2025 多学会临床共识声明：执行和报告疑似急性肺栓塞的CT血管造影的最佳方法

Graphical Abstract

 pulmonary embolism • computed tomography • reference standards • outcome • prognosis • diagnosis

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Introduction

Early recognition and accurate diagnosis of acute pulmonary embol ism (PE) is key in the timely initiation of appropriate treatment. 1 – 5 Computed tomography angiography (CTA), often referred to as com puted tomography pulmonary angiography, is the imaging modality of choice for diagnosing PE if it cannot be ruled out by using a clinical decision-making tool and D-dimer test. 1 , 2 In addition to aiding the clin ician in the diagnosis of PE, CTA images provide crucial information to guide the initial treatment approach (e.g. parameters of right ventricular overload or dysfunction are well-recognized predictors of short-term prognosis). Moreover, clot morphology as determined by CT imaging has been shown to predict long-term complications of acute PE 1 , 2 , 6 and may guide planning of advanced reperfusion strategies in selected patients. Finally, CTA may suggest alternative diagnoses in patients with dyspnoea or chest pain, such as the finding of pulmonary oedema, pericarditis, or aortic dissection, as well as clues to the underlying cause of the PE (e.g. cancer). Given the broad range of information that can be extracted from a CTA, the report should be timely and structured in a way that conveys all relevant clinical, functional, and prognostically rele vant findings. 7 , 8 However, to date, a formal standard for reporting a CTA in suspected acute PE derived through expert consensus and dis tillation of existing evidence does not exist.

For this purpose, representatives of the ESC; Working Group on Pulmonary Circulation & Right Ventricular Function, The Association for Acute Cardiovascular Care, and The European Association of Cardiovascular Imaging of the ESC together with representatives of the Fleischer Society convened to address this unmet need. A multidis ciplinary task force was installed with experts in PE diagnosis and man agement, radiological imaging as well as acute cardiovascular care, all representatives of the above-mentioned scientific societies ( $50\%$ ESC representation, $50\%$ Fleischer Society representation). The main aims were to produce a consensus statement that (i) describes current CT techniques for diagnosing PE, (ii) provides state-of-the-art best practices to achieve CTA scans with optimal quality, thereby reducing the number of non-diagnostic scans, (iii) standardizes commonly used nomenclature in CTA reports, and (iv) establishes a core set of CTA findings along with assessment instructions that are relevant for all acute PE patients and are advised to be routinely reported.

Methodology

Initially, the task force undertook an extensive overview of the litera ture concerning currently available and recommended CT techniques, diagnostic criteria for acute PE, criteria for optimising image quality, and strategies to overcome challenges in achieving diagnostic image quality.

A glossary was developed with frequently used terminology to describe the spectrum of pulmonary artery filling defects that can be seen on CTA. The glossary of definitions was extracted from the literature or when not available, determined by task force consensus.

Second, the task force undertook a comprehensive literature search to identify all radiological findings that have been studied for their prog nostic relevance for patients with a CTA diagnosis of PE. The search was performed using a predefined search string (see Supplementary data online, Appendix A ) by 2 independent readers and was integrated by cross-referencing, and additionally included a search of relevant ab stracts presented at international congresses. Relevant papers were screened, identified, and summarized in predefined outcome tables per radiological parameter. Selection of the core set of radiological find ings relevant for all PE patients was undertaken in an online three-round modified Delphi process: all CTA findings that were identified in the lit erature search to be consistently demonstrated to have prognostic va lue for the short (first 3 months after diagnosis) and/or long-term (beyond the first 3 months of follow-up) prognosis of PE patients were eligible. The following adverse events were deemed to be relevant for PE prognosis: death, admittance to the intensive care unit, haemo dynamic collapse, right ventricular failure, respiratory insufficiency, need for cardiopulmonary support, bleeding, recurrent venous thromboembolism, symptom burden, persistent symptoms, chronic thromboembolic pulmonary disease with/without pulmonary hyper tension, poor quality of life, change in New York Heart Association functional class, post-PE syndrome, post-PE impairment, myocardial in farction, stroke, systemic embolism, and health care costs. Using the RAND–University of California (Los Angeles, CA) method to reach consensus, all task force members were required to vote (excluding the patient representatives) to determine which outcomes should be kept for assessment in relation to the radiological findings. 9 The results of each vote were reviewed by all voting members of the task force be fore the next voting round. Inclusion in the final core set required that at least $80\%$ of the task force voted an item as essential. Essential CTA find ings were subdivided into ‘must-haves’ and ‘nice-to-haves’. The latter in dicated that the finding was considered relevant but not critical. CTA findings were excluded if at least an $80\%$ majority voted an item as not advised. In the last voting round, a $70\%$ majority was accepted as decisive. Lastly, an image atlas was created to illustrate the identified core set of CTA findings, including instructions on how these are to be assessed.

From inception, four patient representatives were involved in the planning of the project and task force activities, not only providing the patient perspective but also providing text for the lay language ver sion of the imaging atlas.

## CT scanning technology Chest CTA with single-energy CT

Over the last decades, the role of CT in the diagnostic approach of acute PE has exclusively relied on single-energy CT. The continuous technical evolution of multi-detector row CT (MDCT) has allowed for more flexible and high-performance protocols that match diagnos tic needs without compromising detail and coverage. The precise scan parameters depend on the number of slices that can simultaneously be acquired, gantry rotation speed, table speed, and beam width. Protocols differ according to the number of X-ray sources, the number of detector rows (currently ranging from 16 to 320 detector rows). The radiation dose of chest CTA examination has been reduced by the introduction of low-kilovoltage (kV) scanning. Hybrid- or model-based iterative reconstructions or deep learning reconstructions have been shown to reduce noise better than the more traditional filtered back projection and are considered the current technical standard. 10 , 11

Whatever the CT equipment available, the choice of scanning para meters follows universal recommendations. First, the highest temporal resolution (i.e. shortest rotation time) should be selected to avoid

respiratory motion artefacts and minimize cardiac motion artefacts. Second, the entire thorax should be covered at the highest pitch for non-pregnant persons, keeping in mind that the entire thorax can be currently covered in less than one second with high-pitch scanning modes. This can be of major interest in the emergency department, in tensive care, or for elderly patients where apnoea cannot be sustained. Shallow breathing is preferred to breath-hold techniques in dyspnoeic patients for better tolerance. Low-kV imaging is advised as it increases intravenous contrast material attenuation and minimizes radiation dose. 12 The optimal selection can be obtained using weight-based tube voltage selection or by means of automatic tube voltage selection. 13

Examinations are typically obtained using automatic triggering of data acquisition when the attenuation within the vessel of interest reaches a pre-defined threshold (i.e. timing bolus or bolus tracking). The trad itional CTA examination relies on the positioning of a region of interest (ROI) at the level of the pulmonary trunk with an exclusive opacification of the pulmonary arterial circulation at an optimal phase. Exclusive opa cification of the pulmonary arterial circulation is not encouraged be cause (i) the absence of opacification of the systemic circulation (aorta) does not give access to aortic differential diagnoses in the event of chest pain, (ii) in case of retrograde systemic- to-pulmonary artery shunts, very misleading images simulating filling defects may be ob served, and (iii) hypertrophy of the bronchial arteries (visible only in cases of global pulmonary and systemic opacification) can help detect chronic thromboembolism pulmonary hypertension (CTEPH).

An additional option is to scan the entire thorax while the pulmonary and systemic arterial circulations are simultaneously opacified, both at an optimal phase; the ROI is positioned at the level of the ascending aor ta or left atrium. This technique simultaneously allows for detection of endovascular pulmonary clots, and a comprehensive analysis of the chest organs at a systemic arterial phase with a single acquisition. It also provides adequate enhancement of cardiac cavities that may har bour acute thromboembolic disease. Contrast enhancement of the ves sels is mainly determined by the iodine concentration and injection rate (iodine flux). A rapid uniphase injection bolus is needed to achieve a high intensity of contrast opacification. 14 Table 1 summarizes the key scanning parameters for an optimized CTA examination in adults. All examinations are standard, non-electrocardiogram (ECG)-gated acquisitions. Of note, a recent expert consensus document of the Society of Cardiovascular Computed Tomography suggests that it would be appropriate to ECG gate aortic dissection, aneurysm and PE CTA examinations in men $>45$ years and women ${>}55$ years to analyse and report the coronary arteries, a recommendation that was followed by the European Association of Cardiovascular Imaging (EACVI). 15 , 16

In pregnant patients, larger blood volumes and increased cardiac out put can lead to earlier contrast opacification of the pulmonary arteries and dilution of contrast. 17 , 18 Poorly enhanced normal vessels can be misinterpreted as PE or fail to allow for visualization of PE. Tailoring CTA protocols in this patient population is essential to optimize con trast opacification and minimize radiation exposure to both the patient and foetus. Scanning the patient from the diaphragm to the top of the aorta reduces radiation exposure by $70\%$ , without sacrificing important diagnostic information. 19 Table 2 highlights CTA protocol optimization for PE in pregnant patients. When applied in a prospective trial, the number of non-diagnostic scans was very low. 20

Adequate contrast opacification is critical for diagnostic quality, which depends upon patient weight, cardiac output, scan duration, breath hold ing, and contrast delivery protocol. 14 , 17 , 18 , 21 – 29 The objective is to obtain homogenous opacification of pulmonary arteries that optimizes the diag nostic image quality for detection of acute PE. Arterial enhancement de pends on the amount of contrast delivered per unit of time (injection flow rate) and the injection duration, measured in seconds. With early MDCT scanners (i.e.16-MDCT), the theoretic minimum attenuation of blood

Table 1 Optimal CTA scan protocol for routine clinical practice

|Acquisition parameters||| |---|---|---| |Tube voltage|● 80-140 kV according to BMI|| |||● Possibility to use automatic kV selection (low kV in slim patients)| |Tube current||● Tube current varies based on the kilovoltage, patient size and region thickness| |||(image quality factor determined in protocol)| ||● Use of automatic tube current modulation|| |Rotation time|● Shortest rotation time|| |Collimation|● Thinnest collimation|| |Scanning direction|● Cranio-caudal or caudo-cranial|| ||| ● Alternative for severely dyspnoeic patients: caudo-cranial imaging to decrease respiratory motion artefacts in the lung bases | |Respiratory instructions|● Breath-hold at deep inspiration|| |||● Breath-hold at vital capacity or shallow breathing if chest pain/dyspnoea| |Reconstruction parameters||| |Section thickness|• 1-mm thick transverse CT sections|| |Field of view| • Adapted to the patient size || |Kernels of reconstruction||● Soft-tissue and high-spatial-resolution kernels for mediastinal and lung images, respectively| |Reconstructions||● Iterative reconstruction or deep learning reconstruction| |Injection parameters||| |Venous access|● > 20G in antecubital vein; smaller if poor venous access|| |Flow rate||● 3-5 ml/s in antecubital vein; lower if poor venous access (with higher iodine concentration)| |Concentration of the iodinated contrast material| ● 300-370 mg |/mL || |Volume administered|• 80-100 mL||

Table 2 Special considerations in pregnant patients

|Pregnancy-related concerns||Protocol|| |---|---|---|---| |Radiation dose reduction to maternal breast|Tube voltage||• Use of low (80-100) kV| |tissue and fetus|Tube current||● 100 kV and fixed mAs value around 80-100 mAs for a non-obese| ||||women| |Constant factors|Field of view||● Adapted to the patient size| ||Rotation time||Shortest rotation time| ||Breathing||Breath-holding after mild inspiration (vital capacity) or| ||||alternatively simple apnoea with an open mouth to avoid Valsalva| ||Scanning direction||Caudocranial imaging to decrease respiratory motion and dense| ||||contrast in SVC| || Section thickness Reconstruction kernels ||1- mm section thickness| |||| Soft tssue (mediastinal images) and high-spatial frequency (lung images) kernels | |Poor opacification based on expanded blood volume,|Contrast media injection||● > 20G intravenous access in antecubital vein| | hyperdynamic state and higher risk of transient interruption of contrast |||● Higher flow: 5 mL/s| ||||● Higher contrast concentration than standard protocol| ||||● Patient coaching to minimize contrast interruption|

required to see acute thromboemboli up to the segmental level was calculated to be 93 HU, a threshold not applied in clinical routine. 30 In cur rent practice, on a 64-detector CT, a mean pulmonary artery opacifica tion of 250 HU can be achieved with $1.2\,\mathsf{m L}/\mathsf{k g}$ of 350 mg I/mL injected at 4 mL/s. 14 The scan duration depends upon the scanner.

With a faster scanner, contrast volume can be decreased but timing be comes more crucial as the bolus duration shortens. 31

Although a contrast flow rate of at least $3\,\mathsf{m L}/s$ is associated with a lower frequency of insufficient contrast enhancement during chest CT, a flow rate of more than 4 mL/s using an 20-gage (G) cannula has been

suggested optimal for pulmonary thromboembolism (5, 21). 14 , 32 , 33 A lower volume of contrast and iodine dose can be administered when using a higher iodine concentration (350 mg iodine/mL vs. $300\;\mathsf{m g/m L}$ ) without compromising diagnostic image quality. 34 , 35 Intravenous contrast needs to be adjusted for patients with higher body mass index (BMI) (starting with a BMI exceeding $30\;\mathrm{kg/m^{\breve{2}}})$ . 26 Increasing contrast flow rate to ideally around $5{\mathrm{-}}6~{\mathsf{m L}}/{\mathsf{s}},$ , increasing contrast volume to at least 90 mL and using higher contrast concentra tion are effective in improving pulmonary arterial enhancement. 36 To minimize the risk of contrast extravasation, unnecessary high injection pressure and increased contrast viscosity, an 18-G peripheral venous catheter or, even better, a 20-G fenestrated peripheral venous catheter is placed in an antecubital position. Fenestrated catheters are more re cently available peripheral intravenous access devices with multiple side holes as opposed to a single end hole of standard catheters. While their smaller size improves the successful placement rate especially in pa tients with smaller veins, the 20-G fenestrated catheter allows an infu sion rate as high as a traditional 18-G catheter at 5.0–7.5 mL/s. 37

Chest CT angiography with spectral imaging and subtraction imaging

Dual-energy CT (DECT) involves the acquisition of two or more CT measurements with distinct energy spectra. Using the differential at tenuation of tissues and materials at different x-ray energies, DECT al lows distinction of tissues and materials beyond that possible with conventional CT. 38 DECT technologies can operate at the source or detector level. Dual-source, rapid tube-voltage switching, and dual-layer detector CT are the most commonly used DECT technologies. Although contrast-to-noise levels for unfiltered DECT data vary, in creasing with increasing energy separation, final image quality is mainly determined by the sophisticated noise suppression algorithms used by all vendors. Most of the currently available technologies typically use two energy levels, commonly referred to as DECT. Radiation dose with DECT is similar to that with single energy CTA acquired at $120\,\mathrm{kV}$ but usually higher than that of CTA acquired at lower kV.

With the use of two or more energy bins, photon-counting detector CT (PCD-CT) can provide the same information as multi-energy CT. Preliminary studies suggest that PCD-CT can perform routine CT with similar image quality and lower radiation dose as compared with DECT. 39 – 46 Optimized protocols for chest CT angiography with PCD-CT combine ultra-high-resolution and high-pitch data acquisition that improve the overall image quality at lower radiation doses com pared with traditional scanners equipped with energy-integrating de tectors. 47 , 48 As these approaches allow the creation of perfused blood volume images, a higher concentration of iodine $(350{\mathrm{-}}400\;{\mathrm{m}}{\mathrm{g/m}}\mathsf{L})$ is usually advised for the injection protocol.

Subtraction imaging also relies on the acquisition of two measure ments: one before contrast injection and one at peak contrast enhance ment. A low-kV technique is used and the pre-contrast scan is performed with a $30–50\%$ lower dose than the post-contrast scan. By subtracting the pre-contrast from the post-contrast scan, an iodine enhancement map is created requiring a non-rigid registration to ac commodate changes in inspiration. In addition, vessels are masked out and image noise is suppressed to provide a parenchymal enhance ment map, similar to ones employed with dual-source DECT. 49 – 51 Analogous to DECT, scans have to be timed so that there is already substantial pulmonary venous enhancement in addition to pulmonary arterial enhancement, to ensure that the capillary bed of the lung is suf ficiently enhanced and perfusion differences can be reliably detected.

CT lung perfusion imaging does not correspond to a comprehensive blood flow analysis but provides a static, single time point map of the iodine content within the distal pulmonary bed (i.e. arterioles, capillar ies, and venules) after injection of contrast material. It differs from true perfusion imaging, which requires imaging of an anatomic ROI at a

series of time points or from nuclear perfusion imaging which relies solely on pulmonary arterial supply. 52 CT lung perfusion with the CTA protocol is a snapshot of iodine distribution within distal pulmon ary arteries and capillaries. CT lung perfusion with a general CTA protocol provides information at a later time point, thus showing systemic-to-pulmonary artery shunts in case of abnormal systemic col lateral supply. The images can be generated as grey-scaled or as colour-coded images. The perfusion maps can be fused with conventional CT images, allowing simultaneous assessment of morphological and physio logic information. 53 , 54 In the context of acute PE, CT lung perfusion im aging improves the diagnostic capabilities of CT by demonstrating PE-type defects (i.e. pleural-based, triangular defects) as well as ob structive clots, enhancing the detection of peripheral clots. 55

Based on the technique of two-material decomposition into a soft tissue image and an iodine image, virtual monoenergetic images (VMI) are generated which demonstrate how the image object, in particular the iodine, would look if the X-ray source produced $\times$ -rays at a single energy level. In the context of acute PE, VMIs at low energy (usually $45–55\;\mathsf{k e V})$ ) result in increased iodine attenuation, and thus detection of endoluminal filling defects. An additional advantage of monochro matic imaging is the reduction of iodine load for routine chest CT angio graphic examinations. Reduction of iodine load may be critically important for reducing post-imaging renal impairment in patients with moderate or severe renal insufficiency. 56 , 57

CT venography

Lower extremity ultrasound is the preferred method of evaluation for deep vein thrombosis (DVT). It is radiation-free, readily available, and in expensive. 58 Indirect CT venography (CTV) of the abdomen, pelvis, and lower limbs to search for concomitant DVT is possible after CTA but is rarely performed in the setting of (suspected) acute PE. For conventional CTV non-helical sequential scanning slice widths between 5 and 10 mm and slice intervals up to 5 cm are used. This technique bears the risk of missing shorter segmental clots. 59 Modern helical technique uses 2.5– 10 mm reconstructed image thickness with maximum table speed pos sible and carefully adjusted mA settings with automated dose modulation protocols. Scanning should include the deep venous system from the in ferior vena cava (IVC) and iliac veins down to the popliteal fossae. Ideal scan delay is usually 180 s after the beginning of a larger contrast bolus administration than CTA. Shorter delays can lead to false-positive pseudo-thrombotic findings due to incomplete recirculation and uneven mixing of injected contrast into the venous blood pool. 60 – 63 Elastic stock ings have been recommended to enhance deep venous filling, but this is not a practical option, particularly in critically ill patients. 63 CTV should not be part of routine care, but may be considered in rare situations where, for instance, CUS is not feasible or available, i.e. rare venous mal formations or extreme morbid obesity, or in case of suspected inferior vena cava or iliac vein thrombosis.

Diagnostic image quality

The major criteria for diagnostic image quality in this setting are ad equate arterial enhancement on images devoid of motion artefacts. A non-diagnostic CTA examination secondary to insufficient image qual ity should be repeated to secure a final diagnosis regarding the presence or absence of PE, to avoid under- and overtreatment. The scan should be analysed to detect the cause of suboptimal image quality, and the cir cumstances/scan parameters should be revised accordingly. Table 4 summarizes the most frequent causes of non-diagnostic CTA scans and provides solutions to improve image quality.

Adequacy of pulmonary artery opacification in clinical practice is usu ally performed qualitatively, relying on a homogeneous column of con trast within the arterial lumen. Pulmonary artery opacification can also be quantitatively assessed by measuring the attenuation values within central and peripheral pulmonary arteries. A described minimum

Table 3

Relevance of the level of analysability of the pulmonary arteries for the diagnostic value of the CT

|Mediastinal images||Perfusion images|| |---|---|---|---| | Level of analysability of pulmonary arteries | Diagnostic value of mediastinal images alone || Diagnostic value of CT Based on combined reading of mediastinal and perfusion images | | PAs analysable down to the subsegmental level |Negative down to the subsegmental level| No segmental/subsegmental perfusion defects |Truly negative| | PAs analysable down to the segmental level | Negative down to the segmental level (does not exclude subsegmental clots) | No segmental/subsegmental perfusion defectsperfusion defects Presence of segmental/ |Truly negative| ||| Presence of segmental/ subsegmental perfusion |Peripheral acute PE (after combined| ||||assessment of perfusion and morphology)| |Only central PA analysable|Only central clots excluded| No diagnostic value of perfusion images |Indeterminate for PE| |PAs not analysable|PE not excluded| No diagnostic value of perfusion images |Non-diagnostic examination|

Table 4 Causes of and solutions to nondiagnostic CTA

|Finding|Potential aetiology|Proposed solution|| |---|---|---|---| |Poor level of|Incorrect placement of the ROI||| |opacification within|||Repeat after correct positioning of the ROI| |PAs| Inadequate HU threshhold to start exam Delayed transit time ||Repeat after correction| |||Repeat|| ||● Due to low cardiac output (most often RV)||● After selecting a longer start delay (if CTA)| || ● Due to increased pulmonary vascular resistance (acute airspace disease; focal lung abnormalties) || ● Repeat with a ROl in the ascending aorta/left atrium (general CTA protocol) | ||Dilution of the column of contrast||| ||● Due to patent foramen ovale||● Repeat after mild inspiration| ||• Septal defects||● No attempt to repeata| ||• Retrograde systemic-to-pulmonary artery shunt||• No attempt to repeata| |Transient interruption| Deep inspiration in a patient with large volume of unopacified blood from the inferior vena cava diluting the bolus of contrast material |Repeat using mild inspiration or simple apnoea|| |on contrast (TIC)||ECMO flow should be reduced to a minimum during the CTA|| || Veno-arterial extracorporeal membrane oxygenation (ECMO) may cause changes in the filling of the pulmonary arteries ||| ||causes:||| |Motion artefacts|• Respiratory motion||● Repeat (caudo-cranial) if patient cooperation possible| ||• Patient movement during the examination||● Repeat (caudo-cranial) with shallow breathing if patient| ||||| |Streak artefact| ● Cardiac motion: usually most pronounced in Ieft Iower lobe and lingula and on older scanners ||● Repeat (caudo-cranial) if patient cooperation possible| |Streak artefact|Beam-hardening artefacts due to ||• No attempt to repeat| |Streak artefact|● Dense contrast material||• No attempt to repeat| |Streak artefact|||● Post-processing with algorithms suppressing metal artefacts| |Streak artefact|● Metal implants or bullets||(manufacturor dependent) or reconstruction of high-energy images| |Streak artefact|||(if acquisition with DECT/ PCD-CT)|

a Potential alternative : administration of more contrast (120–150 mL), at low flow rate (3 mL/s) with a long start delay

to ensure opacification of pulmonary arteries as well as shunt

veins.

Table 5 Continued developments in CT technology have led to marked improvement in spatial resolution and improved detection of all types of intraluminal filling defects on CT pulmonary angiography. However, not all filling defects represent acute pulmonary emboli. The following glossary of CT findings define the spectrum of pulmonary artery filling defects

|term|Definition|| |---|---|---| ||Acute PE is characterized by iling defects within the pulmonary arteries that essentialy retain the cylindrical shape of the|| |Acute PE|dislodged thrombi that either may remain intact or may fragment on their way through the heart. On images|| |Acute PE|perpendicular to the vessel, acute emboli present as round filling defects in the centre of a pulmonary artery or, when|| |Acute PE|eccentric, they tend to form acute angles with the vessel wall No signs of deformation due to (auto)lytic activity of the|| ||embolus are seen. Acute emboli may totally occlude a pulmonary artery. No contrast enhancement is seen beyond this|| |||point. As a result, the diameter of the artery expands to its maximum, usually larger than arteries of comparable| || anatomic locations elsewhere. In non-occlusive emboli flow may be seen distal to the filling defect. These tend to be more common at arterial bifurcations. || |Central PE|PE is located in either the pulmonary trunk, main pulmonary artery, or lobar pulmonary artery.|| |Chronic PE|Persistent filling defects after acute PE:. The cross-section of these filling defects is thread-like, band-like, web-like, or|| |||| |Embolus|An embolus is a thrombus that has dislodged and is located at a site diferent from its vessel of origin.|| |Incidental PE|PE identified on a CT scan ordered for any other reason than suspected PE.|| |In-situ pulmonary thrombus| In-situ pulmonary thrombus presents as a wall-adherent filing defect, usually in large or enlarged pulmonary arteries. The most common location is along the superior aspect of the main right pulmonary artery and intralobar pulmonary artery. || |||| ||These fillng defects may be associated with some calcification. Unlike with chronic pulmonary emboli, mosaic || ||attenuation is unusual. It oftentimes occurs in the setting of slow flow and pulmonary hypertension. They are commonly|| || seen in various causes of pulmonary hypertension, most notably Eisenmenger syndrome in the setting of a longstanding right-to-left shunt. || |Isolated subsegmental PE|Subsegmental PE Iimited to a single subsegmental artery.79|| |Peripheral PE|PE located in a segmental or more distal pulmonary artery.|| |Pulmonary artery filling defect|Pulmonary arteries on contrast-enhanced CT normally show homogeneous contrast enhancement. Fillng defects are|| ||areas within an afected pulmonary artery that show no contrast enhancement while other pulmonary arteries do|| || enhance. Pulmonary artery filing defects are caused by pulmonary emboli;, pulmonary thrombosis, or intravascular tumour. || |Pulmonary thrombosis| Thrombi in the pulmonary arteries are usually the result of venous thromboembolism, but may also be local pulmonary thrombosis. This has been recognized in patients with pulmonary hypertension, chronic obstructive pulmonary disease, || |||| ||sickle cell disease, and quite extensively in patients with COVID-19. Differentiation between venous thromboembolism|| |Reduced pulmonary contrast|and in situ thrombosis can currently not be reliably made based on CTA.| Filling defects must be distinguished from regions of reduced contrast enhancement due to early timing of a scan series on| |enhancement||contrast-enhanced CT or due to slow flow. They are artefacts associated with scan timing or patient factors (breathing or | || pulsation artefacts). The measured CT attenuation is higher than that of an unenhanced pulmonary artery but lower than that of a well-enhanced vessel. || |||| |Right ventricular dilatation| A number of methods have been studied to define right ventricular dilatation based on CTA findings with or without ECG alignment. A practical approach consists of measuring the largest ventricle diameters in the axial view in both ventricles, || |Right ventricular dilatation| alignment. A practical approach consists of measuring the largest ventricle diameters in the axial view in both ventricles, as defined by the distance between the endocardium and the interventricular septum. As a confirmation, the same || |Right ventricular dilatation|measurement can be done taking the largest ventricle diameters at the level of the heart valves. RV/LV ratio measured at|| ||CT may be different from measured at echocardiography when the CT is performed without ECG alignment.|| |Right ventricular hypertrophy|Increased thickness of the right ventricle free wall exceeding 4 mm.|| | Saddle embolism Subacute PE |A large central PE that straddles the pulmonary trunk bifurcation.|| ||The shape of the emboli begins to change due to lytic activity. Instead of a round cross-section, concave portions max|| ||occur, and the cross-section become increasingly irregular. Findings of chronic emboli (namely, mosaic attenuation and|| |Subsegmental PE|A contrast defect in a subsegmental artery, i.e. the first arterial branch division of any segmental artery independent of || || artery diameter, visible in at least two consecutive axial slices, using a CT scanner with a desired maximum collimator width of ||

Table 6 Result of the delphi analysis on core CTA findings to be included in CTA radiology reports: percentage agreement is indicated. In the first 2 rounds, agreement wat defined as an $\mathbf{80\%}$ majority, in the third round, this was $\mathbf{\nabla\mathfrak{v}o}\%$ majority

|CTA findings|Excluded|Included|Specifics| |---|---|---|---| |1. RV/LV ratio (axial images)||100%|92% ‘must have’| |2. Central location||100%|85% ‘must have’| |3. (lsolated) subsegmental PE||92%|| |4. Septum deviation||85%|81% ‘must have’| |5. IVC reflux|81%||81% ‘must have'| |6. PA trunk diameter||81%|75% ‘nice to have'| |7. Coronary artery calcification score|81%||| |8. Qanadli score|85%||| |9. Organized mural thrombi||859%|75% ‘nice to have'| |10. Complete arterial occlusion||94%|75% ‘nice to have’| |11. Intravascular webs or bands||100%|75% ‘must have’| |12. Pulmonary artery retraction||87%|75% ‘must have'| |13. Bronchial artery dilatation||87%|80% ‘must have’| |14. RV hypertrophy||94%|75% ‘must have’|

threshold is ∼ 200–250 HU. Simultaneous reading of lung and medias tinal images is mandatory when analysing segmental and subsegmental pulmonary arteries to make sure that breathing or cardiogenic motion artefacts mimicking endoluminal clots are ruled out, although this is not always achievable. Because image graininess due to image noise can al ter the diagnostic value of images, one should anticipate this as a poten tial cause of reduced image quality and carefully select scanning parameters, in particular the kilovoltage. These challenges tend to be more difficult to mitigate in the relatively common scenario of patients with conditions associated with elevated risk of PE, such as severe ill ness, obesity, and pregnancy. 64 Whereas the detection of endoluminal clots allows an easy diagnosis of acute PE, the level of analysability of pulmonary arteries is relevant for the diagnostic value of the negative pulmonary CTA examination and should be included in the CTA report ( Table 3 ). If only the central pulmonary artery can be evaluated, the scan is ‘indeterminate for PE’. More commonly, in degraded studies some segmental arteries remain analysable, while others are not. Such region al suboptimal enhancement usually has an explanation such as paren chymal compression-infiltration, which should be stated in the report.

Despite technological advances, the CTA can occasionally be nondiag nostic. Table 4 highlights potential causes for nondiagnostic examinations and corrective measures that we proposed to restore a diagnostic image quality. Competitive inflow of unopacified blood from IVC can limit pul monary artery opacification due to mixing with opacified blood from the superior vena cava (SVC) during deep inspiration. This can manifest as ‘transient interruption of contrast’, observed after deep inspiration that in creases the intrathoracic negative pressure with subsequent inflow of un opacified blood from the IVC into the right heart and pulmonary circulation. Transient interruption of contrast is suggested when dense contrast is visualized in the SVC in the setting of unopacified blood within segments of pulmonary artery and the right heart. 23 , 30 Another cause of poor opacification within pulmonary arteries can be observed after deep inspiratory breath hold with a Valsalva manoeuvre. During this manoeuvre, there may be a shunt of contrast material from the right to the left atrium through a patent foramen ovale, recognized by the simultaneous finding of poor pulmonary artery enhancement and dense opacification of the aorta. In both situations, technologists should coach patients to maintain a

shallow breath hold at the time of the repeat examination. In patients too dyspnoeic to hold their breath, acquisitions at shallow free breathing are alternatives to evaluate central pulmonary arteries. 24 Model-based it erative image reconstructions and deep learning reconstructions can sub stantially reduce image noise without dose increase. Increasing tube current, slowing the gantry rotation time and lowering the table’s pitch can increase the signal-to-noise ratio, especially in situations in which a sub stantial increase of radiation exposure is required, for example, due to morbid obesity. 26 , 28 A lower pitch prolongs the study and can also exacer bate motion artefacts. Automatic tube current modulation technology is available on most scanner manufacturers to assess body size from the scout image and modulate the tube current in the x , y , and z axes to achieve a prescribed image quality. Finally, veno-arterial extracorporeal membrane oxygenation causes changes in the filling of the pulmonary arteries when given at high volumes; therefore, its flows should be temporarily halted or reduced to a minimum during the execution of CTA.

Recently, artificial intelligence has shown promising accuracy for the diagnosis of acute PE. It has also shown promise in detecting acute on chronic PEs and in risk stratification. These have the potential to reduce time to diagnosis, facilitate the activation of PE response teams, and in crease the reproducibility of the diagnosis. 65 A rapid evolution of arti ficial intelligence algorithms in patients with suspected or confirmed PE has to be expected in the years to come.

Diagnosis of acute PE on CT

The diagnosis of acute PE rests on the detection of a well-defined area of low attenuation in the enhanced pulmonary artery. The filling defect should be identifiable on more than one plane and on several consecu tive slices, and should have distinct borders in order to avoid confusion with flow. Many radiologic signs have been used in diagnosing acute PE, including the rim sign which refers to contrast surrounding a central fill ing defect and the tram-track or railway sign referring to a vessel imaged in plane where the contrast around a PE takes on the appearance of train tracks. 66 Images should be windowed at the picture archiving and communication system workstation so that the reference intravas cular structures can be seen (e.g. the moderator band). If these

 Figure 1 Image atlas of core set of CTA findings to be routinely mentioned in CTA reports.

 Image atlas of core set of CTA findings to be routinely mentioned in CTA reports in lay language for patients.

structures can be viewed, then a PE should be visible. Most acute PE will be central within the vessel lumen. When eccentric, acute PE tend to form acute angles with the vessel wall. Acute PE may locally distend the vessel, especially when it is occlusive. Occlusive PE will lead to a de fect on lung perfusion images from DECT or subtraction CT. A reduc tion in pulmonary blood volume can be seen if a clot leads to a major obstruction but no occlusion.

Additional findings supportive of a PE diagnosis can be seen on lung windows. Pulmonary infarcts manifest as peripheral airspace opacities that have heterogeneous decreased or absent enhancement compared with atelectatic lung. 67 – 69 They may present with an internal ground-glass or sponge-like appearance with a rim of more well-defined con solidation. This manifestation is sometimes referred to as the reversed halo sign and reflects the dual blood supply to the lung with foci of pre served non-infarcted lung adjacent to infarcted lung. On lung perfusion images from DECT or subtraction CT pulmonary infarcts show no en hancement within but sometimes increased enhancement in the imme diately adjacent normal lung. Very rarely, an area of lung with decreased attenuation will be seen with the classic radiographic Westermark sign. Most often, no parenchymal abnormality is detected. Of note, mosaic attenuation and enlarged bronchial arteries are not seen in the context of acute PE alone. Their presence should prompt detailed search of vas cular features of chronic thromboembolic pulmonary vascular disease (CTEPD) with or without pulmonary hypertension that might suggest acute PE superimposed on CTEPD. 70 – 78 Any CT performed for PE should also address any potential source of embolic disease. These include central catheters, upper extremity venous thrombosis or cardiac cavities. Table 5 highlights the definition of often used termin ology in CTA reports.

Delphi

A literature review (see Supplementary data online, Appendix A ) was performed to identify all prospective or retrospective studies reporting on prognostic relevance of any CTA findings; studies in less than 100 patients were excluded. The search was performed on 1 June 2022 and yielded 589 articles. After screening the literature search results and integrating with the results of cross-referencing and personal com munications from the members of the task force, 43 studies fulfilled our inclusion criteria for at least one outcome. The correlations of the dif ferent CTA findings with either short- or long-term prognosis as de scribed in those papers were summarized (see Supplementary data online, Appendix B and C ) and discussed by the task force. 50 , 72 , 80 – 110 Duplication of data results between individual studies and meta-analysis was minimized. The studies involved mostly haemodynamically stable patients with low rates of adverse events. CT scan techniques, assess ment of the CTA findings, thresholds of measurements as well as clin ical outcomes and duration of follow-up were highly variable across the studies. Independent adjudication of outcomes was usually lacking and reproducibility of the assessment of the CTA findings was only rarely reported. More often, the reported multivariable models did not in clude all possible relevant CTA findings; we could therefore not deter mine which parameters were truly independent predictors of prognosis. Based on the results from the literature, the task force agreed on the selection of 14 CTA findings for the consensus process: those were consistently reported to have a positive association with the prognosis of PE patients and assumed to be easily assessed manually without the need for dedicated experience ( Table 6 ).

During the consensus process the task force members were re minded before each voting round to be mindful of time (how long it takes to assess the parameter), required expertise (some variables can possibly not be assessed in a valid and reproducible way by less experienced radiologists during busy shifts) and the interobserver agreement as presented in the studies we identified. Ultimately, eight CTA findings were considered ‘must-haves’ and

three ‘nice-to-haves’. The remaining three were not considered suf ficiently indicative and included the following: inferior vena cava re flux, the Qanadli score to quantify thrombus burden and the coronary artery calcification score. 111

The selected 11 CTA findings included the following ( Figures 1 and 2 ):

(i) the location of acute PE (central location, subsegmental PE), (ii) indicators of right ventricular overload which appeared to predict early haemodynamic collapse and death (RV/LV ratio, PA trunk diam eter, septum deviation), and (iii) predictors of persistent respiratory symptoms, post-PE syndrome, and CTEPH: RV/LV ratio, PA trunk diameter, RV hypertrophy, sep tum deviation, organised mural thrombi, complete arterial occlusion, intravascular webs or bands, pulmonary artery retraction, and bron chial artery dilatation.

The location of the clot but mostly signs of acute RV overload are pre dictive of short-term adverse outcomes and death. 1 , 112 Subsegmental PE may in some circumstances be left untreated. 79 , 113 – 115 Moreover, clot lo cation is relevant for the assessment of the suitability of the patient for percutaneous reperfusion treatment. Any additional descriptors of loca tion or extent of clot burden may be included as ‘nice to have’ findings. These descriptors, while not useful in prognostication, may be helpful for identifying clot resolution on follow-up imaging, particularly post lytic or mechanical interventions. Of note, prognostic information of the clot cannot be estimated after resuscitation as chest compression may lead to the migration of clots in the more peripheral arteries.

The combination of several of the signs of CTEPH (more than their isolated presence at the time of index PE) pointed to the presence of a pre-existing CTEPH or its subsequent diagnosis. 70 – 72 , 77 , 78 , 116 , 117 The assessment of signs of pre-existing CTEPH may allow for a more timely diagnosis of CTEPH which can be safely made after three months of ef fective anticoagulation. Patients with CTEPH are considered unsuitable candidates for a catheter-based mechanical embolectomy because they do not benefit, and with increasing pulmonary pressures any pulmonary vascular intervention becomes more risky. 73 – 76 , 118

Patient perspective

The task force included patients and caregivers from Europe and North America with personal experience with PE. They believe that under standing what it means to have a PE, and getting relevant information about our personal disease is very important. A standardized advice for reporting scans will allow all doctors to share the same, most im portant information among themselves and their patients, even across borders. They express the hope this new standard will give doctors and patients the best information and tools to become better partners in managing PE, improving both knowledge and outcomes.

Conclusion

This clinical consensus statement provides a current update of CTA techniques, a definition of often used nomenclature and recommenda tions on the proposed content of CTA reports along with a detailed image atlas with instructions on how to assess all relevant CTA findings and a lay language guidance on the meaning of these findings. Upon im plementation, this document may help to standardize CTA radiology reports across the globe and make all relevant prognostic CT findings available for treating physicians to guide management decisions, ultim ately improving outcomes of care for PE patients.

Supplementary data

Supplementary data are available at European Heart Journal - Cardiovascular Imaging online.

Author’s contributions

F.A.K., S.B., and M.R.J. prepared the first draft of this clinical consensus statement. All authors revised the manuscript for important intellectual content and approved the submitted version.

Funding

M.H. is supported by a state funding managed by the National Research Agency according to the Investments for the Future programme integrated into France 2030, under the reference ANR-18-RHUS-0006 (DESTINATION 2024).

Confilict of interest : F.A.K. reports grants or contracts from Bayer, BMS, BSCI, AstraZeneca, MSD, Leo Pharma, Actelion, Farm-X, The Netherlands Organisation for Health Research and Development, The Netherlands Organisation for Health Research and Development, The Dutch Thrombosis Association, The Dutch Heart Foundation and the Horizon Europe Program, all unrelated to this work and paid to his institution. M.H. reports institutional speaker, consultant, or steering committee fees from Aerovate, Altavant, AOP Orphan, Bayer, Chiesi, Ferrer, Janssen (Actelion), Merck (Acceleron), MorphogenIX, Shou Ti, United Therapeutics and institu tional research grants from AOP Orphan, Janssen (Actelion), MSD (Acceleron), Shou Ti. L.B. reports institutional speaker, consultant and non-financial support from BMS-Pfizer, Léo-Pharma, MSD, and Viatris; and insti tutional research grants from Bayer and MSD; outside the submitted work. I.M.L. has relationships with drug companies including AOP-Health, Actelion-Janssen, MSD, United Therapeutics, Medtronic, Neutrolis and Ferrer. In addition to being investigator in trials involving these companies, re lationships include consultancy service, research grants, and membership of scientific advisory boards. The other authors do not have any disclosures.

Data availability

This is a consensus document; data availability is not applicable.

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