NMSK 6 - MRI and CT SDL

Outline the basic principles of image production during CT examination.

- Uses ionising radiation (x-rays) that rotate around the circular opening of the gantry.

- The x-ray tube moves rotates around the patient, shooting narrow beams of x-rays through the body

- Quicker than MRI, longer than CT

How does CT image acquisition compare to normal radiographic imaging?

- CT scanner detectors do not produce an image

- Information is retrieved on the depth by measuring the transmission of x-rays through a full CT of the body from different angels.

- The CT computer then uses mathematically algorithms to construct a 2D image slice.

What is the relative dose to the patient of irradiation to a normal radiograph?

The relative dose of irradiation is higher for CTs than radiographs.

For which tissues of the body does CT provide good clinical information?

- Bones

- Soft tissues

- Blood vessels

- Organs

Explain the basic principles of image production during MRI examination.

- Produce images of thin slices of tissues.

- Use magnets to produce a strong magnetic field, forcing protons in the body to align with the field.

- A radiofrequency is applied, causing protons to align against the field in a high-energy state.

- The radiofrequency pulse is turned off and the protons relax, resuming their alignment within the magnetic field

- The radiowaves released from the protons are transmitted to the MRI receiver, which creates an image.

Discuss the health and safety implications of MRI imaging to both the patient and operator.

Magnetic field risk: metal will be drawn into the MRI as it is a magnet

What is the principle of a proton density image?

Tissues with a higher proton density will generate stronger radiowaves, appearing brighter on the image.

Explain the contrast agent gadolinium is and how it can be used in the investigation of the CNS.

- Gadolinium contrasts agent is paramagnetic as gadolinium have seven unpaired electrons.

- It reduces the relaxation time of protons, improving the contrast of the scan

- The signal is increased in tissues with increased blood flow, helping differentiation of tissue.

List the basic image properties of common tissues on T1 and T2 weighted MRI images.

T1-weighted enhances the signal of fatty tissue

- Show normal soft tissue anatomy and fat

- Fluid appears dark

- Fat appears bright

T2-weighted enhances the signal of fluid

- Show fluid and abnormalities, tumours, inflammation, and trauma

- Fluid and fat appears bright

For which tissues of the body does MRI provide good clinical information?

- Brain

- Spinal cord

- Nerves

- Soft tissues