10/16/14. Ultrasound Physics & Instrumentation 5 th Edition. License Agreement. Chapter Outline. All Copyright Laws Apply.

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1 Ultrasound Physics & Instrumentation 5 th Edition Companion Presentation Frank R. Miele Pegasus Lectures, Inc. License Agreement This presentation is the sole property of Pegasus Lectures, Inc. 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. Chapter Outline Chapter 1: Math Chapter : Waves Chapter 3: Aenua5on Level Chapter 4: Pulsed Wave Chapter 5: Transducers Chapter 6: System Opera5ons Chapter 7: Doppler Chapter 8: Ar5facts Chapter 9: Bioeffects Chapter 10: Contrast and Harmonics Chapter 11: Quality Assurance Chapter 1: Fluid Dynamics Chapter 13: Hemodynamics Chapter 14: MSK Chapter 15: HIFU Chapter 16: Elastography Chapter 17: IMT Ultrasound Imaging Chapter 18: Strain Imaging Chapter 19: Pa5ent Care 1

2 Anechoic No Echogenicity Anechoic Mass (Cyst) in the Liver Hypoechoic Low Echogenicity A Small (5-6 mm) hypoechoic Mass in the Liver Hyperechoic High Echogenicity Transverse View Through a Normal Liver with a Hyperechoic Area from the Ligamentum Teres

3 Calcified Strongly echogenic, usually with acoustic shadowing Calcified Plaque with Acoustic Shadowing at the Origin of the ICA Complex Mixed Echogenicity with or without acoustic shadowing : Complicated Plaque with Multiple Levels of Echoes at the Origin of the ICA Attenuation Rates Attenuation rates through various media have been empirically determined to be approximately as follows: Soft Tissue: 0.5 db/(cm * MHz) Muscle: 1.0 db/(cm * MHz) Blood: 0.15 db/(cm * MHz) Note that attenuation already implies a decrease. The fact that the rates are specified in decibels demonstrates that attenuation is a non-linear process. Attenuation increases exponentially with both depth and transmit frequency. 3

4 Specular Reflection Specular Reflection from the Humeral Head in the Shoulder Specular Reflection Specular Reflection from the Anterior Leaflet of the Mitral Valve and Aortic Valve Cusp Specular Reflection Specular Reflection from a Prosthetic Mitral Valve 4

5 Specular Reflections Specular Reflections from Spiny Processes and the Cranial Bone Scattering Coarse Speckle Pattern (loss of definition between muscle and gland) Fine Speckle Pattern (neck muscles visible anterior to thyroid) 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. % Reflection I z z Reflected 1 = = I z + z Total 1 We will now apply the reflection equation to a specific imaging situation. 5

6 Acoustic Impedance Mismatch between PZT and Tissue 38 MRayls MRayls % Reflection = = = = = MRayls + MRayls % Transmission = 0.19 (One way ) % Transmission = = or 3.6% ( Roundtrip) The Use of a Matching Layer 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. High Impedance Mismatch with Air 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. 6

7 Small Impedance Mismatches Small impedance mismatches may result in the inability to visualize a structure in the body, even if the structure is relatively large. Shadowing from Bone 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) Effects of Refraction Refraction can result in a lateral displacement of structures within an image as demonstrated in the associated figure. 7

8 Determining Refraction Direction As seen in the animation associated to pages 49 and 50, the direction 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, C is greater than C1, resulting in the refraction as shown in the figure. Lateral Displacement from Refraction Refractive Shadowing and the Critical Angle 8

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