Imaging Methods in Monitoring and Diagnosis

Dr Lizzie Peachey

Imaging Modalities

X Rays Ultrasound Magnetic Resonance Imaging Nuclear Medicine

X-Rays

Discovered by Roentgen in 1895

Ionising radiation Higher frequency /

short wavelength

X-Rays

X-rays produced by the x-ray tube pass through the body leaving a ‘shadow’ on the film

X-Rays

X-Ray Production

Contrast

Plain Digital Radiography

Computerised Tomography (CT)

CT X-Ray Beam

Helical CT

Computerised Tomography

Computerised Tomography

X-RaysPros 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

Utilises sound waves at ultrasonic frequency Above 20KHz is ultrasound but usually 3–10

MHz for medical imaging purposes Transducer sends and receives ultrasonic

waves Echoes from tissue can be detected and

data interpreted digitally to produce image Position and depth of the echoes builds up a

complete picture Gel is used to improve imaging

Medical Ultrasound (MU)

MU Imaging

MU Imaging

Image Manipulation

MU Imaging

Doppler Imaging

Medical UltrasoundPros Cons

◦ Non-invasive◦ No ionising radiation◦ Dynamic technique◦ Portable◦ Can image soft tissue

effectively◦ Flexible equipment◦ Relatively cheap

◦ Limited in what can be imaged

◦ VERY user dependent

Greatest detail of all the imaging modalities Uses a powerful magnetic field to align the

magnetization of atoms in the body Data detected can be digitally converted

into an image Utilises tomographic techniques of CT but

no radiation

Magnetic Resonance Imaging

Human body = 70% water – H2O MRI uses the spin of hydrogen atoms

◦ Single positively charged proton Spin causes tiny magnetic field All in different directions – PRECESSION Spin frequency depends on the type of

atom or molecule – LARMOR FREQUENCY Hydrogen atoms in different tissues have

different Larmor Frequencies

MR Imaging Principle

Alignment of Atoms

MR Imaging

MR Imaging

Image Manipulation

MR ImagingPros Cons

◦ Non-invasive◦ Does not use ionising

radiation◦ Excellent for imaging

soft tissues◦ Can image function◦ Good spatial resolution◦ Good at cancer diagnosis

◦ Very expensive◦ Has health and safety

issues◦ Has ‘acceptability’ issues

with some patients

Use of radioisotopes Attached to pharmaceuticals Drugs absorbed preferentially by target

organ(s) Gamma emitter so can be detected Images produced digitally from data

gathered

Nuclear Medicine

Nuclear Medicine Images

Nuclear Medicine Images

PET-CT

Nuclear MedicinePros 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

What information is required? Does structure or function need to be seen? 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?

Which should be used?