Siting a gamma camera: floor loading, power, cooling and the commissioning sequence
What has to be true about a room before a gamma camera can be delivered into it: structural checks, delivery route survey, power quality and earthing, cooling and humidity control, cable routes and a commissioning order that protects the hospital.
A gamma camera arrives in a crate that does not fit through a standard hospital door, weighs more than the lift was designed for, and is scheduled to be unloaded from a truck that cannot get into the lane. None of this is a surprise to anybody who has done an installation, and all of it is a surprise to most hospitals the first time, because the site preparation work happens months before the equipment exists as far as the clinical team is concerned.
The site planning document is the specification
Every manufacturer issues a site planning pack for the specific configuration you bought. Get it at contract signature, before the room is chosen, and issue it to the civil contractor as a contract document rather than as background reading. If the contractor has not priced against it, the contractor will not build to it.
Room dimensions, including the clearances needed for gantry rotation and couch travel at their extremes, not the average.
Floor loading figures: total mass and, separately, the point load under each mounting foot.
Floor flatness and level tolerance across the equipment footprint.
Electrical supply requirements, earthing requirements and the acceptable variation on the supply.
Heat output, which sets the cooling load, and the acceptable temperature and humidity range.
Cable route sizes, duct positions and the separation required between power and signal runs.
Service access clearance, which is the dimension most often lost when somebody decides to build a store cupboard into a corner of the room.
Read the service access clearance twice. A camera installed hard against a wall works perfectly until the first detector service, when the engineer cannot open the cover and the hospital pays to move the wall.
Floor loading and structure
Two numbers matter and they are not the same number. The total mass tells you about the distributed load on the slab. The point load under each foot tells you whether the slab will punch through locally, and it is the one that fails. A floor that carries a ward full of beds comfortably can still be inadequate under a concentrated gantry load.
Have a structural engineer check the actual slab against the site planning figures, with the reinforcement drawings if they exist. In a conversion where the drawings are missing that means a physical investigation, and it takes time. Start it early.
Check the route as well as the final position. A crate on a pallet truck concentrates its load on small wheels and imposes a higher local load in the corridor than the camera does in the room. Corridors over car park voids are where this goes wrong.
Two further structural points. If the room is on an upper floor, the shielding walls add dead load on top of the equipment load and the two are assessed together. And where the site plan states a floor flatness tolerance, treat it as a real constraint: a gantry that cannot be levelled within its adjustment range means re-screeding a floor after the epoxy has been laid.
Getting the crate in
Survey the route from the truck standing position to the room, measuring every door width and height, every corner, every ramp and every threshold, and record it with photographs.
Check the lift against crate mass and crate internal dimensions, and check the lobby turning circle at both ends. A lift that takes the mass but not the length is a common finding.
Confirm the truck can physically reach the unloading point at the time of day the delivery is scheduled. A narrow lane, a market that sets up in the morning and an overhead cable at the gate are all real constraints in Dhaka and none of them appear on the hospital drawing.
Agree in writing who removes and refits door leaves and frames, and who makes good afterwards.
If the route fails, plan a temporary wall opening and get it into the civil scope early, with the reinstatement priced at the same time.
Agree a crate storage location on site in case the room is not ready: dry, secure, guarded, at ground level, and not under anything that carries water.
That last point is where projects lose equipment. A crate left in a corridor beneath a leaking air conditioning condensate drain through a monsoon week becomes a warranty argument that nobody wins, and the hospital is the party with the least bargaining power.
Power quality, earthing and the UPS
Bangladesh supplies 230 V single phase and 400 V three phase at 50 Hz, and the nameplate is never the problem. The problem is what the supply actually does over a working day, and imaging electronics fail on the transients rather than on the outages.
A dedicated feeder from the panel. Nothing else on the circuit, and specifically no lifts, no motors, no air conditioning compressors. Shared circuits are how a camera acquires an intermittent fault that only appears at certain times of day.
A servo controlled voltage stabiliser sized for the equipment plus its stated inrush, not sized for the room. Undersized stabilisers are common and they fail closed, passing the fluctuation straight through.
A dedicated earth pit for the imaging equipment, with the resistance measured and recorded at handover. Re-measure it annually, because earth resistance rises through the dry season as the ground dries out, and a system that was fine in September can be marginal in March.
Neutral to earth voltage measured before the engineer arrives. A high neutral to earth voltage causes image artefacts and network faults that get blamed on the equipment for weeks.
A UPS sized for the console and detector electronics, with enough runtime to complete an acquisition in progress, ride through a generator changeover and perform a controlled shutdown. It is not there to let you keep scanning through a four hour outage.
Surge protection at the panel and at the equipment, coordinated rather than duplicated, and inspected after every significant event.
Generator changeover behaviour understood in advance. An open transition changeover puts a break and then a surge onto the line. That transient, repeated several times a day, is what ages imaging power supplies.
The pattern that damages a camera here is not the long outage everybody plans for. It is the repeated short interruptions and the switching transients around them.
Air conditioning and humidity
Size the cooling against the heat output in the site planning document plus the lighting, the staff and the solar gain on any external wall. Then provide redundancy the sensible way: two units each capable of holding the room on its own, rather than one large unit with nothing behind it. A single unit means a compressor failure stops the department until a spare arrives.
The room has to be conditioned continuously, overnight and at weekends. This is the recommendation hospitals most often decline on cost grounds, and it is a false economy by a wide margin. A sodium iodide crystal assembly is sealed against moisture, but seals age, and what ages them is repeated thermal cycling combined with high ambient humidity. The electricity saved by switching off the air conditioning at night for a year does not approach the cost of a crystal.
Condensation is the specific monsoon failure. The room is cooled hard, the air conditioning trips or is switched off during a changeover, warm humid outside air enters through a door or a poorly sealed duct, and moisture condenses on cold electronics. Keep the room envelope sealed, keep door discipline, and put the air conditioning on the essential supply so that a changeover does not stop it.
Install a temperature and humidity logger in the room and keep the record with the QA file, so that an environmental cause can be proved or ruled out when a fault occurs.
Route condensate drains away from the gantry, the console and any cable duct. Never above the equipment.
Seal duct penetrations through shielded walls properly, both for shielding integrity and to stop humid air tracking in.
Cable routes and the console position
Ducts and trunking installed to the site plan and laid before the floor finish goes down. Cutting a chase through a cured epoxy floor means relaying the floor.
A pull cord left in every duct, so that the next cable does not become a civil works job.
Separation maintained between power and signal runs along the whole route, not only where it is convenient.
Console positioned with a clear sight line to the patient through leaded glass, and a door that does not open into the operator's chair.
Network drops for the acquisition workstation and the PACS link, plus at least one spare, terminated and tested before delivery.
The commissioning sequence
Civil and shielding works complete, with walls inspected and photographed before they were closed.
Power, earthing and air conditioning energised and running stably for a period before delivery, with voltage, earth resistance, temperature and humidity readings recorded over that period.
Radiation survey of the room and regulatory submission progressed as far as the licence route requires.
Delivery, unpacking and mechanical installation, with the crate condition photographed on arrival.
Vendor calibration, detector tuning and system configuration.
Acceptance testing against the purchase specification, witnessed by the hospital's medical physicist, with raw data retained by the hospital.
Baseline QA measurements recorded and filed as the reference set for the life of the system.
Staff training on the hospital's own protocols using the department's own phantoms, with attendance recorded.
Handover pack: manuals, as-built site plan, electrical and earthing test records, acceptance data, spare parts list and service escalation path.
Do not let acceptance become the vendor engineer showing a good looking flood image on the console. Acceptance is a measurement against the specification the hospital paid for, taken by the hospital's physicist, with the numbers written down and signed. It is also the last point at which the hospital still has any real bargaining power.
A readiness checklist to hand to the contractor
Item
Ready means
Signed off by
Room dimensions and clearances
Measured on site against the site plan, including door swing and service access
Project engineer
Floor
Load checked against point and distributed figures, level within tolerance, finish laid and cured
Structural engineer
Shielding
Installed, inspected before closing, photographed at every seam and penetration
Medical physicist
Power
Dedicated feeder, stabiliser, UPS and surge protection installed and load tested
Electrical engineer
Earthing
Dedicated pit, resistance measured and recorded, neutral to earth voltage measured
Electrical engineer
Air conditioning
Running continuously with temperature and humidity logged for a period before delivery
Facilities
Ducts and cable routes
Installed, clear, pull cords in place, network drops terminated and tested
Project engineer
Delivery route
Surveyed end to end, obstructions removed or scheduled, lift capacity confirmed
Project engineer
Regulatory
Licence application filed, shielding design and survey reports submitted
Radiation safety officer
Circulate that table at the project meeting every fortnight from contract signature. The items that are still blank eight weeks before the delivery date are the ones that will move the delivery date.