Computed tomography of acute pulmonary embolism: state-of-the-art

Derivation of Best-Practice Scan Speeds and Excess Scan Durations for CT Pulmonary Angiography: Analysis Using Registry Data for 166,769 Examinations Across 121 Sites

Background: Radiology practices' potential use of a fixed scan speed results in scanning some patients more slowly than necessary for the clinical scenario. For CT pulmonary angiography (CTPA), use of fixed scan speeds can lead to prolonged breath-hold requirements and potentially lower image quality from motion artifact. Objective: To develop best-practice scan speeds for CTPA examinations as well as to assess the extent of variation from these speeds and resulting excess scan durations in real-world clinical practice. Methods: This retrospective study included 192,779 acquisitions from 166,769 CTPA examinations performed in adult patients (97,649 male, 68,925 female; median age, 60 years) from January 1, 2016 to January 1, 2021, at 121 sites using 277 physical scanners representing 28 scanner models from four vendors. The examinations were identified from an international CT dose registry. Acquisition characteristics were extracted from the registry and used to calculate scan speeds and durations. Acquisitions were stratified into five equally size radiation dose categories using CTDIvol values. For each combination of scanner model and dose category, best-practice scan speed was calculated as the 95th-percentile actual speed, although a higher dose category's best-practice speed was assigned if faster. Excess scan durations were calculated with respect to hypothetical durations if acquisitions used best-practice speeds. Results: The acquisitions had speeds that, on average, were 30% slower than the best-practice scan. A total of 87% of acquisitions were slower than the best-practice speed; 62% were >20% slower than the best-practice speed. Acquisitions had a median scan duration of 4.8 seconds; use of best-practice scan speeds would have saved a median of 1.2 seconds. The 95th-percentile excess scan duration was 7.1 seconds, which was exceeded by at least one examination for 58% of sites. Conclusion: CTPA commonly uses speeds slower than the proposed best-practice speeds for a given scanner's capabilities, potentially leading to greater motion artifact, suggesting widespread opportunity for improvement. Simple protocol modifications can decrease scan duration while still allowing adequate radiation dose. Clinical Impact: The findings indicate widespread opportunity for CTPA protocol improvement through simple adjustments designed to shorten scan speeds at a maintained dose output that preserves image quality.

Clinical application of third-generation dual-source CT-based dynamic imaging reconstruction for pulmonary embolism imaging

BACKGROUND

To evaluate the clinical diagnostic value of third-generation dual-source CT for pulmonary embolism, focusing on the optimization of dual-source CT scanning with dynamic reconstruction in acute pulmonary embolism (PE) and various imaging manifestations.

METHODS

Eighty-two patients with pulmonary embolism were enrolled and randomly divided into standard CT angiography (SCTA) and dynamic CT angiography (DCTA). DCTA patients were divided into dynamic CT angiography arterial phase (DCTAa), time phase Angiography reconstruction (TMIP-CTA), and 4D noise reduction TMIP-CTA according to the image reconstruction. The region of interest was selected in the region of the pulmonary trunk and its branches, respectively. The vessel CT value and image background noise (IN) of each subgroup were also determined, and the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Simultaneously two radiologists performed a subjective evaluation of the quality of the picture images.

RESULTS

The DCTA group had a lower contrast dose than the SCAT group, but the vessel CT value, IN, CNR, and SNR were significantly higher in the DCTA group compared with the SCTA group. CT of the vascular lumen was generally higher in all subgroups of DCTA than in SCTA, with the highest in the TMIP-CIA group. IN was significantly higher in both the DCTAa and TMIP-CTA groups than in the SCTA group. SNR and CNR were elevated in TMIP-CTA and 4D noise reduction TMIP-CTA compared to the SCTA group. In addition, the subjective image quality scores of the DCTA group were significantly higher than those of SCTA, and the 4D noise reduction TMIP-CTA had the most. However, the ED of the SCTA group was lower than that of the DCTA group.

CONCLUSION

4D noise reduction TMIP-CTA based on DCTA reconstruction significantly improves the quality of pulmonary artery CTPA images and increases the clinical diagnostic rate, with potential for clinical dissemination.

Bone cement implantation syndrome: the role of echocardiography and multidisciplinarity

Bone cement implantation syndrome (BCIS) is a potentially serious complication after joint replacement surgery, resulting from bone marrow debris and cement embolisation, culminating in pulmonary and cardiovascular collapse. Echocardiography aids in diagnosis and management. We present a woman in her 80s with grade II BCIS. CT angiogram was inconclusive, but echocardiography revealed hyperechogenic material and right ventricular dysfunction, confirming the diagnosis. She received cardiovascular and respiratory support in a level II intensive care unit, showing full recovery of the right ventricle function when it was later reassessed. This potentially fatal condition is successfully managed if recognised early with adequate supportive care. Echocardiography might guide the diagnosis, consolidating supportive measures.

Modern imaging of acute pulmonary embolism

The first-choice imaging test for visualization of thromboemboli in the pulmonary vasculature in patients with suspected acute pulmonary embolism (PE) is multidetector computed tomography pulmonary angiography (CTPA) - a readily available and widely used imaging technique. Through technological advancements over the past years, alternative imaging techniques for the diagnosis of PE have become available, whilst others are still under investigation. In particular, the evolution of artificial intelligence (AI) is expected to enable further innovation in diagnostic management of PE. In this narrative review, current CTPA techniques and the emerging technology photon-counting CT (PCCT), as well as other modern imaging techniques of acute PE are discussed, including CTPA with iodine maps based on subtraction or dual-energy acquisition, single-photon emission CT (SPECT), magnetic resonance angiography (MRA), and magnetic resonance direct thrombus imaging (MRDTI). Furthermore, potential applications of AI are discussed.

Alterations and Significance of Computed Tomography Pulmonary Angiography-Derived Parameters in Older Patients With Acute Pulmonary Embolism

OBJECTIVE

This study aimed to investigate changes of computed tomography pulmonary angiography (CTPA)-derived parameters in older adults with acute pulmonary embolism (APE).

METHODS

According to the pulmonary artery obstruction index (PAOI), patients with APE were divided into the A1 (PAOI ≥30%, n = 57) and A2 (PAOI <30%, n = 40) groups. Participants without APE were placed in group B (n = 170). The left atrial (LA) and left ventricular (LV) parameters among the three groups were compared, and the parameter changes in the 44 patients with APE were analyzed before and after treatment. The correlation between APE severity and the parameters was analyzed using correlation analysis.

RESULTS

The left-to-right diameters (LR) of LA, and LR × anteroposterior diameters (AP) of LA and LV: A1 < A2 < B; LR of LV: A1 < A2, B; AP of LA and LV: A1, A2 < B. After treatment, LR and LR × AP of the LA and LV were significantly increased in the group A1 and LR of the LV and LR × AP of the LA and LV were elevated in the group A2. Acute pulmonary embolism severity was closely associated with LR × AP ( r = -0.557) and LR ( r = -0.477) of LA.

CONCLUSIONS

With an increase in the degree of obstruction, older adults had a smaller LA and LV. Furthermore, the LR and LR × AP values of the LA were significantly decreased. These results contribute to in-time risk stratification.

Detection and severity quantification of pulmonary embolism with 3D CT data using an automated deep learning-based artificial solution

PURPOSE

The purpose of this study was to propose a deep learning-based approach to detect pulmonary embolism and quantify its severity using the Qanadli score and the right-to-left ventricle diameter (RV/LV) ratio on three-dimensional (3D) computed tomography pulmonary angiography (CTPA) examinations with limited annotations.

MATERIALS AND METHODS

Using a database of 3D CTPA examinations of 1268 patients with image-level annotations, and two other public datasets of CTPA examinations from 91 (CAD-PE) and 35 (FUME-PE) patients with pixel-level annotations, a pipeline consisting of: (i), detecting blood clots; (ii), performing PE-positive versus negative classification; (iii), estimating the Qanadli score; and (iv), predicting RV/LV diameter ratio was followed. The method was evaluated on a test set including 378 patients. The performance of PE classification and severity quantification was quantitatively assessed using an area under the curve (AUC) analysis for PE classification and a coefficient of determination (R²) for the Qanadli score and the RV/LV diameter ratio.

RESULTS

Quantitative evaluation led to an overall AUC of 0.870 (95% confidence interval [CI]: 0.850-0.900) for PE classification task on the training set and an AUC of 0.852 (95% CI: 0.810-0.890) on the test set. Regression analysis yielded R² value of 0.717 (95% CI: 0.668-0.760) and of 0.723 (95% CI: 0.668-0.766) for the Qanadli score and the RV/LV diameter ratio estimation, respectively on the test set.

CONCLUSION

This study shows the feasibility of utilizing AI-based assistance tools in detecting blood clots and estimating PE severity scores with 3D CTPA examinations. This is achieved by leveraging blood clots and cardiac segmentations. Further studies are needed to assess the effectiveness of these tools in clinical practice.

Improved image quality in CT pulmonary angiography using deep learning-based image reconstruction

We investigated the effect of deep learning-based image reconstruction (DLIR) compared to iterative reconstruction on image quality in CT pulmonary angiography (CTPA) for suspected pulmonary embolism (PE). For 220 patients with suspected PE, CTPA studies were reconstructed using filtered back projection (FBP), adaptive statistical iterative reconstruction (ASiR-V 30%, 60% and 90%) and DLIR (low, medium and high strength). Contrast-to-noise ratio (CNR) served as the primary parameter of objective image quality. Subgroup analyses were performed for normal weight, overweight and obese individuals. For patients with confirmed PE (n = 40), we further measured PE-specific CNR. Subjective image quality was assessed independently by two experienced radiologists. CNR was lowest for FBP and enhanced with increasing levels of ASiR-V and, even more with increasing strength of DLIR. High strength DLIR resulted in an additional improvement in CNR by 29-67% compared to ASiR-V 90% (p < 0.05). PE-specific CNR increased by 75% compared to ASiR-V 90% (p < 0.05). Subjective image quality was significantly higher for medium and high strength DLIR compared to all other image reconstructions (p < 0.05). In CT pulmonary angiography, DLIR significantly outperforms iterative reconstruction for increasing objective and subjective image quality. This may allow for further reductions in radiation exposure in suspected PE.

An artificial intelligence algorithm for pulmonary embolism detection on polychromatic computed tomography: performance on virtual monochromatic images

OBJECTIVES

Virtual monochromatic images (VMI) are increasingly used in clinical practice as they improve contrast-to-noise ratio. However, due to their different appearances, the performance of artificial intelligence (AI) trained on conventional CT images may worsen. The goal of this study was to assess the performance of an established AI algorithm trained on conventional polychromatic computed tomography (CT) images (CPI) to detect pulmonary embolism (PE) on VMI.

METHODS

Paired 60 kiloelectron volt (keV) VMI and CPI of 114 consecutive patients suspected of PE, obtained with a detector-based spectral CT scanner, were retrospectively analyzed by an established AI algorithm. The CT pulmonary angiography (CTPA) were classified as positive or negative for PE on a per-patient level. The reference standard was established using a comprehensive method that combined the evaluation of the attending radiologist and three experienced cardiothoracic radiologists aided by two different detection tools. Sensitivity, specificity, positive and negative predictive values and likelihood ratios of the algorithm on VMI and CPI were compared.

RESULTS

The prevalence of PE according to the reference standard was 35.1% (40 patients). None of the diagnostic accuracy measures of the algorithm showed a significant difference between CPI and VMI. Sensitivity was 77.5% (95% confidence interval (CI) 64.6-90.4%) and 85.0% (73.9-96.1%) (p = 0.08) on CPI and VMI respectively and specificity 96.0% (91.4-100.0%) and 94.6% (89.4-99.7%) (p = 0.32).

CONCLUSIONS

Diagnostic performance of the AI algorithm that was trained on CPI did not drop on VMI, which is reassuring for its use in clinical practice.

CLINICAL RELEVANCE STATEMENT

A commercially available AI algorithm, trained on conventional polychromatic CTPA, could be safely used on virtual monochromatic images. This supports the sustainability of AI-aided detection of PE on CT despite ongoing technological advances in medical imaging, although monitoring in daily practice will remain important.

KEY POINTS

• Diagnostic accuracy of an AI algorithm trained on conventional polychromatic images to detect PE did not drop on virtual monochromatic images. • Our results are reassuring as innovations in hardware and reconstruction in CT are continuing, whilst commercial AI algorithms that are trained on older generation data enter healthcare.

Right-to-left ventricular ratio is higher in systole than diastole in patients with acute pulmonary embolism

OBJECTIVES

In acute pulmonary embolism (PE), the right ventricle (RV) may dilate compromising left ventricular (LV) size, thereby increasing RV/LV ratio. End-diastolic RV/LV ratio is often used in PE risk stratification, though the cause of death is RV systolic failure. We aimed to confirm our pre-clinical observations of higher RV/LV ratio in systole compared to diastole in human patients with PE.

METHODS

We blinded and independently analyzed echocardiograms from 606 patients with PE, evaluated by a Pulmonary Embolism Response Team. We measured RV/LV ratios in end-systole and end-diastole and fractional area change (FAC). Our primary outcome was a composite of 7-day clinical deterioration, treatment escalation or death. Secondary outcomes were 7-day and 30-day all-cause mortality.

RESULTS

RV/LV ratio was higher in systole compared to diastole (median 1.010 [.812-1.256] vs. .975 [.843-1.149], p < .0001). RV/LV in systole and diastole were correlated (slope = 1.30 [95% CI 1.25-1.35], p < .0001 vs. slope = 1). RV/LV ratios in both systole and diastole were associated with the primary composite outcome but not with all-cause mortality.

CONCLUSION

The RV/LV ratio is higher when measured in systole versus in diastole in patients with acute PE. The two approaches had similar associations with clinical outcomes, that is, it appears reasonable to measure RV/LV ratio in diastole.

Low concordance between CTPA and echocardiography in identification of right ventricular strain in PERT patients with acute pulmonary embolism

PURPOSE

Right ventricular strain (RVS) is used to risk stratify patients with acute pulmonary embolism (PE) and influence treatment decisions. Guidelines suggest that either computed tomography pulmonary angiography (CTPA) or transthoracic echocardiography (TTE) can be used to assess RVS. We sought to determine how often CTPA and TTE yield discordant results and to assess the test characteristics of CTPA compared to TTE.

METHODS

We analyzed data from a single-center registry of PE cases severe enough to warrant activation of the hospital's Pulmonary Embolism Response Team (PERT). We defined RVS as a right ventricular to left ventricular ratio (RV/LV) ≥ 1 or radiologist's interpretation of RVS on CTPA or as the presence of either RV dilation, hypokinesis, or septal bowing on TTE.

RESULTS

We included 554 patients in our analysis, of whom 333 (60%) had concordant RVS findings on CTPA and TTE. Using TTE as the reference standard, CTPA had a sensitivity of 95% (95% CI 92-97%) and a specificity of 4% (95% CI 2-8%) for identifying RVS.

CONCLUSIONS

In a selected population of patients with acute PE for which PERT was activated, CTPA is highly sensitive but not specific for the detection of RVS when compared to TTE.

Does the clot burden as assessed by the Mean Bilateral Proximal Extension of the Clot score reflect mortality and adverse outcome after pulmonary embolism?

Background

Rapid diagnosis and risk stratification are important to reduce the risk of adverse clinical events and mortality in acute pulmonary embolism (PE). Although clot burden has not been consistently shown to correlate with disease outcomes, proximally located PE is generally perceived as more severe.

Purpose

To explore the ability of the Mean Bilateral Proximal Extension of the Clot (MBPEC) score to predict mortality and adverse outcome.

Methods

This was a single center retrospective cohort study. 1743 patients with computed tomography pulmonary arteriography (CTPA) verified PE diagnosed between 2005 and 2020 were included. Patients with active malignancy were excluded. The PE clot burden was assessed with MBPEC score: The most proximal extension of PE was scored in each lung from 1 = sub-segmental to 4 = central. The MBPEC score is the score from each lung divided by two and rounded up to nearest integer.

Results

We found inconsistent associations between higher and lower MBPEC scores versus mortality. The all-cause 30-day mortality of 3.9% (95% CI: 3.0-4.9). The PE-related mortality was 2.4% (95% CI: 1.7-3.3). Patients with MBPEC score 1 had higher all-cause mortality compared to patients with MBPEC score 4: Crude Hazard Ratio (cHR) was 2.02 (95% CI: 1.09-3.72). PE-related mortality was lower in patients with MBPEC score 3 compared to score 4: cHR 0.22 (95% CI: 0.05-0.93). Patients with MBPEC score 4 did more often receive systemic thrombolysis compared to patients with MBPEC score 1-3: 3.2% vs. 0.6% (p < .001). Patients with MBPEC score 4 where more often admitted to the intensive care unit: 13% vs. 4.7% (p < .001).

Conclusion

We found no consistent association between the MBPEC score and mortality. Our results therefore indicate that peripheral PE does not necessarily entail a lower morality risk than proximal PE.

Dual-Source Photon-Counting Computed Tomography-Part III: Clinical Overview of Vascular Applications beyond Cardiac and Neuro Imaging

Photon-counting computed tomography (PCCT) is an emerging technology that is expected to radically change clinical CT imaging. PCCT offers several advantages over conventional CT, which can be combined to improve and expand the diagnostic possibilities of CT angiography. After a brief description of the PCCT technology and its main advantages we will discuss the new opportunities brought about by PCCT in the field of vascular imaging, while addressing promising future clinical scenarios.

Right ventricular area predicts short-term mortality in acute pulmonary embolism based on CT pulmonary angiography: A retrospective study

We performed this cohort study to assess the prognostic value of right ventricular size, including diameter, area, and volume, in short-term mortality of acute pulmonary embolism (APE) based on 256-slice computed tomography compared with D-dimer, creatine kinase muscle and brain isoenzyme, and Wells scores. A total of 225 patients with APE, who were followed up for 30 days were enrolled in this cohort study. Clinical data, laboratory indices (creatine kinase, creatine kinase muscle and brain isoenzyme, and D-dimer), and Wells scores were collected. The 256-slice computed tomography was used to quantify cardiac parameters (RVV/LVV, RVD/LVD-ax, RVA/LVA-ax, RVD/LVD-4ch, RVA/LVA-4ch) and the diameter of the coronary sinus. Participants were divided into non-death and death groups. The values mentioned above were compared between the 2 groups. The RVD/LVD-ax, RVA/LVA-ax, RVA/LVA-4ch, RVV/LVV, D-dimer, and creatine kinase levels were significantly higher in the death group than in the non-death group (P < .05). The active period of the malignant tumor, heart rate ≥ 100 beats/minutes, and RVA/LVA-ax were positively correlated with early death from APE (P < .05). Active stage of malignant tumor (OR:9.247, 95%CI:2.682-31.888, P < .001) and RVA/LVA-ax (OR:3.073, 95%CI:1.447-6.528, P = .003) were independent predictors of early death due to APE. According to the receiver operating characteristic curve, the cutoff point of RVA/LVA-ax was 1.68 with a sensitivity of 46.7% and specificity of 84.8%. The measurement of ventricular size in the short-axis plane is more convenient and reliable than that in the 4-chamber cardiac plane. RVA/LVA-ax is an independent predictor of early death from APE, and when RVA/LVA-ax > 1.68, the risk of early death from APE increases.

"Triple low" free-breathing CTPA protocol for patients with dyspnoea

AIM

To assess the performance of a "triple-low" free-breathing protocol for computed tomography pulmonary angiography (CTPA) evaluated on patients with dyspnoea and suspected pulmonary embolism and discuss its application in routine clinical practice for the study of the pulmonary parenchyma and vasculature.

MATERIAL AND METHODS

This study was conducted on a selected group of dyspnoeic patients referred for CTPA. The protocol was designed using fast free-breathing acquisition and a small, fixed volume (35 ml) of contrast agent in order to achieve a low-exposure dose. For each examination, radiodensity of the pulmonary trunk and ascending aorta, and the dose-length product (DLP) were recorded. A qualitative analysis was performed of pulmonary arterial enhancement and the pulmonary parenchyma.

RESULTS

This study included 134 patients. Contrast enhancement of the pulmonary arteries (409 ± 159 HU) was systematically >250 HU. The duration of acquisition ranged from 0.9 to 1.3 seconds for free-breathing imaging. The mean DLP was in the range of low-dose chest CT acquisitions (145 ± 73 mGy·cm). The analysis was deemed optimal in 90% (120/134) of cases for the pulmonary parenchyma. Sixty-nine per cent (92/134) of cases demonstrated homogeneous enhancement of the pulmonary arteries to the subsegmental level. Only 6% (8/134) of examinations were considered uninterpretable.

CONCLUSION

The present "triple-low" CTPA protocol allows convenient analysis of the pulmonary parenchyma and arteries without hindrance by respiratory motion artefacts in dyspnoeic patients.

Quantitative volumetric computed tomography embolic analysis, the Qanadli score, biomarkers, and clinical prognosis in patients with acute pulmonary embolism

Detailed descriptions of acute pulmonary emboli (PE) morphology, total embolic volume (TEV), and their effects upon patients’ clinical presentation and prognosis remain largely unexplored. We studied 201 subjects with acute PE to the emergency department of a single medical center from April 2009 to December 2014. Patient hemodynamics, Troponin I and D-dimer levels, echocardiography, and the 30-day, 90-day and long-term mortality were obtained. Contrast-enhanced computed tomography (CT) of pulmonary structures and 3-dimensional measures of embolic burden were performed. The results showed a linear association between the greater TEV and each of the following 4 variables (increasing incidence of right ventricular (RV) dysfunction, higher systolic pulmonary artery pressure (sPAP), greater RV diameter, and RV/left ventricular (LV) ratio (all p < 0.001)). Among the measures of CT and echocardiography, TEV and RV/LV ratio were significantly associated with impending shock. In backward stepwise logistic regression, TEV, age and respiratory rate remained independent associated with impending shock (OR: 1.58, 1.03, 1.18, respectively and all p < 0.005).Total embolic burden assessed by CT-based quantification serves as a useful index for stressed cardiopulmonary circulation condition and can provide insights into RV dysfunction and the prediction of impending shock.

Comparative Study of Diagnostic Efficacy of Single Phase-Computed Tomography Pulmonary Angiography and Dual Phase-Computed Tomography Pulmonary Angiography in the Diagnosis of Pulmonary Embolism

Objective

We compared the efficacy of single phase-computed tomography pulmonary angiography (SP-CTPA) and dual phase-computed tomography pulmonary angiography (DP-CTPA) for the diagnosis of pulmonary embolism (PE).

Methods

We recruited 1,019 consecutive patients (359 with PE) who underwent DP-CTPA (phase I: pulmonary artery phase; phase II: aortic phase) for suspected PE between January and October 2021. Phase I of DP-CTPA was used as SP-CTPA, and the final clinical diagnosis (FCD) was used as the gold standard.

Results

Three hundred fifty-two cases of PE were detected by both methods, with the same sensitivity of 98.1% (99.6–99.5%). Using SP-CTPA, 142 cases [13 pulmonary insufficiency artifacts (PIA) and 129 systemic-pulmonary shunt artifacts (S-PSA)] were false-positive with specificity of 78.5% (75.3–81.6%). No false-positive was found with DP-CTPA, with specificity of 100%, positive predictive value of 1, and negative predictive value of 0.990 (Net Reclassification Improvement = 0.215; P < 0.05). According to FCD, the positive results of SP-CTPA were divided into PIA, S-PSA, and true-positive (TP_SP−CTPA) groups, and pairwise comparisons were performed. The bronchiectasis and hemoptysis rate in S-PSA group was higher than that in PIA and TP groups (P < 0.001), and the pulmonary hypertension (PH) rate in PIA group was higher than that in S-PSA and TP groups (P < 0.001).

Conclusion

The diagnostic efficiency of DP-CTPA for the diagnosis of PE was high. SP-CTPA may misdiagnose PIA (common in patients with PH) and S-PSA (common in patients with bronchiectasis and hemoptysis) as PE.

CT Angiography for the Detection of Pulmonary Embolism: Role of Tube Voltage and Contrast Injection Rate on Diagnostic Confidence

RATIONALE AND OBJECTIVES

Pulmonary CTA is the current standard method to assess for suspected pulmonary embolism. In some instances, the test results in low confidence interpretations. Our purpose was to compare the diagnostic confidence for three different scan protocols.

MATERIALS AND METHODS

Pulmonary CTA images from 401 patients were retrospectively analyzed. 202 studies used a tube voltage of 120 kVp and a contrast injection rate of 4 cc/s, 99 studies 120 kVp and 5 cc/s, and 100 studies 100 kVp and 4 cc/s. The level of diagnostic confidence was extracted from the final clinical reports. For each study, attenuation of the pulmonary artery, image noise, signal-to-noise ratio (SNR), and radiation dose were compared.

RESULTS

The 120 kVp, 5 cc/s protocol resulted in high diagnostic confidence in 84% of cases, more than with the 120 kVp, 4cc/s (65%) and the 100 kVp protocol (65%, p < 0.004). The 100 kVp protocol had a lower radiation dose, higher image noise, lower SNR, but equal and higher attenuation values of the pulmonary artery.

CONCLUSION

The reduction of tube voltage to 100 kVp at 4 cc/s maintains diagnostic confidence with lower radiation exposure, but does not equal the higher confidence achieved with 120 kVp at 5cc/s.

The echocardiographic ratio tricuspid annular plane systolic excursion/pulmonary arterial systolic pressure predicts short-term adverse outcomes in acute pulmonary embolism

AIMS

Right ventricular (RV) failure causes death from acute pulmonary embolism (PE), due to a mismatch between RV systolic function and increased RV afterload. We hypothesized that an echocardiographic ratio of this mismatch [RV systolic function by tricuspid annular plane systolic excursion (TAPSE) divided by pulmonary arterial systolic pressure (PASP)] would predict adverse outcomes better than each measurement individually, and would be useful for risk stratification in intermediate-risk PE.

METHODS AND RESULTS

This was a retrospective analysis of a single academic centre Pulmonary Embolism Response Team registry from 2012 to 2019. All patients with confirmed PE and a formal transthoracic echocardiogram performed within 2 days were included. All echocardiograms were analysed by an observer blinded to the outcome. The primary endpoint was a 7-day composite outcome of death or haemodynamic deterioration. Secondary outcomes were 7- and 30-day all-cause mortality. A total of 627 patients were included; 135 met the primary composite outcome. In univariate analysis, the TAPSE/PASP was associated with our primary outcome [odds ratio = 0.028, 95% confidence interval (CI) 0.010-0.087; P < 0.0001], which was significantly better than either TAPSE or PASP alone (P = 0.017 and P < 0.0001, respectively). A TAPSE/PASP cut-off value of 0.4 was identified as the optimal value for predicting adverse outcome in PE. TAPSE/PASP predicted both 7- and 30-day all-cause mortality, while TAPSE and PASP did not.

CONCLUSION

A combined echocardiographic ratio of RV function to afterload is superior in prediction of adverse outcome in acute intermediate-risk PE. This ratio may improve risk stratification and identification of the patients that will suffer short-term deterioration after intermediate-risk PE.

Canadian Society of Thoracic Radiology/Canadian Association of Radiologists Best Practice Guidance for Investigation of Acute Pulmonary Embolism, Part 1: Acquisition and Safety Considerations

Acute pulmonary embolism (APE) is a well-recognized cause of circulatory system compromise and even demise which can frequently present a diagnostic challenge for the physician. The diagnostic challenge is primarily due to the frequency of indeterminate presentations as well as several other conditions which can have a similar clinical presentation. This often obliges the physician to establish a firm diagnosis due to the potentially serious outcomes related to this disease. Computed tomography pulmonary angiography (CTPA) has increasingly cemented its role as the primary investigation tool in this clinical context and is widely accepted as the standard of care due to several desired attributes which include great accuracy, accessibility, rapid turn-around time and the ability to suggest an alternate diagnosis when APE is not the culprit. In Part 1 of this guidance document, a series of up-to-date recommendations are provided to the reader pertaining to CTPA protocol optimization (including scan range, radiation and intravenous contrast dose), safety measures including the departure from breast and gonadal shielding, population-specific scenarios (pregnancy and early post-partum) and consideration of alternate diagnostic techniques when clinically deemed appropriate.

An optimized test bolus for computed tomography pulmonary angiography and its application at 80 kV with 10 ml contrast agent

Computed tomography pulmonary angiography (CTPA) is usually used for pulmonary embolism (PE) detection. However, the determination of scan timing remains a challenge due to the short scan duration of CTPA. We aimed to develop an optimized test bolus to determine scan delay in CTPA. The time-enhancement curves were obtained by measuring the enhancement within a region of interest in the main pulmonary artery and vein. A total of 70 patients were randomly divided into two groups (n = 35 each): the control group underwent CTPA using the test bolus approach and the test group underwent CTPA using the biphasic time-enhancement curves approach. Tube voltages of 100 kVp and 80 kVp and 20 ml and 10 ml contrast agent were adopted in the control and test groups, respectively. The CT numbers, image quality, PE detection was evaluated. There was a point of intersection between the pulmonary artery and vein test bolus enhancement curves. The scan delay time (T_DELAY) was obtained based on the time at intersection (T_CROSS) and the scan duration (T_SD): T_DELAY = T_CROSS − T_SD. The mean CT numbers for pulmonary vein in the control were higher than those in the test group (all p < 0.001). The image quality for the pulmonary arteries in the test group was better than that in the control group (p < 0.01), with artifact reduction in the superior vena cava. Segmental PE could be detected using the optimized protocol. The radiation dose and iodine load in the test group were all lower than those in the control (p < 0.01). We established an approach to calculate the scan delay of CTPA, and this approach could be used for CTPA at 80 kVp with 10 ml contrast agent.

[Sudden chest pain and lower abdominal pain : The usual suspects]

CLINICAL PROBLEM

Sudden chest pain and sudden abdominal pain are among the most common reasons that lead patients to the emergency room. The heterogeneous field of possible, sometimes serious diagnoses requires a structured and rapid interdisciplinary clarification in order to be able to promptly provide patients with an adequate therapy.

STANDARD RADIOLOGICAL PROCEDURES

Knowing the "usual suspects" of sudden chest and abdominal pain enables the radiologist to quickly select the appropriate imaging method that allows a diagnosis to be made without delay. In addition to pain localization and character, age, gender, any previous illnesses and laboratory results are taken into account in the differential diagnosis.

METHODICAL INNOVATION AND EVALUATION

The technical state of computer tomography (CT) now ensures that most diagnoses can be clarified due to its excellent spatial and temporal resolution. In the abdomen, however, ultrasound should continue to be used at least for primary evaluation. Only if there is a further need for abdominal imaging afterwards is CT indicated for clarification. Magnetic resonance imaging is rarely used in the emergency setting of abdominal pain except to avoid radiation exposure in children or pregnant women.

RECOMMENDATION FOR THE PRACTICE

Knowledge of the usual diagnoses that cause sudden chest or abdominal pain, as well as knowledge of the appropriate examination procedures and classic radiological signs are essential to avoid errors and delays in the emergency diagnosis of sudden chest and abdominal pain.

Computed tomography pulmonary angiography for acute pulmonary embolism: prediction of adverse outcomes and 90-day mortality in a single test

Purpose

Pulmonary embolism (PE) is a potentially fatal cardiopulmonary disease; therefore, rapid risk stratification is necessary to make decisions of appropriate management strategies. The aim of this study was to assess various computed tomography (CT) findings in order to find new prognostic factors of adverse outcome and mortality.

Material and methods

The study enrolled 104 patients with acute PE. Based on their outcome, patients were categorised into four groups. Comorbidities such as ischaemic heart disease were obtained from their medical records. Patients CT angiography were reviewed for recording variables such as main pulmonary artery diameter and right ventricle (RV)/left ventricle (LV) ratio. Patient deaths up to three months since diagnosis of PE had been registered. Logistic regression analysis was performed to find predictors.

Results

Based on multiple logistic regression, RV/LV ratio, LV diameter, and right-sided pulmonary infarction are predictors of mortality in 30 days. An RV/LV ratio of 1.19 could successfully discriminate patients who died within 30 days and those who did not.

Conclusions

RV/LV ratio, LV diameter, right-sided pulmonary infarction, assessed with helical CT, can help predict 30-day mortality.

Computed tomography pulmonary angiography using high-pitch dual-source scanner technology

Objectives:

To compare use of ultra-fast high-pitch dual-source free-breathing computed tomography pulmonary angiogram (CTPA) with conventional standard-pitch single-source breath-hold CTPA.

Methods:

This retrospective comparative study was conducted in Radiology Department at King Fahad Military Medical Complex Dhahran, Saudi Arabia from July 2016 to December 2017. Patients (N=130) were divided into 2 groups, each having 65 consecutive patients; Group-1 (single-source CT) and Group-2 (dual-source CT). Previously treated pulmonary embolism cases, pregnant patients and those with incomplete data were excluded. Image quality was subjectively assessed by 2 readers for adequacy of contrast opacification and pulmonary vessel outline, and presence of artifacts (breathing motion, cardiac pulsation, and contrast related). Scan acquisition times and radiation doses were also compared. Chi-square and t-test were used to determine association.

Results:

Improved image quality (optimal studies without artifacts 91%) was seen in Group-2 compared to Group-1 (optimal studies without artifacts 75.4%). Also, reduced scan time (1-2 sec.) and radiation dose (mean dose length product (DLP)-248 mGy-cm) were observed in Group-2 compared to Group-1 (scan time- 6.5 sec, mean DLP-375). Results were found significant (p<0.05).

Conclusion:

High-pitch dual-source CT with free-breathing yields better image quality, reduces image acquisition time and radiation doses.

Optimization of computed tomography pulmonary angiography protocols using 3D printed model with simulation of pulmonary embolism

Background

Three-dimensional (3D) printing has been shown to accurately replicate anatomical structures and pathologies in complex cardiovascular disease. Application of 3D printed models to simulate pulmonary arteries and pulmonary embolism (PE) could assist development of computed tomography pulmonary angiography (CTPA) protocols with low radiation dose, however, this has not been studied in the literature. The aim of this study was to investigate optimal CTPA protocols for detection of PE based on a 3D printed pulmonary model.

Methods

A patient-specific 3D printed pulmonary artery model was generated with thrombus placed in both main pulmonary arteries to represent PE. The model was scanned with 128-slice dual-source CT with slice thickness of 1 and 0.5 mm reconstruction interval. The tube voltage was selected to range from 70, 80, 100 to 120 kVp, and pitch value from 0.9 to 2.2 and 3.2. Quantitative assessment of image quality in terms of signal-to-noise ratio (SNR) was measured in the main pulmonary arteries and within the thrombus regions to determine the relationship between image quality and scanning protocols. Both two-dimensional (2D) and 3D virtual intravascular endoscopy (VIE) images were generated to demonstrate pulmonary artery and thrombus appearances.

Results

PE was successfully simulated in the 3D printed pulmonary artery model. There were no significant differences in SNR measured in the main pulmonary arteries with 100 and 120 kVp CTPA protocols (P>0.05), regardless of pitch value used. SNR was significantly lower in the high-pitch 3.2 protocols when compared to other protocols using 70 and 80 kVp (P<0.05). There were no significant differences in SNR measured within the thrombus among the 100 and 120 kVp protocols (P>0.05). For low dose 70 and 80 kVp protocols, SNR was significantly lower in the high-pitch of 3.2 protocols than that in other protocols with different pitch values (P<0.01). 2D images showed the pulmonary arteries and thrombus clearly, while 3D VIE demonstrated intraluminal appearances of pulmonary wall and thrombus in all protocols, except for the 70 kVp and pitch 3.2 protocol, with visualization of thrombus and pulmonary artery wall affected by artifact associated with high image noise. Radiation dose was reduced by up to 80% when lowering kVp from 120 to 100 and 80 kVp with use of 3.2 high-pitch protocol, without significantly affecting image quality.

Conclusions

Low-dose CT pulmonary angiography can be achieved with use of low kVp (80 and 100) and high-pitch protocol with significant reduction in radiation dose while maintaining diagnostic images of PE. Use of high pitch, 3.2 in 70 kVp protocol should be avoided due to high image noise and poorer quality.

High-pitch versus standard mode CT pulmonary angiography: a comparison of indeterminate studies

PURPOSE

To compare the causes of indeterminate CT pulmonary angiograms using standard mode and high-pitch mode, and determine at what level of the pulmonary arterial tree studies were non-diagnostic.

METHODS

IRB approval was obtained. A retrospective review of patients at our institution who underwent a CT pulmonary angiogram, between November 1, 2015 and February 10, 2016 was performed. CT pulmonary angiograms using both high-pitch mode and standard mode were evaluated with positive and indeterminate rates calculated. Causes of indeterminate studies and the level of the pulmonary arterial tree at which the study became non-diagnostic were determined by a board certified radiologist by looking at the images of each indeterminate study. The indeterminate rates were compared between high-pitch and standard modes using a generalized estimating equation.

RESULTS

Five hundred fifty-nine CT pulmonary angiograms using high-pitch mode were evaluated, while 661 standard mode scans were evaluated. 69/559 (12.3%) scans with high-pitch mode were positive and 84/661 (12.7%) scans with standard mode were positive (not statistically significant, p > 0.05). There was a higher rate of indeterminate scans with standard mode compared to the high-pitch mode (80 [12.1%] standard vs. 25 [4.5%] high-pitch, p value < 0.0001). Findings were indeterminate at the lobar level in 4 (16%), at the segmental level in 11 (44%), and at the subsegmental level in 10 (40%) using high-pitch mode. The most common causes of an indeterminate scan using high-pitch mode were motion in 11 (44%), transient interruption of contrast in 6 (24%), and contrast timing in 5 (20%). Findings were indeterminate at the main pulmonary artery level in 1 (1.3%), at the lobar level in 13 (16.3%), at the segmental level in 28 (35.0%), and at the subsegmental level in 38 (47.5%) using the standard mode. The most common causes of an indeterminate scan using the standard mode were motion in 53 (66.3%), transient interruption of contrast in 19 (23.8%), and contrast timing in 15 (18.8%).

CONCLUSIONS

High-pitch mode results in statistically significant fewer indeterminate studies compared with standard mode. Furthermore, there were statistically significant fewer indeterminate studies due to motion artifact with high-pitch mode compared with standard mode.

A proof of concept for epidemiological research using structured reporting with pulmonary embolism as a use case

OBJECTIVE

This paper studies the possibilities of an integrated IT-based workflow for epidemiological research in pulmonary embolism (PE) using freely available tools and structured reporting (SR).

METHODS

We included a total of 521 consecutive cases which had been referred to the radiology department for CT pulmonary angiography with suspected PE. Free-text reports were transformed into structured reports using a freely available IHE Management of Radiology Report Templates-compliant reporting platform. D-dimer values were retrieved from the hospitals laboratory results system. All information was stored in the platform's database and visualized using freely available tools. For further analysis, we directly accessed the platform's database with an advanced analytics tool (RapidMiner).

RESULTS

Results: We were able to develop an integrated workflow for epidemiological statistics from reports obtained in clinical routine. The report data allowed for automated calculation of epidemiological parameters. Prevalence of PE was 27.6%. The mean age in patients with and without PE did not differ (62.8 years and 62.0 years, respectively, p = 0.987). As expected, there was a significant difference in mean D-dimer values (10.13 and 3.12 mg l-1 fibrinogen equivalent units, respectively, p < 0.001).

CONCLUSION

SR can make data obtained from clinical routine more accessible. Designing practical workflows is feasible using freely available tools and allows for the calculation of epidemiological statistics on a near realtime basis. Therefore, radiologists should push for the implementation of SR in clinical routine. Summary sentence: Implementing practical workflows that allow for the calculation of epidemiological statistics using SR and freely available tools is easily feasible. Advances in knowledge: Theoretical benefits of SR have long been discussed, but practical implementation demonstrating those benefits has been lacking. Here, we present a first experience providing proof that SR will make data from clinical routine more accessible.

Dual-Energy Computed Tomography in Cardiothoracic Vascular Imaging

Dual energy computed tomography is becoming increasingly widespread in clinical practice. It can expand on the traditional density-based data achievable with single energy computed tomography by adding novel applications to help reach a more accurate diagnosis. The implementation of this technology in cardiothoracic vascular imaging allows for improved image contrast, metal artifact reduction, generation of virtual unenhanced images, virtual calcium subtraction techniques, cardiac and pulmonary perfusion evaluation, and plaque characterization. The improved diagnostic performance afforded by dual energy computed tomography is not associated with an increased radiation dose. This review provides an overview of dual energy computed tomography cardiothoracic vascular applications.

90-kVp low-tube-voltage CT pulmonary angiography in combination with advanced modeled iterative reconstruction algorithm: effects on radiation dose, image quality and diagnostic accuracy for the detection of pulmonary embolism

OBJECTIVE

To evaluate low-tube-voltage 90-kVp CT pulmonary angiography (CTPA) with advanced modeled iterative reconstruction algorithm (Admire) compared to 120-kVp equivalent dual-energy (DE) acquisition with regards to radiation exposure, image quality and diagnostic accuracy for pulmonary embolism (PE) assessment.

METHODS

CTPA studies of 40 patients with suspected PE (56.7 ± 16.3 years) performed on a third-generation 192-slice dual-source CT scanner were retrospectively included. 120-kVp equivalent linearly-blended (60% 90-kVp, 40% 150-kVp) and 90-kVp images were reconstructed. Attenuation and noise of the pulmonary trunk were measured to calculate contrast-to-noise ratios (CNR). Three radiologists assessed the presence of central and segmental PE and diagnostic confidence. Interobserver agreement was calculated using intraclass correlation coefficient (ICC). Radiation exposure was assessed as effective dose (ED).

RESULTS

Pulmonary trunk CNR values were significantly increased in 90-kVp compared to linearly-blended series (15.4 ± 6.3 vs 11.3 ± 4.6, p < 0.001). Diagnostic accuracy for PE assessment was similar in both series with excellent interobserver agreement (p = 0.48; ICC, 0.83; p = 0.48). Overall confidence for PE assessment was rated excellent for both series with a significant advantage for linearly-blended series (p < 0.001; 4.1 vs 3.8). ED was reduced by 37.2% with 90-kVp compared to 120-kVp equivalent image series (1.1 ± 0.6 vs 1.7 ± 0.7 mSv, p < 0.001).

CONCLUSION

90-kVp CTPA with Admire provided increased quantitative image quality with similar diagnostic accuracy and confidence for PE assessment compared to 120-kVp equivalent acquisition, while radiation dose was reduced by 37.2%. Advances in knowledge: 90-kVp CTPA with an advanced iterative reconstruction algorithm results in excellent image quality and reduction of radiation exposure without limiting diagnostic performance.

Value of Dual-energy Lung Perfusion Imaging Using a Dual-source CT System for the Pulmonary Embolism

Objective

To investigate the diagnostic value of dual-energy lung perfusion imaging (DEPI) using a dual-source CT system for the pulmonary embolism (PE).

Methods

50 patients in high acute PE prevalence were enrolled to accept the DEPI (lung perfusion image and CTA image of pulmonary artery acquired through the Dual Energy software) and emergent DSA angiography (golden diagnostic criterion).

Results

Patients using CT had significantly reduced examination duration and dosage of contrast agent than those using DSA examination, (P < 0.05). In total, 260 pulmonary arteries and 1020 pulmonary segments were examined through CTA, in which embolisms were identified in 50 lobes of lung, 108 pulmonary segments and 82 sub-segments. Reduction or lack of perfusion was identified through DEPI in 48 lobes of lung (concordance rate of 96.0%), 103 pulmonary segments (concordance rate of 95.4%) and 78 subsegments (concordance rate of 95.1%). The comparison of embolism quantity and morphological characteristics of pulmonary artery between CTA images and DEPI images showed no statistically significant difference.

Conclusion

Better application value can be achieved in the diagnosis of pulmonary embolism by dual-energy lung perfusion imaging using a dual-source CT system.

Vascular CT and MRI: a practical guide to imaging protocols

Non-invasive cross-sectional imaging techniques play a crucial role in the assessment of the varied manifestations of vascular disease. Vascular imaging encompasses a wide variety of pathology. Designing vascular imaging protocols can be challenging owing to the non-uniform velocity of blood in the aorta, differences in cardiac output between patients, and the effect of different disease states on blood flow. In this review, we provide the rationale behind—and a practical guide to—designing and implementing straightforward vascular computed tomography (CT) and magnetic resonance imaging (MRI) protocols.

Teaching Points

• There is a wide range of vascular pathologies requiring bespoke imaging protocols.

• Variations in cardiac output and non-uniform blood velocity complicate vascular imaging.

• Contrast media dose, injection rate and duration affect arterial enhancement in CTA.

• Iterative CT reconstruction can improve image quality and reduce radiation dose.

• MRA is of particular value when imaging small arteries and venous studies.

Comparison of the effect of radiation exposure from dual-energy CT versus single-energy CT on double-strand breaks at CT pulmonary angiography

PURPOSE

To compare the effect of dual-source dual-energy CT versus single-energy CT on DNA double-strand breaks (DSBs) in blood lymphocytes at CT pulmonary angiography (CTPA).

METHODS AND MATERIALS

Sixty-two patients underwent either dual-energy CTPA (Group 1: n = 21, 80/Sn140 kVp, 89/38 mAs; Group 2: n = 20, 100/Sn140 kVp, 89/76 mAs) or single-energy CTPA (Group 3: n = 21, 120 kVp, 110 mAs). Blood samples were obtained before and 5 min after CTPA. DSBs were assessed with fluorescence microscopy and Kruskal-Walls tests were used to compare DSBs levels among groups. Volume CT dose index (CTDIvol), dose length product (DLP) and organ radiation dose were compared using ANOVA.

RESULTS

There were increased excess DSB foci per lymphocyte 5 min after CTPA examinations in three groups (Group 1: P = .001; Group 2: P = .001; Group 3: P = .006). There were no differences among groups regarding excess DSB foci/cell and percentage of excess DSBs (Group 1, 23%; Group 2, 24%; Group 3, 20%; P = .932). CTDIvol, DLP and organ radiation dose in Group 1 were the lowest among the groups (all P < .001).

CONCLUSION

DSB is increased following dual-source and single-source CTPA, while dual-source dual-energy CT protocols do not increase the estimated radiation dose and also do not result in a higher incidence of DNA DSBs in patients undergoing CTPA.

Acute kidney injury in patients with nephrotic syndrome undergoing contrast-enhanced CT for suspected venous thromboembolism: a propensity score-matched retrospective cohort study

OBJECTIVES

To determine whether intravenous iodinated contrast material administration increases the risk of acute kidney injury (AKI) in patients with nephrotic syndrome undergoing contrast-enhanced CT.

METHODS

Patients with nephrotic syndrome undergoing contrast-enhanced CT were retrospectively identified (n = 701). Control group consisted of patients with nephrotic syndrome receiving non-contrast CT (n = 1053). Two different 1:1 propensity score matching models using three or 10 variables were developed for each estimated glomerular filtration (eGFR) subgroup. Incidence of post-CT AKI for the two groups was assessed and compared by standard AKI criteria and Acute Kidney Injury Network (AKIN) criteria.

RESULTS

After matching with three variables, the AKI incidence in the contrast-enhanced CT and non-contrast CT groups was 2.7% vs 2.5% (standard AKI criteria) and 4.2% vs. 6.7% (AKIN criteria) (p = 1.00 and 0.05), respectively. After matching with 10 variables, AKI incidences were 3.1% vs. 2.6% (standard AKI criteria) and 4.1% vs. 7.4% (AKIN criteria) (p = 0.72 and 0.03), respectively. AKI incidences of each eGFR subgroup in the contrast-enhanced CT group were not higher than in the non-contrast CT group (lowest p = 0.46).

CONCLUSION

Intravenous contrast material administration during CT was not found to be a risk factor for AKI in this large cohort of patients with nephrotic syndrome.

KEY POINTS

• AKI incidence of contrast-enhanced CT and non-contrast CT had no difference. • AKI incidences of eGFR subgroup in contrast-enhanced CT were not increased. • Studies without a non-contrast CT control group may overestimate CIN incidence.

Opportunities for new CT contrast agents to maximize the diagnostic potential of emerging spectral CT technologies

The introduction of spectral CT imaging in the form of fast clinical dual-energy CT enabled contrast material to be differentiated from other radiodense materials, improved lesion detection in contrast-enhanced scans, and changed the way that existing iodine and barium contrast materials are used in clinical practice. More profoundly, spectral CT can differentiate between individual contrast materials that have different reporter elements such that high-resolution CT imaging of multiple contrast agents can be obtained in a single pass of the CT scanner. These spectral CT capabilities would be even more impactful with the development of contrast materials designed to complement the existing clinical iodine- and barium-based agents. New biocompatible high-atomic number contrast materials with different biodistribution and X-ray attenuation properties than existing agents will expand the diagnostic power of spectral CT imaging without penalties in radiation dose or scan time.

Imaging of acute and chronic thromboembolic disease: state of the art

Acute pulmonary embolism (PE) is a life-threatening condition that requires prompt diagnosis and treatment. Recent advances in imaging allow acute and rapid recognition even by the non-specialist radiologist. Most acute emboli resolve on anticoagulation without sequelae; however, some emboli fail to fully resolve becoming endothelialised with the development of chronic thromboembolic disease (CTED). Increased pulmonary vascular resistance arising from CTED may lead to chronic thromboembolic pulmonary hypertension (CTEPH) a debilitating disease affecting up to 5% of survivors of acute PE. Diagnostic evaluation is more complex in CTEPH/CTED than acute PE with subtle imaging features often being overlooked or misinterpreted. Differentiation of acute from chronic PE and from other forms of pulmonary hypertension has profound therapeutic implications. Diverse imaging techniques are available to diagnose and monitor PEs both in the acute and chronic setting. Broadly they include techniques that provide data on lung parenchymal perfusion (ventilation-perfusion [VQ] scintigraphy), angiographic techniques (computed tomography [CT], magnetic resonance imaging [MRI], and invasive angiography) or a combination of both (MR angiography and time-resolved angiography or dual-energy CT angiography). This review aims to describe state of the art imaging highlighting the strength and weaknesses of individual techniques in the diagnosis of acute and chronic PE.

CT Angiography: Post-processed Contrast Enhancement for Improved Detection of Pulmonary Embolism

RATIONALE AND OBJECTIVES

The study aimed to improve the detection of pulmonary embolism via an iodine contrast enhancement tool in patients who underwent suboptimal enhanced computed tomography angiography (CTA).

MATERIALS AND METHODS

We evaluated the CT examinations of 41 patients who underwent CTA for evaluation of the pulmonary arteries which suffered from suboptimal contrast enhancement. The contrast enhancement of the reconstructed images was increased via a post-processing tool (vContrast). Image noise and contrast-to-noise ratio (CNR) were assessed in eight different regions: main pulmonary artery, right and left pulmonary arteries, right and left segment arteries, muscle, subcutaneous fat, and bone. For subjective image assessment, three experienced radiologists evaluated the diagnostic quality.

RESULTS

While employing the post-processing algorithm, the CNR for contrast-filled lumen and thrombus/muscle improves significantly by a factor of 1.7 (CNR without vContrast = 8.48 ± 6.79/CNR with vContrast = 14.46 ± 5.29) (P <0.01). No strengthening of artifacts occurred, and the mean Hounsfield unit values of the muscle, subcutaneous fat, and the bone showed no significant changes. Subjective image analysis illustrated a significant improvement using post-processing for clinically relevant criteria such as diagnostic confidence.

CONCLUSIONS

vContrast makes CT angiograms with inadequate contrast applicable for diagnostic evaluation, offering an improved visualization of the pulmonary arteries. In addition, vContrast can help in the significant reduction of the iodine contrast material.

State-of-the-Art Pulmonary CT Angiography for Acute Pulmonary Embolism

OBJECTIVE

Pulmonary CT angiography (CTA) is the imaging modality of choice in suspected acute pulmonary embolism (PE). Current pulmonary CTA techniques involve ever lower doses of contrast medium and radiation along with advanced postprocessing applications to enhance image quality, diagnostic accuracy, and provide added value in patient management. The objective of this article is to summarize these current developments and discuss the appropriate use of state-of-the-art pulmonary CTA.

CONCLUSION

Pulmonary CTA is well established as a fast and reliable means of excluding or diagnosing PE. Continued developments in CT system hardware and postprocessing techniques will allow incremental reductions in radiation and contrast material requirements while improving image quality. Advances in risk stratification and prognostication from pulmonary CTA examinations should further refine its clinical value while minimizing the potential harm from overutilization and overdiagnosis.

Low-tube-voltage selection for triple-rule-out CTA: relation to patient size

Objectives

To investigate the relationship between image quality and patient size at 100 kilovoltage (kV) compared to 120 kV ECG-gated Triple-Rule-Out CT angiography (TRO-CTA).

Methods

We retrospectively included 73 patients (age 64 ± 14 years) who underwent retrospective ECG-gated chest CTA. 40 patients were scanned with 100 kV while 33 patients with 120 kV. Body mass index (BMI), patients’ chest circumference (PC) and thoracic surface area (TSA) were recorded. Quantitative image quality was assessed as vascular attenuation in the ascending aorta (AA), pulmonary trunk (PA) and left coronary artery (LCA) and the signal-to-noise ratio (SNR) in the AA.

Results

There was no significant difference in BMI (26.0 ± 4.6 vs. 28.0 ± 6.7 kg/m²), PC (103 ± 7 vs. 104 ± 10 cm²) and TSA (92 ± 15 vs. 91 ± 19 cm²) between 100 kV and 120 kV group. Mean vascular attenuation was significantly higher in the 100 kV compared to the 120 kV group (AA 438 vs. 354 HU, PA 460 vs. 349 HU, LCA 370 vs. 299 HU all p < 0.001). SNR was not significantly different, even after adjusting for patient size. Radiation dose was significantly lower in the 100 kV group (10.7 ± 4.1 vs. 20.7 ± 10.7 mSv; p < 0.001).

Conclusions

100 kV TRO-CTA is feasible in normal-to-overweight patients while maintaining image quality and achieving substantial dose reduction.

Key Points

• 100 kV protocols result in a significantly lower radiation dose.

• Mean vascular attenuation is significantly higher using 100 kV.

• SNR and CNR are not significantly different between 100 kV and 120 kV.

• 100 kV CTA is feasible regardless of patient size while maintaining image quality.

Detection of pulmonary fat embolism with dual-energy CT: an experimental study in rabbits

OBJECTIVES

To evaluate the use of dual-energy CT imaging of the lung perfused blood volume (PBV) for the detection of pulmonary fat embolism (PFE).

METHODS

Dual-energy CT was performed in 24 rabbits before and 1 hour, 1 day, 4 days and 7 days after artificial induction of PFE via the right ear vein. CT pulmonary angiography (CTPA) and lung PBV images were evaluated by two radiologists, who recorded the presence, number, and location of PFE on a per-lobe basis. Sensitivity, specificity, and accuracy of CTPA and lung PBV for detecting PFE were calculated using histopathological evaluation as the reference standard.

RESULTS

A total of 144 lung lobes in 24 rabbits were evaluated and 70 fat emboli were detected on histopathological analysis. The overall sensitivity, specificity and accuracy were 25.4 %, 98.6 %, and 62.5 % for CTPA, and 82.6 %, 76.0 %, and 79.2 % for lung PBV. Higher sensitivity (p < 0.001) and accuracy (p < 0.01), but lower specificity (p < 0.001), were found for lung PBV compared with CTPA. Dual-energy CT can detect PFE earlier than CTPA (all p < 0.01).

CONCLUSION

Dual-energy CT provided higher sensitivity and accuracy in the detection of PFE as well as earlier detection compared with conventional CTPA in this animal model study.

KEY POINTS

• Fat embolism occurs commonly in patients with traumatic bone injury. • Dual-energy CT improves diagnostic performance for pulmonary fat embolism detection. • Dual-energy CT can detect pulmonary fat embolism earlier than CTPA.

Computed tomography angiography with pulmonary artery thrombus burden and right-to-left ventricular diameter ratio after pulmonary embolism

Purpose

Computed tomography angiography is used for quantifying the significance of pulmonary embolism, but its reliability has not been well defined.

Methods

The study cohort comprised 10 patients randomly selected from a 150-patient prospective trial of ultrasound-facilitated fibrinolysis for acute pulmonary embolism. Four reviewers independently evaluated the right-to-left ventricular diameter ratios using the standard multiplanar reformatted technique and a simplified (axial) method, and thrombus burden with the standard modified Miller score and a new, refined Miller scoring system.

Results

The intraclass correlation coefficient for intra-observer variability was .949 and .970 for the multiplanar reformatted and axial methods for estimating right-to-left ventricular ratios, respectively. Inter-observer agreement was high and similar for the two methods, with intraclass correlation coefficient of .969 and .976. The modified Miller score had good intra-observer agreement (intraclass correlation coefficient .820) and was similar to the refined Miller method (intraclass correlation coefficient .883) for estimating thrombus burden. Inter-observer agreement was also comparable between the techniques, with intraclass correlation coefficient of .829 and .914 for the modified Miller and refined Miller methods.

Conclusions

The reliability of computed tomography angiography for pulmonary embolism was excellent for the axial and multiplanar reformatted methods for quantifying the right-to-left ventricular ratio and for the modified Miller and refined Miller scores for quantifying of pulmonary artery thrombus burden.