Role of Dual source CT angiography and perfusion in the diagnosis of pulmonary embolism

Transcription

1 Role of Dual source CT angiography and perfusion in the diagnosis of pulmonary embolism Poster No.: C-1145 Congress: ECR 2011 Type: Educational Exhibit Authors: P. S. Naphade, A. A. Raut, A. keraliya, R. gujrathi, P. nagure, B. PAI ; Mumbai/IN, Mumbai, MH/IN, mumbai/in, MUMBAI, MAHARASHTRA/IN Keywords: Lung, Pulmonary vessels, CT-Angiography, Embolism / Thrombosis DOI: /ecr2011/C-1145 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 25

2 Learning objectives To describe the technique of pulmonary perfusion imaging on a dual source CT scanner. To illustrate the normal imaging appearance of lungs on perfusion imaging. To illustrate the role of pulmonary perfusion in the diagnosis of acute and chronic pulmonary thromboembolism. In this educational exhibit, we will illustrate the role of dual energy CT angiography and perfusion scan in the diagnosis and management of pulmonary thromboembolism. Background Pulmonary thromboembolism is a common condition presenting in the emergency department. The classic clinical presentation of PTE is sudden onset dyspnea and chest pain. However atypical presentation is common. Early diagnosis is essential for appropriate thrombolytic therapy. Accurate diagnosis of PTE is possible with CT pulmonary angiography. With the advent of dual energy CT scanners, it is now possible to demonstrate the both the occlusive thrombus as well as perfusion defect simultaneously without need of any additional contrast. Dual energy CT - Dual source CT is used commonly for this purpose. In this CT scanner, two X-ray tubes are located in the gantry orthogonally to each other. Both tubes can operate at different voltages. The FOV of the detector corresponding to lower KV X-ray tube is limited (26cm). As the KV of both the tubes is different, the emergent X-ray beams are of different energies. Different types of tissues have different attenuation properties. Depending upon how a tissue behaves at different energies, we can know about the tissue composition. Dual energy scan can also be performed with a single source CT scanner. The rapid kilovoltage switching technique switches the tube energy from 80 to 140 KV to acquire dual energy images. Multilayer detector technology can be used to acquire dual energy images, in which the deeper detector receive higher energy X-rays. Page 2 of 25

3 The basic principle of dual-energy CT is material decomposition based on attenuation differences at different energy levels. The lung parenchyma is scanned simultaneously at 80 KV and 140 KV after contrast injection. The iodine in contrast medium has K-edge significantly higher than rest of body tissues. This causes increase attenuation of iodine containing substances at 80KV than at 140 KV. This provides information regarding the Iodine distribution in the lung parenchyma. TECHNIQUEWith the use of AP and lateral topograms, central position of the lungs in the gantry is ascertained as FOV of tube B is limited. ACQUISITION PARAMETERS Tube A Tube B KV Ref. mas Effective mas Care Dose 4D tube current modulation is very important in reducing the radiation dose. Collimation - 64x0.6mm Pitch Scan time- 8 sec ROI - Pulmonary artery Trigger HU- 100 Contrast - nonionic contrast mg I/ml at 4ml/sec followed by 50 ml saline at 4ml/ sec Delay - 6 to 8 seconds Dual energy mode scans in caudocranial direction Radiation dose- Equivalent to the single energy pulmonary angiography. Three datasets are formed- 140KV, 80KV and Weighted average images. Page 3 of 25

4 These datasets are processed with dual energy software on a workstation. These are displayed with PBV (Pulmonary blood volume) mode and Lung Vessel enhancement mode. In this exhibit, we will describe the normal imaging appearance of iodine map, imaging in acute and chronic pulmonary thromboembolism, artefacts and limitations in current technique. Imaging findings OR Procedure details Three datasets are formed from the dual energy raw data. The weighted average images contain 70% data from 140KV and 30% data from 80 KV datasets. These images are used for initial evaluation of pulmonary emboli in the pulmonary arterial branches. As 80KV dataset accentuates the contrast enhancement, sensitivity of detection of the emboli in peripheral arteries can be increased. Page 4 of 25

5 Fig.: Fig.1a: 80 KV post contrast axial CT image Page 5 of 25

6 Fig.: Fig.1b: 140 KV post contrast axial CT image Page 6 of 25

7 Fig.: Fig.1c: Weighted average axial CT image Dual energy application- These images are then loaded in the dual energy application. To display the iodine distribution map, two modes are commonly used. These are PBV and Lung Vessel enhancement. In the PBV mode, the parenchymal perfusion can be assessed by iodine distribution map. Several presets are available for demonstration of fusion images. The gray scale 8 bit and hot body 8 bit are commonly used. Iodine distribution maps appear homogenous without any focal defects in colour coded maps in a normally perfused lung parenchyma. Page 7 of 25

8 Fig.: Fig.1d: Axial PBV (Pulmonary Blood Volume) image reveals normal homogenous color coded iodine distribution map without any perfusion defects. Pericardiac pseudo increased perfusion is seen due to cardiac motion. Page 8 of 25

9 Fig.: Fig.1e: Axial PBV (Pulmonary Blood Volume) image with lung isolation shows normal pulmonary perfusion. In the Lung Vessel enhancement mode, the basic principle is to differentiate between the vessels with and without intraluminal iodine. The commonly used preset for this is gray scale 8 bit and hot metal 8 bit. The vessels containing iodine are demonstrated as red while those which are thrombosed appear blue.thus it allows easy and accurate differentiation between the normal and thrombosed vessels. Page 9 of 25

10 Fig.: Fig.1f: Axial Lung Enhancement image reveals peripheral pulmonary arteries in red shade suggest the presence of intraluminal iodine and this rules out presence of any thrombus within. Acute pulmonary thromboembolism Filling defects are seen in the contrast opacified branches of pulmonary artery on weighted average images. They may be occlusive causing complete obstruction of Page 10 of 25

11 vessel and mild dilatation of artery secondary to the thrombus. Nonocclusive thrombi are eccentric and form an acute angle with the vessel wall. PBV Mode - Reveals the perfusion defects caused by the occlusive thrombi as a defect in the colour coded images. They are usually peripheral located, wedge shaped and are in segmental/sub segmental or lobar distribution. Extent of the perfusion defects can help in predicting the functional significance of pulmonary emboli. Resolution of perfusion defect during the follow up of these patients rules out the presence of occlusive thrombi. Lung Vessel Mode -Detection of emboli in segmental and sub segmental arteries can be challenging on a single energy datasets. Lung Vessel mode allows the detection of these emboli confidently as it accurately differentiate the vessels with and without intraluminal iodine. Page 11 of 25

12 Fig.: Fig.2a: Axial image of CT pulmonary angiography reveals occlusive thrombus in the left descending pulmonary artery and the thrombus in right descending pulmonary artery forms an acute angle with the vessel wall. Page 12 of 25

13 Fig.: Fig.2b: Axial PBV image reveals classic multiple, wedge shaped perfusion defects in bilateral lung parenchyma corresponding to thrombi in pulmonary arteries. Page 13 of 25

14 Fig.: Fig.2c: Coronal reconstruction of CT pulmonary angiography reveals thrombi in bilateral descending pulmonary arteries. Page 14 of 25

15 Fig.: Fig.2d: Coronal PBV image reveals multiple perfusion defects in both lower lobes. Page 15 of 25

16 Fig.: Fig.2e: Coronal reconstruction of CT pulmonary angiography reveals peripheral branches of both descending pulmonary arteries to be thrombosed. Page 16 of 25

17 Fig.: Fig.2f: Coronal Lung Enhancement image reveals blue colour in the peripheral branches of bilateral descending pulmonary arteries suggestive of thrombosis. Page 17 of 25

18 Fig.: Fig.2g: Sagittal reconstruction of CT pulmonary angiography reveals segments of partial and complete thrombosis of descending pulmonary artery. Page 18 of 25

19 Fig.: Fig.2h: Sagittal Lung Enhancement image clearly demonstrates segments of partial (both blue and red colour) and complete (blue colour) thrombosis of descending pulmonary artery. CHRONIC PTE Page 19 of 25

20 In chronic pulmonary thromboembolism, eccentric thrombi form obtuse angle with the vessel wall. The thrombosed vessels are constricted. Signs of pulmonary arterial hypertension such as dilated main pulmonary artery can be seen. Mosaic perfusion is seen on lung windows because of vascular attenuation distal to the thrombus. PBV Mode- Demonstrates the patchy areas of perfusion defects in the iodine map. Page 20 of 25

21 Fig.: Fig.3a: Axial image of CT pulmonary angiography reveals partially occlusive thrombus in left main pulmonary artery forming obtuse angle with the vessel wall. Recanalisation of thrombus in right main pulmonary artery is seen. Main pulmonary artery is dilated suggestive of pulmonary hypertension. Fig.: Fig.3b: Axial CT scan of thorax (lung window) in a case of chronic pulmonary thromboembolism reveals mosaic perfusion. Page 21 of 25

22 Fig.: Fig.3c: Coronal PBV image in a case of chronic pulmonary thromboembolism reveals patchy perfusion defects in both lungs. Limitations It is not a dynamic acquisition. Rather it represents the static distribution of iodine in the lung parenchyma at a specific point in time. The FOV of tube B is limited. Peripheral parts of lungs cannot be included during the dual energy scan and therefore the peripheral perfusion defects may be missed especially in obese patients. Artefacts -can limit the usefulness of iodine maps. Page 22 of 25

23 Upper lobes - Dense contrast material in the SVC and brachiocephalic veins causes linear areas of pseudo increased and pseudo decreased perfusion. Middle lobe/lingula- Perfusion defects from cardiac motion. Lower lobes- Diaphragmatic motion creates perfusion alteration. Fig.: Fig.4: Axial PBV image reveals pseudo-increased perfusion in right middle lobe and lingula due to cardiac motion artefact. Page 23 of 25

24 Fig.: Fig.5: Coronal PBV image reveals linear areas of pseudo-increased and pseudo-decreased perfusion in the right upper lobe due to unusually high contrast enhancement in the right subclavian and brachiocephalic vein. The peripheral part of left lung is not covered in the scan field due to limited FOV of detector corresponding to 80 KV tube. Conclusion Dual energy perfusion CT can allow accurate diagnosis of acute and chronic pulmonary thromboembolism. It detects the thrombus in pulmonary artery besides assigning the functional significance to it. It can accurately access the response to thrombolytic treatment. It obviated the need of nuclear scan for assessment of perfusion. Page 24 of 25

25 Personal Information P.S.Naphade, Department of Radiology, SevenHills Hospital, Andheri east, Mumbai-59, Maharashtra,. - References 1. Sven F. Thieme, Thorsten R. C. Johnson, Christopher Lee, Justin McWilliams, Christoph R. Becker, Maximilian F. Reiser, Konstantin Nikolaou, Dual-Energy CT for the Assessment of Contrast Material Distribution in the Pulmonary Parenchyma, AJR 2009; 193: Sven F. Thieme, Sandra Hoegl, Konstantin Nikolaou, Juergen Fisahn, Michael Irlbeck, Daniel Maxien, Maximilian F. Reiser, Christoph R. Becker, Thorsten R. C. Johnson, Pulmonary ventilation and perfusion imaging with dual-energy CT, Eur Radiol (2010) 20: Coursey CA, Nelson RC, Boll DT, Paulson EK, Ho LM, Neville AM, Marin D, Gupta RT, Schindera ST, Dual-Energy Multide-tector CT: How Does It Work, What Can It Tell Us, and When Can We Use It in Abdominopelvic Imaging?, RadioGraphics 2010; 30: Kang MJ, Park CM, Lee CH, Goo JM, Lee HJ, Dual-Energy CT: Clinical Applications in Various Pulmonary Diseases, Radiographics 2010 May;30(3): Page 25 of 25