physics 2 final overall
================================================================
SECTION 1: FUNDAMENTALS OF ARTIFACTS
================================================================
CARD 1
Q: What is the pulse-echo technique?
A: The foundational method of ultrasound — the system sends out a pulse and receives an echo back. Round-trip timing is how the machine determines depth.
~~~
CARD 2
Q: What is the definition of an artifact?
A: Anything on the image that does NOT represent a real anatomical structure — anything that "doesn't belong."
~~~
CARD 3
Q: How do you confirm whether something on the screen is an artifact?
A: Four steps:
1. Change the scanning plane (transverse → sagittal)
2. Change the acoustic window or angle the probe
3. Use color Doppler to rule out a real vessel
4. If it disappears with a different angle/window → it's an artifact. If it stays → likely real.
~~~
CARD 4
Q: How do you tell a cyst from a blood vessel on a transverse scan?
A: A cyst stays the SAME shape (circular) when you turn the probe. A blood vessel ELONGATES when turned. Confirms whether the structure is fluid-filled focal (cyst) or tubular (vessel).
~~~
================================================================
SECTION 2: THE 6 MACHINE ASSUMPTIONS
================================================================
CARD 5
Q: Why memorize the 6 machine assumptions?
A: Because every artifact is caused by a violation of one of them. Knowing the assumption tells you the why behind the artifact.
~~~
CARD 6
Q: What is the STRAIGHT PATH assumption?
A: The machine assumes sound travels in a straight path from the transducer to the reflector. Violation → mirror image, refraction.
~~~
CARD 7
Q: What is the STRAIGHT RETURN assumption?
A: The machine assumes sound returns directly back to the transducer along the same path. Violation → mirror image, refraction artifacts.
~~~
CARD 8
Q: What is the SPEED ACCURACY assumption?
A: The machine assumes sound travels at exactly 1540 m/s (1.54 mm/μs) in all soft tissue. Violation → propagation speed error (broken diaphragm).
~~~
CARD 9
Q: What is the THIN IMAGING PLANE assumption?
A: The machine assumes the imaging plane is infinitely thin (ignores the third dimension/thickness). Violation → slice thickness / partial volume / elevational resolution artifact.
~~~
CARD 10
Q: What is the ATTENUATION CORRELATION assumption?
A: The machine assumes echo amplitude is directly related to the tissue characteristics that produced it. Violation → shadowing, enhancement.
~~~
CARD 11
Q: What is the 13 MICROSECOND RULE?
A: The machine assumes 13 μs of round-trip time = 1 cm of depth in soft tissue. This is how it places structures at the correct depth.
~~~
================================================================
SECTION 3: RESOLUTION TYPES
================================================================
CARD 12
Q: What is spatial resolution?
A: The OVERALL detail of the image — combination of AXIAL + LATERAL + CONTRAST resolution.
TRAP: Spatial resolution does NOT include elevational.
~~~
CARD 13
Q: What is axial resolution?
A: Ability to distinguish structures PARALLEL to the sound beam (along the beam axis).
Determined by: SPATIAL PULSE LENGTH (SPL).
~~~
CARD 14
Q: What is lateral resolution?
A: Ability to distinguish structures PERPENDICULAR to the sound beam (in the scan plane).
Determined by: WIDTH of the sound beam.
~~~
CARD 15
Q: What is elevational resolution?
A: AKA section thickness, partial volume artifact, slice thickness artifact.
Beam thickness PERPENDICULAR to the scan plane. Echoes from this thickness get collapsed into the flat 2D image, creating false echoes inside anechoic structures.
~~~
CARD 16
Q: Classic clinical example of elevational resolution artifact?
A: False echoes inside an anechoic gallbladder mistaken for SLUDGE, or a simple cyst mistaken for a COMPLEX/COMPLICATED CYST.
~~~
CARD 17
Q: Quick wording trick — parallel vs. perpendicular?
A:
- Parallel to sound beam → AXIAL
- Perpendicular to sound beam (in scan plane) → LATERAL
- Perpendicular to scan plane → ELEVATIONAL
~~~
================================================================
SECTION 4: PROPAGATION ARTIFACTS
================================================================
CARD 18
Q: What is acoustic speckle?
A: Caused by CONSTRUCTIVE and DESTRUCTIVE interference of returning echoes. Creates a "salt and pepper" / grainy appearance throughout the image. Frequency changes alter the speckle pattern.
~~~
CARD 19
Q: What is reverberation (reverb)?
A: Multiple, EQUALLY SPACED echogenic lines caused by sound bouncing back and forth between the transducer and a strong reflector — or between two strong reflectors.
Appearance: ladder/venetian-blind pattern with distinct SPACES.
~~~
CARD 20
Q: Classic example of reverb?
A: Imaging a NEEDLE — the metal edges are strong reflectors, sound bounces back and forth inside it. Also seen with gel right when you put the probe down (superficial reverb).
~~~
CARD 21
Q: What is ring down artifact?
A: A type of reverb caused specifically by GAS / AIR bubbles. Continuous bright echogenic stream that WIDENS as it goes deeper. NO distinct spaces between echoes. Brightness stays the same throughout — doesn't fade.
~~~
CARD 22
Q: What is comet tail artifact?
A: Single long hyperechoic line parallel to the beam, caused by media with very high propagation speed (METAL).
Appearance: TAPERS — gets narrower and FADES as it goes deeper.
Classic example: St. Jude artificial heart valve.
~~~
CARD 23
Q: Reverb vs. Ring Down vs. Comet Tail — fastest way to tell apart?
A:
- REVERB → distinct SPACES between bright lines
- RING DOWN → continuous, WIDENS with depth, GAS-caused
- COMET TAIL → continuous, TAPERS with depth, METAL-caused
~~~
CARD 24
Q: What is mirror image artifact?
A: A SECOND COPY of a structure placed DEEPER than the original. A strong reflector acts as the "mirror" — true reflector and artifact are EQUAL distances from it.
~~~
CARD 25
Q: Most common cause of mirror image?
A: The DIAPHRAGM. Classic example: a liver cyst mirrored on the other side of the diaphragm, looking like it's in the lung.
~~~
CARD 26
Q: What is crosstalk?
A: A form of mirror imaging seen on SPECTRAL DOPPLER. The waveform appears duplicated/flipped on the opposite side of the baseline.
~~~
CARD 27
Q: What is color mirroring?
A: Duplication of a vessel and its color flow BELOW the real structure (a reflection). Often caused by a calcified vessel wall acting as a strong reflector. You can even get a spectral waveform from the artifact vessel.
~~~
CARD 28
Q: What is refraction artifact (the propagation type)?
A: SIDE-BY-SIDE duplication of a structure at the SAME depth.
Cause: sound trajectory bends due to oblique incidence + different propagation speeds between media.
Examples: duplicated aorta, duplicated gestational sac (mistaken for twins).
~~~
CARD 29
Q: Mirror vs. Refraction — quick distinction?
A:
- MIRROR = deeper duplicate (different depth)
- REFRACTION = side-by-side duplicate (same depth)
~~~
================================================================
SECTION 5: TRANSDUCER ARTIFACTS
================================================================
CARD 30
Q: What are side lobes?
A: Extra acoustic energy outside the main beam, produced by SINGLE-ELEMENT transducers (older, not commonly used today).
~~~
CARD 31
Q: What are grating lobes?
A: Off-axis sound beams produced by ARRAY transducers (which is everything we use now). They DEGRADE LATERAL resolution by making the effective beam wider.
~~~
CARD 32
Q: How do we compensate for grating lobes?
A: Two methods:
1. SUBDICING — cutting piezoelectric elements into smaller pieces
2. APODIZATION — exciting INNER elements with HIGHER voltages and OUTER elements with WEAKER voltages
~~~
CARD 33
Q: What is apodization in detail?
A: A process that REDUCES the strength of side and grating lobes by:
- Sending stronger electrical signals to INNER (central) elements
- Sending weaker signals to OUTER elements
This concentrates energy into the main beam and reduces off-axis lobes.
~~~
================================================================
SECTION 6: SPEED & DEPTH ARTIFACTS
================================================================
CARD 34
Q: What is propagation speed error (speed error)?
A: An artifact that occurs when the medium speed is anything other than 1540 m/s. The machine misplaces structures AXIALLY based on incorrect timing.
~~~
CARD 35
Q: If sound travels SLOWER than 1540 m/s, where does the structure get placed?
A: Sound takes LONGER to return → machine calculates a longer round-trip → places structure too DEEP (more posterior).
Classic example: focal fatty liver / focal steatosis → "broken diaphragm" appearance.
~~~
CARD 36
Q: If sound travels FASTER than 1540 m/s, where does the structure get placed?
A: Sound returns FASTER than expected → machine thinks distance is shorter → places structure too SHALLOW (closer to transducer).
~~~
CARD 37
Q: What is range ambiguity?
A: An echo from a PREVIOUS pulse arrives AFTER the next pulse has been sent. The machine assumes the echo belongs to the most recent pulse → places structure too SHALLOW.
Caused by very high PRF (HPRF).
~~~
CARD 38
Q: Speed error vs. range ambiguity — what's the placement difference?
A:
- SPEED ERROR (slower medium) → too DEEP
- RANGE AMBIGUITY (high PRF) → too SHALLOW
~~~
================================================================
SECTION 7: ATTENUATION ARTIFACTS
================================================================
CARD 39
Q: What is shadowing?
A: WEAKENING of echoes distal to a strongly attenuating structure.
~~~
CARD 40
Q: Clean vs. dirty shadowing?
A:
- CLEAN shadowing = completely anechoic (BLACK) — gallstones, kidney stones
- DIRTY shadowing = cloudy, GRAY appearance — caused by GAS or air
~~~
CARD 41
Q: What is edge shadowing?
A: AKA refraction shadowing. Occurs at the edges of CURVED reflectors due to refraction. This is the second "refraction" — the attenuation type.
~~~
CARD 42
Q: What is enhancement?
A: STRENGTHENING of echoes distal to a WEAKLY attenuating structure. The area posterior to a fluid-filled structure (like a cyst) appears BRIGHTER than surrounding tissue.
~~~
CARD 43
Q: What is focal enhancement (focal banding)?
A: A bright HORIZONTAL band across the image at the level of the focal zone.
Fix: adjust the focal zones or TGCs.
~~~
CARD 44
Q: What is spatial compounding used for in artifact reduction?
A: To REDUCE shadowing and enhancement by sending scan lines through the same area from MULTIPLE ANGLES and averaging the frames.
Clinical example: seeing a femoral vein hidden behind a calcified, shadowing femoral artery in a diabetic patient.
~~~
CARD 45
Q: Why don't we always use spatial compounding to remove shadowing?
A: Because shadowing and enhancement are often USEFUL ARTIFACTS for diagnosis — they tell you a structure is a stone (shadowing) or a cyst (enhancement). Only suppress them when you NEED to see what's behind.
~~~
================================================================
SECTION 8: NOISE & ELECTRICAL INTERFERENCE
================================================================
CARD 46
Q: What is noise on an ultrasound image?
A: Small, low-level echoes that don't represent any real anatomy. Just stuff that doesn't belong.
~~~
CARD 47
Q: What causes electrical interference?
A: Other electronic devices in the room — BP monitors, dialysis machines, ventilators, respirators. Appears as echogenic bands or specific patterns across the screen.
~~~
================================================================
SECTION 9: DOPPLER ALIASING & NYQUIST
================================================================
CARD 48
Q: What is aliasing?
A: The most common Doppler artifact. An IMPROPER REPRESENTATION of velocity — what happens when blood velocity exceeds the system's ability to sample it accurately.
~~~
CARD 49
Q: How does sample volume DEPTH affect PRF and aliasing?
A:
- SHALLOW depth → HIGH PRF (pulses sent more often) → HIGH Nyquist → LESS aliasing
- DEEP depth → LOW PRF (must wait longer) → LOW Nyquist → MORE aliasing
~~~
CARD 50
Q: What is the Nyquist limit and its formula?
A: The MAXIMUM Doppler frequency shift that can be measured without aliasing.
Formula: Nyquist Limit = 0.5 × PRF (or PRF ÷ 2)
~~~
CARD 51
Q: PRF = 6. Where does aliasing occur — at velocities 2, 3, or 4?
A: Nyquist = 0.5 × 6 = 3.
- 2 → no aliasing (below limit)
- 3 → no aliasing (right at limit, still OK)
- 4 → ALIASING (exceeds limit)
~~~
================================================================
SECTION 10: DOPPLER MODALITIES
================================================================
CARD 52
Q: Which Doppler modalities ALIAS?
A:
- Pulsed Doppler → ALIASES
- Color Doppler → ALIASES (mosaic / turquoise pattern)
~~~
CARD 53
Q: Which Doppler modalities do NOT alias?
A:
- Continuous Wave (CW) Doppler → does NOT alias
- Power Doppler → does NOT alias
~~~
CARD 54
Q: What's the disadvantage of CW Doppler?
A: RANGE AMBIGUITY — caused by very high PRF. The machine can't tell which pulse a returning echo belongs to (no depth resolution).
~~~
CARD 55
Q: What does power Doppler show?
A: AMPLITUDE of moving red blood cells. Highly sensitive to slow flow.
LIMITATION: Does NOT give VELOCITY (no speed, no direction).
~~~
CARD 56
Q: What's the difference between speed and velocity?
A:
- SPEED = magnitude only. "60 mph"
- VELOCITY = speed + direction. "60 mph WEST" or "60 cm/s toward the probe"
Power Doppler gives amplitude only — not velocity.
~~~
================================================================
SECTION 11: SPECTRAL & COLOR DOPPLER ARTIFACTS
================================================================
CARD 57
Q: What is shadowing in Doppler?
A: Elimination or weakening of Doppler signals posterior to a highly attenuating object — creates a DROPOUT (no signal area).
~~~
CARD 58
Q: What is clutter?
A: LOW-FREQUENCY Doppler shifts on the SPECTRAL display caused by motion of vessel walls, heart muscle, or valves. Obscures the baseline.
~~~
CARD 59
Q: What is ghosting?
A: The COLOR DOPPLER version of clutter. Low-frequency shifts from vessel wall / heart muscle / valve motion appearing as COLOR OUTSIDE the vessel boundaries.
~~~
CARD 60
Q: How do you fix clutter and ghosting?
A: Use the WALL FILTER. It eliminates low-frequency signals.
- In SPECTRAL: creates a visible gap between baseline and the start of the waveform
- In COLOR: removes color "bleeding" outside the vessel
~~~
CARD 61
Q: What is flash artifact?
A: A sudden BURST of color caused by rapid motion (patient coughing, breathing, etc.) — NOT from blood flow.
~~~
CARD 62
Q: What is the ureteral jet — and why is it useful?
A: A USEFUL flash-type artifact seen in the bladder. Confirms patency of the ureters and rules out obstruction.
- If not seen immediately, hold the probe for several minutes
- Hydration helps
- Document on worksheet (e.g., "left jet seen, right not seen")
~~~
================================================================
SECTION 12: BEAM FORMER
================================================================
CARD 63
Q: What's the path of an echo through the ultrasound system?
A: Transducer → BEAM FORMER → SIGNAL PROCESSOR → IMAGE PROCESSOR → DISPLAY
~~~
CARD 64
Q: What are the 7 components of the beam former?
A:
1. Pulser
2. Pulse delays
3. T/R switch
4. Transmit/Receive amplifiers
5. Analog-to-digital converter (ADC)
6. Echo delays
7. Summer
~~~
CARD 65
Q: What does the pulser do?
A: Operates during TRANSMISSION. Creates electronic signals (~0–500 V) that excite the crystals in the probe. Adjustable.
- HIGH output → stronger sound, brighter image
- LOW output → weaker sound, darker image
~~~
CARD 66
Q: Other names for the pulser?
A: Output power, output gain, acoustic power, pulsing power, energy output, "power."
NOTE: This is the sound going INTO the patient — different from overall gain/TGCs (received echoes).
~~~
CARD 67
Q: What measurements relate to pulser output?
A: Mechanical Index (MI) and Thermal Index (TI). Both go up when output power increases.
~~~
CARD 68
Q: What do pulse delays do?
A: Together with the pulser, they control:
- Beam STEERING
- Beam FOCUSING
- APERTURE size
By coordinating timing of electrical signals to each crystal. Includes apodization for lobe reduction.
~~~
CARD 69
Q: What is a channel?
A: One piezoelectric crystal element + its individual electronic connection (wire, pulser, delay). The number of channels = how many crystals can be excited simultaneously or sequentially.
~~~
CARD 70
Q: What are the two functions of the T/R switch?
A:
1. ROUTES signals — pulser to transducer during transmit; transducer to receiver during receive
2. PROTECTS sensitive receive electronics from the high voltages used during transmission
~~~
CARD 71
Q: What do the receive amplifiers do?
A: Operate during RECEPTION. Amplify the weak returning echo signals (because of attenuation). Each signal undergoes equal amplification.
- Overall gain → makes whole image brighter/darker
- TGC (Time Gain Compensation) = DGC (Depth Gain Compensation) → selectively amplifies signals from deeper structures
- Units: decibels (dB)
~~~
CARD 72
Q: Why do we need amplifiers — and what DON'T they improve?
A: We need them because of ATTENUATION (sound weakens as it travels deeper).
TRAP: Amplifiers do NOT improve signal-to-noise ratio (SNR). They amplify signal and noise equally.
~~~
CARD 73
Q: What 3 things DO improve signal-to-noise ratio (SNR)?
A:
1. CODED EXCITATION
2. HARMONIC IMAGING
3. PERSISTENCE (frame averaging / temporal compounding)
~~~
CARD 74
Q: What does the ADC (analog-to-digital converter) do?
A: Converts the analog (waveform) voltage signal into DIGITAL (binary 0s and 1s). Computers can only process digital info.
~~~
CARD 75
Q: What do echo delays + summer do?
A: ECHO DELAYS accomplish reception dynamic focus and steering using:
- PHASING (small time delays)
- SEQUENTIAL firing (specific crystals fire in order)
The SUMMER adds the signals from all channels together → produces ONE SCAN LINE.
~~~
CARD 76
Q: What is line density?
A: How many scan lines fit in the image. More scan lines = HIGHER line density = better detail.
~~~
================================================================
SECTION 13: SIGNAL PROCESSOR
================================================================
CARD 77
Q: What are the 3 jobs of the signal processor?
A:
1. FILTERING (band-pass, harmonics)
2. DETECTION / DEMODULATION
3. COMPRESSION (dynamic range)
~~~
CARD 78
Q: How does filtering work in the signal processor?
A: A TUNED AMPLIFIER with a BAND-PASS FILTER allows only frequencies within a specific range (the bandwidth) to pass. Frequencies outside this range get filtered out as not useful.
~~~
CARD 79
Q: What are harmonic frequencies?
A: Even multiples of the operating frequency (typically DOUBLE the fundamental). The 2nd harmonic is what's used for the image.
~~~
CARD 80
Q: Why use harmonic imaging?
A:
- Higher fundamental → higher harmonic → BETTER RESOLUTION
- Improves signal-to-noise ratio (SNR)
- Reduces artifacts
- Better for difficult body habitus
~~~
CARD 81
Q: What is detection (demodulation)?
A: The FINAL stage of the signal processor. Converts echo voltages from electrical form into VIDEO form for display.
KEY: AMPLITUDE is preserved during this conversion.
~~~
CARD 82
Q: What is compression — and what's its other name?
A: Compression = DYNAMIC RANGE. Combines the huge range of raw signals into manageable groups so the computer can process and display them.
Determines the number of GRAY SHADES visible.
~~~
CARD 83
Q: Narrow vs. wide dynamic range — what does each give you?
A:
- NARROW dynamic range → FEWER gray shades → HIGH contrast (mostly black & white)
- WIDE dynamic range → MANY gray shades → LOW contrast → MORE diagnostic info
~~~
CARD 84
Q: Clinical use of dynamic range?
A: A liver with metastatic cancer appears HETEROGENEOUS due to varying signal levels. A wide dynamic range helps differentiate structures (e.g., a cyst within a kidney).
~~~
================================================================
SECTION 14: IMAGE PROCESSOR
================================================================
CARD 85
Q: What does the image processor do?
A: Converts already-digitized, filtered, detected, and compressed echo info into a displayable image. Stores frames in memory using pixels, bits, and binary numbers (scan conversion).
~~~
CARD 86
Q: What is pre-processing?
A: Anything done BEFORE the FREEZE button is pressed. Applied as data is being stored in memory (during scan conversion).
~~~
CARD 87
Q: List the pre-processing features.
A:
- TGC
- Dynamic range / compression
- Write magnification
- Edge enhancement
- Pixel interpolation
- Persistence (temporal compounding)
- Panoramic imaging
- Spatial compounding
- 3D / 4D imaging
~~~
CARD 88
Q: What is edge enhancement?
A: A pre-processing feature that SHARPENS the edges of structures in the image to make them appear clearer and more defined.
~~~
CARD 89
Q: What is pixel interpolation?
A: When echo info from a small area is missing, the machine looks at the BRIGHTNESS of surrounding pixels and "fills in" the missing area based on what's around it.
~~~
CARD 90
Q: What is persistence — and what are its other names?
A: Persistence = TEMPORAL COMPOUNDING = FRAME AVERAGING = FRAME COMPOUNDING.
Holds 4+ frames in a buffer and averages them together before display.
~~~
CARD 91
Q: Pros and cons of persistence?
A:
PROS:
- Increases SNR
- Helps differentiate real echoes from noise/speckle/artifact
- Improves image quality
CONS:
- DEGRADES temporal resolution (slows frame rate)
- Bad for moving structures (heart)
~~~
CARD 92
Q: When is persistence ideal?
A: For STATIONARY structures — abdomen, liver. High frame rate isn't critical there.
~~~
CARD 93
Q: What is panoramic imaging?
A: Slide the transducer across a wide area to create a single EXTENDED image frame.
- No new info is added — existing info is just spread out spatially
- The machine compares echoes to place new info in the proper location
~~~
CARD 94
Q: When is panoramic imaging useful?
A: Measuring LARGE structures that don't fit on a standard screen. Examples:
- A spleen over 20 cm
- Large fluid collections
- Big masses
~~~
CARD 95
Q: What is spatial compounding?
A: Through STEERING and PHASING, scan lines are sent through the same area from MULTIPLE ANGLES. Frames are averaged to produce a more accurate image with fewer artifacts.
~~~
CARD 96
Q: What does spatial compounding eliminate?
A: SHADOWING and ENHANCEMENT. Allows you to see structures hidden behind objects that attenuate the beam.
Example: seeing a femoral vein behind a calcified, shadowing femoral artery.
~~~
CARD 97
Q: Spatial vs. temporal compounding — quick distinction?
A:
- SPATIAL compounding = multiple ANGLES, same time. Reduces shadowing/enhancement.
- TEMPORAL compounding = multiple FRAMES, same angle. Same as persistence. Reduces noise/speckle.
~~~
CARD 98
Q: What are 3D and 4D imaging?
A:
- 3D = takes many 2D images and pieces them together → STILL 3D image
- 4D = 3D in REAL-TIME (3D plus the dimension of time)
~~~
CARD 99
Q: What is post-processing?
A: Manipulation of stored image data AFTER FREEZE is pressed. Operator-controlled and REVERSIBLE.
~~~
CARD 100
Q: List the post-processing features.
A:
- READ magnification
- Black-and-white inversion
- Contrast variation
- Color manipulation on frozen frames (machine-dependent)
- Persistence (also pre)
- Smoothing
- Pixel interpolation
~~~
CARD 101
Q: Read vs. write magnification?
A:
- WRITE magnification = pre-processing (during data acquisition). Preserves detail and pixel density.
- READ magnification = post-processing (zoom on a frozen image). Just enlarges existing pixels — may look grainier.
Memory hook: "You can't READ what hasn't been WRITTEN."
~~~
================================================================
SECTION 15: PIXELS, BITS & STORAGE
================================================================
CARD 102
Q: What is a pixel?
A: "Picture element" — the smallest building block of a digital picture. Each pixel represents one shade of gray. SMALLER pixels = better detail.
~~~
CARD 103
Q: What is pixelation?
A: Making pixels LARGER to obscure detail (e.g., used on TV to hide a face in witness protection). In ultrasound, smaller pixels = better detail.
~~~
CARD 104
Q: Low vs. high pixel density?
A:
- LOW pixel density → fewer, larger pixels → blurrier image, LOWER spatial resolution
- HIGH pixel density → more, smaller pixels → BETTER spatial resolution
~~~
CARD 105
Q: What is a bit?
A: "Binary digit" — the smallest unit of computer memory. Determines the number of GRAY SHADES (contrast resolution).
~~~
CARD 106
Q: What is a bistable image?
A: An image based on pure binary code (0s and 1s) — strictly BLACK AND WHITE in 2D imaging. No gray shades.
~~~
CARD 107
Q: How do you calculate the number of gray shades a system can display?
A: Number of gray shades = 2^n, where n = number of bits.
Examples:
- 7-bit memory = 2^7 = 128 shades
- 8-bit memory = 2^8 = 256 shades
~~~
CARD 108
Q: Pixels vs. Bits — quick summary?
A:
- PIXELS = image elements → image detail → SPATIAL resolution
- BITS = computer memory → number of gray shades → CONTRAST resolution
~~~
CARD 109
Q: What is image memory?
A: Where images are stored AFTER scan conversion and pre-processing.
~~~
CARD 110
Q: What does the freeze button do?
A: Captures a SINGLE frame out of the many being generated each second.
~~~
CARD 111
Q: What is CineLoop?
A: A feature that lets the sonographer review previous frames that occurred RIGHT BEFORE the freeze button was pressed.
Useful when a patient is breathing rapidly and the desired structure (like the CBD) was only visible for a split second.
~~~
================================================================
SECTION 16: DISPLAY & ARCHIVING
================================================================
CARD 112
Q: What displays do modern ultrasound systems use?
A: LCD (Liquid Crystal Display) / flat-panel displays. Older systems used CRT (Cathode Ray Tube).
~~~
CARD 113
Q: What is PACS?
A: PICTURE ARCHIVING AND COMMUNICATION SYSTEMS. The system used to STORE all medical images.
~~~
CARD 114
Q: What is DICOM?
A: DIGITAL IMAGING AND COMMUNICATIONS IN MEDICINE. NOT an output device — it's a SET OF RULES/PROTOCOLS regarding how image data is stored and protected within PACS.
~~~
CARD 115
Q: PACS vs. DICOM — quick distinction?
A:
- PACS = the SYSTEM that stores images
- DICOM = the RULES that govern how those images are stored/protected within PACS
~~~
================================================================
SECTION 17: DOPPLER & HEMODYNAMICS
================================================================
CARD 116
Q: How much of the SPI exam is Doppler/hemodynamics?
A: Approximately 34% — the biggest single section.
~~~
CARD 117
Q: What does color Doppler show?
A: Location and DIRECTION of blood flow (toward probe = red by default; away = blue).
~~~
CARD 118
Q: What is duplex imaging?
A: Grayscale image + color superimposed = TWO things → "duplex."
~~~
CARD 119
Q: What is triplex (spectral) Doppler?
A: Grayscale + color + spectral graph = THREE things → "triplex."
Provides VELOCITY, DIRECTION, and waveform SHAPE of blood flow.
~~~
CARD 120
Q: What is power Doppler also called?
A: Color Power Angio. Shows AMPLITUDE of moving RBCs. Very sensitive to slow flow. No velocity, no direction.
~~~
CARD 121
Q: What is hemodynamics?
A: The study of blood moving through the circulatory system. Doppler is used to detect and evaluate this flow — finding regurgitation (backward flow) and stenosis (vessel narrowing).
~~~
CARD 122
Q: What is volumetric flow rate?
A: The volume of blood moving during a unit of time.
~~~
================================================================
SECTION 18: BLOOD FLOW CATEGORIES
================================================================
CARD 123
Q: What is pulsatile flow?
A: Variable velocity due to systole and diastole. Found in ARTERIAL circulation.
~~~
CARD 124
Q: What is phasic flow?
A: Variable velocity in response to pressure changes during respiration. Found in VENOUS circulation (legs, hepatic veins).
~~~
CARD 125
Q: What is steady flow?
A: Constant velocity — no changes with time. Found in:
- Portal vein normally
- Veins during breath-holds
~~~
CARD 126
Q: Hepatic vein vs. portal vein — flow type?
A:
- HEPATIC veins → PHASIC (undulating, big velocity changes — even though they're veins)
- PORTAL vein → STEADY (smooth flow into the liver)
~~~
CARD 127
Q: What does it mean if you see red and blue alternating quickly on a portal vein waveform?
A: FLOW REVERSAL — blood coming OUT of the liver instead of in. SERIOUS clinical finding.
~~~
CARD 128
Q: What is plug flow?
A: Found at the BEGINNING of large vessels (e.g., aorta leaving the left ventricle). Velocities across the vessel are UNIFORM.
~~~
CARD 129
Q: What is laminar flow?
A: Blood flowing in PARALLEL LAYERS. The CENTER of the vessel moves fastest because the walls slow down the outer layers. Why we always place sample volume in the center.
~~~
CARD 130
Q: What is parabolic flow?
A: A bullet-shaped profile where layers slide over each other.
KEY: Average velocity = MAXIMUM velocity ÷ 2.
~~~
CARD 131
Q: What is disturbed flow?
A: A type of LAMINAR flow where parallel lines are altered by bifurcations or narrowing.
NOT always pathological — vessels normally branch and turn.
~~~
CARD 132
Q: What is turbulent flow?
A: PATHOLOGICAL flow with chaotic, swirling "EDDY" currents. Many velocities and directions at once.
- Associated with stenosis and heart murmurs
- Causes SPECTRAL BROADENING on a waveform
~~~
CARD 133
Q: What is spectral broadening?
A: FILLING IN of the spectral window beneath the waveform. Indicates turbulent flow.
TRAP: Can also appear normally in fast-flowing vessels (renal artery, carotid) without true pathology.
~~~
================================================================
SECTION 19: REYNOLDS, PRESSURE, RESISTANCE
================================================================
CARD 134
Q: What is the Reynolds number used for?
A: Predicts whether flow will be LAMINAR or TURBULENT.
Critical value: ~2,000.
- Approaching 2,000 → potentially turbulent
- Above 2,000 → definitely turbulent
~~~
CARD 135
Q: What is the Reynolds number formula?
A: Re = (Velocity × Diameter × Density) ÷ Viscosity
~~~
CARD 136
Q: What is the major form of energy in circulating blood?
A: POTENTIAL ENERGY (which is pressure).
~~~
CARD 137
Q: What is hydrostatic pressure?
A: The WEIGHT of a column of blood. Increases when standing — makes it harder for blood to return from the feet to the heart.
Why ankles/feet swell first when there's venous insufficiency.
~~~
CARD 138
Q: What are the 3 forms of energy loss?
A:
1. VISCOUS — due to thickness of blood; measured in poise; related to hematocrit
2. FRICTIONAL — energy converted to heat as blood rubs against walls
3. INERTIAL — fluid resists changes in velocity (acceleration, deceleration, bifurcations)
~~~
CARD 139
Q: What is viscosity measured in — and what does it relate to?
A: Measured in POISE. Related to HEMATOCRIT (% of red blood cells). Higher hematocrit = thicker blood = more viscosity.
~~~
CARD 140
Q: Why is blood fastest in the center of a vessel?
A: Because of FRICTIONAL energy loss — blood rubbing against vessel walls slows the outer layers, while the center has no walls to slow it.
~~~
CARD 141
Q: What is a pressure gradient?
A: The pressure DIFFERENCE between two locations divided by the distance between them. Blood flows from HIGH pressure to LOW pressure.
GREATER difference = GREATER flow rate.
~~~
CARD 142
Q: Pressure-Flow-Resistance equations?
A:
- Pressure Gradient = Flow × Resistance
- Flow = Pressure Gradient ÷ Resistance
- Resistance = Pressure Gradient ÷ Flow
~~~
CARD 143
Q: What 3 factors determine resistance?
A:
1. VISCOSITY (↑ viscosity → ↑ resistance)
2. VESSEL LENGTH (↑ length → ↑ resistance)
3. VESSEL RADIUS (↑ radius → ↓ resistance)
Radius is the BIGGEST factor.
~~~
================================================================
SECTION 20: POISEUILLE'S EQUATION
================================================================
CARD 144
Q: Poiseuille's equation — what does it relate?
A: Flow (Q), pressure gradient (ΔP), and resistance (R).
Q = (ΔP × π × r⁴) ÷ (8 × η × L)
~~~
CARD 145
Q: Why is radius the biggest factor in Poiseuille's equation?
A: Because radius is raised to the FOURTH POWER (r⁴).
- DOUBLE the radius → 16× increase in flow
- HALVE the radius (50% decrease) → 95% DECREASE in flow
~~~
CARD 146
Q: Quick relationships from Poiseuille's?
A:
- ΔP ↑ → Flow ↑
- Diameter ↑ → Flow ↑
- Length ↑ → Flow ↓
- Viscosity ↑ → Flow ↓
~~~
CARD 147
Q: Continuity rule vs. Poiseuille's — do they contradict?
A: NO — they apply to different scopes:
- CONTINUITY RULE: AT a stenosis (small section). If diameter goes DOWN, velocity goes UP.
- POISEUILLE'S: across the WHOLE vessel. If diameter goes UP, flow goes UP.
~~~
================================================================
SECTION 21: VENOUS HEMODYNAMICS
================================================================
CARD 148
Q: Vein characteristics?
A:
- Thin walls
- Highly compressible (used in compression test for DVT)
- Normally LOW resistance
~~~
CARD 149
Q: What does it mean if a vein doesn't compress under probe pressure?
A: Likely a THROMBUS inside. Compression test is the foundation of DVT exams.
~~~
CARD 150
Q: What is transmural pressure?
A: Pressure across the vessel wall.
- HIGH transmural pressure → vein is EXPANDED, circular cross-section
- LOW transmural pressure → vein is FLATTENED, dumbbell-shaped
~~~
CARD 151
Q: What happens during inspiration to abdominal and thoracic pressure?
A:
- Diaphragm moves DOWN
- Abdominal pressure INCREASES → DECREASES venous return from LEGS
- Thoracic pressure DECREASES → INCREASES venous return from ARMS to heart
~~~
CARD 152
Q: What happens during expiration to abdominal and thoracic pressure?
A:
- Diaphragm moves UP
- Abdominal pressure DECREASES → INCREASES venous return from LEGS
- Thoracic pressure INCREASES → DECREASES venous return from arms
~~~
================================================================
SECTION 22: STENOSIS, BERNOULLI & VASCULAR ANATOMY
================================================================
CARD 153
Q: What happens at a stenosis?
A:
- Pressure DROPS
- Velocity INCREASES
- This is the BERNOULLI EFFECT
~~~
CARD 154
Q: How is stenosis severity measured?
A: Flow is measured at 3 spots:
1. BEFORE the stenosis (proximal)
2. AT the stenosis
3. AFTER the stenosis (distal)
~~~
CARD 155
Q: How do you visually spot a stenosis on color Doppler?
A: COLOR ALIASING — turbulent flow appearance (mosaic / turquoise).
~~~
CARD 156
Q: What is the Bernoulli equation?
A: ΔP = 4v²
Critical for ECHOCARDIOGRAPHY pressure gradient calculations.
~~~
CARD 157
Q: ECA (External Carotid Artery) features?
A:
- HIGH-resistance waveform
- HAS BRANCHES in the neck (first = superior thyroid artery)
- Supplies the FACE
~~~
CARD 158
Q: ICA (Internal Carotid Artery) features?
A:
- LOW-resistance waveform
- Typically NO branches in the neck
- Supplies the BRAIN
~~~
CARD 159
Q: How can you quickly identify the ECA from the ICA on imaging?
A: Look for branches. The ECA has them in the neck (first branch = superior thyroid artery). The ICA does not.
~~~
CARD 160
Q: What is subclavian steal syndrome?
A: RETROGRADE (backward) flow seen in the vertebral artery. Caused by a SUBCLAVIAN ARTERY BLOCKAGE — the body steals blood from the contralateral vertebral to supply the affected arm.
~~~
CARD 161
Q: Why do worksheets ask for vertebral flow direction (antegrade vs. retrograde)?
A: To screen for SUBCLAVIAN STEAL. Retrograde flow in the vertebral = positive finding for steal.
~~~
CARD 162
Q: What does it mean that arteries are "compliant"?
A: Arteries EXPAND when blood is forced into them, then CONTRACT to push the blood forward.
Some arteries (e.g., femoral) normally show a small amount of flow REVERSAL in diastole.
~~~