Combined invasive techniques
For the most accurate mediastinal staging, especially in lung cancer, combined endoscopic approaches are used. Simultaneous performance of endoscopic ultrasonography with fine-needle aspiration (EUS-FNA) and endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) by a single physician demonstrates the highest sensitivity—96%. This figure surpasses the efficacy of each method individually. Such minimally invasive procedures are expected to become the clinical practice standard.
Magnetic resonance imaging (MRI)
MRI is increasingly being introduced into routine thoracic imaging, primarily for detailed characterization of chest wall and mediastinal neoplasms.
Historical challenges of lung MRI:
- Low signal-to-noise ratio (few protons in lung tissue).
- Artifacts from respiration and heartbeat.
- Extremely short T2* decay time.
Modern solutions:
- Single-shot techniques (e.g., HASTE) allow T2-weighted scans of the entire lung within a single breath-hold.
- 3D gradient echo (GRE) is used for rapid T1-weighted imaging.
- Gating (triggering), including the use of navigator echoes for diaphragmatic motion control, minimizes artifacts.
Specific MRI sequences
- T2-WI: help prove the cystic structure of lesions that appear solid on CT due to dense contents.
- Contrast-enhanced T1-WI (gadolinium): superior to computed tomography in determining diaphragmatic invasion (e.g., in mesothelioma).
- STIR (fat suppression): useful for distinguishing adipose tissue from hemorrhage; sometimes more effective than PET in lymph node staging for non-small cell lung cancer (NSCLC).
- Chemical shift: differentiates thymic hyperplasia ("rebound") from true tumor recurrence or metastasis.
Experimental MRI techniques
In addition to standard protocols, new technologies are actively developing:
- Ultrashort echo time (UTE) and zero echo time (ZTE): allow capturing signals from lung parenchyma (tissues with very short T2*).
- Diffusion-weighted imaging (DWI): thanks to new synchronization methods, helps differentiate histological subtypes of mesothelioma and stage lymph nodes in NSCLC.
- Hyperpolarized gas MRI: detects regional ventilation abnormalities, but requires expensive infrastructure.
- Oxygen-enhanced MRI: uses oxygen as a contrast agent to assess alveolar ventilation.
- Fourier decomposition MRI: creates non-contrast ventilation and perfusion maps.
Radionuclide diagnostics
Radionuclide methods continue to play an important role in thoracic imaging.
- Ventilation-perfusion scintigraphy (V/Q): a classic non-invasive method for assessing pulmonary blood flow and ventilation. The main indication is suspected pulmonary embolism (PE), especially with a normal radiograph.
- SPECT: three-dimensional emission tomography is now considered preferable to traditional planar V/Q scintigraphy.
- PET: hybrid technologies (PET/CT, PET/MRI) provide crucial metabolic and anatomical information critical for staging thoracic tumors.
Briefly: answers to topical questions
Why is SPECT currently considered preferable to traditional planar V/Q scintigraphy?
Single-photon emission computed tomography (SPECT) is preferred over traditional planar scintigraphy due to its ability to acquire three-dimensional images and high diagnostic accuracy.
Advantages of the method:
- Three-dimensional imaging (3D SPECT) — provides volumetric assessment of ventilation and perfusion unlike two-dimensional planar scintigraphy.
- High accuracy — in diagnosing pulmonary embolism, it is comparable to and sometimes surpasses computed tomography pulmonary angiography (CTPA).
- Reduced radiation dose — the radiation dose is traditionally about 1/3 of that in CT angiography.
- Hybridization (SPECT-CT/VQ) — the method is often combined with low-dose CT.
Class and exam questions
What is the advantage of gadolinium-enhanced T1-weighted images?
They surpass CT in detecting tumor invasion (e.g., pleural mesothelioma) into the diaphragm.
What is the value of the STIR (fat-suppression) MRI sequence?
It helps differentiate fat from hemorrhage in the mediastinum and may be more accurate than PET in lymph node staging for patients with NSCLC.
Why is classical lung MRI difficult to perform?
Due to the small number of protons in air-containing tissue (low signal), respiratory and cardiac pulsation artifacts, and a very short T2* decay time.
Which radionuclide method is currently preferred for assessing ventilation and perfusion?
Instead of classical planar two-dimensional scintigraphy, it is now preferable to use three-dimensional SPECT, often combined with low-dose CT.
What else to study on this topic
- Technique of combined endoscopic ultrasonography (EUS-FNA and EBUS-TBNA)
- Assessment of chest wall tumor invasion using MRI
- Application of navigator echoes in lung MRI
- Role of diffusion-weighted imaging (DWI) in NSCLC staging
- Methodology of inhaled contrast gas MRI
- Comparison of SPECT and traditional scintigraphy in PE
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