Ventilation perfusion pulmonary scintigraphy in the evaluation of pre-and post-lung transplant patients

The Past, Present, and Future Role of Artificial Intelligence in Ventilation/Perfusion Scintigraphy: A Systematic Review

Ventilation-perfusion (V/Q) lung scans constitute one of the oldest nuclear medicine procedures, remain one of the few studies performed in the acute setting, and are amongst the few performed in the emergency setting. V/Q studies have witnessed a long fluctuation in adoption rates in parallel to continuous advances in image processing and computer vision techniques. This review provides an overview on the status of artificial intelligence (AI) in V/Q scintigraphy. To clearly assess the past, current, and future role of AI in V/Q scans, we conducted a systematic Ovid MEDLINE(R) literature search from 1946 to August 5, 2022 in addition to a manual search. The literature was reviewed and summarized in terms of methodologies and results for the various applications of AI to V/Q scans. The PRISMA guidelines were followed. Thirty-one publications fulfilled our search criteria and were grouped into two distinct categories: (1) disease diagnosis/detection (N = 22, 71.0%) and (2) cross-modality image translation into V/Q images (N = 9, 29.0%). Studies on disease diagnosis and detection relied heavily on shallow artificial neural networks for acute pulmonary embolism (PE) diagnosis and were primarily published between the mid-1990s and early 2000s. Recent applications almost exclusively regard image translation tasks from CT to ventilation or perfusion images with modern algorithms, such as convolutional neural networks, and were published between 2019 and 2022. AI research in V/Q scintigraphy for acute PE diagnosis in the mid-90s to early 2000s yielded promising results but has since been largely neglected and thus have yet to benefit from today's state-of-the art machine-learning techniques, such as deep neural networks. Recently, the main application of AI for V/Q has shifted towards generating synthetic ventilation and perfusion images from CT. There is therefore considerable potential to expand and modernize the use of real V/Q studies with state-of-the-art deep learning approaches, especially for workflow optimization and PE detection at both acute and chronic stages. We discuss future challenges and potential directions to compensate for the lag in this domain and enhance the value of this traditional nuclear medicine scan.

Aerosolised micro and nanoparticle: formulation and delivery method for lung imaging

Purpose

The application of contrast and tracing agents is essential for lung imaging, as indicated by the wide use in recent decades and the discovery of various new contrast and tracing agents. Different aerosol production and pulmonary administration methods have been developed to improve lung imaging quality. This review details and discusses the ideal characteristics of aerosol administered via pulmonary delivery for lung imaging and the methods for the production and pulmonary administration of dry or liquid aerosol.

Methods

We explored several databases, including PubMed, Scopus, and Google Scholar, while preparing this review to discover and obtain the abstracts, reports, review articles, and research papers related to aerosol delivery for lung imaging and the formulation and pulmonary delivery method of dry and liquid aerosol. The search terms used were "dry aerosol delivery", "liquid aerosol delivery", "MRI for lung imaging", "CT scan for lung imaging", "SPECT for lung imaging", "PET for lung imaging", "magnetic particle imaging", "dry powder inhalation", "nebuliser", and "pressurised metered-dose inhaler".

Results

Through the literature review, we found that the critical considerations in aerosol delivery for lung imaging are appropriate lung deposition of inhaled aerosol and avoiding toxicity. The important tracing agent was also found to be Technetium-99m (^99mTc), Gallium-68 (⁶⁸Ga) and superparamagnetic iron oxide nanoparticle (SPION), while the essential contrast agents are gold, iodine, silver gadolinium, iron and manganese-based particles. The pulmonary delivery of such tracing and contrast agents can be performed using dry formulation (graphite ablation, spark ignition and spray dried powder) and liquid aerosol (nebulisation, pressurised metered-dose inhalation and air spray).

Conclusion

A dual-imaging modality with the combination of different tracing or contrast agents is a future development of aerosolised micro and nanoparticles for lung imaging to improve diagnosis success.

Graphical abstract

Lung transplantation in patients with a history of anatomical native lung resection

OBJECTIVES

History of anatomical lung resection complicates lung transplantation (LTx). Our aim was to identify indications, intraoperative approach, and outcome in these challenging cases in a retrospective multicentre cohort analysis.

METHODS

Members of the ESTS Lung Transplantation Working Group were invited to submit data on patients undergoing LTx after a previous anatomical native lung resection between 01/2005 and 07/2020. The primary end-point was overall survival (Kaplan-Meier estimation).

RESULTS

Out of 2690 patients at 7 European centers, 26 (1%) patients (14 male; median age 33 years) underwent LTx after a previous anatomical lung resection. Median time from previous lung resection to LTx was 12 years. The most common indications for lung resection were infections (n = 17), emphysema (n = 5), lung tumour (n = 2), and others (n = 2). Bronchiectasis (cystic fibrosis (CF) or non-CF related) was the main indication for LTx (n = 21), followed by COPD (n = 5). Two patients with a previous pneumonectomy underwent contralateral single LTx and 1 patient with a previous lobectomy had ipsilateral single LTx. The remaining 23 patients underwent bilateral LTx. Clamshell incision was performed in 12 (46%) patients. Moreover, LTx was possible without extracorporeal life support in 13 (50%) patients. 90-day mortality was 8% (n = 2) and the median survival was 8.7 years.

CONCLUSIONS

History of anatomical lung resection is rare in LTx candidates. The majority of patients are young and diagnosed with bronchiectasis. Although the numbers were limited, survival after LTx in patients with previous anatomical lung resection, including pneumonectomy is comparable to reported conventional LTx for bronchiectasis.

Nuclear cardiology for a cardiothoracic surgeon

Cardiac surgeons are commonly faced with issues regarding the balance between the potential risk and the potential benefit of a surgical procedure. Nuclear cardiology procedures such as single-photon emission computed tomography and positron emission tomography provide the surgeon with objective information that augments standard clinical and angiographic assessments related to the diagnosis, prognosis, and potential benefit from any intervention. Myocardial perfusion is imaged with the use of radiopharmaceuticals that accumulate rapidly in the myocardium in proportion to the myocardial blood flow. Radionuclide lung imaging most commonly involves the demonstration of pulmonary perfusion using technetium-99 m macro aggregate albumin (Tc-99 m MAA), as well as the assessment of ventilation using inspired inert gas, usually xenon, or Tc-99 m-labelled aerosols. Nuclear cardiology is extensively used as a part of the work-up of ischemic heart disease and cardiac failure in deciding the optimal therapeutic strategy with its ability to predict the severity of the disease. It has also proved extremely useful in the management of congenital heart disease and the diagnosis of pulmonary embolism, among many other applications. Myocardial perfusion imaging is a basic adjunct to the noninvasive assessment of patients with stable angina, baseline electrocardiogram (ECG) abnormalities, post-revascularisation assessment, and heart failure. This review article covers a summary of basic concepts of nuclear cardiology about what a cardiac surgeon should be aware of. To many, it is just a perfusion test, but the versatility, reliability, and future of the technology are without a doubt.

Anesthetic considerations in lung transplantation: past, present and future

Lung transplantation is a very complex surgical procedure with many implications for the anesthetic care of these patients. Comprehensive preoperative evaluation is an important component of the transplant evaluation as it informs many of the decisions made perioperatively to manage these complex patients effectively and appropriately. These decisions may involve pre-emptive actions like pre-habilitation and nutrition optimization of these patients before they arrive for their transplant procedure. Appropriate airway and ventilation management of these patients needs to be performed in a manner that provides an optimal operating conditions and protection from ventilatory injury of these fragile post-transplant lungs. Pain management can be challenging and should be managed in a multi-modal fashion with or without the use of an epidural catheter while recognizing the risk of neuraxial technique in patients who will possibly be systemically anticoagulated. Complex monitoring is required for these patients involving both invasive and non-invasive including the use of transesophageal echocardiography (TEE) and continuous cardiac output monitoring. Management of the patient's hemodynamics can be challenging and involves managing the systemic and pulmonary vascular systems. Some patients may require extra-corporeal lung support as a planned part of the procedure or as a rescue technique and centers need to be proficient in instituting and managing this sophisticated method of hemodynamic support.

Ventilation-Perfusion Scan: A Primer for Practicing Radiologists

Lung scintigraphy, or ventilation-perfusion (V/Q) scan, is one of the commonly performed studies in nuclear medicine. Owing to variability in clinical applications and different departmental workflows, many trainees are not comfortable interpreting the results of this study. This article provides a simplified overview of V/Q imaging, including a review of its technique, interpretation methods, and established and emerging clinical applications. The authors review the role of V/Q imaging in evaluation of acute and chronic pulmonary embolism, including the role of SPECT/CT and comparing V/Q scan with CT angiography. In addition, a variety of other applications of pulmonary scintigraphy are discussed, including congenital heart disease, pretreatment planning for lung cancer and emphysema, posttransplant imaging for bronchiolitis obliterans, and less common vascular and nonvascular pathologic conditions that may be detected with V/Q scan. This article will help radiologists and residents interpret the results of V/Q scans and understand the various potential clinical applications of this study. Online supplemental material is available for this article. ^©RSNA, 2021.

Prognostic impact of ventilation-perfusion defects and pulmonary diffusing capacity after single lung transplantation

BACKGROUND

Ventilation-perfusion (VQ) scintigraphy and lung function testing are often used to assess allograft function after single lung transplantation (SLTX). However, it is unknown whether allograft defects on VQ scintigraphy presage all-cause mortality after SLTX.

OBJECTIVE

To investigate whether allograft defects on VQ scintigraphy portend poorer lung function and increased mortality after SLTX.

METHODS

We retrospectively identified 45 consecutive patients in which a VQ scintigraphy was performed as part of the routine workup 12 weeks after SLTX. VQ scintigraphies were scored for matched and mismatched perfusion defects in the allograft. Lung function testing was performed according to established guidelines six months after SLTX. Time to all-cause mortality was the endpoint.

RESULTS

19 (42%) patients had matched VQ defects. After a median follow-up of 4.1 (IQR 1.5-7.9) years since SLTX, 35 (78%) had died. Those with matched defects in the allograft had lower diffusing capacity (mean 42 [SD 14] versus mean 54 [SD 18] % of predicted, p < .05) and increased mortality (univariable HR 2.06, 95% CI: 1.05-4.06, p = .04). However, in multivariate analysis, only lower post-transplantation diffusing capacity remained associated with mortality (HR 1.08, 95% CI: 1.02-1.30 per % lower diffusing capacity of predicted, p = .003).

CONCLUSION

In SLTX patients, a lower diffusing capacity appeared to explain the increased mortality among those with matched VQ defects in the allograft.