Old Material - US Safety, CEU, Panoramic, Elastography, TDI, Speckle Tracking, & Strain, Harmonics, Signal Processing, Doppler Signal Processing

Hand Hygiene

Most effective method for preventing the spread of microorganisms

Cleaning

Removal of visible soil

Soap & water

Essential before HLD and sterilization

Low-Level Disinfection (LLD)

Destruction of most bacteria and some viruses and fungi

Does not inactivate tuberculosis or bacterial spores

High-Level Disinfection (HLD)

Destruction of all micro-organisms, except bacterial spores

Sterilization

Destroys all forms of microbial life

Uses chemical sterilants or germicides, steam under pressure, dry heat, ethylene oxide (EtO) gas, hydrogen peroxide gas plasma, and liquid chemicals

Ergonomics

The science of fitting your work environment to you rather than fitting you to your working environment

Probably applicable to hobbies and leisure activities also

Manufacturer Responsibilities

Ultrasound system - machine, monitor, transducers, exam table, chairs

Employer Responsibilities

Risk management

Protocols and scheduling

Examination area

Computer workstation

Sonographer Responsibilities

Neutral posture

Safe patient handling

Practicing ALARA

Increase overall gain

Decrease power

Avoid high TI and MI values

Minimize scanning time

Avoid using Doppler on early embryos

Power

Rate at which energy is transmitted

Intensity

Power/Energy ÷ Area

Bioeffects

Adverse effects that ultrasound causes on biological tissues

Thermal Index (TI)

Power that raises temperature in tissues

TIS - soft tissue

TIB - bone

TIC - cranial bone

Thermal Index (TI) Intensities

B-mode < color Doppler < spectral Doppler

Mechanical Index (MI)

Pressure amplitude estimation related to cavitation - potentially forms/bursts gas bubbles

≤ 1.9

Spatial Peak (SP)

Intensity at the center of the beam

Spatial Average (SA)

Intensity averaged across the entire beam

Temporal Peak (TP)

Maximum intensity in the pulse - measured when pulse is on

Temporal Average (TA)

Average intensity over one beam cycle - from beginning of one push to the beginning of the next

Pulse Average (PA)

Average intensity over a single pulse

Beam Intensities in PW

TP > PA > TA

Beam Intensities in CW

TP = TA

Good Patient Care Skills

Utilize patient safety techniques for transfers

Make sure the patient is comfortable & informed

Maintain cleanliness

Listen

Contrast Imaging

Utilization of an agent to enhance the contrast of structures or fluids in the human body

Microbubbles

Designed to remain within vasculature

Suspended in fluid solution

Inner Component of Microbubble

Gas bubble

Degrade at capillary level - clear from bloodstream via lungs

Outer Component of Microbubble

Phospholipid shell

Broken down by macrophages in liver & spleen

Microbubble Longevity

Determined by chemical composition and equipment settings

Longer longevity = better image with fewer injections

Echoes Created by Microbubbles

Linear reflection - acoustic mismatch

Non-linear scatter - bubble size

Non-linear harmonics - expansion/contraction

Behavior of Microbubbles

Compressible - allows bubbles to vibrate, expand, and contract to produce echoes at harmonic frequencies

Microbubbles with Low Pressures & MI

Greater linear reflection and backscatter

Microbubbles with High Pressures & MI

Greater non-linear backscatter and harmonics

Microbubbles with Very High Pressures & MI

Bubble destruction

Equipment Parameters for Contrast Imaging

Sensitivity

Specificity

Resolution

Dual Display

Assist in determining if lesions are benign or malignant

Recognizing vascular phases, hypoenhancement, & hyperenhancement

Current CEUS Uses

Cardiac - endocardial boarders

Abdomen - liver & kidneys

Vascular - thrombus

Future CEUS Uses

Targeted microbubbles - more sensitive & earlier detection

Delivery of targeted therapies

CEUS Risks

Hypersensitivity reactions - rash

Allergic reactions - anaphylaxis

Contraindications for CEUS

Known intracardiac shunt

Pregnancy

Sensitivity/allergy

EFOV/Panoramic Imaging

Multiple frames are acquired while detecting scan line position & angle - 15-20/second

Increased contrast resolution, SNR, and tissue differentiation

Decreased speckle artifact

Frame rate is not affected

EFOV/Panoramic Imaging Transducers

Linear

Curvilinear

Real-Time EFOV/Panoramic Imaging

Current anatomy is shown as the transducer is moved

Live feed until the image is frozen

Static EFOV/Panoramic Imaging

Previously scanned anatomy is shown - image grows larger as the transducer is moved

Machine continuously takes still images and combines them into a larger image

Applications of EFOV/Panoramic Imaging

Tracking/following a structure

Showing anatomical relationships & orientation

Showing dimensions of larger pathologies

EFOV/Panoramic Imaging Artifacts

Smearing - mistakes in sweep speed

Stacking/Misregistration - scan head is not perpendicular to skin/rotated/off-axis, will see a jagged edge in frames

EFOV/Panoramic Imaging Optimization Techniques

Pre-scan

Consistent speed

Transducer perpendicular to skin

Have patient hold breath/stay still

Elasticity

Tendency of tissue to resist deformation with applied force or resume its original shape after removal of force

Longitudinal Waves

Motion is parallel to direction of sound beam

Shear Waves

Motion is perpendicular to direction of sound beam

Elastography

Evaluates tissue stiffness/elasticity

Form of strain imaging - does not replace 2D imaging

Disadvantages of Elastography

Normal values depend on vendor and are not interchangeable

Cannot compare values to MRI elastography

Strain Imaging

Measures physical tissue displacement parallel to the applied normal stress

Strain Elastography (SE)

Measures tissue displacement from manual compression or internal physiologic motion (heart)

Stress is parallel to direction of sound beam

Measured by radiofrequency echo correlation-based tracking and Doppler processing

Acoustic Radiation Force Impulse Strain Imaging (ARFI)

Measures tissue displacement from stress applied by high-intensity acoustic radiation force (pushing pulse) from the transducer

Stress is parallel to direction of sound beam

Measured by radiofrequency echo correlation-based tracking and Doppler processing

Shear Wave Imaging

Uses dynamic stress to generate shear waves (can be parallel or perpendicular)

Wave speed provides estimates of tissue elasticity

1D Transient Elastography (TE)

Non-imaging method

A-mode images

Utilizes transducer and mechanical vibrating device to apply external stress

2D Shear Wave Elastography (SWE)

ARFI utilized at a single point to induce tissue displacement

Measures speed of shear waves perpendicular to direction of stress

Used on B-Mode

Point Shear Wave Elastography (pSWE/ARFI quantification)

ARFI utilized with multiple points to induce stress

Real-time visualization of elastogram

Used on B-Mode

Most common color coding on Elastography

Blue = Increased stiffness/hard

Red = Decreased stiffness/soft

List the clinical applications for Elastography

Liver pathologies/diseases - fibrosis, hepatitis, cirrhosis, alcoholic or autoimmune disease

Characterization of lesions - breast, prostate, thyroid, kidney, lymph nodes

Tissue Doppler Imaging (TDI)

Uses Doppler/frequency shifts to detect movement in myocardium

Best when motion is parallel to sound beam

Cannot distinguish between passive and active motion of muscle fibers

Used with color and PW Doppler

Tissues

Low velocity

High amplitude

Blood

High velocity

Low amplitude

PW TDI

Measures peak & mean velocities in systole (Sa/Sm), early diastole (Ea/Em), and end diastole (Aa/Am).

Systole - Annulus descending

Early diastole - annulus ascends (away from apex)

End diastole - atrial contraction

Advantages of PW TDI

High temporal resolution

Can compare to MV inflow Doppler

Disadvantages of PW TDI

Cannot assess multiple segments simultaneously

Color TDI

Myocardial motion & velocities represented by color on 2D image

Advantages of Color TDI

Better spatial resolution

Able to assess multiple segments at one time

Speckle Tracking

Uses strain rate to detect LV wall motion and myocardial thickening

Advantages of Speckle Tracking

Easy to use

Only need one cardiac cycle

Can assess more than on plane in a single image

Independent angle of insonation

Can detect disease early

Reproducible

Better interpretation of ventricular pacing than TDI

Disadvantages of Speckle Tracking

Needs clear image of boarders to work

Needs high temporal resolution

Difficult to use on large LV

Uses for Speckle Tracking

Coronary Artery Disease

Cardiomyopathy

Valvular Disease

LVH

Dyssynchrony

Heart Failure

EF

Ablation

Right Ventricular Function

Tissue Tracking

Must recognize end-diastole & end-systole

Must define a region of interest

Strain

Deformation of an object from its original shape due to applied stress

Dimensionless - percentage of deformation

Change in length of an object to its original length

Strain Formula

(Change in length - original length) ÷ original length

Strain Measures...

Regional LV function

Peak systolic strain

Average deformation within a myocardial segment

Local shortening, thickening, & lengthening of myocardium

Strain Timing

Based on QRS complex

Positive Strain

Elongation (diastole)

Negative Strain

Shortening (systole)

Advantage of Strain Imaging

Detects local myocardial dysfunction before global ventricular impairment

Uses of Strain Imaging

Systemic Hypertension

Duchenne Muscular Dystrophy

Hypertrophic Cardiomyopathy

Myocardial Infarction

Dyskinesis (Disorganized movement)

Severe pulmonary regurgitation (after repair of Tetralogy of Fallot)

Ischemic heart disease

Diabetic heart disease

Amyloidosis (Protein build up in tissue)

Hypertrophy

Follow up other treatment plans

Spatial Correlation Method of Strain

Uses 2-dimensional pattern-matching

Uses before and after deformation images

Shows longitudinal and lateral displacement

Long processing time

Phase-Shift Tracking Method of Strain

Based on autocorrelation

Can rapidly & precisely determine longitudinal tissue motion

Cannot measure large displacements with aliasing

Does not compensate for movements

Combined Autocorrelation Method of Strain

Uses phase-domain processing

No aliasing

Rapid detection of longitudinal displacement

Compensates for movements

Strain Rate

Speed of deformation of an object from its original shape

Change in velocity related to distance between segments

Rate of change in strain per second

Strain Rate Formula

(V2 - V1) ÷ Distance

Strain Rate Measures...

Rate/speed of deformation of myocardial walls

Apical Strain Rate

Rate of lengthening

PSAX Strain Rate

Rate of thickening

2 objects can have the same strain, but different strain rates

History of Harmonics

1990's - harmonic frequencies can be generated in native tissues

Harmonics

Frequencies that are integer multiple of the fundamental frequency

Original/Fundamental Frequency

One frequency

Sine wave

Attenuation begins as soon as pulse enters body

Harmonic Frequency

Multiples of the original frequency - often integer multiples of 2

Non-linear wave/non-linear propagation

Generated at center of beam where intensity is the highest

Begins after skin line, strengthens with depth, then looses intensity

Returning harmonic signals is less intense than the original frequency

Linear Sound Propagation

Sine wave

Small acoustic pressure

Tissue shows elasticity

No new harmonic frequencies created