Perform Ultrasound Examinations
23%of exam
Wave BasicsDecibel MathAttenuationImpedance + RangePulsed Parameters
Manage Ultrasound Transducers
7%of exam
ConstructionBeam + ArraysTransducer TypesDamping
Optimize Sonographic Images
26%of exam
ResolutionGain + TGCProcessingDisplay ModesArtifacts
Apply Doppler Concepts
34%of exam
Doppler EquationCW vs PWSpectral + ColorHemodynamicsDoppler Artifacts
Provide Clinical Safety & QA
10%of exam
Bioeffects + ALARAQA PhantomsStats + SafetyALARA
Quick Facts
- Exam
- SPI
- Body
- ARDMS / Inteleos
- Questions
- ~110 MCQ
- Time
- 2 hours
- Passing Score
- 555 / 700 scaled
- Fee
- $275
- Outline
- V24.1 (task-based)
- Biggest Domain
- Doppler, 34%
- Prerequisite
- Physics course, grade C+
- Validity Window
- 5 yrs with specialty
Decibel Doubling Rule
+3 dB doubles; -3 dB halves intensity
+3dB: ×2-3dB: ÷2+10dB: ×10+20dB: ×100
Wave Basics & Speed
- Period (T)
- T = 1/frequency
- Frequency (f)
- f = 1/period
- Propagation speed eq
- c = f × λ
- Soft tissue speed
- c = 1540 m/s
- Speed alt unit
- 1.54 mm/µs
- λ shortcut (mm)
- λ = 1.54/f(MHz)
- 5 MHz period
- 0.2 µs
- 5 MHz wavelength
- 0.308 mm
- Diagnostic freq range
- 2–15 MHz
- Ultrasound threshold
- Above 20 kHz
- Speed order (slow→fast)
- Air, fat, tissue, bone
- Speed depends on
- Stiffness up, density down
Decibel (dB) Math
- dB formula
- 10 × log(I2/I1)
- +3 dB
- Doubles intensity
- -3 dB
- Halves intensity
- +10 dB
- ×10 intensity
- -10 dB
- ÷10 intensity
- +20 dB
- ×100 intensity
- -6 dB
- Quarter of intensity
- Amplitude → power
- Power ∝ amplitude²
- 2× amplitude
- 4× power (quadruples)
Attenuation & Loss
- Attenuation coefficient
- 0.5 dB/cm/MHz soft tissue
- Total attenuation (dB)
- 0.5 × freq × depth
- HVL / DOP
- Depth at −3 dB
- Absorption
- Dominant loss, converts heat
- Reflection
- Large smooth boundary echo
- Scattering
- Small or rough surfaces
- Attenuation rises with
- Higher frequency, greater depth
- Frequency selection rule
- Highest freq that penetrates
Impedance, Refraction & Range
- Acoustic impedance (Z)
- Z = ρ × c
- Impedance units
- Rayls
- IRC
- ((Z2−Z1)/(Z2+Z1))²
- ITC
- 1 − IRC
- Bigger Z mismatch
- Stronger reflected echo
- Specular reflection
- Angle-dependent, large surface
- Rayleigh scattering
- Angle-independent, small surfaces
- Refraction requires
- Oblique angle + speed change
- Snell's Law
- sinθt/sinθi = c2/c1
- Range equation
- Depth = (c × t)/2
- Range eq factor of 2
- Round-trip travel time
Pulsed Ultrasound Parameters
- PRP
- PRP = 1/PRF
- Imaging PRF range
- 1–10 kHz
- Round-trip per 1 cm
- ~13 microseconds
- Pulse duration (PD)
- # cycles × period
- Spatial pulse length
- # cycles × wavelength
- Duty factor
- PD/PRP = PD × PRF
- Imaging duty factor
- 0.1%–1%
- CW duty factor
- 100%
- PD & SPL control
- Fixed by transducer only
- Bandwidth
- Range of freqs in pulse
- Q-factor
- Frequency ÷ bandwidth
- Imaging Q-factor
- Low, wide bandwidth
- CW Q-factor
- High, narrow bandwidth
- Damping effect
- Shortens pulse, lowers sensitivity
Transducer Construction
- PZT crystal
- Active piezoelectric ceramic element
- Curie point
- Polarization temperature threshold
- Overheat past Curie
- Permanently destroys piezoelectric effect
- Piezoelectric effect
- Reciprocal: voltage ↔ vibration
- Resonant frequency
- c(PZT) ÷ (2 × thickness)
- Thinner element
- Higher resonant frequency
- Matching layer
- ¼ wavelength, steps impedance
- Backing material
- Dampens pulse, shortens SPL
Beam Geometry & Arrays
- Near zone length (NZL)
- D² / (4 × λ)
- NZL alt form
- Radius² ÷ wavelength
- Larger diameter/freq
- Lengthens near zone
- Beam waist
- End of near zone
- Focusing effect
- Narrows beam at set depth
- Linear/curved array
- Sequential firing, rectangular/trapezoidal image
- Phased array
- Full aperture, electronic steer
- Annular array
- Ring elements, mechanical steer
- 2D matrix array
- Rows + columns, real-time 3D/4D
- CW pencil probe
- 2 crystals, no image
- CW limitation
- Range ambiguity, no depth
Axial Resolution Synonyms (LARRD)
Longitudinal, Axial, Range, Radial, Depth resolution
L: LongitudinalA: AxialR: RangeR: RadialD: Depth
Axial vs Lateral Resolution
Axial
- = SPL / 2
- Along beam axis
- Set by pulse length
Lateral
- = beam width
- Across beam axis
- Best at focus
Depth direction vs side-to-side
Artifact Cause Identification
- Parallel bands, decreasing brightness→Reverberation(2 strong reflectors)
- Duplicate structure past diaphragm→Mirror image
- Anechoic band deep to mass→Acoustic shadowing
- Bright band deep to cyst→Posterior enhancement
- Thin shadow at cyst edge→Refraction artifact
- Structure at wrong depth→Speed displacement(Non-1540 m/s path)
Resolution Types & Formulas
- Axial resolution
- SPL ÷ 2
- Axial resolution value
- ~0.5 mm typical
- Axial improves with
- Higher freq, more damping
- LARRD
- Axial resolution synonymsmnemonic
- Axial NOT affected by
- PRF, depth, gain, power
- Lateral resolution
- = beam width
- Lateral best at
- Transmit focal zone
- LATA
- Lateral resolution synonymsmnemonic
- Multiple focal zones
- Better lateral, lower frame rate
- Elevational resolution
- Set by element height
- 1.5D array benefit
- Electronic elevational focusing
- Temporal resolution
- Controlled by frame rate
- Frame rate decreases with
- Depth, width, lines, foci up
- M-mode temporal res
- Highest, single scan line
Lateral Resolution Synonyms (LATA)
Lateral, Angular, Transverse, Azimuthal resolution
L: LateralA: AngularT: TransverseA: Azimuthal
Gain vs Output Power
Gain
- Post-echo amplification
- No bioeffect change
- Adjust freely
Output Power
- Pre-echo, patient dose
- Raises bioeffect risk
- ALARA: minimize first
Receiver control vs transmitter control
Gain, TGC & Dynamic Range
- Pulser
- Sets transmit pulse amplitude
- Output power up
- Raises intensity + bioeffect risk
- Apodization
- Tapers aperture, cuts side lobes
- Overall gain
- Amplifies all depths equally
- Gain vs bioeffects
- Gain does not raise risk
- TGC / DGC
- Corrects attenuation by depth
- Only patient-dose control
- Output power, not gain/TGC
- Dynamic range
- dB, largest to smallest signal
- Narrow dynamic range
- More contrast, fewer shades
- Wide dynamic range
- Less contrast, more shades
Reverberation vs Mirror Image
Reverberation
- Equally spaced bands
- 2 parallel reflectors
- Decreasing brightness
Mirror Image
- Single duplicate structure
- 1 strong reflector
- Beyond true structure
Repeating vs single duplicate
Signal Processing & Storage
- Pre-processing
- Before storage, not adjustable later
- Post-processing
- After storage, adjustable on freeze
- Write zoom
- Rescans, truly improves resolution
- Read zoom
- Magnifies pixels, no new data
- Persistence
- Frame averaging, lowers temporal res
- Gray shades formula
- 2^(bits per pixel)
- Standard bit depth
- 8 bits = 256 shades
- DICOM
- Medical image file standard
- PACS
- Stores, distributes DICOM images
Shadowing vs Enhancement
Shadowing
- Anechoic band below
- Strong attenuator
- TGC assumption too high
Enhancement
- Bright band below
- Weak attenuator
- TGC assumption too low
High vs low attenuation
Display Modes & Harmonics
- A-mode
- Amplitude spikes, ophthalmic use
- B-mode
- Brightness dots, standard 2D
- M-mode
- Position vs time tracing
- M-mode use
- Rapid repetitive motion, valves
- Harmonic frequency
- ~2× fundamental transmit frequency
- Harmonics origin
- Generated in tissue, not interface
- Harmonic imaging benefit
- Less clutter, better lateral res
- Contrast harmonic imaging
- Exploits microbubble nonlinear signal
- Spatial compounding
- Multi-angle average, less speckle
- Frequency compounding
- Multi-band average, less speckle
- Panoramic imaging
- Stitched sweep, not real-time
- 3D acquisition
- Wobbling 1D or matrix array
- 4D imaging
- Real-time 3D, live volumes
- Contrast microbubbles
- IV gas bubbles, capillary-sized
- Contrast + high MI
- Can rupture microbubbles
Propagation & Attenuation Artifacts
- Reverberation
- Equal parallel bands, decreasing brightness
- Mirror image
- Duplicate past strong reflector
- Speed displacement
- Wrong depth, non-1540 path
- Range ambiguity
- PRF too high for depth
- Acoustic shadowing
- Anechoic band, strong attenuator
- Posterior enhancement
- Bright band, weak attenuator
- Refraction edge shadow
- Thin shadow at curved edge
- Grating lobes
- Full-strength, element spacing ≥λ
- Side lobes
- Lower-intensity, any transducer
- Beam-width artifact
- Worst away from focal zone
- Slice-thickness artifact
- Elevational plane partial volume
- Beam-geometry artifact fix
- Technique change, not gain/TGC
Color Doppler Convention (BART)
Blue Away, Red Toward the transducer
B: BlueA: AwayR: RedT: Toward
PW vs CW Doppler
PW
- Sample gate depth
- Has Nyquist limit
- Can alias
CW
- No depth gate
- No Nyquist limit
- Never aliases
Depth localization vs velocity range
PW vs CW Doppler Selection
- Need high velocity, stenosis→CW Doppler(No upper limit)
- Need depth localization→PW Doppler(Sample gate)
- Suspect PW aliasing→Raise PRF, scale(First fix)
- Aliasing at max PRF→Switch to CW(No Nyquist limit)
- Flow mostly one direction→Shift baseline(Reallocates display)
- Need exact depth of jet→PW, not CW(CW = range ambiguity)
Doppler Equation & Angle
- Doppler shift equation
- fD = 2×ft×v×cosθ/c
- fD definition
- fD = fr − ft
- Flow toward transducer
- Positive Doppler shift
- Flow away from transducer
- Negative Doppler shift
- c in Doppler eq
- 1540 m/s, assumed constant
- cos 0°
- = 1, max shift
- cos 60°
- = 0.5, half shift
- cos 90°
- = 0, no shift
- Max angle rule
- 60° or less for velocity
- Angle correction cursor
- Align to vessel/flow direction
Color vs Power Doppler
Color
- Shows direction + velocity
- Can alias
- Mean frequency shift
Power
- Shows presence only
- Never aliases
- Signal amplitude
Velocity map vs sensitivity map
Aliasing Fix Sequence
- Aliasing on PW/color→Increase PRF, scale
- Scale already maxed→Lower transmit frequency
- Still aliasing→Increase Doppler angle
- Flow one-directional→Shift baseline
- Exceeds all PW limits→Switch to CW Doppler
CW, PW & Nyquist Limit
- CW Doppler crystals
- 2 crystals, transmit + receive
- CW aliasing
- Never aliases, no PRF
- CW velocity range
- No upper limit
- CW depth limitation
- Range ambiguity, no localization
- PW Doppler crystal
- 1 crystal, sample gate
- Nyquist limit
- PRF / 2
- Aliasing trigger
- True shift exceeds PRF/2
- Deeper sample volume
- Lower max PRF, more aliasing
- Sample gate size
- Sensitivity vs depth accuracy
- Fix aliasing (best)
- Raise PRF, scale
- Fix aliasing (other)
- Shift baseline, lower freq
- Fix aliasing (switch mode)
- Use CW Doppler
Spectral, Color & Power Doppler
- Spectral display
- FFT of Doppler signal
- FFT output
- Velocity vs time
- Spectral broadening
- Fills window, turbulence or technical
- Wall filter
- Removes low-freq wall motion
- Wall filter too high
- Erases real slow flow
- Velocity scale control
- = PRF setting
- Color Doppler method
- Autocorrelation, mean shift
- BART convention
- Toward = red, away = blue
- Power Doppler
- Amplitude, not direction/velocity
- Power Doppler aliasing
- Never aliases
- Power Doppler strength
- More sensitive, low flow
- Tissue Doppler (TDI)
- Low-velocity, high-amplitude tissue motion
Hemodynamics & Measurements
- Laminar flow
- Orderly, narrow spectral window
- Turbulent flow
- Disorganized, fills spectral window
- Parabolic profile
- Fast center, zero at wall
- Plug flow
- Uniform velocity, large vessels
- Bernoulli equation
- ΔP = 4v²
- Resistive Index (RI)
- (PSV − EDV) / PSV
- Pulsatility Index (PI)
- (PSV − EDV) / mean
- Velocity from shift
- v = fD×c/(2×ft×cosθ)
Doppler & Color Artifacts
- Aliasing cause
- Shift exceeds Nyquist, PRF/2
- Twinkling artifact
- Red/blue mosaic, renal calculus
- Blooming artifact
- Color overflows vessel wall
- Blooming cause
- Excess color gain/power
- Flash artifact
- Motion overwhelms wall filter
- Artifactual broadening
- Oversized sample gate, not disease
ALARA Priority Order
Gain first, minimize time, output power last
1. Increase gain2. Limit dwell time3. Lower output power4. Freeze when idle
TI vs MI
TI
- Thermal risk index
- TIS/TIB/TIC variants
- Tied to power/dwell
MI
- Cavitation risk index
- Pr / √freq
- FDA limit 1.9
Heat risk vs cavitation risk
Bioeffects, TI, MI & ALARA
- Bioeffect mechanisms
- Thermal + mechanical, cavitation
- Absorption up with
- Higher frequency, longer dwell
- Bone absorption
- Highest, hot spot at interface
- Inertial cavitation
- Violent collapse, free radicals
- Thermal Index (TI)
- Power used ÷ 1°C-rise power
- TI variants
- TIS, TIB, TIC
- Mechanical Index (MI)
- Peak rarefaction pressure/√freq
- FDA output limit
- ISPTA ≤ 720 mW/cm²
- FDA ophthalmic limit
- ISPTA ≤ 50 mW/cm²
- FDA MI limit
- MI ≤ 1.9
- ALARA priority
- Gain over output power
- ODS standard
- Real-time on-screen TI/MI
Sensitivity vs Specificity
Sensitivity
- TP / (TP+FN)
- True-positive detection
- Rules out disease
Specificity
- TN / (TN+FP)
- True-negative detection
- Rules in disease
SnNout vs SpPin
QA & Tissue Phantoms
- Phantom speed
- 1540 m/s, matches assumption
- Core QA tests
- DOP, axial/lateral res, dead zone
- More core tests
- Distance accuracy, uniformity
- Depth of penetration
- Max depth, weak echoes
- Transducer integrity check
- Detects dead/dropped elements
- Dropped element sign
- Dark stripe artifact
- QA documentation
- Dated, retained every check
Stats, Infection & Patient Safety
- Sensitivity
- TP / (TP + FN)
- Specificity
- TN / (TN + FP)
- PPV
- TP / (TP + FP)
- NPV
- TN / (TN + FN)
- Accuracy
- (TP+TN) / total
- Sens/spec vs PPV/NPV
- Intrinsic vs prevalence-dependent
- Spaulding: critical devices
- Require sterilization
- Spaulding: semicritical
- High-level disinfection, TV/TR probes
- Spaulding: noncritical
- Low-level disinfection
- Patient ID check
- 2 identifiers before scanning
- Contrast safety
- Screen contraindications, monitor reaction
Common Traps
Frequency vs Resolution
Higher freq = better res ≠ Higher freq = less penetration
Gain vs Output Power
Gain: no patient dose ≠ Output power: raises patient dose
Axial vs Lateral Resolution
Axial = pulse length ≠ Lateral = beam width
PW vs CW Aliasing
PW can alias ≠ CW never aliases
TI vs MI
TI = thermal risk ≠ MI = cavitation risk
Sensitivity vs Specificity
Sensitivity finds true positives ≠ Specificity finds true negatives
Legacy vs V24.1 Outline
Legacy: 5 topics, retired ≠ V24.1: 5 tasks, current
Reverberation vs Mirror Image
Reverberation: repeating bands ≠ Mirror: single duplicate
Write Zoom vs Read Zoom
Write zoom: adds resolution ≠ Read zoom: just magnifies
Last Minute
- 1.Doppler 34%: biggest domain
- 2.c = 1540 m/s in tissue
- 3.Wavelength(mm) = 1.54 / f(MHz)
- 4.Axial resolution = SPL / 2
- 5.Nyquist limit = PRF / 2
- 6.Doppler shift = 2ft·v·cosθ/c
- 7.Attenuation = 0.5 dB/cm/MHz
- 8.MI limit ≤ 1.9, FDA
- 9.ISPTA limit ≤ 720 mW/cm²
- 10.60° = max Doppler angle
- 11.Fix aliasing: raise PRF first
- 12.ΔP = 4v², Bernoulli equation
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