Prognostic value of pulmonary diffusing capacity for carbon monoxide and ventilation-perfusion SPECT findings in pulmonary arterial hypertension.

Reduced pulmonary diffusing capacity for carbon monoxide (DLCO) can be observed in pulmonary arterial hypertension (PAH) and associates with increased mortality. However, the prognostic value of DLCO when corrected for haemoglobin (DLCOc), an independent modifier of DLCO, remains understudied. Additionally, the prognostic role of ventilation (V)-perfusion (Q) emission computed tomography (V/Q SPECT) findings in patients with PAH, which may concurrently be performed to rule out chronic thromboembolic pulmonary hypertension, is uncertain. A retrospective cohort study was conducted on 152 patients with PAH referred to a tertiary hospital for evaluation from January 2011 to January 2020. Lung function tests, clinical data and V/Q SPECT were ascertained. Cox regression analysis was performed to evaluate the association between DLCOc, DLCO and V/Q SPECT defects at referral with all-cause mortality. In equally adjusted Cox regression analysis, each percentage increase in DLCOc % predicted (%pred) (hazard ratio (HR) 0.97; 95% CI: 0.94-0.99) and DLCO%pred (HR 0.97; 95% CI: 0.94-0.99) was similarly associated with all-cause mortality. There was no detectable difference in area under the curve for prediction of all-cause mortality by DLCOc%pred and DLCO%pred (C-index 0.71 and 0.72, respectively, P = 0.85 for difference). None of the defects noted on V/Q SPECT were significantly associated with mortality, but mismatched defects were associated with lower values of DLCOc%pred and DLCO%pred. DLCOc%pred and DLCO%pred perform equally as prognostic markers in PAH, supporting the use of either metric when available for prognostic stratification.

A systematic literature review and meta-analysis of spectral CT compared to scintigraphy in the diagnosis of acute and chronic pulmonary embolisms.

PURPOSE: To examine the diagnostic accuracy of spectral CT pulmonary angiography (S-CTPA) using ventilation-perfusions lung scintigraphy (V/Q-scan) as a reference standard in the diagnosis of acute or chronic pulmonary embolism (APE/CPE) and chronic thromboembolic pulmonary hypertension (CTEPH). METHODS: PubMed, Embase, Scopus, and Web of Science were searched for the period from 1 Jan 2006 to 7 Feb 2019; eligible studies had > 10 patients over 18 years old, a diagnostic outcome of PE or CTEPH, and used V/Q scan as a reference standard. Bias and applicability were assessed using QUADAS-2 tools. Sensitivities, specificities, and predictive values were noted or calculated from available information. Meta-analysis employed a fixed-effects model of Mantel and Haenszel. Heterogeneity was assessed with I-squared statistics. RESULTS: Four hundred ninety-three unique records were identified. Following screening by title, 53 studies were included in the abstract and full-text assessment. A total of six articles were included; four were suitable for a meta-analysis. Pooled sensitivity was 94.2% (95% CI, 88.3-100%), pooled specificity was 88.5% (95% CI, 81.3-95.6%), and positive and negative predictive values were 87.8% (95% CI, 80.3-95.4%) and 94.5% (95% CI, 89.3-99.7%), respectively. CONCLUSION: Data on S-CTPA for PE/CTEPH remains promising, but limited; only small studies with methodological issues are available. Evidence is best for CPE/CTEPH whereas no firm conclusions are possible for APE. There is a need for larger, prospective studies with a robust composite reference standard including state-of-the-art CTPA and V/Q-scans. KEY POINTS: • S-CTPA has high sensitivity and specificity for perfusion defects in patients with PE or CPETH. • Methodological issues and diversity of reference standards were found in the small number of included studies. • There is a need for larger prospective studies with more robust composite reference standards.

Data-driven respiratory gating for ventilation/perfusion lung scan.

BACKGROUND: Ventilation/perfusion lung scan is subject to blur due to respiratory motion whether with planar acquisition or single photon emission computed tomography (SPECT). We propose a data-driven gating method for extracting different respiratory phases from lung scan list-mode or dynamic data. METHODS: The algorithm derives a surrogate respiratory signal from an automatically detected diaphragmatic region of interest. The time activity curve generated is then filtered using a Savitzky-Golay filter. We tested this method on an oscillating phantom in order to evaluate motion blur decrease and on one lung SPECT. RESULTS: Our algorithm reduced motion blur on phantom acquisition: mean full width at half maximum 8.1 pixels on non-gated acquisition versus 5.3 pixels on gated acquisition and 4.1 pixels on reference image. Automated detection of the diaphragmatic region and time-activity curves generation were successful on patient acquisition. CONCLUSIONS: This algorithm is compatible with a clinical use considering its runtime. Further studies will be needed in order to validate this method.

Lobar Quantification by Ventilation/Perfusion SPECT/CT in Patients with Severe Emphysema Undergoing Lung Volume Reduction with Endobronchial Valves.

BACKGROUND: Endoscopic lung volume reduction (ELVR) therapy using one-way valves is used to treat chronic obstructive pulmonary disease patients with severe heterogeneous emphysema. A successful treatment results in atelectasis of the treated pulmonary lobe with subsequent reduction of ventilation (V) and perfusion (Q). OBJECTIVE: We evaluated the effects of ELVR on the targeted lobe using a new 3-dimensional ventilation and perfusion (V/Q) single-photon emission computed tomography (SPECT)/computed tomography (CT) analysis, which allows for simultaneous semi-automatic lobar pulmonary quantification of volume, ventilation and perfusion, on the first consecutive patients treated with ELVR at Rigshospitalet, Denmark. V/Q planar scintigraphy and V/Q SPECT/CT and lung function measurements were performed before and 6 months after intervention. RESULTS: We included 24 subjects (60 years, range 46-74 years; 37.5% men) with a baseline FEV1 of 25% predicted and RV of 257% predicted. V/Q SPECT/CT-assessed volume of the targeted lobe decreased by a mean of -395 mL and a relative mean of -26.8%, whilst ventilation and perfusion decreased by a relative mean of -37.1 and -25.7%. There was a significant increase in the same parameters of the non-targeted lobe(s) on the ipsilateral side. None of these changes were found in the analysis of planar V/Q imaging. The total lung volume decreased on average by -420 mL. Six months after ELVR, FEV1 had increased by 22%. Significant correlations were found between changes in FEV1 and changes in the volume of the treated lobe (SPECT/CT). CONCLUSION: Semi-automatic SPECT/CT analysis can quantify volume, ventilation and perfusion changes in pulmonary lobes and may be used in the assessment of patient eligibility for ELVR, identifying target lobes, and evaluation of the regional effects of treatment.

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.

Comparison of three diagnostic strategies for suspicion of pulmonary embolism: planar ventilation-perfusion scan (V/Q), CT pulmonary angiography (CTPA) and single photon emission CT ventilation-perfusion scan (SPECT V/Q): a protocol of a randomised controlled trial.

INTRODUCTION: Pulmonary embolism (PE) is a challenge to diagnose and when missed, exposes patients to potentially fatal recurrent events. Beyond CT pulmonary angiography (CTPA) and planar ventilation/perfusion (V/Q) scan, single photon emission CT (SPECT) V/Q emerged a new diagnostic modality of scintigraphic acquisition that has been reported to improve diagnostic performances. To date, no management outcome study or randomised trial evaluated an algorithm based on SPECT V/Q for PE diagnosis. We present the design of a randomised multicentre, international management study comparing SPECT V/Q with validated strategies. MATERIAL AND METHODS: We will include a total of 3672 patients with suspected PE requiring chest imaging, randomised into three different groups, each using a different diagnostic strategy based on SPECT V/Q, CTPA and planar V/Q scan. Randomisation will be unbalanced (2:1:1), with twice as many patients in SPECT V/Q arm (n=1836) as in CTPA and planar V/Q arms (n=918 in each). Our primary objective will be to determine whether a diagnostic strategy based on SPECT V/Q is non-inferior to previously validated strategies in terms of diagnostic exclusion safety as assessed by the 3-month risk of thromboembolism in patients with a negative diagnostic workup. Secondary outcomes will be the proportion of patients diagnosed with PE in each arm, patients requiring additional tests, the incidence of major and clinically relevant non-major bleeding and the incidence and cause of death in each arm. ETHICS AND DISSEMINATION: This trial is funded by a grant from Brest University Hospital and by INVENT. The study protocol was approved by Biomedical Research Ethics Committee. The investigator or delegate will obtain signed informed consent from all patients prior to inclusion in the trial. Our results will inform future clinical practice guidelines and solve the current discrepancy between nuclear medicine guidelines and clinical scientific society guidelines. TRIAL REGISTRATION NUMBER: NCT02983760.

Pilot study for comparative assessment of dual-energy computed tomography and single-photon emission computed tomography V/Q scanning for lung perfusion evaluation in infants.

OBJECTIVE: To evaluate clinical applications of dual-energy computed tomography (DECT) in pediatric-specific lung diseases and compare ventilation and perfusion findings with those from single-photon emission computed tomography (SPECT-CT) V/Q. METHODS: All patients at our institution who underwent exams using both techniques within a 3-month period were included in this study. Two readers independently described findings for DECT, and two other readers independently analyzed the SPECT-CT V/Q scan data. All findings were compared between readers and disagreements were reassessed and resolved by consensus. Inter-modality agreements are described throughout this study. RESULTS: Eight patients were included for evaluation. The median age for DECT scanning was 3.5 months (IQR = 2). Five of these patients were scanned for both DECT and SPECT-CT V/Q studies the same day, and three had a time gap of 7, 65, and 94 days between studies. The most common indications were chronic lung disease (5/8; 63%) and pulmonary hypertension (6/8; 75%). DECT and SPECT-CT V/Q identified perfusion abnormalities in concordant lobes in most patients (7/8; 88%). In one case, atelectasis limited DECT perfusion assessment. Three patients ultimately underwent lobectomy with corresponding perfusion abnormalities identified by all reviewers on both DECT and SPECT-CT V/Q in all resected lobes. CONCLUSION: DECT is a feasible technique that could be considered as an alternative for SPECT-CT V/Q for lung perfusion evaluation in infants.

Non-invasive assessment of intrapulmonary shunt and ventilation to perfusion ratio in children with hepatopulmonary syndrome before and after liver transplantation.

OBJECTIVES: To use the oxyhaemoglobin dissociation curve (ODC) to non-invasively measure the ventilation perfusion ratio (VA/Q) and right-to-left intrapulmonary vascular shunt before and after liver transplantation (LT) in children with hepatopulmonary syndrome (HPS). To investigate whether the right-to-left shunt derived by ODC correlated with the shunt derived by technetium-99 labelled macroaggregated albumin lung perfusion scan (MAA). METHODS: A retrospective cohort study at King's College Hospital NHS Foundation Trust, London, UK was performed between 1998 and 2016. The VA/Q and right-to-left shunt were non-invasively measured pre and post LT. The pre-LT right-to-left intrapulmonary shunt was also measured by MAA. The non-invasively derived pre-LT shunt was correlated with the shunt derived by MAA. RESULTS: Fifteen children with HPS were studied with a median (IQR) age at LT of 8.8 (6.6-12.9) years. The median (IQR) pre-LT VA/Q [0.49 (0.42-0.65)] was lower compared to the post-LT VA/Q [0.61 (IQR 0.54-0.72), p = 0.012]. The median (IQR) pre-LT shunt was 19 (3-24) % which decreased to zero in all but one children post-LT, (p = 0.001). The MAA-derived shunt was significantly positively correlated with the ODC-derived shunt (r = 0.783, p = 0.001). The mean (SD) difference between shunt derived by ODC and shunt derived by MAA was 0.5 (7.2) %. CONCLUSIONS: Ventilation/perfusion impairment reverses but not completely resolves after liver transplantation in children with hepatopulmonary syndrome. The non-invasive method for estimating intrapulmonary shunting could be used as an alternative to the macroaggregated albumin scan in this population.

Beyond the clot: perfusion imaging of the pulmonary vasculature after COVID-19.

A compelling body of evidence points to pulmonary thrombosis and thromboembolism as a key feature of COVID-19. As the pandemic spread across the globe over the past few months, a timely call to arms was issued by a team of clinicians to consider the prospect of long-lasting pulmonary fibrotic damage and plan for structured follow-up. However, the component of post-thrombotic sequelae has been less widely considered. Although the long-term outcomes of COVID-19 are not known, should pulmonary vascular sequelae prove to be clinically significant, these have the potential to become a public health problem. In this Personal View, we propose a proactive follow-up strategy to evaluate residual clot burden, small vessel injury, and potential haemodynamic sequelae. A nuanced and physiological approach to follow-up imaging that looks beyond the clot, at the state of perfusion of lung tissue, is proposed as a key triage tool, with the potential to inform therapeutic strategies.

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

BACKGROUND: Many patients with pulmonary embolism (PE) report dyspnea on exertion following long-term treatment. Increased physiological dead space proportion (VD/VT) and decreased cardiac stroke volume reserve may distinguish persistent effects of PE itself from symptoms reflecting comorbid conditions or deconditioning. METHODS: This retrospective study analyzed a consecutive series of incremental symptom-limited cardiopulmonary exercise tests that had been ordered to evaluate persistent dyspnea on exertion following long-term treatment for acute PE. Physiological VD/VT was determined at anaerobic threshold from exhaled CO2 and transcutaneous Pco2 (validated against Paco2 measurements). Cardiac stroke volume reserve was estimated at rest and at anaerobic threshold by using oxygen consumption/pulse and previously validated estimates of the arteriovenous oxygen content difference. RESULTS: Cardiopulmonary exercise tests were performed on 40 patients with post-PE dyspnea. In 65.0% (95% CI, 50.2-79.8), VD/VT at anaerobic threshold was abnormally elevated, stroke volume reserve was decreased, or both defects occurred. VD/VT at anaerobic threshold was abnormally elevated (≥ 0.27) in 35.0% (95% CI, 20.2-49.8). VD/VT at anaerobic threshold significantly correlated with the extent of unmatched perfusion defects on subsequent ventilation-perfusion scans (P = .0085). In 55.0% (95% CI, 39.6-70.4), stroke volume reserve at anaerobic threshold was abnormally decreased (≤ 128% of the resting value). Both defects were present in 25.0% (95% CI, 11.6-38.4). CONCLUSIONS: Increased VD/VT at anaerobic threshold and decreased stroke volume reserve during exercise are common among patients with dyspnea on exertion after long-term treatment of PE. The defects can be disclosed noninvasively by using cardiopulmonary exercise testing.

Trends in Imaging for Suspected Pulmonary Embolism Across US Health Care Systems, 2004 to 2016.

Importance: In response to calls to reduce unnecessary diagnostic testing with computed tomographic pulmonary angiography (CTPA) for suspected pulmonary embolism (PE), there have been growing efforts to create and implement decision rules for PE testing. It is unclear if the use of advanced imaging tests for PE has diminished over time. Objective: To assess the use of advanced imaging tests, including chest computed tomography (CT) (ie, all chest CT except for CTPA), CTPA, and ventilation-perfusion (V/Q) scan, for PE from 2004 to 2016. Design, Setting, and Participants: Cohort study of adults by age group (18-64 years and ≥65 years) enrolled in 7 US integrated and mixed-model health care systems. Joinpoint regression analysis was used to identify years with statistically significant changes in imaging rates and to calculate average annual percentage change (growth) from 2004 to 2007, 2008 to 2011, and 2012 to 2016. Analyses were conducted between June 11, 2019, and March 18, 2020. Main Outcomes and Measures: Rates of chest CT, CTPA, and V/Q scan by year and age, as well as annual change in rates over time. Results: Overall, 3.6 to 4.8 million enrollees were included each year of the study, for a total of 52 343 517 person-years of follow-up data. Adults aged 18 to 64 years accounted for 42 223 712 person-years (80.7%) and those 65 years or older accounted for 10 119 805 person-years (19.3%). Female enrollees accounted for 27 712 571 person-years (52.9%). From 2004 and 2016, chest CT use increased by 66.3% (average annual growth, 4.4% per year), CTPA use increased by 450.0% (average annual growth, 16.3% per year), and V/Q scan use decreased by 47.1% (decreasing by 4.9% per year). The use of CTPA increased most rapidly from 2004 to 2006 (44.6% in those aged 18-64 years and 43.9% in those ≥65 years), with ongoing rapid growth from 2006 to 2010 (annual growth, 19.8% in those aged 18-64 years and 18.3% in those ≥65 years) and persistent but slower growth in the most recent years (annual growth, 4.3% in those aged 18-64 years and 3.0% in those ≥65 years from 2010 to 2016). The use of V/Q scanning decreased steadily since 2004. Conclusions and Relevance: From 2004 to 2016, rates of chest CT and CTPA for suspected PE continued to increase among adults but at a slower pace in more contemporary years. Efforts to combat overuse have not been completely successful as reflected by ongoing growth, rather than decline, of chest CT use. Whether the observed imaging use was appropriate or was associated with improved patient outcomes is unknown.

PET/CT Lung Ventilation and Perfusion Scanning using Galligas and Gallium-68-MAA.

Ventilation/Perfusion (V/Q) positron emission tomography computed tomography (PET/CT) is now possible by substituting Technetium-99m (99mTc) with Gallium-68 (68Ga), using the same carrier molecules as conventional V/Q imaging. Ventilation imaging can be performed with 68Ga-carbon nanoparticles using the same synthesis device as Technegas. Perfusion imaging can be performed with 68Ga-macroaggregated albumin. Similar physiological processes can therefore be evaluated by either V/Q SPECT/CT or PET/CT. However, V/Q PET/CT is inherently a superior technology for image acquisition, with higher sensitivity, higher spatial and temporal resolution, and superior quantitative capability, allowing more accurate delineation and quantification of regional lung function. Additional advantages include reduced acquisition time, respiratory-gated acquisition, and a lower impact on human resources. V/Q PET imaging offers an opportunity to improve the accuracy and utility of V/Q imaging in various pulmonary conditions. For pulmonary embolism, V/Q PET/CT scan may improve the diagnostic performance of the test owing to a better characterization of the pattern of defects and allow an accurate quantification of the extent of vascular obstruction. Establishing an accurate functional map of the regional ventilation and perfusion in the lungs may be relevant in many other clinical situations, including preoperative assessment of the lung cancer patients, radiotherapy planning, or presurgical evaluation of patients undergoing lung volume reduction surgery.

Ventilation/Perfusion SPECT Imaging-Diagnosing Other Cardiopulmonary Diseases Beyond Pulmonary Embolism.

Ventilation/perfusion single-photon emission computed tomography (V/P SPECT) is the scintigraphic technique recommended primarily for the diagnosis of acute pulmonary embolism (PE) and is golden standard for the diagnosis of chronic PE. Furthermore, interpreting ventilation and corresponding perfusion images enables pattern recognition of many other cardiopulmonary disorders that affect lung function and also allows quantification of their extent. Using Technegas for the ventilation imaging, grading of small airway disease in COPD is possible and the method is recommended for PE diagnosis in patients with severe COPD that is not possible with radiolabelled liquid aerosols. An optimal combination of nuclide activities, acquisition times for ventilation and perfusion, collimators, and imaging matrix yields an adequate V/P SPECT study in approximately 20 minutes of imaging time. The holistic interpretation strategy of V/P SPECT uses all relevant information about the patient and ventilation/perfusion patterns. PE is diagnosed when there is more than one subsegment showing a V/P mismatch representing an anatomic lung unit. Apart from PE, other pathologies should be identified and reported, such as obstructive lung disease, heart failure, and pneumonia according to the European Association of Nuclear Medicine guidelines.

CTPA, DECT, MRI, V/Q Scan, and SPECT/CT V/Q for the noninvasive diagnosis of chronic thromboembolic pulmonary hypertension: A protocol for systemic review and network meta-analysis of diagnostic test accuracy.

BACKGROUND: To determine the diagnostic accuracy of techniques with chronic thromboembolic pulmonary hypertension (CTEPH) patients via a protocol for systemic review and network meta-analysis. METHODS: We will search PubMed, EMBASE, Web of Science, and Google Scholar from inception to October 1, 2018. The reference lists of the retrieved articles are also consulted. Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) will be used to assess the risk of bias in each study. The direct meta-analyses, network meta-analyses, and ranking of competing diagnostic tests will be used by STATA 12.0 and WINBUGS 1.4. Heterogeneity and inconsistency are assessed. RESULTS: This study is ongoing, will be submitted to a peer-reviewed journal publication once completed. CONCLUSION: This study will provide a comprehensive evidence summary of diagnostic test accuracy in detecting the CTEPH, and can help patients and clinicians to select appropriate or best diagnostic test. ETHICS AND COMMUNICATION: No ethical approval and patient consent are required, because it is based on published researches. PROSPERO REGISTRATION NUMBER: CRD42019121279.

Lung Ventilation/Perfusion Single Photon Emission Computed Tomography (SPECT) in Infants and Children with Nonembolic Chronic Pulmonary Disorders.

Single photon emission computed tomography (SPECT) provides high contrast three dimensional images of the regional distribution of a radiotracer. SPECT is a widely used technique in pulmonary investigations of the ventilation (V) and perfusion (Q) in the adult patient, mainly in the diagnosis of pulmonary embolism. However, safety concerns among practitioners due to radiation exposure and the use of macroaggregate albumin for the perfusion scan have historically precluded the use of SPECT in pediatric patients with nonembolic pulmonary disorders. Additionally, patient cooperation at ventilation tracer administration and image artifacts from patient movements due the long acquisition times, have further limited the application of SPECT in pediatric patients. With the introduction of technegas aerosol for ventilation studies and the use of high sensitive multihead gamma cameras, both the total amount of administered activity and acquisition time have drastically been reduced allowing the application of SPECT in pediatric patients. Modern hybrid gamma camera/computed tomography systems (SPECT/CT) also brings the possibility of adding a fully diagnostic CT to the SPECT images, incrementing the clinical value of the investigation. Besides pulmonary embolism, there is now some clinical evidence that lung SPECT has diagnostic value in several pulmonary pathologies causing V/Q mismatching, which are specific to the pediatric age group. In this work, we will exemplify and briefly discuss some of these applications based on the literature and our routine clinical experience. Consideration to the risks and safety aspects associated to performing pediatric V/Q SPECT are also discussed.

Assessment of the Reconstructed Pulmonary Circulation With Lung Perfusion Scintigraphy After Unifocalization and Repair of Tetralogy of Fallot With Major Aortopulmonary Collaterals.

BACKGROUND: Pulmonary vascular supply in tetralogy of Fallot (TOF) with major aortopulmonary collaterals (MAPCAs) is highly variable. Our approach to surgical management of this condition emphasizes early repair including unifocalization and reconstruction of the pulmonary circulation, incorporating all lung segments and addressing stenoses both proximal to and within the lung, in addition to ventricular septal defect closure. At our institution, we have over 15 years of experience using lung perfusion scintigraphy (LPS) to assess the distribution of pulmonary blood flow after complete unifocalization and repair. METHODS: We reviewed clinical and quantitative LPS data in 310 patients who underwent complete unifocalization and repair of TOF/MAPCAs from 2003 to 2018 at our institution. Postrepair relative lung perfusion distributions were determined from LPS initially obtained at our institution within 60 days after repair and thereafter. RESULTS: Total lung perfusion to the right and left lungs was 58.0% ± 14.2% and 42.0% ± 14.2%, respectively. Perfusion was balanced in 75% of patients and unbalanced in 25%, including 11% in whom it was extremely unbalanced. On multivariable analysis, older age at repair, surgery other than a single-stage complete unifocalization, and native anatomy consisting of unilateral pulmonary blood supply through a ductus arteriosus were associated with unbalanced perfusion. CONCLUSION: We present our experience using LPS as an outcome measure after surgical repair of TOF/MAPCAs. Balanced lung perfusion was present in the majority of patients who had complete repair of TOF/MAPCAs performed at our center.