Venous thromboembolism Diagnosis These slides were kindly provided by AstraZeneca

2. Venous thromboembolism Venous thromboembolism (VTE) is a composite term for deep vein thrombosis (DVT) and pulmonary embolism (PE). VTE is a condition that begins with the formation of a blood clot, or thrombus, in one of the veins. This process is called DVT. The end of the thrombus often breaks free, forming an embolus that circulates in the blood until it becomes lodged in a vessel. If the emboli become lodged in the vessels of the lung the result is a potentially fatal PE. Even if DVT is asymptomatic, after some years post-thrombotic syndrome may develop as a result of damaged vasculature. This is a chronic condition that may contribute to long-term morbidity. Affected areas of soft tissue are also more susceptible to bacterial infection leading to ulceration. Pulmonary hypertension may develop from PE and also contribute to the long-term morbidity and even poor survival. Venous thromboembolism (VTE) is a composite term for deep vein thrombosis (DVT) and pulmonary embolism (PE). VTE is a condition that begins with the formation of a blood clot, or thrombus, in one of the veins. This process is called DVT. The end of the thrombus often breaks free, forming an embolus that circulates in the blood until it becomes lodged in a vessel. If the emboli become lodged in the vessels of the lung the result is a potentially fatal PE. Even if DVT is asymptomatic, after some years post-thrombotic syndrome may develop as a result of damaged vasculature. This is a chronic condition that may contribute to long-term morbidity. Affected areas of soft tissue are also more susceptible to bacterial infection leading to ulceration. Pulmonary hypertension may develop from PE and also contribute to the long-term morbidity and even poor survival.

3. Deep vein thrombosis Formation of a blood clot or thrombus commonly occurs in the femoral or more distal veins of the legs where a large volume of blood tends to collect at low pressure. Blood stasis can then occur, favouring development of a long thrombus. This process is called deep vein thrombosis (DVT). Proximal and distal DVT are defined as thrombi located in the deep veins above and below the knee (trifurcation of pes anserinus), respectively.Formation of a blood clot or thrombus commonly occurs in the femoral or more distal veins of the legs where a large volume of blood tends to collect at low pressure. Blood stasis can then occur, favouring development of a long thrombus. This process is called deep vein thrombosis (DVT). Proximal and distal DVT are defined as thrombi located in the deep veins above and below the knee (trifurcation of pes anserinus), respectively.

4. DVT: ultrasonography, venography PE: scintigram, spiral CT, angiography Diagnosis of VTE

5. Clinical probability of VTE Can be assessed through prediction rules Not accurate enough to rule in or out the disease Accurate enough to: refine interpretation of diagnostic tests identify a low-risk group in which the diagnostic workup may be simplified Patients with DVT often present with symptoms that are common for other conditions too. A clinical scoring system, derived from analysis of large databases, can be used to improve accuracy (Wells et al 1997). It is generally accepted, however, that clinical assessment is only valuable in combination with objective tests. PE also presents with non-specific symptoms. In the study using the Geneva Prediction Score (GPS) for clinical assessment, the prevalence of PE was 10%, 38% and 81% in patients classified as having a low, intermediate and high probability of PE, respecitvely (Wicki et al 2001). A comparison of clinical assessments with angiographic results revealed that clinical assessments were only correct in 68% of cases in which clinical suspicion was classified as high. When clinical suspicion was classified as low, PE was found in 9% of patients (PIOPED Investigators 1990). Thus, as for DVT, clinical assesments alone are not adequate. In addition to the problem of non-specific, unreliable symptoms, diagnosis of DVT and PE is hampered by the number of asymptomatic cases. References: Wells PS, Anderson DR, Bormanis J, Guy F, Mitchell M, Gray L et al. Value of assessment of pre test probability of deep vein thrombosis in clinical management. Lancet 1997;350:1795-8. Wicki J, Perneger TV, Junod AF, Bounameaux H, Perrier A. Assessing clinical probability of pulmonary embolism in the emergency ward: a simple score. Arch Intern Med 2001;161:92-7. PIOPED Investigators. Value of the ventilation/perfusion scan in acute pulmonary embolism. Result of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED). JAMA 1990;263:2753-9.Patients with DVT often present with symptoms that are common for other conditions too. A clinical scoring system, derived from analysis of large databases, can be used to improve accuracy (Wells et al 1997). It is generally accepted, however, that clinical assessment is only valuable in combination with objective tests. PE also presents with non-specific symptoms. In the study using the Geneva Prediction Score (GPS) for clinical assessment, the prevalence of PE was 10%, 38% and 81% in patients classified as having a low, intermediate and high probability of PE, respecitvely (Wicki et al 2001). A comparison of clinical assessments with angiographic results revealed that clinical assessments were only correct in 68% of cases in which clinical suspicion was classified as high. When clinical suspicion was classified as low, PE was found in 9% of patients (PIOPED Investigators 1990). Thus, as for DVT, clinical assesments alone are not adequate. In addition to the problem of non-specific, unreliable symptoms, diagnosis of DVT and PE is hampered by the number of asymptomatic cases. References: Wells PS, Anderson DR, Bormanis J, Guy F, Mitchell M, Gray L et al. Value of assessment of pre test probability of deep vein thrombosis in clinical management. Lancet 1997;350:1795-8. Wicki J, Perneger TV, Junod AF, Bounameaux H, Perrier A. Assessing clinical probability of pulmonary embolism in the emergency ward: a simple score. Arch Intern Med 2001;161:92-7. PIOPED Investigators. Value of the ventilation/perfusion scan in acute pulmonary embolism. Result of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED). JAMA 1990;263:2753-9.

6. Specific fibrin degradation product– Sign of activated coagulation and fibrinolysis High sensitivity for VTE (95-99%)– Nearly all with VTE test positive High negative predictive value (95-99%)– Normal D-dimer excludes VTE Low specificity– Positive test does not differentiate between VTE or other cause, e.g. infection D-dimer Plasma D-dimer is a degradation product of cross-linked fibrin and has been shown to be elevated in patients with DVT and PE. Fibrin and therefore plasma D-dimer is produced in a variety of conditions, however, such as cancer, inflammation and infection. Thus, although D-dimer is specific for fibrin, fibrin is not specific for DVT and PE, limiting the application of this technique. This test may play a valuable role in excluding DVT and therefore minimising the need for more elaborate diagnostic techniques (Anderson & Wells 1999; Perrier & Bounameaux 2001) References: Anderson DR, Wells PS. Improvements in the diagnostic approach for patients with suspected deep vein thrombosis or pulmonary embolism. Thromb Haemost 1999;82:878-86. Perrier A, Bounameaux H. Cost-effective diagnosis of deep vein thrombosis and pulmonary embolism. Thromb Haemost 2001;86:475-87 Plasma D-dimer is a degradation product of cross-linked fibrin and has been shown to be elevated in patients with DVT and PE. Fibrin and therefore plasma D-dimer is produced in a variety of conditions, however, such as cancer, inflammation and infection. Thus, although D-dimer is specific for fibrin, fibrin is not specific for DVT and PE, limiting the application of this technique. This test may play a valuable role in excluding DVT and therefore minimising the need for more elaborate diagnostic techniques (Anderson & Wells 1999; Perrier & Bounameaux 2001) References: Anderson DR, Wells PS. Improvements in the diagnostic approach for patients with suspected deep vein thrombosis or pulmonary embolism. Thromb Haemost 1999;82:878-86. Perrier A, Bounameaux H. Cost-effective diagnosis of deep vein thrombosis and pulmonary embolism. Thromb Haemost 2001;86:475-87

7. Deep vein thrombosis – symptoms and signs are unreliable Patients with DVT often present with redness, pain and swelling of the affected limb. These symptoms are not reliable indicators of DVT, however, as they are common symptoms of other conditions too. It is generally accepted that clinical assessment is only valuable in combination with objective tests.Patients with DVT often present with redness, pain and swelling of the affected limb. These symptoms are not reliable indicators of DVT, however, as they are common symptoms of other conditions too. It is generally accepted that clinical assessment is only valuable in combination with objective tests.

8. Diagnosis of DVT - venography Venography is the gold standard for the diagnosis of DVT with sensitivity and specificity reported to be nearly 100% (Tapson et al 1999). The venous circulation is visualised via injection of radiographic contrast medium into a vein. A filling defect in one of the veins is indicative for thrombosis. This procedure offers good visualisation at all levels of the calf and tigh and shows both the presence and extent of thrombosis. In addition, serial procedures can be performed to track progress. As an invasive procedure, however, it is now largely replaced by non-invasive alternatives, most commonly ultrasonography for DVT. Reference: Tapson VF, Carroll BA, Davidson BL, Elliott CG, Fedullo PF, Hales CA et al. The diagnostic approach to acute venous thromboembolism. Clinical practice guideline. American Thoracic Society. Am J Respir Crit Care Med 1999;160:1043-66.Venography is the gold standard for the diagnosis of DVT with sensitivity and specificity reported to be nearly 100% (Tapson et al 1999). The venous circulation is visualised via injection of radiographic contrast medium into a vein. A filling defect in one of the veins is indicative for thrombosis. This procedure offers good visualisation at all levels of the calf and tigh and shows both the presence and extent of thrombosis. In addition, serial procedures can be performed to track progress. As an invasive procedure, however, it is now largely replaced by non-invasive alternatives, most commonly ultrasonography for DVT. Reference: Tapson VF, Carroll BA, Davidson BL, Elliott CG, Fedullo PF, Hales CA et al. The diagnostic approach to acute venous thromboembolism. Clinical practice guideline. American Thoracic Society. Am J Respir Crit Care Med 1999;160:1043-66.

9. Diagnosis of DVT - ultrasonography Compression ultrasonography is the non-invasive technique of choice for the diagnosis of DVT. A transducer coated in gel is placed on the leg and moved along the deep venous system. As the transducer roams it emits sound waves, which are reflected off internal structures. These echoes are then translated to produce a visual image that can be viewed on a monitor. In the absence of DVT, gentle pressure applied to the skin through the transducer causes the vein to collapse such that the anterior and posterior walls become superimposed. In contrast, in patients with DVT it is not possible to collapse the vein lumen even with pressure sufficient to occlude the adjacent artery. The vein is assessed for compressibility at regular intervals along the deep venous system. A Doppler flow study, which uses emitted sound waves to detect the direction, velocity and turbulence of blood flow is often performed in combination with this technique. The sensitivity of compression ultrasonography has been shown to be 97% for proximal DVT, but only 73% for distal DVT. Venography remains only reliable test for DVT in the calf veins, iliac veins or vena cava. In addition, ultrasonography has a relatively poor sensitivity as a screening test in asymptomatic patients (Wells et al 1995) Reference: Wells PS, Lensing AW, Davidson BL, Prins MH, Hirsh J. Accuracy of ultrasound for the diagnosis of deep vein thrombosis in asymptomatic patients after orthopaedic surgery: metaanalysis. Ann Intern Med 1995;122:47-53.Compression ultrasonography is the non-invasive technique of choice for the diagnosis of DVT. A transducer coated in gel is placed on the leg and moved along the deep venous system. As the transducer roams it emits sound waves, which are reflected off internal structures. These echoes are then translated to produce a visual image that can be viewed on a monitor. In the absence of DVT, gentle pressure applied to the skin through the transducer causes the vein to collapse such that the anterior and posterior walls become superimposed. In contrast, in patients with DVT it is not possible to collapse the vein lumen even with pressure sufficient to occlude the adjacent artery. The vein is assessed for compressibility at regular intervals along the deep venous system. A Doppler flow study, which uses emitted sound waves to detect the direction, velocity and turbulence of blood flow is often performed in combination with this technique. The sensitivity of compression ultrasonography has been shown to be 97% for proximal DVT, but only 73% for distal DVT. Venography remains only reliable test for DVT in the calf veins, iliac veins or vena cava. In addition, ultrasonography has a relatively poor sensitivity as a screening test in asymptomatic patients (Wells et al 1995) Reference: Wells PS, Lensing AW, Davidson BL, Prins MH, Hirsh J. Accuracy of ultrasound for the diagnosis of deep vein thrombosis in asymptomatic patients after orthopaedic surgery: metaanalysis. Ann Intern Med 1995;122:47-53.

10. Diagnosis of DVT - ultrasonography Compression ultrasonography is the non-invasive technique of choice for the diagnosis of DVT. A transducer coated in gel is placed on the leg and moved along the deep venous system. A Doppler flow study, which uses emitted sound waves to detect the direction, velocity and turbulence of blood flow is often performed in combination with this technique. The vein is assessed for compressibility at regular intervals along the deep venous system Compression ultrasonography is the non-invasive technique of choice for the diagnosis of DVT. A transducer coated in gel is placed on the leg and moved along the deep venous system. A Doppler flow study, which uses emitted sound waves to detect the direction, velocity and turbulence of blood flow is often performed in combination with this technique. The vein is assessed for compressibility at regular intervals along the deep venous system

11. Diagnosis of DVT - ultrasonography Compression ultrasonography is the non-invasive technique of choice for the diagnosis of DVT. A transducer coated in gel is placed on the leg and moved along the deep venous system. As the transducer roams it emits sound waves, which are reflected off internal structures. These echoes are then translated to produce a visual image that can be viewed on a monitor. The vein is assessed for compressibility at regular intervals along the deep venous system. A Doppler flow study, which uses emitted sound waves to detect the direction, velocity and turbulence of blood flow is often performed in combination with this technique. The following criteria are used to diagnose DVT with ultrasonography: Thrombus visible as an echogenic structure within the lumen of the vein Non-compressibility of the vein lumen as a result of the thrombus Changes in the flow dynamics within the vein detected by Doppler ultrasonography Compression ultrasonography is the non-invasive technique of choice for the diagnosis of DVT. A transducer coated in gel is placed on the leg and moved along the deep venous system. As the transducer roams it emits sound waves, which are reflected off internal structures. These echoes are then translated to produce a visual image that can be viewed on a monitor. The vein is assessed for compressibility at regular intervals along the deep venous system. A Doppler flow study, which uses emitted sound waves to detect the direction, velocity and turbulence of blood flow is often performed in combination with this technique. The following criteria are used to diagnose DVT with ultrasonography: Thrombus visible as an echogenic structure within the lumen of the vein Non-compressibility of the vein lumen as a result of the thrombus Changes in the flow dynamics within the vein detected by Doppler ultrasonography

12. Compression ultrasonography The compression manoeuvre is performed with the transducer held transverse to the vein. Pressure is applied to the surface of the skin through the transducer. This is transmitted to the deeper structures and causes the vein to collapse. The artery should not deform before the vein.The compression manoeuvre is performed with the transducer held transverse to the vein. Pressure is applied to the surface of the skin through the transducer. This is transmitted to the deeper structures and causes the vein to collapse. The artery should not deform before the vein.

13. Compression ultrasonography – normal veins The sonographic evaluation of the lower-extremity veins is mostlly focused on the performance of the compression ultrasound along the full length of both the femoral and popliteal veins. Imaging is done with the transducer held transverse to the vein. The deep artery and accompaning vein(s) are identified. Pressure is applied to the surface of the skin through the transducer. This is transmitted to the deeper structures and causes the vein to collapse, creating the illusion of a “wink”. The artery should not deform before the vein. (Video clip) The sonographic evaluation of the lower-extremity veins is mostlly focused on the performance of the compression ultrasound along the full length of both the femoral and popliteal veins. Imaging is done with the transducer held transverse to the vein. The deep artery and accompaning vein(s) are identified. Pressure is applied to the surface of the skin through the transducer. This is transmitted to the deeper structures and causes the vein to collapse, creating the illusion of a “wink”. The artery should not deform before the vein. (Video clip)

14. Doppler ultrasonography – normal veins Ultrasound color Doppler image showing a normal vascular examination with the transducer placed in the right groin. Visualised in cross-section is the common femoral vein (CFV) in blue, greater saphenous vein (SAPH) at the junction with the CFV and the common femoral artery (shown in red, adjacent to the CFV, at 10 and 11 o´clock. Ultrasound color Doppler image showing a normal vascular examination with the transducer placed in the right groin. Visualised in cross-section is the common femoral vein (CFV) in blue, greater saphenous vein (SAPH) at the junction with the CFV and the common femoral artery (shown in red, adjacent to the CFV, at 10 and 11 o´clock.

15. Doppler ultrasonography – normal veins The longitudinal image taken at the level of the popliteal vein. Color Doppler flow imaging can easily display the flow patterns within the lumen of the vein. (Video clip)The longitudinal image taken at the level of the popliteal vein. Color Doppler flow imaging can easily display the flow patterns within the lumen of the vein. (Video clip)

16. Doppler ultrasonography - DVT A. Non colour-flow ultrasound image of the external iliac artery (EIA) and vein (EIV) that shows noncompressibility of the external iliac vein due to presence of a thrombus. Non-compressibility of a vein is the primary diagnostic criterion on compression ultrasonography for acute venous thrombosis. B. Transverse view of the same vessels using colour-flow Doppler ultrasonography showing partially occluding thrombusA. Non colour-flow ultrasound image of the external iliac artery (EIA) and vein (EIV) that shows noncompressibility of the external iliac vein due to presence of a thrombus. Non-compressibility of a vein is the primary diagnostic criterion on compression ultrasonography for acute venous thrombosis. B. Transverse view of the same vessels using colour-flow Doppler ultrasonography showing partially occluding thrombus

17. Compression ultrasonography – DVT Transverse imaging of the vena femoralis dex. Non-compressibility of a vein is the primary diagnostic criterion on compression ultrasonography for acute DVT Transverse view of the same vessel using colour-flow Doppler ultrasonography showing a partially occluding thrombus The longitudinal image using colour-flow Doppler ultrasonography (Video clip)Transverse imaging of the vena femoralis dex. Non-compressibility of a vein is the primary diagnostic criterion on compression ultrasonography for acute DVT Transverse view of the same vessel using colour-flow Doppler ultrasonography showing a partially occluding thrombus The longitudinal image using colour-flow Doppler ultrasonography (Video clip)

18. Pulmonary embolism – symptoms and signs are unreliable Cough Dyspnea Chest pain Syncope Symptoms may be vague or absent Tachycardia Hypotension Hypo- or hyperventilation Low PaO2 – normal PaCO2 Deep vein thrombosis? Just as as deep vein thrombosis (DVT), pulmonary embolism (PE) also presents with unreliable symptoms such as cough, dyspnea, chest pain and syncope. Thus, as for DVT, clinical assessments alone are not adequate. In addition, clinical symptoms may be vague or absent.Just as as deep vein thrombosis (DVT), pulmonary embolism (PE) also presents with unreliable symptoms such as cough, dyspnea, chest pain and syncope. Thus, as for DVT, clinical assessments alone are not adequate. In addition, clinical symptoms may be vague or absent.

19. Diagnosis of PE - pulmonary angiography Pulmonary angiography is the diagnostic tool of choice in all patients where non-invasive tests are inconclusive, unavailable or contraindicated. PE is identified by complete obstruction of a vessel or a filling defect apparent following injection of a contrast medium directly into the pulmonary artery, via a catheter, as the patient inhales deeply. Pulmonary angiography is the gold standard for the diagnosis of PE. As an invasive procedure, however, it is now largely replaced by non-invasive alternatives, most commonly scintigraphy and spiral CT.Pulmonary angiography is the diagnostic tool of choice in all patients where non-invasive tests are inconclusive, unavailable or contraindicated. PE is identified by complete obstruction of a vessel or a filling defect apparent following injection of a contrast medium directly into the pulmonary artery, via a catheter, as the patient inhales deeply. Pulmonary angiography is the gold standard for the diagnosis of PE. As an invasive procedure, however, it is now largely replaced by non-invasive alternatives, most commonly scintigraphy and spiral CT.

20. Diagnosis of PE - pulmonary scintigraphyPerfusion imaging Pulmonary scintigraphy is the most commonly used diagnostic tool for PE, offering the key advantages of being non-invasive and having a proven safety record in extensive clinical trials. There are two components, namely perfusion and ventilation imaging. With perfusion imaging a radioactive isotope is injected intravenously to reveal any obstructions in blood flow in the lung. Perfusion abnormalities may be due to other conditions, however, such as pneumonia, in which part of the lung is shut off from both ventilation and perfusion. Ventilation imaging, which involves the patient inhaling gas labelled with a radioactive isotope, is therefore performed to eliminate these other possibilities. In patients with PE the perfusion, but not the ventilation scan, appears abnormal.Pulmonary scintigraphy is the most commonly used diagnostic tool for PE, offering the key advantages of being non-invasive and having a proven safety record in extensive clinical trials. There are two components, namely perfusion and ventilation imaging. With perfusion imaging a radioactive isotope is injected intravenously to reveal any obstructions in blood flow in the lung. Perfusion abnormalities may be due to other conditions, however, such as pneumonia, in which part of the lung is shut off from both ventilation and perfusion. Ventilation imaging, which involves the patient inhaling gas labelled with a radioactive isotope, is therefore performed to eliminate these other possibilities. In patients with PE the perfusion, but not the ventilation scan, appears abnormal.

21. Diagnosis of PE - pulmonary scintigraphyTwo types of imaging Pulmonary scintigraphy is the most commonly used diagnostic tool for PE, offering the key advantages of being non-invasive and having a proven safety record in extensive clinical trials. There are two components, namely perfusion and ventilation imaging. With perfusion imaging a radioactive isotope is injected intravenously to reveal any obstructions in blood flow in the lung. Perfusion abnormalities may be due to other conditions, however, such as pneumonia, in which part of the lung is shut off from both ventilation and perfusion. Ventilation imaging, which involves the patient inhaling gas labelled with a radioactive isotope, is therefore performed to eliminate these other possibilities. In patients with PE the perfusion, but not the ventilation scan, appears normal. Pulmonary scintigraphy is the most commonly used diagnostic tool for PE, offering the key advantages of being non-invasive and having a proven safety record in extensive clinical trials. There are two components, namely perfusion and ventilation imaging. With perfusion imaging a radioactive isotope is injected intravenously to reveal any obstructions in blood flow in the lung. Perfusion abnormalities may be due to other conditions, however, such as pneumonia, in which part of the lung is shut off from both ventilation and perfusion. Ventilation imaging, which involves the patient inhaling gas labelled with a radioactive isotope, is therefore performed to eliminate these other possibilities. In patients with PE the perfusion, but not the ventilation scan, appears normal.

22. Mammalian alveolar blood vessels (in-body photograph). An embolus has blocked the blood flow to an area of the lung. This unique in-body photograph shows stagnation of the blood flow in the alveolar circulation.Mammalian alveolar blood vessels (in-body photograph). An embolus has blocked the blood flow to an area of the lung. This unique in-body photograph shows stagnation of the blood flow in the alveolar circulation.

23. Diagnosis of PE - pulmonary scintigraphy Pulmonary scintigraphy is the most commonly used diagnostic tool for PE, offering the key advantages of being non-invasive and having a proven safety record in extensive clinical trials. Different evaluation criteria for scintigraphy resuts have been proposed such as the Biello, PIOPED and subsequently revised PIOPED criteria (Biello et al 1979; PIOPED Investigators 1990; Gottschalk et al 1993, Sostman et al 1994). According to the Biello and revised PIOPED criteria, results can be categorised into normal, low, intermediate or high probability of PE. A high probability scan plus a high clinical probability has been shown to indicate PE in 87-96% of cases. When a high probability scan is coupled with a low clinical probability, the probability of PE is reduced to 33-56% (PIOPED Investigators 1990; Wells et al 1998). One disadvantage of scintigraphy is that more than 50% of results will be classified as not high probability, necessitating the use of additional diagnostic procedures to verify or exclude the diagnosis of PE. References: Biello DR, Mattar AG, McKnight RC, Siegel BA. Ventilation-perfusion studies in suspected pulmonary embolism. Am J Roentgenol 1979;133:1033-7. PIOPED Investigators. Value of the ventilation/perfusion scan in acute pulmonary embolism. Result of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED). JAMA 1990;263:2753-9. Gottschalk A, Sostman H, Coleman R et al. Ventilation-perfusion scintigraphy in the PIOPED study. Part II. Evaluation of the scintigraphic criteria and interpretations. J Nucl Med 1993;34:1119-26. Sostman H, Coleman R, DeLong D et al. Evaluation of revised criteria for ventilation-perfusion scintigraphy in patients with suspected pulmonary embolism. Radiology 1994;193:103-7 Wells PS, Ginsberg JS, Anderson DR, Kearon C, Gent M, Turpie AG et al. Use of a clinical model for management of patients with suspected pulmonary embolism. Ann Intern Med 1998;129:997-1005.Pulmonary scintigraphy is the most commonly used diagnostic tool for PE, offering the key advantages of being non-invasive and having a proven safety record in extensive clinical trials. Different evaluation criteria for scintigraphy resuts have been proposed such as the Biello, PIOPED and subsequently revised PIOPED criteria (Biello et al 1979; PIOPED Investigators 1990; Gottschalk et al 1993, Sostman et al 1994). According to the Biello and revised PIOPED criteria, results can be categorised into normal, low, intermediate or high probability of PE. A high probability scan plus a high clinical probability has been shown to indicate PE in 87-96% of cases. When a high probability scan is coupled with a low clinical probability, the probability of PE is reduced to 33-56% (PIOPED Investigators 1990; Wells et al 1998). One disadvantage of scintigraphy is that more than 50% of results will be classified as not high probability, necessitating the use of additional diagnostic procedures to verify or exclude the diagnosis of PE. References: Biello DR, Mattar AG, McKnight RC, Siegel BA. Ventilation-perfusion studies in suspected pulmonary embolism. Am J Roentgenol 1979;133:1033-7. PIOPED Investigators. Value of the ventilation/perfusion scan in acute pulmonary embolism. Result of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED). JAMA 1990;263:2753-9. Gottschalk A, Sostman H, Coleman R et al. Ventilation-perfusion scintigraphy in the PIOPED study. Part II. Evaluation of the scintigraphic criteria and interpretations. J Nucl Med 1993;34:1119-26. Sostman H, Coleman R, DeLong D et al. Evaluation of revised criteria for ventilation-perfusion scintigraphy in patients with suspected pulmonary embolism. Radiology 1994;193:103-7 Wells PS, Ginsberg JS, Anderson DR, Kearon C, Gent M, Turpie AG et al. Use of a clinical model for management of patients with suspected pulmonary embolism. Ann Intern Med 1998;129:997-1005.

24. Diagnosis of PE - Spiral Computed Tomography (CT) Spiral Computed Tomography (CT) with intravenous contrast enhacement allows the direct visualisation of pulmonary emboli within the pulmonary arteries. In comparison with ordinary CT, it has higher sensitivity for the detection of PE. One major drawback of this technique is the risk of small emboli going undetected. Slide: Spiral CT showing a free thrombus in the right main pulmonary artery extending into the lower lobe pulmonary artery with a small section in a left segmental pulmonary artery.Spiral Computed Tomography (CT) with intravenous contrast enhacement allows the direct visualisation of pulmonary emboli within the pulmonary arteries. In comparison with ordinary CT, it has higher sensitivity for the detection of PE. One major drawback of this technique is the risk of small emboli going undetected. Slide: Spiral CT showing a free thrombus in the right main pulmonary artery extending into the lower lobe pulmonary artery with a small section in a left segmental pulmonary artery.

25. Diagnosis of PE - Spiral Computed Tomography (CT) Spiral Computed Tomography (CT) with intravenous contrast enhacement allows the direct visualisation of pulmonary emboli within the pulmonary arteries. In comparison with ordinary CT, it has higher sensitivity for the detection of PE. One major drawback of this technique is the risk of small emboli going undetected. Slide: A large embolus can be seen in the major vessels of both the right and the left lung.Spiral Computed Tomography (CT) with intravenous contrast enhacement allows the direct visualisation of pulmonary emboli within the pulmonary arteries. In comparison with ordinary CT, it has higher sensitivity for the detection of PE. One major drawback of this technique is the risk of small emboli going undetected. Slide: A large embolus can be seen in the major vessels of both the right and the left lung.