- Slides: 64
X rays Basic principles Sacco Simone
X rays Electromagnetic Waves. - In Physics "wave" = “perturbation that originates from a source and spreads out through the space, carrying out energy displacement of matter" - May propagate both through the matter and the vacuum.
Wave length Y = Amplitude Space
X rays X-rays: same nature than visible light but with a different wave-length.
Electromagnetic Waves Spectrum Tra 10 -9 m e 10 -12 m
X rays Electromagnetic Waves The energy propagates through the space-time in the form of the electromagnetic radiation generating an electric and a magnetic field Remember that the electromagnetic radiation has a quantized nature fully described only with quantum mechanics, with the double feature of wave and photons beam, that travels in the vacuum at the speed of light.
A short History… Discovery of x-rays: Roentgen discovered the X rays during the night of November 8 1895. He published this breakthrough in December 28, 1895 to the Physical-Medical Society of Wurzburg in a paper entitled "A new species of rays. “ Roentgen showed that the ionizing radiation emitted by a cathode within the ray tube is capable to cross an opaque body and impress a photographic film. The Radiology was born…
Wilhelm Conrad Röntgen Remscheid, 27 marzo 1845 – Monaco di Baviera, 10 febbraio 1923 The first medical radiography performed by Roentgen December 22, 1895 at the left hand of his wife Anna Berthe. The wedding ring is also visible
X rays – production They are generated in the Rontgen’s tube after the collision of the electrons produced on a hot filament in the cathode into the anode releasing energy as radiation X.
Remember… • The higher the intensity of the electric current (measured in milli-amperes) the greater is the number of electrons produced • The greater is the potential difference supplied to the tube (measured in Kilovolt), much more violent is the collision of electrons against the plaque of tungsten and the shorter and the wavelength of the radiation generated.
X Rays - properties 1) They pass through objects made of various composition. (Law of absorption) 2) Ability to impress radiographic films 3) Ability to change the physical and chemical state of matter (Radiotherapy)
Absorption Law The absorption is: 1. Directly proportional to the atomic number of the object. 2. Directly proportional to the thickness of the object. 3. Directly proportional to the wavelength of the radiation.
Radiodiagnostic • Analog radiogram: the X-ray image is impressed on a sensitive film exposed to the radiation beam emerging from the body part examined: Tissues that absorb more X-rays appear as bright areas (radiopaque) The tissues that absorb less radiation appear as darker areas (radiolucent)
Radiodiagnostic Digital radiogram: the X-ray image is impressed on sensitive detectors exposed to the radiation beam emerging from the body and is then analized and elaborated by a computer that displays the image on the monitor: The tissues that absorb more X-rays appear as light areas (radiopaque) on the monitor The tissues that absorb the radiation to a lesser extent appear as darker areas on the monitor
Remember • The radiologist looks at the patient's face. Right Left
Radiodiagnostic • Projection: Path of radiation in the body • It is expressed with two adjectives: The first indicates the entry point of radiation, according to the exit point. • At least two more to represent the three dimensions of space !!!
Radiodiagnostic • X rays Where? ? ? Chest. Abdomen. Skeleton. Other (urography, cystography)
Radiodiagnostica. • Xray skeleton: When? ? ? -To Confirm the clinical suspect of fracture, define the type and location or evaluate the dislocation of a joint. -To Ensure that a fracture has been properly treated and stabilized -To Assess the damage caused by bone or joint infections, arthritis, abnormal bone growth and bone diseases like osteoporosis - To highlight skeletal malformations or degenerative processes. - To identify and locate foreign bodies. - To confirm the suspect of neoplasia. - To estimate the physiological age based on bone growth
Fractures and controls after treatment.
Radiodiagnostic. • RX Chest: Why? - Study of the Lung: Pneumonia, primary or secondary malignancies, pleural effusion - Study of the heart: Heart disease in general, cardiogenic pulmonary edema, the study of vascular structures, coarse study of the aorta and the pulmonary arteries, the study of bone structures rib.
Radiodiagnostic. • Xray Abdomen: When? • Basal (direct abdomen): Acute abdominal pain (STAT); e. g. Subocclusive state post-surgery • Contrast: Today infrequently used A) Barium: - enema> colonoscopy / CT - Ileum> endoscopy. B) Iodinated: Cystoscophy, Urography.
U Basic principles Sacco Simone
Definition ULTRASOUND • Diagnostic imaging procedure that utilizes high-frequency mechanical waves based on the principle of the echo transmission • Ultrasound travels in the form of waves produced by an object (e. g. speaker) that pushes forward the surrounding air causing small changes in air pressure
Acustic wave Wave lenght λ λ = v T = v/F Freq = 1/T High pressure Low pressure
Acustic wave The humans can perceive acustic waves from 20 and 20000 hz Ultrasounds are acustic waves above 20000 hz
PHYSICS 4. The piezoelectric effect "Piezo", derived from the Greek piezein, which means to squeeze or press Piezo electricity refers to the charge which accumulates in certain solids in response od a mechanical stress
PHYSICS 4. The piezoelectric effect Conversely, when an electric field runs a piezoelectric material, this one contracts or expands. If the electric field is an alternating current, the effect will be a vibration of the piezoelectric material tension compression
PHYSICS 4. The piezoelectric effect When the current is switched on, the probe produces ultrasounds which travel through the body Transmission time = 80 nanoseconds When the current is switched off, the reflection of the utrasounds stimulates the piezoelectric cristals generating a current, which is used to create the image Listening : 200 -300 milliseconds
PROPERTIES 2. Wve parameters The ultrasound to propagate needs to move a certain quantity of matter (they do not propagate in the vacuum) Their speed varies depending on the density of the medium Velocity (m/s) Air 300 fat 1430 liver 1500 muscle 1545 bone 2000 -4000 In the soft tissues the velocity is approximated constant at 1540 m/s
PROPERTIES • The ultrasound to propagate needs to move a certain quantity of matter • Like any other type of wave phenomenon ultrasound they are subject to the phenomena of reflection, refraction and diffraction • These phenomenon are exploited to produce the ultrasound image
Reflection 6. Types of reflections Specular reflection is responsible of the bright appearance of fibrous or hard structures, such as tendons, ligaments or cortical bone surface. Large reflector Specular reflection
Diffraction 6. Types of reflections Scattered reflection is characteristic of soft tissues: small amounts of energy are absorbed and retransmitted in all directions Small reflectors scattering
Acoustic Impedence Acoustic impedence is the physical property exploited to create contrast between tissues Impedance: how difficult it is for sound to penetrate a material). • It depends on the density and on the speed of the sound in the material • The amount of sound which is transmitted or reflected depends on the difference of impedance between the 2 materials (greater difference, more reflection) Medium Impedance (standard unit) air 0, 000429 water 1, 50 blood 1, 59 Fat 1, 38 muslcle 1, 70 bone 6, 50
Acoustic impedence ( how difficult it is for sound to penetrate a material. Because of the great difference of impedance between air and skin, a gel is applied on the skin of the patient to reduce the impedence and facilitate the transmission of US
Diagnostic frequencies • 2 - 6 mhz – abdominal ultrasound, obstetrical and gynecological exam, echocardiography, trans-cranial Doppler • 7. 5 - 14 mhz – small parts, vascular Doppler, musculoskeletal ultrasound • 10 - 20 MHz – ophthalmology, special vascular examimations • 20 - 50 MHz – endoluminal exam, ultrasound biomicroscopy (ophthalmology, dermatology)
Creation of an image 5. Creation of an image • A-mode • B-mode or 2 D mode: In B-mode (brightness mode) ultrasound, a linear array of transducers simultaneously scans a plane through the body that can be viewed as a two-dimensional image on screen. • M-mode: In M-mode (motion mode) ultrasound, pulses are emitted in quick succession – each time, either an A-mode or B-mode image is taken. Over time, this is analogous to recording a video. • Doppler mode: This mode makes use of the Doppler effect in measuring and visualizing blood flow • Color Doppler: Velocity information is presented as a color-coded overlay on top of a B-mode image
A - MODE 5. Creation of an image Amplitude (A-scan) or monodimensional. Each spike represents a signal reflected by a different anatomic structure after some time, which is related to a certain distance to the probe amplitide time
B - MODE 5. Creation of an image B-scan (brightness) The amplitude of each returning signal controls the brightness of a spot which represents the reflection. The largest reflection gives back the largest amplitude and brightness
REAL TIME B-MODE 5. Creation of an image Real time B-scan In the modern ultrasound an array of piexoelectric cristals act as individual transmitters and receivers The image is build up from these multiple signals
Appearance of tissues TISSUE APPEARANCE WATER BLACK SOFT TISSUE Shades of gray BONE Reflecting white boundary AIR BAD!
Appearance of tissues Muscle fibers fat Muscle tissue is dark on ultrasound, but the aspect is msrbled due to the fat inside the muscle and the interface fat-muscle fiber which is bright
7. Appearance of tissues Bone appearance presents a remarkably bright line due to the interface soft tissuebone, and delow is completely black because of the complete reflection of ultrasound from the cortical bone
Appearance of tissues 7. Appearance of tissues Fluid, blood effusion or cyst appear usually black, because of the small reflection of the ultrasound. Fluid for this property is called anechoic.
5. Creation of an image B- MODE IN ABDOMINAL REGION
5. Creation of an image B- MODE IN OBSTETRICS
5. Creation of an image B- MODE IN MUSCULOSKELETAL ULTRASOUND Meniscal Tear
Doppler effect When the ultrasound beam encounters a moving structures (blood in the vessels), the echo received by the probe have a phase shift If the object (blood flow) is moving towards the probe, the phase shift will be positive If the blood flow is moving away the phase shift will be positive Faster is the object moving, greater the phase shift
Conventional doppler techniques continous pulsed
Applications of doppler Arterial examinations • Stenosis • Aneurism • Dissections
Colour flow mapping Venous thrombosis
Colour flow mapping Mass vascularization