B scan
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Ultrasonography, also known as B-scan, was first used in ophthalmology in the 1940s. It uses high frequency sound waves to generate images of the inside of the eye. B-scans can be used to evaluate conditions like tumors, retinal detachments, and vitreous opacities. The document discusses the history, physics, principles and various applications of B-scan ultrasonography for examining the eye. Key aspects covered include probe orientation, scan types, interpretation of echogenicity and advantages in providing a non-invasive evaluation of intraocular structures.
B scan
- 1. ULTRASONOGRAPHY (B-SCAN) VASIUR RAHMAN Dr R. P. Centre, AIIMS
- 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. 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. physics Ultrasound ○ Longitudinal wave ○ Alternating compressions and rarefactions of molecules >20khz (20,000 oscillations /sec) Ultrasound Similar to sound waves Reflected Refracted
- 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. 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. based on physical principles of pulse-echo technology Echoes are generated at adjoining tissue interfaces greater the difference, the stronger the echo
- 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. 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. ULTRASOUND PRINCIPLES AND PHYSICS Angle of incidence: Perpendicularity to the area of interest always should be maintained to achieve the strongest echo.
- 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. Transverse scan Longitudinal Axial B-scan Probe Orientations
- 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. 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. 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. 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. 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. 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. Measured in decibels Higher gain – Display weaker echos like vitreous opacities Lower gain Stronger echoes (retina and sclera) Better resolution Gain
- 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. VITREOUS HAEMORRHAGE To detect extent, density, location and cause Fresh haemorrhage shows dots or lines Old haemorrhage the dots gets brighter
- 25. CHOROIDAL DETACHMENT KISSING CHOROIDS
- 29. SILICON OIL FILLED VITREOUS
- 30. Complete PVD
- 32. Endophthalmitis
- 33. Intra ocular foreign body
- 34. 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:
- 35. Disadvantages High frequency sounds waves have limited penetration
- 36. THANK YOU