HD

This is a lecture outline for a talk I am giving on 2013-02-28 in Nice, France at the CEORL conference.

High-definition Laryngology is using high and low technology to optimally visualize pathology of the vocal cords and larynx.

There are two components to Imaging which can be divided into 

• high technology and 
• low technology.

High technology is inherently expensive and low technology is inexpensive.

• Money buys high technology.
• Knowledge buys low technology.

While the optimum combination might be to have the most expensive and newest equipment as well as a complete working knowledge of diagnostic laryngology, there are numerous other cost effective combinations that can yield a high ratio of correct diagnosis.

High-definition laryngology is primarily maximizing the number of pixels exposed to the pathology.

Color enhancement adds quality to the pixels.

Assumptions

1. Some type of device is needed to visualize the larynx since it does not lie directly in the line of vision.
2. An endoscope is the most common device, even though it is possible to view the larynx with a mirror.
3. A recording device is a key component, because the movement in the larynx means that details can be fleeting.
4. A stroboscope slows the apparent motion even further revealing additional details.
5. Three types of endoscopes can be considered:

• Fiberoptic transnasal endoscope with attached camera
• Chip transnasal endoscope with intrinsic camera
• Rigid transoral endoscope with attached camera

Although cameras can be roughly divided into SD (Standard Definition) and HD (High Definition) , there are actually numerous, perhaps unending levels of definition that are available to be recorded.

While images can still be recorded on videotape (analog or digital), most of the world has moved to digital capture. There are many different software and hardware capture devices with many different algorithms for capture, compression and recording of the images.

But setting aside some of these details temporarily, in general terms, the closer the endoscope is to the pathology, the more of the image that will be filled with the pathology. Alternatively, one could say the more pixels there will be on the pathology. Consequently, resolution is highly distance related. The closer the sensor to the pathology, the more impressive the image and the more understandable the pathology.

Abstract

High-definition Laryngology is using high and low technology to optimally visualize pathology of the vocal cords and larynx. While high technology is expensive and low technology is inexpensive, an optimum combination leads to a cost-effective, high yield of correct diagnosis for laryngeal pathology. Some of the important variables include the choice of flexible fiberoptic endoscopes, chip endoscopes and rigid transoral endoscopes of various angles which can then be combined with Standard Definition or various levels of High(er) Definition video processors for recording examinations. Selective color imaging also improves visualization of laryngeal pathology. The most often overlooked improvements in definition are the closeness of the camera to the pathology and knowing where to position the endoscope. The orientation of the camera as well as the angle, type and intensity of lighting impacts the perception of the pathology. Automatic video gain, digital noise and depth of field impact perception of pathology significantly. As a general rule, the closer the endoscope is to the pathology, the more pixels that will be filled with the pathology, leading to a higher definition examination. The closer the endoscope is to the pathology, the more light is available to clarify pathology. Stroboscopy and high speed video are alternative means of dynamically viewing laryngeal function. Varying the vowel, pitch and volume are very effective and very inexpensive tools to elucidate vocal cord margin lesions, glottic gaps and stiffness. Video compression has a smaller impact on the resolution, but there are many choices, and the number of chips in the camera also has an impact on the image. In this lecture, these many variables will be reviewed for their role and relationships in a High-definition laryngology examination.

Example Case

History - 72 year old female

Mitral Valve Surgery - she undergoes a cardiac procedure

1. Risk of left recurrent nerve injury moves up in the differential diagnosis since the recurrent laryngeal nerve wraps around the aortic arch. (In my experience this injury is more common than in the medical literature because voice impairments are assumed by surgeons & patients to be less important than the primary surgery. There is some grand assumption that almost all voice injuries resolve on their own. - And most improve, but a great many people are left with some residual impairment.)
2. Either Recurrent laryngeal nerve can be injured at the anterior branch by prolonged compression from a high position of the endotracheal tube cuff along with overinflation. (Again this is a more common than anticipated injury. The majority of anesthesiologists that I observe over-inflate the cuff. It is frequently located higher in the airway than the anesthesiologists believes.)
3. Less commonly, the vocal cords can be directly traumatized by the intubation. (Although this usually causes diplophonia initially rather than aphonia or hypophonia since trauma causes swelling and narrows the glottis whereas neurologic impairment allows the vocal cord to lateralize initially before reinnervation occurs some weeks to months later.)

Complications - After surgery she is intubated for 10 days

1. Arytenoid reduced mobility is a common finding. Paralysis, paresis or scaring of the posterior glottis should now be high in the differential diagnosis.
   • Ulceration of the medial surface of the vocal process/arytenoid is common even after a 2 hour indwelling endotracheal tube.
   • After 10 days ulceration is certain to occur.
   • Granulation tissue will form.
   • If granulation tissue bridges the gap across the posterior glottis and then epithelializes, permanent fixation occurs.
2. Subglottic trauma and scaring are also common injuries from prolonged intubation for the same reason as #1

Symptoms

1. Hoarse for two months after endotracheal tube removed
   • Initially very weak voice
   • Gradually stronger
2. Then develops shortness of breath and gasping

Consultations with Doctors

1. ER - Emergency Room
   • Treated with epinephrine, bronchodilators
   • Chest X-ray, VQ Scan
   • Not pulmonary embolism
   • probably emphysema
2. Pulmonary
   • On bronchoscopy notice a vocal cord problem
3. ENT
   • On laryngoscopy notes a vocal cord paralysis
4. Laryngology
   • On laryngoscopy diagnosis bilateral paralysis
     • Orders EMG
     • Prescribes pantaprazole bid
5. Neurolaryngology
   • EMG is abnormal
   • Botulinum toxin injection (right vocal cord)
   • She develops a louder stridor
6. Laryngology: Comes for a second opinion
   • High definition laryngology reveals the problem
     • Understanding the likely pathology from the history
     • Correlating the vocal capabilities findings with her symptoms
     • Topical anesthesia combined with
     • A detailed examination of the larynx reveals a posterior glottis web creating a glottic stenosis

Result

1. 6 months of the patient’s life have passed
   • How much work time has been lost by the patient’s family taking her to appointments?
   • How much has the family spent on medical care until they received an accurate diagnosis?
2. She is more stridorous since the botulinum toxin injection because of Bernoulli effect on the previously synkinetic, but now paretic and passive right vocal cord
3. She cannot walk up stairs limiting her activities

Low Definition Laryngology

1. Is where physicians have high technology equipment, even a high technology education, but;

• they don’t realize where to aim the endoscope, or 
• don’t take the time to record quality images of the pathology or 
• do not understand the need for using low technology wisely to bring the pathology into focus
• and/or do not review for mistakes to learn from them.

High technology is the equipment being purchased to go into a voice lab.

Voice Laboratory

1. Endoscope
2. Camera & Processor
3. Stroboscope
4. High Speed
5. Recording Video
   • Hardware
   • Software

Endoscope

• Flexible Fiberoptic attached to a camera
• Chip Endoscope with integrated camera
• Rigid Endoscope attached to a camera

Flexible Fiberoptic endoscope

• attached to a separate camera

Flexible endoscopes have a wider angle lens than rigid endoscopes and a wider angle perspective than the human eye:

• Close objects appear relatively larger than farther away objects
• High depth of field
• Greater apparent perspective distortion
• Endoscopes with a more gentle curve in the tip and the curve close to the tip of the endoscope are easier to maneuver

Rigid endoscopes

Angle of view

• 70 degree
• 90 degree

Quick Focus vs more light

Long lens

1. Deliver more light than a flexible or chip scope and the greater the light that is delivered, the greater the depth of field
2. But because of the long lens, there is inherently a shallower depth of field, (a narrower range of distance which is in focus simultaneously)

Camera & Processor

Definition

Video format classification

• SD
  • 525i
• HD
  • 720p
  • 1080i

Graphic format classification

1. Highly variable, almost any x:y variation of pixels
2. The camera and processor are usually sold as a package.
3. Often the light source is integrated into the processor

Determining the video output of the processor affects the resolution that can be captured.

Interface formats

Carrying audio and video signals along a cable

• DVI - Digital Video interface (carries analog or digital signals, SD or HD, but no audio)
• HDMI - High Definition Multimedia Interface (SD, HD, video, audio)
• SDI  - Serial Digital Interface (single cable)
• HD-SDI - High Definition Serial Digital Interface 
• Firewire 400, 800 - 

Video codecs

1. Compression algorithms

• MPEG-4
• MPEG-2
• H-264
• WMV (Windows Media Video)
• Apple ProRes 422
• DV

Slow apparent motion

• Stroboscope
• High Speed

Light

• Xenon
• Halogen
• LED

Selective Color imaging

• Selective highlighting of red color by selecting for certain bands of light in the blue and green wavelengths which are absorbed by hemoglobin. Blood then appears dark or black in the images adding additional contrast with the surrounding tissue. 
• Identifies vascular problems

Recording Video

1. Hardware
2. Computer graphics vs video signals from camera
3. SD vs HD signals
4. Video scalers
5. Hardware encoding
6. Computers for capture
7. Software

Proprietary

Commercial

Eg (Final Cut Pro, iMovie, Adobe Premiere Pro, etc.)

Closeness

1. Topical anesthesia
2. Camera orientation
   1. Rotate camera 90 degrees for rigid
   2. HD 16:9 ratio matches vocal cord anatomy in terms of length:width
3. Laryngeal Maneuvers
   1. Choose a vowel
      1. /I/ opens larynx
   2. Alter Pitch
      1. High pitch
         1. highlights vocal margin
         2. Augments stiffness
      2. Low pitch
         1. highlights weakness
         2. Typically removes compensation
         3. From SLN (CT muscle)
      3. Alter Volume
         1. Low volume
            1. Highlights gaps, stiffness, elevations
         2. High volume
            1. Highlights weakness

 

If you can hear it, you can see it.

All hoarseness derives from either

1. Air leak
2. Diplophonia.

Vocal capabilities are a robust means of 

• Determining if there is a disorder of vibration
• Classifying disorders of vibration

Vocal Capabilities Battery

1. Comfortable Speaking Pitch
2. Lowest Pitch
3. Highest Pitch
4. Loud sound
5. Vegetative sounds
6. Soft singing voice - swelling test

III. Problems - hindrances

Anatomy

1. Gagging
   1. Typically greater with rigid
2. Anatomy
   1. Limited room to avoid obstructions with rigid
3. Supraglottic squeeze
   1. Flexible can bypass most obstructions (at times after topical anesthesia)

Video artifact

1. Moire effect from two grids overlaid (fibers and digital sensors)
   1. Auto gain
   2. Digital Noise (random variations of color and brightness)
      1. Graininess
      2. Redness
      3. Banding
      4. With inadequate lighting there are random current fluctuations in the sensors that cause artifactual findings in the image

Perspective

1. Rigid - perpendicular orientation
2. Flexible - perpendicular or parallel orientation

Lighting

1. Color
2. Shadows

Multiple pathology

1. Which pathology dampens the vibrations?
   1. Creating diplophonia
   2. Creating air leak