Specialized Diagnostic Equipment PDF

SPECIALIZED DIAGNOSTIC EQUIPMENT E. HERBERT  Basic principles of x-ray production Origin of radiographic images Interaction processes of x-rays with the body How radiographic images is converted into a form suitable for visual interpretation However: Specialised techniques and...

SPECIALIZED DIAGNOSTIC EQUIPMENT E. HERBERT  Basic principles of x-ray production Origin of radiographic images Interaction processes of x-rays with the body How radiographic images is converted into a form suitable for visual interpretation However: Specialised techniques and equipment is often used in radiography Use of particular radiographic techniques Mammography Computer Tomography MRI Pediatric Rad Fluoroscopy Mobile Radiography Dental radiography Digital Radiography Interventional Angiography Cardiography  ENHANCES SPECIAL TECHNIQUES Mammography is a low voltage technique – to enhance contrast in breast tissue High voltage radiography- useful when increased x- ray output/ better penetration is required Magnification always occurs- undesirable but it can be useful Computer Tomography (CT) a CT unit uses an x-ray tube and a detector array to gather anatomical data from patient anatomy  Magnetic Resonance Imaging (MRI): produces high contrast images without using radiation Pediatric Radiography, no special equipment but specialized techniques and accessories is needed Fluoroscopy: Fluoroscopic imaging systems use much of the same technology as radiographic systems, with some modifications and additions. Depending on the intended use, a fluoroscopic system may require a high power generator and a high heat capacity X ray tube.  Mobile Radiography: making used of mobile equipment Dental Radiography: Imaging of the teeth via x-rays  Digital radiography CR is the most widely used form of DR CR makes use of a x-ray sensitive plate that is encased in a protective cassette DR is the interaction of x-rays with an image receptor Digital images whether CR or DR can be transmitted digitally by means of: teleradiology (moving images via telephone lines to and from remote locations) PACS: digital image is digitized so that the images could be sent from computer to computer.  Angiography, radiologic imaging of bloodvessels after injection of contrast media. Cardiography, imaging of the heart and associated structures Interventional Radiography: radiologic procedures that intervene in a disease process, providing a therapeutic outcome. Subtraction techniques used to eliminate unwanted information from an image Making diagnostically important information easier to visualise Subtraction is often used in digital radiography  Bone densitometry: For assessment of low bone mass and structural deterioration of the skeletal system by making use of various technologies SPECIALIZED X-RAY TUBES  STEEP ANGLE TARGET TUBES DESIGN STATIONARY ANODE: COPPER CYLINDER: Rectangular tungsten target Acts as support for the embedded in sloping surface target. of copper cylinder. Holds it in required position. ROTATING ANODE: ELECTRICAL CONDUCTOR: Rotating disc is the target. -Allows easy flow of electrons Its shaft is the stem of the from target. anode. Made of molybdenim. STATIONARY ANODE ROTATING ANODE  ADVANTAGES Rotating anode allows Target is set at an angle electron beam to allowing free access for interact with a larger approaching electron target area. beam. i.e. heating of anode is confined to one small The steeper the angle, spot. the larger the heated Line-focus principle area. →improves spatial Biangular targets resolution. produce two focal spot →high anode heating sizes. with small effective focal spots.  ADVANTAGES Line-focus principle Biangular targets  DISADVANTAGES Slow rotation because of Heel effect →reduces x- bearing damage results ray intensity on the in anode separation and anode side. surface melting. Sloping face of target Pits or cracks occur due forms a limiting boundary to repeated overloading to the edge of the useful and exceeding maximum beam. heat capacity. Line-focus principle also leads to heel effect. Repeated overload DISADVANTAGES Anode separation and surface melting Heel effect Exceeding maximum heat storage capacity  APPLICATIONS Steep angle of 15º-20º Smaller steep angle -Used as a compromise Smaller focus received between a large with same tube effective focal size and charge. large field size. -Due to anodes point of Gives sharper images. cut off. Steep angle of 17º -Provides an x-ray beam big enough to cover a field of 43cm on a 100cm focal film distance (FFD). APPLICATIONS Steep angle sizes  SPECIALIZED X-RAY TUBES Grid controlled x-ray Designed to switch on or Tube off rapidly. Extra electrode between Confines electron beam cathode and anode to small area of anode. Controls flow of electrons Focusing cup Focusing cup (Pg. 132) is effectiveness: the grid & also exposure Size & shape switch Position of filament Filament embedded in within focusing cup. focusing cup. Determines focal spot Focusing cup – charged size & power of tube Voltage between focusing cup & filament acts as on & off switch SPECIALIZED X-RAY TUBES grid controlled tube DSA, Digital =Used in pulsed radiography, cine work Cineradiography Current less than 100mA Pediatric work Applications: Portable capacitor discharge imagers,  FOCUSING CUP Focusing cup GRID TUBE: VARIABLE FOCUS Used with macroradiography Micro focus limited Does not restrict use normal use of dual Loading can be focus tube increased - by Provides small foci water cooling tube 0.1mm² ADVANTAGES & DISADVANTAGES Advantages: No delicate parts Provides multiple to fail exposures at precise exposure Disadvantage: times Cost: tube & Modified focusing biasing unit cup more economical If grid fails, modified focusing grid can still be used HIGH SPEED X-RAY TUBES Design 3-Phase allows 9000 modification allows revolutions per better minute. performance Greater rotational Metal/ceramic speed possible with casing frequency Construction: converter. Stator windings Increased input supplied with 3- load; up to 75% phase electrical more. Only short supply. exposure times. HIGH SPEED X-RAY TUBES Advantages: Disadvantages: ↑ Short-time Initial cost loading expensive; more ↑ mA sophisticated ↓ exposure time equipment ↓ Risk of motional Expensive to unsharpness replace tube ↑ Input loading → Longer “Prep”↑ smaller focal spots time needed to Micro-focus; reach higher macroradiography rotational speed HIGH SPEED X-RAY TUBES Disadvantages: ↓ Bearing ↑ Wear on bearings protection ↑ Heat injection: Requires braking heat ↑ 9kW system to rapidly produced by stator reduce rotation windings speed ↑ Stress on anode stem BI-ANGULAR X-RAY TUBES Target face Advantage: beveled Choice: Provides 2 different High loading with angles average focal spot size 2 Different cathode electrons from Lower loading on smaller effective filament (directed focal spot to different angles) Dual focus allows for various radiographic examinations. Biangular targets  HEAVY DUTY ANODES Very large heat Centre block: storage capacity Molybdenum & ↑ Loading provided titanium & by ↑ diameter of zirconium target disc Back plate: Compound disc graphite (Various materials) Discus shaped Target face: target: provides tungsten & rhenium greater strength  HEAVY DUTY ANODES Graphite & molybdenum: light materials → increase diameter & thicken disc without producing extra weight Anode disc: considerable block; large heat storage capacity SPECIALIZED X-RAY TUBES ADDITIONAL COOLING MECHANISMS.  Temperature stability within medical imaging systems is critical to enhance imaging performance, increase system reliability, and maximize equipment uptime. Temperature fluctuations not only impact image resolution, but also long-term operation of key components. Due to the fact that so much heat is built up by these specialized equipment special cooling or additional cooling is needed.  EXTERNAL AIR CIRCULATOR It blows cool air over the warm casing and thus transfers warm air to the external environment. Due to the above procedure 36000 HU/min is being removed. The fan cannot cool the tube sufficiently therefore additional cooling is needed.  HEAT EXCHANGER Utilised in Angiography, where huge amounts of heat occurs.  HOW DOES THE HEAT EXCHANGE PROCESS WORK? The warm oil moves from the target area via copper anode cylinders through long supple tubes to an external heat exchange unit. Heat exchange occurs and the oil is cooled down. After this process the oil is pumped back to the tube. Via this process 100000 HU/min can be removed.  Advantages Disadvantages It improves air More expensive circulation around the tube housing. Tube is heavier Extends tube life. Tube warming is Prevents cracks in however essential the glass casing.  WATER COOLING Cools anode due to cold water that circulate in tubes behind the anode disk Used when the heat conduction process is not adequate It is a closed system to exclude water leakage Often used in Mammography Also where high amounts of heat is needed eg. angiography and CT  DESIGN Glass casing is replaced with metal for better heat radiation Ceramic/Al oxide is used for electrical isolation Bearings on both sides to ensure stability and decrease tension on the tube Decreases convection & electrical stability extends tube life Forced cooling increases the output of the tube (more examinations can be done)  ADVANTAGES Better image quality Tempo of heat transfer is higher Higher loads is possible Tube life is extended Compact  DISADVANTAGES Cost Tube housing not exchangeable Filament temperature is a limitation  WATER COOLING SYSTEM Stationary anode Water cooling tubes Focal spot Water in Circulating pump Water out DIAGNOSTIC X-RAY TUBE FAILURE  Extremely high voltage Excessive heat generation Poor cooling system Rough-handling / Careless Aging  FACTORS EXTENDING TUBE LIFE Role of Correct installation Manufacturers, & adjustment Equipment suppliers Careful handling & Radiographers Knowledge of Attention to design operation & Care in limitations manufacture Good radiographic Tube selection practice suitability X-RAY TUBE: PERFORMANCE FUNCTION X-Ray tubes have Trauma: ↓ Time and different sizes, ↑mAs designs, abilities & Fluoroscopy: long PRICES continuous exposure (↓mAs ± 3 NB: Performance mA) function Orthopaedic: fine Pediatric: short detail exposure time and Mammography: low mAs fine detail & macroradiography  X-RAY PERFORMANCE FUNCTION Mobile units: ? Type Cine radiography: of patients; ? very short exposures Examinations, ? at high tempo – Stable power supply high heat loading Angiography: CT: ↑ heat loading, ↓exposures, long ↑kV series exposures, Dental radiography: high heat loading, small objects, ↓ heat good resolution loading, good resolution  GOOD RADIOGRAPHIC PRACTICE Prevention of Extension of tube damage to tube filament life anode 3. Use low mA 1. Avoid high tube current or FF – Holding unit motivate “prepare” minimum 2. “Run-up” time procedure before 4. Minimise careless large injection of tube handling heat to a cold anode – motivate  GOOD RADIOGRAPHIC PRACTICE 5. Reduction of wear on the bearing of the rotating anode 6. Reduction in the rate of tungsten deposit 7. Use of rating chart and full understanding of protective devices 8. Checking of the tube shield  GOOD RADIOGRAPHIC PRACTICE FEEDBACK High tube current or using FF unnecessarily Exposure loading will approach maximum permissible loading esp repeat exposures without adequate cooling time Anode can form cracks  GOOD RADIOGRAPHIC PRACTICE FEEDBACK “Run-up” procedure before large injection of heat to a cold anode Failure to do this can cause cracking of target disc, due to differential expansion. Result: diminished x-ray output Remedy: Use lowest necessary power Largest possible focal spot Longer exposures at reduced power  GOOD RADIOGRAPHIC PRACTICE FEEDBACK “Run-up” procedure before large injection of heat to a cold anode When temperature of the anode increase during a single exposure localized surface melting will occur. This will cause pitting of the anode. Result in irregular surface – variable & reduced radiation output.  GOOD RADIOGRAPHIC PRACTICE FEEDBACK Holding unit “prepare” minimum time “Prep” of filament supplied with higher boosted current. Tungsten evaporate from filament more rapidly than when on standby Need short time for current to be boosted.  GOOD RADIOGRAPHIC PRACTICE FEEDBACK Minimize careless tube handling May cause mechanical damage to filament  GOOD RADIOGRAPHIC PRACTICE FEEDBACK Reduction of wear on the bearing of the rotating anode Keep running time of rotating anode at top speed to the minimum. High speed units can be fitted with a braking system which rapidly slows down to limit wear Avoid long exposures. Imbalanced ball bearings: Jamming Increased bearing noises Anode stop rotating This causes: Increased rotational friction Expansion due to excessive heat of the rotor bearings Remedy: Use of silver & gallium as lubricants Broken Stator windings No power supply to make the anode rotate Causes: Heavy x-ray exposures Excessive heat in the target material, rotor and bearings Difference in thermal expansion of various components used in the anode Remedy: Provide safety circuit to terminate exposure  GOOD RADIOGRAPHIC PRACTICE FEEDBACK Reduction in the rate of tungsten deposit Tungsten deposited on tube walls by condensation of tungsten vapor. Limiting of generated heat reduces amount of vapor deposited. Lead to interference with electron flow from the cathode to the anode Remedy: Use of an automatic Filament boosting circuit Use of 1-2% Thorium with the Tungsten filament  GOOD RADIOGRAPHIC PRACTICE FEEDBACK Use of rating chart and full understanding of protective devices Ensure optimum use of equipment Rating chart provides specifications of each tube. Provides limitations for use.  Different types Radiographic rating charts Anode heating/cooling Housing heating/cooling RADIOGRAPHIC RC  ANODE Determines max heat capacity of the anode Determines the length of time tube must be allowed to cool down before next exposure  HOUSING COOLING/HEATING Max heat capacity of the tube housing 1-1.5 million HU Complete cooling after max heat capacity may take up to 1-2 hrs  GOOD RADIOGRAPHIC PRACTICE FEEDBACK Checking of the tube shield Detecting oil leak timeously will allow replacement of oil before too much is lost. Prevents strain of tube.  “X-RAY EQUIPMENT WITHOUT AN X-RAY TUBE IS LIKE A HUMAN BODY WITHOUT A HEART” THANK YOU