ultrasound

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Alternative Diagnostic Imaging Techniques
Radiation-based alternative diagnostic imaging techniques Angiography- - radiographic examination of blood vessels by injection of radiopaque substances into the blood vessels. Applications  detection of stenosis  detection of septal defects  aid in angioplasty Cystography - radiographic examination of the urinary bladder and urinary tract by injection of radiopaque substances into the urinary tract. Applications  detection of rupture of urinary bladder  detection of blockade in the urinary tract  detection of hemorrhage and tumors  Cholecystography - radiographic examination of the gall bladder and biliary system by injection of radiopaque substances into the gall bladder. Applications  detection of choleliths  detection of bile duct patency  detection of rupture, enlargement, tumors in gall bladder Fluoroscopy ➢ diagnostic medical procedure that uses X rays to view the internal structure and processes of the body that are actually functioning. ➢ uses relatively low doses of X rays. Applications  view malfunctioning organs  insertion of catheter in artery  removal of foreign objects Computed Tomography Other Names ➢ Computerized Tomography ➢ Computerized Axial Tomography ➢ CAT (scan) ➢ CT (scan) Features  radiation-based (X-ray) imaging technique that compares the density of an area of the body with the density of water

thin fan-shaped X-ray beams penetrate the body  image produced is a two- or threedimensional tissue density map of the anatomic slab scanned  conventional X-ray view the body from one angle, CT view is a “slice” of the body from many angles  CT machines view a “slice” of the body from many angles by revolving an X-ray tube around the patient. Sensitive detectors record what scanner sees.  Large molecules (e.g. bones) absorb X rays as they pass through the body, masking what lies behind them.  Computer reconstructs the many views to make a single video image Limitations  small size, use for small animals only  high cost  presence of ionizing radiation Applications  overcome shortcomings of general imaging techniques, e.g. superimposition or summation of densities which limit visible detail  allows visualization of organs surrounded by bone, e.g. brain  able to characterize soft tissue and osseous changes before identification by clinical or general radiographic means  Scintigraphy Other Names ➢ Positron Emission Tomography (PET) ➢ Single Photon Emission Computed Tomography (SPECT) ➢ Nuclear Medicine ➢ Gamma Scanning ➢ Radionuclide Scanning These rays shoot in opposite directions and strike crystals in a ring of detectors around the patient’s head, causing the crystals to light up. Injected radioactive solution emits positrons which upon collision release gamma rays. A computer records the location of each flash and plots the source of radiation, translating that data into an image. Patient on a PET scanner. Images trace amounts of radioisotopes in the heart to determine whether muscle tissues are receiving a normal supply of blood.

Electrodes on the chest record an electrocardiogram. Features  administration of radiopharmaceutical (e.g. technetium) alone or bound to a substrate (e.g. glucose)  imaging of the distribution of the gamma rays from many angles.  basis for imaging is the differential localization of the radiopharmaceutical in tissues and organs and differences between healthy and diseased tissues.  From highest to lowest rate of activity: red, orange, green, blue Limitations  requires sedation (60 sec for imaging)  high cost  presence of ionizing radiation Applications  detect areas of increased metabolism  differentiate healthy and diseased tissues Digital Subtraction Angiography Features  One application of the expanding field of computed angiography  Angiography with digital enhancement  Digital biplane angioscope provides views of the heart from two different angles. Procedures  Take plain radiograph  Store image in the computer  Take angiograph  Store angiograph in computer  Computer subtracts first image from second image, producing an image of angiograph without surrounding tissues A picture of the heart is made by a digital scanner. Next, as a contrast agent is injected through a catheter into the coronary arteries, a second X ray image is made showing the agent flowing through the heart’s vessels. A computer subtracts the first image from the second, leaving only what has changed – blood vessels containing the agent and highlighting a blockade. Applications  Guide for angioplasty  Monitor circulation to organs  Block blood vessels, e.g. bleeding, tumors Densitometry Features

➢ a method which determines density of
tissues and organs ➢ machine passes a thin, carefully directed beam of X rays through the body ➢ machine detects X rays which pass through ➢ a computer calculates amount of X rays absorbed Techniques of densitometry  single-photon absorptiometry  dual-photon absorptiometry  monoenergetic x-ray densitometry  dual-energy projection radiography Application Bone densitometry Non-radiation-based alternative diagnostic imaging techniques Endoscopy - direct visualization of a body part using an instrument with a light source Characteristics ➢ direct real-time imaging of organs and tissues ➢ absence of ionizing radiation ➢ relatively cheaper Types  Rigid endoscope Metal tube for bladder (cystoscopy), abdomen (laparoscopy) and joints (arthroscopy)  Flexible endoscope Fiber optics for viewing the colon (colonoscopy), larynx (laryngoscopy), stomach and duodenum (gastroscopy). Components  fiber to transmit light  fiber to bring back an image  tube for insertion of catheter  instrument for biopsy  tube for washing  tube for cleaning with air  camera Disadvantages  cannot be used for solid structures  imaging limited only to organs or tissues with natural openings Applications  visualization of tubular organs  visualization of inaccessible places of the body Thermography Features

noninvasive imaging technique that measures infrared emissions of the body which show differences in temperature ➢ a two-dimensional surface temperature video map is generated by an infrared detector used at a distance from the patient ➢ signals are converted into black and white, sometimes color-coded, images with higher temperatures as bright areas. Applications  provides information on local vascular distribution and regional tissue metabolism  detects vascular changes caused by inflammation  detects abnormal soft tissue areas  Used for medical diagnosis, search and rescue, energy audits of buildings, law enforcements, etc. ➢ Magnetic Resonance Imaging Characteristic - images provide both anatomical information of CT and physiological information of scintigraphy without the detrimental effects of ionizing radiation Features ➢ relies on the principle that hydrogen atoms, when subjected to a magnetic field, line up like so many soldiers ➢ if a radio frequency is aimed at these atoms, it changes the alignment of their nuclei ➢ when radio waves are turned off, the nuclei realign themselves, transmitting a small electrical signal ➢ image is generated from returning pulses from organs and tissues ➢ The MRI scanner surrounds the body with powerful electromagnets. Supercooled by liquid helium, they create a magnetic field as much as 60,000 times as strong as that of the earth. Disadvantages ➢ high cost ➢ needs a room completely insulated from external radio frequencies ➢ cannot be used in patients with metallic implants (e.g. horseshoes) Applications  imaging of CNS  imaging of musculoskeletal system

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Ultrasonography Other Names diagnostic ultrasound ultrasonic diagnosis - a technique used to locate or delineate deep tissues or structures in the body by measuring the transmission or reflection of ultrasonic waves Characteristics real-time image is produced absence of ionizing radiation portable equipment rapid procedure Disadvantages cannot be used in the presence of air or bone needs direct contact between transducer and tissues/organs to be imaged Applications detection of edema, fluid accumulations, fibrosis and tumors detection of abnormal structures such as choleliths, uroliths and foreign bodies used for ultrasound-guided biopsy diagnosis of various heart and vascular disorders

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