MRI

Question 1

The very basic principles of an MRI machine

Answer 1

• A MRI machine is a giant magnet in which the patient in placed into a uniform magnetic field.
• This causes the protons (hydrogen atoms) that make up the body and its water to align with the magnetic field.
• A radio frequency pule is applied and the energy absorbed by the protons causes them to change to a higher energy state and synchronise their spin
• This time taken for this energy to be released from the protons as radio frequency energy is different depending on tissue type.
• The machine uses this difference in time to display detailed images using only magnetic fields and radio waves

Question 2

MRI uses

Answer 2

• Scans of soft tissues (which you don’t get from X-ray)
• Scans show abnormal body water – cysts, swelling, infection
• MRI is better at telling the difference between types of soft tissues and between normal and abnormal soft tissues than CT
• Non invasive (but maybe claustrophobic and sedation may be required)
• Can be noisy by the various moving parts and the RF energy and magnetic fields –ear protection or music can be offered)
• Different types of MRI can investigate different conditions – Functional MRI (FMRI) links to brain localisation
• Contrast dyes may be used to enhance the image

Question 3

MRI Limitations

Answer 3

• The time needed for MRI is longer than that needed for CT. Also, MRI is usually less likely to be immediately available than CT. Therefore, CT may be better in emergencies, such as serious injuries and stroke. MRI is also more expensive than CT.
• Claustrophobia and sometimes difficulty fitting within the MRI scanner because it is a small, enclosed space
• The effects of the magnetic field on metal devices implanted in the body such as pacemakers, cochlear implants, and magnetic metallic clips can be damaged overheat or malfunction and may move
• Reactions to the contrast agent can occur

Question 4

MRI for injury and trauma

Answer 4

• As MRI shows soft and hard tissues so it better than other imaging if more than bone involved
• It is non invasive
• It does not expose the person to radiation
• There is a good contrast between tissue types
• Provides high resolution images that can show very small tissue changes can be detected to support diagnosis and treatment
• Allows images from a range of angles

Question 5

X-ray

Answer 5

• X-rays are ionising radiation so can damage tissue
• As they pass through the body, the energy from X-rays is absorbed at different rates by different parts of the body.
• Dense parts of your body that X-rays find it more difficult to pass through, such as bone, show up as clear white areas on the image.
• Softer parts that X-rays can pass through more easily, such as your heart and lungs, show up as darker areas
• There is a clear contrast but low definition and little information on muscles and other soft tissues, small blood clots and tumors may not show up.
• Quick, painless and can be used in real time to support positioning of medical aids in the body such as catheters.
• Can carry a small risk during pregnancy- risk vs benefits approach needed recommended for use in emergency only