DIAGNOSTIC ULTRASOUND INSTRUMENETATION AND OPERATION

ULTRASOUND TRANSDUCER

Converts electrical energy into sound (mechanical) energy, and vice versa.

ULTRASOUND TRANSDUCER

It contains the piezoelectric crystals

2MHz-20MHz

Operating frequency range of ultrasound transducer

Transmit(ultrasound beam) Electrical to Mechanical

Receive (reflected echoes.) Mechanical to Electrical

function of piezoelectric crystals (2)

Physical Housing

This contains all the individual components including the crystals, electrodes, matching layer, and backing materials.

Physical Housing

Provides the necessary structural support and acts as an electrical and acoustic (mechanical) insulator.

Electrodes

are connected to the UTZ machine which generates the short burst of electrical pulses to excite the crystals.

Outside electrode “Grounded Electrode”

Inside electrode “Live Electrode”

2 types of electrode

Outside electrode

aka “Grounded Electrode”

Outside electrode “Grounded Electrode”

protects patients from electrical shock

Outside electrode “Grounded Electrode”

sandwiched between the piezoelectric component and matching layer.

Inside electrode “Live Electrode”

abuts against a thick backing block

Inside electrode “Live Electrode”

sandwiched between the piezoelectric component and backing block

Piezoelectric element

Heart of the transducer, also known as transducer element, active element and crystal.

Piezoelectric element

Most important component that approximately measures 6-19mm in diameter and 0.2-2mm thick.

higher resonant frequencies

Thinner piezoelectric materials produce ____

Piezoelectricity

states that some materials produced a voltage when deformed by an applied pressure.

Piezoelectricity

results in the production of a pressure when an applied voltage deforms these materials.

Lead Zirconate Titanate (PZT)

a man made ceramic, commonly used because it is more efficient, with better sensitivity and can be easily shaped

Piezoelectric element

vibrates to generate a sound wave when applied with a voltage

Piezoelectric element

generates a voltage when applied with vibration (ultrasonic wave)

Matching Layer

sandwiched between the piezoelectric crystal and the patient.

Matching Layer

has acoustic impedance value halfway between that of the crystal and the soft tissue. . This results in more transmitted energy entering the patient and improves the signal strength of returning echoes, which in turn improves UTZ system’s sensitivity and resolution.

Backing/ Damping Layer

consists of tungsten powder and plastic or epoxy resin.

Backing/ Damping Layer

attached to the back face of the crystal.

Backing/ Damping Layer

eliminate the vibrations from the back face and to control the length of vibrations from the face of the crystals

Backing/ Damping Layer

Reducing excessive vibration will cause the element to generate ultrasonic waves with a shorter pulse length, improving axial resolution in images.

Acoustic Absorber/Acoustic lens

For a single element transducer, sound may be focused by adding lens or by using a curved piezoelectric crystal.

Acoustic Absorber/Acoustic lens

This will improve image lateral resolution by reducing the beam width of the transducer.

LATERAL RESOLUTION

Remember that the width of the beam determines the ______.

Aluminum

Perspex

Polystyrene

ACOUSTIC LENS MATERIALS

SONOGRAPHIC RESOLUTION

The ability of an imaging system to differentiate between structures, images or events and display them as a separate entities.

SPATIAL RESOLUTION

This is the ability to display two structures situated close together as separate images.

SPATIAL RESOLUTION

It is also called Detail Resolution

highest frequency

adequate penetration

In order to optimized spatial resolution, the _____, consistent with ______, should be selected

AXIAL RESOLUTION

also referred to as: (1)Linear (2) Longitudinal (3) Depth (4) Range

Linear, Longitudinal, Depth, Range

AXIAL RESOLUTION is also referred to as: (4)

AXIAL RESOLUTION

is the ability to distinguish two objects PARALLEL to the ultrasound beam

better axial resolution

Shorter SPL =

axial resolution

(High beam frequency =

AXIAL RESOLUTION

Determined by Spatial Pulse length and Frequency

Spatial Pulse Length

Frequency

Axial resolution is determined by ____ and ____

Poor Penetration

Good Axial resolution

Less energy=

Wideband=

Good Penetration

Poor Axial Resolution

More Energy=

Narrowband=

LATERAL / AZIMUTHAL RESOLUTION

also referred to as: (1)Transverse (2) Angular (3)Horizontal

LATERAL / AZIMUTHAL RESOLUTION

is the ability to distinguish two objects PERPENDICULAR to the ultrasound beam

LATERAL / AZIMUTHAL RESOLUTION

Determined by beam diameter/ beam width and frequency

Transverse, Angular, Horizontal

LATERAL / AZIMUTHAL RESOLUTION is also referred to as:

LATERAL / AZIMUTHAL RESOLUTION

Ultrasound beam can be made narrower at higher. frequency therefore Higher frequency improves ____.

Better lateral resolution

The narrower the beam width = ______ but can be controlled using the focusing the beam (Best at focal range)

CONTRAST RESOLUTION

Difference in brightness level

CONTRAST RESOLUTION

Ability to detect small changes in the characteristic echo pattern of an organ

CONTRAST RESOLUTION

refers to the ability to distinguish between different echo amplitudes of adjacent structures

TEMPORAL RESOLUTION

is the time from the beginning of one frame to the next; it represents the ability of the ultrasound system to distinguish between instantaneous events of rapidly moving structures

TEMPORAL RESOLUTION

Frame rate required for real time imaging is to observe moving structures should be 25 frames per second or more

ULTRASOUND BEAM

The area through which the sound energy emitted from the ultrasound transducer travels is known as the

ARRAY

Is the arrangement of crystals within the transducer

Footprint

___of a probe refers to the physical size of the part of the ultrasound that contacts the patient.

field of view

is the width of the image that is seen on the screen.

Linear Array

Frequency Range: Higher (8-15 MHz)

Depth of Imaging: Superficial (1-4 cm)

Field of View: Linear, limited (depends on foot print)

Sector (Phased Array)

Frequency Range: Lower (2-6 MHz)

Depth of Imaging: Deeper (4-8 cm)

Field of View: Trapezoidal, wider at depth, narrow at the surface

Curved Linear Array

Frequency Range: Higher (2-12 MHz)

Depth of Imaging: Intermediate (2-6 cm)

Field of View: Trapezoidal, wide at surface and depth

LINEAR ARRAY

produces parallel scan lines and has a rectangular field of view.

LINEAR ARRAY

used to image superficial structures and vessels and therefore operate at frequencies above 4MHz

LINEAR ARRAY

extensively used for vascular, small parts and musculoskeletal applications

CURVILINEAR ARRAY

transducer face is formed into a curve (convex in shape) which provides a wide field of view which diverges with depth.

CURVILINEAR ARRAY

operate at lower frequencies, typically around 3.5MHz and are best suited to image deep lying structures.

CURVILINEAR ARRAY

main applications are in abdominal and obstetric scanning

PHASED/SECTOR ARRAY

sound waves that are generated originate from a single point and fan outward.

PHASED/SECTOR ARRAY

This probe has a smaller and flatter footprint than the curvilinear one, which allows the user to maneuver more easily between the ribs and small spaces

PHASED/SECTOR ARRAY

ideal for echocardiography

PHASED/SECTOR ARRAY

Typically operating at frequencies similar to curvilinear transducers, they are used to image deep-lying structures and perform trans cranial investigations.

Sequencing, Phasing

Arrays are operated in two ways :

Phasing

is operated by applying voltage pulses to most or all elements in the assembly but small time differences between them so that the resulting sound pulse is sent out in a specific path direction

Sequencing

involves the application of voltage pulses to groups of elements sequentially

Near Field ( Fresnel Zone)

Region nearest the transducer face, characterized by a highly collimated beam with more uniform intensity.

Far Field (Fraunhofer Zone)

region farthest from the transducer and characterized by the divergence of the beam with great variation in intensity.

Side lobes (Grating lobes)

are multiple beams of low amplitude ultrasound energy from the transducer that radiates at various angles from the transducer face

Side lobes (Grating lobes)

they cause degradation of lateral resolution due to the effective widening of the beam in the scan plane.

1. Linear Sequential Array (Switched array)

2. Linear Phased Array (Vector, Sector)

3. Curved Sequential Array (Convex Array, Curvilinear Sequential Array)

4. Curved Phased Array ( Convex array, Curvilinear phased array)

5. Annular Array

Modern Term for Transducer Array Types: (5)

Annular Array

constructed using a concentric ring of crystals ( annular means ring).

Curved Phased Array

Convex array, Curvilinear phased array

Curved Sequential Array

Convex Array, Curvilinear Sequential Array

Linear Phased Array

Vector, Sector

Linear Sequential Array

Switched array

Aqueous Gel

Mineral Oil

White Petrolatum

The most-used coupling agents in the direct-contact are (3)

Water

COUPLING MEDIUM

____ is used in the immersion technique

COUPLING MEDIUM

Improves sound transmission into and out of the patient by eliminating air reflection

COUPLING MEDIUM

Composition: EDTA, Carbomer, Propylene glycol, Trolamine, Distilled water

STANDOFF PAD

It can be placed in between the probe and the skin, which places the structure of interest at the focal zone

PROBE COVERS OR SHEATHS

protect probes from contamination and the patient from potential infection

Superficial structures

can be difficult to scan due to echoes that appear in the near field as a result of reverberation artifacts produced by the transducer

Quartz

Rochelle Salt

Tourmaline

Natural Piezoelectric Element

Lead Zirconate Titanate (PZT)

Barium Titanate

Lead Metaniobate

Ammonium Dihydrogen Phosphate

Lithium Sulphate

Synthetic Piezoelectric Element (5)

Voltage

plating electrodes; electric field; shape

sound waves

Backing Block; returning echoes

Echoes; transducer ; physical compression

1. A sudden burst or pulse of ____ is applied.

2. The _____ ( live and ground) behave as capacitors, the voltage between them produces the ____ which in turn causes the crystal to change in ___.

3. the crystal vibrates and generates _____ from the front and back.

4. The ____ quickly dampens the vibrations to prime the transducer to its 2nd function which is to detect the ____.

5. ____ reflect back toward the transducer from each tissue interface. These echoes carries energy, and they transmit their energy to the _____, causing a _______ of the crystal element.

Focus or Focal Point

the location where the beam reaches its minimum diameter.