Lung Perfusion Imaging Research Articles

Image quality of lung perfusion with photon-counting-detector CT: comparison with dual-source, dual-energy CT.

To evaluate the quality of lung perfusion imaging obtained with photon-counting-detector CT (PCD-CT) in comparison with dual-source, dual-energy CT (DECT). Seventy-one consecutive patients scanned with PCD-CT were compared to a paired population scanned with dual-energy on a 3rd-generation DS-CT scanner using (a) for DS-CT (Group 1): collimation: 64 × 0.6 × 2 mm; pitch: 0.55; (b) for PCD-CT (Group 2): collimation: 144 × 0.4 mm; pitch: 1.5; single-source acquisition. The injection protocol was similar in both groups with the reconstruction of perfusion images by subtraction of high- and low-energy virtual monoenergetic images. Compared to Group 1, Group 2 examinations showed: (a) a shorter duration of data acquisition (0.93 ± 0.1 s vs 3.98 ± 0.35 s; p < 0.0001); (b) a significantly lower dose-length-product (172.6 ± 55.14 vs 339.4 ± 75.64 mGy·cm; p < 0.0001); and (c) a higher level of objective noise (p < 0.0001) on mediastinal images. On perfusion images: (a) the mean level of attenuation did not differ (p = 0.05) with less subjective image noise in Group 2 (p = 0.049); (b) the distribution of scores of fissure visualization differed between the 2 groups (p < 0.0001) with a higher proportion of fissures sharply delineated in Group 2 (n = 60; 84.5% vs n = 26; 26.6%); (c) the rating of cardiac motion artifacts differed between the 2 groups (p < 0.0001) with a predominance of examinations rated with mild artifacts in Group 2 (n = 69; 97.2%) while the most Group 1 examinations showed moderate artifacts (n = 52; 73.2%). PCD-CT acquisitions provided similar morphologic image quality and superior perfusion imaging at lower radiation doses. The improvement in the overall quality of perfusion images at lower radiation doses opens the door for wider applications of lung perfusion imaging in clinical practice. The speed of data acquisition with PCD-CT accounts for mild motion artifacts. Sharply delineated fissures are depicted on PCD-CT perfusion images. High-quality perfusion imaging was obtained with a 52% dose reduction.

Imaging the pulmonary vasculature in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized by a redistribution of regional lung perfusion that impairs gas exchange. While speculative, experimental evidence suggests that perfusion redistribution may contribute to regional inflammation and modify disease progression. Unfortunately, tools to visualize and quantify lung perfusion in patients with ARDS are lacking. This review explores recent advances in perfusion imaging techniques that aim to understand the pulmonary circulation in ARDS. Dynamic contrast-enhanced computed tomography captures first-pass kinetics of intravenously injected dye during continuous scan acquisitions. Different contrast characteristics and kinetic modeling have improved its topographic measurement of pulmonary perfusion with high spatial and temporal resolution. Dual-energy computed tomography can map the pulmonary blood volume of the whole lung with limited radiation exposure, enabling its application in clinical research. Electrical impedance tomography can obtain serial topographic assessments of perfusion at the bedside in response to treatments such as inhaled nitric oxide and prone position. Ongoing technological improvements and emerging techniques will enhance lung perfusion imaging and aid its incorporation into the care of patients with ARDS.

Magnetic Resonance Imaging of Lung Perfusion.

"Lung perfusion" in the context of imaging conventionally refers to the delivery of blood to the pulmonary capillary bed through the pulmonary arteries originating from the right ventricle required for oxygenation. The most important physiological mechanism in the context of imaging is the so-called hypoxic pulmonary vasoconstriction (HPV, also known as "Euler-Liljestrand-Reflex"), which couples lung perfusion to lung ventilation. In obstructive airway diseases such as asthma, chronic-obstructive pulmonary disease (COPD), cystic fibrosis (CF), and asthma, HPV downregulates pulmonary perfusion in order to redistribute blood flow to functional lung areas in order to conserve optimal oxygenation. Imaging of lung perfusion can be seen as a reflection of lung ventilation in obstructive airway diseases. Other conditions that primarily affect lung perfusion are pulmonary vascular diseases, pulmonary hypertension, or (chronic) pulmonary embolism, which also lead to inhomogeneity in pulmonary capillary blood distribution. Several magnetic resonance imaging (MRI) techniques either dependent on exogenous contrast materials, exploiting periodical lung signal variations with cardiac action, or relying on intrinsic lung voxel attributes have been demonstrated to visualize lung perfusion. Additional post-processing may add temporal information and provide quantitative information related to blood flow. The most widely used and robust technique, dynamic-contrast enhanced MRI, is available in clinical routine assessment of COPD, CF, and pulmonary vascular disease. Non-contrast techniques are important research tools currently requiring clinical validation and cross-correlation in the absence of a viable standard of reference. First data on many of these techniques in the context of observational studies assessing therapy effects have just become available. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 5.

3D-Quantitated Single Photon Emission Computed Tomography/Computed Tomography: Impact on intended Management Compared to Lung Perfusion Scan in Marginal Candidates for Pulmonary Resection

ObjectivesBased on previous studies, single-photon emission computed tomography/computed tomography (SPECT/CT) has been proven more accurate and reproducible than planar lung perfusion scintigraphy to assess lobar perfusion. However, the impact of 3D-quantitated SPECT/CT on intended management in functionally marginal candidates for pulmonary resection is unknown. The evaluation of this impact was the main aim of this study. MethodsConsecutive candidates for lung resection underwent preoperative evaluation according to ERS/ESTS Algorithm and underwent preoperative lung perfusion imaging. The lobar contribution to the total lung perfusion was estimated using established planar scintigraphic methods and 3-dimensional quantitative SPECT/CT method (CT Pulmo3D and xSPECT-Quant, Siemens). The difference in estimated lobar perfusion with resulting changes in predicted postoperative (ppo) lung function and extent of lung resection were analyzed to reveal possible changes in operability. In-hospital outcome was assessed. ResultsOne hundred twenty patients (46 females) were enrolled. The mean age (±SD) of patients was 68 ± 9 years, target lesions were in upper lobes in 57.7% and in lower lobes in 33.5%. The median FEV1 (forced expiratory volume in 1 second) was 70.5% (IQR 52-84) and median DLCO (diffusion capacity of lung for carbon monoxide) was 56.6% [47.1-67.4]. The planar posterior oblique method, compared to 3D-quantitated SPECT/CT, underestimated the perfusion of upper lobes by a median difference of 5% (right [2-9], left [2.5-8]; P = <.0001), while it overestimated the perfusion of lower lobes (left by 4% [2-7], right by 6% [2-9]; P = <.0001). In contrast to planar scintigraphy-based evaluation, 4 patients (3.3%), all with upper lobe lesions, were classified as inoperable when 3D-quantitated SPECT/CT was used for calculation of the ppo lung function. ConclusionsIn selected patients with upper lobe lesions, 3D-quantitated SPECT/CT would have changed the treatment strategy from operable to inoperable. Importantly, postoperative mortality in this particular subgroup was disproportionally high. 3D-quantitated SPECT/CT shall be further evaluated as it might improve preoperative risk stratification in functionally marginal candidates.

Ultra-High-Resolution Photon-Counting CT Imaging of the Chest: A New Era for Morphology and Function.

After a decade of preclinical testing, photon-counting computed tomography (PCCT) has now entered daily routine, enabling radiologists to start investigating thoracic disorders in unprecedented conditions. The improved spatial resolution of the ultra-high-resolution (UHR) scanning mode is a major step for the analysis of bronchopulmonary disorders, making abnormalities at the level of small anatomical structures such as secondary pulmonary lobules accessible to radiologists. Distal divisions of pulmonary and systemic vessels also benefit from UHR protocols as alterations of lung microcirculation were previously excluded from confident analysis with energy-integrating detector CT. Although noncontrast chest CT examinations were the initial target of UHR protocols, the clinical value of this mode is also applicable to chest CT angiographic examinations with improved morphological evaluation and higher-quality lung perfusion imaging. The clinical benefits of UHR have been evaluated in initial studies, allowing radiologists to foresee the field of future applications, all combining high diagnostic value and radiation dose reduction. The purpose of this article is to highlight the technological information relevant to daily practice and to review the current clinical applications in the field of chest imaging.

Comparison of dual-energy CT with positron emission tomography for lung perfusion imaging in patients with non-small cell lung cancer

Objective. Functional lung avoidance (FLA) radiotherapy treatment aims to spare lung regions identified as functional from imaging. Perfusion contributes to lung function and can be measured from the determination of pulmonary blood volume (PBV). An advantageous alternative to the current determination of PBV from positron emission tomography (PET) may be from dual energy CT (DECT), due to shorter examination time and widespread availability. This study aims to determine the correlation between PBV determined from DECT and PET in the context of FLA radiotherapy. Approach. DECT and PET acquisitions at baseline of patients enrolled in the HI-FIVE clinical trial (ID: NCT03569072) were reviewed. Determination of PBV from PET imaging (), from DECT imaging generated from a commercial software (Syngo.via, Siemens Healthineers, Forchheim, Germany) with its lowest () and highest () smoothing level parameter value (R), and from a two-material decomposition (TMD) method () with variable median filter kernel size (L) were compared. Deformable image registration between DECT images and the CT component of the PET/CT was applied to PBV maps before resampling to the PET resolution. The Spearman correlation coefficient (r s) between PBV determinations was calculated voxel-wise in lung subvolumes. Main results. Of this cohort of 19 patients, 17 had a DECT acquisition at baseline. PBV maps determined from the commercial software and the TMD method were very strongly correlated [r s( ) = 0.94 ± 0.01 and r s( ) = 0.94 ± 0.02]. was strongly correlated with [r s( ) = 0.67 ± 0.11]. Perfusion patterns differed along the posterior-anterior direction [r s( ) = 0.77 ± 0.13/0.57 ± 0.16 in the anterior/posterior region]. Significance. A strong correlation between DECT and PET determination of PBV was observed. Streak and smoothing effects in DECT and gravitational artefacts and misregistration in PET reduced the correlation posteriorly.

Dual-energy computed tomography pulmonary angiography with ultra-low dose contrast administration: Comparison of image quality with standard computed tomography pulmonary angiography.

This study aims to compare quantitative and qualitative image quality between standard computed tomography pulmonary angiography and dual-energy computed tomography pulmonary angiography protocols. Between September 2017 and August 2018, a total of 91 consecutive patients (34 males, 57 females; mean age: 65.9±15 years; range, 37 to 91 years) who were referred for computed tomography pulmonary angiography were randomly imaged with either a standard or dual-energy protocol. Standard protocol (n=49) was acquired with a 64-slice multidetector computed tomography scanner using 60 mL contrast media (18 g iodine). A third-generation dual-energy computed tomography scanner was utilized to acquire dual-energy computed tomography pulmonary angiography and simultaneous lung perfusion imaging (n=42), which required 40 mL contrast media (12 g iodine). Two radiologists reviewed images separately to determine interobserver variability. Attenuation and noise in three central and two segmental pulmonary arteries were measured; signal-to-noise ratio and contrast-to-noise ratio were calculated. A five-point scale was utilized to evaluate image quality and image noise qualitatively. The standard protocol required a significantly higher amount of iodine. Comparison of two groups employing quantitative measurements (attenuation value in five pulmonary arteries, mean attenuation value, mean background noise, signal-to-noise ratio, and contrast-to-noise ratio) and employing qualitative measurements (five-point scale scores of image quality and image noise) revealed no significant difference between dual-energy and standard groups (p>0.05). Qualitative and quantitative evaluations demonstrated low interobserver variability. Dual-energy computed tomography pulmonary angiography protocol delivers image quality equal to standard protocol, while requiring less amount of iodinated contrast medium and providing simultaneous lung perfusion imaging to contribute the diagnosis of pulmonary embolism.

Lung aeration, ventilation, and perfusion imaging.

Lung imaging is a cornerstone of the management of patients admitted to the intensive care unit (ICU), providing anatomical and functional information on the respiratory system function. The aim of this review is to provide an overview of mechanisms and applications of conventional and emerging lung imaging techniques in critically ill patients. Chest radiographs provide information on lung structure and have several limitations in the ICU setting; however, scoring systems can be used to stratify patient severity and predict clinical outcomes. Computed tomography (CT) is the gold standard for assessment of lung aeration but requires moving the patients to the CT facility. Dual-energy CT has been recently applied to simultaneous study of lung aeration and perfusion in patients with respiratory failure. Lung ultrasound has an established role in the routine bedside assessment of ICU patients, but has poor spatial resolution and largely relies on the analysis of artifacts. Electrical impedance tomography is an emerging technique capable of depicting ventilation and perfusion at the bedside and at the regional level. Clinicians should be confident with the technical aspects, indications, and limitations of each lung imaging technique to improve patient care.

3D-quantitated lung perfusion SPECT/CT: Impact on intended management compared to lung perfusion scan in marginal candidates for lung resection surgery

Abstract Objective Based on previous studies, single-photon emission computed tomography/computed tomography (SPECT/CT) has been proven to be more accurate and reproducible than planar lung perfusion scintigraphy. We conducted a study to evaluate the impact of 3D-quantitated lung perfusion SPECT/CT on intended management in candidates for lung resection surgery. Methods Retrospective study including candidates for lung resection surgery with lung perfusion imaging. Patients underwent preoperative evaluation according to ERS/ESTS algorithm. The lobar contribution to the total lung perfusion was estimated using planar antero-posterior, posterior oblique and three-dimensional anatomical SPECT/CT method (CT Pulmo 3D and xSPECT- Quant, Siemens). The difference in lobar perfusion with resulting changes in the extent of lung resection were analyzed to reveal possible changes in operability. Results 120 patients (46 females) with known lung cancer or pulmonary lesion considered for resection with available lung perfusion scintigraphy and SPECT/CT were enrolled. The mean age (±SD) of patients was 68 ±9 years, the target lesions were located in upper lobe in 57.7% and in lower lobe in 33.5%. The median [IQR] FEV1 was 70.5% [52–84] and median DLCO 56.6% [47.1–67.4]. The planar posterior oblique method, compared to 3D-quantitated SPECT/CT, underestimated the perfusion of upper lobes by a median difference of 5% (right [2–9; IQR]; left [2.5–8], p= &amp;lt; 0.0001), while it overestimated the both lower lobes (left by 4% [2–7]; right by 6% [2–9], p= &amp;lt; 0.0001). In contrast to the planar scintigraphy based evaluation, 4(3.3%) patients with upper lobe lesions were classified as inoperable when 3D-quantitated SPECT/CT was used for calculation of predicted postoperative lung function. Conclusion In selected patients with upper lobe lesions, 3D-quantitated SPECT/CT would have changed the treatment strategy from operable to inoperable. Importantly, post-operative mortality in this particular subgroup was disproportionally high. 3D-quantitated SPECT/CT shall be further evaluated as it might improve preoperative risk stratification in marginal lung resection candidates.

Diagnostic Reference Levels for nuclear medicine imaging in Austria: A nationwide survey of used dose levels for adult patients

PurposeTo assess dose levels in routine nuclear medicine (NUC) procedures in Austria as a prior to a legislative update of the National Diagnostic Reference Levels (NDRL). MethodAs part of a nationwide survey of common NUC-examinations between June 2019 and November 2019, data sets were collected from 33 Austrian hospitals with NUC equipment. All hospitals were asked to report the NUC imaging devices in use (model, type, year of manufacture, detector material, collimators), the standard protocol parameters for selected examinations (standard activity, collimator, average acquisition time, reconstruction type, use of time-of-flight) and to report data from 10 representative examinations (e.g. injected activity, weight), incl. the most common NUC-examinations for planar imaging/SPECT and PET. Median/mean values for injected activity were calculated and compared to current Austrian and international NDRL. A Pearson correlation coefficient was computed comparing different variables. ResultsIn total, all 33 hospitals (100% response rate) reported data for this study for 60 SPECT devices, 21 PET/CT devices and 23 scintigraphy devices. Fixed activity values for scintigraphy/SPECT and PET were employed by about 90% and 56% of the hospitals, respectively. The most widely performed examinations for scintigraphy/SPECT are bone imaging, thyroid imaging, renal imaging (with MAG3/EC) and lung perfusion imaging (in 88% of the hospitals) and F-18 FDG-PET studies for oncology indications (in 100% of the hospitals). Significant correlations were found for patient weight and injected activity (scintigraphy/SPECT), use of iterative reconstruction and injected activity (PET) as well as size of field-of-view and injected activity (PET). ConclusionsThe reported injected activity levels were comparable to those in other countries. However, for procedures for which NDRL exist, deviations in injected activities of >20% compared to the NDRL were found. These deviations are assumed to result mainly from advances in technology but also from deviations between NDRL and prescribed activities as given in the information leaflets of the radiopharmaceuticals.

Effect of Balloon Pulmonary Angioplasty on Homogenization of Lung Perfusion Blood Volume by Dual-Energy Computed Tomography in Patients with Chronic Thromboembolic Pulmonary Hypertension.

Balloon pulmonary angioplasty (BPA) is used to treat patients with inoperable chronic thromboembolic pulmonary hypertension (CTEPH); the goal is to improve pulmonary perfusion. We aimed to evaluate lung perfusion blood volume (PBV) with haemodynamic and exercise-capacity parameters to assess the efficacy of BPA in the treatment of CTEPH. We retrospectively studied 33 patients over a 6-year period. DECT pulmonary angiography was performed before and after BPA. DECT provided iodine distribution maps; whole-lung and regional PBV images and quantification were generated using post-processing software. A mosaic pattern suggesting perfusion inhomogeneity is typical in CTEPH. Hypothetically, BPA treatment would promote homogenization that would be reflected in the calculated standard deviation. Lung perfusion images showed decreased heterogeneity after BPA. There was a significant difference before and after BPA in the whole-lung PBV and in the regional standard deviation for pulmonary arterial pressure (R = 0.37, p = 0.032 and R = 0.57, p = 0.006), pulmonary vascular resistance (R = 0.51, p = 0.023 and R = 0.60, p = 0.002), transtricuspid pressure gradient (R = 0.50, p = 0.0028 and R = 0.61, p = 0.0001), brain natriuretic peptide (R = 0.54, p = 0.0012 and R = 0.46, p = 0.0078), and 6-min walking distance (R = 0.59, p = 0.003 and R = 0.26, p = 0.14). The effects were especially pronounced after the first BPA procedure. Decreased lung heterogeneity may suggest BPA efficacy in treating CTEPH. After BPA treatment, improved lung PBV and improved regional standard deviation showed a strong positive correlation with haemodynamic parameters and exercise capacity, which also suggests that BPA is effective in treating CTEPH.

Three broad classifications of acute respiratory failure etiologies based on regional ventilation and perfusion by electrical impedance tomography: a hypothesis-generating study

BackgroundThe aim of this study was to validate whether regional ventilation and perfusion data measured by electrical impedance tomography (EIT) with saline bolus could discriminate three broad acute respiratory failure (ARF) etiologies.MethodsPerfusion image was generated from EIT-based impedance–time curves caused by 10 ml 10% NaCl injection during a respiratory hold. Ventilation image was captured before the breath holding period under regular mechanical ventilation. DeadSpace%, Shunt% and VQMatch% were calculated based on lung perfusion and ventilation images. Ventilation and perfusion maps were divided into four cross-quadrants (lower left and right, upper left and right). Regional distribution defects of each quadrant were scored as 0 (distribution% ≥ 15%), 1 (15% > distribution% ≥ 10%) and 2 (distribution% < 10%). Data percentile distributions in the control group and clinical simplicity were taken into consideration when defining the scores. Overall defect scores (DefectV, DefectQ and DefectV+Q) were the sum of four cross-quadrants of the corresponding images.ResultsA total of 108 ICU patients were prospectively included: 93 with ARF and 15 without as a control. PaO2/FiO2 was significantly correlated with VQMatch% (r = 0.324, P = 0.001). Three broad etiologies of ARF were identified based on clinical judgment: pulmonary embolism-related disease (PED, n = 14); diffuse lung involvement disease (DLD, n = 21) and focal lung involvement disease (FLD, n = 58). The PED group had a significantly higher DeadSpace% [40(24)% vs. 14(15)%, PED group vs. the rest of the subjects; median(interquartile range); P < 0.0001] and DefectQ score than the other groups [1(1) vs. 0(1), PED vs. the rest; P < 0.0001]. The DLD group had a significantly lower DefectV+Q score than the PED and FLD groups [0(1) vs. 2.5(2) vs. 3(3), DLD vs. PED vs. FLD; P < 0.0001]. The FLD group had a significantly higher DefectV score than the other groups [2(2) vs. 0(1), FLD vs. the rest; P < 0.0001]. The area under the receiver operating characteristic (AUC) for using DeadSpace% to identify PED was 0.894 in all ARF patients. The AUC for using the DefectV+Q score to identify DLD was 0.893. The AUC for using the DefectV score to identify FLD was 0.832.ConclusionsOur study showed that it was feasible to characterize three broad etiologies of ARF with EIT-based regional ventilation and perfusion. Further study is required to validate clinical applicability of this method.Trial registration clinicaltrials, NCT04081142. Registered 9 September 2019—retrospectively registered, https://clinicaltrials.gov/show/NCT04081142.

A model-based source separation algorithm for lung perfusion imaging using electrical impedance tomography

Objective. Electrical impedance tomography (EIT) for lung perfusion imaging is attracting considerable interest in intensive care, as it might open up entirely new ways to adjust ventilation therapy. A promising technique is bolus injection of a conductive indicator to the central venous catheter, which yields the indicator-based signal (IBS). Lung perfusion images are then typically obtained from the IBS using the maximum slope technique. However, the low spatial resolution of EIT results in a partial volume effect (PVE), which requires further processing to avoid regional bias. Approach. In this work, we repose the extraction of lung perfusion images from the IBS as a source separation problem to account for the PVE. We then propose a model-based algorithm, called gamma decomposition (GD), to derive an efficient solution. The GD algorithm uses a signal model to transform the IBS into a parameter space where the source signals of heart and lung are separable by clustering in space and time. Subsequently, it reconstructs lung model signals from which lung perfusion images are unambiguously extracted. Main results. We evaluate the GD algorithm on EIT data of a prospective animal trial with eight pigs. The results show that it enables lung perfusion imaging using EIT at different stages of regional impairment. Furthermore, parameters of the source signals seem to represent physiological properties of the cardio-pulmonary system. Significance. This work represents an important advance in IBS processing that will likely reduce bias of EIT perfusion images and thus eventually enable imaging of regional ventilation/perfusion (V/Q) ratio.

Preparation of Heat-Denatured Macroaggregated Albumin for Biomedical Applications Using a Microfluidics Platform.

Albumin is widely used in pharmaceutical applications to alter the pharmacokinetic profile, improve efficacy, or decrease the toxicity of active compounds. Various drug delivery systems using albumin have been reported, including microparticles. Macroaggregated albumin (MAA) is one of the more common forms of albumin microparticles, which is predominately used for lung perfusion imaging when labeled with radionuclide technetium-99m (99mTc). These microparticles are formed by heat-denaturing albumin in a bulk solution, making it very challenging to control the size and dispersity of the preparations (coefficient of variation, CV, ∼50%). In this work, we developed an integrated microfluidics platform to create more tunable and precise MAA particles, the so-called microfluidic-MAA (M2A2). The microfluidic chips, prepared using off-stoichiometry thiol-ene chemistry, consist of a flow-focusing region followed by an extended and water-heated curing channel (85 °C). M2A2 particles with diameters between 70 and 300 μm with CVs between 10 and 20% were reliably prepared by adjusting the flow rates of the dispersed and continuous phases. To demonstrate the pharmaceutical utility of M2A2, particles were labeled with indium-111 (111In) and their distribution was assessed in healthy mice using nuclear imaging. 111In-M2A2 behaved similarly to 99mTc-MAA, with lung uptake predominately observed early on followed by clearance over time by the reticuloendothelial and renal systems. Our microfluidic chip represents an elegant and controllable method to prepare albumin microparticles for biomedical applications.

A data and knowledge driven approach for SPECT using convolutional neural networks and iterative algorithms

Abstract We propose a data and knowledge driven approach for SPECT by combining a classical iterative algorithm of SPECT with a convolutional neural network. The classical iterative algorithm, such as ART and ML-EM, is employed to provide the model knowledge of SPECT. A modified U-net is then connected to exploit further features of reconstructed images and data sinograms of SPECT. We provide mathematical formulations for the architecture of the proposed networks. The networks are trained by supervised learning using the technique of mini-batch optimization. We apply the trained networks to the problems of simulated lung perfusion imaging and simulated myocardial perfusion imaging, and numerical results demonstrate their effectiveness of reconstructing source images from noisy data measurements.

Deep Learning-Based Computed Tomography Perfusion Mapping (DL-CTPM) for Pulmonary CT-to-Perfusion Translation.

Our purpose was to develop a deep learning-based computed tomography (CT) perfusion mapping (DL-CTPM) method that synthesizes lung perfusion images from CT images. This paper presents a retrospective analysis of the pulmonary technetium-99m-labeled macroaggregated albumin single-photon emission CT (SPECT)/CT scans obtained from 73 patients at Queen Mary Hospital in Hong Kong in 2019. The left and right lung scans were separated to double the size of the data set to 146. A 3-dimensional attention residual neural network was constructed to extract textural features from the CT images and reconstruct corresponding functional images. Eighty-four samples were randomly selected for training and cross-validation, and the remaining 62 were used for model testing in terms of voxel-wise agreement and function-wise concordance. To assess the voxel-wise agreement, the Spearman's correlation coefficient (R) and structural similarity index measure between the images predicted by the DL-CTPM and the corresponding SPECT perfusion images were computed to assess the statistical and perceptual image similarities,respectively. To assess the function-wise concordance, the Dice similarity coefficient (DSC) was computed to determine the similarity of the low/high functional lung volumes. The evaluation of the voxel-wise agreement showed a moderate-to-high voxel value correlation (0.6733 ± 0.1728) and high structural similarity (0.7635 ± 0.0697) between the SPECT and DL-CTPM predicted perfusions. The evaluation of the function-wise concordance obtained an average DSC value of 0.8183 ± 0.0752 for high-functional lungs (range, 0.5819-0.9255) and 0.6501 ± 0.1061 for low-functional lungs (range, 0.2405-0.8212). Ninety-four percent of the test cases demonstrated high concordance (DSC >0.7) between the high-functional volumes contoured from the predicted and ground-truth perfusions. We developed a novel DL-CTPM method for estimating perfusion-based lung functional images from the CT domain using a 3-dimensional attention residual neural network, which yielded moderate-to-high voxel-wise approximations of lung perfusion. To further contextualize these results toward future clinical application, a multi-institutional large-cohort study is warranted.

Reply to Comment on: Lung Perfusion Imaging with Technetium-99m-macroaggregated Albumin should be Combined with Contrast-enhanced Echocardiography for the Diagnosis of Hepatopulmonary Syndrome.

Reply to Comment on: Lung Perfusion Imaging with Technetium-99m-macroaggregated Albumin should be Combined with Contrast-enhanced Echocardiography for the Diagnosis of Hepatopulmonary Syndrome.

Deep learning SPECT lung perfusion image classification method based on attention mechanism

SPECT lung perfusion is an important functional imaging technology. It can capture the functional lesions of the lung in a non-invasive manner and has become an important clinical detection method for diseases such as pulmonary embolism. In order to realize the automatic detection of the degree of pulmonary embolism, this paper studies and constructs a deep classification model based on the attention mechanism. First, the normalization technique is used to convert the original lung perfusion file into a SPECT image; secondly, in view of the over-fitting phenomenon of the deep learning model caused by the small amount of medical image data and the unbalanced data, the image translation and rotation techniques are used to perform effective expansion; then, in order to improve the model’s feature extraction ability, the attention mechanism is combined with the depth classification model to build a SPECT lung perfusion image classification model; finally, a set of real SPECT lung perfusion images were used to carry out comparative experiments on various depth classification models. The experimental results show that the model proposed in this paper can effectively detect the extent of lung disease lesions, and the classification accuracy rate exceeds 88%, which verifies the effectiveness and reliability of the classification model.

Lung Perfusion Imaging with Technetium-99m Macroaggregated Albumin should be Combined with Contrast-enhanced Echocardiography for the Diagnosis of Hepatopulmonary Syndrome

Lung Perfusion Imaging with Technetium-99m Macroaggregated Albumin should be Combined with Contrast-enhanced Echocardiography for the Diagnosis of Hepatopulmonary Syndrome

Influence of overdistension/recruitment induced by high positive end-expiratory pressure on ventilation\u2013perfusion matching assessed by electrical impedance tomography with saline bolus

BackgroundHigh positive end-expiratory pressures (PEEP) may induce overdistension/recruitment and affect ventilation–perfusion matching (VQMatch) in mechanically ventilated patients. This study aimed to investigate the association between PEEP-induced lung overdistension/recruitment and VQMatch by electrical impedance tomography (EIT).MethodsThe study was conducted prospectively on 30 adult mechanically ventilated patients: 18/30 with ARDS and 12/30 with high risk for ARDS. EIT measurements were performed at zero end-expiratory pressures (ZEEP) and subsequently at high (12–15 cmH2O) PEEP. The number of overdistended pixels over the number of recruited pixels (O/R ratio) was calculated, and the patients were divided into low O/R (O/R ratio < 15%) and high O/R groups (O/R ratio ≥ 15%). The global inhomogeneity (GI) index was calculated to evaluate the ventilation distribution. Lung perfusion image was calculated from the EIT impedance–time curves caused by 10 ml 10% NaCl injection during a respiratory pause (> 8 s). DeadSpace%, Shunt%, and VQMatch% were calculated based on lung EIT perfusion and ventilation images.ResultsIncreasing PEEP resulted in recruitment mainly in dorsal regions and overdistension mainly in ventral regions. ΔVQMatch% (VQMatch% at high PEEP minus that at ZEEP) was significantly correlated with recruited pixels (r = 0.468, P = 0.009), overdistended pixels (r = − 0.666, P < 0.001), O/R ratio (r = − 0.686, P < 0.001), and ΔSpO2 (r = 0.440, P = 0.015). Patients in the low O/R ratio group (14/30) had significantly higher Shunt% and lower VQMatch% than those in the high O/R ratio group (16/30) at ZEEP but not at high PEEP. Comparable DeadSpace% was found in both groups. A high PEEP caused a significant improvement of VQMatch%, DeadSpace%, Shunt%, and GI in the low O/R ratio group, but not in the high O/R ratio group. Using O/R ratio of 15% resulted in a sensitivity of 81% and a specificity of 100% for an increase of VQMatch% > 20% in response to high PEEP.ConclusionsChange of ventilation–perfusion matching was associated with regional overdistention and recruitment induced by PEEP. A low O/R ratio induced by high PEEP might indicate a more homogeneous ventilation and improvement of VQMatch.Trial registrationClinicalTrials.gov, NCT04081155. Registered on 9 September 2019—retrospectively registered.