imaging methods - radiography

Imaging Methods in Monitoring and Diagnosis

Walter Hall

School of Health Sciences

University of Ulster

Imaging Modalities

• X-Rays

• Nuclear Medicine

• Medical Ultrasound

• Magnetic Resonance Imaging

X-Rays

X-Rays

• Discovered in 1895 by Roentgen

• An ionising radiation at a higher level on EM spectrum

• Higher frequency or shorter wavelength

X-Ray Production

Plain Digital Radiography

Computerised Tomography

CT X-ray Beam

Helical CT

Computerised Tomography

X Rays: Pros and Cons

• Non-Invasive• Well established

technology• Still evolving• Flexible• Readily available and

therefore relatively cheap

• Ionising Radiation• Not good at imaging

soft tissue on its own

Nuclear Medicine

• Use of unsealed radioisotopes

• Attached to pharmaceuticals

• Drugs absorbed preferentially by target organ(s)

• Gamma emitter so can be detected

• Images digitally produced from data gathered

Nuclear Medicine Images

PET-CT

Nuc Med: Pros and Cons

• Can image wide variety of tissue types

• Easy to target specific tissue

• Can image function• Utilises by-products of

other processes so cost effective

• Uses ionising radiation

• Could be described as invasive

• Has many radiation protection issues associated with it

• Better applications are expensive

Magnetic Resonance Imaging

• Manipulation of natural magnetic field

• Nuclear magnetic resonance is detectable and measurable

• Data detected can be digitally converted to an image

• Utilises tomographic techniques of CT

MRI Principle

• Atoms have magnetic moments

• They spin in a magnetic field – Precession

• Spin frequency depends on the type of atom or molecule – Larmor Frequency

• Examine the spin of hydrogen atoms

• Hydrogen atoms in different tissues have different Larmor Frequencies

MRI Advantages

• X-rays are absorbed in different amounts by different tissues

• Variation between tissues is very small

• MRI measures three different quantities

• Some or all are very different for different tissues

• MRI can penetrate bone

MR Imaging

Using Data Manipulation

Image Manipulation

Pros and Cons

• Non-Invasive• Does not use ionising

radiation• Excellent for soft

tissue imaging• Can image function

• Very Expensive • Has its own health

and safety issues• Has “acceptability”

issues with some patients

Medical Ultrasound

• Utilises sound waves at ultrasonic frequency

• Above 20KHz is ultrasound but usually 3 - 10 MHz for medical imaging purposes

• Echoes from tissue can be detected and data interpreted digitally to produce image

• Position and depth of the echoes builds up a complete picture

MU Imaging

Image Manipulation

Doppler Imaging

Pros and Cons

• Non-Invasive• No ionising radiation• Dynamic technique• Can image soft tissue

effectively• Flexible equipment• Relatively cheap

• Limited in what can be imaged

• VERY user dependant

Which do we use?

• What information do we require?

• Do we wish to see function or structure?

• What can the patient tolerate?

• What would the clinician prefer?

• What is available for use?

• Is there a safer/cheaper alternative?

• Can potential risks be justified?

QUESTIONS?