Design of Health Technologies Medical Sensors

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Design of Health TechnologiesMedical Sensors
EEG Electroencephalogram

• Biosensors
• EEG Electroencephalogram
• Hernia Repair (Herniorrhaphy)
• Diabetes / Implantable insulin pumps
• Implantable Cardioverter defibrillator (ICD)
• Glucose monitoring
• Other systems

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Advanced Sensing Systems

• Biosensors
• EEG Electroencephalogram
• Hernia Repair (Herniorrhaphy)
• Diabetes / Implantable insulin pumps
• Implantable Cardioverter defibrillator (ICD)
• Glucose monitoring
• Other systems

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EEG Electroencephalogram (Monitoring Brain waves)

• Brain cells communicate by producing tiny
  electrical impulses. In an EEG, electrodes are
  placed on the scalp over multiple areas of the
  brain to detect and record patterns of electrical
  activity and check for abnormalities.
• You apply between 16 and 25 metal discs
  (electrodes) in different positions on your scalp
  which are held in place with a paste. The
  electrodes are connected by wires to an amplifier
  and a recorder.
• EEG is used to help diagnose the presence and
  type of seizures, to look for causes of
  confusion, and to evaluate head injuries, tumors,
  infections, degenerative diseases, and metabolic
  disturbances that affect the brain.
• It is also used to evaluate sleep disorders and
  to investigate periods of unconsciousness. The
  EEG may be done to confirm brain death in a
  comatose patient.

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Hernia Repair (Herniorrhaphy)

• A hernia occurs when part of an organ (usually
  the intestines) protrudes through a weak point or
  tear in the thin muscular wall that holds the
  abdominal organs in place.
• Hernia repair is performed as an outpatient
  procedure using local or general anesthesia.
  First, through an incision, the segment of bowel
  is placed back into the abdominal cavity. Next,
  the muscle and fascia are stitched closed to
  repair the hernia. A piece of plastic mesh is
  often used to reinforce the defect in the
  abdominal wall.
• A hernia occurs where any part of the body
  abnormally protrudes into any other area.

Hernia operation Animation
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Diabetes / Implantable insulin pumps

• Implantable insulin pumps are emerging
  insulin-delivery devices that can be surgically
  implanted under the skin of individuals with
  diabetes. The pump delivers a continuous basal
  dose of insulin through a catheter and into the
  patients abdominal cavity.
• Implantable insulin pumps are devices that can be
  surgically implanted in individuals with diabetes
  as an insulin-delivery device. They are usually
  placed on the left side of the abdomen.
• The disk-shaped pumps are about the diameter of a
  hockey puck but much thinner. They weight about 5
  to 8 ounces when filled. The reservoir holds up
  to several months worth of insulin and is
  refilled via a syringe injection through
  abdominal tissue. Depending on the dosage of
  insulin, the battery in an implanted pump lasts
  about eight to 13 years, according to one
  manufacturer.

Diabetes Type I and II
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Implantable Cardioverter defibrillator (ICD)

• Summary
• An implantable cardioverter defibrillator (ICD)
  is a device that is implanted in the chest to
  constantly monitor and correct abnormal heart
  rhythms (arrhythmias). The devices were developed
  originally to correct heart rhythms that are too
  fast, but recent technological advances have
  increased the pool of possible patients who may
  benefit from an ICD. 
• ICDs are mainly used to treat two forms of
  abnormal heart rhythms, both of which occur in
  the ventricles, or lower pumping chambers of the
  heart. If the ventricles begin to beat too
  quickly (ventricular tachycardia), the device may
  emit low-energy electrical pulses that allow the
  heart to regain its normal rhythm. If the
  tachycardia progresses to a very rapid,
  life-threatening rhythm that causes the
  ventricles to quiver rather than beat
  (ventricular fibrillation), the device may
  deliver a relatively stronger jolt to reset the
  heart rate (defibrillation).

Heart Conduction Animation
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Implantable Cardioverter defibrillator (ICD) cont

• Left Ventricular Assist Device Animation
• Heart Bypass Surgery
• Angiogram
• Stress Test
• Hypertension

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Vitamins and Minerals

• Vitamins and minerals are naturally occurring
  nutrients found in foods that are needed by the
  body for normal functioning and overall health.
  These essential nutrients must be obtained from
  the diet because the body cannot manufacture
  them. They are often referred to as
  micronutrients because they are needed in small
  amounts by the body. A lack of any of the
  essential micronutrients from the diet may lead
  to deficiencies, compromising the ability to
  function and impairing health. There is also a
  risk of toxicity with certain micronutrients when
  too much are consumed daily.
• Several vitamins and minerals, as well as some
  phytochemicals, are classified as antioxidants.
  Recently, antioxidants have received a lot of
  attention for their possible role in disease
  prevention due to their ability to reduce
  cellular damage caused by free radicals. However,
  further research is needed. In addition, some
  researchers claim that certain vitamins and
  minerals are helpful in the prevention and/or
  treatment of various heartrelated conditions.
  There is also a substance called coenzyme Q10
  that acts like an antioxidant vitamin. Scientists
  and researchers know the roles the following
  vitamins and minerals play in our bodies, and
  this group may have hearthealthy effects

• Vitamin and Mineral Animation

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Magneto-elastic sensors (Grimes)

• The magneto-elastic material resonates at a
  characteristic frequency when excited by a
  magnetic field.

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Magneto-elastic sensors

• The magneto-elastic ribbon is made of a
  commercial sheet called Metglas.
• The polymer is a custom co-polymer made by the
  Grimes group. It is believed to work because
  glucose bonds to sites on polymer chains that
  separate them from other chains. This allows the
  polymer to absorb water.

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Magneto-elastic sensors

• Its frequency response (in air) shows a sharp
  peak which is determined by the density of the
  polymer layer

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Magneto-elastic sensors

• Resonant frequency in a liquid is lower, and the
  peak is not as sharp.

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Magneto-elastic sensors

• Frequency response in water varies with the
  glucose concentration, in an almost perfectly
  linear curve.

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Sensor measurement

• The electronics are simple. A sharp spike is
  applied to a driving coil, and a response is
  measured in a sense coil.

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Sensor measurement

• The magnetic spike is short, about 3 gauss for 16
  micro-seconds (earths magnetic field is about
  0.5 gauss, and a refrigerator magnet about 10
  gauss).
• The pickup coil measures sensor activity for a
  further 8 milli-seconds. The response is
  transformed with an FFT to determine the
  frequency peak.
• This should be easy to do with a small,
  battery-powered device. Because the sensors
  response is quite slow (tens of minutes to
  respond), it is enough to take readings every few
  minutes.

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Biosensor status

• There are many promising systems on the horizon,
  but the only commercially-deployed biosensors are
  glucose monitors (4B). 3 main types
• Single Use Disposable sensing material, often
  static measurement. Cheap and portable, but low
  sensitivity and accuracy.
• Intermittent Use Often use hydrodynamics
  generally much better performance from sensing a
  moving fluid. Its still a challenge to move these
  out of the lab and onto a chip.

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Biosensor status

• Continuous (In Vivo) Sensors Very economical,
  but very hard to calibrate and may suffer from
  unknown amount of drift.

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Biosensor design

• We give a brief introduction to micro-fluidic
  sensor design.
• While these were originally fabricated in silicon
  using MEMS techniques, the trend is toward glass
  and plastic as the substrate.
• Both glass and many plastics allow optical
  measurements, but silicon is opaque to visible
  light.
• Glass and plastic are also more resistant to
  contamination from the chemicals used in the
  measurement.

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Biosensor design

• Surface immobilization The first step is sensing
  is creating a selective surface to react to the
  sensed agent

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Biosensor design

• Bead immobilization A variation that uses beads
  to increase relative surface area.

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Biosensor design

• Detection Several methods, including resonant
  frequency of MEMS cantilevers. But amperometry
  (current measurement) is the most widely used
  approach. Typical mechanisms for current flow
  include redox cycles between the target group and
  variants.

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Biosensor design

• Optical Detection A 2D array of agent/antigen
  reactions produces fluorescent traces

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Biosensor design

• Magnetic Detection The antibodies are
  immobilized on a surface and magnetic beads bind
  to sites where the analyte is attached.

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Enzyme-Linked Immunosorbent Assay
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Reuse

• Most immunosensors use bound antibodies and
  immobilization. Removing the bound species can be
  difficult without destroying the sensors.
• Methods and results vary, but a recent detector
  for Chagas disease used glycine-HCl to wash the
  sensor, and reported efficacy for more than 30
  cycles.

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Biosensor design

• Systems-on-a-chip are promising but coming
  slowly. Biosensing still seems a long way from
  commercial viability. But there are some
  promising prototypes

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Discussion Questions

1. It may be a while before we have highly
   integrated sensors for many pathogens (and
   economics dictates that they will come for
   first-world diseases first). Can you think of
   telemedicine/information tools to help facilitate
   traditional (but simple) lab methods?
2. Sensors for medical diagnosis may always be a
   difficult economic proposition. Can you think of
   other models that might work? E.g. home testing?