Tuesday, April 15, 2008

Planning Imaging Areas (X-Ray Units Part I)

In looking at how to best parse the various imaging modalities: MRI, Nuclear medicine, Ultrasound, etc. I have decided to simply lump all of the x-ray units into one long blog entry. I think doing it this way will accomplish two things: First, it will help make a clear differentiation between x-ray and non-x-ray imaging technologies, and second, it will help to show the variations in x-ray devices. While somewhat remedial for a clinician, a medical equipment planning project will often include team members who are not as well versed in these nuances. The role of a medical equipment planner is to educate the entire design team to the technologies being used. This helps to elevate the overall level of medical planning knowledge.

An x-ray is an x-ray. But there are various types of x-ray units to address different needs. These can be broken into 2 basic groups:

1) Body part(s) to be imaged
2) Portability

When the patient can come to the x-ray unit, the x-ray device and room can be specialized to the type of study or body part. Teeth, Jaw, breast, foot, chest, etc. If the unit comes to the patient, the x-ray unit is more universal: Portable X-ray unit or Mobile C-arm. There are in fact 2 sizes of C-arm, the smaller of the 2 (Mini C-arm) typically used to image limbs (hands, wrists, feet, etc).

Specialty clinics will typically have dedicated rooms and task-specific x-ray units:
Dental office > Dental x-ray unit (Teeth)
Podiatry office > Podiatry x-ray unit (Foot)
Womens Clinic > Mammography X-ray Unit (Breast)
Cardiology Department > Cath Lab (Heart)

The more generic a department patient population, the more universal the x-ray device:
Emergency Departments and Imaging Departments usually share access to multiple imaging rooms:
General Radiographic - Skeletal system
General Rad/Tomography - 3D views of skeletal system
R&F (Radiographic/Fluoroscopic) - Video images and clips of internal structures
CT (Computed Tomography) - 3D images of structures

In addition, the ER usually has access to a portable X-ray and Mobile C-arm when the patient cannot be easily moved, or time is of the essence. More on these distinctions in later blogs...

X-rays are a form of radiation and therefore require the room to be shielded. Lead is the most common form of shielding, due mostly to its density. Using concrete or other shielding substance will greatly increase the thickness of the walls and complicate the design of surrounding rooms. The greater the throughput of the the x-ray device, the greater the cumulative amount of radiation produced. When a patient is having an x-ray, the amount of radiation given at at a single sitting is not dangerous. It is the cumulative exposure over time that is dangerous. Each of us can go in for dental x-rays, a routine chest x-ray, or a visit to the ER if we sprain or break something. These infrequent exposures represent no health risk to us.

The rooms are shielded for the protection of those who work in the vicinity of the room. The offices, exam rooms, conference rooms and staff work areas.

A patient may receive a series x-rays (Usually 1 - 8, but can be more) in a single sitting. The x-ray tech may see 3 - 4 patients per hour over an 8 hour shift. So that would be over 200 exposures per day. Without the lead shielding, the clerk who sits at the desk on the adjacent wall or the family members sitting in the waiting room across the hall would be exposed to these very large cumulative doses. So we are shielding the people who are working, visiting or being cared for in the adjacent areas.

Radiation scatters, so think not only about the 4 walls, but also the floor and ceiling. A licensed physicist will calculate the amount of shielding required, but typically every x-ray room can be shielded with a simple 1/8 inch leaded sheet rock. The critical factor is the installation. Joints, corners, and punch outs need to be installed correctly to avoid any leakage.

The source of all x-rays is an x-ray tube. The tube is housed in an articulating arm, (wall, table or ceiling mounted) or within the unit itself. The other components of an X-ray unit have a specific purpose related to: patient positioning, power generation, or image acquisition.

Patient positioning. X-rays produce images because they pass through bone, tissue and fluid at different rates. Dense structures appear in white and less dense appears in black on the image. The goal of patient positioning is to make the x-rays pass through the patient in a path that will have the least interference to the structure the radiologist wants to view. If you have ever shifted, moved, or repositioned yourself to get a better view of something, you have been "positioning". So standing, laying down, sitting, or otherwise being contorted into the "ideal" position to yield the best image of a bone, organ or structure the radiologist wants to read. The table is the most basic positioning device. These can tilt up, side to side and telescope to allow the technician to move a patient into the ideal position. This articulation requires ample room.

When a design team takes a "department tour" you typically see an imaging table in its flat position. Here is a unit articulated up to a 90 degree position:

Think of a swiss army knife in your pocket. Then think of it with every blade and tool extended. The x-ray room needs to accommodate the table in all of its various extensions. So when you do a walking tour of the department and see the table in its "closed" position, you may not get a sense of the space it needs to move around within. I find that 1 in 5 departments I have visited had at least 1 room with a conflict between the range of motion of the imaging table and 1 of the walls or cabinets.

Power Generation. X-ray tubes require a lot of energy. Most will require a dedicated 480v feed into the power cabinet. From there, the vendors equipment usually steps down the power required for the various other system components - electronics, table, x-ray tube, control panel, etc. There may be floor trenches, wall ducting and cable trays to distribute the power and data lines. Every vendor is a little bit different, so a vendor site-specific drawing is critical to ensure your room is adequately sized and designed. The problem is that technology evolves so quickly and manufacturers have a tendency to leap frog one another every year or so, it is difficult for an administrator or department head to commit to the exact manufacturer and model more than just a few months in advance. This typically leaves the design team and contractor with a dilemma. How to complete the room on schedule. The best alternative I have found is to skip the room until the PO for the X-ray unit is issued. Yes, pouring the floor, working in the ceiling, and hanging leaded dry wall will add some punch list items to your project. But, it will be cheaper than tearing out walls, ceiling and cutting/breaking out new troughs.

Image acquisition. Image acquisition is simply the process of capturing an x-ray image. Traditionally, a film cassette is placed behind the patient. The X-ray tube generates a burst of x-rays that pass through the patient and into the x-ray film cassette. The x-ray film captures the image. The film cassette is placed in a "bucky" or simply leaned up against the patient. A bucky is a device that holds the x-ray film cassette. Today, there are digital x-ray units that have almost eliminated the need for film. The x-ray image is captured digitally in a receptor and processed directly into an image (DR or Direct Radiography) or the image is captured on a phosphorous plate that is read in a "Plate Reader". Think of a phosphor plate as a high-tech "Etch-a-sketch".

The plate reader converts the image into digital format, then clears the phosphor plate. These plates are re-used many times before needing to be replaced.

Here is a wall bucky:

Here is a plate reader:

Here is a laser imager:

The plate readers and laser imagers are now an integral part of the image acquisition process. Fewer and fewer "wet processing" systems are in use. "Wet processing" is the catch-all term for traditional x-ray film processing that involves the use of chemicals (developer & fixer) and film processors in a dark room.

No less important in all of this is the image viewer. The image viewer is a high definition computer monitor. It displays the x-ray image and allows the operator to zoom, edit and make adjustments to make the image much easier to view. These have taken the place of x-ray view boxes (Illuminators), which were used to view hard copy x-rays.

Here is a PACs Viewer (Top) and PACS reading station (Bottom):

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