As mentioned before, the spins of some hydrogen nuclei are in the same direction as the magnetic field. Since these nuclei choose to be in the same direction as the magnetic field, they do not need much energy (you can think of them to be the “lazy” ones). In our diagrams, as shown below, I will label these “low energy nuclei” as “Low” . On the day of your MRI scan, you should be able to eat, drink and take any medication as usual, unless you're advised otherwise. Andrew Murphy, et al. MRI sequences (overview). Radiopaedia.org, the wiki-based collaborative Radiology resource. [Internet] (Accessed: 21st March 2020). Available from: [ LINK] The radiographer may ask you to hold your breath for a few seconds or follow other instructions during the scan.

It very important to keep in mind that, because of the above phenomenon, that the magnet is always ON. Even when the MRI machine appears to be “OFF” and the staff gone home for the night, the magnet keeps on working. Lesions that appear hyperintense on DWI are said to show “diffusion restriction,” which is always a pathological finding.[ 11] The mechanism for restricted diffusion of water may be varied; however, for e.g. in abscesses, the motion of water molecules is limited by the viscosity of the fluid and dense inflammatory infiltrate. In ischemia or severe demyelinating optic neuritis, cytotoxic edema results in cellular swelling and decreased intercellular spaces with cellular swelling and resultant diffusion restriction. In highly cellular tumors, such as lymphomas, reduced interstitial spaces result in similar diffusion restriction. An additional calculated map called the apparent diffusion coefficient (ADC) map, which is similar to an inverted color image, is also provided. True diffusion restriction will appear hypointense on ADC maps and hyperintense on DWI. Advanced applications based on diffusion include quantitative analysis of the degree of diffusion restriction, which allows differentiation between benign and malignant lesions.[ 12] The fat signal can be suppressed to enable a better view of pathology in and around anatomical structures – particularly oedema. This is useful in adrenal tumours or bone marrow pathology, where the image will appear homogenous with surrounding tissue due to fat content. Magnetic resonance imaging is a rapidly developing imaging modality, both technologically and in its clinical application. This growth is due to the originality of its foundations, at the crossroads of nuclear physics, mathematics, chemistry, biology and physiology. It is these technical characteristics that differentiate it from other medical imaging modalities. They give it multiple capabilities: morphological imaging with high tissue contrast, functional imaging of movement, flow, perfusion or even chemical composition. Knowing the Basics of MRI for interpretation

After the scan, you can resume normal activities immediately. But if you have had a sedative, a friend or relative will need to take you home and stay with you for the first 24 hours. In some cases, you may be asked not to eat or drink anything for up to 4 hours before the scan, and sometimes you may be asked to drink a fairly large amount of water beforehand. This depends on the area being scanned. Assoc Prof Frank Gaillard. Meningioma shown more clearly by gadolinium contrast with a dural tail. Licence: [CC BY-SA]. Available from: [ LINK] Hydrogen nuclei have a quantum physics property called “spin “. Now you probably imagine hydrogen nuclei “spin” to look something like this. Dr Hidayatullah Hamidi. Normal brain MR shows differences between T1 and T2 images. Licence: [CC BY-SA].

Depending on which part of your body is being scanned, you may need to wear a hospital gown during the procedure. You might also be interested in our OSCE Flashcard Collection which contains over 2000 flashcards that cover clinical examination, procedures, communication skills and data interpretation. Now something fascinating happens to the hydrogen nuclei with low energy. These hydrogen nuclei with low energy absorb the energy sent from the RF coil. We are now ready to start understanding how the MRI machine works. The MRI machine cannot just simply “see the hydrogen nuclei which lie “hidden” in the water molecules distributed in the patient.To save space and to generate a strong enough field, the wire is usually wound into a coil. In my previous explanations, I had drawn the magnet as two green coils on either side of the patient. This I did to make the images less cluttered. Now let us return to discussing the MRI machine. You will recall that we said that MRI machines can “see” hydrogen nuclei contained in water molecules.