Novel assessment of retrospective on-demand analysis of venous thromboembolism by dual-layer spectral-detector CT

Abstract

Because the prognosis of pulmonary thromboembolism (PTE) will be often poor, early diagnosis and assessing severity at the first visit is important.

A 76-year-old man with suspected venous thromboembolism and a contrast deficit in the pulmonary artery (PA) was revealed by contrast-enhanced computed tomography (CT) imaging by dual-layer spectral-detector CT (IQon Spectral CT^®, Philips Healthcare, Best, The Netherlands). The lung perfusion image showed decreased perfusion in the culprit lesion. The dual-energy analysis of the virtual monoenergetic imaging showed clear visualization of deep vein thrombosis (DVT).

In a 64-year-old man, an IQon Spectral CT^® revealed a small contrast deficit in the PA. However, no perfusion abnormality was detected in the lung perfusion analysis.

The IQon Spectral CT^® enables the detection of lung perfusion abnormalities in addition to PTE. The IQon Spectral CT^® imaging may be useful for the “one-stop shop” evaluation of PTE and DVT.

<Learning objective: The prognosis of pulmonary thromboembolism (PTE) will be often poor, so early diagnosis and assessing severity at the first visit is important. The dual-layer spectral-detector computed tomography imaging for PTE, whereby the iodine map provided information regarding lung perfusion, whereas virtual monoenergetic images enabled clear visualization of deep vein thrombosis.>

Introduction

Acute pulmonary thromboembolism (PTE) is a pathological condition in which thrombus forms mainly in the peripheral vein of the lower extremities and moves to the pulmonary artery by blood flow and occludes the pulmonary artery. Approximately 90% of acute PTE cases originate from the deep vein of the lower extremity [1]. In cases with massive PTE that occludes the pulmonary artery truncus or main pulmonary artery it is reported that more than 40% of patients die within several days after onset [2]. The mortality rate increases as the hemodynamics at the time of onset is poor, and life prognosis is poor in patients who develop cardiopulmonary arrest or severe shock (circulatory collapse). Thus, early diagnosis is expected to improve the prognosis by allowing an earlier start of treatment. As a result, determining an appropriate treatment strategy and assessing severity at the first visit is important.

Case report 1

A 76-year-old man with a history of chemoradiotherapy for a nasal tumor and associated neck lymph node metastasis presented to an emergency department with a left forearm fracture. Despite the absence of venous thromboembolism (VTE) symptoms (dyspnea, leg swelling, etc.), the plasma D-dimer level in the emergency department was 15.5 μg/mL, and a VTE was suspected. The patient underwent contrast-enhanced computed tomography (CT) imaging by dual-layer spectral-detector CT (IQon Spectral CT^®, Philips Healthcare, Best, The Netherlands). This instrument acquires both conventional images and dual-energy images by measuring the low-energy regions of the emitted spectrum from the upper layer of the detector and high-energy regions from the deeper layer of the detector, allowing for the measurement of iodine density as well as clear visualization of thromboembolism. The CT images revealed a contrast deficit in the right superior pulmonary artery (Fig. 1A). The lung perfusion image from the dual-energy analysis showed decreased perfusion in the right upper lobe (Fig. 1C), and the iodine density of the lung was lower in the right upper lobe than in the left upper lobe (0.9 mg/mL vs 2.5 mg/mL). The patient was diagnosed with VTE [non-massive PTE and deep vein thrombosis (DVT)], and anticoagulation therapy with 60 mg of edoxaban (Lixiana^® and Savaysa^®, Daiichi Sankyo, Inc., Tokyo, Japan) daily was initiated. The follow-up contrast-enhanced CT performed 18 days after the initiation of anticoagulation therapy revealed that the thrombi had disappeared (Fig. 1B) and the lung perfusion had improved (2.6 mg/mL vs 2.6 mg/mL lung iodine density in the right and left upper lobe, respectively) (Fig. 1D).

Fig. 1.

Thoracic contrast-enhanced CT (A, B) and lung perfusion images (fused CT and iodine images) (C, D) in a 76-year-old man with PTE before (A, C) and after the anticoagulation therapy (B, D) and lower-extremity contrast-enhanced CT before therapy (E). PTE (A, arrow) is associated with decreased lung perfusion (C, asterisk). After therapy, PTE and the perfusion abnormality disappeared (B, D). On the retrospective virtual monoenergetic CT images (E), lower keV images show clear visualization of deep vein thrombosis (E, arrows). The contrast between venous lumen and thrombus is comparable between 120-kVp conventional and 70-keV monoenergetic images.

CT, computed tomography; PTE, pulmonary thromboembolism.

We conducted a delayed-phase CT scan 5 min after the contrast injection to evaluate DVT. The results showed a thrombus in the left lower extremity (peroneal vein, soleal vein, and popliteal vein) (Fig. 1E). The dual-energy analysis of the virtual monoenergetic imaging from 40 keV to 70 keV showed clear visualization of DVT due to the increased attenuation of iodine (contrast agent) in the vein in the lower energetic images (Fig. 1E).

Case report 2

A 64-year-old man with non-small cell lung carcinoma was hospitalized in the respiratory department to receive anticancer treatment. The patient complained of right upper and lower extremity swelling and pain for 10 days. The plasma D-dimer level on admission was 21.4 μg/mL, and VTE was suspected. An IQon Spectral CT^® revealed a small contrast deficit in the right inferior pulmonary artery (Fig. 2A). However, no perfusion abnormality was detected in the lung perfusion analysis (2.6 mg/mL vs 2.6 mg/mL lung iodine density in the right and left lower lobe, respectively) (Fig. 2B). The delayed-phased images showed there was DVT in the right upper extremity (subclavian and brachiocephalic veins) and both legs (femoral and soleal veins). The patient was diagnosed with VTE (non-massive PTE and DVT), and appropriate anticoagulation therapy was initiated.

Fig. 2.

Thoracic contrast-enhanced computed tomography (A) and lung perfusion image (B) in a 64-year-old man with pulmonary thromboembolism. A thrombus in the right inferior pulmonary artery is present (A, arrow), but the retrospective lung perfusion image shows no significant reduction in perfusion area (B).

Discussion

Contrast-enhanced CT is a feasible and established method for the diagnosis of both PTE and DVT, and it is becoming the first choice for PTE diagnosis [3]. However, conventional contrast-enhanced CT has two major problems for the evaluation of PTE and DVT. First, conventional contrast-enhanced CT lacks lung perfusion information despite the high detection of pulmonary arterial thrombosis. Second, a venous thrombus in the lower extremity may be often difficult to identify due to the poor contrast between the thrombus and weakly opacified lumen of the deep vein. A promising approach to overcome these problems is the use of dual-energy technology. In a dual-energy CT scan the data for both high- and low-energy are simultaneously acquired. These polyenergetic datasets enable the calculation and reconstruction of iodine-selective images and virtual monoenergetic images [4]. The CT number of iodine (contrast agent) is dependent on X-ray energy and increases at lower energy levels; thus, low-energy images result in higher contrast resolution.

In previous dual-energy CT approaches such as temporally two sequential rotations (Canon Medical, Tokyo, Japan), dual-source CT (Siemens Healthcare, Forchheim, Germany), and fast-switching dual-kVp CT (GE Healthcare, Little Chalfont, UK), dual-energy data acquisition must be performed prospectively, which means that the acquisition is applied in only selected patients. By contrast, the dual-layer spectral-detector CT, or IQon Spectral CT^®, has a different mechanism to acquire dual-energy CT data by using a single tube potential beam and two layered scintillation detectors [5]. That is, the dual-layer spectral-detector CT is always operating in a dual-energy mode. The main advantage of the IQon Spectral CT^® is the retrospective dual-energy analysis with no additional radiation dose. Using the conventional machine, dual-energy CT scanning is clinically performed for the assessment of PTE, but it is not generally applied for the assessment of DVT from the abdomen to the legs due to increase in radiation dose and image noise. On the other hand, IQon Spectral CT^® visualizes not only PTE and associated perfusion abnormality but also DVT with high contrast resolution and minimal image noise, leading to “one-stop shop” evaluation of PTE and DVT. We believe that pulmonary vascular diseases and aortic/peripheral artery diseases are suitable for IQon Spectral CT^® because it can clearly visualize these diseases in the long scan range with high contrast-to-noise ratio. Furthermore, the analyzing time is short and clinically acceptable. The spectral based image data are generated on the IQon Spectral CT^® console and transferred to a dedicated client/server system [Spectral Diagnostic Suite (SpDS), Philips] in approximately 3 min. The lung perfusion and virtual monoenergetic CT images are displayed in 1 min on the SpDS viewer application. These features enable the astute detection of both PTE and lung perfusion abnormality in addition to clear visualization of DVT in the lower extremity on virtual low keV images. In the present report, the iodine map for case 1 showed decreased lung perfusion in the PTE area, and monoenergetic images at low keV improved the visualization of DVT in the leg. Furthermore, dual-energy CT images after treatment demonstrated improved lung perfusion qualitatively and quantitatively. Conversely, the PTE of case 2 did not possibly cause a perfusion abnormality because the thrombus was small and collateral circulation was present.

We presented cases of PTE and DVT diagnosed by dual-layer spectral-detector CT imaging, whereby the iodine map provided information regarding lung perfusion, whereas virtual monoenergetic images enabled clear visualization of DVT. The dual-layer spectral-detector CT imaging may be useful for the “one-stop shop” evaluation of PTE and DVT.

The patients provided consent for publication.

Funding sources

None