification of a solitary segmental perfusion defect within middle lobe and lingula is often impossible or, at best, difficult. With tomographic images these changes are well delineated.

It is important to be aware that mismatch findings not having segmental character do not usually represent PE. Non segmental mismatch means that perfusion defects do not conform to segmental anatomy and are caused by other diseases. This is observed in patients with heart failure (Jögi et al., 2008), pneumonia, mediastinal adenopathy, post radiation therapy etc. Total absence of perfusion in one lung without any other region of mismatch is often caused by pathology other than PE, such as a central tumour or abscess.

#### **3.3 Follow up**

Follow up is a frequently overlooked aspect of diagnostic strategies although it is essential both for clinical and scientific reasons. The follow up is necessary to assess the effect of treatment, especially to see the effect of anticoagulant therapy (Fig 4b) and in these cases to be able to adjust therapy or, if necessary, continue with thrombolysis (Fig 4c).

Quantitative Ventilation/Perfusion Tomography:

shows mismatch along the lung periphery.

and sub-segmental nature of perfusion defects caused by PE.

method for clinical diagnosis, follow up and research (Bajc et al., 2009b).

**considerations** 

V/Pquotient images show mismatch along the lung periphery (Fig 6).

occlusive disease is a rare but important differential diagnosis.

The Foremost Technique for Pulmonary Embolism Diagnosis 193

normal. In some patients mismatch without clear segmental or sub-segmental pattern is observed. Peripheral zones of the lung lack perfusion. The centre of the lung is hyperperfused. The lung appears significantly smaller on perfusion images compared to ventilation and the

In recent guidelines for the diagnosis and treatment of pulmonary hypertension it is stated that "ventilation/perfusion scan remains the screening method of choice for chronic pulmonary hypertension" (Galie et al., 2009). It was also pointed out that pulmonary veno-

Fig. 6. Patient with pulmonary hypertension caused by chronic PE. Peripheral zones of the lung lack perfusion (arrows). The centre of the lung is hyperperfused .V/Pquotient images

In a clinical study, 53 % more mismatch points were identified with V/P SPECT compared to planar technique (Bajc et al., 2004). Similar results have been found by others (Gutte et al., 2010; Reinartz et al., 2001). SPECT eliminates superimposed structures, clarifying segmental

The value of V/P SPECT is further confirmed in clinical studies (Bajc et al., 2008; Gutte et al., 2009; Leblanc et al., 2007; Lemb & Pohlabeln, 2001). V/P SPECT is today the recommended

Powell reported that sensitivity and specificity of CT for central PE are about 90% (Powell & Muller, 2003). Perrier et al. found in a broad clinical material that CT had a sensitivity of 70% for PE and a specificity of 91 % (Perrier et al., 2001). They concluded: "clinical CT should not

**4. Sensitivity and specificity of V/P SPECT and other methodological** 

Moreover follow up is important


For follow up, V/P SPECT is the only suitable method for the following reasons:


To be able to study the efficacy of treatment, in individual patients the same method should be used both for diagnosis and follow up. This is a further strong argument in favour of V/P SPECT as the primary diagnostic method for PE.

Fig. 5. Patient with chronic PE. Frontal slices. Multiple perfusion defects are seen (arrows). MDCT was normal.

#### **3.4 Chronic pulmonary embolism**

Chronic PE is a progressive disease that develops in about 5 % of patients, even after treatment (Begic et al., 2011; Pengo et al., 2004), after an acute episode of PE . However, it often has an insidious onset. It might lead to pulmonary hypertension, right heart failure and arrhythmia, which are frequent causes of death. The value of ventilation/perfusion scintigraphy is well established. It has recently been confirmed in a head to head comparison between MDCT and planar scintigraphy with pulmonary angiography as reference. Among patients with pulmonary hypertension, scintigraphy had a sensitivity of 96-97% and specificity of 90 %, while MDCT had a sensitivity of 51% (Tunariu et al., 2007). The conclusion was that ventilation/perfusion scintigraphy "has a higher sensitivity than MDCT as well as very good specificity in detecting chronic pulmonary thromboembolic disease as a potentially curable cause of pulmonary hypertension". Scintigraphic features of chronic PE vary. Figure 5 illustrates a case of multiple perfusion defects which are similar to acute PE. MDCT was

• To assess the need for prolonged oral anticoagulation beyond 6 months, where there are

• To allow differentiation between new and old PE, where a recurrence of PE is

• To explain physical incapacity after PE in case of permanently impaired lung function.

• To identify patients with remaining perfusion defects after treatment as these could be

• Detection of all emboli requires that the whole lung is examined with a sensitive

To be able to study the efficacy of treatment, in individual patients the same method should be used both for diagnosis and follow up. This is a further strong argument in favour of V/P

Fig. 5. Patient with chronic PE. Frontal slices. Multiple perfusion defects are seen (arrows).

Chronic PE is a progressive disease that develops in about 5 % of patients, even after treatment (Begic et al., 2011; Pengo et al., 2004), after an acute episode of PE . However, it often has an insidious onset. It might lead to pulmonary hypertension, right heart failure and arrhythmia, which are frequent causes of death. The value of ventilation/perfusion scintigraphy is well established. It has recently been confirmed in a head to head comparison between MDCT and planar scintigraphy with pulmonary angiography as reference. Among patients with pulmonary hypertension, scintigraphy had a sensitivity of 96-97% and specificity of 90 %, while MDCT had a sensitivity of 51% (Tunariu et al., 2007). The conclusion was that ventilation/perfusion scintigraphy "has a higher sensitivity than MDCT as well as very good specificity in detecting chronic pulmonary thromboembolic disease as a potentially curable cause of pulmonary hypertension". Scintigraphic features of chronic PE vary. Figure 5 illustrates a case of multiple perfusion defects which are similar to acute PE. MDCT was

• The cumulative radiation dose is a central issue when the indication for PE is relative • V/P SPECT is the only method which enables functional impairment to be determined due to increased dead space from non-perfused lung units and increased pulmonary

• To evaluate and compare drugs and treatment strategies.

vascular resistance due to a reduced vascular bed.

SPECT as the primary diagnostic method for PE.

particularly susceptible to developing pulmonary hypertension

For follow up, V/P SPECT is the only suitable method for the following reasons:

Moreover follow up is important

extensive remnants of PE.

suspected.

method.

MDCT was normal.

**3.4 Chronic pulmonary embolism** 

normal. In some patients mismatch without clear segmental or sub-segmental pattern is observed. Peripheral zones of the lung lack perfusion. The centre of the lung is hyperperfused. The lung appears significantly smaller on perfusion images compared to ventilation and the V/Pquotient images show mismatch along the lung periphery (Fig 6).

In recent guidelines for the diagnosis and treatment of pulmonary hypertension it is stated that "ventilation/perfusion scan remains the screening method of choice for chronic pulmonary hypertension" (Galie et al., 2009). It was also pointed out that pulmonary venoocclusive disease is a rare but important differential diagnosis.

Fig. 6. Patient with pulmonary hypertension caused by chronic PE. Peripheral zones of the lung lack perfusion (arrows). The centre of the lung is hyperperfused .V/Pquotient images shows mismatch along the lung periphery.
