X-Ray Tube and Equipment - Radiology - PDF

Adler Chapter 8 (p89 – 103) Bushong Chap7 (p113-126) Radiographic and Fluoroscopic Equipment & X-ray Tube  Objectives  Discuss the role of the radiographer in maximizing diagnostic yield.  Identify the typical features of a radiographic...

Adler Chapter 8 (p89 – 103) Bushong Chap7 (p113-126) Radiographic and Fluoroscopic Equipment & X-ray Tube  Objectives  Discuss the role of the radiographer in maximizing diagnostic yield.  Identify the typical features of a radiographic system.  Explain radiographic equipment manipulation.  Explain the purpose of the collimation assembly and its importance in radiation protection.  Distinguish among the various types of radiographic tables and their functionality.  Explain the major controls on the radiographic system control console.  Objectives (Cont.)  Differentiate between the types of tube support systems.  Briefly explain the operation of photostimulable phosphor (PSP) technology.  Explain the purpose of the upright image receptor and its functionality.  Discuss the concept of alignment of the various radiographic system components.  Briefly discuss the two classes of digital imaging detectors and future technologies resulting from digital detectors.  Summarize the significant R/F equipment design changes that have resulted in modern-day equipment design and functionality.  Discuss mobile radiographic systems and their applications.  Diagnostic Yield  The amount of clinically useful information on a diagnostic image  Different medical imaging modalities provide different types of information Radiography Fluoroscopy Sonography CT scanning MRI scanning Nuclear medicine  Diagnostic Yield (Cont.)  Each modality has its own considerations for ordering the procedure.  Physicians expect a certain amount of diagnostic yield when exams are ordered.  Diagnostic yield of information must outweigh the input factors of the procedure.  Competent imaging professionals will strive to maximize diagnostic yield using a minimum of input factors.  Diagnostic Efficacy  The accuracy of diagnostic information on a medical image is its diagnostic efficacy.  Any extraneous information on an image that does not reflect the patient’s true medical condition detracts from diagnostic efficacy.  Diagnostic efficacy and diagnostic yield must be optimized as the standard of care. X-Ray Machine Design Features  Radiographic table  X-ray generator and control  Upright image receptor Chest stand  X-ray tube and x-ray tube support  Collimator assembly  X-Ray Tube Design  Tube is inside a lead-lined metal housing.  Made of heat tolerant, Pyrex glass with high vacuum.  Produces X-radiation when high-energy electricity passes through the tube.  X-radiation exits the tube through a window in the housing and is directed toward a patient.  Radiographic Table  May be fixed height or variable height  Typically has a four-way “floating” tabletop  Some table designs permit a variable-speed, tilting capability.  Uniform radiolucent surface  Must be: Easy to clean Free of crevices that could collect contrast media Difficult to scratch  Bucky tray  Tilting Radiographic Table A tilting radiographic/fluoroscopic table in the full upright position  These designs permit table tilt from horizontal position to vertical, upright position, to Trendelenburg.  Most tables have four- way tabletop travel.  Tables typically do not have variable height capabilities.  Bucky Assembly  Consists of a receptor tray and radiographic grid  Tray holds receptor tightly in position and is centered to longitudinal axis of table.  Radiographic grid oscillates during exposure to blur out the lead grid lines.  Upright Bucky Assembly Vertical Upright Upright Bucky with Bucky Assembly Lateral Chest Support Arm FIG. 8-10 Upright vertical Bucky showing three automatic exposure FIG. 8-13 Upright vertical Bucky with a “pistol-grip” locking mechanism.. control (AEC) detector chamber positions. Detectors may be selected separately, in tandem, or as a triad.  Console FIG. 8-8 Radiographic generator operator’s control. Exposure controls are convenient push buttons with visual display of selected exposure factors. In this version, exposures may be made using prep and expose buttons or a two- position switch firmly attached to the control (upper right corner).  Control console is the interface between the radiographer and the sophisticated electronics of the x-ray machine.  Console features include the exposure button.  Operating/Control Console  Most are microprocessor controlled and use a simple computer interface.  Permits selection of all exposure factors. o mA, Time (S), mAs o kVp o Focal spot size o Automatic exposure control (AEC)  Console  Operating console Can be digital with touch screen technology Anatomical programming (APR) Uses icons to indicate body parts, size, and shape  Newer systems may be integrated with a digital radiographic (DR) detector  Exposure Technique Selection  Consists of three key factors kVp – penetrating power of the beam mAs – number of x-ray photons in the beam SID – distance from the source to the IR Other factors Automatic exposure control (AEC) may be optional. Focal spot size selection Exposure technique selection may be anatomically programmed.  Technique selection is critical to good radiography.  Anatomically Programmed Radiography (APR)  APR is a radiographic system that allows the radiographer to select a particular button on the control panel that represents an anatomic area.  A preprogrammed set of exposure factors is displayed and selected for use.  Once an anatomic part and projection or position has been selected, the radiographer can adjust the exposure factors that are displayed.  Exposure Switch  Used to take the x-ray  Type Deadman switch  Method of use Depress in one motion to maximize tube life  Features Separate anode and rotor switches also used E.g. Prep before the exposure Mobile equipment requires 1.8 meters (approx. 2m) or (6-foot cord) External Components of X-ray Room  Ceiling support system  Allows for longitudinal and transverse travel of the x-ray tube.  Telescoping column attaches the x-ray tube housing to the rails allows for variable SID  Detent position  position the x-ray tube assumes when it is centered above the x-ray table  Locks  Locks the tube in place or allows the tube to ‘float’  X-Ray Tube Supports  Two basic designs: Floor Mounted Ceiling suspended  Other Features Facilitate easy and efficient positioning of the x-ray tube assembly around the patient in any orientation Capable of various motions depending on need Ergonomically friendly Aesthetically pleasing and not intimidating to patients  Two Types of X-Ray Tube Support Designs  FIG. 8-11 X-ray tube support systems come in two basic designs: floor-mounted tubestands (A, B, D) and ceiling- suspended tubecrane systems (C).  Overhead Tubecrane (OTC) Motions FIG. 8-14 Basic movements of a typical diagnostic radiographic tube are longitudinal, transverse, vertical, rotation, and tube angulation.  Tube Travel  Vertical travel  Longitudinal Transverse l  Vertical axis rotation  Tubehead rotation  Collimator Assembly  Controls the size and shape of the x-ray field directed toward the patient  Projects a high- intensity light field on the patient, which represents the area of the x-ray field exposure FIG. 8-2 X-ray tube collimator assembly with control knobs for adjusting the x-ray field dimension.  May be manual or automatic (PBL)  User-Friendly Overhead Tube/crane Controls (OTC)  Newer overhead tube crane(OTC) designs permit selection of exposure factors at the tube head control, with a flat panel screen.  Digital radiography systems may display the image from the last exposure for review.  Auto-tracking feature permits synchronous movement of OTC and vertical upright holder.  Exposure requires the operator to be behind the control booth.  Image Receptors  Receive remnant  Referred to as flat-panel radiation from patient technology. and convert x-ray Receptor is a cassette- energy into electronic style design. Often referred to as a signals. “panel”  Most systems are digital DR systems use thin-film radiography (DR). transistors (TFTs). o Indirect digital detector  Computed Radiography technology (CR) also called PSP is o Direct digital detector in limited use and technology quickly being replaced with DR.  Type of X-ray System  Digital Radiography (DR)- uses flat panel detectors Indirect Direct  Computed Radiography (CR)- uses reusable phosphor plates to capture images  Fluoroscopy  Provides live, real-time images of patients using x-rays  Requires special equipment designs that feature an x-ray tube with attached image receptor in a perpendicular relationship  Used for a wide array of diagnostic procedures  Radiographic/Fluoroscopic (R/F) System  Capable of static radiographic imaging as well as live imaging (fluoroscopy)  Complete system consists of R/F table, image receptor, x- ray generator and control, ceiling-mounted x-ray tube and video display monitor.  Image intensifier above the table Newer systems replace the image intensifier with a flat panel fluoroscopy detector.  Tilting Radiographic Table  These designs will tilt the table from horizontal position to vertical upright position to Trendelenburg.  These tables typically do not have variable height capabilities.  Mobile X-Ray Imaging  Mobile radiographic units are used extensively in hospitals and clinical settings.  Travel movement is motorized.  X-ray capabilities similar to those of a fixed radiographic unit.  Mobile X-Ray Unit  High-frequency output  Limited power for X- ray studies.  Commonly referred to as a “portable”.  Need to be plugged into wall outlet for charging when not in use  Mobile X-Ray Features  Newer systems use a wireless portable DR detector to replace cassette.  Exposure switch on a coiled cord to maximize distance from patient during FIG. 8-26 Digital radiographic detector with tether cord attached. exposure Length = Approx 2 meters  Mobile Fluoroscopy  Commonly called a “C- arm” due to its design.  Fixed SID and centered to X-ray tube.  System components. C-arm and generator Monitor cart with on- board computer Image processing and enhancement Typically, 2- monitors  C-Arm Fluoroscopy System  Used in a variety of settings. ER Surgery Pain clinics Interventional fluoroscopy procedures E.g. Heart stenting  Mini-C arms popular for small body parts. Limited power  Newer systems use digital technology  X-ray Production Process  What year was x-  X-rays were discovered ray discovered? in 1895.  X-ray beam energy is produced using high- voltage electricity.  X-rays pass through matter and strike an image receptor.  Image receptor converts the energy of x-rays into an image  X-Ray Production Requirements  X-ray tube with a vacuum inside.  Source of electrons. o Cathode filament  Method to accelerate electrons to great speed. o Voltage  Method to stop electrons and cause energy transformation. o Target  X-ray Tubes  Tube is inside a lead-lined metal Glass x-ray tubes are made of Pyrex housing. (borosilicate glass) that is resistant to heat, chemicals, and electricity.  Made of heat tolerant, Pyrex glass with high vacuum.  Produces X-radiation when high- energy electricity passes through the tube.  X-radiation exits the tube through a window in the housing and is directed toward a patient.  Oil bath –a thermal cushion to dissipate heat  What is a vacuum?  An empty space in which there is no air or other gas  Why a Vacuum?  Allows for efficient x-ray production if the tube become gassy – electron flow from cathode to anode is reduced.  Leakage Radiation  Radiation exiting the x-ray tube at areas other than the window of the tube  Tube Design  Cooling Fan  Tube Window To Dissipate Heat Area of glass or Oil expands when metal enclosure that heated – bellows-like is thin to allow device allows for expansion and a passage of x-ay microswitch activated to beam prevent exposure if expansion is too great.  Function of Cathode  Negative side of the x-ray tube has two parts – filament & focusing cup.  An electric current will cause the filament to glow an emit heat & electrons  Small & Large Filament Sizes  Small used with the small focal spot Used to image small body parts.  Large used with the large focal spot. Used to image large body parts.  Material of Filament  Coil of tungsten wire. Unlikely to burn out or takes longer to vaporize. Has a very high melting point  Focusing Cup  Negatively charged to confine electrons to a small area on the anode  The focusing cup forces the emitted electrons to keep together as they travel to the anode With a focusing cup Without a focusing cup  Anode  Plays a vital role in the production of x-ray  Dissipates heat  Positive side of the x-ray tube  Components: Anode Stator Rotor 46  Material of Anode  Tungsten (tungsten- rhenium alloy)  The stem is made of molybdenum the rotor made of copper  Graphite is the material immediately below the tungsten  Why Tungsten?  High melting point (3400⁰C. vs. 1100 for copper) can withstand higher tube currents without pitting or bubbling  High thermal conductivity – Efficient metal for dissipating heat Thermal conductivity Ability of a given material to conduct/transfer heat  THE TARGET  Area on the anode struck by electrons from the cathode Stationary anode uses tungsten alloy embedded in copper anode. Rotating anode – entire anode disc is the target  Useful Beam  X-rays emitted from the x-ray tube window x-rays are emitted isotopically (equal intensity in all direction.)  What is Anode Heat?  The heating of the anode with electron bombardment  Kinetic energy of projectile electron is converted to heat. Doubling the tube current doubles, the heat produced Heat produce is directly related to increased kVp  Tube Failure  Too rapid heating of anode Glass housing can crack Vaporized tungsten on the glass or metal enclosure can disturb the electric balance of the x- ray tube current – leading to arcing and tube failure. Prolonged heating of anode – causes pitting and melting or cracking Damage to the ball bearing – causes a wobble anode rotation Broken filament  Extending Tube Life  Using factor appropriate  Faster imaging systems  Heat Dissipation in X-ray Tubes  Occurs by x-ray exposure caused by Radiation transfer of heat by emission of electromagnetic radiation, including x-rays, visible light, ultraviolet, and infrared  Heat Dissipation in X-ray Tubes  After the exposure Conduction – From the stem to rotor assemble to oil bath transfer of heat by touch Convection –Within the oil bath –transfer of heat by the movement of a heated particles from one place to another Purpose of Warm-Up Procedure  To spread heat over the entire target surface  Prevent uneven thermal expansion or concentration of heat in a single spot Should be performed if the tube has not be used for an extended period E.g. of warm up exposure: Two 70kV exposures at low mA and 3 seconds  Important to Remember!  The only radiation that is of any clinical value is: Remnant radiation absorbed in the detector. Converted to an electrical signal, digitized, and sent to a computer for processing. Creates electronic data set Finally presented as a radiographic image for interpretation.  Conclusion  The highest diagnostic yield and efficacy of images are constant goals.  Radiographic equipment has various designs but many common features.  Receptor technology will continue to evolve into digital world.  Equipment design will incorporate digital detectors and user-friendliness.