Computed Tomography

CTContributors to this section include Stefan Novosel, Kate Renner, Andrew Petty, Andrew and Frank Zilm

Initially called computerized axial tomography (CAT) and still known among much of the public by this name, this technology is now called computed tomography (CT) by virtually all medical staff and professionals.

Computed tomography is an x-ray technique which generates cross-sections through the body. This eliminates the superimposition problem of standard radiographs, where structures are hidden behind others. The patient lies on a table that is moved into the center of a gantry, in which an x-ray source and a detector revolve opposite one another. In this way, information about the patient’s body in the axial plane is obtained. Sophisticated computer programs are used to translate the collected data into not only transverse section (axial plane) images, but images in other planes (coronal and sagittal) or even three-dimensional images as well. CT scans depend on the differing absorption (attenuation) of x-rays in different tissues, just as radiographs do, however the resolution provided by CT is much higher than that of standard radiographs. Conventional CT technology produced cross-sectional images one at a time in much the same way as radiographs are produced. Newer technology uses a helical scanning technique in which the patient is continuously scanned as the bed they lie on is steadily moved through the gantry; this produces a stream of images from which a three-dimensional digital model of the structure of interest can be produced. Multislice CT scanners represent the most recent area of innovation in the technology, providing significantly greater resolution and shorter scan times; this translates into less time patients need to hold their breath to avoid producing motion artifacts in the images, as well as enabling near freeze-motion views of the entire body. The most recent CT scanners can capture 256 slices at once. These short scan times make CT viable for guiding some procedures instead of fluoroscopy.

CT technology is significantly more expensive than radiography or fluoroscopy and, while its applications are increasing, it is still found mostly in hospitals or specialized imaging centers. CT is used to image a wide variety of bodily structures, and may be used for further investigation following a radiograph.

CT is increasingly replacing more invasive exploratory measures, but x-ray exposure is a greater concern with CT than with radiography or fluoroscopy. While different scans result in widely varying exposure levels and innovations have also led to decreasing exposure by optimizing the scan, the desire for higher resolution or more sophisticated scans means CT is still regarded as typically moderate to high exposure. This is a special concern for pediatrics.

Space Requirements

Based on a research study* that included 19 facilities throughout the United States with a total of 33 CT imaging exam rooms,
33 rooms/19 facilities = 1.737 rooms/facility on average

For the patient imaging room alone, without control area:
Average area = 388 square feet
Largest area = 486 square feet
Smallest area = 299 square feet

For the patient imaging room with control area:
Average area = 504 square feet
Largest area = 636 square feet
Smallest area = 335 square feet


Functional and Space Requirements

GE CT Typical The GE CT typical Specifications recommend a 336 square foot imaging room with a 208 square foot control room with a lead glass window(image on right). This space should have a 9' ceiling height and a 44" wide by 83" high door frame.



Discovery VCT Room

The GE PET CT specifications recommend 430 square feet (not including the control room and other support spaces), a 133 square foot control room with a lead glass viewing window, an 9' ceiling height and a 44" wide, 83" high door frame to accommodate the Discovery VCT imaging machine.


*Study of imaging department research areas conducted by principal investigators,

David Allison, AIA, ACHA, Professor/Director of Architecture+Health at Clemson University
D. Kirk Hamilton, FAIA, FACHA, Adjunct Professor at Texas A&M University
Frank Zilm, D.Arch, FAIA, FACHA, of Frank Zilm & Associates

with the aid of graduate student investigators,

Megan Gerend of Clemson University
John Grant of Texas A&M University
Scott Weinhoff of Clemson University

and sponsored by,

Academy of Architecture for Health Foundation
American College of Healthcare Architects
Frank Zilm & Associates
McKahan Planning Group, Inc.

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