Here's some info on chest MRIs from medline. Generally speaking MRIs are for soft tissue, but can be used to clarify X-ray results. With link:
http://www.nlm.nih.gov/medlineplus/ency/article/003794.htm
A
chest MRI uses powerful magnets and radio waves to construct pictures of the body. Unlike conventional radiography and computed tomographic (CT) imaging, which make use of potentially harmful radiation (x-rays) that passes through a patient to generate images, magnetic resonance imaging (MRI) is based on the magnetic properties of atoms.
A powerful magnet generates a magnetic field roughly 10,000 times stronger than the Earth's. A very small percentage of hydrogen atoms within the body will align with this field. Radio wave pulses are broadcast towards the aligned hydrogen atoms in tissues of interest, returning a signal of their own. The subtle differing characteristics of that signal from different tissues enables MRI to differentiate between various organs, and potentially, provide contrast between benign and malignant tissue.
Any imaging plane, or "slice", can be projected, and then stored in a computer or printed on film. MRI can easily be performed through clothing and bones, however, certain types of metal in or around the area of interest can cause significant errors in the reconstructed images.
Why the test is performed
An MRI provides detailed pictures of tissues within the chest cavity, without obstruction by overlying bone. It may be used to:
Clarify findings from previous x-rays or CT scans.
Show the structures of the chest from multiple planes.
Help diagnose abnormal growths and provide information for the staging (such as the size, extent, and spread) of tumors in the chest cavity. MRI can distinguish tumors or other lesions from normal tissues.
Show lymph nodes and blood vessels.
Evaluate blood flow.
Avoid the dangers of angiography, or of repeated exposure to radiation.
Normal Values Return to top
A normal MRI would not show any abnormalities in the size or position of organs in the chest cavity, as viewed from any plane. The MRI would not reveal any new growths or lesions. Organs would appear to be functioning normally (for those organs where MRI can indicate function).
What abnormal results mean Return to top
The sensitivity of MRI depends, in part, on the experience of the radiologist.
A chest MRI may reveal disorders including:
Thymus tumor
Lung masses
Esophageal mass
Other masses (aggregations of cells) or tumors of the chest
Abnormal lymph nodes
Swollen glands and enlarged lymph nodes in any location of the chest
Staging of tumors including invasion of blood vessels
Alveolar bullae (COPD)
Bronchial abnormalities
Bronchiectasis
Cystic lung lesions
Pleural abnormalities, including thickening or pleural effusion
Abnormal pulmonary vessels
Coarctation of the aorta
Aortic stenosis
Aortic dissection
Pericardial effusion
Thoracic aortic aneurysm
Additional conditions under which the test may be performed:
Atrial myxoma
Atrial septal defect
Cardiac tamponade
Ischemic cardiomyopathy
Mitral regurgitation - acute
Mitral regurgitation - chronic
Mitral valve prolapse
Pericarditis - bacterial
Pericarditis - constrictive
Pericarditis - post-MI
Pulmonary edema
Restrictive cardiomyopathy
Skin lesion of histoplasmosis
SVC obstruction
Special considerations
MRI is more accurate than CT scan or other tests for certain conditions, but less accurate for others. The disadvantages include the high cost, long duration of the scan, and sensitivity to movement. People with claustrophobia, or who are confused or anxious, may have difficulty lying still for the relatively long scan times.
MRI is not portable and is incompatible with some metallic implants, life support-devices, traction apparatus, and similar equipment.
MRI is a superior technique in most cases where differentiation of soft tissues is necessary. It can show organs without obstruction by bone and foreign bodies. It is capable of showing the tissues from multiple viewpoints and is a noninvasive way to evaluate blood flow. Currently, MRI is not valuable in the evaluation of subtle changes of the lung tissue, since the lungs contain mostly air and are difficult to image.