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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