1
Q
Define endoscopy
A
Looking inside the body for medical reasons using an endoscope
2
Q
What is an endoscope?
A
Instrument inserted directly into an organ to examine to interior of a hollow organ or cavity of the body
- fibroscope optimised for medical applications
3
Q
Requirements of endoscopy
A
- direct view of the tissue
- sufficient light to see it
4
Q
Endoscopy Developing
A
Stage 1 = simple tube, insert in stomach, rigid, light bulb for distal illumination
Stage 2 = using series of lenses to transmit images, semi flexible
Stage 3 = fibre optic endoscopes to transmit an image of reasonable quality, greater flexibility
5
Q
How many fibres are carried in an endoscope and why?
A
Bundles of 10,000 fibres
- To carry more pixels for a greater quality image with better resolution
- Also enlarges the image, don’t want it too big as will not be able to use for in vivo imaging
6
Q
Components of an endoscope system
A
- rigid or flexible tube protecting fibres inside
- light delivery system to illuminate organs of interest
- fibre optics system to transmit image to viewer
- additional channel to allow medical instruments to be inserted into the body (e.g. forceps to take a sample for pathology)
7
Q
What are rigid endoscopes used for?
A
- spinal surgery
- larynx/throat
8
Q
What is a fibroscope?
A
Fibres based endoscope
9
Q
Advantages of a flexible endoscope
A
- insert and advancement easier
- less risk of trauma
- general anaesthetic unecessary
- patient can breathe spontaneously
- nose or mouth can be used for access
10
Q
Advantages of a rigid endoscope
A
- greater diameter of light transmitting components = better image & resolution
- easy to maintain airway
- larger/more robust surgical tools can be used
- removal of foreign bodies much more successful
- larger suction capabilities
- more precise targeting of laser beams
11
Q
Fibre-Optic Technology
A
- light is transmitted along a glass fibre to be directed to a specific location
- low weight
- small size
- low data loss
- good electrical isolation/ low noise/low signal loss
- very high bandwidth
- long distance travel possible
- fibroscope for imaging
12
Q
2 categories of optical fibre use
A
1 - guiding light
2 - communications
13
Q
Optical Fibres to Guide Light
A
MEDICAL USES
- guiding laser light to destroy tumors
- endoscopy
14
Q
Optical Fibres for Communications
A
- reasons they were developed
- 95% of telephone communications
15
Q
Types of endoscopes
A
- angioscope = veins/arteries
- arthroscope = joints
- bronchoscope = bronchi
- choledochoscope = bile duct
- colonoscope = colon
- colposcope = uterus
- cystoscope = bladder
- gastroscope = stomach
- laparoscope = peritoneum
- laryngoscope = larynx
- oesophagoscope = oesophagus
16
Q
Controlling Light Paths using fibre optics
A
- controlled by refractive index of materials
- refractive index is the amount by which a material slows down light
- high refractive index = light slowed more
- smallest refractive index = 1
17
Q
What is the equation for refractive index of materials?
A
n = c/v n = refractive index c = speed of light in vacuum v = speed of light in medium
18
Q
What is the speed of light?
A
3 x 10^8 m/s
19
Q
What happens if there is a boundary between a high refractive index material and a low refractive index material?
A
- light will hit boundary
- defraction will occur at the boundary
- governed by Snell’s Law
20
Q
Snell’s Law
A
Angle between light ray and normal ray = angle of incidence
Angle of refraction can be calculated
n^2 sin02 = n1 sin01
21
Q
How does fibre optics use Snell’s Law?
A
To cause a light beam to refract back into the first material
22
Q
What happens as the angle of incidence increases (01)?
A
The angle of refraction will reach 90 degrees
As it increases further, the incident light is reflected back into the first material = Total Internal reflection
23
Q
What is the critical angle?
A
Where 02 = 90 degrees
Angle of reflection = 90 degrees
24
Q
When does TIR happen?
A
When the critical angle is greater than 90 degrees
- light will go into the second media
- only when going from a higher index medium to a lower one
25
How does fibre optic technology use 2 materials?
- fibre has refractive index of n1
- coated with a second material of lower refractive index n2
- creates TIR and so light is reflected along a constant angle along fibre
26
What can go wrong with fibre optic signals?
- contamination on glass changes refractive index = light can escape
- glass is very thin to be flexible but also very delicate = tiny scratches/cracks propagate if bent
27
How to prevent problem with glass contamination?
- - prevent this with cladding = cover fibre with another layer of glass
- core inside has slightly larger refractive index than cladding
- cladding keeps core clean
28
How to prevent problem of delicate glass cracking/scratches?
- cover with plastic layer (primary buffer)
| - outside of the cladding
29
What is the main structure of the fibre optic?
Core -> Cladding -> Primary buffer layer
| Often also surrounded by PVC jacket too
30
What is the role of the primary buffer layer?
- mechanical protection
31
Cone of Acceptance
Easily determined as light enters and leaves at same angles
Also we know the refractive index of the core, cladding and the critical angle
Any angle greater than this will leave the fibre and not be guided through as angle will not be greater than the critical angle
- The numerical aperture
32
The numerical aperture
- larger = better capability for fibre to collect the light
- light gathering capability of a fibre
- square root of = n^2 core-n^2cladding
33
What formula relates numerical aperture & acceptance angle?
Acceptance angle = sin^-1 NA
34
What is the normal acceptance angle of glass and plastic fibres?
```
Glass = 14-15 degrees
Plastic = 27 degrees
```
35
How does the path of light vary?
- within the cone of acceptance, the light path for any ray depends on the incidence angle
36
Different rays of light path
1) Axial Ray
2) Meridonal Ray
3) Skew Ray
37
Axial Ray
- straight down the centre of the fibre will travel straight
38
Meridonal Ray
- once a light ray passes through the centre, it will always reflect to pass back through the centre
39
Skew Ray
- off centre will never travel throuh the centre but will bounce around the outside of the core
40
Transmission Losses
- unclean glass leads to absorption (impurities after manufacture block light of hydroxyl ions/trace metals)
- light scattering occurs as goes in different directions as gets lost
- fresnel reflection
- bending losses
41
What wavelength windows do we use?
1300nm and 1550nm = long distance telecomms, smaller losses
42
Rayleigh scattering
- light scattering
- small localised changes in refractive index of core/cladding
- imperfections cause scattering of light at that point
- affects a small region where critical angle>incident angle
- extent of loss depends on size of discontinuity to light wavelength (shorter wavelength = more scattering)
43
Fresnel Reflection
- when light hits a refractive surface at an angle close to normal, most passes through but some is reflected back
- occurs when light leaves/enters a fibre
- preventing by using fibre matching gels between fibres which has the same refractive index as the core or use similar fibres
44
Bending Losses
- bending the fibre changes the angle between the core + incident light
- ray is then outside the critical angle and escapes
- tighter bend = worse losses
- single fibre, cladding, buffer can bend to a radius of around 50mm
45
Dispersion
- all rays of light entering a fibre take different paths so arrive at different times
- images get mixed up
46
What is a MODE?
- each possible pathway a ray can take
- number of modes depends on numerical aperature and diameter of the core
- large NA or core = more possible modes
- small core + small NA = reduced modes
47
Single mode optical fibre
Single mode of propagation
| - reduces dispersion problems
48
Solution to model dispersion
GRADED INDEX FIBRE
- change the refractive index progressively from the centre to the outside of the core
- make it larger in the middle and smaller when closer to the cladding
- can make rays follow a curved path
49
Coherent Fibre Bundle of the Endoscope
- fibres held together by a sheath
- each fibre carrier incident light independently of other fibres
- to transmit a picture, fibres in a bundle have to be kept in same relative positions so each one contributes to image formation
- lens at either end of fibre optic focuses image for viewing and allows magnification
- more fibres = more detailed pictures
- 40,000 fibres in a good quality endoscope packed into 3mm bundle
- each fibre is clad to prevent cross-talk
50
Properties of fibres
- each is 10-20um across
51
What affects light collection?
- fibre diameter
| - NA
52
What affects image resolution?
- improves with smaller core diameters
53
How to select fibre size?
- fibre diameter
| - NA
54
What does thick cladding do?
- minimises crosstalk
- but reduces NA
- creates poor resolution with limited info. between fibres
55
Typical fibre sizes
- core = 10-20um
- cladding = 1.5-2.5um
- gives ratio core;cladding around 50%
- fibroscope contains 50,000 fibres
56
What affects light source?
- if fibres are not coherent
- large NA for maximum light
- white light source for real tissue colour
- larger fibres (13-100um) for illumination
- bundle of multimode fibre (400+)
57
Thin & Ultrathin fibrescopes
- for cardiology, neurosurgery
| - precise imaging of small elements
58
Size of thin fibrescopes
- outer diameter = 1-2mm
- core diameter = 5um
- 10,000 fibres
59
Size of ultrathin fibrescopes
- outer diameter = <1mm
- core diameter = 3-4um
- 3000-4000 fibres
60
Properties of the distal tip
- houses optical and mechanical components
- 1 or 2 light guides
- tip of imaging bundle with miniature objective lens (altered for different fields of view/focal lengths)
- flushing port (covered generally with blood/secretions so need to keep clean)
- end of ancillary channel (for suction tool or mechanical surgery tools)
61
Properties of the proximal end
- viewing optics and controls
- optics = focusing unit attached to eyepiece
- video equipment regularly attached to view during surgical use (complex processing used to optimise images from fibre optics)
- attachments for the wine and knobs at the distal end
- ports = inputs for distal, fluids,/air/gases, suction output, surgical tools
62
Flexible Shaft
- connects distal and proximal ends
- holds light guide, imaging bundles, ancillary ports together
- constructed with a steel mesh to stiffen endoscope and protect
- sheathed in a biologically inert plastic and hermetically sealed
63
Surgery with endoscopes
- without invasion
| - view inside whilst carrying out procedures
64
Why is surgery with endoscopes not ideal?
- limited freedom of movement
- no direct contact with tissue
- feedback from instruments poor
- 2D images only
65
Different types of surgery from invasive to minimally invasion
- open
- hand associated laparoscopic (1 hand within the body + laparascopic set up)
- small incision (direct view of tissue but no ability to manipulate)
- laparoscopic
66
Advantages of open surgery
- faster
- less complex
- greater functionality
- reduced time under anaesthesia
- cheaper
67
Advantages of minimally invasive surgery
- reduction in trauma/body cooling/pain/recovery time/risk of wound infection/hospital stay
- cheaper
68
Main requirements of laparoscopic surgery
- need suitable observation of surgical site
- hand eye co-ordination
- force transmission to tools
69
How to have suitable observation of surgical site?
- clearly lit images
- ease of viewing resulting image
- positioning endoscopes and knowing what is being viewed
- creating 3D understanding of image
- keeping lens clean
70
How to enable good hand-eye co-ordination?
- location of camera picture
- surgeon looking forward to a monitor not at hands
- misorientation of instrument movements
- difference between endoscope and surgeons line of sight
71
Force transmission to tools
- feedback from tissues (pulse, structure/properties)
- know force applied to grasp tissues
- pressure distribution across contact area
- degree of freedom & freedom of movement reduced
- preventing tissue damage while grasping
72
How to resolve the main concerns of laparoscopic surgery?
- suitable observation of surgical site
73
How to allow suitable observation of surgical site?
- bright white lights
- endoscope positioners
- shadow techniques/ sterero-endoscopes
- automated lens clearers
74
Light source importance
- essential for optimal vision
- high intensity & colour distribution = white light
- often use 2 light sources with different intensities = creates shadows and so depth perception
75
Endoscope Image Collection Importance
- most modern endoscopes use mini CCD cameras at distal end and transmit image with electronics
- noise resistance
- minimal transmission loss
- less image distortion
- fibre optics for light transmission
76
Stereo-endoscopes
- 2 camera images to regain some depth perception
| - must ensure each eye only sees image from correct lens
77
Endoscope Positioners
- control position during surgery
- passive = move to position, held by friction, need to let go of instruments
- active = driven by electrical motors, hand or foot control, still need to let go of instruments, foot control dangerous as can mix up with electrosurgery
78
Endo-periscope
- steerable tip to view organs from different sides
- obtain natural line of sight
- see behind things
Surgical Techniques & Safety
flashcards
Decks in class (5)
# Cards
