Imaging

Radionuclide imaging techniques provide noninvasive information about global and regional lung function, physiology and biology. The ventilation/perfusion scan is an established test for detecting pulmonary embolism. Its clinical role has shifted from the acute setting towards the workup of CTEPH. Other routine clinical applications include quantification prior to lung surgery and assessment of right-left shunting. In lung cancer, PET with the glucose analogue ¹⁸F deoxyglucose currently serves as a first line staging tool and may be used more extensively for monitoring of therapy in the future. Other imaging markers of molecular mechanisms are penetrating the clinical arena, e.g. in inflammatory conditions, and those are expected to lead to further molecular imaging applications in lung disease. Finally, the advent of hybrid imaging devices such as SPECT-CT, PET-CT and, more recently, PET/magnetic resonance, has led to the convergence of tomographic imaging techniques towards a multi-modality, multi-parametric environment for precise, integrated imaging of lung morphology, physiology and molecular function. This is expected to aid in the personalisation of pulmonary medicine.

Lung cancer screening has become a reality in the USA. Results of the National Lung Screening Trial showed a 20% mortality benefit in a defined population for annual screening with CT. However, the benefits of CT screening in high-risk individuals was accompanied by a very high false-positive rate, which in most cases resulted in multiple short-term additional follow-up CT examinations. In the USA, screening and insurance reimbursement are required by federal law for eligible current and former smokers with both private and public insurance. The American College of Radiology has developed a reporting system (Lung-RADS) that associates findings with guideline-based management decisions. The most recently revised seventh edition of the lung cancer TNM staging system correlates with patient prognosis and is now utilised for small cell lung cancer, nonsmall cell lung cancer and bronchopulmonary carcinoid tumours. The assignment of correct tumour (T), nodal (N) and metastasis (M) classifications is crucial not only to allow for clear physician communication across specialties, but also to direct appropriate therapy in this patient population.

Routine radiological investigation has long been part of the regular assessment of patients with a diagnosis of COPD. However, practical interpretation and use (especially of newer radiological techniques) can often provide confusion and identify unexpected pathology. Recent advances in understanding the radiological as well as clinical phenotypes of COPD patients and the frequency of incidental findings will lead to more focused patient management and appropriate subsequent investigations.

A chest radiograph is the most common means of identifying pleural disease; however, physician-performed ultrasound is now frequently performed prior to other investigations. As experience with this technique improves, ultrasound will be used more commonly to identify pleural and diaphragmatic thickening and nodularity, and for the diagnosis of pneumothorax and, potentially, cardiac failure. Ultrasound can guide intervention and can also be used to assess treatment success post-pleurodesis. Multislice CT (MSCT) remains a common investigation for the detection of mediastinal and extrapleural disease, and provides an excellent overview of the volume of pleural disease. MSCT remains the technique of choice in differentiating benign from malignant disease, but new developments in MRI and PET/CT suggest they may also have a role. Both MRI and PET/CT may also play a role in helping differentiate different malignancies or subtypes of malignancies, and may be used as biomarkers for prognosis and disease response.

Pulmonary hypertension (PH) is a haemodynamic condition that leads to a progressive increase in pulmonary vascular resistance and mean pulmonary artery pressure. Irrespective of its aetiology, the main cause of death in PH patients is right ventricular (RV) failure. Noninvasive imaging techniques play an essential role in diagnosing PH and monitoring disease progression. This chapter provides an overview of the most important noninvasive imaging tools for assessing pulmonary pressures, RV function and monitoring.

Repetitive imaging is required in cystic fibrosis (CF) lung disease in order to provide detailed information on regional distribution for severity assessment and therapy monitoring in clinical routine as well as interventional trials. CT has long overtaken the use of chest radiography because it provides higher morphological detail with respect to airway and parenchymal changes. This is closely linked to an increase in radiation exposure in CF individuals, who are referred for imaging procedures from a critically susceptible young age and may accumulate relevant doses during their lifetime. MRI, as an ionising radiation-free cross-sectional imaging modality, has taken the first step into the clinical arena in CF. MRI can depict the morphological hallmarks of CF lung disease such as bronchial wall thickening, bronchiectasis, mucus plugging, small airways disease and infiltrates at lower spatial resolution compared to CT but excels due to enhanced tissue characterisation and comprehensive functional imaging capabilities. These include imaging of respiratory mechanics, ventilation and, in particular, lung perfusion, of which four-dimensional perfusion imaging is currently most valuable. These tools make MRI an ideal modality to monitor potentially reversible lung abnormalities such as ventilation and perfusion impairment (air trapping), which could sensitively react to therapy and might even be regarded as precursor lesions to irreversible bronchiectatic destruction.

Much of our understanding of both healthy and diseased lung is based on quantitative morphological assessment using pathology. However, the development of new therapies for lung disease requires measurements and tools that can noninvasively measure lung structure and function both on a global and a regional scale. Medical imaging technologies allow us to “see” the complex internal structures of the lung in three dimensions so that detailed anatomical measurements can be taken, while other imaging modalities can also measure how the lung functions. In this chapter we highlight three techniques that have impacted pulmonary imaging research with an emphasis on quantitative measurements: CT, hyperpolarised noble gas MRI and OCT. For each of these imaging modalities, we discuss the quantitative measurements that can be derived as well as discussing the pulmonary diseases where each technique has demonstrated utility, some drawbacks that are unique to each technique and some important directions for future research.

One of the quintessential applications of CT is the detection and evaluation of thoracic pathology. CT examinations of the chest are likely to increase with the advent of screening for lung cancer and the increasing role of CT in parenchymal disease assessments and cardiac CT applications. There are risks associated with undergoing CT related to radiation dose and the use of iodine based contrast agents. The actual risk is a subject of much discussion and debate. At all times, the risk–benefit of a CT study should be considered in terms of the information likely to be derived and the benefit to the patient versus the risks albeit very small. With the advent of novel CT reconstruction techniques, dual-source CT machines and attention to basic principles of CT scanning, the radiation dose of CT is set to be lowered dramatically in the future. In this chapter we will focus on the two main sources of risk related to the use of iodinated contrast agents and radiation dose.