UltrasoUnd Physics & instrUmentation - Pegasus Lectures

10. Exercises ..............................................................................................................................................108
11. Relating Wave Characteristics to Application and Relevance in Diagnostic Ultrasound ...................110
12. Wave Characteristics and Parameters ..................................................................................................110
12.1 Frequency and Period ................................................................................................................110
12.2 The General Term Frequency ....................................................................................................110
12.2.1 Classifications of Sound ...............................................................................................111
12.2.2 Intravascular Ultrasound (Frequencies Above the Typical Diagnostic Range) ...........113
12.2.3 Therapeutic Ultrasound (Physiotherapy and HIFU) ....................................................113
12.2.4 Relation to Future Topics .............................................................................................114
12.3 Propagation Velocity ..................................................................................................................114
12.3.1 General .........................................................................................................................114
12.3.2 Terminology: Elasticity, Compressibility, Stiffness, and Bulk Modulus .....................114
12.3.2.1 Elasticity .....................................................................................................114
12.3.2.2 Compressibility...........................................................................................115
12.3.2.3 Stiffness (Inelasticity) .................................................................................115
12.3.2.4 Bulk Modulus .............................................................................................115
12.3.2.5 Table Relating Terminology .......................................................................115
12.3.3 The Propagation Velocity Analogy ..............................................................................116
12.3.4 Relating the Analogy to the Speed of Sound ...............................................................118
12.3.5 Putting the Pieces Together to Create the Equation .....................................................119
12.3.6 Propagation Velocities for Various Materials ..............................................................120
12.3.7 Discussion of Values in the Materials Table ................................................................120
12.3.8 What Affects Velocity Most in the Body .....................................................................121
12.3.9 Propagation Velocities in the Body ..............................................................................121
12.3.10 Discussion of Values in the Biological Table...............................................................122
12.3.11 The Propagation Velocity Assumed by the Ultrasound System ..................................122
12.3.12 Relation to Future Topics .............................................................................................123
12.4 Wavelength ................................................................................................................................123
12.4.1 The Equation and its Importance .................................................................................123
12.4.2 Control of the Wavelength ..........................................................................................123
12.4.3 Calculating the Wavelength .........................................................................................123
12.4.4 Relation to Future Topics .............................................................................................125
12.5 Amplitude ..................................................................................................................................125
12.5.1 Control of Electrical Amplitude and Transmit Gain ....................................................125
12.5.1.1 Effect on Acoustic Pressure Field ...............................................................125
12.5.1.2 Relationship to Acoustic Power..................................................................126
12.5.1.3 Relationship to Acoustic Intensity ..............................................................127
12.5.2 Relation to Future Topics .............................................................................................129
13. Decibels (dB) .......................................................................................................................................130
13.1 The Need for Decibels ...............................................................................................................130
13.2 The Definition of Decibels ........................................................................................................130
13.3 The Equation for Decibels .........................................................................................................130
13.4 Applying the Equation for Decibels ..........................................................................................131
13.5 The Amplitude Form of the Decibel Equation ..........................................................................132
13.6 Why Two Forms and When to Use Which Form ......................................................................133
13.7 Exercises ....................................................................................................................................134
14. Comparing Frequency with Amplitude ...............................................................................................135
14.1 Frequency and Amplitude are Disjoint ......................................................................................135
14.2 Graphical Representation ..........................................................................................................135
14.3 Exercises ....................................................................................................................................136
15. Conceptual Questions ..........................................................................................................................137
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