**6. Some non-embolic pathological patterns that can be recognized on V/Q SPECT**

Although other pulmonary pathologies are not an indication for V/Q SPECT, diagnostic patterns have been described and validated for several situations and their recognition can provide useful information to the referring physician.

#### **6.1 COPD**

In COPD, ventilation is usually diffusely more affected than perfusion. The exact configuration depends on the severity of the process as well as the relative contribution of emphysema and bronchitis (figures 15 to 17). With a relatively pure bronchitis, the changes

It is therefore highly recommended that image interpretation is made with full knowledge of the clinical data and that correlation should be made with a recent chest x-ray. Correlation with existing anterior thoracic CT may be helpful in selected pathological cases. In this manner, high specificity can be achieved. Also, equivocal cases should be interpreted in light of the pre-test probability and knowledge of prior pulmonary pathology. Evidently, knowledge of prior PE or venous thrombotic disease is essential for the correct interpretation of positive cases. This type of interpretation ("holistic" or "Gestalt") is now considered as standard in most parts of the world and has been officially endorsed by the guidelines of the European Association of nuclear medicine

Fig. 13. Small apical mismatch caused by a bullae. This should be suspected in all non-

Although other pulmonary pathologies are not an indication for V/Q SPECT, diagnostic patterns have been described and validated for several situations and their recognition can

In COPD, ventilation is usually diffusely more affected than perfusion. The exact configuration depends on the severity of the process as well as the relative contribution of emphysema and bronchitis (figures 15 to 17). With a relatively pure bronchitis, the changes

segmental apical mismatch, although scarring may also cause a similar image.

**6. Some non-embolic pathological patterns that can be recognized** 

provide useful information to the referring physician.

(Bajc, Neilly et al. 2009).

**on V/Q SPECT** 

**6.1 COPD** 

Fig. 14. Asthma, acute attack (retrospective diagnosis). Aerosol therapy was begun before V/Q SPECT. Notice multiple non-vascular looking partial mismatches.

are mainly seen on the ventilation part of this study. Distribution is heterogeneous and, in the more severe cases, there may be focal deposition of Technegas in Airways. With advanced disease, there may be widespread focal deposition. On the other hand, perfusion is usually better preserved. With a pattern of relatively pure and advanced emphysema, perfusion and ventilation are more matched, reflecting mainly focal architectural pulmonary changes. It has been demonstrated that the degree of heterogeneity on the ventilation study, as well as the degree of heterogeneity of perfusion and ventilation matching, are both proportional to the severity of COPD. In fact, these measures appear to be more sensitive to the presence of COPD than high-resolution CT which, despite its higher resolution, has a limited capacity for the detection of airway closure. However, heterogeneous distribution of ventilation and perfusion can also be found in pulmonary oedema, lung fibrosis and infectious or non-infectious diffuse lung inflammation.

#### **6.2 Cardiac failure and volume overload**

Although pulmonary oedema is usually well demonstrated on a chest x-ray, in the early stages of volume overload the only sign will be vascular redistribution to the upper lung zone. On a V/Q SPECT study, this is very easily appreciated. Typically, the examination being performed in a supine position, redistribution will be most marked anteriorly and superiorly and will usually be much more apparent on perfusion then on ventilation (figure 18). In the earliest stages, the ventilation gradient will be totally preserved which produces a rather large scale partial mismatch. It is important that this pattern be recognized and not confused with bilateral partially occluding inferior lobar PE. It should be noted that cardiac failure is not the only cause of vascular redistribution. Volume overload, whether iatrogenic or caused by hepatic of renal failure may produce the same images.

Ventilation Perfusion Single Photon Emission

focal deposition on ventilation.

**6.3 Pneumonia and atelectasis** 

Tomography (V/Q SPECT) in the Diagnosis of Pulmonary Embolism 155

Fig. 17. Severe COPD. Multiple matched perfusion and ventilation defects associated with

In most cases, ventilation will be totally absent while perfusion will be partially preserved at least to some extent. Sometimes, a pattern of total reverse mismatch will be observed (absent ventilation with normal perfusion). It is unusual for PE to present with absent ventilation and some degree of residual perfusion. Also, in many cases of pneumonia, the distribution of the defect will not be compatible with a vascular anomaly (not pleural based, transsegmental or orientation not compatible with vascular anatomy). Preservation of some perfusion in the presence of an x-ray anomaly favours a non-embolic cause (figure 19).

Fig. 15. Mild to moderate COPD (selected coronal slices). Diffusely mottled ventilation with better preservation of perfusion.

Fig. 16. Moderate COPD. Focal deposition of Technegas with heterogeneous ventilation. Perfusion is also mottled but to a lesser degree.

Fig. 15. Mild to moderate COPD (selected coronal slices). Diffusely mottled ventilation with

Fig. 16. Moderate COPD. Focal deposition of Technegas with heterogeneous ventilation.

Perfusion is also mottled but to a lesser degree.

better preservation of perfusion.

Fig. 17. Severe COPD. Multiple matched perfusion and ventilation defects associated with focal deposition on ventilation.

#### **6.3 Pneumonia and atelectasis**

In most cases, ventilation will be totally absent while perfusion will be partially preserved at least to some extent. Sometimes, a pattern of total reverse mismatch will be observed (absent ventilation with normal perfusion). It is unusual for PE to present with absent ventilation and some degree of residual perfusion. Also, in many cases of pneumonia, the distribution of the defect will not be compatible with a vascular anomaly (not pleural based, transsegmental or orientation not compatible with vascular anatomy). Preservation of some perfusion in the presence of an x-ray anomaly favours a non-embolic cause (figure 19).

Ventilation Perfusion Single Photon Emission

(mismatched or not) (figures 20 and 21).

Fig. 20. Pleural effusion. Left: transverse slices show upward displacement of lung on both ventilation and perfusion, creating a non-segmental defect. Note band of hyperventilation indicating partially compressed lung. Right: sagittal slices in another patient show relatively preserved perfusion but absent ventilation. In this case, the effusion does not permit lung

**6.4 Interstitial pneumonitis** 

atelectasis.

expansion.

**6.5 Pleural effusion** 

Tomography (V/Q SPECT) in the Diagnosis of Pulmonary Embolism 157

Some recent work suggests that usual interstitial pneumonitis (UIP) can give rise to a rather specific pattern of sub pleural mismatch of crescent shape (Suga, Kawakami et al. 2009). The posterior surfaces of the lungs have to be excluded from the analysis however because in a supine position, this phenomenon is frequently observed because of gravity dependent

Pleural effusions of significant size are usually well recognized on V/Q SPECT. On transverse sections, the patient being in a supine position, the lung is displaced in the anterior direction as the effusion occupies the posterior region. On sagittal slices, there is loss of posterior angle. The perfusion and ventilation are typically matched although a thin band of hyperventilation is common at the lung-effusion interface because of compressed lung tissue. It is not uncommon however that the perfusion is better preserved. In that case, there is failure of the vasoconstriction reflex combined with lung compression which cannot be overcome by deep inspiration. For confident interpretation of a non-embolic effusion, there should not be any mismatches elsewhere and there should not be any hint of a wedge-shaped perfusion defect underlying the effusion

Fig. 18. Cardiac failure (volume overload). Note vascular redistribution to the super-anterior regions while normal gradient is preserved in ventilation.

Fig. 19. Pneumonia (triangulation in coronal, sagittal and tranverse slices). Note the large trans-segmental defect. Absent ventilation with some partial residual perfusion.
