omi term 2 flowmetry

Question 1

what is flowmetry

Answer 1

measurement of flow

typically this will include

ultrasound
-A scan and B scan

ultrasound flowmetry
doppler flowmetry
retinal oximetry

Question 2

what is ultrasound

Answer 2

consists of high freq acoustic wave which are beyond upper freq limit of human range >20kHz

sound waves are analogous to light waves
they have freq and amp

speed is freq times wavelength

wavelength is related to spatial resolution
smaller wavelength is higher freq and smaller the details tha are detected
short wavelength are higher res

its converted to voltage and viewed on oscilloscope and changes in signal are displayed over time

time tkaen for ultrasonic wave to reflect from surface and return to originating point measured and converted to distance

used to measure

• axial length
• position of lens
• thickness of cornea

Question 3

ultrasound a scan

Answer 3

short for amp scan

gives info in one dimension only
good for measuring length of eye and for IOL power

single sound beam sent from transducer and echo tha returns are converted to series of spikes with heught proportional to strength of echo. this depends on type of tissue

spike deflections indciate pos of reflecting surfaces.

Question 4

ultrasound b scan

Answer 4

short for brightness scan
consists of 2d slices of tissue images which combine to give 3d image and used on outside of closed eyelid
echoes in b scan converted to dots with brightness intensity that is proportional to the echo amplitude
high amp echoes appear as hyperechoic (white)
absent echoes appear as anechoic(black)

used in opthalmology to asses eye disease

• retinal detachment
• tumours

Question 5

ultrasound review

Answer 5

adv
-safe does not use raditation
-widely accessible
relatively low cost compared to oct

disadv
low res
high amount of interoperator variablity

Question 6

doppler effect

Answer 6

change in freq or wavelength of wave in relation to an observer moving relative to wave source

noise maker will make cosntant sound(evenlyy spaced sounds)
as noise maker moves away from you sound waves appear more spaced apart and as it moves closer they appear closer

Question 7

ultransound doppler

Answer 7

doppler ultransonic velocitmeter detects and processes ultrasonic echoes issued from pulses reflected by micro particles in flowing liquid

singel transducer emits ultrasonic particles and recieves echoes
sampling causes incoming echoes at same time relative to emission of pulses
variations of positions of scatters are measured and so are thier velcoities

characteristics of spectral wave in cardiac cycle

s=systole-heart muscles contract,pump blood from chambers into arteries

d=diastole-heart muscle relax and chambers fill w blood

p-pulse amp

Question 8

ultrasound doppler adv and disadv

Answer 8

adv- non invasive and doesnt use radiation

disadv- relatively low res

Question 9

doppler effect light

Answer 9

if light moves towards u it has shorter gaps in wavelengths so would be blue shifted

if light moves away from you it has longer gaps so would be red shifted

Question 10

doppler flowmetry

Answer 10

method of non invasive continuous measuremnt of micro circulation of capillaries
technique based on value of doppler effect of low power laser light
light scattered radnomly by static structured and movin tissue particles
in human body doppler flowmetry can measure velocity of blood within a vessel
vessel under observation is perpindicular to axis of measuring wave

light source split into two coherent beams of light
light focussed at poin tthat makes interference fringes
as particles pass through fringes they reflect back to photodetector and here they cross region of constructive interference
reflected light fluctuates in intensity and frequency is equivalent to doppler shift between incident and scattered light so its proportional to particle velocity

signal at photodetector is a sinusodial wave
bandpass freq filter determines freq
speed is fringe spacing x f

Question 11

doppler flowmetry adv and disadv

Answer 11

adv non invasive and high res

disadv single point measurement

Question 12

retinal oximetry

Answer 12

fundus camera with attached image splitter
mirrors split beam from camera into smaller beams based on lights wavelength and retinal camera simultaneously acquires 2 images of retina at 2 wavelengths
at these wavelengths contrast of blood vessels is related to degree of oxygen saturation of haemoglobin
allows calulation of relative oxygen saturation of retinal blood vessels

548nm not sensitve to haemoglobin

610 nm senditbie to haemoglobin and retina appearslighter at this wavelength due to decreased absorption of light by retinal pigments

Question 13

retinal oximetry adv and disadv

Answer 13

adv non invasive and large fov and easy to intepret

disadv n/a