Magnetic Resonance Imaging: Basic Principles

                                             Orhan  Konez, MD                                Türkçe
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WHY MRI?

Magnetic Resonance Imaging (MRI) became the most popular imaging modality within recent years.  There are some basic reasons why MRI became so popular in such a short time.   It is clear today that the popularity and the use of this imaging modality will probably be further increased with implementation of new imaging techniques and sequences allowing this MRI to be used for many new indications.   

   

Reasons why MRI has been gaining attention:

1. In diagnostic radiology, there are 3 basic technical features of any imaging modality that can be used for comparison purposes:

a) Resolution

b) Sensitivity

c) Specificity

MRI has the highest soft tissue contrast among all available radiological imaging modalities. As seen in Table 1.1, the spacial resolution of MRI is not significantly different from other modalities (particularly CT). In fact, in the early years of MRI, because of the use of low matrixes such as 64 x 64, the resolution of MRI was not better than CT. However, with the rapid development of MRI technology, higher matrixes such as 256 x 256, even 512 x 512 became available for routine clinical work, which improved the resolution of MRI significantly.  On the other hand, MRI provides significantly better soft tissue contrast. This means that MRI has a high sensitivity (MRI can separate abnormal soft tissues from normal tissues much easier than other imaging modalities). However, the specificity of this imaging modality is not that good when compared to other imaging modalities. In some situations, similar signal abnormality can be caused by various medical conditions; therefore, the diagnosis may be challenging despite the fact that the abnormality is easily noticeable.  

2. With MRI, it is possible to obtain cross-sectional images on any plane without repositioning the patient. This feature is called “Multiplanar Imaging”.  This is due to the different way of obtaining images than other imaging modalities.  With other imaging modalities (particularly CT), the imaging plane can not be sagittal or oblique, and coronal images can be obtained only in some body parts (sinuses etc.). Whereas, MRI allows one to obtain images on any imaging plane without moving the patient on the MRI table. This feature allows one to assess the abnormality in various dimensions, therefore, to assess the abnormality more accurately without any additional discomfort to the patient. 

3. There is no ionizing radiation involved with MRI. If certain regulations and limitations are followed, there are no reported adverse biological effects. Because of this, MRI can be used on volunteers for research and on children safely. Also, patients can undergo multiple MRIs. 

4. The conventional way of obtaining vascular images is a catheter-based arteriography, which requires an invasive approach and also requires the use of vascular contrast (which may have side effects to the patient). MRI allows one to obtain vascular images, so called “MR Angiography” or “MRA”, without using any vascular contrast or any invasive approach. In most clinical settings today, MRA is used for screening; however, with the rapid improvement of the technique, MRA may replace the conventional angiography completely in the near future. 

5. One other important feature of this technique is the MR Spectroscopy.  Although this technique has not been used extensively, MR Spectroscopy may gain momentum, and even may overshadow the MRI (imaging) in the future.   MR Spectroscopy allows one to analyze the biochemical properties and metabolic activities of the tissues.

6. Although there are some artifacts specific to MRI, major limitations or artifacts of the other techniques (such as bone artifacts in CT and air/gas related limitations of Ultrasonography) do not pose any significant artifact or limitation with MRI. Therefore, many body parts (e.g., posterior possa, spine) that can not be studied with other techniques can easily be imaged with MRI. Because of this, MRI rapidly became the first line imaging modality in the head and spine.

 

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Disclaimer: This page is intended to be an alternative source for medical professionals who deals with magnetic resonance, in clinical practice or research, but should not replace a formal education, teaching or training in the field. The author of this web source, Orhan Konez, MD, holds no responsibility for accuracy of this information, data or images. This web page does not establish any form of consultation with Dr. Konez.  Information, statement or images can not be copied, duplicated and distributed in any form without permission.     

 

Links:

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