B scan
- 1. B- SCAN By Dr. Alshymaa Moustafa Ohthalmology specialist
- 2. Principles of Ocular Ultrasonography ■ Ultrasonography utilizes sound waves to capture images. ■ Sound has a better penetration profile than light and can be used in patients with media opacities.
- 3. ■ generation of sound waves at a high frequency and back reflection to the transducer from the tissue in its path. ■ When the sound waves return, the piezoelectric crystal in the transducer vibrates, resulting in electrical impulses that are translated into an image or other data. ■ Higher-frequency waves penetrate less into tissue but have better resolution. In contrast, lower-frequency waves penetrate more deeply but have suboptimal resolution.
- 4. Transducers and Probes ■ The basic element of an ultrasound probe, the piezoelectric crystal, usually consists of lead zirconate titanate. ■ Recently, polymeric fluoride-based crystals have also been used, and lead-free and fluoride-free transducers are being developed. ■ In the current practice, probes of various frequencies, including 10, 20, and 50 MHz, are available for ocular ultrasonography.
- 7. Comparison of ultrasound B-scan of the posterior segment using 10 MHz (a) . 20 MHz (b) probes. • Note: The vitreoretinal interface, layers, and the choroidal layers can be more easily differentiated using the high-resolution 20 MHz probe
- 8. B- mode Ultrasound ■ B-scan is also known as the brightness scan. ■ B-scan can be performed by directly placing the probe on the corneal surface after adequate anesthesia, or by placing it over the eyelids using adequate coupling agents such as a jelly-based medium. ■ Ocular B-scan converts the reflected echoes into a two-dimensional structure of the eye, providing relevant anatomy of the globe when the scan is performed in all the gazes and positions. ■ The echoes in B-scan are converted to dots with brightness intensity that is proportional to the echo amplitude.
- 9. Gain ■ Gain is a frequently used index in ocular examination. 1. Higher gain increases the signal strength and thereby improves the sensitivity of the examination. 2. Gain can be used to detect vitreous hemorrhages, syneresis, posterior hyaloid interface, and inflammatory cells. 3. Low gain values improve the resolution in order to detect various layers such as retina, choroid, and hyaloid; retinal breaks and tears; macular edema; or vascularity of tumors.
- 10. Positions of B-scan ■ Axial scan (horizontal or vertical): 1. In this scan, the orientation of display is anterior-to-posterior with the patient looking straight ahead. 2. The probe marker is nasal (horizontal, labeled HAX) or upwards (vertical, labeled VAX).
- 11. ■ Transverse scan: 1. In this scan, the scan plane traverses several clock hours. 2. This technique is used for scanning different quadrants (superior, nasal, inferior, or temporal). 3. The probe marker is nasal (for S,I ) , or upwards (for N,T). 4. The scan sweeps the acoustic section posterior to anterior.
- 12. ■ Longitudinal scan: 1. In this mode, each clock hour is scanned one by one. 2. The orientation of display is anterior to posterior. 3. The posterior part (ie, the optic nerve) is always at the bottom of the scan. 4. The probe is placed at the limbus and the marker is pointing towards the clock hour. 5. This scan is used for localizing foreign bodies or retinal tears and for documenting the macula.
- 13. Ultrasound B-scan in a case of intraocular foreign body shows a hyperechoic shadow in the posterior vitreous cavity. A-scan (superimposed on the B-scan) shows high-amplitude spikes suggestive of a metallic foreign body. This scan is a longitudinal scan at the 6 o’clock position
- 14. High-resolution ultrasound B-scan of the posterior segment shows macular edema (yellow arrow) in a patient with diabetic maculopathy
- 15. Ocular UltrasoundTechnique ■ One can examine the entire globe in just five maneuvers, i.e. four dynamic quadrant views and one more static slice through the macula and optic disc, also known as longitudinal macula (LMAC). ■ The quadrants views are designatedT12,T3,T6, andT9. ■ These numbered quadrants correspond to a clock face superimposed on the eye. ■ For example, T12 is a view through the superior quadrant of the eye, T3 the nasal quadrant of the right eye (temporal quadrant of the left eye), and so on.
- 16. ■ Ultrasound images can be obtained through the patient's eyelids or with the probe directly on the surface of the eye with appropriate topical anesthesia. ■ Begin with the gain on high. The patient should look in the direction of the quadrant to be evaluated. ■ The marker on the probe is always oriented superiorly or nasally by convention. ■ Use a limbus-to-fornix rocking, rotational motion so that the tip of the probe moves a small distance, while the base of the probe moves a larger distance. ■ The probe rotates around the globe so that the sound waves always pass through the center of the eye. ■ This rotational motion will maximize the amount of retina visualized during the scan.
- 17. Schematic of ultrasound quadrants Limbus-to-fornix rotational motion
- 18. TransverseView 1:T12 (quadrant centered at 12 o'clock) ■ Ask the patient to look up. ■ Place your probe on the inferior aspect of the globe with the marker oriented nasally. ■ Begin at the limbus (L) and locate the optic nerve shadow, both to orient yourself and assure you are imaging the posterior segment. ■ Slowly sweep your probe toward the inferior fornix (F) until visualization of theT12 quadrant is complete. ■ Repeat if necessary. ■ Remember to center any pathology along the equatorial plane of the image for the best resolution.
- 21. TransverseView 2:T6 (quadrant centered at 6 o'clock) ■ Ask the patient to look down. ■ Place your probe on the superior aspect of the globe with the marker aimed nasally. Again, begin at the limbus (L)). ■ Ensure you have an image of the retina and optic nerve before sweeping the probe toward the superior fornix (F). ■ Repeat if necessary. ■ centering any pathology.
- 24. TransverseView 3:T3 (quadrant centered at 3 o'clock) ■ Remember, to scan the medial and lateral quadrants of the eye, the probe marker should point superiorly. ■ For theT3 quadrant of the patient's right eye, instruct the patient to look left. ■ Place the probe on the temporal limbus (L). ■ After obtaining an image of the retina and optic nerve, gently sweep the probe to the fornix (F) to complete evaluation of this quadrant. ■ To view theT3 quadrant of the left eye, the patient should still gaze to the left, but the probe will be placed at the medial limbus, with the marker oriented superiorly.
- 27. TransverseView 4:T9View (quadrant centered at 9 o'clock) ■ Scanning the T9 quadrant of the right eye is simply the reverse scan of the T3 quadrant. ■ With the probe marker oriented superiorly, instruct the patient to direct their gaze to the right. ■ Place the probe on the globe at the nasal limbus (L). ■ For the T9 quadrant of the left eye, place the probe at the temporal limbus. Proceed, again with a limbus-to-fornix (F) rotational sweeping movement.
- 30. Longitudinal Macula (LMAC)View ■ The LMAC view allows for proper visualization of the macula and optic nerve. ■ Gently place the probe on the nasal aspect of the eye with the patient's gaze directed temporally. ■ Note: For this position, the marker of the probe should be directed toward the pupil, instead of superiorly. ■ A longitudinal scan is the only scan where this occurs! In this view, the optic nerve will be below the macula. ■ Maneuver the probe to bring the macula into the center of the image to obtain the best resolution.
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