Basic Principles of Ultrasound Imaging

Introduction Ultrasound imaging have different meaning to to different

categories of people based on profession or vocation In the Heath Sector- Clinicians, Patients

In Commerce- Business & Industry

Definition : Ultrasound Imaging (Scanning)

Commonly referred to as “Scanning,,” is the act of acquiring and interpreting images using sound waves

Medically : Involves the use of high frequency ( higher than human hearing) sound waves to produce images of internal organs of the body.

Technically, it is a noninvasive medical procedure that allow internal structures of the body and hemodynamics of blood flow to be accessed or viewed as real-time images on a screen.

Ultrasound transducers send out high frequency sound waves into the body tissues and receive reflected echoes , that are processed and displayed as images.

For diagnostic purposes Ultrasound Doppler frequency range is 2.0 -10.5 MHz . The frequency range for scanners for industrial or commercial use is different

Normal hearing sound wave frequency for adults is 2.5- 3.5 MHz

Basic Facts:

One major fact about Ultrasound Imaging(Scanning) that distinguishes it from other Non Invasive Diagnostic technology tools in the health industry is that...

“ The accuracy of the noninvasive examination is almost exclusively dependent on the skill and the experience of the operator.’’

Therefore, if the Operator misses the disease during the

process of scan, No matter how knowledgeable the interpreter (Reader) is, it is unlikely that it will not be detected unless... Other diagnostic tests were ordered

This places a unique responsibility on the operator to strive and gain the knowledge and competency required, as patient mistreatment / misdiagnosis due to professional incompetence and performance is more dangerous than the disease itself..

Overview of Presentation

Part 1Review Basic Ultrasound Principles

Definitions and Terminologies

Ultrasound Physics

The Transducer ( Probe )

Review Ultrasound Modalities in Cardiovascular Testing

Part 2 I Demonstrations

Exercises

Probe Handing , Orientation and Scanning techniques

Scanning to identify body organs

Objectives

Update awareness of various Ultrasound tests available

Enhance professional skills acquisition by Physicians to enable proper evaluation of scanning reports or images given to patients.

Enhance appropriate use of ultrasound systems in patient management

Improve overall quality of patient care delivery through accurate diagnosis

Descriptive Definitions

Terminologies

A

Cephalad / caudal (toward the head/toward the tail): used interchangeably with superior and inferior.

Superior / inferior (above/below): for location of a structure along the long axis of the body. Dorsal / ventral (backside / belly side): ventral always refers to the belly side .

Proximal / distal (nearer the trunk or attached end.

Superficial / deep (toward or at the body surf ace / away from the body surface or more internal).

Anterior / posterior (front / back): anterior structures are those that are most forward—the face, chest, and abdomen.

Medial/lateral (toward the midline / away from the midline or median plane):

Descriptive Definitions Terminologies Body Planes

Imaginary surface or line called a plane that lie at right angles to one

another.

Sagittal plane: divides the body into equal parts, right down the median plane of the body, it is called a median, or mid sagittal plane.

Frontal (coronal) plane: divides the body (or an organ) into anterior and posterior parts.

Transverse plane: divides the body into superior and inferior parts.

The terms above assume the person is in the anatomical position

Descriptive DefinitionTerminologies Sonography

• ANECHOIC - Being echo-free or without echoes (e.g., a fluid-filled cyst). ECHOGENICITY- Echogenic: the ability to create an ultrasound echo .ECHOLUCENT- same as above.HETEROGENEOUS - mixed echoic pattern within plaque- areas of sonolucence and echogenicity. HOMOGENEOUS - uniform plaque texture.HYPERECHOIC - Producing echoes of higher amplitude than normal for the surrounding medium. HYPOECHOIC - Producing echoes of lower amplitude than normal for the surrounding medium.ISOECHOIC- Areas which have similar echogenicity to each other. An isoechoic "property" makes it more difficult to see the desired tissue structure.SONOLUCENT- Allowing passage of ultrasonic waves without echoes

Ultrasound PhysicsEcho Doppler Principle

Mechanism of Sound Wave Generation:

Ultrasound transducers have elements made of Piezoelectric crystals. Major Kinds of Transducers Generated Doppler Waves

Continuous Wave (CW) Doppler and Pulse Wave(PW) Doppler

When stimulated with electricity , the crystals oscillate to produce a high frequency sound wave signal.

Transducers send sound out and receive returning echoes from moving reflectors in the body ( Blood and tissues ).

The wave frequency difference between the transmitted waves and the reflected waves due to movement is called Doppler Shift frequency

If the returning wave frequency is lower than the transmitted frequency, the Doppler shift is considered a NEGATIVE (-)

If the returning frequency is higher, the Doppler shift is POSITIVE (+)) Dopplers and Pulse Wave (PD)

Doppler Shift

Echo Doppler transmission is the principle mechanism use in

Ultrasound systems to detect and measure blood flow dynamics .

Doppler shift frequency is expressed as a positive or negative value, depending on the direction of flow relative to the Doppler beam direction

Ultrasound physicsThe Doppler Equation

The Doppler Equation is used to calculate blood flow velocity if the speed of sound in tissue is known as well as the angle between blood flow and the ultrasound beam.

The Equation follows V= C (±Δf ) Where 2 foCosѲ

V= Blood flow velocity (meters/s)

C = Speed of sound in tissue; approx 1540mm/s

Δf =Doppler frequency Shift (Hz)

fo = transmitted frequency

CosѲ = Cosine function of angle between ultrasound beam and the blood flow vector

Doppler Wave formParameters

Pulse Wave Doppler(PW)

have single crystal to send &receive transmissionRange Gate (TGC) (Sample Volume) at any specific depth. - Sets Time interval in PW Mode . Amplified contrast of reflected sound waves to form images Pulse Repetition Interval(PRF) is number of pulse echo cycles per second PRF is expressed in Hertz; 11/2 PRF = Nyquist LimitAliasing occurs when Doppler shift frequency exceeds 11/2 of PRF. To reduce Aliasing; increase PRF; Decrease frequency; Decrease sample volume depth volume

Wall Filters (Hz) are set to detect or eliminate low flow As PRF increases; Wall filters increases

The Transducer (Probe)

The Scanning Techniques

Protocols

“Standard" Protocol remain unchanged if proven To be effective, Cost effi cient and accurate, Have been no better replacements.

Protocols change as

Better methods evolve Technological advances New technologies mandate new test methods

Applications

Angle of Insonation

Range 45 ⁰ To 60⁰

Applications of Ultrasound Imaging in Cardiovascular Testing

Stroke ScreeningCarotid plaque estimation

Carotid Artery Duplex ExaminationnCVA stenosis evaluation

Peripheral Arterial Disease (PAD) Imaging Segmental pressure scan stdies forr localization

Plethysmography-Skin per Fusion evaluation of blood flow with IFR photosensors

Venous Duplex Scan for ThrombosisDuplex studies for blood clot in vessels

Trans Cranial ImagingMeningeal arterial flow studies

Abdominal Aorta Imaging for AneurysmsAbdominal scan for aneurysms

Renal Vascular StudiesRenal vascular flow studies

In Conclusion

Ultrasound scanning has become the most affordable diagnostic tool in our hospitals and clinics today.

There is need for professional improvement on the overall quality of patient care delivery through accurate diagnosis and knowledge based evaluation of patient reports from Scanning Facilities by physicians .

Thank You.

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