Physics Chapters 1-12 Review PDF

**[Physics Chapters 1-12 Review]** - All numerical values should have corresponding units - Macro= Bigger Micro= Smaller - The board exam will not ask you for the uncommon metric prefixes. The two most common is 1.) 10^9^ meaning *billion.* Prefix *giga* and 2.) 10^-6^ meaning *mill...

**[Physics Chapters 1-12 Review]** - All numerical values should have corresponding units - Macro= Bigger Micro= Smaller - The board exam will not ask you for the uncommon metric prefixes. The two most common is 1.) 10^9^ meaning *billion.* Prefix *giga* and 2.) 10^-6^ meaning *millionth* prefix *micro* - The acoustic propagation properties are the effects of the medium on the **SOUND WAVE.** - Sound is a type of wave that carries **ENERGY** and is a series of compressions and rarefactions. - Compressions are areas of INCREASED pressure and density - Rarefactions are areas of DECREASED pressure and density - Sound *CANNOT* travel in a vacuum. - Sound is a **mechanical** and **longitudinal** wave.\[NOT TRANSVERSE\] and it travels in a straight line. \*This will be a board question. *Three Acoustic Variables that Identify Sound Waves* - Pressure -- concentration of force within an area **force/area**. Units: **Pascals (Pa)** - Density -- concentration of mass within a volume. Units **kg/cm^3^** - Distance 0 measure of particle motion. Units: **distance, Ex: mm or cm.** ***Transverse Wave-*** Particles move in a perpendicular direction. (right angles or 90^0^) to the wave's direction. ***Longitudinal Wave-*** Particles move back and forth in the same direction as the wave. - Compressions: are regions of *HIGHER* pressure & density - Rarefactions: are regions of *LOWER* pressure & density *Parameters to describe Sound Waves* **[Period and Frequency]** are inversely related- determined by the sound source **[Amplitude, Power, and Intensity]** -- directly related- can be changed by the sonographer. **[Wavelength-]** Determined by both the sound source and the medium **[Speed-]** determined by the MEDIUM ONLY! **THREE BIGNESS PARAMETERS** ------------------------------ Amplitude Power Intensity They all behave in the same way- they all describe a sound beam's strength. And can all be adjusted by the Sonographer. - **[Period-]** Time required to complete a single cycle- start of one cycle to the start of the next. Measured in units of microseconds- or any unit of time. *CANNOT* be changed by the sonographer. - **[Frequency-]** Number of certain events that occur in a particular time duration. Units: per second, Hertz, Hz. Determined by sound source. CANNOT be changed by sonographer. Frequency Heard by Man ------------ ----------------------------- -------------------------- Audible Between 20 Hz and 20,000 Hz yes Ultrasound Greater than 20,000 Hz No frequency is too high Infrasound Less than 20 Hz No frequency is too low - *A board question may say what is the frequency for Ultra-sound?* When period DECREASES frequency INCREASES When period is UNCHANGED, frequency is also UNCHANGED ***Shorter Period=Higher Frequency*** ***Longer Period=Lower Frequency*** *POWER IS PROPORTIONAL TO THE WAVE'S AMPLITUDE SQUARED!* - **[Wavelength-]** The length or distance of a single cycle. Units of length. The only parameter determined by BOTH the sound source and the medium. - **[EQUATION]** Wavelength (mm) = [propagation speed (mm/microseconds)] Frequency (MHz) *Higher frequency sound has short wavelengths* *Lower Frequency sound has longer wavelengths* - **[Propagation Speed-]** the rate that sound travels through a medium. Determined by: THE MEDIUM ONLY. CANNOT be changed by Sonographer. - Speed and Wavelength are directly related Rule of Thumbs - Stiffness and Speed- Same direction (faster) - Density and Speed- opposite directions (slower) - Compressibility and Elasticity are opposites of stiffness - \*\*\*\*\*Bulk Modulus is the same as stiffness. So, when bulk modulus increases, speed increases.\*\*\* Phase Relationships - Constructive Interference occurs when the amplitude of the new, combined wave is greater than the original two waves. In Phase waves interfere constructively. - Destructive Interference occurs when the amplitude of the new wave is less than one of the original wave. Out-of-phase waves interfere destructively. In diagnostic imaging, short pulses of acoustic energy are required to created anatomic images. Pulsed ultrasound on- transmit time off- receive time - **REMEMBER- A PULSE IS A PULSE IS A PULSE. - A transducer's talking time does not change when the sonographer changes imaging.** *Equation: Pulse Duration ( microseconds) = \# cycles in pulse x period ( microseconds)* - **[Spatial Pulse Length-]**The distance or length from the start to the end of one pulse. Units Distance Cannot be changed by sonographer. - *Shorter pulses create higher quality images* - *Equation: Spatial Pulse length (mm) = \# of cycles x wavelength (mm)* - *Pulses that are short in time are also short in distance* *Pulse Repetition Period & Pulse Repetition Frequency* +-----------------------------------------------------------------------+ | - *As PRP increases, imaging depth increases* | +=======================================================================+ | - *As PRP decreases, imaging depth decreases* | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | - Shallow imaging, HIGHER PRF | +=======================================================================+ | - Deep imaging, LOWER PRF | +-----------------------------------------------------------------------+ *By adjusting the IMAGING DEPTH, the operator changes the **pulse repetition period, pulse repetition frequency, and the duty factor.*** - **[Intensity]** Is the concentration of the power in a beam. It is not uniform across a sound beam. - Two Types: Spatial and Temporal FIVE KEY WORDS IN RELATION TO INTENSITY - Peak- Maximum Value - Average- Mean Value - Spatial- referring to distance or space - Temporal- referring to all time (transmit and receive) - Pulsed- referring only to the time the pulse exits (transmits only) - SPTP- Spatial peak, temporal peak -- HIGHEST VALUE - SPTA- Spatial peak, temporal average \*\*Most relevant for thermal bioeffects\*\* ***JUST REMEMBER THIS ABOUT THE VARYING INTENSITIES*** SPTA Related to tissue heating ------ --------------------------- SPTP greatest SPTA Smallest DECIBELS AND LOGARITHMS - A logarithmic scale is a relative comparison or ratio between the final to the initial strengths. - Positive decibels means getting bigger. The intensity is increasing - 10dB means TEN TIMES BIGGER. - Negative decibels means getting smaller. The intensity is decreasing. - -10 dB means one-tenth. We have falled to 1/10^th^ of the original value. ***INTERACTION OF SOUND AND MEDIA*** THERE ARE THREE COMPONENTS OF ***ATTENTUATION*** 1. Absorption- primary, sound converted into heat 2. Scattering 3. Reflection ***Less Attenuation*** ***More Attenuation*** ------------------------ ------------------------ *Shorter distance* *Longer distance* *Lower frequency* *Higher frequency* *Attenuation in different media* - *Air- much much more attenuation than in soft tissue. (Gel is used to remove air from the path of ultrasound)* - *Lung & Bone- more than soft tissue. Bone absorbs and reflects. Lung scatters* - *Water- much much less than soft tissue.* - *Attenuation in blood is less than that in soft tissue* In soft tissue, lower frequency results in less attenuation. Thus, we penetrate further with a lower frequency sound wave. Attenuation ultimately limits the maximum imaging depth from which meaningful reflections are obtained. - Reflections from a smooth reflector (mirror) are SPECULAR and return in one direction. - Diffuse reflection or backscatter when a boundary is ruff, reflected sound is disorganized and become random. Diffuse AKA Backscatter. - If a reflector is much smaller than the wavelength of sound, sound is uniformely distributed in all directions aka RAYLEIGH SCATTERING ***In soft tissue, the attenuation coefficient is one half of the transducer's frequency*** Impedence is calculated, not measured **Normal incidence Synonyms** - Perpendicular - Orthogonal - Right angle - Ninety degrees Oblique incidence is anything other than 90 degrees: not at right angles [Intensity Transmission Coefficient (ITC]) - The percentage of the incident intensity that, after striking a boundary, continues on in the same general direction that it was originally travelling. *Reflection with normal incidence occurs only if the two media at the boundary have **different acoustic impendences.*** **[Refraction]**- is transmission with a bend. It requires both: - Oblique Incidence - Different Speeds - ***Snells Law -- Describes the physics of refraction*** ***Process*** ***What Is Required*** ----------------------------------- ------------------------------------------------- Reflection with normal incidence Look for different impendances Reflection with oblique incidence We do not know! Transmission Derive this from reflection information Refraction Look for oblique incidence and different speeds **[Time of Flight:]** The time neeed for a pulse to travel TO and FRONM the transducer and the reflector. - Go- return time - Time-of-flight - Round trip time \**When time of flight is measured, we can determine reflector depth* **13 microsecond rule-** in soft tissue, every 13 microseconds of go- return time means the reflector is 1cm deeper in the body. **[BASIC TRANSDUCERS]** Transducer is any device that converts one form of energy into another Piezoelectric Materials -- Synthetic -- lead Zirconate Titanate (PZT) Curie Temperature (point) When PZT is heated above this temperature, its PZT properties are destroyed the PZT is DEPOLARIZED. Thus, never heat steralize or autoclave a transducer. **Active Element:** The piezoelectric crystal , also called the ceramic, PZT, or Cyrstal. It is ½ wavelength thick. **Case:** Protects the internal components from damage and insulates the patient from electric shock. - **DON'T use a transducer with a cracked case due to the potential for electrical shoch to the patient.** *The matching layer is one-quarter wavelength thick and has impedence between those of the skin and the active element to increase transmission between the active element and the skin.* Damping Element or Backing Material: Short pulses create more accurate images **[BANDWIDTH AND QUALITY FACTOR ]** The bandwidth is the range of frequencies Imaging transducers use backing material- therapeutic transducers do not The Quality Factor is a unitless number related to extent of damping. Low Q = damping and wide bandwidth, imaging (pulsed) transducers High Q= no damping and narrow bandwith. (CW and therapeutic transducers) **[PULSED TRANSDUCERS]** The main and center frequency of sound from a pulsed trasducer is determined by 2 characteristics of the cystal: 1. Thickness 2. Propagation Speed of the PZT *For Pulsed Transducers* *Higher Frequency* *Lower Frequency* -------------------- ------------------- *Thin crystal* *Thick Crystal* *Fast PZT* *Slow PZT* - *When a PZT crystal is half as thick, the sound's frequency is twice as high* **[ANATOMY OF A SOUND BEAM ]** RULE: NARROW BEAMS CREATE BETTER IMAGES As sound travels, the width of the beam changes. Starts out exactly the same size as the transducer diameter (aperture) Gets progressively narrower until it reaches its smalles diameter( FOCUS) then the beam diverges ***NEAR ZONE-*** short name Fresnel Zone ***FAR ZONE-** longer name Fraunhofer Zone* ***FOCAL ZONE***- The region surrounding the focus where the beam is 'sort of narrow' and the picture is relatively good is the focal zone. ***FOCAL DEPTH-***determined by the transducer diameter and the frequency of the ultrasound ***SOUND BEAM DIVERGENCE-*** describes the spread of the sound beam in the deep far zone. - In the far field, the beam is narrow and lateral resolution is best with large diameter, high frequency sound. - In the far field, beam is wide (lateral resolution is worse) with small diameter, low frequency sound. **DIFFRACTION-**V-Shaped wave, also called HUYGEN'S WAVELET ***HUYGEN'S PRINCIPLE-*** Explains the hourglass shape of an imaging transducer's sound beam **[AXIAL AND LATERAL RESOLUTION]** AXIAL RESOLUTION -- THE ABILITY TO DISTINGUISH TWO STRUCTURES THAT ARE CLOSE TO EACHOTHER FRONT TO BACK, PARALLEL, OR ALONG THE BEAM'S MAIN AXIS. (LARRD) LATERAL RESOLUTION- THE MINIMUM DISTANCE THAT TWO STRUCTURES ARE SEPERATED BY SIDE TO SIDE, PERPENDICULAR, TO THE SOUND BEAM THAT PRODUCES TWO DISTINCT ECHOES. (LATA) - LATERAL RESOLUTION IS EQUAL TO BEAM DIAMETER *Clinical Compromise* - *High frequencies improve image detail (axial resolution)* - *Low frequencies provide deeper penetration.* *Focusing* *Alters the beam in three ways* 1. *Narrower "waist" in the US beam* 2. *Shallower focus* 3. *Smaller focal zone* - ***Phased array means adjustable or multi-focusing*** - ***Fixed focus transducers have the poorest lateral resolution*** - ***Single crystal transducers are alwaysa fixed focus*** - ***Phased array transducers are said to have better overall lateral resolution.*** **[TWO-DIMENSIONAL IMAGING]** Mechanical scanning the active element is moved by a motor, oscillating crystal or mirror through a pathway, automatically creating a scan plane Defective crystal destroys the entire image Phased arrays are adjustable focus, achieved electronically. If one element malfunctions, the steering and focusing become erratic. Electronic Slope - creates beam steering Electronic Curvature- creates beam transmit focusing Annular Phased Array transducers crystals are small in number of ring-shaped elements and it focuses in all planes at all depths. Steering is performed MECHANICALLY. Defective crystal causes band dropout. Curvilinear Arrays (what we use)- PZT crystals arranged in a curve to provide a natural sector image. T***he acoustic footprint describes the area of contact between the transducer and the skin.*** **-4-D imaging is rela time 3-D imaging.** **3-D image quality is determined by the number of slices** **3-D imaging provides more accurate volume measurements** Vector Arrays- trapezoidal imaging or expanded view. Phased array transducer due to multiple focal zones. **[CONTRAST, SPATIAL, AND TEMPORAL RESOLUTION]** Contrast- visualizing a variety of gray shades in an image Spatial Resolution- detail in an image -- affected by axial resolution, lateral resolution, line density Frame Rate is determined by 2 settings: 1. Imaging depth 2. Number of pulses per image Frame rate is limited by 2 factors: 1. The speed of sound in medium 2. Imaging depth Temporal resolution improves when the image is shallower or made of fewer pulses. Less time to create an image. More frames created each second. *Shallow depth of view makes a frame faster and improves temporal resolution* ***Shallow Imaging -- Higher Frame Rate*** ***Better Temporal Resolution*** ***Deep Imaging -- Lower Frame Rate*** ***Worse Temporal Resolution*** - ***More focal points makes temporal resolution worse and frame rate slower*** - ***Smaller sector angle creates images with fewer pulses, improving temporal resolution.*** - ***Line density images use fewer pulses and have better temporal resolution. However, lower line density degrades spatial resolution.*** **[Frame Rate Vs. Image Quality ]** - As temporal resolution improves, image quality may degrade - As temporal resolution degrades (lower frame rate) image quality may improve - Increasing the line density degrades temporal resolution - Using multi-focus degrades temporal resolution but improves lateral resolution.