EANM guidelines for ventilation/perfusion scintigraphy

Value of lung perfusion scintigraphy in patients with idiopathic pulmonary arterial hypertension: a patchy pattern to consider

The ventilation/perfusion lung scan is recommended to exclude chronic thromboembolic pulmonary hypertension in the diagnostic algorithm of pulmonary hypertension, but its role in pulmonary arterial hypertension (PAH) has not been well explored. We characterized the lung perfusion pattern assessed by lung perfusion scintigraphy in idiopathic PAH (IPAH) patients and evaluate the potential prognostic significance of the patchy pattern perfusion defect. A total of 318 patients with IPAH confirmed by right heart catheterization who performed lung perfusion scintigraphy were included. On lung perfusion scintigraphy, 134 patients had normal lung perfusion and 184 patients showed patchy perfusion defects. In comparison to patients with normal lung perfusion, patients with patchy perfusion defects experienced significantly higher mean pulmonary arterial pressure (58.0 ± 15.4 mmHg vs. 54.1 ± 16.2 mmHg, P = 0.027) and total pulmonary resistance (1192.6 ± 533.7 dyn·s·cm⁻⁵ vs. 1067.2 ± 549.3 dyn·s·cm⁻⁵, P = 0.042). During a median follow-up period of 884.0 days, 53 patients reached the primary endpoint of all-cause mortality. On univariate Cox analysis, the patchy pattern of perfusion defect was significantly associated with the all-cause mortality (hazard ratio [HR] = 2.47, 95% confidence interval [CI] = 1.32–4.63, P = 0.005). Patients with patchy perfusion defects had a worse outcome (log-rank = 8.605, P = 0.003). On multivariate analysis, the patchy pattern remained as a significant independent predictor of the endpoint (HR = 2.30, 95% CI = 1.22–4.31, P = 0.010). IPAH patients presented with heterogeneity in lung perfusion and the patchy pattern of lung perfusion defect commonly existed. Patients with patchy pattern identified by lung perfusion scintigraphy were associated with more severe disease and worse outcome.

The conclusions drawn from ventilation/perfusion single-photon emission computed tomography compared with lung perfusion single-photon emission computed tomography and chest radiography in patients with suspected pulmonary thromboembolism

PURPOSE

There are conflicting results from studies on whether ventilation scintigraphy can be safely omitted or replaced by chest radiography. These studies were based on planar ventilation/perfusion (V/Q) scintigraphy. We evaluated the value of the ventilation single-photon emission computed tomography (SPECT) on the final conclusion drawn from a V/Q SPECT and the possible role of the chest radiography as a surrogate for the ventilation SPECT.

PATIENTS AND METHODS

Raw data of V/Q SPECT images and chest radiography acquired within 48 h over an 18-month period were retrieved, reprocessed and reviewed in batches. The ventilation SPECT, perfusion SPECT and chest radiography were reviewed separately and in combination. Data on the presence and nature of defects and chest radiography abnormalities were recorded. The V/Q SPECT images were interpreted using the criteria in the EANM guideline and the perfusion SPECT and chest radiography images were interpreted using the PISAPED criteria. Agreement between the diagnosis on the V/Q SPECT review and the perfusion SPECT and chest radiography review was analysed.

RESULTS

Overall, 21.1% of the patients were classified as 'PE present' on the V/Q SPECT review, whereas 48.9% were classified as 'PE present' on the perfusion SPECT and chest radiography review. Only 5.4% of defects observed on ventilation SPECT had matched chest radiography lung field opacity.

CONCLUSION

Our study showed that the omission of a ventilation SPECT led to a high rate of false-positive diagnoses and that the ventilation scan cannot be replaced by a chest radiography.

Ventilation perfusion single photon emission computed tomography: Referral practices and diagnosis of acute pulmonary embolism in the quaternary clinical setting

INTRODUCTION

Ventilation perfusion single photon emission computed tomography (V/Q SPECT) and CTPA are the two leading imaging studies used to investigate acute pulmonary embolism. V/Q SPECT is often the first line investigation for pregnant patients and young females. Historically, V/Q Planar studies have high rates of indeterminate findings resulting in a preference for CTPA studies. The purpose of this research is to examine current V/Q SPECT referral practices in the quaternary clinical setting and to confirm V/Q SPECT studies have low rates of equivocal findings.

METHODS

Retrospective study of a 6-month period of all completed V/Q SPECT studies (± LDCT) indicated for investigation of acute PE. V/Q SPECT studies were reported using the European Association of Nuclear Medicine guidelines. Patient demographic data and V/Q SPECT findings were recorded. CTPA and Doppler Ultrasound report findings were included if performed 48 hours prior to, or following V/Q SPECT study. Standard descriptive statistical analysis was undertaken.

RESULTS

Ninety-nine percent of V/Q SPECT studies had reports positive or negative for acute PE, with 1% inconclusive. Twenty-two percent of patients had either CTPA or Doppler Ultrasound studies within a 48- hour period prior to, or following V/Q SPECT, with the majority having a negative Doppler ultrasound prior to negative V/Q SPECT. Sixty-eight percent of patients referred for V/Q SPECT were females under the age of 55, 40% of whom were pregnant.

CONCLUSIONS

Ventilation perfusion single photon emission computed tomography has low rates of equivocal findings with referral practices indicating pregnant patients and young women are considered to most benefit from V/Q SPECT as a first line investigation for acute PE.

A prospective study comparing 99mTc-MIBI and 99mTc-MDP with 99mTc-DTPA for lung ventilation scintigraphy in pulmonary thromboembolism

OBJECTIVE

The aim of the study was to assess the efficacy of technetium 99m-methyl diphosphonate (Tc-MDP) and technetium 99m-methoxyisobutylisonitrile (Tc-MIBI) as radioaerosol alternatives to technetium 99m-diethylenetriaminepentacetate (Tc-DTPA) in the evaluation of pulmonary thromboembolism, as the direct consequence of the possible outcome could be cost saving.

PATIENTS AND METHODS

Patients referred to our institution from August 2015 to July 2017 for a ventilation-perfusion scan who fulfilled the inclusion criteria were enrolled into the study as participants. Each ventilation agent was used to ventilate 43 participants, making a total of 129 participants in the study. Images were assessed for quality and alveolar clearance qualitatively and semiquantitatively correspondingly by a nuclear medicine physician blinded to the agent used.

RESULTS

Tc-MIBI had higher count rates than Tc-DTPA and Tc-MDP, with a statistically significant difference when compared with Tc-DTPA (P=0.021). Tc-MIBI clearly showed slower alveolar clearance when compared with the clearance of Tc-DTPA (P≤0.0001) and Tc-MDP (P≤0.001). In terms of image quality, Tc-MIBI generally had better quality images as compared with the other two radioaerosols, with a statistically significant difference when compared with Tc-DTPA (P=0.001).

CONCLUSION

Tc-MIBI had superior image quality and slower alveolar clearance when compared with Tc-DTPA. Alongside Tc-MDP, these agents can replace Tc-DTPA whenever clinically and economically applicable.

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.

Diagnosing and grading heart failure with tomographic perfusion lung scintigraphy: validation with right heart catheterization

Aims

Pulmonary congestion remains a diagnostic challenge in patients with heart failure (HF). The recommended method, chest X‐ray (CXR), lacks in accuracy, whereas quantitative tomographic lung scintigraphy [ventilation/perfusion single‐photon emission computed tomography (V/P SPECT)] has shown promising results but needs independent validation. The aim of this study is to evaluate V/P SPECT as a non‐invasive method to assess and quantify pulmonary congestion in HF patients, using right heart catheterization as reference method. The secondary objective was to investigate the performance of V/P SPECT in the clinical setting compared with CXR.

Methods and results

Forty‐six consecutive patients with HF that were under consideration for heart transplantation were studied prospectively. All participants were examined with V/P SPECT, CXR, and right heart catheterization. Pulmonary artery wedge pressure served as reference method. Quantitative perfusion gradients were derived from V/P SPECT images. Ventilation/perfusion single‐photon emission computed tomography images were also assessed both by expert readers and clinical nuclear medicine physicians. Expert readers correctly identified 87% of all patients with an elevated pulmonary artery wedge pressure > 15 mmHg. The average sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for V/P SPECT assessed by the expert readers were 87%, 72%, 85%, and 75%, respectively. In the clinical nuclear medicine setting, V/P SPECT had 87% sensitivity, 63% specificity, 81% PPV, and 71% NPV. Clinically, V/P SPECT outperformed CXR, which had 27% sensitivity, 75% specificity, 67% PPV, and 35% NPV.

Conclusions

Ventilation/perfusion single‐photon emission computed tomography can be used as a non‐invasive method to diagnose and quantify pulmonary congestion in patients with HF and is more accurate than CXR in diagnosing pulmonary congestion in the clinical setting.

Dual-energy CT (DECT) lung perfusion in pulmonary hypertension: concordance rate with V/Q scintigraphy in diagnosing chronic thromboembolic pulmonary hypertension (CTEPH)

OBJECTIVES

To evaluate the concordance between DECT perfusion and ventilation/perfusion (V/Q) scintigraphy in diagnosing chronic thromboembolic pulmonary hypertension (CTEPH).

METHODS

Eighty patients underwent V/Q scintigraphy and DECT perfusion on a 2nd- and 3rd-generation dual-source CT system. The imaging criteria for diagnosing CTEPH relied on at least one segmental triangular perfusion defect on DECT perfusion studies and V/Q mismatch on scintigraphy examinations.

RESULTS

Based on multidisciplinary expert decisions that did not include DECT perfusion, 36 patients were diagnosed with CTEPH and 44 patients with other aetiologies of PH. On DECT perfusion studies, there were 35 true positives, 6 false positives and 1 false negative (sensitivity 0.97, specificity 0.86, PPV 0.85, NPV 0.97). On V/Q scans, there were 35 true positives and 1 false negative (sensitivity 0.97, specificity 1, PPV 1, NPV 0.98). There was excellent agreement between CT perfusion and scintigraphy in diagnosing CTEPH (kappa value 0.80). Combined information from DECT perfusion and CT angiographic images enabled correct reclassification of the 6 false positives and the unique false negative case of DECT perfusion.

CONCLUSION

There is excellent agreement between DECT perfusion and V/Q scintigraphy in diagnosing CTEPH. The diagnostic accuracy of DECT perfusion is reinforced by the morpho-functional analysis of data sets.

KEY POINTS

• Chronic thromboembolic pulmonary hypertension (CTEPH) is potentially curable by surgery. • The triage of patients with pulmonary hypertension currently relies on scintigraphy. • Dual-energy CT (DECT) can provide standard diagnostic information and lung perfusion from a single acquisition. • There is excellent agreement between DECT perfusion and scintigraphy in separating CTEPH and non-CTEPH patients.

SPECT V/Q for the diagnosis of pulmonary embolism: protocol for a systematic review and meta-analysis of diagnostic accuracy and clinical outcome

INTRODUCTION

Single photon emission computed tomography ventilation/perfusion (SPECT V/Q) imaging has many proponents within the nuclear medicine community and has already largely replaced planar V/Q scintigraphy in daily practice for the diagnosis of pulmonary embolism (PE). However, the test is still described in clinical guidelines as an experimental test because of insufficient evidence.

METHODS AND ANALYSIS

We will conduct a systematic review and a meta-analysis of diagnostic accuracy and management outcome studies involving patients evaluated with V/Q SPECT for suspected acute PE. We will search from inception to 19 December 2017 MEDLINE, Embase and the Cochrane Central Register of Controlled Trials for diagnostic accuracy studies, randomised controlled trials and observational cohort studies. Two reviewers will conduct all screening and data collection independently. The methodological quality and risk of bias of eligible studies will be carefully and rigorously assessed using the Quality Assessment of Diagnostic Accuracy Studies-2, the Cochrane Collaboration's tool and the Risk Of Bias In Non-randomised Studies - of Interventions (ROBINS-I) tools. The primary outcomes will be sensitivity, specificity and likelihood ratios of V/Q SPECT for the diagnosis of acute PE. The secondary outcomes will be the rate of venous thromboembolism during a 3-month follow-up period in patients left untreated after a negative diagnostic work-up based on SPECT V/Q.

ETHICS AND DISSEMINATION

This study of secondary data does not require ethics approval. It will be presented internationally and published in the peer-reviewed literature.

PROSPERO REGISTRATION NUMBER

CRD42018084095.

Pre-operative quantification of pulmonary function using hybrid-SPECT/low-dose-CT: A pilot study

RATIONALE

Pre-operative lobar function is estimated by scintigraphy in patients with pulmonary malignancies and compromised function. This study compared the lobar perfusion determined by scintigraphy (PS) with data from SPECT/low-dose-CT (SPECT/ldCT) analyzed manually and semi-automatic.

METHODS

Retrospective analysis on 39 patients (m/f = 25/14; age: 72.5 [22-89] years) with indication for pulmonary perfusion scintigraphy. Imaging was performed using SPECT/ldCT. Data was analyzed manually and by semi-automatic software. Readers' confidence in 3D-segmentation was scored by two independent readers. Interrater agreement was calculated. In addition, Spearman's rank correlation and Wilcoxon's test were used.

RESULTS

Results from PS differed significantly from SPECT/ldCT processed manually or semi-automatically in 4/5 lobes (total difference ≤21.6%; rho ≥0.44) and in 3/5 (total difference 21.6%; rho ≥0.37), respectively. Readers' confidence in 3D-segmentation showed a perfect interrater agreement (κ = 0.98).

CONCLUSION

Quantification of lobar perfusion by SPECT/ldCT differs significantly from planar scintigraphy (e.g., with potential influence on therapy). The semi-automatic software analysis provides an applicable methodology.

Ventilation/perfusion single-photon emission computed tomography: a service evaluation

OBJECTIVES

To identify the positive rate and negative predictive value (NPV) of our ventilation/perfusion (V/Q) single-photon emission computed tomography (SPECT) service as respective markers of overcalling (false positives) and undercalling (false negatives). We also identified the indeterminate rate as an indicator of the technical quality of the scans and reporter confidence.

PATIENTS AND METHODS

V/Q SPECT studies carried out over 5 years were classified into positive, negative and indeterminate results. Patients who had died or had pulmonary emboli on imaging within 3 months of a negative V/Q SPECT were identified as false negatives, from which the NPV was calculated. The total number of positive and indeterminate studies as a proportion of all studies was calculated as the positive and indeterminate rates.

RESULTS

The positive rate, NPV and indeterminate rates in nonpregnant patients were 24, 98.7-100 and 3.6%, respectively. The positive rate, NPV and indeterminate rates in pregnant patients were 6.8, 100 and 2.3%, respectively.

CONCLUSION

The positive rate and NPV for nonpregnant patients were similar to the published literature. This suggests that we provide a safe service. The indeterminate rate was slightly higher than the stated guidelines. The study shows that the positive rate and NPV are achievable indicators of potential overcalling and undercalling in a V/Q SPECT service.This is also one of the first studies to report a positive rate in pregnant patients undergoing V/Q SPECT that other institutions can use as a standard when evaluating their services.

MCNPX CALCULATIONS OF SPECIFIC ABSORBED FRACTIONS IN SOME ORGANS OF THE HUMAN BODY DUE TO APPLICATION OF 133Xe, 99mTc and 81mKr RADIONUCLIDES

Monte Carlo simulations were performed to evaluate treatment doses with wide spread used radionuclides 133Xe, 99mTc and 81mKr. These different radionuclides are used in perfusion or ventilation examinations in nuclear medicine and as indicators for cardiovascular and pulmonary diseases. The objective of this work was to estimate the specific absorbed fractions in surrounding organs and tissues, when these radionuclides are incorporated in the lungs. For this purpose a voxel thorax model has been developed and compared with the ORNL phantom. All calculations and simulations were performed by means of the MCNP5/X code.

Signal enhancement ratio imaging of the lung parenchyma with ultra-fast steady-state free precession MRI at 1.5T

BACKGROUND

Lung perfusion MRI after i.v. gadolinium (Gd) contrast administration is commonly based on spoiled gradient-echo acquisitions, such as volume-interpolated breath-hold examinations (VIBE), suffering from low signal-to-noise in the parenchyma.

PURPOSE

To investigate the lung signal enhancement ratio (SER) with ultra-fast steady-state free precession (ufSSFP) after Gd-administration.

STUDY TYPE

Retrospective.

SUBJECTS

Ten subjects with healthy lungs; nine patients with pulmonary diseases (chronic obstructive pulmonary disease [COPD], lung cancer, pulmonary fibrosis, lung contusion).

FIELD STRENGTH/SEQUENCE

VIBE and ufSSFP imaging of the chest was performed at 1.5T before and 3 minutes after i.v. gadobenate dimeglumine.

ASSESSMENT

A workflow including deformable image registration and median filtering was used to compute 3D SER maps. SER was analyzed in the lung, blood pool, liver, muscles, and fat. The artifacts were assessed by a radiologist. In the COPD patients, ufSSFP-SER was compared to ^99m Tc-MAA-SPECT/CT by visual scoring of lung enhancement deficits.

STATISTICAL TESTS

Mean signal, standard deviation (SD), intersubject SD, and coefficient of variation (CV) were calculated for SER. Statistical significance of differences in signal and artifacts were determined using Wilcoxon signed-rank paired test. Intermodality agreement between ufSSFP-SER and SPECT/CT was calculated by Cohen's kappa (κ_q ).

RESULTS

In healthy lungs, ufSSFP-SER (99% ± 23%, mean ± pooled intrasubject SD, CV = 23%) was significantly higher (P < 10^-3 ) and more homogeneous (P < 10^-3 ) than VIBE (47% ± 26%, CV = 57%). UfSSFP-SER was significantly higher (P < 10^-3 ) for the lungs (99% ± 9%, mean ± intersubject SD) than for the blood (81% ± 7%) and other tissues (liver 33% ± 8%, muscle 26% ± 5%, fat 2% ± 1%). In the lung ufSSFP-SER exhibits homogeneity on iso-gravitational planes, and an anterior-posterior gradient. In COPD patients, ufSSFP-SER was reduced and less homogeneous compared to the control group (73% ± 33%, mean ± pooled intrasubject SD, CV = 42%). ufSSFP-SER had moderate intermodality agreement with SPECT/CT (κ_q  = 0.64).

DATA CONCLUSION

UfSSFP-SER of the lung is a rapid and simple method. Our preliminary data show plausible results in different pulmonary diseases, motivating further evaluation in larger cohorts.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018.

Lung ventilation/perfusion SPECT for diagnosing pulmonary embolism

V/P-SPECT is a sensitive and specific procedure for the detection or exclusion of pulmonary embolism. It is important to conform to the guidelines in order to obtain reliable results. The sequence usually starts with the ventilation, followed by the perfusion scan. According to the current guidelines the count rate of the second study should be at least 3 times that of the first study. It is not always easy to meet this requirement, particularly since the deposed quantity of ventilation activity is not well known. The aim was therefore to analyse data from a multicentre survey to determine whether this essential precondition was strictly met. Methods. In a multicentre survey 48 tertiary hospitals were asked to submit projections of all V/P-SPECT studies performed in January 2014. In total, 286 complete data sets from 16 institutions could be evaluated. First, the count rates of the first projections from the V-studies were subtracted from those of the P-studies. The resulting count rates in the first SPECT projections were then divided to calculate the activity ratios between the pure perfusion and ventilation scans (P/V-ratio at least 3 according to the guidelines). Results: The range of the P/V ratio was 0.57–78.71, the mean P/V ratio was 6.94 ± 9.56. For 71 of the 286 external V/P studies (about 25%) the P/V ratio was< 3, in 23 studies (about 8%) the ratio failed to even reach the factor 2. Conclusions: An activity ratio of 3 between the perfusion and ventilation scan was not reached in about 25% of the 286 V/P studies (in around 8% the P/V ratio was<2), so that V/P studies were performed inadequately in a considerable number of procedures. Controlling the count rate increase during the perfusion tracer application (e. g. by handheld monitor) is therefore essential to avoid insufficient data.

Automatic lung segmentation in functional SPECT images using active shape models trained on reference lung shapes from CT

Objective

Image segmentation is an essential step in quantifying the extent of reduced or absent lung function. The aim of this study is to develop and validate a new tool for automatic segmentation of lungs in ventilation and perfusion SPECT images and compare automatic and manual SPECT lung segmentations with reference computed tomography (CT) volumes.

Methods

A total of 77 subjects (69 patients with obstructive lung disease, and 8 subjects without apparent perfusion of ventilation loss) performed low-dose CT followed by ventilation/perfusion (V/P) SPECT examination in a hybrid gamma camera system. In the training phase, lung shapes from the 57 anatomical low-dose CT images were used to construct two active shape models (right lung and left lung) which were then used for image segmentation. The algorithm was validated in 20 patients, comparing its results to reference delineation of corresponding CT images, and by comparing automatic segmentation to manual delineations in SPECT images.

Results

The Dice coefficient between automatic SPECT delineations and manual SPECT delineations were 0.83 ± 0.04% for the right and 0.82 ± 0.05% for the left lung. There was statistically significant difference between reference volumes from CT and automatic delineations for the right (R = 0.53, p = 0.02) and left lung (R = 0.69, p < 0.001) in SPECT. There were similar observations when comparing reference volumes from CT and manual delineations in SPECT images, left lung (bias was − 10 ± 491, R = 0.60, p = 0.005) right lung (bias 36 ± 524 ml, R = 0.62, p = 0.004).

Conclusion

Automated segmentation on SPECT images are on par with manual segmentation on SPECT images. Relative large volumetric differences between manual delineations of functional SPECT images and anatomical CT images confirms that lung segmentation of functional SPECT images is a challenging task. The current algorithm is a first step towards automatic quantification of wide range of measurements.

Current incidence of venous thromboembolism and comparison with 1998: a community-based study in Western France

In 1998 we estimated the incidence of venous thromboembolism (VTE) to be 1.8/1,000 per year. The aim of this study was to compare current VTE incidence to that observed in 1998. We prospectively recorded all cases of symptomatic pulmonary embolism (PE) and deep vein thrombosis (DVT) of the lower limbs diagnosed between March 1, 2013 and February 28, 2014 in hospitals and in the community, using the same method and geographic area than in 1998. The 2013 incidence rates of VTE were computed and compared with those of 1998 using age- and sex-specific standardised incidence ratios (SIRs). In 2013, we recorded 576 VTE cases (279 isolated DVT and 297 PE ± DVT). Among 367,911 inhabitants, the overall incidence of VTE was 1.57/1,000 (95 % CI 1.44–1.69). The overall VTE incidence was significantly lower in 2013 as compared with 1998: SIR 0.72 (95 % CI 0.67–0.79) as well as the incidence of isolated DVT: SIR 0.53 (95 % CI 0.47–0.60); conversely, the overall incidence of PE was unchanged: SIR 1.10 (95 % CI, 0.98–1.23) despite an increase in the incidence of isolated PE: SIR 1.29 (95 % CI, 1.10–1.52). In 1998, 4.4 % of PE cases were diagnosed using CTPA as compared with 73.7 % in 2013 (p < 0.001). In conclusion, between 1998 and 2013, the incidence of symptomatic DVT decreased. Conversely, we found no similar reduction in the incidence of symptomatic PE; whether this is due to changes in diagnostic tests and algorithms in the management of suspected PE requires further investigations.

Supplementary Material to this paper is available online at www.thrombosis-online.com.

Pulmonary Arterial Hypertension With Abnormal V/Q Single-Photon Emission Computed Tomography

OBJECTIVES

This study aimed to evaluate the incidence and clinical outcomes of abnormal ventilation/perfusion (V/Q) single-photon emission computed tomography (SPECT) without thromboembolism, especially in patients with group I pulmonary arterial hypertension (PAH).

BACKGROUND

American Heart Association/American College of Cardiology and European Society of Cardiology guidelines recommend V/Q scan for screening for chronic thromboembolic pulmonary hypertension. The significance of patients with abnormal V/Q SPECT findings but no thromboembolism demonstrated in further investigations remained unclear. A distinct pattern of global patchy changes not typical of thromboembolism is recognized, but guidelines for reporting these in the context of PAH are lacking.

METHODS

A total of 136 patients who underwent V/Q SPECT and right-sided heart catheterization showing mean pulmonary arterial pressure ≥25 mm Hg were included. V/Q SPECT findings were reported using European Association of Nuclear Medicine criteria for pulmonary embolism followed by computed tomography pulmonary angiography screening for positive thromboembolism and further invasive pulmonary angiography for distal thromboembolism. The abnormal V/Q SPECT images were further analyzed according to perfusion pattern into focal or global perfusion defects.

RESULTS

V/Q SPECT showed thromboembolic disease in 44 patients, but 19 of these patients had no thromboembolism demonstrated by pulmonary angiography. Among these patients, 15 of 19 (78.9%) had group I PAH, and the majority had diffuse, patchy perfusion defects. After redefining V/Q SPECT images according to the perfusion pattern, those patients with global perfusion defects had higher mean pulmonary arterial pressure compared with patients with focal perfusion defects and normal scans (mean difference +13.9 and +6.2 mm Hg, respectively; p = 0.0002), as well as higher pulmonary vascular resistance (mean difference +316.6 and +226.3 absolute resistance units, respectively; p = 0.004). Among patients with PAH, global perfusion defects were associated with higher all-cause mortality with a hazard ratio of 5.63 (95% confidence interval: 1.11 to 28.5) compared with patients with focal or no perfusion abnormalities.

CONCLUSIONS

There is a high incidence of abnormal V/Q SPECT scans in nonthromboembolic PAH. Further studies are needed to investigate the poor outcome associated with abnormal V/Q SPECT findings in the context of PAH.

Assessing lung function using contrast-enhanced dual-energy computed tomography for potential applications in radiation therapy

PURPOSE

There is an increasing interest in the evaluation of lung function from physiological images in radiation therapy treatment planning to reduce the extent of postradiation toxicities. The purpose of this work was to retrieve reliable functional information from contrast-enhanced dual-energy computed tomography (DECT) for new applications in radiation therapy. The functional information obtained by DECT is also compared with other methods using single-energy CT (SECT) and single-photon emission computed tomography (SPECT) with CT. The differential function between left and right lung, as well as between lobes is computed for all methods.

METHODS

Five lung cancer patients were retrospectively selected for this study; each underwent a SPECT/CT scan and a contrast-injected DECT scan, using 100 and 140 Sn kVp. The DECT images are postprocessed into iodine concentration maps, which are further used to determine the perfused blood volume. These maps are calculated in two steps: (a) a DECT stoichiometric calibration adapted to the presence of iodine and followed by (b) a two-material decomposition technique. The functional information from SECT is assumed proportional to the HU numbers from a mixed CT image. The functional data from SPECT/CT are considered proportional to the number of counts. A radiation oncologist segmented the entire lung volume into five lobes on both mixed CT images and low-dose CT images from SPECT/CT to allow a regional comparison. The differential function for each subvolume is computed relative to the entire lung volume.

RESULTS

The differential function per lobe derived from SPECT/CT correlates strongly with DECT (Pearson's coefficient r = 0.91) and moderately with SECT (r = 0.46). The differential function for the left lung shows a mean difference of 7% between SPECT/CT and DECT; and 17% between SPECT/CT and SECT. The presence of nonfunctional areas, such as localized emphysema or a lung tumor, is reflected by an intensity drop in the iodine concentration maps. Functional dose volume histograms (fDVH) are also generated for two patients as a proof of concept.

CONCLUSION

The extraction of iodine concentration maps from a contrast-enhanced DECT scan is achieved to compute the differential function for each lung subvolume and good agreement is found in respect to SPECT/CT. One promising avenue in radiation therapy is to include such functional information during treatment planning dose optimization to spare functional lung tissues.

The Economic Value of Hybrid Single-photon Emission Computed Tomography With Computed Tomography Imaging in Pulmonary Embolism Diagnosis

Objective

The objective was to quantify the potential economic value of single‐photon emission computed tomography (SPECT) with computed tomography (CT; SPECT/CT) versus CT pulmonary angiography (CTPA), ventilation–perfusion (V/Q) planar scintigraphy, and V/Q SPECT imaging modalities for diagnosing suspected pulmonary embolism (PE) patients in an emergency setting.

Methods

An Excel‐based simulation model was developed to compare SPECT/CT versus the alternate scanning technologies from a payer's perspective. Clinical endpoints (diagnosis, treatment, complications, and mortality) and their corresponding cost data (2016 USD) were obtained by performing a best evidence review of the published literature. Studies were pooled and parameters were weighted by sample size. Outcomes measured included differences in 1) excess costs, 2) total costs, and 3) lives lost per annum between SPECT/CT and the other imaging modalities. One‐way (±25%) sensitivity and three scenario analyses were performed to gauge the robustness of the results.

Results

For every 1,000 suspected PE patients undergoing imaging, expected annual economic burden by modality was found to be 3.2 million (SPECT/CT), 3.8 million (CTPA), 5.8 million (planar), and 3.6 million (SPECT) USD, with a switch to SPECT/CT technology yielding per‐patient‐per‐month cost savings of $51.80 (vs. CTPA), $213.80 (vs. planar), and $36.30 (vs. SPECT), respectively. The model calculated that the incremental number of lives saved with SPECT/CT was six (vs. CTPA) and three (vs. planar). Utilizing SPECT/CT as the initial imaging modality for workup of acute PE was also expected to save $994,777 (vs. CTPA), $2,852,014 (vs. planar), and $435,038 (vs. SPECT) in “potentially avoidable”’ excess costs per annum for a payer or health plan.

Conclusion

Compared to the currently available scanning technologies for diagnosing suspected PE, SPECT/CT appears to confer superior economic value, primarily via improved sensitivity and specificity and low nondiagnostic rates. In turn, the improved diagnostic accuracy accords this modality the lowest ratio of expenses attributable to potentially avoidable complications, misdiagnosis, and underdiagnosis.

"Pulmonary embolism diagnostics of pregnant patients: What is the recommended clinical pathway considering the clinical value and associated radiation risks of available imaging tests?"

Pulmonary embolism (PE) during pregnancy remains the leading preventable cause of maternal morbidity and mortality in the developed countries. Diagnosis of PE in pregnant patients is a challenging clinical problem, since pregnancy-related physiologic changes can mimic signs and symptoms of PE. Patient mismanagement may result into unjustified anticoagulant treatment or unnecessary imaging tests involving contrast-related or/and radiation-related risks for both the expectant mother and embryo/fetus. On the other hand, missing or delaying diagnosis of PE could lead to life-threatening conditions for both the mother and the embryo/fetus. Thus, a timely and accurate diagnostic approach is required for the optimal management of pregnant patients with suspected PE. Aim of the current review is to discuss a pregnancy-specific clinical pathway for the early diagnosis of PE with non-ionizing radiation- and ionizing radiation-based imaging modalities taking into account previously reported data on diagnostic value of available imaging tests, and radiation related concerns.

Chronic Thromboembolic Pulmonary Hypertension: Pearls and Pitfalls of Diagnosis

Chronic thromboembolic pulmonary hypertension (CTEPH) is characterized by chronic obstruction of major pulmonary arteries by organized thromboembolic material. Untreated CTEPH can result in pulmonary hypertension and eventually right heart failure, yet it is the only form of pulmonary hypertension that is potentially curable with surgical or catheter-based intervention. While early diagnosis is key to increasing the likelihood of successful treatment, CTEPH remains largely underdiagnosed. This article reviews the role of echocardiogram, ventilation/perfusion scan, and other available modalities in the diagnosis of CTEPH.

New developments and future challenges of nuclear medicine and molecular imaging for pulmonary embolism

Although widely validated, current tests for pulmonary embolism (PE) diagnosis, i.e. computed tomography pulmonary angiography (CTPA) and V/Q planar scintigraphy, have some limitations. Drawbacks of CTPA include the radiation dose, some contra indications and a rising concern about a possible overdiagnosis/overtreatment of PE. On the other hand, V/Q planar scintigraphy has a high rate of non-diagnostic tests responsible for complex diagnostic algorithms. Since the PIOPED study, imaging equipment and radiopharmaceuticals have greatly evolved allowing the introduction of techniques that improve imaging of lung ventilation and perfusion. Single photon emission computed tomography (SPECT) and SPECT/CT techniques are already largely used in daily practice and have been described to have greater diagnostic performance and much fewer non-diagnostic tests as compared with planar scintigraphy. However, they have not yet been firmly validated in large scale prospective outcome studies. More recently, it has also been proposed to image pulmonary perfusion and ventilation using positron emission tomography (PET), which has an inherent technical superiority as compared to conventional scintigraphy and may provide new insight for pulmonary embolism. Regardless of modality, these new thoracic imaging modalities have to be integrated into diagnostic strategies. The other major challenge for venous thromboembolism diagnosis may be the potential additional value of molecular imaging allowing specific targeting of thrombi in order, for example, to differentiate venous thromboembolism from tumor or septic thrombus, or acute from residual disease. In this article, the new imaging procedures of lung ventilation perfusion imaging with SPECT, SPECT/CT and PET/CT are discussed. We also review the current status and future challenge of molecular imaging for the in vivo characterization of venous thromboembolism.

Identifying the heterogeneity of COPD by V/P SPECT: a new tool for improving the diagnosis of parenchymal defects and grading the severity of small airways disease

Introduction

Airway obstruction and possible concomitant pulmonary diseases in COPD cannot be identified conventionally with any single diagnostic tool. We aimed to diagnose and grade COPD severity and identify pulmonary comorbidities associated with COPD with ventilation/perfusion single-photon emission computed tomography (V/P SPECT) using Technegas as the functional ventilation imaging agent.

Methods

94 COPD patients (aged 43–86 years, Global Initiative for Chronic Obstructive Lung Disease (GOLD) stages I–IV) were examined with V/P SPECT and spirometry. Ventilation and perfusion defects were analyzed blindly according to the European guidelines. Penetration grade of Technegas in V SPECT measured the degree of obstructive small airways disease. Total preserved lung function and penetration grade of Technegas in V SPECT were assessed by V/P SPECT and compared to GOLD stages and spirometry.

Results

Signs of small airway obstruction in the ventilation SPECT images were found in 92 patients. Emphysema was identified in 81 patients. Two patients had no signs of COPD, but both of them had a pulmonary embolism, and in one of them we also suspected a lung tumor. The penetration grade of Technegas in V SPECT and total preserved lung function correlated significantly to GOLD stages (r=0.63 and −0.60, respectively, P<0.0001). V/P SPECT identified pulmonary embolism in 30 patients (32%). A pattern typical for heart failure was present in 26 patients (28%). Parenchymal changes typical for pneumonia or lung tumor were present in several cases.

Conclusion

V/P SPECT, using Technegas as the functional ventilation imaging agent, is a new tool to diagnose COPD and to grade its severity. Additionally, it revealed heterogeneity of COPD caused by pulmonary comorbidities. The characteristics of these comorbidities suggest their significant impact in clarifying symptoms, and also their influence on the prognosis.

Lung perfusion: MRI vs. SPECT for screening in suspected chronic thromboembolic pulmonary hypertension

Purpose

To assess the diagnostic accuracy of magnetic resonance imaging (MRI) perfusion against perfusion single photon emission tomography (SPECT) screening for chronic thromboembolic pulmonary hypertension (CTEPH). Ventilation/perfusion (V/Q) scintigraphy is recommended to screen for suspected CTEPH. It has previously been shown that 3D dynamic contrast‐enhanced (DCE) lung perfusion MRI has a similar sensitivity for diagnosing CTEPH in comparison to planar perfusion scintigraphy; however, planar scintigraphy has now been largely replaced by SPECT, due to higher spatial resolution and sensitivity.

Materials and Methods

Consecutive patients with suspected CTEPH or unexplained pulmonary hypertension attending a referral center, who underwent lung DCE perfusion MRI at 1.5T, perfusion SPECT, and computed tomography pulmonary angiography (CTPA) within 14 days of right heart catheterization, from April 2013 to April 2014, were included. DCE‐MR, SPECT, and CTPA were independently analyzed by two blinded radiologists. Disagreements were corrected by consensus. The gold standard reference for the diagnosis of chronic thromboemboli was based on a review of multimodality imaging and clinical findings.

Results

In all, 74 patients with suspected CTEPH underwent all three modalities. Forty‐six were diagnosed with CTEPH (36) or chronic thromboembolic disease (CTED) (10). 3D DCE perfusion MRI correctly identified all patients (sensitivity of 100%), compared with a 97% sensitivity for SPECT.

Conclusion

DCE lung perfusion MRI has increased sensitivity when compared with perfusion scintigraphy in screening for CTEPH. As MRI does not use ionizing radiation, it should be considered as a first‐line imaging modality in suspected CTEPH.

Level of Evidence: 3

Technical Efficacy: Stage 3

J. Magn. Reson. Imaging 2017;46:1693–1697.

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.

Diagnosis of chronic thromboembolic pulmonary hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is the only potentially curable form of pulmonary hypertension. Rapid and accurate diagnosis is pivotal for successful treatment. Clinical signs and symptoms can be nonspecific and risk factors such as history of venous thromboembolism may not always be present. Echocardiography is the recommended first diagnostic step. Cardiopulmonary exercise testing is a complementary tool that can help to identify patients with milder abnormalities and chronic thromboembolic disease, triggering the need for further investigation. Ventilation/perfusion (V'/Q') scintigraphy is the imaging methodology of choice to exclude CTEPH. Single photon emission computed tomography V'/Q' is gaining popularity over planar imaging. Assessment of pulmonary haemodynamics by right heart catheterisation is mandatory, although there is increasing interest in noninvasive haemodynamic evaluation. Despite the status of digital subtraction angiography as the gold standard, techniques such as computed tomography (CT) and magnetic resonance imaging are increasingly used for characterising the pulmonary vasculature and assessment of operability. Promising new tools include dual-energy CT, combination of rotational angiography and cone beam CT, and positron emission tomography. These innovative procedures not only minimise misdiagnosis, but also provide additional vascular information relevant to treatment planning. Further research is needed to determine how these modalities will fit into the diagnostic algorithm for CTEPH.

Development of an ex vivo human-porcine respiratory model for preclinical studies

Anatomical models to study aerosol delivery impose huge limitations and extrapolation to humans remains controversial. This study aimed to develop and validate an ex vivo human-like respiratory tract model easy to use and relevant to compare to in vivo human data. A human plastinated head is connected to an ex vivo porcine pulmonary tract ventilated artificially by passive expansion. A physiological study measures “pleural” depressions, tidal volumes, and minute ventilation for the respiratory rates chosen (10, 15, and 20 per minute) with three inspiratory/expiratory ratios (1/1, 1/2, and 1/3). Scintigraphy with ^81mKrypton assesses the homogeneity of the ventilation. Forty different experiments were set for validation, with 36 (90%) ventilating successfully. At a respiratory rate of 15/minute with inspiratory/expiratory ratio of 1/2, the tidal volume average was 824 mL (standard deviation, 207 mL). The scintigraphy performed on 16 ex vivo models (44.4%), showed homogenous ventilation with great similarity to human physiological studies. Ratio of the peripheral to central count rates were equally correlated with human data published in the literature. This new model, combining research feasibility and human physiology likeness, provides a realistic approach to human inhalation and therefore can be an interesting tool in aerosol regional deposition studies.

Acute pulmonary embolism detection with ventilation/perfusion SPECT combined with full dose CT: What is the best option?

AIM

To compare diagnostic accuracy of Ventilation/Perfusion (V/P) single-photon emission computed tomography (SPECT) combined with simultaneous full-dose CT with a hybrid SPECT/CT scanner versus planar ventilation/perfusion (V/P) SPECT and CT angiography (CTA) in patients suspected with acute pulmonary embolism (PE).

METHODS

Between 2009 and 2011, consecutive patients suspected of acute PE were referred for V/P SPECT/CT (reviewed board approved study). A contrast agent was administered to patients who had no contraindications. Non-contrast V/P SPECT/CT was performed on the remaining patients. All patients were followed-up for at least 3 months.

RESULTS

A total of 314 patients were available during the study period, with the diagnosis of PE confirmed in 70 (22.29%) of them. The overall population sensitivity and specificity was 90.91% and 92.44%, respectively for V/P SPECT, 80% and 99.15%, respectively, for CTA, and 95.52% and 97.08% for V/P SPECT/CT. SPECT/CT performed better than V/P SPECT (AUC differences=0.0419, P=0.0043, 95% CI; 0.0131-0.0706) and CTA (AUC differences=0.0681, P=0.0208, 95% CI; 0.0103-0.1259)). Comparing imaging modalities when contrast agent could be administered, sensitivity and specificity increased and V/P SPECT/CT was significantly better than CTA (AUC differences=0.0681, P=0.0208, 95% CI; 0.0103-0.1259) and V/P SPECT (AUC differences=0.0659, P=0.0052, 95% CI; 0.0197-0.1121). In case of non-contrast enhancement, there was non-significant increase of specificity. Secondary findings on CT impacted patient management in 14.65% of cases.

CONCLUSION

Our study shows that combined V/P SPECT/CT scanning has a higher diagnostic accuracy for detecting acute PE than V/P SPECT and CTA alone. When feasible, V/P SPECT/CT with contrast enhancement is the best option.

Imaging for the exclusion of pulmonary embolism in pregnancy

BACKGROUND

Pulmonary embolism is a leading cause of pregnancy-related death. An accurate diagnosis in pregnant patients is crucial to prevent untreated pulmonary embolism as well as unnecessary anticoagulant treatment and future preventive measures. Applied imaging techniques might perform differently in these younger patients with less comorbidity and altered physiology, who largely have been excluded from diagnostic studies.

OBJECTIVES

To determine the diagnostic accuracy of computed tomography pulmonary angiography (CTPA), lung scintigraphy and magnetic resonance angiography (MRA) for the diagnosis of pulmonary embolism during pregnancy.

SEARCH METHODS

We searched MEDLINE and Embase until July 2015. We used included studies as seeds in citations searches and in 'find similar' functions and searched reference lists. We approached experts in the field to help us identify non-indexed studies.

SELECTION CRITERIA

We included consecutive series of pregnant patients suspected of pulmonary embolism who had undergone one of the index tests (computed tomography (CT) pulmonary angiography, lung scintigraphy or MRA) and clinical follow-up or pulmonary angiography as a reference test.

DATA COLLECTION AND ANALYSIS

Two review authors performed data extraction and quality assessment. We contacted investigators of potentially eligible studies to obtain missing information. In the primary analysis, we regarded inconclusive index test results as a negative reference test, and treatment for pulmonary embolism after an inconclusive index test as a positive reference test.

MAIN RESULTS

We included 11 studies (four CTPA, five lung scintigraphy, two both) with a total of 695 CTPA and 665 lung scintigraphy results. Lung scintigraphy was applied by different techniques. No MRA studies matched our inclusion criteria.Overall, risk of bias and concerns regarding applicability were high in all studies as judged in light of the review research question, as was heterogeneity in study methods. We did not undertake meta-analysis. All studies used clinical follow-up as a reference standard, none in a manner that enabled reliable identification of false positives. Sensitivity and negative predictive value were therefore the only valid test accuracy measures.The median negative predictive value for CTPA was 100% (range 96% to 100%). Median sensitivity was 83% (range 0% to 100%).The median negative predictive value for lung scintigraphy was 100% (range 99% to 100%). Median sensitivity was 100% (range 0% to 100%).The median frequency of inconclusive results was 5.9% (range 0.9% to 36%) for CTPA and 4.0% (range 0% to 23%) for lung scintigraphy. The overall median prevalence of pulmonary embolism was 3.3% (range 0.0% to 8.7%).

AUTHORS' CONCLUSIONS

Both CTPA and lung scintigraphy seem appropriate for exclusion of pulmonary embolism during pregnancy. However, the quality of the evidence mandates cautious adoption of this conclusion. Important limitations included poor reference standards, necessary assumptions in the analysis regarding inconclusive test results and the inherent inability of included studies to identify false positives. It is unclear which test has the highest accuracy. There is a need for direct comparisons between diagnostic methods, including MR, in prospective randomized diagnostic studies.

Assessment of regional pulmonary blood flow using 68Ga-DOTA PET

Background

In vivo determination of regional pulmonary blood flow (PBF) is a valuable tool for the evaluation of many lung diseases. In this study, the use of ⁶⁸Ga-DOTA PET for the in vivo quantitative determination of regional PBF is proposed. This methodology was implemented and tested in healthy pigs and validated using fluorescent microspheres. The study was performed on young large white pigs (n = 4). To assess the reproducibility and consistency of the method, three PET scans were obtained for each animal. Each radiotracer injection was performed simultaneously to the injection of fluorescent microspheres. PBF images were generated applying a two-compartment exchange model over the dynamic PET images. PET and microspheres values were compared by regression analysis and Bland–Altman plot.

Results

The capability of the proposed technique to produce 3D regional PBF images was demonstrated. The correlation evaluation between ⁶⁸Ga-DOTA PET and microspheres showed a good and significant correlation (r = 0.74, P < 0.001).

Conclusions

Assessment of PBF with the proposed technique allows combining the high quantitative accuracy of PET imaging with the use of ⁶⁸Ga/⁶⁸Ge generators. Thus, ⁶⁸Ga-DOTA PET emerges as a potential inexpensive method for measuring PBF in clinical settings with an extended use.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-017-0259-2) contains supplementary material, which is available to authorized users.

Incidence of a single subsegmental mismatched perfusion defect in single-photon emission computed tomography and planar ventilation/perfusion scans

OBJECTIVE

This study aims to compare the incidence of ventilation/perfusion (V/Q) scans interpreted as indeterminate for the diagnosis of pulmonary embolism (PE) using single-photon emission computed tomography (SPECT) versus planar scintigraphy and to consider the effect of variable interpretation of single subsegmental V/Q mismatch (SSM).

METHODS

A total of 1300 consecutive V/Q scans were retrospectively reviewed. After exclusion and matching for age and sex, 542 SPECT and 589 planar scans were included in the analysis. European Association of Nuclear Medicine guidelines were used to interpret the V/Q scans, initially interpreting SSM as negative scans. Patients with SSM were followed up for 3 months and further imaging for PE was collected.

RESULTS

Indeterminate scans were significantly fewer in the SPECT than the planar group on the basis of the initial report (7.7 vs. 12.2%, P<0.05). This is irrespective of classification of SSM as a negative scan (4.6 vs. 12.1%, P<0.0001) or an indeterminate scan (8.3 vs. 12.2%, P<0.05). Of the 21 patients who had SSM, 19 underwent computer tomography pulmonary angiogram and embolism was found in one patient. None of these patients died at the 3-month follow-up.

CONCLUSION

V/Q SPECT has greater diagnostic certainty of PE, with a 41% reduction in an indeterminate scan compared with planar scintigraphy. This is irrespective of the clinician's interpretation of SSM as negative or intermediate probability. Patients with SSM would not require further computer tomography pulmonary angiogram imaging.

Imaging Pregnant and Lactating Patients

As use of imaging in the evaluation of pregnant and lactating patients continues to increase, misperceptions of radiation and safety risks have proliferated, which has led to often unwarranted concerns among patients and clinicians. When radiologic examinations are appropriately used, the benefits derived from the information gained usually outweigh the risks. This review describes appropriateness and safety issues, estimated doses for imaging examinations that use iodizing radiation (ie, radiography, computed tomography, nuclear scintigraphy, and fluoroscopically guided interventional radiology), radiation risks to the mother and conceptus during various stages of pregnancy, and use of iodinated or gadolinium-based contrast agents and radiotracers in pregnant and lactating women. Maternal radiation risk must be weighed with the potential consequences of missing a life-threatening diagnosis such as pulmonary embolus. Fetal risks (ie, spontaneous abortion, teratogenesis, or carcinogenesis) vary with gestational age and imaging modality and should be considered in the context of the potential benefit of medically necessary diagnostic imaging. When feasible and medically indicated, modalities that do not use ionizing radiation (eg, magnetic resonance imaging) are preferred in pregnant and lactating patients. Radiologists should strive to minimize risks of radiation to the mother and fetus, counsel patients effectively, and promote a realistic understanding of risks related to imaging during pregnancy and lactation.

Is it safe to withhold long-term anticoagulation therapy in patients with small pulmonary emboli diagnosed by SPECT scintigraphy?

Background

The need for anticoagulation therapy (AC) in patients with subsegmental pulmonary embolism (SSPE) diagnosed by computed tomography of the pulmonary arteries (CTPA) has been questioned, as these patients run low risk for recurrent venous thromboembolism (VTE) during 3 months of follow-up. Whether this applies also to patients with small PE diagnosed with pulmonary scintigraphy has not yet been evaluated, however.

Methods

We therefore retrospectively evaluated 54 patients (mean age 62 ± 19 years, 36 [67 %] women) with small PE diagnosed by ventilation/perfusion singe photon emission computed tomography (V/P SPECT) who did not receive conventional long-term AC.

Results

More than half of our patients (36[67 %]) received less than 48 h of AC, 11 (20 %) patients were treated for 2–14 days, and 7 (13 %) for 15–30 days. The majority (28 [52 %]) of our patients had a non-low simplified pulmonary emboli severity index (S-PESI), and 7 (13 %) had malignancy. D-dimer was negative in 18 (33 %), positive in 10 (19 %), and not analyzed in 28 (52 %) patients. Phlebography of the lower extremities had been performed with negative result in one patient.

During 90 days of follow up no deaths or PE occurred. Seven patients were readmitted to hospital, whereof two (2/54 [4 %]) were diagnosed with deep venous thrombosis (DVT) necessitating AC therapy.

Conclusion

In conclusion, withholding longterm AC therapy in patients with SSPE diagnosed by V/P SPECT resulted in 4 % risk for recurrence of VTE during 90 days of follow up, and can therefore currently not be recommended.

Additional value of combining low-dose computed tomography to V/Q SPECT on a hybrid SPECT-CT camera for pulmonary embolism diagnosis

OBJECTIVES

The aim of the study was to assess the potential interest of combining a low-dose computed tomography (ldCT) to ventilation/perfusion (V/Q) single-photon emission computed tomography (SPECT) for the diagnosis of pulmonary embolism (PE). We addressed three main questions: Could ldCT be used in substitution to ventilation SPECT? Could ldCT improve the diagnostic performance of V/Q SPECT? Could ldCT provide alternative diagnoses to PE?

METHODS

A total of 393 patients previously analysed in a management outcome study that aimed at assessing the safety of V/Q SPECT for PE diagnosis were assessed. All patients underwent an ldCT under the same SPECT-computed tomography camera, which was not used at the time of initial interpretation. Three retrospective analyses were performed: Q SPECT combined with ldCT, V/Q SPECT combined with ldCT and ldCT only.

RESULTS

On the basis of initial V/Q SPECT interpretation, 110 (28%) patients were positive and 283 (72%) were negative for PE.With Q SPECT-ldCT, 139 (35%) patients were positive and 254 (65%) were negative, with 55 (19%) discrepancies when compared with V/Q SPECT. Of the 283 patients with negative V/Q SPECT, 42 were positive with V/Q SPECT-ldCT, and among the 110 patients with positive V/Q SPECT 13 were negative with V/Q SPECT-ldCT. On using V/Q SPECT-ldCT, 97 (25%) patients were positive and 296 (75%) were negative, with 13 (3%) discrepancies when compared with V/Q SPECT (all had had a positive V/Q SPECT but a negative V/Q SPECT-ldCT). Finally, 67 (24%) ldCT scans showed a potential alternative diagnosis to PE.

CONCLUSION

For PE diagnosis with lung SPECT, the use of ldCT in substitution to ventilation SPECT is associated with a high risk of overdiagnosis. The diagnostic value of ldCT in addition to V/Q SPECT remains unclear. Further studies are needed to determine its potential role in PE diagnosis.

Historical Evolution of Imaging Techniques for the Evaluation of Pulmonary Embolism

As we celebrate the 100th anniversary of the founding of the Radiological Society of North America (RSNA), it seems fitting to look back at the major accomplishments of the radiology community in the diagnosis of pulmonary embolism. Few diseases have so consistently captured the attention of the medical community. Since the first description of pulmonary embolism by Virchow in the 1850s, clinicians have struggled to reach a timely diagnosis of this common condition because of its nonspecific and often confusing clinical picture. As imaging tests started to gain importance in the 1900s, the approach to diagnosing pulmonary embolism also began to change. Rapid improvements in angiography, ventilation-perfusion imaging, and cross-sectional imaging modalities such as computed tomography (CT) and magnetic resonance imaging have constantly forced health care professionals to rethink how they diagnose pulmonary embolism. Needless to say, the way pulmonary embolism is diagnosed today is distinctly different from how it was diagnosed in Virchow's era; and imaging, particularly CT, now forms the cornerstone of diagnostic evaluation. Currently, radiology offers a variety of tests that are fast and accurate and can provide anatomic and functional information, thus allowing early diagnosis and triage of cases. This review provides a historical journey into the evolution of these imaging tests and highlights some of the major breakthroughs achieved by the radiology community and RSNA in this process. Also highlighted are areas of ongoing research and development in this field of imaging as radiologists seek to combat some of the newer challenges faced by modern medicine, such as rising health care costs and radiation dose hazards.

Diagnosing venous thromboembolism in pregnancy

OBJECTIVE

We report the imaging outcomes of all pregnant patients referred for suspected thromboembolism over a 43-month period.

METHODS

We identified 168 patients who underwent ventilation/perfusion (VQ) single-photon emission CT (SPECT), CT pulmonary angiography (CTPA) or a Doppler ultrasound scan of the lower legs, as well as a control group of 89 non-pregnant age- and sex-matched patients who underwent VQ SPECT during the same period. Imaging outcomes were recorded, and radiation doses were calculated for individual patients.

RESULTS

VQ SPECT and CTPA were equally likely to diagnose pulmonary embolism (PE) in about one patient out of every seven patients investigated. One in three CTPA scans was of suboptimal quality. A Doppler ultrasound examination of the legs will find deep venous thrombosis much less often, in about 1 patient out of every 15 patients investigated. The prevalence of PE in pregnant patients (as diagnosed by VQ SPECT) was similar to that in the non-pregnant, age- and sex-matched control group. The effective dose and the absorbed radiation dose to the maternal breast were lower with VQ SPECT. The foetal dose is comparable for both VQ SPECT and CTPA.

CONCLUSION

VQ SPECT and CTPA provide a similar diagnostic yield for diagnosing PE during pregnancy, but VQ SPECT does so with a lower radiation dose to the mother (effective dose and breast dose).

ADVANCES IN KNOWLEDGE

Ours is the first report of the diagnostic performance of VQ SPECT, rather than planar VQ scans, in pregnancy in a routine clinical setting.

Gas Phase UTE MRI of Propane and Propene

Proton magnetic resonance imaging (¹H MRI) of gases can potentially enable functional lung imaging to probe gas ventilation and other functions. Here, ¹H MR images of hyperpolarized (HP) and thermally polarized propane gas were obtained using ultrashort echo time (UTE) pulse sequence. A 2-dimensional (2D) image of thermally polarized propane gas with ∼0.9 × 0.9 mm² spatial resolution was obtained in <2 seconds, showing that even non-HP hydrocarbon gases can be successfully used for conventional proton magnetic resonance imaging. The experiments were also performed with HP propane gas, and high-resolution multislice FLASH 2D images in ∼510 seconds and non-slice-selective 2D UTE MRI images were acquired in ∼2 seconds. The UTE approach adopted in this study can be potentially used for medical lung imaging. Furthermore, the possibility of combining UTE with selective suppression of ¹H signals from 1 of the 2 gases in a mixture is shown in this MRI study. The latter can be useful for visualizing industrially important processes where several gases may be present, eg, gas–solid catalytic reactions.