Transcript

RADIOGRAPHER: It does make a very loud drilling noise, okay? So what we’re going to do is pop these earphones ...

NARRATOR: To obtain images, the patient is placed in a large, static magnetic field produced by a superconducting magnet. This powerful field, typically one and a half teslas in strength, causes the nuclei of the hydrogen atoms in the body to line up. But they can also be flipped into another direction by a radio frequency pulse.

The way these nuclei then relax back to their original position depends on the environment of the hydrogen atoms. In other words, on tissue type. When imaging small parts of the body, specialised coils are used to detect the radio frequency signal given off by the relaxing nuclei. Here a head coil is being used for this purpose.

Laser alignment is used so that the patient can be moved to the correct position in the scanner.

RADIOGRAPHER: Okay?

NARRATOR: Because the powerful magnetic fields can disrupt pacemakers, and cause heating of metal implants, every patient must be carefully checked before entering the scanner room.

RADIOGRAPHER: Okay, so we’re just going to start the scan now. Okay, so what we do first is an initial pilot scan. So that’s so we can exactly locate the patient within the scanner.

NARRATOR: With MRI, it’s possible to choose any direction for the image slices. In this case, the radiographer is taking an axial pilot scan, to give a series of coronal images.

RADIOGRAPHER: What we’ve done now is we’ve planned to scan through that area of this person’s head and we’re going to scan from front to back there. And so, okay, your first scan’s just about to start. Each scan will take about five minutes, okay? And then, after that, we can have a look through the images and we can see what we’ve got.

NARRATOR: There are many different imaging sequences that can be used. But most of them produce an image where the intensity depends mainly on one of three characteristics – T₁, T₂ or proton density. The intensity in these images depends largely on T₂, the spin-spin relaxation time.

Substances with a long T₂, such as water, appear bright. This is very obvious if you look at the eyes in this image.

RADIOGRAPHER: We’ve now gone on to sagittal images. This is a T₁. So we’ve got bright fat and the fluid’s dark on these images. This is a way that we can differentiate contrast to see different pathologies or anatomy. We also scanned in the axial plane, so that’s head to toe. And again, this is T₂ with bright fluid. You can see the eyes. And finally, these ones are proton density. So this is weighting – where each tissue is the protons that are actually there, rather than any specific weighting.

NARRATOR: Thankfully for this patient, the images show no abnormality.