imaging methods - radiography
TRANSCRIPT
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
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?