Lecture 2: Introduction to Radiology (Medical Images) PDF

Lecture 2: Introduction to Radiology (Medical images) Biomedical instrumentation design Uni. of Thi-Qar Faculty of Engineering. 5th stage. 1 By Ali Basim Mahdi  Study of Medical Imaging = h the It is concerned with interaction o...

Lecture 2: Introduction to Radiology (Medical images) Biomedical instrumentation design Uni. of Thi-Qar Faculty of Engineering. 5th stage. 1 By Ali Basim Mahdi  Study of Medical Imaging = h the It is concerned with interaction of all forms of radiation with tissues in the body. + The development of appropriate technology to extract clinically useful information (usually displayed in an image format) from observation of this technology + Non-invasive visualization of internal organs, tissues, and body parts, etc. Holographic models? Biomedical instrumentation design Uni. of Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi 2 Understanding Visual Information: Technical, Cognitive and Social Factors  Medical Imaging The overall objective of medical imaging is to acquire useful information about physiological processes or organs of the body by using external or internal sources of energy. Biomedical instrumentation design Uni. of 3 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  Sources of energy External Internal Actually (MIX) Reflected Penetrated U/S X-Ray(s) Biomedical instrumentation design Uni. of Thi-Qar Faculty 4 of Engineering. 5th stage. By Ali Basim Mahdi  Internal source of energy Actually (MIX) Biomedical instrumentation design Uni. of 5 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  Major Types of Medical Imaging Modalities X-ray Imaging 1) Conventional X-ray + Film processing 2) Digital X-ray + Film processing 3) Fluoroscopy (guided process, diag. or thera.) as C- arm, Cath. Lab, O- arm, angiography + (image intensifier + Flat panel detector FPD) 4) Mammography 5) Bone densitometer (dual-energy x-ray absorptiometry (DXA) or bone densitometry. It’s used to diagnose osteoporosis, to assess an individual's risk for developing osteoporotic fractures. DXA is today's established standard for measuring bone mineral density (BMD). 6) Computed Tomography (CT) + Film processing 7) Last and not the least Den…. Magnetic Resonance Imaging (MRI) + Film processing Nuclear Imaging – γ camera, Positron Emission Tomography (PET) Ultrasound Imaging Fundus images Biomedical instrumentation design Uni. of Thi-Qar Faculty of Engineering. 5th stage. By 6 Ali Basim Mahdi  Brief review For nearly 100 years now, the photographic film has been used to record images For over 60 years, intensifying screens have been used with x-ray films to obtain high quality images with lower radiation doses Very recently it has become possible to record x-ray images without the use of conventional film-screen systems (CR and DR systems) But even now, radiography using film-screen technology accounts for about 65 % of all diagnostic examinations Biomedical instrumentation design Uni. of 7 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  Radiography o Radiography was the first medical imaging technology, made possible when the physicist Wilhelm Roentgen discovered x-rays. o Radiography defined the field of radiology and gave rise to radiologists, physicians who specialize in the interpretation of medical images. Radiography is performed with an x- ray source on one side of the patient and a (typically flat) x-ray detector on the other side. o A short-duration (typically less than ½ second) pulse of x-rays is emitted by the x-ray tube, a large fraction of the x-rays interact in the patient, and some of the x-rays pass through the patient and reach the detector, where a radiographic image is formed. Biomedical instrumentation design Uni. of 8 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  Radiography  The homogeneous distribution of x-rays that enters the patient is modified by the degree to which the x-rays are removed from the beam (i.e., attenuated) by scattering and absorption within the tissues.  The attenuation properties of tissues such as bone, soft tissue, and air inside the patient are very different, resulting in a heterogeneous distribution of x-rays that emerges from the patient.  The radiographic image is a picture of this x-ray distribution. The detector used in radiography can be photographic film (e.g., screen-film radiography) or an electronic detector system (i.e., 9 digital radiography). Biomedical instrumentation design Uni. of Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  Radiography o Transmission imaging refers to imaging in which the energy source is outside the body on one side, and the energy passes through the body and is detected on the other side of the body. o Projection imaging refers to the case when each point on the image corresponds to information along a straight line trajectory (path) through the patient. o Radiographic images are useful for a very wide range of medical indications, including the diagnosis of broken bones, lung cancer, cardiovascular disorders, etc. Biomedical instrumentation design Uni. of 10 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  Image properties Contrast Spatial resolution Biomedical instrumentation design Uni. of 11 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  Contrast Contrast is the difference in luminance or color that makes an object (or its representation in an image or display) distinguishable. Also, contrast is determined by the difference in the color and brightness of the object and other objects within the same field of view (FOV). X-ray contrast is produced by differences in tissue composition, which affect the local x-ray absorption coefficient. Contrast in MRI is related primarily to the proton density and to relaxation phenomena (i.e., how fast a group of protons gives up its absorbed energy). Contrast in ultrasound imaging is largely determined by the acoustic properties of the tissues being imaged. BRIGHTNESS can be defined as the amount of energy output by a source of light relative to the source we are comparing it to. 12 Biomedical instrumentation design Uni. of Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi Spatial resolution Resolve fine details in the body parts. Resolve= separate into constituent parts Resolution is the way that objects and the spaces between them are counted equally. The ability to see small details, and an imaging system has higher spatial resolution if it can demonstrate the presence of smaller objects in the image. The limiting spatial resolution is the size of the smallest object that an imaging system can resolve. We have deep resolution and lateral resolution In ultrasound imaging, the wavelength of sound is the fundamental limit of spatial resolution(depth limitation). At 3.5 MHz, the wavelength of sound in soft tissue is about 0.50 mm. At 10 MHz, the wavelength is 0.15 mm. ALSO: Temporal resolution is defined as the amount of time needed to revisit and acquire data for the exact same location. Biomedical instrumentation design Uni. of 13 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  Biomedical instrumentation design Uni. of 14 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  Each imaging modality generates contrast based on different physical parameters in the patient. Biomedical instrumentation design Uni. of 15 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  MEDICAL IMAGING: from PHYSIOLOGY TO INFORMATION 1. Understanding Image medium: Tissue density is a static property that causes attenuation of an external radiation beam in X-ray imaging modality, BUT WE HAVE VARIETY OF TISSUES IN THE HUMAN BODY. Blood flow, perfusion and cardiac motion are examples of dynamic physiological properties that may alter the image of a biological entity (structure). Biomedical instrumentation design Uni. of 16 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  MEDICAL IMAGING: FROM PHYSIOLOGY TO INFORMATION 2. Physics of Imaging: The next important consideration is the principle of imaging to be used for obtaining the data. For example, X-ray imaging modality uses transmission of X-rays through the body as the basis of imaging. On the other hand, in the nuclear medicine modality, Single Photon Emission Computed Tomography (SPECT) uses emission of gamma rays resulting from the interaction of radiopharmaceutical substance with the target tissue (internally ray source). Biomedical instrumentation design Uni. of 17 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  MEDICAL IMAGING: FROM PHYSIOLOGY TO INFORMATION 3. Imaging instrumentation: The instrumentation used in collecting the data is one of the most important factors defining the image quality in terms of signal-to Noise ratio (SNR or S/N, is defined as the ratio of signal power to the noise power which measures the original signal corruption), resolution and ability to show diagnostic information. [image quality] Source specifications of the instrumentation directly affect imaging capabilities. In addition, detector responses such as non-linearity, low efficiency and long decay time may cause artifacts in the image. Biomedical instrumentation design Uni. of 18 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  MEDICAL IMAGING: FROM PHYSIOLOGY TO INFORMATION 4. Data Acquisition Methods for Image formation: The data acquisition methods used in imaging play an important role in image formation. Optimized with the imaging instrumentation, the data collection methods become a decisive (unmistakable) factor in determining the best spatial resolution. Biomedical instrumentation design Uni. of 19 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  MEDICAL IMAGING: FROM PHYSIOLOGY TO INFORMATION 5. Image Processing and Analysis: Image processing and analysis methods are aimed at the enhancement of diagnostic information (enhancement from different sides such as technical, cost, easy to use, good quality …. Etc.) to improve manual or computer-assisted interpretation of medical images. Biomedical instrumentation design Uni. of Thi-Qar Faculty of 20 Engineering. 5th stage. By Ali Basim Mahdi  X- ray Modality 1 Biomedical instrumentation design Uni. of 21 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  Medical Modalities: 1- X- ray machine In the figure, something is missing, what is that? Biomedical instrumentation design Uni. of 22 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi X- ray machine is divided into FOUR major components: 1. X-Ray Tube 2. Control Panel (Operation Console) 3. High voltage generator 4. Film holder Bucky (chest or erect stand and table) 23 Biomedical instrumentation design Uni. of Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  2 4 1 3 Biomedical instrumentation design Uni. of Thi-Qar Faculty of 24 Engineering. 5th stage. By Ali Basim Mahdi 1. X-RAY TUBE * Attached to a tube support. * Produces X-rays (& Heat). * Operated at high voltage (20 - 200 kVp). * Insulation required. * Oil used to cool X-ray tube during exposures * Oil also acts as an insulator. * X-ray tube lead lined. * Incorporate safety interlocks. * Light Beam Diaphragm. * Integrated Collimation. 25 Biomedical instrumentation design Uni. of Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi Construction of the X-ray tube The X-ray tube contains two principal elements: 1.1. Cathode: provides a source of electrons form from (filament from tungsten + focusing cup from nickel), connected to step down transformer to heat filament and then emit electrons. Note: Most rotating anode x-ray tubes have two filaments mounted in the cathode assemble “side by side,” creating large and small focal 26 spot sizes. Biomedical instrumentation design Uni. of Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi In a dual-focus x-ray tube, focal spot size is controlled by heating one of the two filaments. Small focal spots range from 0.1 to 1 mm; large focal spots range from 0.3 to 2 mm. Each filament of a dual filament A, Without a focusing cup, the electron beam is cathode assembly is embedded in the spread beyond the anode because of mutual focusing cup. The small focal spot size is electrostatic repulsion among the electrons. associated with the small filament and the B, With a focusing cup that is negatively charged, large focal spot size with the large filament. the electron beam is condensed and An electric current is directed through the directed to the target. appropriate 27 filament. Biomedical instrumentation design Uni. of Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi 1.2. Anode: Acts as the target for electrons and releases x-rays There are two designs: 1. Stationary anode 2. Rotating anode (3000- 3600, 9000-10000 r.p.m), connected to step up transformer to increase line voltage to attract the electrons. Stationary anode tube with a 1-mm focal spot may have a target area of 4 mm2. A comparable 15-cm–diameter rotating anode tube can have a target area of approximately 1800 mm2, which Biomedical instrumentation design Uni. of Thi-Qar Faculty of Engineering. 5th stage. increases the heating capacity of 28 By Ali Basim Mahdi the tube by a factor of nearly 500. Additional components include: 1. Expansion bellows (provide space for oil to expand) 2. Tube envelope (evacuated) 3. Tube housing 4. Cooling dielectric oil 5. Rotor 6. Induction stator 7. Tube window Biomedical instrumentation design Uni. of 29 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi 2. CONTROL PANEL (OPERATION CONSOLE) * THREE primary controls 1) kVp – quality 2) mA quantity 3) Time ** Auxiliary control (anatomical programs@ AEC control) Almost there are two modes for operation manual and automatic Biomedical instrumentation design Uni. of 30 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  Biomedical instrumentation design Uni. of 31 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  Biomedical instrumentation design Uni. of 32 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  Biomedical instrumentation design Uni. of 33 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi Higher kilo voltage (kVp) and lower milli amperage (mAs) reduces patient dose. A, The use of high kVp and low mAs results in a high-energy, penetrating x-ray beam and a small patient (absorbed) dose. B, The use of low kVp and high mAs results in a low-energy x- ray beam, most of which is easily absorbed by the patient. Biomedical instrumentation design Uni. of Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim 34 Mahdi  Biomedical instrumentation design Uni. of 35 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  Biomedical instrumentation design Uni. of 36 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  Biomedical instrumentation design Uni. of 37 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi  3- X-Ray Generator Supplies electrical power to x-ray tube – high voltage between anode & cathode – filament voltage Controls exposure timing – Turns exposure on and off – High voltage switched on and off Filament heated before exposure Biomedical instrumentation design Uni. of 38 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi How we can divide the biomedical instruments (according to what) ? Biomedical instrumentation design Uni. of 39 Thi-Qar Faculty of Engineering. 5th stage. By Ali Basim Mahdi