Whole-Body Magnetic Resonance Imaging (MRI)

 

Recent trends in radiology

Whole-body magnetic resonance imaging has developed as an alternative diagnostic method in relation to other methods of imaging pathological organic changes. It is important to remember that the term "whole-body magnetic resonance imaging" was introduced in 1980 and meant then the study of regions of the body other than the brain, spinal cord, and structures of the spine (ie organs of the chest, abdomen, and extremities).

Only a few years ago, only one limited part of a patient's body could be examined for a reasonable amount of time. Today, whole-body magnetic resonance imaging allows imaging of the entire body "from head to toe" in just one procedure.

The first whole-body magnetic resonance imaging, namely angiography, provided an image of the arterial bed from head to toe, which was obtained in one study after a single bolus injection of contrast agent. Shortly thereafter, whole-body magnetic resonance imaging was used to detect tumors and bone metastases. Today, the study and assessment of the muscular and skeletal systems, parenchymal organs, blood vessels, and the heart, even the intestines, has become possible in one procedure.

 

Description of the diagnostic procedure for magnetic resonance imaging of the whole-body

Different types of tomographs can teach images of tissues of one or another organ in different ways. Unlike computed tomography (CT), MRI can examine only one area of the body in one procedure, limited by the field of view of the apparatus of 40-50 cm. For an extended study of the patient, each part of his body (within 40-50 cm) was examined separately. Because of the limitation of the number of sensors on the tomograph table, it was required to put the patient either with his head toward the opening of the tomograph or with his feet toward it. It was also necessary to transfer the coils to this or that organ during the research. If contrast was injected, then the study could be carried out only in one or two departments, because optimal contrast enhancement from these drugs occurs in the first minutes after intravenous injection (depending on the type of pathological process and the tissue under study) and lasts up to 45 minutes. All these limitations of the old models of MRI machines led to an increase in the study time of the patient and were stressful for him.

Recent advances in technology have removed such limitations when performing whole-body MRI scans for patients. Now there is no need to move the patient on the table. For MRI, it is covered with one coil from head to toe, which also does not need to be shifted. The table of the apparatus has become movable within 200 cm and has all the necessary sensors. The tomograph itself has a magnetic field of 3 Tesla (T) and can take patients with a large weight - up to 200 kg for examination.

 

Indications for full body magnetic resonance imaging and clinical results

Atherosclerosis

MRI research provides a unique opportunity to identify possible disorders that could arise during Atherosclerosis of the human arterial system. MRI angiography has become comparable in informational value to invasive imaging methods for selective angiography performed on the carotid arteries, kidney, or limb arteries. When carrying out a patient's magnetic resonance angiography (MRI of the vessels) of the whole body, the examination time and the amount of injected contrast agent (contrast) no longer require an increase. This significantly reduces the cost of diagnostics. Over time, further improvement in the detail of the MRI image is expected as the technical part of the apparatus itself improves.

 

Examination of the arteries of the cardiovascular system

Based on the modern research method with magnetic resonance angiography (MRI of the vessels) of the whole body, it became possible to see the vasculature of the brain, heart, and peripheral arteries from the carotid artery to the lower leg. The modern technique of MRI angiography optimizes the dose of contrast agent administered intravenously to the patient during diagnosis. As a result, it becomes possible to obtain high-quality images within 45-60 minutes with any organs being examined. It is possible to identify not only macroscopic changes in the arterial bed (excluding coronary vessels) but potential damage as a result of infectious myocarditis, stroke, or microangiopathy of cerebral vessels.

 

MRI angiography of veins (MR venography)

Venous MRI angiography has traditionally been performed using X-ray contrast media. After the introduction of paramagnetic contrast agents for MRI into clinical practice in 1988, contrast-enhanced MRI angiography of veins became available. Now, most of the specialized departments of hospitals (cardiology, intensive care, vascular surgery, etc.) began to conduct their patients with MRI angiography of the pulmonary artery, which became possible to supplement MRI with venography of the lower extremities, abdominal cavity, and small pelvis to diagnose and search for a potential source of embolism pulmonary artery. The high accuracy of MRI angiography of veins, comparable to classical phlebography with radiography, is much safer in the diagnosis of veins in pregnant women because there is no radiation exposure to the patient and the fetus. Another advantage of whole-body magnetic resonance angiography is the search for arteriovenous malformations (AVMs) of the brain and various types of spinal cord hemangiomas.

 

Diagnosis of tumors and metastases with whole-body magnetic resonance imaging

In clinical practice, there is a wide range of situations when it is necessary to identify or exclude the presence of metastases possible in cancer in a cancer patient. this will determine the choice of the method of treatment he needs (surgery or chemotherapy with radiation therapy). Usually, when looking for metastases, doctors prescribe skeletal scintigraphy, computed tomography (CT), ultrasound, laboratory blood tests for tumor markers, etc. depending on the type of tumor in the patient. MRI tomography has also traditionally been used for the targeted diagnosis of various organs for the presence of metastases. Using traditional contrast-enhanced MRI, we searched for:

• metastases in regional lymph nodes
• liver metastases
• brain metastases
• spinal metastases

Modern full-body magnetic resonance imaging (MRI) is now widely available to detect stage M tumors (metastases).

Whole-body magnetic resonance imaging can detect bone infiltration with lymphoma, metastases, and infection (osteomyelitis). Also, this diagnostic method reveals damage to the parenchymal organs. Thus, whole-body magnetic resonance imaging can replace scintigraphy and computed tomography (CT). Metastases to the vertebral bodies are more distinguishable on MRI than on bone scintigraphy.

The three-dimensional volumetric images obtained with MRI after the injection of contrast have high resolution. They characterize the degree of damage to the parenchyma of an internal organ, bone, or soft tissue much better. With their help, it is possible to examine not only the bones but also the lungs, abdominal organs, and lymph nodes and ducts. MRI tomography detects almost all metastases of the lungs and brain visible on computed tomography (CT). Compared to scintigraphy, the vertebrae and pelvic bones are better visualized on MRI. The patient undergoes an MRI scan within 15 minutes, so this method is an alternative to scintigraphy when looking for metastases.

Positron emission tomography (PET) together with computed tomography (CT) and whole-body magnetic resonance imaging show similar diagnostic results when looking for distant metastases. MRI is preferred when looking for bone or liver metastases. But it should be borne in mind that MRI has the property of overdiagnosis of such tumor stages as T (tumor) and N (node). If positron emission tomography (PET) and computed tomography (CT) are not possible, or if children are reexamined (high risk of repeated exposure), whole-body magnetic resonance imaging may be an acceptable alternative. MRI is also relevant for patients with an allergy to iodine-containing contrast agents (idiosyncrasy), administered intravenously with computed tomography (CT).