1. Volume I Companion Presentation Frank R. Miele Pegasus Lectures, Inc.
Ultrasound Physics & Instrumentation 4th Edition
Volume I
Companion Presentation
Frank R. Miele
Pegasus Lectures, Inc.
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2. License Agreement Pegasus Lectures, Inc. All Copyright Laws Apply.
This presentation is the sole property of
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No part of this presentation may be copied or used for any purpose other than as part of the partnership program as described in the license agreement. Materials within this presentation may not be used in any part or form outside of the partnership program. Failure to follow the license agreement is a violation of Federal Copyright Law.
All Copyright Laws Apply.
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3. Volume I Outline Pegasus Lectures, Inc. Chapter 1: Mathematics
Chapter 2: Waves
Chapter 3: Attenuation
Level 1
Level 2
Chapter 4: Pulsed Wave
Chapter 5: Transducers
Chapter 6: System Operation
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4. Chapter 3: Attenuation - Level 2
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5. Fig. 21a: Anechoic Mass (Cyst) in the Liver (Pg 160)
No Echogenicity
Fig. 21a: Anechoic Mass (Cyst) in the Liver (Pg 160)
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6. Fig. 21b: A Small (5-6 mm) hypoechoic Mass in the Liver (Pg 160)
Low Echogenicity
Fig. 21b: A Small (5-6 mm) hypoechoic Mass in the Liver (Pg 160)
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7. Hyperechoic Pegasus Lectures, Inc. High Echogenicity
Fig. 21c: Transverse View Through a Normal Liver with a Hyperechoic Area from the Ligamentum Teres (Pg 160)
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8. Calcified Pegasus Lectures, Inc.
Strongly echogenic, usually with acoustic shadowing
Fig. 21d: Calcified Plaque with Acoustic Shadowing at the Origin of the ICA (Pg 161)
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9. Complex Pegasus Lectures, Inc.
Mixed Echogenicity with or without acoustic shadowing
Fig. 21e: Complicated Plaque with Multiple Levels of Echoes at the Origin of the ICA (Pg 161)
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10. Attenuation Rates Pegasus Lectures, Inc.
Attenuation rates through various media have been empirically determined to be approximately as follows:
Note that attenuation already implies a decrease. The fact that the rates are specified in decibels demonstrates that the attenuation is a non-linear process. Attenuation increases exponentially with both depth and transmit frequency.
Soft Tissue: 0.5 dB/(cm * MHz)
Muscle: dB/(cm * MHz)
Blood: dB/(cm * MHz)
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11. Fig. 22a: Specular Reflection from the Humeral Head in the Shoulder
(Pg 165)
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12. Specular Reflection Pegasus Lectures, Inc.
Fig. 22b: Specular Reflection from the Anterior Leaflet of the Mitral Valve and Aortic Valve Cusp (Pg 165)
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13. Fig. 22c: Specular Reflection from a Prosthetic Mitral Valve (Pg 166)
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14. Specular Reflections Pegasus Lectures, Inc.
Fig. 22d: Specular Reflections from Spiny Processes and the Cranial Bone (Pg 166)
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15. Scattering Pegasus Lectures, Inc.
Fig. 23a: Coarse Speckle Pattern (loss of definition between muscle and gland)
(Pg 168)
Fig. 23b: Fine Speckle Pattern (neck muscles visible anterior to thyroid)
(Pg 168)
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16. Reflection – Equation Applied
In Level 1 of this Chapter, we learned that the amount of reflection from a boundary is determined by the acoustic impedance mismatch.
We will now apply the reflection equation to a specific imaging situation.
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17. Acoustic Impedance Mismatch between PZT and Tissue
Fig. 24: (Pg 170)
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18. The Use of a Matching Layer
Tissue
Fig. 25: Impedance Matching (pg 171)
The use of a matching layer is to improve the transmission efficiency by reducing the acoustic impedance mismatch of the high impedance of the crystal and the low impedance of the tissue.
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19. High Impedance Mismatch with Air
Fig. 26: (Pg 172)
The impedance mismatch to air is enormous, resulting in very poor transmission into and out of the patient. The use of gel is to eliminate the air that would otherwise be trapped on the surface of the patient between the skin and the matching layer of the transducer.
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20. Small Impedance Mismatches
Fig. 27: (Pg 173)
Small impedance mismatches may result in the inability to visualize a structure in the body, even if the structure is relatively large.
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21. Shadowing from Bone Pegasus Lectures, Inc.
High reflectivity from large acoustic impedance mismatch and high absorption rate results in signal dropout (shadowing) below the bones
(in this case from the vertebral spinous process bone)
Fig. 28: (Pg 173)
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22. Fig. 29: Lateral Displacement Caused by Refraction (Pg 176)
Effects of Refraction
Refraction can result in a lateral displacement of structures within an image as demonstrated in the associated figure.
Fig. 29: Lateral Displacement Caused by Refraction (Pg 176)
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23. Determining Refraction Direction
As seen in the animation of page 154, the direction of in which the beam refracts can be determined by drawing the change in speed of the wavefront at the interface between the two media. In this case, C2 is greater than C1, resulting in the refraction as shown in the figure.
Fig. 30: (Pg 177)
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24. Lateral Displacement from Refraction
Fig. 32: Where a structure would appear from a bent path length with a change in propagation speed (Pg 177)
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25. Refractive Shadowing and the Critical Angle
Fig. 33: (Pg 178)
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26. Notes: