Ultrasound Physics and Instrumentation PDF

Ultrasound Physics and Instrumentation MRD535 Image Orientation and Scanning Limitation By Dr Leong Sook Sam Learning objectives Describe the principle, physics, instrumentations, accessories and image recording in ultrasonography (PLO1, C2) Explain the principles of ultra...

Ultrasound Physics and Instrumentation MRD535 Image Orientation and Scanning Limitation By Dr Leong Sook Sam Learning objectives Describe the principle, physics, instrumentations, accessories and image recording in ultrasonography (PLO1, C2) Explain the principles of ultrasonography including ultrasound physics Contents 1. Transducer selection 2. Image orientation 3. Scanning limitation 4. Stand-off pads Transducer Selection Linear Transducer The piezoelectric crystal arrangement is linear The shape of the beam is rectangular High frequency The near-field resolution is good Transducer Selection (cont) Linear Transducer Application Vascular Venipuncture Breast Small parts Thyroid MSK Transducer Selection Curvilinear Transducer The piezoelectric crystal arrangement is curvilinear The shape of the beam is convex Low frequency Good for in-depth examination Transducer Selection (cont) Curvilinear Transducer Application Abdomen Vascular OB/GYN MSK Transducer Selection Phase Array Transducer Named after the piezoelectric crystal arrangement which is called phased array Low frequency Good for in-depth examination Transducer Selection (cont) Phase Array Transducer Application Abdomen Cardiac Brain Transducer Selection Endocavitary Transducer To perform internal examination Middle frequency Good for resolution Transducer Selection (cont) Endocavitary Transducer Application Prostate Female reproductive organ Image Orientation Transducer position Mark on the side of transducer The correct direction and image orientation  Transducer position Longituidinal Marking on the transducer pointing towards patient head  Image orientation Anterior Longitudinal Inferior The symbol in the top right of Superior image – original orientation Superior – patient head Inferior – patient feet Posterior Anterior – top of image Posterior – bottom of image  Transducer position Transverse Marking on the transducer pointing to the side Marking pointing towards operator/ patients' right side  Image orientation Anterior Transverse Right Left Right – patient right Left – patient left Anterior – Top of image Posterior – Bottom of image Posterior  Terminology Echogenicity: refers to the ability to reflect or transmit US waves. Whenever there is an interface of structures with different echogenicities, a visible difference in contrast will be apparent on the screen. Hyperechoic: refers to the echoes returning from a structure. Hyperechoic tissues generate a greater echo usually displaying as lighter colors during ultrasound imaging. Echogenic: A bright white appearance when scanning with a black background.  Terminology (cont) Hypoechoic: the echoes are weaker or fewer than normal or in the surrounding regions. Usually displaying as darker color. Anechoic: no internal echoes are emitted and there is a completely black appearance. This is most seen with fluid-filled structures since ultrasound waves pass through fluid without reflecting any echoes back to the ultrasound machine Isoechoic: specific structure gives off similar echoes relative to another structure on the ultrasound screen. Terminology (cont) Homogenous: Uniform shade of grey throughout organ, usually associated with normal appearance of an organ. Heterogenous: Nonuniform shades of grey throughout the organ, usually associated with abnormal appearance of organ. Scanning Limitation Ultrasound cannot accurately diagnose the intestines and parts that are obscured by the intestines. Air (gas) particles are much more spread out, farther apart and have less interaction with each other compared to the particles in a denser medium. When ultrasound waves travel through air, the arrangement of air molecules makes it difficult for the waves to propagate. The energy of the ultrasound waves dissipates quickly in the air, leading to a rapid decrease in intensity over a short distance. Scanning Limitation (cont) Ultrasound cannot diagnose the bony structure. When ultrasound waves encounter bone, they can partially penetrate it, but they also reflect and scatter due to the density differences between soft tissues and bone. This scattering and reflection make it challenging to obtain clear and detailed images of bones using standard ultrasound techniques. Bones are dense and highly reflective, which can cause shadowing artifacts in the images, making it difficult to visualize structures behind the bone.  Scanning Limitation (cont) Ultrasound limits the survey in overweight and obese people. Increased Depth: higher amounts of adipose (fat) tissue, the ultrasound waves have to travel through a greater depth of tissue before reaching the organs or structures being examined. Deeper penetration can reduce image resolution. Attenuation of Ultrasound Waves: Adipose tissue attenuates (absorbs and scatters) ultrasound waves more than lean tissue. As the waves pass through layers of fat, their energy is reduced, making it more challenging for the ultrasound machine to receive strong and clear echoes. Poor Sound Wave Transmission: Fat has different acoustic properties compared to muscle or organs. When ultrasound waves encounter fat layers, there can be poor transmission of sound waves between tissues of differing densities. Scanning Limitation (cont) Scanning Limitation (cont) Certain areas of the body, such as curved or uneven surfaces limits/ complicate the image acquisition. Transducer designs have a curved surface, they may also struggle to contact the skin towards the edges of the transducer surface, especially if the region examined is curved or uneven surfaces Region of interest are very superficial limits the visualization of the lesion. Scanning Limitation (cont) Standoff pads are typically a flexible, material that is placed between the transducer surface and the patient’s skin. They cause minimal attenuation of ultrasound and typically appear anechoic or black on the ultrasound image. Stand-off gel pad brings the superficially placed lesions into the transducer focal zone Scanning Limitation (cont) Advantages: Improved Image Quality: The gel pad eliminates air gaps between the transducer and the skin. Air pockets or uneven contact between the transducer and the skin can cause shadows and artifacts in ultrasound images. Enhanced Visualization: The gel pad helps in achieving better contact between the transducer and these challenging areas, allowing for improved visualization during the ultrasound examination. Scanning Limitation (cont) Advantages: Comfort for the Patient: The gel pad provides a cushioning effect. It reduces the pressure applied by the transducer on the skin, especially in sensitive or bony areas, enhancing the overall patient experience. Thank you