Video Stacks & Endoscopy Systems

Video Stacks & Endoscopy
Systems
Steven Lewis
Clinical Engineering
United Lincolnshire Hospital Trust

Endoscopy Systems & Video Stacks
Endoscopy is a minimally invasive medical procedure directly visualising any part of the inside
of the body using an endoscope, this will be used with a stack containing various equipment
such as a monitor, light source, insufflator, camera, and printer all connected through an
isolation transformer. These stacks are used in theatres and various clinics, such as Ear, Nose,
and Throat (ENT).
Endoscopes
An endoscope is a long, thin, rigid or flexible tube that consists of two or three main optical
cables, each of which comprises up to 50,000 separate optical fibres (made from optical-quality
glass or plastic). One or two of the cables carry light down into the patient's body; another one
carries reflected light (the image of the patient's body) back up to the physician's eyepiece (or
into a camera, which can display it on a monitor).
The optics of an endoscope are similar to those in a telescope. At the remote (distal) end, there
is an objective lens, which links to one or more bendy sections of fibre-optic cable that carry the
light back out of the patient's body to a second lens in an eyepiece or to a camera, which can be
manipulated to adjust the focus.
Endoscopes can be inserted into the body through a natural opening, such as the mouth and
down the throat, or through the anus. Alternatively, an endoscope can be inserted through a
small surgical cut made in the skin (known as keyhole surgery). Images of the inside of the body
are relayed to a Monitor. The instrument may not only provide an image for visual inspection
and photography, but may also be capable of taking biopsies or the retrieval of foreign objects.
Some of the most commonly used types of endoscope include:
Colonoscopes: used to examine the large intestine (colon).
Gastroscopes: used to examine the oesophagus and stomach.
Endoscopic Retrograde Cholangiopancreatography (ERCP): used to check for
gallstones.
Broncoscopes: used to examine the lungs and airways.
Other types of endoscope include:
Arthroscopes: used to examine joints.
Hysteroscopes: used to examine the womb (uterus).
Cystoscopes: used to examine the bladder.
Endoscopy can involve;
The Gastrointestinal Tract (GI tract): oesophagus, stomach and duodenum
(esophagogastroduodenoscopy), small intestine, colon, (colonoscopy, proctosigmoidoscopy).
The Respiratory Tract: the nose (rhinoscopy), the lower respiratory tract
(bronchoscopy), the urinary tract (cystoscopy).
The Female Reproductive System: The cervix (colposcopy), the uterus
(hysteroscopy), the Fallopian tubes (Falloscopy).
Normally closed body cavities (through a small incision): the abdominal or pelvic
cavity (laparoscopy), the interior of a joint (arthroscopy), Organs of the chest
(thoracoscopy and mediastinoscopy).

An endoscopy is normally carried out while a patient is conscious. It is not usually painful, but
can be uncomfortable, so a local anaesthetic or sedative may be given.
The exception is keyhole surgery, such as a laparoscopy or an arthroscopy, which are performed
under general anaesthetic. (Martin, 2014)
Endoscopy procedures are usually safe, and the risk of serious complications is low. Possible
complications of an endoscopy include an infection in the part of the body that the endoscope is
used to examine, damage to the body part which may in turn cause excessive bleeding.
Monitors
Monitors used on modern video stacks are high quality high definition (HD) flat panel screens,
with excellent colour reproduction and a wide viewing angle. Most will have various video
connections on the back such as S-Video, BNC, DVI, HDMI, etc. Some older video stacks may
have a non HD flat panel monitor or a CRT monitor.
Light Source & Lamps
The light source may form part of a video or endoscopic stack, be a stand-alone unit often used
in ENT procedures, or be attached to a microscope providing illumination to the area under
investigation, the light is usually transmitted via a fibre optic cable to the lens end of a scope.
High-Intensity Discharge Lamps
High Pressure Sodium (HPS), Metal Halide, Mercury Vapour and Self-Ballasted Mercury Lamps
are all high intensity discharge lamps (HID). Compared to fluorescent and incandescent lamps,
HID lamps produce a large quantity of light from a relatively small bulb.
HID lamps produce light by striking an electrical arc across tungsten electrodes housed inside a
specially designed inner glass tube. This tube is filled with both gas and metals. The gas aids in
the starting of the lamps, then, the metals produce the light once they are heated to a point of
evaporation. High intensity discharge lamps, such as xenon, are ubiquitous within the field of
endoscopy for minimally invasive surgery and diagnosis. Coupling light into a small diameter
fibre bundle is difficult, so an extremely bright light source is required. Historically, the light
source of choice has been the 180 to 300 W xenon lamp, which could deliver 1,000+ lumens of
light at the distal end of the fibre bundle. While xenon bulbs achieve the technical requirements
for endoscopy, they have a very short life, 500 - 1,000 hours, and can be expensive.
LED Lighting
The medical device industry is constantly changing. New technologies and products enter the
market, replacing outdated or inefficient equipment. LED lighting is one of these, and there are
numerous benefits in using LEDs for medical illumination applications including; longer life, less
heat, dynamic control, lower energy consumption, and in many cases, lower cost. LED
technology has improved significantly over the years, and is currently being integrated into
medical devices, including surgical lighting, exam lights, phototherapy, and endoscopy. Ongoing
advancements in LEDs that are driving the technology’s use in medical devices include
improvement in light intensity, product size and weight; long-term reliability, and
heat/temperature management, a line of high performance LEDs optimised to displace xenon
technology for endoscopy have been developed.

Fibre Optic
The light in a fiber-optic cable travels through the core by constantly bouncing from the
cladding (mirror-lined walls), a principle called total internal reflection. The cladding does not
absorb any light from the core, enabling the light wave to travel great distances.
Fig 1 - Fibre Optic Cable
Light source intensity is either adjusted manually via a dial or slider on the unit. If a camera and
processor are attached they can monitor the amount of light at the scope end and adjusts the
intensity automatically.
Different wavelengths of light are needed for different procedures;
Auto Fluorescence Imaging (AFI) is based on the detection of natural tissue fluorescence
emitted by endogenous molecules (fluorophores) such as collagen, flavins, and porphyrins.
After excitation by a short-wavelength light source, mucosal tissue emits a green fluorescence.
A difference in the intensity of this fluorescence is seen between healthy and unhealthy tissue.
These colour differences in fluorescence emission can be captured in real time during
endoscopy and used for lesion detection or characterisation.
Narrow Band Imaging (NBI) is a powerful optical image enhancement technology that
improves the visibility of blood vessels and other structures on the bladder mucosa. This makes
it an excellent tool for diagnosing bladder cancer during cystoscopy.
White light is composed of an equal mixture of wavelengths. The shorter wavelengths only
penetrate the top layer of the mucosa, while the longer wavelengths penetrate deep into the
mucosa. NBI light is composed of just two specific wavelengths that are strongly absorbed by
haemoglobin.
The shorter wavelength in NBI is 415 nm light, which only penetrates the superficial layers of
the mucosa. This is absorbed by capillary vessels in the surface of the mucosa and shows up
brownish on the video image. This wavelength is particularly useful for detecting tumours,
which are often highly vascularised. The second NBI wavelength is 540 nm light, which
penetrates deeper than 415 nm light. It is absorbed by blood vessels located deeper within the
mucosal layer, and appears cyan on the NBI image. This wavelength allows a better
understanding of the vasculature of suspect lesions. (Olympus, 2014)
Fig 2 – Absorption of Narrow Band Illumination

Insufflator
An Insufflator provides distension of the required cavity for diagnostic or operative procedures.
The insufflator pumps CO 2 into the cavity to a set pressure, this stretches the area being worked
on making it easier to manipulate tools, assess the surgical site or perform the operative
procedure. The maximum pressures of cavity’s should be observed when using an insufflator to
prevent any problems, for example, Prolonged intra-abdominal pressures greater than 20mmHg
should be avoided as they can cause any of the following problems;
Decreased respiration due to pressure on the diaphragm.
Decreased venous return.
Decreased Cardiac output.
CO 2 is now preferred over air as CO 2 is absorbed 150 times faster than the nitrogen in air, and is
promptly eliminated via the lungs. This also means that patients are not subjected to extended
discomfort from bloating and cramping.
Camera System
The camera on a video stack consists of two parts, the camera head, where scopes and light
guides are attached, and a processer unit which feeds the image taken by the camera to a
monitor, image capture device or printer.
The aperture opens and closes to control how much light travels from the subject through a
series of curved lens and through coloured filters focused on a digital sensor, which converts it
into a digital (numerical) format. This is then processed and fed to the image capture system,
monitor and printer.
Image Capture System
Image capture systems are image management systems that have the ability to record images
and videos to their internal hard drive. They can also be connected to the hospital network
where they can be integrated with PACS and other similar systems.
Many image capture systems are generally windows based systems with a dedicated user
interface. Very little maintenance of this system is required, at ULHT the only thing in the way
service and repair we carry out is to take an image of the hard-drive at acceptance in case of any
faults during its life, functional and visual checks and electrical safety testing.
Isolation Transformer
An isolation transformer is a transformer used to transfer electrical power from a source of
alternating current (AC) power to some equipment or device while isolating the powered device
from the power source, usually for safety reasons. Isolation transformers are used to protect
against electric shock, to suppress electrical noise in sensitive devices, or to transfer power
between two circuits which must not be connected. All true transformers are isolating as the
primary and secondary are not connected physically but only by induction. However, in an
isolation transformer the windings are completely insulated from each other to ensure good
isolation.

In a normal supply the earth conductor is referenced to the neutral
connector at source, which gives a potential voltage between live
and earth of 240V. This means that touching either the live or
neutral makes you part of the return path and can result in
electrocution.
With an isolation transformer the output voltage is not referenced
to ground, so you could safely touch the live conductor and ground
and not received a shock. This system is safer but if there is a fault,
the operator touched both live and neutral connections or there
was capacitive coupling between the secondary windings and
earth. This would allow current to flow from either of the
secondary connections through the operator/ patient to ground
and electrocution could still occur.
Maintenance & Service Procedures
Endoscopes
These are generally managed by the user, this includes cleaning.
Cameras and Image Capture devices
Cameras should have visual inspection and function test, checking image quality and focus also
ensuring the various buttons work as they should.
Image capture devices should also be visually inspected paying attention to the screen and case
all functions should then be checked including the touch screen responds if applicable. This
should then be safety tested.
Light Sources
A thorough visual inspection to include the case, mains lead, and the bulb for any
damage/pitting should be performed. A filter clean/change and an electrical safety test are
often all that is required.
Light sources that used arc lamps or HID lamps require a scheduled lamp change, usually at
approx. 500 hours of use.
Before HID lamps are disposed of in an appropriate manner the xenon gas should be discharged.
Insufflators
A Visual inspection should be performed taking special care to inspect any gas connections and
hoses including the pin index.
A Check of output pressure and flow rates for conformity and accuracy against manufacturer’s
specification. Check all controls work and that any alarms sound, including excess pressure and
empty cylinder alarm.
An Electrical Safety Test (EST) should then be completed to the appropriate standard.

Bibliography
Blackwell Publishing, 2014. Basic Endoscopic Equipment. [Online]
Available at: https://www.blackwellpublishing.com/xml/dtds/4-
0/help/10003420_chapter_1.pdf
[Accessed December 2015].
Martin, T., 2014. Principles of Gastrointestinal Endoscopy. Surgery (Oxford), 32(3), pp. 139-144.
Olympus, 2014. Olympus - Narrow Band Imaging. [Online]
Available at:
http://www.olympus.co.uk/medical/en/medical_systems/applications/urology/bladder/narro
w_band_imaging__nbi_/narrow_band_imaging__nbi_.html
[Accessed Febuary 2014].
ustudy, 2011. Endoscopy Working Principle. [Online]
Available at: http://www.ustudy.in/node/5066
[Accessed December 2015].