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Lung Perfusion with Dual-energy Multidetector-row CT (MDCT)

Posted Nov 30, 2008 Updated Apr 7, 2023
By François Pontana MD , Jean-Baptiste Faivre MD , Martine Remy-Jardin MD PhD , Thomas Flohr PhD , Bernhard Schmidt PhD , Nunzia Tacelli MD , Vittorio Pansini MD , Jacques Remy MD
10 min read

Rationale and Objectives

To investigate the accuracy of dual-energy computed tomography in the depiction of perfusion defects in patients with acute pulmonary embolism (PE).

Materials and Methods

One hundred seventeen consecutive patients with clinical suspicion of acute PE underwent dual-energy multidetector computed tomographic (CT) angiography of the chest with a standard injection protocol. Two radiologists evaluated, by consensus, the presence of endoluminal clots on ( ) transverse “diagnostic” scans (contiguous 1-mm-thick averaged images from tubes A and B) and ( ) lung perfusion scans.

Results

Seventeen patients showed CT features of acute PE, with the depiction of 75 clots within the lobar (n = 15), segmental (n = 43) and subsegmental (n = 17) pulmonary arteries. A total of 17 clots were identified as complete filling defects (ie, obstructive clots), located within segmental (12 of 17) and subsegmental (5 of 17) arteries. Fourteen of the 17 obstructive clots were seen with the concurrent presence of corresponding perfusion defects, whereas cardiac motion and/or contrast-induced artifacts precluded the confident recognition of perfusion abnormalities in the remaining two segments and one subsegment. Four subsegmental perfusion defects were depicted without the visualization of endoluminal thrombi within the corresponding arteries. Perfusion defects were identified beyond five nonobstructive clots.

Conclusion

Simultaneous information on the presence of endoluminal thrombus and lung perfusion impairment can be obtained with dual-energy computed tomography.

Since the introduction of multidetector-row computed tomography with high spatial and temporal resolution, computed tomographic (CT) angiography (CTA) has become the reference standard for diagnosing acute pulmonary embolism (PE), with sensitivity and specificity varying between 83% and 100% and 89 and 97%, respectively ( ). Although the depiction of endoluminal clots within central pulmonary arteries is an easy task, it may be more difficult to identify filling defects within small-sized pulmonary arteries. This potential limitation of CTA could be theoretically compensated for by the detection of ischemic lung zones beyond the level of obstructive clots, provided both morphologic and functional information can be derived from the same data set. Moreover, despite the availability of high-resolution images of pulmonary arteries, CTA does not allow the analysis of lung perfusion impairment after acute PE, which is especially valuable in patients with underlying respiratory disease.

On the basis of single-source computed tomography, two approaches have been investigated for the detection of perfusion abnormalities, one using color-coded maps of lung density in humans ( ) and the other a subtraction technique using pre- and postcontrast conventional CT images in experimental animal studies ( ). Although both approaches have demonstrated the detectability of perfusion defects on computed tomography, the feasibility of these approaches in clinical practice have substantial limitations pertaining to scanning times and levels of radiation exposure to patients. The recent availability of dual-source computed tomography and the subsequent possibility to scan patients with dual energy offers another alternative for lung functional imaging. Preliminary experiences have shown that this technique could be applied to the analysis of lung perfusion, with radiation doses below the legally required levels ( ). The purpose of this study was to investigate the detectability of perfusion defects with dual-energy computed tomography in the clinical context of acute PE.

Materials and methods

Population

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Scanning Protocol

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Reconstructed Scans

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Figure 1, A 58-year-old man (weight, 72 kg; height, 170 cm) with normal results on computed tomographic angiography and on perfusion scanning. This example illustrates the three series of lung perfusion scans generated from each data set. (a) Native perfusion scan, 2 mm thick, obtained at the level of the upper lung zones. (b) Maximum intensity projection, 4 mm thick, obtained at the same level as that of (a) . Note the more homogeneous appearance of lung perfusion compared with (a) . (c) Fusion of the native perfusion scan and the mediastinal diagnostic scan, both reconstructed with the same section thickness (2 mm thick) at the same anatomic level. The fused image allows the simultaneous depiction of lung perfusion and surrounding anatomic structures.

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CT Parameters Analyzed

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Conditions of CT Interpretation

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Results

Analysis of Diagnostic Scans

Overall Quality of Diagnostic Scans

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Detection of Endoluminal Clots

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Figure 2, A 46-year-old man (weight, 93 kg; height, 173 cm) with bilateral acute pulmonary embolism. This example illustrates the similar depiction of endoluminal clots on averaged images from tubes A and B and transverse computed tomographic scans reconstructed from tube B acquisition. (a) Averaged image from tubes A and B obtained at the level of the right middle lobar bronchus, showing a partial filling defect in the right interlobar pulmonary artery ( arrow ). Note the lower image noise compared with (b) . (b) Tube B scan obtained at the same level as that shown in (a) , illustrating the similar depiction of the endoluminal clot ( arrow ) on the image acquired at 80 kV.

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Analysis of Perfusion Scans

Overall Quality of Perfusion Scans

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Figure 3, Same patient as shown in Figure 1 , illustrating the appearance of the peripheral rim devoid of perfusion information because of the small size of tube B. (a) Fused image of the native perfusion scan and mediastinal diagnostic scan at the level of the aortic arch. Perfusion imaging of both lungs was available. (b) Fused image of the native perfusion scan and mediastinal diagnostic scan at the level of the lower lung zones. Note the presence of an asymmetric peripheral rim ( arrows ), devoid of perfusion information.

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Analysis of Lung Perfusion

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Figure 4, A 26-year-old woman (weight, 70 kg; height, 173 cm) with bilateral acute pulmonary embolism. This example illustrates the depiction of a perfusion defect beyond an obstructive clot. (a,b) Mediastinal diagnostic images of the left hemithorax ( a , transverse computed tomographic scan; b , sagittal oblique reformation), enabling the depiction of an obstructive clot within a subsegmental artery of the anterior segment of the left upper lobe ( large arrow in a and b ). Note the additional presence of a nonobstructive clot at the level of the left lower lobar pulmonary artery ( small arrow in b ). (c) Fused image of the native perfusion scan and the mediastinal diagnostic scan (same orientation as that of b ), enabling the simultaneous depiction of the obstructive clot within the subsegmental artery of the anterior segment of the left upper lobe ( large arrow ) and the perfusion defect beyond it. Note the lack of alteration of lung perfusion beyond the nonobstructive clot within the left lower lobar pulmonary artery ( small arrow ). On this image, the endoluminal clots are color coded within the arterial lumen. (d) Lung diagnostic scan of the left hemithorax (same orientation as those of b and c ) demonstrating normal lung parenchyma in the area of perfusion defect.

Figure 5, Same patient as shown in Figure 4 , illustrating the ability to depict perfusion defects within airspace consolidation. (a,b) Mediastinal and lung diagnostic scans obtained at the same anatomic level, showing the presence of an obstructive clot within a subsegmental branch of the posterobasal segmental artery of the right lower lobe (arrow in a and b ). (c,d) Mediastinal and lung diagnostic scans obtained at the same anatomic level, 4 cm below (a) and (b) , showing the presence of peripheral airspace consolidation above the right-sided pleural effusion. Note a highly attenuating lateral portion of the consolidated lung ( arrow in c ), sharply demarcated from the hypoattenuated medial zone ( arrowheads in c ), which appears heterogeneous. (e,f) Maximum intensity projection (e) and corresponding fused image (f) of the native and diagnostic scans at the same anatomic level. Note the presence of a triangular, sharply delineated area of hypoperfusion in the posterobasal segment of the right lower lobe ( arrows in e and f ), contrasting with the surrounding normally perfused lung parenchyma. The highly attenuating portion of the peripheral airspace consolidation is normally perfused. The arrowhead (e) points to a peripheral triangular zone of hypoperfusion in which no endoluminal thrombus was depicted on computed tomographic angiography.

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Radiation Dose for Dual-energy CTA

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Discussion

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Academic Radiology, Volume 15, Issue 12
Journals General Radiology
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