CT safety 301 张帅
Introduction Safety is the number one concern when you service a CT system. To protect yourself and others, you must be aware of the various potential hazards in a CT scanner and the techniques to control them. Prevention and Control
purpose Identify the various causes and types of hazards in CT systems Recognize commonly available safety resources in your organization Associate preventive techniques with each type of hazard
Common CT Hazards Normal CT component conditions, such as heat from the x- ray tube or tube movement when the alignment light is pressed. Improperly-working CT components, such as generator overloads. Medical equipment and devices, such as needles, tubing, or gauze. Service engineers who ignore safety and electro-static discharge (ESD) guidelines, do not use correct procedures, skip steps, or do not use correct tools.
Hazards Types Pathogenic Mechanical Electrical Radiation Thermal Laser
Resources Documentation, Training, and Equipment Documentation on CT system: includes service procedures and the correct tools to use during service. Courses or manuals on environmental health and safety: includes techniques to reduce your risk to all types of hazards. Review this material before you perform service. Personal protective equipment (PPE): may include safety shoes, safety glasses, etc.
Emergency Switches All CT systems have an emergency room switch and emergency system switches. Find them before you service a system. Room switch: disables the power to the A-1 contactor. System switches: Located on and inside the gantry and on the console. Disable power to X-ray generator assembly. Abort Scan immediately. Table and Gantry drive assembly
Energy Control and Power Lockout (ECPL) Equipment The ECPL equipment keeps the power from being turned on to the CT system & its component during service. Attach this lockout/tagout equipment to the A-1 contactor before you begin service procedures.
Torque Wrenches Service operations that require a torque wrench are primarily on the rotating assembly of the gantry. Use calibrated torque wrenches. The correct setting on the torque wrench ensures that you tighten the bolts correctly.
Prevention Techniques General: apply to general set-up before and during service. Specific: apply to specific hazards in a CT system
Before Service Locate the customer's room emergency switches and system emergency switches. Review procedures prior to service. Become familiar with the normal conditions on the system. Listen for unusual sounds, vibrations, lights, or odors arising from it. During Service Follow safety steps. They are usually part of the procedure. Observe the status and condition of equipment as you service each device. Use the proper tools to perform service. Substitutes can result in more hazards.
Pathogenic Hazard Prevention Ensure the customer has completely cleaned the table, head holder, accessories, and area before you perform service. Cover and protect open wounds. Wear surgical gloves when you work on a machine or an area that is questionable. Check for needles, swabs, gauze, and any other material on/in the table, floor, gantry, or console that could carry a pathogen.
Mechanical Hazard Prevention You can prevent mechanical hazards with these techniques: Secure the equipment before you service it. Use hoists, pins, blocks, or any device to secure the hazard. Properly torque all fasteners. Inspect for loose or leftover hardware, especially inside the gantry.
Electrical Hazard Prevention For electrical hazards, follow these techniques: Turn off the power to the system or a specific device before service. Use the ECPL equipment to insure there is no power going to any component. Verify power is disabled. Use a volt meter. Set up test equipment correctly. When you apply power to a device, perform the steps in the correct order and be prepared to disable power immediately.
Radiation Hazard Prevention To prevent a radiation hazard, follow these guidelines: Do not enter a room during scan procedures. If you need to be in the CT room during a scan, use leadshielded portable walls and aprons. Watch for audible and visible signals on the equipment. This indicates radiation production. Use the system emergency switch to disable power to the x-ray generator. Use the Abort Scan Button to halt X-ray.
Thermal Hazard Prevention To prevent thermal hazards, follow these guidelines: Check for heat radiating around the device prior to performing service.
Laser Hazard Prevention To prevent laser hazards, follow these guidelines: Limit the amount of time the laser beam is turned on while you perform service. Do not look into the laser beam. Do not use objects to reflect the beam toward your eyes.
Overview All major devices in CT systems contain potential hazards. Ours goal are to control the hazards. You can increase your awareness of hazards and limit the potential for accidents if you study this section. Component Hazards
Hazard Locations Factory-supplied labels mounted on the gantry, table, PDU, and operator console show the locations of possible hazards. These labels are reminders only. Over time and use, labels may become illegible or lost. Rely on your service procedures, common sense, and awareness of the equipment status and conditions
Power Distribution Unit (PDU) All points inside the PDU contain electrical hazards normal to the equipment. Click on the buttons to locate the hazards in these examples. Power Sources The incoming power to the PDU is usually 480 volts and may be distributed at 700 volts DC or 480 AC. Some systems also have a 24-hour power source that remains on even though you have turned off power to the system. Always disable the main, incoming power before you perform service to the PDU. Caution: Hospital "X-ray On" lights may also apply power to the PDU even though the main power (A1) is shut
Capacitor In systems with large capacitors, a charge will hold for several hours after the power is removed from the Capacitor. Check the manuals for procedures to discharge the capacitors.
Resistor Some systems have a large wattage resistor. When you disable the power to the unit, the resistor maintains high temperatures. Perform service when the resister is comfortable to touch.
Operator Console The primary hazard in the operator console is electrical power going to the monitors and processors. The incoming power is from 110 to 220 VAC. When needed, you may use circuit breakers in the PDU to disable power to the console.
Table or Couch Potential electrical and mechanical hazards are part of the table. Table Power The incoming power to the table is in the range of 110 to 220 volts. Disconnect the power to the table before performing any maintenance. This prevents electrical hazards and reduces the possibility of mechanical hazards, such as the table
Table Support and Movement Support You have a potential support hazard when you remove pressure springs, hydraulic cylinders, or worm screws. These hold the weight of the table. Use a device of sufficient size and strength to support the table when you maintain the vertical support hardware.
Movement Table vertical movement and horizontal cradle movement are also mechanical hazards. Do not place your hands on the table or cradle parts until they are secured properly.
Gantry Hazards The gantry includes multiple hazard types and areas. In this topic, you will learn about specific hazards you may encounter during service. Rotation and gantry sides Balance Cables Pinch points Housing, radiator, and lines Bolts and covers Power Slip rings Tilt X-ray radiation Laser beam
Gantry Rotation Hazards The rotating section of the gantry weighs at least 800 pounds and rotates up to two times per second. This requires high speed and power. The gantry rotation produces a force of four to fourteen Gs. This may cause loose components to fly off the gantry. To be safe: Disable the power to the gantry Stay clear of the sides of the gantry during rotation. Never place tools or equipment on the rotating or tilt frame.
Balance The manufacturer designed the gantry to be optimally counterbalanced. If you remove a part, the balance is disturbed. This may result in an uncontrolled partial rotation. Lock the gantry in place before removing components
Cables During service on the gantry, you may have to remove tie wraps around sets of cables. Be sure to replace the tie wraps properly to prevent the cables from catching in the gantry or producing additional damage to the machine. Trimming tie wraps with the proper tool is important so that the tie wrap itself doesn't become a safety hazard.
Pinch Points There are several pinch points in the gantry in which the rotating frame is within one inch of the stationary frame. Keep your hands and tools away from this area
Tube Housing and Lines In the normal CT environment, x- ray generation causes the tube, housing, radiator, and oil cooling lines to become hot. Check for radiant heat around these devices before you perform service.
Slip Rings Slip rings contain the electrical connections to the rotating sections of the gantry. Typically, there are protective covers over the slip rings. Once the covers are removed, the slip rings are exposed electrical conductors which have high voltage and high current, either direct or alternating. Some power slip rings hold a capacitive charge even after power is removed. Do not touch exposed slip rings because oil and salt from your hands contaminate the rings and brushes
Tilt The gas springs and hydraulic cylinders, used to control the gantry tilt, are under pressure. When you remove them, follow the service procedures and keep your hands out of the way.
Bolts and Covers Parts can become damaged during a rotation if you do not tighten the bolts correctly, as shown in this bent DAS cover. To prevent damage: Use the torque wrenches to tighten bolts Rotate the gantry manually or at low speed before you start a full-speed rotation Stay away from the gantry sides during rotation
Power The Generator may have: Incoming voltage from 200 to 480 VAC three-phase Output as high as 150,000 VAC A floating ground circuit Use the control switches & ECPL before you service any of the Gantry components
X-ray and Lasers During service and operation, x-ray radiation and laser beams may be present. When you position phantoms during image quality checks, you need the alignment indicators, which may be laser beams. To prevent eye damage, never look directly into the beam source or at a reflection of it. A potential radiation hazard comes from x-ray deflecting off an object or a patient during a scan. Radiation levels vary by system. During various procedures, such as tube warm ups, the collimator may be open. Follow the radiation safety procedures and stay out of the scanning room while the system is
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