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

4.3 Diagnostic Imaging Equipment

Diagnostic imaging equipment encompasses a broad range of technologies comprised of integrated systems of components and accessories with diverse designs, configurations, and principles of operation (Table 4.1). This diversity reflects the wide range of diagnostic tasks, clinical indications, and patient populations that imaging equipment is designed to serve, both for common diagnostic needs (e.g., identifying broken bones) as well as for highly specialized clinical demands (e.g., evaluating blood flow in specific arteries, detecting tumor spread). The MDE Advisory Committee considered the full range of imaging equipment shown in Table 4.1, with initial discussions about accessibility standards occurring within the Diagnostic Imaging Subcommittee (Table 3.2) before full Committee consideration. Although it is a diagnostic imaging device, mammography equipment was addressed initially within its own Subcommittee before full Committee consideration; the issues raised by mammography are sufficiently different that they are described below (Section 4.3). As noted in Section 3.1, ultrasonography echocardiography equipment – technologically related diagnostic imaging modalities – are portable (i.e., configured within free-standing units typically positioned next to a table or stretcher upon which the patient lies during the test). Ultrasonography and echocardiography therefore do not fall under the scope of the proposed accessibility standards.

Table 4.3

Imaging Systems Considered by the MDE Advisory Committee

• Computed tomography (CT)

• Magnetic resonance (MR)

• Single-photon emission computed tomography (SPECT)

• Nuclear medicine (scintigraphy and single photon emission computed tomography) (NM)

• Positron emission tomography (PET)

• X-ray fluoroscopy

• X-ray radiography

• X-ray interventional

• X-ray mobiles

• X-ray C-arms

• Dual-energy X-ray absorptiometry (DXA or DEXA)

• X-ray mammography biopsy tables

• PET/CT combined systems

• NM/CT combined systems

• PET/MR combined system

4.3.1 Overview of Imaging Equipment and Regulatory Environment

Diagnostic imaging equipment uses either ionizing radiation or a very strong magnetic field to produce the images used to diagnose a wide range of medical conditions, such as fractures, blood vessel blockages, various tissue abnormalities, and tumors. These machines typically involve a large capital outlay, last for many years of service, are operated by qualified technicians, and represent significant investments to health care facilities. Generally, this equipment is permanently mounted in a fixed installation within specially designed spaces that must perform specific essential functions, including supporting heavy weight, eliminating vibration, shielding ionizing radiation or magnetic fields, and having specialized high power capacity electrical service (see Section 7 for further description).

All testing using diagnostic imaging equipment is performed only under an order or prescription from a physician. Thus, before patients can have these tests, they must be evaluated by a physician, who then determines and requests the most appropriate diagnostic imaging test for the required evaluation. Diagnostic imaging equipment is operated only by trained and qualified technologists, who must be present during the examination. These technologists are present to assist patients, regardless of their physical abilities, onto the imaging equipment table and must ensure patients are properly positioned for the imaging procedure. Technologists also explain the purpose and necessary actions while they carry out the test. This equipment does not have patient “operable parts” – patients do not activate, deactivate, or adjust the imaging devices.

As described more fully in Sections 2.5 and 7.4, the U.S. Food and Drug Administration (FDA) regulates the majority of diagnostic imaging equipment as Class II medical devices, which need pre-market approval by FDA (510(k) clearance) prior to being placed on the market. The equipment must be designed and manufactured under the Quality System Regulations for medical devices, 21CFR820, which includes design controls and good manufacturing practices. An Occupational Safety and Health Administration (OSHA) credentialed Nationally Recognized Testing Laboratory must test and certify the equipment to demonstrate that it meets the basic safety and essential performance standards required by IEC 60601-1, as well as the applicable IEC 60601-1 series of collateral and particular standards. Devices that produce X-rays must also be certified by FDA as meeting the applicable performance standards for radiation safety found in 21CFRSubchapter J. The design process must include risk-management in accordance with ISO 14971. The Nuclear Regulatory Commission regulates the radioactive sources and radiopharmaceuticals used by nuclear medicine and PET equipment.

4.3.2 Transfer Surfaces and Imaging Equipment Functions

The transfer surface (table) of diagnostic imaging equipment serves two purposes: (1) it allows patients to be positioned properly to produce a high-quality image of the anatomical region of interest (with the lowest possible radiation dose for devices using radiation); and (2) imaging is conducted through the transfer surface. Thus, the transfer surface plays an integral role in the exam, is critical to achieving accurate diagnostic results, and influences radiation exposure of the patient. These requirements, combined with the diverse mechanical, electrical, and physics (e.g., functioning of magnets, electrical fields) aspects and needs of different diagnostic imaging equipment, generate a wide variety of equipment designs and configurations. These demands also place some inherent limitations on the design options for transfer surfaces or tables.

Diagnostic imaging equipment groups roughly into the following categories in terms of the functional role of the transfer surfaces, which has design implications:

• Equipment with bores, including CT, PET, PET/CT, NM, and NM/CT. Here the table plays an integral part in achieving the sub-mm dynamic positioning accuracy needed during the scan.

• Magnetic equipment that is open or has a bore. MR shares many similar aspects as equipment with bores, but has special considerations due to the very strong magnetic field.

• DXA. In DXA, the X-ray source is positioned under the patient in a fixed, known geometry; this positioning maximizes diagnostic effectiveness and minimizes radiation doses (see below).

• Conventional XR and fluoroscopy. This equipment has rectangular, radio-translucent tables that may translate in both directions in the horizontal plane.

• Mobile XR. Mobile XR can be moved to the patient and can utilize detachable detectors that often can be placed behind the patient’s anatomy to be imaged without requiring significant movement by patients.

• Interventional XR. This equipment, such as that used in cardiac catheterization/angiography suites, and “surgical” C-arms, virtually always involves patients who have been sedated to some extent prior to transfer onto the surface. After initial diagnostic evaluation (e.g., identification of location and degree of coronary artery blockages), often therapeutic interventions are performed (e.g., insertion of a stent through the catheter).

• Prone breast biopsy tables. These devices are typically used for interventional procedures such as minimally invasive image guided biopsies. Its unique design must accommodate a physician underneath the patient support surface. Since the device is used in interventional procedures, patient sedation and/or local anesthetics are commonly used. These procedures are only performed after screening mammography and/or diagnostic mammography (or another diagnostic imaging assessment) has been performed. If a patient cannot access the prone table, another potential option is an upright stereotactic biopsy system, where patients are either seated or in a side-lying position.^BB

Thus, diagnostic imaging equipment tables fall largely into two main groupings. The first group involves tables used by equipment with bores, such as CT, MR, and NM systems. These tables are generally long and relatively narrow in order to move the patient into the bore space. They are capable of adjusting with the high precision (sub-millimeter accuracy) needed for accurate diagnostic information both vertically and horizontally. These tables are typically rated for patients in excess of 400 lbs.

The second group is those tables used in X-Ray systems. These tables are also often rated for patients in excess of 400 lbs, but are wider than those used with equipment with bores and in many cases are able to move horizontally in two directions. Most current tables are not designed to adjust vertically, but some are capable of rotating to place the patient in a more vertical position needed for specific diagnostic exam.

As suggested by this technology and clinical overview and detailed further in Section 7.2, current structural requirements of specific imaging technologies have implications for the extent to which transfer surfaces on these devices can presently be height adjustable. Many X-Ray systems have imaging components such as X-Ray tubes, high voltage generators, and/or detectors located underneath the table (transfer surface). These components may, with current designs, impede lowering the table to accessible minimum heights.

An instructive example is the DXA scan (dual energy x-ray absorptiometry), used to measure bone density and identify persons with osteoporosis or osteopenia (low bone density but not yet osteoporosis). Bone loss is especially prevalent among persons with mobility disabilities who cannot perform weight-bearing exercise, such as walking or running. Therefore, access to DXA scans is critically important to a substantial subset of individuals with disabilities.

Typically, DXA scans measure bone density in the hip and spine as patients lie on a table and the scanning device – shaped like a large C with one arm passing above and the other passing immediately below the patient – travels from the hip area up to around the patient’s waist. This C-configuration, which brings the lower arm of the scanner close under the patient, minimizes the x-rays required to perform the test. Thus, the radiation exposure from DXA scans is low. However, to allow sufficient room to accommodate the x-ray technology in the lower arm of the C, the table on which patients must lie during DXA scans is relatively high off the ground. Current DXA technology cannot meet the recommended standards for height-adjustable tables with transfer surfaces at low heights.

As described further in Section 5, an issue closely related to transfer surfaces involves the positioning of supports to assist patient transfers. For diagnostic imaging equipment, patient support devices must meet applicable safety factors as delineated in IEC 60601-1. These factors typically range from 4 to 8 times the indicated weight support: for example, a transfer surface labeled to support a 500 lb patient must be designed and tested up to 4,000 lbs. This may have implications for adjustable height table design if, with current engineering methods, mechanical advantages (leverage) diminish as tables lower to lesser distances from the floor.

Notes

BB The Advisory Committee did not compare the relative effectiveness and safety of the prone breast biopsy table and the alternative upright stereotactic biopsy system to determine whether these are equivalent options for breast biopsies.

4.3.3 Imaging Equipment Used for Interventional and Biopsy Procedures with Sedated Patients

The MDE Advisory Committee viewed imaging systems used for both interventional radiology and biopsy procedures as raising special issues. Biopsies are explicitly diagnostic (i.e., biopsies provide tissue for pathological evaluation), even if they are followed by a procedure viewed as potentially therapeutic (e.g., an excisional biopsy, when an entire mass is removed). Interventional radiology includes such procedures as placement of stents in coronary arteries, opening narrowed blood vessels by dilating balloon catheters, and transarterial chemoembolization to block blood supplies to malignant tumors.
In most instances, patients undergoing these procedures receive some form of sedation prior to transfer.^CC When sedated, all patients – regardless of their physical abilities – are assisted onto the transfer surface. For this reason, the Committee viewed imaging systems used for interventions and biopsies in patients who are typically sedated as outside the scope of the accessibility standards.

Notes

^CC Patients are typically sedated to: minimize their discomfort during the procedure; and minimize their movements during procedures that often require very careful manipulation of instruments within constrained spaces (e.g., blood vessels). Patient movements in these circumstances could cause potentially life-threatening complications.

4.3.4 Industry Considerations in Designing Accessible Imaging Equipment

When considering applying accessibility standards to diagnostic imaging equipment, the MDE Advisory Committee recognized that certain constraints and performance requirements demand consideration, as follows:

• Diagnostic accuracy must be equivalent across all patients;

• Patients’ diagnostic needs and thus the clinical applications of the equipment vary widely;

• Today’s technology has certain technical and diagnostic constraints, some of which relate to basic physics or physical properties of equipment elements (e.g., magnets, Section 7.2);

• Equipment design must maintain accessibility for all patients and patient conditions.

• Accessibility standards (e.g., support equipment) must preserve the physical access of technologists to the patient;

• Equipment design must maintain infection control constraints;

• Designs must adhere to FDA and international technical standards; and

• A one-size-fits-all solution across equipment types is unlikely.

Today, it does not appear that any diagnostic imaging systems meet a minimum transfer height of 17” (see Sections 5 and 7). However, some current equipment with bore tables does lower to 18-19”. Redesign might allow some equipment (e.g., CT) to achieve a 17-19” minimum height standard. According to Committee members representing diagnostic imaging equipment manufacturers, certain aspects of redesign may take up to five years to engineer because of the technological complexities of particular diagnostic imaging systems. As described further in Section 7, most current diagnostic imaging technologies will encounter significant technical or diagnostic barriers to altering the actual transfer surface (table). Creative and alternative solutions are needed to facilitate independent transfers of individuals with disabilities.

As described in Section 7, one potential solution to improve accessibility of current imaging equipment designs are “system accessibility configurations” (referred to as “accessibility packages” during Advisory Committee discussions). However, some Committee members worried about aspects of suggested accessibility configurations, including potential safety hazards. Section 7 discusses these issues in further detail.

4.3.5 Patient Positions During Diagnostic Imaging

Finally, the vast majority of diagnostic imaging exams are conducted while patients are supine, prone, or side-lying on the table. Hence, the Committee focused much of its attention on the M301 standard (see Table 1.3.1(a)). However, given the enormous diversity of imaging equipment and the broad range of diagnostic objectives they seek to achieve, recommendations addressing M302 (diagnostic equipment used by patients in seated positions), M303 (diagnostic equipment used by patients seated in a wheelchair), and M304 (diagnostic equipment used by patients in standing position) are also relevant and were considered by the Committee.

Some nuclear medicine (NM) equipment has a unique design created for convenience: in this design, the table pivots out of the way to allow a scan of a patient seated in a chair or wheelchair. An experienced radiologist who presented to the Committee (see Section 3.3.3) indicated that in some circumstances examinations of equivalent quality may be obtained by patients who are supine on NM tables rather than sitting in chairs. Several Committee members and some radiologists expressed concerns that performing scans of patients while they remain in a wheelchair is not always appropriate and does not always produce images of equivalent quality as those obtained when patients are positioned properly on an imaging device. Therefore, the Committee used only the M301 criteria in making recommendations concerning NM accessibility standards.

Specialized MR and imaging devices using other modalities are designed specifically to scan upper and lower extremities (arms and legs). These specialized devices seat patients in chairs rather than positioning them on tables. The Committee agreed that, for these devices, the chair in which patients are seated should comply with the MDE accessibility standards recommended for chairs.

Certain X-ray exams are performed with patients asked to stand against a wall-like apparatus. In these situations, recommendations relating to M304 would apply (Section 5). Industry representatives on the Committee suggested that the standing supports would likely need to be an accessory or a mounting in the room. Additionally, these supports may also need to serve the diagnostic purpose of properly positioning the patient for the imaging tests. In these circumstances, recommendations relating to M305.3 may require adjustment to maintain diagnostic efficacy.