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B scan

  1. 1. ULTRASONOGRAPHY (B-SCAN) VASIUR RAHMAN Dr R. P. Centre, AIIMS
  2. 2. HISTORY  1793: Lazzaro Spallanzani (Italy) discovered that bats orient themselves with the help of sound whistles while flying in darkness. This was the basis of modern ultrasound application Bats use ultrasounds to navigate in the darkness
  3. 3. INTRODUCTION  first used in the field of ophthalmology by MUNDT and HUGHES.  Oksala et al report the sound velocities in the various compartment of eye.  Contact Bscan was introduced by Bronson and it being portable, become a part of everyday use in ophthalmology.
  4. 4. physics  Ultrasound ○ Longitudinal wave ○ Alternating compressions and rarefactions of molecules  >20khz (20,000 oscillations /sec) Ultrasound  Similar to sound waves  Reflected  Refracted
  5. 5. Low frequency (1 to 5 MHz) Longer wavelength Lower Resolution (abdominal and pelvic structure) Abdominal ultrasound Ophthalmic ultrasound High frequency (8 to 10 MHz) Short wavelength (< 0.2mm) Higher Resolution of minute ocular and orbital structure
  6. 6.  By karl ossoing Sound Wave Velocities Medium Velocity (m/sec) Water 1,480 Aqueous / vitreous 1,532 Soft tissue 1,550 Crystalline lens 1,641 Bone 3,500
  7. 7.  based on physical principles of pulse-echo technology  Echoes are generated at adjoining tissue interfaces greater the difference, the stronger the echo
  8. 8.  having frequency greater than 20khz for imaging the posterior segment-8 to 25 MHz  for imaging the anterior segment-50 MHz  Rule-greater the frequency lesser will be penetration
  9. 9. Probe  thick, with a mark  emit focussed sound beam at frequency 10mhz  mark on the Bscan probe indicates beam orientation-area towards which mark is directed appears at the top of the echogram on display screen
  10. 10. ULTRASOUND PRINCIPLES AND PHYSICS Angle of incidence:  Perpendicularity to the area of interest always should be maintained to achieve the strongest echo.
  11. 11. A scan (amplitude) - single dimensional display of spikes through the eye. The spikes on A scan represent amplitude / reflectivity of an echo A-Scan
  12. 12.  Transverse scan  Longitudinal  Axial B-scan Probe Orientations
  13. 13.  Transverse scan  Movement of transducer is parallel to limbus  Produces a circumferential slice through several meridians  Lateral extent of a lesion Transverse Scan
  14. 14.  Longitudinal scan  Transducer - perpendicular to the limbus  Probe marker - towards centre of cornea  Antero posterior extent of the lesion  Optic disc and posterior aspect of the globe –lower portion of screen  Best – demonstrating the insertion of membranes to optic disc
  15. 15.  Axial scan  Probe centered on the cornea  Easiest to understand (displays lens & optic nerve)  Documenting lesions & membranes in relation to optic disc  Evaluates macular region  Hinder resolution of posterior portion of globe (Sound attenuation and refraction ) AXIAL SCAN
  16. 16. CLOCK HOUR PROBE POSITION CLOCK AREA SCREENED 3-limbus 9-posterior 3-equator 9-equator 3-firnix 9-anterior 6-limbus 12-posterior 6-equator 12-equator 6-fornix 12-anterior
  17. 17. Why we need B-scan..????  Evaluation of intraocular details  Evaluation of retrochoroidal lesions especially tumors  Examination of retrobulbar soft tissue masses  Identification, localization and measurement of foreign bodies  Assessment of damage in trauma cases
  18. 18. PROCEDURE  mostly the Bscanning is done transpalpebrum  Lesions must place at the centre of scanning beam  Lowest possible decibel gain consistent with the maintenance of adequate intensity should be used
  19. 19.  Measured in decibels  Higher gain –  Display weaker echos like vitreous opacities  Lower gain  Stronger echoes (retina and sclera)  Better resolution Gain
  20. 20.  Dot like lesions – vitreous floaters, vitreous hge, vitreous exudates.  Membranous lesions – vitreous membranes, PVD, RD  Mass lesions – choroidal or retinal tumors Echotexture of Lesion
  21. 21. VITREOUS HAEMORRHAGE To detect extent, density, location and cause Fresh haemorrhage shows dots or lines Old haemorrhage the dots gets brighter
  22. 22. CHOROIDAL DETACHMENT KISSING CHOROIDS
  23. 23. POSTERIORLY DISLOCATED LENS
  24. 24. INTRAOCULAR FOREIGN BODY
  25. 25. SILICON OIL FILLED VITREOUS
  26. 26. Complete PVD
  27. 27. Choroidal melanoma
  28. 28. Endophthalmitis
  29. 29. Intra ocular foreign body
  30. 30.  Non invasive  Performed in an office setting  Does not expose to radiation  High resolution echography provides reliable and accurate assessment  Ideal for follow up of lesion Advantages:
  31. 31. Disadvantages  High frequency sounds waves have limited penetration
  32. 32. THANK YOU

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