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Design of a Head Mounted Display for Image-Guided Surgery. Bo Bai Stephanie Dalquist Megan Galbraith 16 May 2002. Introduction. Develop HMD for surgeons Projects diagnostic images on patient Compare digital X-Rays, NMR Overlay text plans High resolution and accuracy

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Design of a Head Mounted Display for Image-Guided Surgery


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design of a head mounted display for image guided surgery

Design of a Head Mounted Display for Image-Guided Surgery

Bo Bai

Stephanie Dalquist

Megan Galbraith

16 May 2002

introduction
Introduction
  • Develop HMD for surgeons
  • Projects diagnostic images on patient
    • Compare digital X-Rays, NMR
    • Overlay text plans
    • High resolution and accuracy
  • Design micro-display for image source
technology goals
Technology goals
  • Full color, 4 bits/color grey scale
  • Minimum frame rate of 100 Hz
  • High resolution – 1280 x 1024
    • Pixel pitch at most 24 μm
  • High contrast ratio, at least 100:1
    • Design for hospital environment, 100 Cd•m-2
    • Minimum brightness 60,000 Cd•m-2
display technology
Display technology
  • Active Matrix Organic LED
    • Fast response time of 3 μs
    • Pixel pitch down to around 12 μm
    • Can reach brightness levels up to 106 Cd•m-2
    • Reliable to 106 hours
  • Preferred over other technologies
    • AMEPD: color difficulties
    • AMLCD: less bright
    • AMELD: not very bright (23 Cd/m2 at 60 V)
grey scale method
Grey scale method
  • Sub-framing
    • Allows for 16 shades from black to white
    • Minimizes flicker at high ν (1600 Hz)
  • Other options
    • Patterning: Too much flicker, too few greys
    • Voltage modulation:
      • Requires high sensitivity to ΔV
      • More complicated drivers
pixel structure
Pixel structure
  • Stacked OLED
  • True color
  • High contrast
  • Bright, emissive
  • Flexible
  • Makes pitch spec
pixel structure7
Pixel structure
  • Stacked OLED preferred
  • Other options:
    • Side-by-side monochrome
      • Large pitch or lower resolution
      • Many have decreased viewing angles
    • Color filters
      • Absorption loss
      • Need efficient blue dyes
pixel circuit
Pixel circuit
  • Diode equivalent for each color
  • Single line addressing
    • Voltage across rows
    • Data down columns
    • High frequency
    • Simpler, cheaper drivers
oled requirements
OLED requirements
  • 9V to reach 60,000 Cd•m-2
  • Current Density of 50 mA/cm2
  • Area = Apixel - Atransistors = 570 μm2
  • Current =2.87 x 10-4 mA
cmos specification
CMOS specification
  • Choose n-doped CMOS: Kn > Kp
    • Lowers power consumption
  • VGS = 0.6V
    • ID = 0.5Kn(VGS-VTn)2
  • VG1 = VGS+Vdiode = 0.6+9 = 9.6V
  • VG2 = VG1+VTn = 9.6+0.5 = 10.1V
  • Column voltage = VG1 = 9.6V
  • Row voltage = VG2 = 10.1V
driver specifications
Driver specifications
  • Generic driver circuit
    • Can be used with OLED, ELD, LCD, etc.
  • Row driver draws 10.1 V
  • Column draws 9.6 V
i o data rate for drivers
I/O data rate for drivers
  • Row data rate
    • Selects a row to update
    • Consider 16 sub-frames for grey scaling
    • 1.6 MHz or 205 Kbps
  • Column data rate
    • Sends color information
    • 6.29 GHz or 786 Mbps
    • Much more data, much faster data rate needed
power consumption
Power consumption
  • Total power consumption of 4 W
    • 2 x 10-6 W per pixel
      • Ppixel = VI = 9V x 2.87x10-4 mA
    • Display requires 4 W
      • Ptotal = PpixelNrowsNcolumns
    • Conservative estimate assuming all pixels on
overall efficiency
Overall efficiency
  • Display efficiency ηdisplay= 27%
    • 4 lumens/Watt power efficiency at 9 V
    • Input Power Pin = 4 W
    • Output Power

Pout = 60,000 Cd/m2 • Area/(4 lm/W • 4π Cd/lm) = 0.9 W

    • ηdipslay = Pout/Pin
  • Optical subsystem ηoptics = 15%
  • Overall ηdisplay •ηoptics= 4%
conclusions
Conclusions
  • Meet target specifications at low cost with current technology
    • Not power hungry
    • Safe (low voltage, amperage, etc.)
  • Take it to the lab for prototyping
  • Revolutionize health-care by 2010