CT is often the preferred recommended modality in the diagnosis of lung cancer. Magnetic resonance diagnosis is primarily indicated for certain specialized problems that cannot be addressed by CT, including evaluation of tumor chest wall invasion, supraglottic sulcus tumors, evaluation of cardiac invasion, and evaluation of distant metastases.
Low-dose spiral CT (LDCT) appears to be the most commonly recommended diagnostic modality for lung cancer screening.
So, is MRI useful for lung cancer diagnosis? What are the advantages and limitations?
I. Magnetic resonance is not commonly used to diagnose lung cancer
Magnetic resonance imaging is a biomagnetic nuclear spin imaging technique with good soft tissue resolution compared to CT; it can display images in cross-sectional, sagittal, coronal, or any dimension as needed; and there is no ionizing radiation to the body.
Magnetic resonance imaging, when used for head, extremity, and abdominal examinations, clearly shows subtle anatomic boundaries and can distinguish details such as hemorrhage, edema, protein exudation, cellular infiltration, and fat infiltration.
However, the use of MRI in lung cancer diagnosis is not widespread because of several limitations that limit its use in lung cancer screening:
(1) The lung changes with respiratory motion, MRI has lower spatial resolution, and its imaging takes longer and is prone to motion artifacts, which further affects spatial resolution, whereas CT has high spatial resolution, scans rapidly, and can complete the examination within a single breath-holding time, which is largely unaffected by respiratory motion.
(2) Around lung tumors, normal alveolar structures are rich in gas. The primary need for imaging is to sensitively detect densely increased tissue in gas-rich structures, rather than to finely differentiate the differences in the nature of different soft tissues. This aspect is not an advantage of MRI, but rather an advantage of CT.
(3) The inability of MRI to show calcified lesions poses some difficulty in identifying pulmonary disease.
II. When does the doctor recommend an MRI?
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At present, for lung cancer, MRI is only used for certain specialized problems that cannot be solved by CT:
1. Evaluation of tumor chest wall invasion
Sometimes, it is difficult to distinguish the status of a tumor growing close to the chest wall, whether it is just close to the mural pleura or has invaded the chest wall.
Magnetic resonance imaging, which can look at whether the fat layer normally present outside the pleura is compartmentalized by other soft tissues, can more accurately determine whether the tumor has directly invaded the chest wall.
It should be noted that, like CT, MRI cannot distinguish between the dirty pleura (surface of the lung) and the mural pleura (within the chest wall), so in most cases, it does not have a significant advantage over CT. Only when CT is not diagnostic is MRI needed to help with the diagnosis.
2. Supraglottic sulcus tumor
Magnetic resonance has some advantages for the evaluation of supraglottic sulcus tumors. This is because MRI 3D reconstructed images can clearly show the invasion of mediastinal vessels and brachial plexus nerves; MRI can also provide accurate information on whether the tumor is invading the vertebral body and spinal cord.
The literature reports that MRI is more than 90% accurate in assessing the extent of supraglottic sulcus tumors, whereas CT is only about 60%.
3. Evaluation of cardiac invasion
Magnetic resonance is able to clearly visualize the pericardium. When a tumor is suspected to have invaded the pericardium, it can be distinguished by MRI, especially using dynamic mode, which allows observation of the relative motion of the tumor and adjacent tissues, with an assessment accuracy of more than 90%.
4. Assessment of distant metastases
Common metastatic sites for lung cancer include the skull, liver, adrenal glands, and bones, all of which are areas of magnetic resonance predominance and require MRI to clarify the presence or absence of invasion and the specifics of invasion, if necessary. In particular, for patients with suspected cranial metastases, MRI has a clear advantage, with higher resolution than CT for small lesions or meningeal metastases.
Extended reading
Diagnostic principles of magnetic resonance
The basis of magnetic resonance imaging, is nuclear spin motion.
“Nucleon” (nucleon) is a chemical and physical term that refers to the particles that make up the nucleus of an atom. “Spin”, is an important property of the nucleus.
The spin motion varies from nucleon to nucleon, and is in a haphazard state. When the body enters a strong magnetic field, the nuclei spin in unison in the direction of the external magnetic field; when the magnetic field is stopped, the nuclei quickly return to their original state (known professionally as “chirality”) and release the corresponding energy. The whole process is like the assembly and disbanding of an army formation. Different nuclei and different magnetic field switching conditions will show different chirality patterns and release different amounts of energy.
The energy released from each part of the body is probed using special equipment and specific magnetic field switching conditions, which is analyzed by computer and converted into specialized images that tell the physician the characteristics of the material structure of the corresponding part of the body. The radiologist can analyze these images to distinguish between diseased and normal tissue, and can also accurately interpret the nature of the lesion through different imaging conditions.
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Co-reviewed by: Guangdong Provincial People’s Hospital Guangdong Provincial Lung Cancer Institute Dr. Pan Yao, Chief Physician Dr. Chen Zhiyong Dr. Zhang Jia Tao