Recommendations on Standards for the Design of Medical Diagnostic Equipment for Adults with Disabilities, Advisory Committee Final Report

7.2 Technological and Scientific Considerations

As described in Section 4.3.2, some types of current diagnostic imaging equipment present serious technical, scientific, and design impediments to improve accessibility of the height of machines’ transfer surfaces, mounting of transfer supports, and/or spaces for portable lifts. For example, today’s DXA and certain x-ray systems cannot be height adjustable due to the functional operation of the equipment (Section 4.3). Two types of imaging equipment with bores offer examples of technical concerns that can affect transfer surface height and other access considerations:

• For magnetic resonance imaging (MRI), the resolution of the images is proportional to the magnetic field strength. The magnets used for MRI scanners are usually solenoidal: a long cylinder with an inside diameter that must accommodate the patient. Most MRI devices today have magnetic fields of 1.5 T (Tesla) and greater. These large magnetic fields can only be achieved with superconducting magnets, which require cryogenics to maintain liquid helium temperatures. Such cryogenics necessarily take up space, but the precise amount of space needed is a matter of engineering. With the trend to go to larger magnetic fields of 3 T and higher to produce higher-resolution images, it is likely that the space requirements might increase in the future. Nonetheless, the Committee noted it is technically feasible for MRIs to lower to accessible heights.

• In contrast, the imaging device of computed tomography (CT) is approximately an annulus (or ring) with an internal diameter sufficient to accommodate the patient. The imaging works by rotating an x-ray tube and detector around the annulus or 360 degrees around the patient, imaging cross-sectional slices that are arranged longitudinally. The need for the rotating imaging places engineering constraints on the size and height of the device. It is currently possible for some CT devices to lower to 18” to facilitate transfers.

Additionally the transfer surface of these imaging devices, the patient table, plays an integral role in achieving the systems’ diagnostic purpose. The tables are necessarily included in the image plane and in many cases must provide sub-millimeter positioning accuracy while being designed to still safely support very large patients (e.g. greater than 450 lbs).

Some features of imaging equipment design affecting height may change in the future. Advisory Committee members repeatedly urged the accessibility recommendations to look forward and motivate this change. To the extent, however, that future imaging technologies continue to rely on specific modalities or energy sources – such as magnetic fields and x-ray tubes and detectors – fundamental laws of nature and physics might constrain or circumscribe what is feasible in adjustability of transfer surface heights.

Other features of current imaging technology design might affect accessibility. For instance, some x-ray tables require bi-directional horizontal movement to generate the specific image required for diagnostic purposes. Many tables, especially in equipment with bores, move into and out of the bore while producing images of the anatomical region undergoing diagnostic evaluation; these tables may have both moveable and stationary components. In these situations involving current technology, supports to aid transfers might not be feasible to attach to the table for several reasons including: lack of structural integrity on the side where the support is affixed; other structural problems, such as compromised tubing and other equipment components; risks of patients being caught in a tableside support; and impeded access of radiology technicians and other clinical staff to patients during the imaging study, such as for administration of imaging agents, providing other drugs, and monitoring patients.