Other imaging techniques Flashcards
wien’s law
maximum wavelength = Wien’s constant / Temperature
What is the application of thermography?
detection of breast cancer
What do thermal images reveal?
regions of high infrared emission associated with underlying tumours
disadvantages of thermal images
infrared radiation has a very low penetration depth in tissue (due to absorption by water), so thermal images can only display temperature variation on the surface. The images have very poor sensitivity to smaller tumours located deep below the skin surface.
Why is microwave radiation considered to be safe at intensities low enough not to produce a significant heating effect?
because it is non-ionising so it doesn’t produce a significant effect at low intensities
What happens to the absorption of shorter wavelength microwaves in tissue?
it is much higher than that at longer wavelengths
What is a 2nd inherent problem of using microwaves for imaging?
significant diffraction which occurs when microwaves transmit across tissue
What’s it the consequence of significant diffraction occurring when microwaves transmit across tissue?
image reconstruction is not straightforward
What is a second inherent problem of using microwaves for imaging?
coupling microwave radiation into tissue requires an index matching medium to prevent reflection occurring at the surface
How is the problem of coupling microwaves at the surface usually addressed?
The coupling problem is usually addressed by submerging the patient and microwave apparatus in a water bath
Diffuse optical imaging
visible or near-infrared light, which scatters within biological tissue, losing directionality after about 1mm.
Transillumination
illuminated tissue from behind, revealing features like hydrocephalus and testicular cancer by exploiting water’s low scatter and blood’s absorption.
What are the key differences between oxy-haemoglobic and deoxy-haemoglobin in terms of absorption of optical radiation?
Oxy-haemoglobin and deoxy-haemoglobin exhibit characteristic differences in absorption , particularly noticeable in the near-infrared range, enabling optical measurements to assess blood oxygenation
What is the primary advantage of near-infrared range in optical imaging of biological tissue?
The near-infrared range offers low absorption by blood, facilitating deep penetration of light into tissue, a crucial factor for optical imaging techniques
how does diffuse optical tomography (DOT) function, and what does it enable in terms of brain imaging?
DOT utilizes optical fibers on the scalp to measure changes in diffusely reflected light, allowing real-time functional imaging of brain activitiy during stimuli responses, brain development and clinical conditions such as epilepsy