Pilot study comparing SPECT perfusion scintigraphy with CT pulmonary angiography in chronic thromboembolic pulmonary hypertension

Observational cohort study to validate SEARCH, a novel hierarchical algorithm to define long-term outcomes after pulmonary embolism

BACKGROUND

Chronic dyspnoea and exercise impairment are common after acute pulmonary embolism (PE) but are not defined and quantified sufficiently to serve as outcomes in clinical trials. The planned project will clinically validate a novel method to determine discrete, clinically meaningful diagnoses after acute PE. The method uses an algorithm entitled SEARCH, for symptom screen, exercise testing, arterial perfusion, resting echocardiography, confirmatory imaging and haemodynamic measurements. SEARCH is a stepwise algorithm that sorts patients by a hierarchical series of dichotomous tests into discreet categories of long-term outcomes after PE: asymptomatic, post-PE deconditioning, symptoms from other causes, chronic thromboembolism with ventilatory inefficiency, chronic thromboembolism with small stroke volume augmentation, chronic thromboembolic disease and chronic thromboembolic pulmonary hypertension.

METHODS

The project will test the inter-rater reliability of the SEARCH algorithm by determining whether it will yield concordant post-PE diagnoses when six independent reviewers review the same diagnostic data on 150 patients evaluated at two time points after PE. The project will also determine whether the post-PE diagnoses are stable, according to the SEARCH algorithm, between the first evaluation and the subsequent one 6 months later.

IMPLICATIONS

Validation of the SEARCH algorithm would offer clinicians a straightforward method to diagnose post-PE conditions that are rarely distinguished clinically. Their categorisation and definition will allow post-PE conditions to be used as endpoints in clinical trials of acute PE treatment.

TRIAL REGISTRATION NUMBER

NCT05568927.

Utility of Lung Perfusion SPECT/CT in Detection of Pulmonary Thromboembolic Disease: Outcome Analysis

Purpose

To evaluate the clinical outcome of Q-SPECT/CT in pulmonary thromboembolic disease.

Methods

From Jan 2020 to Jan 2021, 30 consecutive patients (M:F = 8:22; median age = 52 year (21-89)) suspected of having acute pulmonary embolism (PE) or chronic thromboembolic pulmonary hypertension (CTEPH) were referred for non-contrasted Q-SPECT/CT. All patients were COVID-19 PCR negative. MSKCC Q-SPECT/CT and/or PISAPED criteria were used to determine the presence of thromboembolic disease in Q-SPECT/CT. Final diagnosis was made based on composite reference standards that included at least 2-month clinical cardiorespiratory assessment and follow-up imaging.

Results

Q-SPECT/CT was positive in 19 patients: indeterminate in 1 and 10 were negative. Three false positive cases were observed during follow-up. Of the remaining 16 true positives, all patients' cardiorespiratory symptom were improved or stabilised after treatment with anticoagulants. The overall sensitivity, specificity, PPV, NPV and accuracy of Q-SPECT/CT were 100% (95% CI, 79.41-100%), 78.57% (95% CI, 49.20-95.34%), 84.21% (95% CI, 66.41-93.57%), 100% and 90.00% (95% CI, 73.47-97.89%) respectively.

Conclusions

In the current COVID-19 pandemic, Q-SPECT/CT can be an alternative modality to detect pulmonary thromboembolic disease. Normal Q-SPECT/CT excludes pulmonary thromboembolic disease with high degree of certainty. However, false positive has been observed.

Clinical Presentations and Multimodal Imaging Diagnosis in Chronic Thromboembolic Pulmonary Hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare but life-threatening pulmonary vascular disease caused by the presence of a prolonged thrombus in the pulmonary artery. CTEPH is a distinct disease entity classified as group 4 pulmonary hypertension according to the World Symposium on Pulmonary Hypertension. It is the only potentially curable cause of pulmonary hypertension. However, timely diagnosis and treatment are often hampered by nonspecific symptoms and signs and a lack of physician awareness regarding the condition. Thus, it is important to be familiar with the clinical features of CTEPH and the associated diagnostic processes. Herein, we cover the diagnostic approach for CTEPH using multimodal imaging tools in a clinical setting.

Evaluation of Dyspnea and Exercise Intolerance After Acute Pulmonary Embolism

Long-term dyspnea and exercise intolerance are common clinical problems after acute pulmonary embolism. Unfortunately, no single test can distinguish among the range of potential pathologic outcomes after pulmonary embolism. We illustrate a stepwise approach to post-pulmonary embolism evaluation that uses a hierarchic series of clinically validated diagnostic tests. The algorithm is represented by the acronym SEARCH, which stands for Symptom screening, Exercise testing, Arterial perfusion, Resting echocardiography, Confirmatory chest imaging, and Hemodynamics measured by right heart catheterization. We illustrate the algorithm with a patient whom we saw in our pulmonary embolism follow-up clinic. Patients are asked at least 6 months after pulmonary embolism whether they have returned to their baseline level of respiratory comfort and exercise tolerance. Patients with dyspnea and exercise intolerance undergo noninvasive cardiopulmonary exercise testing to identify elevated ventilatory dead space ratios, decreased stroke volume augmentation with exercise, and other physiologic abnormalities during exertion. Ventilation-perfusion scanning is performed on those patients with exercise-related physiologic findings to confirm the presence of residual pulmonary arterial obstruction or to suggest alternative diagnoses. Resting echocardiography may provide evidence of pulmonary hypertension; confirmatory imaging with pulmonary angiography or CT angiography may disclose findings characteristic of chronic pulmonary artery obstruction. Finally, right heart catheterization is performed to confirm chronic thromboembolic pulmonary hypertension; if resting pulmonary hemodynamics are normal, then invasive cardiopulmonary exercise testing may disclose exercise-induced defects.

Evaluation and management of patients with chronic thromboembolic pulmonary hypertension - consensus statement from the ISHLT

ISHLT members have recognized the importance of a consensus statement on the evaluation and management of patients with chronic thromboembolic pulmonary hypertension. The creation of this document required multiple steps, including the engagement of the ISHLT councils, approval by the Standards and Guidelines Committee, identification and selection of experts in the field, and the development of 6 working groups. Each working group provided a separate section based on an extensive literature search. These sections were then coalesced into a single document that was circulated to all members of the working groups. Key points were summarized at the end of each section. Due to the limited number of comparative trials in this field, the document was written as a literature review with expert opinion rather than based on level of evidence.

Chronic thromboembolic pulmonary hypertension: evaluation of V/Q SPECT/CT and V/Q Quotient SPECT findings with postoperative results of pulmonary endarterectomy

OBJECTIVES

We aimed to perform a comparison between V/Q single-photon emission computed tomography/computed tomography (SPECT/CT) and V/Q Quotient single-photon emission computerized tomography (SPECT) in the detection of chronic thromboembolic pulmonary hypertension (CTEPH) and in depicting the extent of the disease on per-segment basis in patients with CTEPH.

METHODS

Between January 2015 and November 2019, a total of 412 patients with pulmonary hypertension secondary to CTEPH at the preoperative assessment underwent pulmonary endarterectomy (PEA), of whom 92 consecutive patients with their V/Q SPECT/CT scans have been performed in our institution prior to PEA were included in this study. Histopathological findings and post-PEA fully resected surgical specimens were used as the reference standard.

RESULTS

On a per-patient basis analysis, V/Q SPECT/CT and V/Q Quotient SPECT both revealed CTEPH in the same 85 of the 92 patients (κ = 1) with a detection rate of 92.4%. In six of these patients, chronic thromboembolic disease could not be reported on both of these two methods due to extensive 'matched' V/Q defects. On a per-segment basis analysis, V/Q SPECT/CT and V/Q Quotient SPECT showed a sensitivity of 75.8 and 73.1%, respectively. Correlation analysis results showed a significant correlation (κ = 0.933) between these two methods on a per-segment basis analysis.

CONCLUSION

In the light of histopathological findings and post-PEA surgical specimen examinations, the results of the present study indicated that both V/Q SPECT/CT and V/Q Quotient SPECT showed relatively high efficacy for the detection of CTEPH on per-patient and per-segment bases with an excellent agreement.

Abnormal Pulmonary Venous Filling: An Adjunct Feature in the Computed Tomography Pulmonary Angiogram Assessment of Chronic Thromboembolic Pulmonary Hypertension

Background

Hypodense filling defects within the pulmonary veins on computed tomography described as pulmonary vein sign (PVS) have been noted in acute pulmonary embolism and shown to be associated with poor prognosis. We evaluated venous flow abnormalities in chronic thromboembolic pulmonary hypertension (CTEPH) to determine its usefulness in the computed tomography assessment of CTEPH.

Methods and Results

Blinded retrospective computed tomography analysis of 50 proximal CTEPH cases and 3 control groups—50 acute pulmonary embolism, 50 nonthromboembolic cohort, and 50 pulmonary arterial hypertension. Venous flow reduction was assessed by the following: (1) presence of a filling defect of at least 2 cm in a pulmonary vein draining into the left atrium, and (2) left atrium attenuation (>160 Hounsfield units). PVS was most prevalent in CTEPH. Compared with all controls, sensitivity and specificity of PVS for CTEPH is 78.0% and 85.3% (95% CI, 64.0–88.5 and 78.6–90.6, respectively) versus 34.0% and 70.7% (95% CI, 21.2−48.8 and 62.7–77.8) in acute pulmonary embolism, 8.0% and 62% (95% CI, 2.2–19.2 and 53.7–69.8) in nonthromboembolic and 2.0% and 60% (95% CI, 0.1−10.7 and 51.7−67.9) in pulmonary arterial hypertension. In CTEPH, lobar and segmental arterial occlusive disease was most commonly associated with corresponding absent venous flow. PVS detection was highly reproducible (Kappa=0.96, 95% CI, 0.90–1.01, P<0.001).

Conclusions

PVS is easy to detect with higher sensitivity and specificity in CTEPH compared with acute pulmonary embolism and is not a feature of pulmonary arterial hypertension. Asymmetric enhancement of pulmonary veins may serve as an additional parameter in the computed tomography assessment of CTEPH and can be used to differentiate CTEPH from pulmonary arterial hypertension.

Comparison of V/Q SPECT and CT Angiography for the Diagnosis of Chronic Thromboembolic Pulmonary Hypertension

Background Accurate methods for identifying obstructions in both large and small vessels are crucial for diagnosis and treatment of chronic thromboembolic pulmonary hypertension (CTEPH). Purpose To compare the performance of ventilation-perfusion (V/Q) scanning, V/Q SPECT, and CT pulmonary angiography (PA) in CTEPH by using digital subtraction PA as the reference standard. Materials and Methods This prospective study was conducted from January 2016 to January 2018. A total of 229 participants suspected of having CTEPH were evaluated with V/Q SPECT, V/Q planar scintigraphy, CT PA, and digital subtraction PA. Participants underwent all four procedures within 1 week. Differences in the diagnostic performance of V/Q SPECT, V/Q planar scintigraphy, and CT PA were evaluated with areas under the curve receiver operator curve, the McNemar test, and generalized estimating equations analysis. Results A total of 150 participants (mean age, 42 years ± 15 [standard deviation]; 99 women) were enrolled. Digital subtraction PA assessments confirmed CTEPH in 51 participants and indicated that 602 of 1020 lung segments (20 segments per participant) were obstructed. The three imaging methods showed high sensitivity (V/Q SPECT, 98%; V/Q planar scintigraphy, 98%; CT PA, 94%) and specificity (V/Q SPECT, 89%; V/Q planar scintigraphy, 91%; CT PA, 96%) (all P > .05). However, both V/Q scanning techniques were more sensitive (V/Q SPECT: 85%, P < .001 vs CT PA: 67%; V/Q planar scintigraphy: 83%, P < .001 vs CT PA: 67%), and less specific (V/Q planar scintigraphy: 51%, P = .03 vs CT PA: 60%; V/Q SPECT: 42%, P < .01 vs CT PA: 60%) than was CT PA for segmental analysis. Areas under the curve for CT PA, V/Q planar scintigraphy, and V/Q SPECT were 0.95, 0.95, and 0.94, respectively (all P > .05), for individual analysis, and 0.64, 0.67, and 0.64, respectively, by segment (V/Q planar scintigraphy vs V/Q SPECT, P = .02; V/Q planar scintigraphy vs CT PA, P = .08; V/Q SPECT vs CT PA, P = .94). Conclusion Ventilation-perfusion scanning was more sensitive and less specific than was CT pulmonary angiography for detecting vascular obstructions at the segmental pulmonary arterial level. © RSNA, 2020 See also the editorial by Swift and Rajaram in this issue.

Perfusion Scintigraphy in Diagnosis and Management of Thromboembolic Pulmonary Hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is a life-threatening complication of acute pulmonary embolism (PE). Because the treatment of CTEPH is markedly different from that of other types of pulmonary hypertension, lung ventilation-perfusion (V/Q) scintigraphy is recommended for the workup of patients with unexplained pulmonary hypertension. Lung V/Q scintigraphy is superior to CT pulmonary angiography for detecting CTEPH. Perfusion defect findings of CTEPH can be different from those of acute PE. Familiarity with the patterns of perfusion defects seen during the initial workup of CTEPH and the expected posttreatment changes seen at follow-up imaging is essential for accurate interpretation of V/Q scintigraphy findings. ^©RSNA, 2019.

Dyspnea Postpulmonary Embolism From Physiological Dead Space Proportion and Stroke Volume Defects During Exercise

BACKGROUND

Many patients with pulmonary embolism (PE) report dyspnea on exertion following long-term treatment. Increased physiological dead space proportion (V_D/V_T) and decreased cardiac stroke volume reserve may distinguish persistent effects of PE itself from symptoms reflecting comorbid conditions or deconditioning.

METHODS

This retrospective study analyzed a consecutive series of incremental symptom-limited cardiopulmonary exercise tests that had been ordered to evaluate persistent dyspnea on exertion following long-term treatment for acute PE. Physiological V_D/V_T was determined at anaerobic threshold from exhaled CO₂ and transcutaneous Pco₂ (validated against Paco₂ measurements). Cardiac stroke volume reserve was estimated at rest and at anaerobic threshold by using oxygen consumption/pulse and previously validated estimates of the arteriovenous oxygen content difference.

RESULTS

Cardiopulmonary exercise tests were performed on 40 patients with post-PE dyspnea. In 65.0% (95% CI, 50.2-79.8), V_D/V_T at anaerobic threshold was abnormally elevated, stroke volume reserve was decreased, or both defects occurred. V_D/V_T at anaerobic threshold was abnormally elevated (≥ 0.27) in 35.0% (95% CI, 20.2-49.8). V_D/V_T at anaerobic threshold significantly correlated with the extent of unmatched perfusion defects on subsequent ventilation-perfusion scans (P = .0085). In 55.0% (95% CI, 39.6-70.4), stroke volume reserve at anaerobic threshold was abnormally decreased (≤ 128% of the resting value). Both defects were present in 25.0% (95% CI, 11.6-38.4).

CONCLUSIONS

Increased V_D/V_T at anaerobic threshold and decreased stroke volume reserve during exercise are common among patients with dyspnea on exertion after long-term treatment of PE. The defects can be disclosed noninvasively by using cardiopulmonary exercise testing.

EANM guideline for ventilation/perfusion single-photon emission computed tomography (SPECT) for diagnosis of pulmonary embolism and beyond

These guidelines update the previous EANM 2009 guidelines on the diagnosis of pulmonary embolism (PE). Relevant new aspects are related to (a) quantification of PE and other ventilation/perfusion defects; (b) follow-up of patients with PE; (c) chronic PE; and (d) description of additional pulmonary physiological changes leading to diagnoses of left ventricular heart failure (HF), chronic obstructive pulmonary disease (COPD) and pneumonia. The diagnosis of PE should be reported when a mismatch of one segment or two subsegments is found. For ventilation, Technegas or krypton gas is preferred over diethylene triamine pentaacetic acid (DTPA) in patients with COPD. Tomographic imaging with V/PSPECT has higher sensitivity and specificity for PE compared with planar imaging. Absence of contraindications makes V/PSPECT an essential method for the diagnosis of PE. When V/PSPECT is combined with a low-dose CT, the specificity of the test can be further improved, especially in patients with other lung diseases. Pitfalls in V/PSPECT interpretation are discussed. In conclusion, V/PSPECT is strongly recommended as it accurately establishes the diagnosis of PE even in the presence of diseases like COPD, HF and pneumonia and has no contraindications.

Ten-year-old children with a history of bronchopulmonary dysplasia have regional abnormalities in ventilation perfusion matching

AIM

The ratio of ventilation to blood flow is an important determinant for regional gas exchange in the lung and hypoxemia is one of the clinical hallmarks in infants with bronchopulmonary dysplasia (BPD). We have previously demonstrated ventilation/perfusion ratio (V/Q) abnormalities in infants with BPD at 36 weekś postconceptional age. The status of V/Q matching in older children with a history of BPD in infancy is unknown. In this study, we examined if 10-year-old children with a history of BPD had V/Q impairments.

METHODS

Three-dimensional V/Q-scintigraphy (SPECT) was performed in 26 children.

RESULTS

In the BPD group, lung volume with mismatch, (V>Q) was larger compared to areas with reverse mismatch (Q>V), 26.2% and 11.8%, respectively, implying that perfusion defects contribute more than ventilation defects in the V/Q mismatch. Also, the mean fractional distribution of V and Q to V/Q in children with BPD was reduced compared to healthy children, 31% and 51% compared to 64% and 89%, respectively (P < 0.01).

CONCLUSION

At 10 years of age children with a history of BPD had ventilation/perfusion abnormalities, with prominent perfusion defects. These V/Q abnormalities suggest the presence of residual alveolar-capillary impairment.

Quantitation of Perfused Lung Volume Using Hybrid SPECT/CT Allows Refining the Assessment of Lung Perfusion and Estimating Disease Extent in Chronic Thromboembolic Pulmonary Hypertension

BACKGROUND

We evaluated the feasibility of perfusion SPECT/CT for providing quantitative data for estimation of perfusion defect extent in chronic thromboembolic pulmonary hypertension (CTEPH).

METHODS

Thirty patients with CTEPH underwent Tc-human serum albumin lung perfusion SPECT/CT. Perfusion defects were quantified using 3 different methods: (1) visual, semiquantitative scoring of perfusion defect extent in each lung segment, (2) threshold-based segmentation of perfused lung volumes, and (3) threshold-based segmentation of perfused lung volumes divided by segmented lung volumes at CT (perfusion index). Imaging findings were correlated with right-sided heart catheterization results and N-terminal pro-B-type natriuretic peptide. Receiver operating characteristic analysis was performed to identify SPECT thresholds for mean pulmonary arterial pressure (PAPm) greater than 50 mm Hg.

RESULTS

Assessment of lung perfusion provided similar results using all 3 methods. The perfusion defect score correlated with PAPm (rs = 0.60, P = 0.0005) and was associated with serum levels of N-terminal pro-B-type natriuretic peptide (rs = 0.37, P = 0.04). Perfused lung volume (40% threshold, rs = -0.48, P = 0.007) and perfusion index (40% threshold, rs = -0.50, P = 0.005) decreased as PAPm increased. Receiver operating characteristic analysis showed that perfusion defect score (sensitivity, 88%; specificity, 77%; area under the curve [AUC] = 0.89, P = 0.001), perfused lung volume (sensitivity, 88%; specificity, 64%; AUC = 0.80, P = 0.01), and perfusion index (sensitivity, 88%; specificity, 64%; AUC = 0.82, P = 0.009) could identify patients with PAPm of greater than 50 mm Hg.

CONCLUSIONS

Quantitative analysis of perfusion defects at SPECT is feasible, provides a measure of disease severity, and correlates with established clinical parameters. Quantitation of perfusion SPECT may refine the diagnostic approach in CTEPH providing a quantitative imaging biomarker, for example, for therapy monitoring.

Chronic thromboembolic pulmonary hypertension (CTEPH): Updated Recommendations from the Cologne Consensus Conference 2018

Chronic thromboembolic pulmonary hypertension (CTEPH) is a subgroup of pulmonary hypertension that differs from all other forms of PH in terms of its pathophysiology, patient characteristics and treatment. For implementation of the European Guidelines on Diagnosis and Treatment of Pulmonary Hypertension in Germany, the Cologne Consensus Conference 2016 was held and last updated in spring of 2018. One of the working groups was dedicated to CTEPH, practical and controversial issues were commented and updated. In every patient with suspected PH, CTEPH or chronic thromboembolic disease (CTED, i.e. symptomatic residual vasculopathy without pulmonary hypertension) should be excluded. Primary treatment is surgical pulmonary endarterectomy (PEA) in a multidisciplinary CTEPH centre. Inoperable patients or patients with persistent or recurrent CTEPH after PEA are candidates for targeted drug therapy. There is increasing experience with balloon pulmonary angioplasty (BPA) for inoperable patients; this option, like PEA, is reserved for specialised centres with expertise in this treatment method.

Chronic pulmonary embolism: diagnosis

Chronic thromboembolic pulmonary hypertension (CTEPH) is a complication of venous thromboembolic disease. Differently from other causes of pulmonary hypertension, CTEPH is potentially curable with surgery (thromboendarterectomy) or balloon pulmonary angioplasty. Imaging plays a central role in CTEPH diagnosis. The combination of techniques such as lung scintigraphy, computed tomography and magnetic resonance angiography provides non-invasive anatomic and functional information. Conventional pulmonary angiography (CPA) with right heart catheterization (RHC) is considered the gold standard method for diagnosing CTEPH. In this review, we discuss the utility of these imaging techniques in the diagnosis of CTEPH.

Computed Tomography Angiographic Assessment of Acute Chest Pain

Acute chest pain is a leading cause of Emergency Department visits. Computed tomography angiography plays a vital diagnostic role in such cases, but there are several common challenges associated with the imaging of acute chest pain, which, if unrecognized, can lead to an inconclusive or incorrect diagnosis. These imaging challenges fall broadly into 3 categories: (1) image acquisition, (2) image interpretation (including physiological and pathologic mimics), and (3) result communication. The aims of this review are to describe and illustrate the most common challenges in the imaging of acute chest pain and to provide solutions that will facilitate accurate diagnosis of the causes of acute chest pain in the emergency setting.

Contrast-enhanced CT- and MRI-based perfusion assessment for pulmonary diseases: basics and clinical applications

Assessment of regional pulmonary perfusion as well as nodule and tumor perfusions in various pulmonary diseases are currently performed by means of nuclear medicine studies requiring radioactive macroaggregates, dual-energy computed tomography (CT), and dynamic first-pass contrast-enhanced perfusion CT techniques and unenhanced and dynamic first-pass contrast enhanced perfusion magnetic resonance imaging (MRI), as well as time-resolved three-dimensional or four-dimensional contrast-enhanced magnetic resonance angiography (MRA). Perfusion scintigraphy, single-photon emission tomography (SPECT) and SPECT fused with CT have been established as clinically available scintigraphic methods; however, they are limited by perfusion information with poor spatial resolution and other shortcomings. Although positron emission tomography with 15O water can measure absolute pulmonary perfusion, it requires a cyclotron for generation of a tracer with an extremely short half-life (2 min), and can only be performed for academic purposes. Therefore, clinicians are concentrating their efforts on the application of CT-based and MRI-based quantitative and qualitative perfusion assessment to various pulmonary diseases. This review article covers 1) the basics of dual-energy CT and dynamic first-pass contrast-enhanced perfusion CT techniques, 2) the basics of time-resolved contrast-enhanced MRA and dynamic first-pass contrast-enhanced perfusion MRI, and 3) clinical applications of contrast-enhanced CT- and MRI-based perfusion assessment for patients with pulmonary nodule, lung cancer, and pulmonary vascular diseases. We believe that these new techniques can be useful in routine clinical practice for not only thoracic oncology patients, but also patients with different pulmonary vascular diseases.

Cardiac MR and CT imaging in children with suspected or confirmed pulmonary hypertension/pulmonary hypertensive vascular disease. Expert consensus statement on the diagnosis and treatment of paediatric pulmonary hypertension. The European Paediatric Pulmonary Vascular Disease Network, endorsed by ISHLT and DGPK

Childhood pulmonary hypertension (PH) is a heterogenous disease associated with considerable morbidity and mortality. Invasive assessment of haemodynamics is crucial for accurate diagnosis and guidance of medical therapy. However, adequate imaging is increasingly important in children with PH to evaluate the right heart and the pulmonary vasculature. Cardiac MR (CMR) and computed tomography (CT) represent important non-invasive imaging modalities that may enable comprehensive assessment of right ventricular (RV) function and pulmonary haemodynamics. Here, we present graded consensus recommendations for the evaluation of children with PH by CMR and CT. The article provides a structured approach for the use of CMR and CT imaging, emphasises non-invasive variables of RV function, myocardial tissue and afterload parameters that may be useful for initial diagnosis and monitoring. Furthermore, assessment of pulmonary perfusion and characterisation of the lung parenchyma provides structural information about processes that may cause or be due to PH.

Pulmonary ventilation/perfusion single photon emission tomography--Initial experience of a Nuclear Medicine Department

INTRODUCTION

Lung ventilation/perfusion scintigraphy with planar images (V/QS-planar) is very useful for the diagnosis and follow-up of pulmonary thromboembolism (PTE). Acquiring tomographic images (V/QS-SPECT) is a recent development with potential to increase the technique's accuracy. The purpose of this work is to evaluate the added benefits of V/QS-SPECT studies as opposed to traditional planar imaging.

PATIENTS AND METHODS

We prospectively revised 53 V/QS-planar and V/QS-SPECT exams, performed according to the European Association of Nuclear Medicine guidelines. We evaluated the exams independently, by consensus of two Nuclear Medicine physicians. For both methods, we gave each lung a score expressing the dimension and extension of perfusion defects with normal ventilation. For each lung, we compared the scores with the paired Wilcoxon test, estimating the 95% confidence interval (95 CI) for the respective difference.

RESULTS

We performed V/QS-SPECT exams without technical difficulties. The paired Wilcoxon test estimated the score difference to be -0.75 (95 CI of -1.0 to -0.5; p-value=9.6 × 10(-7)), expressing a statistically significant difference of about 1 subsegmental defect between both methods, with V/QS-SPECT detecting more defects.

DISCUSSION

The results demonstrate that V/QS-SPECT identifies a slightly larger number of perfusion defects than V/QS-planar, suggesting a higher sensitivity of this technique. However, more studies are necessary to evaluate the clinical meaning of this fact.

CONCLUSION

V/QS-SPECT demonstrates a higher capability to identify perfusion defects. This method looks promising, allowing for a greater role of this exam in pulmonary thromboembolism diagnosis and follow-up.

Subsegmental pulmonary embolism: A narrative review

Through the introduction of computed tomography pulmonary angiography (CTPA) for diagnosis of the pulmonary embolism (PE), the high sensitivity of this diagnostic tool led to detecting peripheral filling defects as small as 2-3mm, termed as subsegmental pulmonary embolism (SSPE). However, despite these substantial increases in diagnosis of small pulmonary embolism, there are minimal changes in mortality. Moreover, SSPE patients generally are hemodynamically stable with mild clinical presentation, lower serum level of biomarkers, lower incidence of associated proximal DVTs and less frequent echocardiographic changes compared to the patients with emboli located in more central pulmonary arteries. However, the pros and cons of anticoagulant therapy versus non-treating, monitoring protocol and exact long term outcome of these patients are still unclear. In this article we review existing evidence and provide an overview of what is known about the diagnosis and management of subsegmental pulmonary embolism.

Dual-energy CT for imaging of pulmonary hypertension: challenges and opportunities

Computed tomography (CT) is routinely used in the evaluation of patients with pulmonary hypertension (PH) to assess vascular anatomy and parenchymal morphology. The introduction of dual-energy CT (DECT) enables additional qualitative and quantitative insights into pulmonary hemodynamics and the extent and variability of parenchymal enhancement. Lung perfusion assessed at pulmonary blood volume imaging correlates well with findings at scintigraphy, and pulmonary blood volume defects seen in pulmonary embolism studies infer occlusive disease with increased risk of right heart dysfunction. Similarly, perfusion inhomogeneities seen in patients with PH closely reflect mosaic lung changes and may be useful for severity assessment and prognostication. The use of DECT may increase detection of peripheral thromboembolic disease, which is of particular prognostic importance in patients with chronic thromboembolic PH with microvascular involvement. Other DECT applications for imaging of PH include low-kilovoltage images with greater inherent iodine conspicuity and iodine-selective color-coded maps of vascular perfusion (both of which can improve visualization of vascular enhancement), virtual nonenhanced imaging (which better depicts vascular calcification), and, potentially, ventricular perfusion maps (to assess myocardial ischemia). In addition, quantitative assessment of central vascular and parenchymal enhancement can be used to evaluate pulmonary hemodynamics in patients with PH. The current status and potential advantages and limitations of DECT for imaging of PH are reviewed, and current evidence is supplemented with data from a tertiary referral center for PH.

The accuracy of V/Q SPECT in the diagnosis of pulmonary embolism: a meta-analysis

BACKGROUND

Ventilation perfusion single photon emission computed tomography (V/Q SPECT) and CT pulmonary angiography have all been used in the diagnosis of acute PE. Previous studies have shown higher sensitivity and specificity and a marked decrease in the non-diagnostic rate of V/Q SPECT than planar scan.

PURPOSE

To systematically review and perform a meta-analysis of published data on the performance of V/Q SPECT in the diagnosis of acute PE.

MATERIAL AND METHODS

A comprehensive computer search was conducted on literature published through 31 December 2013 in an effort to find relevant articles on the diagnostic performance of V/Q SPECT in the diagnosis of PE patients. Pooled sensitivity, specificity, negative likelihood ratio (LR), and positive LR, the area under the receiver-operating characteristic (ROC) curve of V/Q SPECT in the diagnosis of PE patients were calculated.

RESULTS

Nine studies, comprising a total sample size of 3454 patients, were included in our meta-analysis. The pooled sensitivity, specificity of V/Q SPECT in the diagnosis of acute PE patients, calculated on a per-patient-based analysis, was 96% (95% confidence interval [CI], 95-97%), 97% (95% CI, 96-98%). The pooled negative LR, positive LR of V/Q SPECT in acute PE patients was 0.06 (range, 0.02-0.19) and 16.64 (range, 9.78-31.54). The area under the ROC curve of V/Q SPECT in the diagnosis of acute PE patients was 0.99 on a per-patient-based analysis.

CONCLUSION

V/Q SPECT is an accurate method in acute PE patients with high sensitivity and high specificity in the diagnosis of PE.

Chronic thromboembolic pulmonary hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is a disease with high mortality and few treatment options. This article reviews the epidemiology of CTEPH and identifies risk factors for its development. The pathobiology and the progression from thromboembolic events to chronically increased right-sided pressures are discussed. The diagnosis and assessment of CTEPH requires several modalities and the role of these is detailed. The pre-operative evaluation assesses peri-operative risk and determines the likelihood of benefit from PTE. Pulmonary thromboendarterectomy (PTE) remains the treatment of choice in appropriate patients. Nonsurgical therapies for CTEPH may provide benefit in patients who cannot be offered surgery.

Recent progress in the diagnosis and management of chronic thromboembolic pulmonary hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is a form of pulmonary hypertension caused by non-resolving thromboembolisms of the pulmonary arteries. In Japan, in contrast to Western countries, CTEPH is more prevalent in women. A Japanese multicenter study reported that a form of CTEPH unrelated to deep vein thrombosis is associated with HLA-B⁎5201, suggesting that this form of CTEPH may be associated with vasculopathy. CTEPH can be cured by pulmonary endarterectomy, provided that the thrombi are surgically accessible; thus, early diagnosis is important, and all patients with exertional dyspnea should be evaluated for pulmonary hypertension. Ventilation/perfusion scans provide an excellent non-invasive means to distinguish CTEPH from pulmonary arterial hypertension. Similarly, computed tomographic pulmonary angiograms allow for the detection of thrombi and evaluation of pulmonary hemodynamics in a minimally invasive manner. Importantly, the absence of subpleural perfusion on pulmonary angiograms can suggest the presence of small vessel disease. Small vessel disease might be involved in the pathogenesis of CTEPH, and its detection is essential in preventing operative death. Although no modern therapies for pulmonary arterial hypertension have been approved for treatment of CTEPH, a recent randomized control trial of riociguat in patients with CTEPH demonstrated that riociguat significantly improved 6-min walking distance. Further investigations into treatments that target endothelial dysfunction and hyperproliferative CTEPH cells are needed. Recently, balloon pulmonary angioplasty has emerged as a promising treatment modality in Japan. A specialized medical team, including at least one expert surgeon, should make decisions regarding patients' candidacy for pulmonary endarterectomy and/or balloon pulmonary angioplasty.

Evaluation of patients with chronic thromboembolic pulmonary hypertension for pulmonary endarterectomy

Pulmonary hypertension as a result of chronic thromboembolic disease (CTEPH) is potentially curable with pulmonary endarterectomy surgery. Consequently, correctly diagnosing patients with this type of pulmonary hypertension and evaluating these patients with the goal of establishing their candidacy for surgical intervention is of utmost importance. And as advancements in surgical techniques have allowed successful resection of segmental-level chronic thromboembolic disease, the number of CTEPH patients that are deemed suitable surgical candidates has expanded, making it even more important that the evaluation be conducted with greater precision. This article will review a diagnostic approach to patients with suspected chronic thromboembolic disease with an emphasis on the criteria considered in selecting patients for pulmonary endarterectomy surgery.