New Material - Modes, B-Flow Imaging, Doppler Artifacts, Interventional & Treatment Instruments, Artificial Intelligence, New Transducers, New Physics Paradigm

A-Mode

1 dimension - axial to beam

Spike on monitor indicates relative echogenicity - higher amplitude = stronger reflector

Based on range equation

A-Mode X & Y Axis

x-axis: depth

y-axis: amplitude

A-Mode Components

Transducer

Timer/Start Pulse Generator (SPG)

Transmitter/High Voltage Pulse Generator (HVPG)

Receiver

Display (oscilloscope, CRT, imaging screen)

Camera for hardcopy and/or digital storage

A-Mode Instrument Controls

Transducer frequency

Depth

A-Mode Artifacts

Shadowing

Reverberation

Enhancement

Beam width artifact

Velocity artifact

Multi-path

Refraction

Transducer defects

Lack of gel

A-Mode Historical Uses

Echoencephalography,

Cardiology

A-Mode Current Uses

Ophthalmology

Tissue characterization

Non-destructive industrial testing

M-Mode

Single sound beam

Signal amplitude information is converted to dot brightness

M-Mode X, Y, & Z Axis

x-axis: change over time

y-axis: depth

z-axis: echo brightness

M-Mode Components

SPG/timer

HVPG/transmitter

Transducer

Receiver

Scan converter

Display

Storage - strip chart recorder, camera, or video tape

M-Mode Controls

Transducer frequency

Depth

Gain & TGC

Sweep speed

EKG & respirometer

M-Mode Artifacts

Shadowing

Reverberation

Enhancement

Beam width artifact

M-Mode Uses

Cardiology

Lung

M-Mode Advantages

Easy measurements

Good temporal & axial resolution

Can see several cycles at once

M-Mode Limitations

Very dependent on cursor placement

Only displays one type of motion - no lateral or perpendicular motion

Difficult to identify echo source if B-mode image is not present - scanning blind

Anatomical M-Mode

Steerable m-mode

Modifies angle to obtain more accurate measurements

Not limited to scan line angles

Static B-Mode

Tx beam controlled by sonographer

Amplitude of signal is represented by the brightness of each dot

Large FOV

Static B-Mode Components

SPG/HVPG

Transducer

Receiver

Scan Converter

Display (CRT)

Registration system

Static B-Mode Controls

Transducer frequency

Depth

Gain & TGC

Measurements

*Scanning Movements

Static B-Mode Artifacts

Shadowing

Reverberation

Enhancement

Beam Width Artifact

Velocity Artifact

Multi-path Artifact

Refraction

Transducer defects

Lack of gel

Misregistration

Static B-Mode Uses

OB-GYN

Abdominal

Vascular (Non-Doppler)

Small Parts

Real-Time B-Mode

Tx beam controlled mechanically or electronically

Produces multiple frames of multiple scan lines

Images continuously gathered & refreshed

Reduced FOV

Real-Time B-Mode Components

SPG/HVPG

Beam Former

Transducer

Timer

Receiver

Scan Converter

Display

Storage

Real-Time B-Mode Controls

Transducer frequency

Depth

Field size

Zoom

Measurements

*Focusing

Real-Time B-Mode Artifacts

Shadowing

Reverberation

Enhancement

Beam width artifact

Velocity artifact

Multi-path artifact

Refraction

Transducer defects

Lack of gel

Misregistration

Real-Time B-Mode Uses

Neurosonology

Vascular

Abdomen

OB-GYN

Cardiac

Small parts

Musculoskeletal

Intervention/guidance

Compound B-Mode

More than one scan line may interact with an interface to "build-up" an image from multiple adjacent or overlapping scan lines

Can be used with static or real-time B-mode or EFOV

Abdominal/Multi-Purpose Frame Rate

16 frames/second

Cardiac Frame Rate

30 frames/second

Doppler Frame Rate

40-60 frames/second

3D

Volume b-mode imaging

3D X, Y, & Z Axis

x-axis: long

y-axis: trans

z-axis: reconstructed horizontal/coronal view

3D Image Acquisition

2D freehand - manual volume

3D automated - mechanical volume

Matrix - electronic volume

Tomographic View/Slice

3D Uses

Cardiology

Vascular

OB

GYN

Transparent Rendering

Allows us to see through the voxels (2D pixels in a 3D matrix)

Surface Rendering

Provides impression of depth by using brightness and shading

Enhances surface visualization of structures

Render Box

Rectangular box to define echoes for render

Render Line

Marks "top of box"

May be curved

aka reference slice

Inversion

Converts anechoic areas into solids

Surrounding echoes are subtracted or erased

May be used as basis for computer aided volume calculation (VOCAL)

aka cavity mode

STIC

Spatio-Temporal Image Correlation

Used in 4D fetal echo

Voxel

aka axis dot

aka reference dot

aka reference voxel

AOI

Area of interest

ROI

Render of interest

VOI

Volume of interest

MPR

Multiplanar Rendering/Reconstructions

B-Flow Imaging

B-mode imaging with flow without the overlay of color Doppler

Both RBCs & tissues are shown

Angle independent & not based on frequency shifts

Creating a B-Flow Image

Digitally coded sound waves transmitted into body

Returning signals are decoded

Subtractive process is used to separate RBCs from tissue

Weak returning signals from RBCs are enhanced

Tissue signals are equalized

All signals are displayed

B-Flow Imaging Uses

Degree of stenosis

Low flow conditions

Flow in vessels that are perpendicular to sound beam

Characterizing hypoechoic ulcerated plaques

B-Flow Imaging Advantages

Does not alias

Increased cavity of vessel lumen & stenotic areas

High frame rate

Better temporal & spatial resolution

Color Aliasing

Doppler frequency shift exceeds Nyquist limit (max detectible frequency)

"Wrap-around" color display

Seen with high velocity/turbulent areas & stenosis

How to Correct Color Aliasing

Lower frequency

Decrease depth

Avoid Doppler angles close to 0°

Incorrect Color Steering/Angle

How to Correct Incorrect Color Steering/Angle

Angle color box so it is parallel with vessel/in line with blood flow

Rocking/tilting motions

Over-Gaining Color

Color speckle/bleeding outside of vessel

Typically noise

Over-amplification of signals

How to Correct Over-Gaining Color

Decrease color gain

Adjust scale/baseline if needed

Under-Gaining Color

Lack/absence of flow - can be mistaken for pathology

Can occur in small vessels or deeper vessels

Under-amplification of signals

How to Correct Under-Gaining Color

Increase color gain

Set to low flow color Doppler setting

Adjust scale/baseline if needed

Incorrect Color Scales

Too high - low flow not detected

Too low - low flow over-represented as noise/color bleeding

How to Correct Incorrect Color Scales

Decrease scale - more low velocities shown

Increase scale - less low velocities shown

Pseudoflow

Color appears in areas that do not contain blood

Shows movement of other fluids - amniotic fluid, urinary jets, ascites, pleural fluid, etc.

How to Correct Pseudoflow

Evaluate anatomy - is it a vessel or not

Apply spectral Doppler to see if there is a correlating waveform

Flash Artifact

Speckles/flashes of color appear for patient or transducer movements

Also present with bruits/high velocity flows

How to Correct Flash Artifact

Have patient stay still/hold breath

Hold transducer steady

Mirror Image

Occurs with strong reflectors

Incorrect structure is shown deeper to actual structure

How to Correct Mirror Image

Change scanning position

Color Edge Artifact

Occurs at the margin of a strong, smooth, specular reflector - stones, bones, catheters, foley balloons, etc.

Displayed as persistent color along reflector's edge

More common with power Doppler

How to Correct Color Edge Artifact

Evaluate without Doppler

Evaluate anatomy

Test with spectral Doppler

Twinkling Artifact

Color motion/flow imitated behind a stationary strong reflector - stones, calcifications, etc.

Artifact looks like a stream of changing colors below reflector

Good for identifying certain pathologies - GB/renal stones

Spectral Aliasing

Doppler frequency shift exceeds Nyquist limit (max detectible frequency)

Wrap-around display on spectral graph

How to Correct Spectral Aliasing

Adjust baseline

Increase scale

Switch to CW if needed

Spectral Mirroring

Presence of flow on both sides of baseline

False flow is usually less amplified and will be the mirror image of true flow

How to Correct Spectral Mirroring

Decrease power

Decrease spectral Doppler gain

Spectral Broadening

Expected when there are multiple velocities being represented in in a given sample region

Occurs with large linear arrays with larger Doppler angles

Some flow is over/underestimated

How to Correct Spectral Broadening

Increase depth

Poor Doppler Angle

Can result in over/underestimated peak velocities

How to Correct Poor Doppler Angle

Rocking/tilting motions to optimize Doppler angle

Poor Doppler Frequency

Too high - poor sensitivity to flow & underestimated velocities

How to Correct Poor Doppler Frequency

Frequency should be as low as possible (unless scanning superficially)

Intravascular/Endovascular Ultrasound

Imaging within blood vessels

Femoral V access in cath lab

Specialized catheter with mini transducer at the tip - produces multi-element electronic (annular) arrays

Uses of Intravascular/Endovascular Ultrasound

Supplement to contrast angiography of coronary arteries

Supplement to contrast angiography of peripheral arteries

Evaluation of venous thrombosis

Assessment of AAA before, during and after interventions/repair

Endosonography

Visualizes GI tract or bronchial tract

Radial Tx - visualization

Linear Tx - FNA or therapeutic interventions

Uses of Endosonography

Staging GI malignancies

Evaluating pancreaticobiliary disease

Evaluating subepithelial abnormalities (GI lining)

Evaluating extraluminal abnormalities (ABNL lymph nodes)

Staging of lung cancer

Therapeutic - Drainings, nerve blocks, drug delivery

High Intensity Focused Ultrasound (HIFU)

Uses heat & cavitation from ultrasound to deliver therapeutic treatments

Performed under ultrasound or MRI guidance

Transducers designed and manipulated to have a very accurate focal spot - goal is to heat/cavitate tissues

Uses of High Intensity Focused Ultrasound (HIFU)

Benign & malignant tumor ablation

Intervention with essential tremors, Alzheimer's, Parkinson's, Depression/Anxiety, etc...

Disruption of blood brain barrier for delivery of treatment agents into brain tissue

Liquifying intracerebral hemorrhage clot

Advantages of High Intensity Focused Ultrasound (HIFU)

Reduced toxicity compared to other ablation techniques

Less painful & invasive

Lower cost than surgery

Less anesthesia

No scarring

Decreased risk of infection

Disadvantages of High Intensity Focused Ultrasound (HIFU)

Limited by patient movement

Near field heating (possible skin burns) & pain

May have long treatment times

Localized unintended tissue damage

Fusion Imaging

Overlaying/co-registration of images from the same or different imaging modalities

Computer software matches ultrasound imaging with CT, MRI, or PET/CT

Uses of Fusion Imaging

Liver biopsies

Guiding ablations

Other guidance procedures

Advantages of Fusion Imaging

Improved diagnostic accuracy

More accurate guidance during procedures

Better characterization of pathologies

Disadvantages of Fusion Imaging

Breathing motion real-time registering with static MRI/CT images

Misregistration of data

Still relatively new

Artificial Intelligence (AI)

Use of computer software to develop machine learning - recognition of patterns in medical images to assist with diagnosis - to mimic human cognition

Ways AI is Used in Ultrasound

Used to assist in recognizing patterns in pathology to speed up workflow & aid diagnosis

TIRADS

BIRADS

Scoring liver fibrosis

Fetal lung maturity

Fetal brain

Ventricular wall motion

Detection of heart diseases

Carotid artery intimal thickness

Micromachined Ultrasound Transducers (MUTs)

Tiny transducers

Usually much higher frequencies

Often used for interventional type imaging or newer hand-held transducers that connect to tablets/cell phones - Butterfly

Capacitive Micromachined Ultrasonic Transducer (cMUT)

Parallel-Plate Capacitor

Integrated with circuitry - "plug and play" design

Higher frequency range

Piezoelectric Micromachined Ultrasonic Transducer (pMUT)

Thin piezoelectric film rather than thick crystal

Integrated with circuitry - "plug and play" design

Lower frequency range

Principle 1

Physical beams

1:1 ratio of pulses to scan lines

Pulse length & width determines detail resolution

Best resolution at focus

Adjusting focus affects frame rate & reduces temporal resolution