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

Base Support [No specific provision—affects M303.2.4]

Recommendation: The final proposal on the base support is for 1½ inch high maximum base support with additional sloping permitted at 25 inches or beyond⁴ to the gantry if needed for additional structural support.

Rationale

The base support is of fundamental importance to mammography equipment and provides structural support, seismic stability, and installation safety. It does obstruct the floor space in front of the gantry and, thus, may limit how close a wheelchair can get to the equipment. To respond to this issue, industry proposed a configuration that would allow wheelchair footrests to ride over it so it causes minimal obstruction to the floor space in front of the gantry. To discuss the maximum base support height, the sub-committee looked at anthropomorphic data regarding footrest heights. The footrest height data measures the height from the floor to the top surface of the footrest at its proximal outside corner. To determine the necessary clearance for the footrests, the subcommittee used the calculated thickness of the footrests (~0.5 inch) minus the footrest height measurement. The ~0.5” thickness is the recommendation from the data supplied by Steinfeld and D’Souza. The anthropomorphic data, as well as the calculated footrest clearances, are below in Tables 4 and 5.

Table 4. Anthropomorphic data on measured footrest heights

Table 5. Actual footrest height clearances

A maximum base support height of 1.5 inches will provide room for the structural components necessary for an effective base support design and will also be accessible by ~92% of manual chair users and over 95% of power chair users.

The subcommittee also discussed adding an allowance for a sloped region at the base of the gantry. Many of the mammography machines today also have important informational displays at the base of the gantry, on top of the base support (shown as the checkered region in Figure 9 below) that display information such as compression force and compression thickness.

Industry input on these displays cited customer feedback. The technologists felt that while positioning the patient’s breast, they were naturally looking downward, and by having the display at the base of the gantry, they could watch the compression force and breast thickness readout while positioning the patient. They suggested this location for the display as a method for improving workflow. On other machines, this region has other mechanical and electrical components that are important to the function of the equipment.

At the full committee meeting, there was extensive discussion regarding the additional sloped region. Several members felt strongly that the additional sloped region must be justified by structural stability since displays could be located elsewhere. Members commented that not all equipment has displays in this region, so it seemed possible for industry to redesign the displays to create less interference.

The subcommittee agreed on adding an allowance for a sloped region as defined by Figure 10 below. Figure 11 below illustrates this region overlaid with the anthropomorphic data.

Figure 10. Summary of base support recommendations.

Figure 11. Base support configuration in red shown over the anthropomorphic data.

Steinfeld and D’Souza supplied this chart plotting their study’s findings on the depth of participant’s footrests. The black lines show the areas with no interference between the footrests and base support interface. The black lines illustrate areas where no footrests would intrude. However, based on the technical feasibility and clinical use considerations discussed in the above sections, industry provided the overlay configuration in red. The base support configuration illustrated above is the final recommendation.

The green dots in the above scatter plot illustration represent observed values for footrest height, (on the vertical axis) and footrest depth (on the horizontal axis) measured for manual wheelchair users to the abdomen point. The footrest clearances (calculated in Table 5 above) are ~0.5” lower than the footrest heights defined here. The footrest depth is the horizontal distance from the abdomen to the distal (forward-most) edge of the footrest. The subcommittee used the data for manual chairs because manual chairs are lower than the power chairs.

Summary Figure: Figure 12 shows the final recommended component dimensions in one diagram.

Figure 12. Summary of final clearance recommendations, to be measured when the top of the breast platform is at 34”.

Notes: 

^4. Measured from the point on the floor where a perpendicular line intersects the front edge of breast platform shown in Figure 10.