May 18, 2009

All Grids Are Not Created Equal
By Leo Reina, RT
Radiology Today
Vol. 10 No. 10 P. 8

Antiscatter x-ray grids are unsung heroes of radiography. They play a critical role in the imaging chain. However, few medical professionals actually consider quality when selecting an x-ray grid supplier for their departments. As economic pressures continue putting a financial strain on radiology department operating budgets, it can be easy to neglect the importance of grid quality when making purchasing decisions. That decision can negatively affect patient care and diagnosis. This article seeks to clarify how antiscatter grid composition, assembly, and manufacturers’ quality systems should be key considerations when selecting x-ray grid suppliers.

Grid Composition
The primary function of antiscatter grids is to absorb scatter radiation emitted by body tissues before reaching the film/IP plate in order to increase image contrast and detail. Generally, grid use is recommended when the anatomy to be x-rayed exceeds 12 cm in thickness or if exposure settings exceed 70 kVp.

There are two types of antiscatter grids: aluminum-interspaced, aluminum-covered grids and fiber-interspaced, carbon-covered grids. Both grids are interspaced with scatter-absorbing lead strips. There are positives and negatives to both types of grids. The focus here is not on aluminum vs. fiber material but the quality of the components used by manufacturers.

To create a high-quality grid, the raw materials must be of superior quality and handled in such a way as to prevent damage during the assembly process. The quality of the lead foil, cut from large rolls, is critical for effective scatter cleanup. Poor quality lead or inconsistent lead thickness can create film density differences, grid artifacts, or other imaging anomalies. High-quality grid manufacturers inspect each roll for variables such as lead thickness, purity (absence of pollutants such as grease), and surface conditions (eg, pinholes, dents, ridges).

Aluminum source material must similarly be congruously free of defects. Meticulous inspection of source material throughout the assembly process must be performed to make a product worthy for radiographic use. Material and quality control is time intensive and costly. Some manufacturers may not invest as heavily in these processes.
Tolerance levels are even tighter for fiber-interspaced grids. These grids, which have the highest level of x-ray transmission yielding the lowest dose, are precision manufactured medical devices. Low-quality fiber-interspaced grids are easy to spot: Before putting the grid to use, just look for the artifacts in the test film.

Grid Assembly
The grid assembly process is critical to the overall quality level of the final product. Grids undergo several manufacturing processes, including bonding, shearing, angling, cutting, milling, and covering. All steps require tools designed specifically for these processes. However, precision tooling is expensive. The degree to which a manufacturer invests in its tooling and processes is reflected in the quality of its finished goods. This can be easily seen by consumers and evidenced by taking test films of grids purchased from various manufacturers and subjecting them to simple flat-field radiographic testing. Companies with precision manufacturing will make grids that test consistently and evenly in flat-field studies.

Quality Control in Manufacturing
Quality programs are comprehensive, enterprisewide quality monitoring systems and essential for manufacturers of antiscatter grids. Quality regulations such as ISO 13485 and the FDA Current Good Manufacturing Practice (21 CFR Part 820) apply to grid manufacturers.

Expensive to establish and maintain, quality programs are audited by external sources on a routine schedule to retain compliance or certification status. During audits, every aspect of the organization is examined, from front-office policy to manufacturing quality controls. Only companies with steadfast procedures and well-trained staff can maintain quality programs such as ISO 13485. Before buying grids, investigate the compliance standard of each potential supplier. Be sure that they meet at least the minimum regulatory standard for your area. (Grids are class 1 medical devices in the United States and class 2 in Canada.)

Great consideration should be taken when replacing or purchasing new grids. Whether they are installed into radiographic equipment or used during bedside portable examinations, selecting a grid should be more than just a price decision. Grid manufacturers provide products of varying price and quality standards. Thus, important questions to consider before buying a grid include the following:

• How are grids tested prior to shipment?

• Can the manufacturer provide proper documentation to ensure that the grid specifications are the same as the label on the product?

• Willful or accidental mislabeling is unacceptable.

• Is the manufacturer an FDA-registered medical device manufacturer? Can it provide a registration number? Do not assume that the dealer has scrutinized the manufacturer prior to offering their wares.

• Does the manufacturer comply with the principles of an ISO 13485 quality system?
If you receive grids from a supplier and are unsure of the quality of the workmanship, consider having a medical physicist qualify your grids.

At first glance, grid products may appear to be the same, although prices vary. The informed purchaser knows that performance and image quality cannot be sacrificed for the benefits of short-term cost savings. Ultimately, the benefits of high-quality grids outweigh additional up-front costs.

— Leo Reina, RT, is founder, president, and CEO of X-Ray Cassette Repair Company, Inc, which does business as Reina Imaging. The author would like to give special thanks for contributions to this article from Dunlee (Aurora, Ill.), and Smit Röntgen (the Netherlands), divisions of Philips Healthcare, and Jungwon Precision Ind Co, Ltd (Seoul, Korea).