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

5.8.2.4 Unobstructed Floor Space Recommendation

The Committee recommends the unobstructed floor space in front of the base support be a minimum of 17 inches deep.

Rationale for the recommendation

The overall knee and toe clearance and unobstructed floor space dimensions dictate how close a patient in a wheelchair can get to the mammography equipment. As was discussed above, the Committee considered anthropomorphic data that defined knee and toe clearances from a person’s abdomen. To consider overall knee and toe clearance, the Committee used female-only anthropomorphic data that defined abdomen-toe depths to ensure that a patient’s toes would not hit the gantry. To consider unobstructed floor space, the Committee used anthropomorphic data that defined abdomen-caster edge depths to ensure that the front caster wheels on a patient’s wheelchair would not hit the front of the base support.

The base support affects how close the patient can get to the mammography machine because it intrudes into the floor space. The purpose of the base support is to eliminate any instability caused by the weight of the cantilevered c-arm. Moving the c-arm further away from the gantry would increase the overall knee and toe clearance, but would also require an increase in the size of the base support in order to stabilize the equipment. The simultaneous increase in the size of the base support will minimize any gains from increasing the knee and toe clearance, since the base support obstructs the floor space. The Committee considered this balance when making final decisions about overall knee and toe space and unobstructed floor space.

While discussing these issues, the Committee also considered positioning methods for patients using wheelchairs. During a mammography procedure, the patient’s chest is flush with the front edge of the breast platform and the technician positions the patient’s breast on the breast platform. In order to image as much of the breast as possible, patients cannot be seated in the “natural” sitting position. They will need to sit up straight in order to situate as much breast tissue as possible on the breast platform. For patients seated in a wheelchair, a common positioning technique is to place towels, pillows, or other positioning aids behind the patient’s back in order to sustain an upright pose during imaging. This upright pose is necessary regardless of how close the patient can naturally get to the breast platform. The pose reduces the abdomen-toe and abdomen-caster edge dimensions by a couple of inches.

To accommodate 95% of female wheelchair users, the anthropomorphic data shows that 30.5 inches and 19.5 inches are the necessary minimum overall knee and toe clearance and unobstructed floor space dimensions, respectively. [Data is below in Tables 5.8.2.4(a) and 5.8.2.4(b)]. Members agreed on reducing these dimensions by 2.5 inches to adjust for the upright pose and to ensure technical feasibility and equipment safety. The final Committee recommendation is to require a minimum of 28 inches overall knee and toe clearance and a minimum of 17 inches unobstructed floor space. Looking purely at the anthropomorphic data, these dimensions accommodate 80% - 90% of the population. In adjusting for the needed upright pose, the dimension works for 95% of the population. Members recognized that these dimensions are an optimal blend of accessibility and technical feasibility .

Table 5.8.2.4(a). Abdomen Depth Data^vii to determine overall knee and toe clearance

Table 5.8.2.4(b) Abdomen-Caster Edge Depth^vii to determine unobstructed floor space 

Section 5 References

vii D’Souza, Steinfeld. “Revised Knee Clearance Depth and Footrest Clearance dimensions for sizing of mammography equipment.” Memorandum. April 23, 2013.