12-Jun-161 ULTRASOUND IMAGING Lec 1: Introduction Ultrasonic Field Wave fundamentals. Intensity, power and radiation pressure.

12-Jun-162 Introduction: Why Medical Imaging? Earlier diagnosis Easier diagnosis More accurate diagnosis Less invasive diagnosis and treatments Greater sharing of knowledge

12-Jun-163 Brief history of Medical Imaging 1895 – Roentgen accidentally discovers x-rays while experimenting with Crookes tube – Felix Bloch and Edward Purcell discover the presence of magnetic resonance in solids and liquid.

12-Jun ’s – The ultrasound is developed. Sonar development during World War ll – The computed tomography scan becomes a reality due to breakthroughs in digital computers.

12-Jun-165 The field of diagnostic radiology has undergone tremendous growth in the past several decades: Angiography developed in the 1950’s Nuclear Medicine in the 1960’s Ultrasound and CT in the 1970’s MRI and interventional radiology in the 1980’s PET in the early 1990’s

12-Jun-166 Image Capturing Technique Radiography Magnetic Resonance Imaging Computed Tomography Ultrasound Nuclear Imaging

12-Jun-167 Radiography Process of creating an image by passing x-rays through a patient to a detector. Relies on natural contrast between radiographic densities of air, fat, soft tissue and bone. Most advantageous in parts of the body with inherently high contrast, e.g. the lungs and the heart.

12-Jun-168 Conventional Radiography Converting to digital Scanning Sampling Conversion Digital Radiography Modifications of plain-film radiography are fluoroscopy, tomography and mammography.

12-Jun-169 Radiography “So excited was the public that each newly radiographed organ or system brought headlines. With everything about the rays so novel, it is easy to understand the frequent appearance of falsified images, such as this much-admired "first radiograph of the human brain," in reality a pan of cat intestines photographed by H.A. Falk in 1896.” -Penn State University College of Medicine © Radiology Centennial, Inc © EarthOps.org Ref: Amy Schnelle, Computer Science, Univ. of Wisconson-Platteville

12-Jun-1610 Fluoroscopy Uses the x-ray beam continuously. Physician can: Evaluate the dynamic processes (e.g. diaphragmatic excursion or bowel peristalsis). Watch contrast medium (e.g. in the blood vessels, bowel, kidneys, or joint spaces). Follow the path of an opaque object (e.g. feeding tube or intravascular cathether).

12-Jun-1611 Mammography Plain film study that uses specially designed equipment with low voltages and a film-screen combination to evaluate breast tissue and calcification with high contrast resolution for detail at a low radiation dose. Breast compression is to reduce radiation exposure and improve image quality.

12-Jun-1612 Ultrasound Ultrasound uses high frequency sound waves 1-10 MHz and their corresponding echoes to create images of the internal structures of patients. The sound waves are directed into the body reflected by various body structures.

12-Jun-1613 The time taken for the reflected waves to return determines the depth of the structures. The amount of beam absorption determines the intensity of the returning wave. Echoes from interfaces between tissues with different acoustic properties yield information on the size, shape, and internal structure of organs and masses.

12-Jun-1614 Why ultrasound is popular? The advantages are the: Portability Lack of ionizing radiation Ability to scan the body in any plane Disadvantages are: Operator dependency Limited usage for imaging the lungs and skeleton

12-Jun-1615 Ultrasound © Radiology Info © Photo Dynamic Imaging Limited Ref: Amy Schnelle, Computer Science, Univ. of Wisconson-Platteville

12-Jun-1616 ULTRASOUND IMAGING Lec 2: Ultrasonic Field Wave fundamentals. Intensity, power and radiation pressure.

12-Jun-1617 Wave fundamentals Sound is a mechanical longitudinal wave and carries energy. Unlike light waves and radio waves, it requires a medium to propagate and cannot pass through a vacuum. The sound acoustic variables include: Pressure Density Temperature Particle motion.

12-Jun-1618 Sound parameters: Frequency, (Hz. Older literature: c/s.) Number of oscillations per second performed by the particles of the medium in which the ultrasound is propagating. Audible sound: 20 Hz – 18 kHz Ultrasound: > 18 kHz Bats:120 kHz Grasshoppers:100 kHz Diagnostic ultrasound: 0.5 – 25 MHz Abdominal scanning:3 MHz Opthalmology:10 MHz

12-Jun-1619 Sound parameters: Period, T (s,  s) The time taken for one complete cycle to occur. T = 1 / [Equation 1.1] Wavelength, (m, mm) Length of space over which one cycle occurs.

12-Jun-1620 Propagation speed, c (ms -1 ) Speed with which an ultrasound wave propagate through a medium. c = [Equation 1.2] c is determined by density,  and stiffness of the medium. Stiffness difference > density difference.  c solid > c liquid > c gas Soft tissues:1540 ms -1 Lung:300 – 1200 ms -1 Bone:2000 – 4000 ms -1 Fat:1450 ms - 1

12-Jun-1621 Amplitude, A (m) The maximum displacement that occurs in an acoustic variable.

12-Jun-1622 Intensity, power and radiation pressure Intensity, I (mWcm -2 ) The intensity of an ultrasonic beam at a point is the rate of flow of energy through unit area perpendicular to the beam at that point. Proportional to the square of amplitude. Determines the sensitivity of the instrument, i.e. the number and sizes of echoes recorded.

12-Jun-1623 Formulas relating intensity I: I = ½ (p 0 2 /  c) [Equation 1.3] I = ½  c(2  f) 2 x 0 2 [Equation 1.4] I = ½  cu 0 2 [Equation 1.5] p 0 = pressure amplitude x 0 = particle-displacement amplitude u 0 = particle-velocity amplitude  = density of the medium f = frequency of ultrasound

12-Jun-1624 Power, P (W, mW) Rate of flow of energy through the whole cross-section of the beam. [Ultrasonic power] = [Ultrasonic Intensity] [Beam cross-sectional area] P = I a[Equation 1.6] Beam area is determined in part by the size and operating frequency of the transducer.