Dual-Energy CT Angiography for Detection of Pulmonary Emboli: Incremental Benefit of Iodine Maps

Abstract

Purpose To determine if there is added benefit of using iodine maps from dual-energy (DE) CT in addition to conventional CT angiography images to diagnose pulmonary embolism (PE). Materials and Methods In this retrospective analysis, 1144 consecutive dual-energy CT angiography examinations performed from January through September 2014 at an oncologic referral center to evaluate for PE were reviewed. The 1144 examinations included 1035 patients (mean age, 58.7 years; range, 15-99 years). First, the location, level, and type (occlusive vs nonocclusive) of PEs on conventional CT angiograms were recorded. Iodine maps were then reviewed for defects suggestive of PE. Last, CT angiograms were rereviewed to detect additional PEs suggested by the iodine map. Consensus reviews were performed for examinations with PEs. The confidence interval of percentages was calculated by using the Clopper-Pearson method. Results On 147 of 1144 (12.8%) CT angiograms, a total of 372 PEs were detected at initial review. After review of the DE CT iodine map, 27 additional PEs were found on 26 of 1144 CT angiograms (2.3%; 95% confidence interval [CI]: 1.5%, 3.3%). Of the 27 additional PEs, six (22.2%) were segmental, 21 (77.8%) were subsegmental, 24 (88.9%) were occlusive, and three (11.1%) were nonocclusive. Eleven of 1144 (1.0%; 95% CI: 0.5%, 1.7%) CT angiograms had a new diagnosis of PE after review of the DE CT iodine maps. Conclusion Dual-energy CT iodine maps show a small incremental benefit for the detection of occlusive segmental and subsegmental pulmonary emboli. © RSNA, 2018.

Figure 1:

Dual-energy CT angiography (CTA) review scheme. Flowchart demonstrates method of consensus review.

Figure 2:

Pulmonary embolism (PE) at CT angiography (CTA) with, A, B, and without, C, D, corresponding finding on iodine map. A, Dual-energy (DE) CT angiogram in a 49-year-old man suspected of having PE. CT angiogram (left) with subsegmental occlusive PE in right lower lobe (arrow) with peripheral wedge-shaped defect (arrows) on iodine map (right). B, DE CT angiogram (left) in a 54-year-old woman suspected of having PE. CT angiogram with segmental occlusive PE in left lower lobe (arrow) with corresponding peripheral wedge-shaped defect (arrows) on iodine map (right). C, DE CT angiogram in a 60-year-old man suspected of having PE. CT angiogram (left) with segmental nonocclusive PE in right lower lobe (arrow) without corresponding finding on iodine map (right). D, DE CT angiogram (left) in a 66-year-old woman suspected of having PE. CT angiogram with subsegmental nonocclusive chronic-appearing PE in right lower lobe (arrow) without finding on iodine map (right).

Figure 3a:

Iodine map findings not reflecting pulmonary embolism (PE). (a) Dual-energy (DE) CT angiogram in a 44-year-old woman suspected of having PE. Peripheral defect (arrows) on iodine map (left) corresponds to consolidation (arrows) in soft-tissue (middle) and lung (right) windows. * = pleural effusion. (b) DE CT angiogram in a 64-year-old woman suspected of having PE. Defect (arrows) on iodine map reflects artifact from dense contrast opacification of the right atrium.

Figure 3b:

Iodine map findings not reflecting pulmonary embolism (PE). (a) Dual-energy (DE) CT angiogram in a 44-year-old woman suspected of having PE. Peripheral defect (arrows) on iodine map (left) corresponds to consolidation (arrows) in soft-tissue (middle) and lung (right) windows. * = pleural effusion. (b) DE CT angiogram in a 64-year-old woman suspected of having PE. Defect (arrows) on iodine map reflects artifact from dense contrast opacification of the right atrium.

Figure 4:

Iodine map suspicious for pulmonary embolism (PE) with, A, B, and without, C, D, CT angiography (CTA) correlate. A, B, PE initially detected on iodine map with correlate on CT angiogram on rereview. C, D, PE suspected on iodine map without correlate on CT angiogram on rereview. A, Dual-energy (DE) CT angiogram in a 64-year-old man suspected of having PE. Peripheral wedge-shaped defect (arrows) found on iodine map (left) suspicious for PE, confirmed upon rereview of CT angiogram (right, arrow). B, DE CT angiogram in a 61-year-old woman suspected of having PE. Small defect (arrows) on iodine map (left) with subsegmental PE (arrow) found on rereview on CT angiogram (right). C, DE CT angiogram in a 60-year-old woman suspected of having PE. Peripheral defects (arrows) on iodine map (left) with patent regional subsegmental pulmonary arteries (arrow) on CT angiogram (right). D, DE CT angiogram in a 40-year-old woman suspected of having PE. Peripheral defects (arrows) on iodine map (left) with patent regional subsegmental pulmonary arteries (arrows) on CT angiogram (right). * = liver dome.