STIR is based on a T2 image, but the image is manipulated in a way that results in fat (and any other materials with similar signals) being nullified. This is helpful to identify pathological signals. They nullify certain tissue types based on their inversion timings, thereby stopping tissues such as fat and CSF from appearing as bright signals. These types of images are manipulations of T1 and T2. Meningioma is shown more clearly by gadolinium contrast with a dural tail 5 Meningiomas will have a homogenous enhancement after the contrast, but will also have a вЂњdural tail,вЂќ meaning the lesion appears continuous with the dura (Figure 2). Typical intracranial abscesses have a вЂњring-enhancementвЂќ pattern, while metastases enhance homogeneously. Gadolinium appears bright in signal, allowing for detection of detailed abnormalities (e.g.

This process involves injecting 5-15ml of contrast intravenously, with images taken shortly thereafter.

arteries) or pathologically-vascular tissues (e.g. This is useful in adrenal tumours or bone marrow pathology, where the image will appear homogenous with surrounding tissue due to fat content. The fat signal can be suppressed to enable a better view of pathology in and around anatomical structures вЂ“ particularly oedema. Normal brain MR shows differences between T1 and T2 images 3 Additional features of T1/T2 weighted images

T2 is generally the more commonly used, but T1 can be used as a reference for anatomical structures or to distinguish between fat vs.

Conversely, the cerebrospinal fluid (CSF) is bright in T2 due to itsвЂ™ water content.

T1 is the most вЂanatomicalвЂ™ image (Figure 1).

T2 вЂ“ TWO tissues are bright: fat and water ( WW2 вЂ“ Water is White in T 2).

Between the two, the key differences you need to be aware of are: T1 and T2 images demonstrate different tissues based on the timing of the RF pulses.

T1-weighted and T2-weighted imaging (T1WI and T2WI).

Different combinations of these will be useful for different clinical presentations, but here are some examples of common images and sequences: There are many factors that lead to the production of a final MR image. For example, diffusion of water molecules can be studied with diffusion-weighted imaging (DWI), or macroscopic movement of blood can be studied, in the case of MR angiographic techniques. MRI can also be used as a dynamic imaging tool. We can also tell the machine to disregard certain values of signals to вЂњsuppressвЂќ them when it comes to viewing the pictures вЂ“ these are known as вЂњfat suppressionвЂќ sequences. Using these principles, you can adjust the machine to detect signals of varying ranges and from varying planes of magnetisation вЂ“ this is where the вЂњweighted imagingвЂќ comes in. The strength of this signal depends on the type of tissue (fat, muscle, water) that the hydrogen ion is in. When the RF pulse is turned off, these ions will attempt to realign with the magnetic field again and release a signal. Applying an RF pulse will change the direction of alignment of these hydrogen ions. When you put a patient in a strong magnetic field, their hydrogen ions align in the direction of the magnetic field. MRI machines work by exploiting the interaction of the magnetic field, hydrogen ions, and radiofrequency (RF) pulse. 1 Consideration should be given to patients who are claustrophobic as well.

MRI is contraindicated in patients who have ferromagnetic metal implants or foreign bodies. It takes slightly longer to acquire MR images and they are more expensive. MRI is particularly helpful in patients with suspected neurological or musculoskeletal pathology, however, they can be used in many other specialities too. They are often reserved for superior viewing of soft tissues. Generally, MRI is used less commonly than plain films and CT scans. 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.

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