Initial non-invasive in vivo sensing of the lung using time domain diffuse optics.

The in vivo diagnosis and monitoring of pulmonary disorders (caused for example by emphysema, Covid-19, immature lung tissue in infants) could be effectively supported by the non-invasive sensing of the lung through light. With this purpose, we investigated the feasibility of probing the lung by means of time-resolved diffuse optics, leveraging the increased depth (a few centimeters) attained by photons collected after prolonged propagation time (a few nanoseconds). We present an initial study that includes measurements performed on 5 healthy volunteers during a breathing protocol, using a time-resolved broadband diffuse optical spectroscopy system. Those measurements were carried out across the spectral range of 600-1100 nm at a source-detector distance of 3 cm, and at 820 nm over a longer distance (7-9 cm). The preliminary analysis of the in vivo data with a simplified homogeneous model revealed a maximum probing depth of 2.6-3.9 cm, suitable for reaching the lung. Furthermore, we observed variations in signal associated with respiration, particularly evident at long photon propagation times. However, challenges stemming from both intra- and inter-subject variability, along with inconsistencies potentially arising from conflicting scattering and absorption effects on the collected signal, hindered a clear interpretation. Aspects that require further investigation for a more comprehensive understanding are outlined.

Impact of residual pulmonary obstruction on the long-term outcome of patients with pulmonary embolism.

The impact of residual pulmonary obstruction on the outcome of patients with pulmonary embolism is uncertain.We recruited 647 consecutive symptomatic patients with a first episode of pulmonary embolism, with or without concomitant deep venous thrombosis. They received conventional anticoagulation, were assessed for residual pulmonary obstruction through perfusion lung scanning after 6 months and then were followed up for up to 3 years. Recurrent venous thromboembolism and chronic thromboembolic pulmonary hypertension were assessed according to widely accepted criteria.Residual pulmonary obstruction was detected in 324 patients (50.1%, 95% CI 46.2-54.0%). Patients with residual pulmonary obstruction were more likely to be older and to have an unprovoked episode. After a 3-year follow-up, recurrent venous thromboembolism and/or chronic thromboembolic pulmonary hypertension developed in 34 out of the 324 patients (10.5%) with residual pulmonary obstruction and in 15 out of the 323 patients (4.6%) without residual pulmonary obstruction, leading to an adjusted hazard ratio of 2.26 (95% CI 1.23-4.16).Residual pulmonary obstruction, as detected with perfusion lung scanning at 6 months after a first episode of pulmonary embolism, is an independent predictor of recurrent venous thromboembolism and/or chronic thromboembolic pulmonary hypertension.

Body height as risk factor for emphysema in COPD.

Pulmonary emphysema is a phenotypic component of chronic obstructive pulmonary disease (COPD) which carries substantial morbidity and mortality. We explored the association between emphysema and body height in 726 patients with COPD using computed tomography as the reference diagnostic standard for emphysema. We applied univariate analysis to look for differences between patients with emphysema and those without, and multivariate logistic regression to identify significant predictors of the risk of emphysema. As covariates we included age, sex, body height, body mass index, pack-years of smoking, and forced expiratory volume in one second (FEV1) as percent predicted. The overall prevalence of emphysema was 52%. Emphysemic patients were significantly taller and thinner than non-emphysemic ones, and featured significantly higher pack-years of smoking and lower FEV1 (P < 0.001). The prevalence of emphysema rose linearly by 10-cm increase in body height (r2 = 0.96). In multivariate analysis, the odds of emphysema increased by 5% (95% confidence interval, 3 to 7%) along with one-centimeter increase in body height, and remained unchanged after adjusting for all the potential confounders considered (P < 0.001). The odds of emphysema were not statistically different between males and females. In conclusion, body height is a strong, independent risk factor for emphysema in COPD.

Pulmonary Infarction: An Often Unrecognized Clinical Entity.

Pulmonary infarction occurs in nearly one-third of the patients with acute pulmonary embolism. Infarcts are still often mistaken for pneumonia or lung cancer because of the deeply rooted belief that they ought to be triangular in shape. In reality, the apical portion of an embolized region is spared from infarction thanks to sufficient collateral blood flow. Infarcts are always arranged peripherally along the surface of the visceral pleura (costal, diaphragmatic, mediastinal, or interlobar). Their free margin is sharp and convex toward the hilum, casting a semicircular or cushion-like density on chest radiography or computed tomography (CT). Focal areas of hyperlucency within the infarction are often seen on CT. Clinical presentation is nonspecific. Pleuritic chest pain, either isolated or in combination with abrupt dyspnea, is the most frequent presenting symptom, whereas hemoptysis is much rarer. Recent data indicate that younger age, increasing body height, and active cigarette smoking are independent predictors of infarction in the setting of acute pulmonary embolism. Correct recognition of pulmonary infarction is fundamental because pleural-based consolidations suggestive of infarction may be the first manifestation of pulmonary embolism.

Predictors of Pulmonary Infarction.

In the setting of acute pulmonary embolism (PE), pulmonary infarction is deemed to occur primarily in individuals with compromised cardiac function.The current study was undertaken to establish the prevalence of pulmonary infarction in patients with acute PE, and the relationship between infarction and: age, body height, body mass index (BMI), smoking habits, clot burden, and comorbidities.The authors studied prospectively 335 patients with acute PE diagnosed by computed tomographic angiography (CT) in 18 hospitals throughout central Italy. The diagnosis of pulmonary infarction on CT was based on Hampton and Castleman's criteria (cushion-like or hemispherical consolidation lying along the visceral pleura). Multivariable logistic regression was used to model the relationship between covariates and the probability of pulmonary infarction.The prevalence of pulmonary infarction was 31%. Patients with infarction were significantly younger and with significantly lower prevalence of cardiovascular disease than those without (P < 0.001). The frequency of infarction increased linearly with increasing height, and decreased with increasing BMI. In logistic regression, the covariates significantly associated with the probability of infarction were age, body height, BMI, and current smoking. The risk of infarction grew with age, peaked at approximately age 40, and decreased afterwards. Increasing body height and current smoking were significant amplifiers of the risk of infarction, whereas increasing BMI appeared to confer some protection.Our data indicate that pulmonary infarction occurs in nearly one-third of the patients with acute PE. Those with infarction are often young and otherwise healthy. Increasing body height and active smoking are predisposing risk factors.

Impact of ventilation/perfusion single-photon emission computed tomography on treatment duration of pulmonary embolism.

PURPOSE: The aim of the study was to establish whether the duration of anticoagulant (AC) therapy can be tailored, on an objective basis, by using ventilation/perfusion single-photon emission computed tomography (V/P SPECT) and to assess the extent of residual perfusion defects over time. In particular, we addressed the following: (a) is the extent of perfusion recovery at 3 months of initial pulmonary embolism (PE) diagnosis a satisfactory criterion for deciding the duration of oral AC? (b) Is it safe to withdraw AC at 3 months if perfusion recovery is complete? PATIENTS AND METHODS: Of 269 consecutive patients with suspected PE, 100 patients were diagnosed with PE using V/P SPECT. Sixty-seven patients with acute PE were followed up clinically and with V/P SPECT at 3 months. Sixty-four patients were subject to review and examination using V/P SPECT for a period of 6 months and 33 were followed up only clinically. Therapy was terminated after 3 months if perfusion was normalized, and patients were free of symptoms and the risk of hypercoagulability. Initial extension of PE did not have an impact on decision making. RESULTS: PE extension varied from 10 to 70% in the acute stage. After 3 months, complete resolution of PE was found in 48 patients. The treating pulmonologist decided to terminate therapy in 35 (73%) patients and to continue AC in 13 patients because of persistent risk factors. Six months later, at the second control stage, 53 patients had complete recovery of pulmonary perfusion. Eleven patients still had perfusion defects at 6 months. No recurrence was identified at 6 months in the 35 patients whose therapy was terminated after 3 months. No bleeding effects were observed in any of the patients during the 6-month follow-up. CONCLUSION: This study shows that AC therapy can be tailored, on an objective basis, by using V/P SPECT. Normalization of perfusion at 3 months of initial PE diagnosis was a reliable indicator that AC could be safely withdrawn in patients who were without hypercoagulability risk.

Survival in COPD: impact of lung dysfunction and comorbidities.

Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality in industrialized countries. Recent studies investigated the impact of comorbidities on the survival in COPD, but most of them lacked a referent group of comorbidity-matched, nonobstructed individuals.We examined the 10-year mortality in a sample of 200 COPD patients and 201 nonobstructed controls. They were part of a larger cohort enrolled in a European case-control study aimed at assessing genetic susceptibility to COPD. By design, the COPD group included patients with a forced expiratory volume in 1 second (FEV1) ≤70% predicted. Cases and controls were matched on age, sex, and cumulative smoking history, and shared a nearly identical prevalence of cardiovascular and metabolic disorders. We estimated the hazard of death with Cox regression and percentiles of survival with Laplace regression. COPD was the main exposure variable of interest. Five comorbidities (hypertension, coronary artery disease, prior myocardial infarction, chronic heart failure, and diabetes) were included as covariates in multiple regression models.The all-cause mortality rate was significantly higher in cases than in controls (43% vs 16%, P < 0.001). The unadjusted hazard of death for COPD was 3-fold higher than the referent category (P < 0.001), and remained nearly unchanged after introducing the 5 comorbidities in multiple regression. Patients with COPD had significantly shorter survival percentiles than comorbidity-matched controls (P < 0.001). Notably, 15% of the nonobstructed controls died by 10.3 years into the study; the same proportion of COPD patients had died some 6 years earlier, at 4.6 years.In a separate analysis, we split the whole sample into 2 groups based on the lower tertile of FEV1 and carbon monoxide lung diffusing capacity (DLCO). The hazard of death for COPD patients with low FEV1 and DLCO was nearly 3.5-fold higher than in all the others (P < 0.001), and decreased only slightly after introducing age and chronic heart failure as relevant covariates.COPD is a strong predictor of reduced survival independently of coexisting cardiovascular and metabolic disorders. Efforts should be made to identify patients at risk and to ensure adherence to prescribed therapeutic regimens.

Residual perfusion defects in patients with pulmonary embolism are related to impaired fibrinolytic capacity.

BACKGROUND: Few studies investigated the relationship between fibrinolysis abnormalities and residual pulmonary perfusion defects after acute pulmonary embolism (PE). OBJECTIVE: To assess the fibrinolytic profile in patients with prior PE in relation to the extent of scintigraphically detectable residual perfusion abnormalities. PATIENTS AND METHODS: We studied 71 consecutive patients with a prior episode of PE, who were examined after one year of the incident embolic event, and at least one month after anticoagulation withdrawal. They underwent lung scintigraphy to assess the recovery of pulmonary perfusion, echocardiography and chest radiography to look for signs of pulmonary hypertension. Clot formation and lysis were evaluated by two turbidimetric methods: Clot and Lysis Assay and Clot Lysis Time. We also measured the in vitro plasmin-mediated lysis of fibrin from purified fibrinogen, and the circulating levels of fibrinolytic inhibitors. The sample was split in two categories based on the extent of residual perfusion defects: <10% (n=53), ≥ 10% (n=18). RESULTS: Patients with perfusion defects >10% had significantly longer lysis time (p<0.05), and higher levels of plasminogen activator inhibitor-1 (p<0.01) than those with perfusion defects <10%. The time interval between symptoms onset and PE diagnosis (time-to-diagnosis) was significantly longer in patients with perfusion defects >10% than in the others (p=0.005). In multivariate logistic regression, both lysis time and time-to-diagnosis were independently associated with perfusion defects >10% (p<0.001). None of the sampled patients had echocardiographic or radiologic signs of pulmonary hypertension. CONCLUSION: Prolonged time-to-diagnosis and fibrinolysis imbalance are independent predictors of incomplete perfusion recovery after acute PE.

Accuracy of chest radiography in predicting pulmonary hypertension: a case-control study.

OBJECTIVE: To assess the accuracy of chest radiography (CXR) in predicting pulmonary hypertension (PH). METHODS: We studied 108 consecutive patients with suspected PH who underwent right heart catheterization (RHC). All were PH treatment naives. Hemodynamic criteria included a mean pulmonary artery pressure >25 mmHg at rest, and a mean pulmonary wedge pressure <15 mmHg. Postero-anterior and lateral CXR were obtained shortly before RHC. To avoid a selection bias which could be introduced by examining only patients with suspected PH, we included in the analysis the CXR of 454 additional patients with different diagnosis: 57 with left heart failure (LHF) and pulmonary venous hypertension at RHC, 197 with chronic obstructive pulmonary disease, and 200 non-obstructed controls. CXR were examined independently by 4 raters, who were blinded to clinical, hemodynamic, and spirometric data. The diagnosis of PH was made if a prominent main pulmonary artery was associated with anyone of: isolated enlargement of right ventricle, right descending pulmonary artery >16 mm in diameter, pruning of peripheral pulmonary vessels. RESULTS: Eighty-two patients had PH confirmed at RHC. Weighted sensitivity of CXR was 96.9% (95% confidence interval, 94.9 to 98.2%), and weighted specificity 99.8% (95% confidence interval, 99.6 to 99.9%). By considering the 165 patients who underwent RHC, weighted sensitivity of CXR was unchanged, and weighted specificity decreased to 99.1%. None of the patients with PH were misclassified as having LHF, and vice versa. CONCLUSIONS: CXR is accurate in predicting PH. It may aid clinicians in selecting patients with suspected PH for hemodynamic ascertainment.

Improved survival in limited scleroderma-related pulmonary artery hypertension.

Reportedly, patients with scleroderma-related pulmonary hypertension (SSc-PAH) respond poorly to new vasoactive drugs (NVD). Forty-nine SSc-PAH patients underwent right heart catheterization (RHC) and, according to NVD availability, divided as follows: Group 1 (n = 23, from 1999 to 2004, poor availability), and Group 2 (n = 26, from 2005 to 2010, good availability). Before diagnostic RHC, NVD had been given to 30 % of the patients in Group 1, and 58 % of those in Group 2 (p = 0.049). At diagnosis, patients in Group 1 had greater heart dilatation (p < 0.01), higher mean pulmonary artery pressure (p < 0.05), lower pulmonary artery capacitance (p < 0.05), and lower carbon monoxide lung diffusing capacity (DLco, p < 0.05) than those in Group 2. At a median follow-up time of 15.5 months, DLco further decreased in Group 1 (p < 0.05), whereas cardiac index increased in Group 2 (p < 0.05). At 36 months of follow-up, 72.4 % of the patients in Group 2 were still alive as opposed to 30.4 % in Group 1 (p = 0.02). In multivariate analysis, DLco and mixed venous oxygen saturation (SvO2) were independent predictors of survival. A value of DLco <7.2 mL/mmHg/min was associated with a hazard ratio (HR) of 5.3 (p < 0.001); for SvO2 <63.8 %, the HR was 3.7 (p < 0.01).NVD have beneficial effects in patients with SSc-PAH. Both DLco and SvO2 are predictors of survival and may assist in planning treatment.

Prognostic value of alveolar volume in systolic heart failure: a prospective observational study.

BACKGROUND: Ventilatory impairment is known to occur in patients with heart failure (HF). Alveolar volume (VA) is measured by the dilution of an inert gas during a single breath-hold maneuver. Such measurement is sensitive to ventilatory disturbances. We conducted a prospective, observational study to establish the prognostic value of VA in systolic HF. METHODS: We studied 260 consecutive patients who were hospitalized for systolic HF. All patients were evaluated under stable clinical conditions, before hospital discharge. Lung function studies included spirometry and determination of the lung diffusing capacity for carbon monoxide (DLCO) by the single-breath method. We also measured the cardiothoracic ratio on frontal chest radiographs, and the circulating levels of N-terminal pro-hormone of B-type natriuretic peptide (NT-proBNP). The hazard ratio (HR) of death was estimated with Cox regression, and the percentiles of survival time with Laplace regression. For survival analysis, VA was categorized as < 80% (n = 135), or ≥ 80% of the predicted value (n = 125). RESULTS: Follow-up had a median duration of 2.7 years (interquartile range, 1.1 to 4.2 years). The crude mortality rate was 27% in the whole sample, 36% in patients with VA < 80%, and 16% in those with VA ≥ 80%. The HR of death was 2.3-fold higher in patients with VA < 80% than in those with VA ≥80% (p = 0.002). After adjusting for age, New York Heart Association class III-IV, cardiothoracic ratio >0.5, NT-proBNP, persistent atrial fibrillation, DLCO, COPD comorbidity, use of beta-blockers and angiotensin converting enzyme inhibitors, the HR decreased to 1.9 but remained statistically significant (p = 0.039). Two percent of the patients with VA < 80% died about 0.9 years earlier than those with VA ≥ 80% (p = 0.033). The difference in survival time at the 20th percentile was 0.8 years. CONCLUSIONS: VA is a significant, independent predictor of reduced survival in patients with systolic HF.

Perfusion SPECT in patients with suspected pulmonary embolism.

PURPOSE: Ventilation/perfusion tomography (V/PSPECT), with new interpretation criteria and newer tracers for ventilation imaging, has markedly improved the diagnostic yield in acute pulmonary embolism (PE). Here, we evaluated the diagnostic performance of perfusion SPECT (PSPECT) without ventilation imaging. METHODS: We studied 152 patients with clinically suspected PE who had been examined with both V/PSPECT and multidetector computed tomographic angiography (MD-CTA). The diagnosis or exclusion of PE was decided by the referring clinician based on both the V/PSPECT and/or MD-CTA findings in combination with the clinical findings. PSPECT images were retrospectively examined by a physician with experience in the interpretation of planar perfusion scans who was blinded to clinical, V/PSPECT and MD-CTA data. PSPECT images were interpreted without the aid of chest radiography. All the patients who were deemed to have PE were given anticoagulant therapy. RESULTS: Of the 152 patients, 59 (39%) received a final diagnosis of PE, and 19 (32%) had associated cardiopulmonary diseases such as pneumonia, COPD, or left heart failure. PSPECT correctly identified 53 (90%) of the 59 patients with PE. The specificity was 88 of 93 (95%). None of the PSPECT images was rated nondiagnostic. PSPECT yielded an overall diagnostic accuracy of 93% (95% confidence interval, CI, 87-96%). At the observed PE prevalence of 39 %, the positive and negative predictive values of PSPECT were 91% (95% CI, 80-97%) and 94% (95% CI, 86-97%), respectively. CONCLUSION: In managing critically ill patients, PSPECT might be a valid alternative to V/PSPECT or MD-CTA since it was able to identify most patients with PE with a low false-positive rate and no inconclusive results.

A computer-aided diagnosis approach for emphysema recognition in chest radiography.

The purpose of this work is twofold: (i) to develop a CAD system for the assessment of emphysema by digital chest radiography and (ii) to test it against CT imaging. The system is based on the analysis of the shape of lung silhouette as imaged in standard chest examination. Postero-anterior and lateral views are processed to extract the contours of the lung fields automatically. Subsequently, the shape of lung silhouettes is described by polyline approximation and the computed feature-set processed by a neural network to estimate the probability of emphysema. Images of radiographic studies from 225 patients were collected and properly annotated to build an experimental dataset named EMPH. Each patient had undergone a standard two-views chest radiography and CT for diagnostic purposes. In addition, the images (247) from JSRT dataset were used to evaluate lung segmentation in postero-anterior view. System performances were assessed by: (i) analyzing the quality of the automatic segmentation of the lung silhouette against manual tracing and (ii) measuring the capabilities of emphysema recognition. As to step i, on JSRT dataset, we obtained overlap percentage (Ω) 92.7±3.3%, Dice Similarity Coefficient (DSC) 95.5±3.7% and average contour distance (ACD) 1.73±0.87 mm. On EMPH dataset we had Ω=93.1±2.9%, DSC=96.1±3.5% and ACD=1.62±0.92 mm, for the postero-anterior view, while we had Ω=94.5±4.6%, DSC=91.0±6.3% and ACD=2.22±0.86 mm, for the lateral view. As to step ii, accuracy of emphysema recognition was 95.4%, with sensitivity and specificity 94.5% and 96.1% respectively. According to experimental results our system allows reliable and inexpensive recognition of emphysema on digital chest radiography.

Risk of recurrence in patients with pulmonary embolism: predictive role of D-dimer and of residual perfusion defects on lung scintigraphy.

The stratification of recurrence risk after a first episode of venous thromboembolism (VTE) is an important topic of research, especially in patients with pulmonary embolism (PE). Elevated D-dimer levels and residual vein obstruction (RVO) at compression ultrasonography have been studied as predictors of recurrence after withdrawing oral anticoagulant treatment (OAT). It is still unknown if residual perfusion defects (PD) on lung scintigraphy are related to recurrent PE. In the present study, we evaluated the association of PD with PE recurrence. The relationship between PD, elevated D-dimer levels, and RVO was also investigated. We prospectively followed 236 consecutive patients who survived a first episode of objectively confirmed PE, with or without deep-vein thrombosis. After at least three months of OAT, treatment was withdrawn in 139 patients. D-dimer levels were evaluated at one month of OAT withdrawal, RVO was measured, and perfusion lung scan (P-scan) was performed to evaluate PD. During follow-up, 20 patients experienced a recurrent episode of VTE. Elevated D-dimer levels were significantly associated with VTE recurrence, (p=0.003). RVO was present in 22% of the patients with recurrence and in 7.5% of those without (p=0.07). No significant association was found between PD >10% and VTE recurrence, D-dimer, or RVO. In conclusion, we confirmed the positive predictive value of elevated D-dimer levels for recurrent VTE. Residual PD on lung scintigraphy are neither predictive of recurrence nor related to D-dimer levels or RVO.

Effects of emphysema on oxygen uptake during maximal exercise in COPD.

The objective of the study is to assess the effects of emphysema on peak oxygen uptake ([Formula: see text]) during a cardiopulmonary exercise test in patients with chronic obstructive pulmonary disease (COPD). We measured [Formula: see text] and oxygen pulse in 80 patients with stable COPD exercising maximally. Oxygen saturation was measured by pulse oximetry (SpO(2)), and the ventilatory response assessed by the ratio of tidal volume (V (T)) at peak to slow vital capacity (SVC) at baseline, and by the percent increase of peak V (T) over baseline. Computed tomography imaging (CT scan) served as the reference diagnostic standard for emphysema. Based on the panel-grading (PG) method, emphysema was rated absent or mild (PG ≤ 30, n = 54), or moderate to severe (PG > 30, n = 26). Multiple quantile regression was applied to estimate the effects of PG > 30 on [Formula: see text]. At peak exercise, the patients with PG > 30 had significantly lower [Formula: see text], oxygen pulse and SpO(2), and featured a blunted ventilatory response with respect to those with PG ≤ 30 (p < 0.001). With multiple quantile regression, the effects of PG > 30 on [Formula: see text] were only partially explained by the degree of lung hyperinflation, a substantial component being imputable to impairment of lung diffusing capacity. In conclusion, chronic obstructive pulmonary disease patients with moderate to severe emphysema feature significantly lower exercise tolerance than those with no or mild emphysema. Our findings underscore the need of tailoring therapeutic interventions for COPD to the predominant clinical phenotype to improve exercise capacity.

The value of tomographic ventilation/perfusion scintigraphy (V/PSPECT) for follow-up and prediction of recurrence in pulmonary embolism.

BACKGROUND: Pulmonary embolism (PE) is diagnosed with imaging techniques such as ventilation/perfusion (V/P) lung scintigraphy or multidetector computed tomography of the pulmonary arteries (MDCT). Lung scintigraphy can be performed with planar (V/P PLANAR) and tomographic (V/P SPECT) techniques. V/P SPECT has higher sensitivity and specificity than V/P PLANAR. As nephrotoxic contrast media are not used during V/P SPECT, examinations can be repeated for evaluation of resolution of perfusion defects after PE. However, the value of residual perfusion defects identified using V/P SPECT for the prediction of recurrent PE has not been thoroughly evaluated. MATERIAL AND METHODS: We evaluated resolution and recurrence of PE in 227 patients (mean age 63 ± 17 years, 134[59%] women) with PE undergoing ≥ 2 SPECT examinations in 2005-2007. PE was defined as minor (<20% perfusion defect on SPECT, n=86), medium (20-50% perfusion defect on SPECT, n=99), or major (>50% perfusion defect on SPECT, n=42). RESULTS: At second V/P SPECT examination, complete resolution of perfusion defects had occurred in 45 (52%) patients with minor PE after 8.2 ± 7.4 months, in 29 (29%) of patients with medium PE after 6.2 ± 5.9 months, and in 2(5%) of patients with major PE after 6.5 ± 0.7 months. During 47 ± 24 months of follow up, 37(16 %) patients suffered recurrent PE. Of these 37, 34 (92%) showed residual perfusion defects at the second V/P SPECT examination. Recurrence of PE was also predicted by advanced age and female gender. However, in multivariate regression analysis, recurrence was only predicted by age (p=0.0013) and residual perfusion defect on V/P SPECT (p=0.0039). CONCLUSION: In conclusion, complete resolution of PE was common in patients with minor PE, whereas residual perfusion defects were widespread in patients with medium and major PE. PE patients identified with persistent perfusion defects at follow-up SPECT have a high risk of PE recurrence.