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
What advantages does diffuse optical tomography offer over BOLD fMRI?
DOT provides superior temporal resolution, portability, cost-effectiveness, and sensitivity to both oxygenated and deoxygenated haemoglobin compared to BOLD fMRI
What challenges exist in extending diffuse optical tomography into 3D imaging?
spatial resolution limitations, particularly in breast tumour detection
need for improved specificity in cancer screening
what are the key principles of optical coherence tomography (OCT)?
OCT measures reflections of light, similar to diagnostic ultrasound but using optical interference for range-gating. It provides high-resolution images of biological tissues
How does OCT achieve depth imaging in biological tissues?
OCT utilizes optical interference to measure reflections from tissue interfaces, with depth scanning achieved by varying the optical path length in the reference arm of the interferometer
What is the dominant application of optical coherence tomography?
ophthalmolgy, particularly imaging the retina
What is the significance of the interference pattern observed in OCT?
the interference pattern in OCT indicates matching optical path lengths in the sample and reference arms, enabling precise depth imaging of biological tissuesW
What is the process involved in generating acoustic waves in photoacoustic imaging?
- a medium is illuminated by a short pulse of light, the photoacoustic effect occurs
- regions within the medium that strongly asorb the light undergo sudden thermoelastic expansion
- the expansion results in the emission of broadband ultrasonic waves, detectable by ultrasound detectors at the surface
How are the 3D images generated in photoacoustic imaging?
- measurements of the time delay between tissue irradiation and acoustic wave detection are utilized
- these measurements, based on pulse-echo ultrasound imaging principles, allow the creation of 3D images depicting the origin of the ultrasound within the tissue
What advantages does photoacoustic imaging offer over other techniques?
Photoacoustic imaging combines high spatial resolution similar to diagnostic ultrasound with the contrast and sensitivity characteristic of optical techniques
Near-infrared wavelengths, with relatively low tissue absorption, allow irradiation of large tissue volumes with penetration depths of several cm
