Magnetic Resonance Imaging (MRI) has emerged as a valuable modality for evaluating the chest, offering distinct advantages over conventional imaging such as chest radiography and computed tomography (CT). While CT remains the workhorse for many thoracic indications due to its speed and high spatial resolution, MRI provides superior soft‑tissue contrast and functional information without ionising radiation. This capability makes it increasingly important for characterising lung and pleural disease, mediastinal masses, chest wall lesions, and vascular abnormalities. Over the past decade, technical innovations have mitigated many of MRI’s traditional limitations in the thorax, expanding its role in both clinical practice and research.

Fundamental Advantages of MRI for Thoracic Imaging

The physical principles of MRI—based on the relaxation properties of hydrogen nuclei in a strong magnetic field—yield several unique benefits for thoracic assessment.

Exceptional Soft‑Tissue Contrast

MRI can distinguish between different types of soft tissues with greater clarity than CT. For a mediastinal mass, MRI reliably separates solid tumour from cystic components, necrotic areas, and adjacent fat planes. It also readily differentiates blood products, oedema, and fibrosis, which is critical for characterising pleural and pericardial processes.

No Ionising Radiation

Repeated imaging—common in follow‑up of lung nodules, evaluation of treatment response, or surveillance of chronic inflammatory disease—exposes patients to cumulative radiation when using CT. MRI eliminates this risk, making it an ideal tool for children, pregnant women, and young adults requiring longitudinal imaging. This radiation‑free advantage also encourages appropriate use in benign or low‑suspicion findings where the risk‑benefit ratio of CT may be unfavourable.

Functional and Quantitative Capabilities

Beyond morphology, MRI can probe tissue physiology. Diffusion‑weighted imaging (DWI) assesses cellularity and can help differentiate malignant from benign lesions based on apparent diffusion coefficient (ADC) values. Dynamic contrast‑enhanced (DCE) MRI evaluates perfusion and capillary permeability, providing biomarkers for tumour angiogenesis. MR elastography, though more commonly used in the liver, is also being investigated for assessing lung fibrosis and pleural stiffness.

Clinical Applications of MRI in Lung and Thoracic Pathologies

Characterisation of Mediastinal and Pleural Masses

For anterior mediastinal masses (e.g., thymoma, lymphoma, germ cell tumours), MRI is often the preferred non‑invasive test. Multi‑sequence imaging—including T1‑weighted in‑ and out‑of‑phase, T2‑weighted fat‑suppressed, and DWI—can identify intralesional fat, cystic degeneration, or haemorrhage, narrowing the differential diagnosis. Pleural lesions such as solitary fibrous tumour, mesothelioma, and metastatic disease are also well evaluated with MRI, particularly when assessing chest wall or diaphragmatic invasion.

Lung Cancer Staging and Assessment

MRI plays an adjunctive but increasingly important role in lung cancer staging. Its superior soft‑tissue contrast is valuable for evaluating mediastinal nodal involvement (N‑stage) when CT is equivocal, and for assessing chest wall or mediastinal invasion (T‑stage). Whole‑body MRI with DWI is being explored as a radiation‑free alternative for M‑staging. Furthermore, functional parameters from DWI and DCE MRI correlate with tumour grade and may predict response to chemoradiotherapy.

Evaluation of Pulmonary Embolism

CT pulmonary angiography (CTPA) remains the first‑line test for acute pulmonary embolism (PE) due to its speed and high sensitivity. However, MRI techniques—specifically unenhanced and contrast‑enhanced magnetic resonance angiography (MRA) and perfusion sequences—can detect central and segmental PE. MRI is particularly useful in patients with contraindications to iodinated contrast (e.g., severe allergy, renal impairment) or when radiation exposure is a significant concern. Combined MRA and MR venography can also assess for deep vein thrombosis in a single session.

Inflammatory and Infectious Lung Diseases

MRI is increasingly used to assess pneumonia, lung abscess, tuberculosis, and fungal infections, especially when differentiation from neoplasm is challenging. The lack of radiation is advantageous in children and immunocompromised patients who require repeated follow‑up. In COVID‑19 pneumonia, MRI has been shown to detect ground‑glass opacities and consolidations with high sensitivity, and it can quantify lung involvement without ionising radiation. For chronic inflammatory conditions such as sarcoidosis or interstitial lung disease, MRI can depict active inflammation and fibrosis, complementing high‑resolution CT.

Vascular and Cardiac Thoracic Abnormalities

MRI is the modality of choice for many thoracic vascular disorders, including aortic coarctation, dissection, aneurysm, and vasculitis. Cardiac MRI provides comprehensive assessment of pericardial disease, cardiac masses, and congenital heart disease, all of which are essential in the thoracic evaluation. Phase‑contrast flow quantification enables measurement of shunts, valvular lesions, and differential pulmonary perfusion.

Technical Challenges and Current Limitations

Despite its advantages, thoracic MRI faces several longstanding hurdles.

Motion Artifacts

The lung and heart are in constant motion from respiration and cardiac pulsation. This degrades image quality if not properly managed. Breath‑hold sequences and respiratory gating are standard, but in patients who cannot hold their breath or have irregular breathing, image quality may suffer. Newer approaches such as radial (e.g., PROPELLER) and spiral k‑space sampling, as well as free‑breathing sequences with real‑time motion correction, are mitigating this problem.

Low Intrinsic Signal from Lung Parenchyma

Lung tissue has low proton density due to air content, resulting in weak MRI signal. This makes it difficult to image the lung parenchyma directly. Ultrashort echo time (UTE) and zero echo time (ZTE) sequences have been developed specifically to capture signal from the lung, enabling visualisation of parenchymal abnormalities such as fibrosis, oedema, and mucus plugging. These techniques are becoming more widely available but are not yet standard in every institution.

Scan Time and Patient Throughput

Comprehensive thoracic MRI protocols can take 30–60 minutes, compared to a few seconds for CT. This reduces patient throughput and increases the likelihood of motion artifacts, especially in claustrophobic or critically ill patients. Accelerated imaging techniques—parallel imaging, compressed sensing, and artificial intelligence‑based reconstruction—are reducing acquisition times without sacrificing diagnostic quality.

Cost and Accessibility

MRI is significantly more expensive than CT or radiography, and its availability is limited in many healthcare settings. The high cost and need for specialised expertise often reserves MRI for problem‑solving cases rather than first‑line diagnostics. However, the radiation‑free nature of MRI can result in overall cost savings when repeated CT examinations are avoided.

Future Directions and Emerging Innovations

Hyperpolarised Gas MRI

Inhalation of hyperpolarised helium‑3 (3He) or xenon‑129 (129Xe) allows direct visualisation of lung ventilation and gas exchange. This technique is transforming the study of obstructive lung diseases (asthma, COPD, cystic fibrosis) and interstitial lung disease. Hyperpolarised gas MRI can detect early regional ventilation defects and gas‑transfer impairment before structural changes occur, enabling earlier intervention and monitoring of therapy.

Artificial Intelligence and Deep Learning

AI is accelerating thoracic MRI in multiple ways: improved motion correction, shorter scan times via undersampled reconstruction, automated segmentation of lung lobes and lesions, and extraction of quantitative biomarkers. Deep learning also helps standardise image quality across sites and scanners, facilitating multicentre clinical trials.

PET/MRI Fusion

Integrated PET/MRI combines the metabolic information of PET with the soft‑tissue resolution of MRI, offering a powerful single‑session modality for oncologic imaging. For lung cancer and lymphoma, PET/MRI has shown comparable diagnostic performance to PET/CT while reducing radiation exposure. The ability to acquire DWI and DCE simultaneously with FDG‑PET further enriches the characterisation of thoracic malignancies.

Functional Lung MRI without Contrast

Techniques like oxygen‑enhanced MRI (using inhaled oxygen as a contrast agent), Fourier decomposition MRI, and phase‑resolved functional lung (PREFUL) allow measurement of regional ventilation and perfusion without exogenous contrast. These methods hold promise for evaluating pulmonary embolism, chronic thromboembolic disease, and lung transplant complications.

Conclusions

MRI has evolved from a niche tool in the thorax to a versatile, radiation‑free modality with expanding clinical applications. Its ability to provide high soft‑tissue contrast and functional information complements CT for characterising mediastinal, pleural, and pulmonary lesions, staging lung cancer, assessing vascular diseases, and monitoring inflammatory conditions. Ongoing technical improvements—ultrashort echo time sequences, motion‑robust acquisitions, hyperpolarised gas imaging, and AI‑driven reconstruction—are overcoming traditional limitations in scan time and image quality. As these innovations become more widely implemented, MRI’s role in thoracic imaging will continue to grow, offering patients safer and more comprehensive diagnostic evaluations.

For further reading, the Radiological Society of North America (RSNA) provide an updated perspective on lung MRI techniques, and detailed clinical protocols can be found in the Radiopaedia chest MRI article. A recent review in Insights into Imaging summarises the current evidence for thoracic MRI across multiple diseases.