Minimizing Patient Exposure Part 7: Grids

In the world of diagnostic radiology, image quality and patient safety must coexist in every decision made by the technologist. While collimation, filtration, and receptor selection all play critical roles in radiation protection, one often misunderstood tool in the imaging chain is the grid. Primarily used to improve image contrast by reducing scatter radiation, grids can also influence patient dose in ways that require careful management and expertise.

In this post, we will explore:

1. What grids are and how they function

2. When and why grids are used

3. How grids impact patient dose

4. Strategies to use grids wisely in support of ALARA principles

What Is a Grid?

A radiographic grid is a device composed of alternating strips of radiopaque material (typically lead) and radiolucent interspaces (often aluminum or plastic). These strips are aligned to allow primary x-ray photons to pass through to the image receptor while absorbing scatter radiation, which travels at oblique angles.

Scatter radiation occurs when x-rays interact with patient tissue and are deflected from their original paths. This scatter does not contribute useful information to the image and instead reduces contrast, making it harder to distinguish between soft tissues or subtle pathology.

By removing scattered photons before they reach the receptor, grids improve image contrast and diagnostic clarity. However, grids also absorb some of the primary beam, which means that more radiation must be used to compensate—a factor that directly affects patient dose.

Grid Ratios and Their Effects

Grids are characterized by their grid ratio, which is the ratio of the height of the lead strips to the distance between them. Common grid ratios include 5:1, 8:1, 10:1, 12:1, and even up to 16:1. Higher grid ratios are more effective at absorbing scatter—but also require higher exposure to maintain adequate image receptor signal.

• Low-ratio grids (5:1 to 8:1) absorb less scatter and require a smaller increase in exposure.

• High-ratio grids (10:1 to 16:1) provide greater contrast improvement but demand significantly more radiation to achieve the same image quality.

Another factor is grid frequency, or the number of lead strips per centimeter. Higher-frequency grids are more aesthetically pleasing on digital images (as they reduce visible grid lines), but like high ratios, they can increase dose requirements.

Therefore, selecting the appropriate grid involves a trade-off: How much scatter needs to be removed versus how much additional dose is acceptable?

When Should Grids Be Used?

Grids are not required for every radiographic exam. Their use is generally reserved for:

• Body parts thicker than 10–12 cm

• Exams using higher kVp techniques (typically > 70 kVp)

• Abdominal, pelvic, and chest radiography

• Portable chest exams with mobile x-ray units

The thicker or denser the tissue, the more scatter is produced. For example, a lateral lumbar spine image or a portable AP abdomen often produces significant scatter, warranting the use of a grid to maintain diagnostic contrast.

However, grids should be avoided in situations where:

• Patient dose must be minimized, such as in pediatric imaging

• The anatomy is thin and produces little scatter

• Digital post-processing can sufficiently enhance contrast without grid use

Grids serve a valuable function, but they must be used selectively and knowledgeably to avoid unnecessary dose escalation. In the next section, we’ll break down how technologists can reduce dose even when grid use is necessary, and how alternatives like air-gap technique can serve as dose-saving strategies.

How Grids Affect Patient Dose

While grids improve image quality by removing scatter, they do so at a cost: increased radiation dose to the patient. Because a grid also absorbs part of the primary beam, more x-ray photons must be generated to achieve sufficient image receptor exposure. This typically requires the technologist to increase mAs, which directly increases patient exposure.

The Dose Multiplier Effect

The amount of dose increase required when using a grid is not negligible. Depending on the grid ratio:

• A 5:1 grid may require 2× the dose compared to a non-grid exposure.

• A 12:1 grid can increase dose by up to 4×.

The higher the grid ratio, the greater the increase in required mAs. Therefore, indiscriminate use of high-ratio grids not only violates ALARA but also negatively impacts patient safety, especially when low-ratio alternatives or non-grid options are viable.

This makes it essential that technologists are aware of:

• The type of grid they are using

• The increase in exposure it necessitates

• Whether grid use is clinically justified for a given exam and patient

Strategies for Using Grids While Minimizing Dose

Grids should never be used blindly. Instead, their use must be part of a dose-conscious imaging strategy. Below are practical ways to optimize their benefit while controlling exposure.

1. Use the Lowest Effective Grid Ratio

Unless extremely high contrast is required, lower grid ratios (such as 8:1 or 10:1) are typically sufficient for most body parts and exam types. These grids still reduce scatter effectively but require less additional exposure than higher-ratio models.

2. Consider Grid Removal for Small or Thin Patients

In smaller patients, especially in pediatric imaging, the amount of scatter produced is significantly lower. In these cases, grid use is often unnecessary and can lead to unjustified increases in dose. For children or small adults, removing the grid and using tight collimation, proper positioning, and post-processing adjustments is often more effective and safer.

3. Tight Collimation Reduces the Need for Grids

The more x-ray beam area is confined to the region of interest, the less scatter is produced. Tight collimation serves two purposes:

• It reduces overall patient exposure by limiting the irradiated volume.

• It decreases scatter, which can reduce or eliminate the need for a grid in borderline cases.

Collimation is an especially important alternative when working with non-grid exams like extremities, mobile x-rays, or pediatric imaging.

4. Proper Positioning Is Crucial

Improper positioning or misalignment with the grid can lead to grid cut-off, where portions of the image are underexposed due to absorption of the primary beam. This results in either:

• A non-diagnostic image that must be repeated, increasing patient dose.

• A compromised image that could affect diagnosis and care.

Technologists must ensure that:

• The x-ray beam is centered properly to the grid.

• The correct SID (source-to-image distance) is used.

• The grid is aligned with the central ray and anatomy.

The Air-Gap Technique: A Grid Alternative

One lesser-known method to reduce scatter without a physical grid is the air-gap technique. This approach involves increasing the distance between the patient and the image receptor, allowing scattered photons to diverge away from the receptor before they can be recorded.

Benefits of the air-gap technique:

• Reduces scatter reaching the image receptor

• Improves contrast without increasing dose as much as a high-ratio grid might

• Eliminates the need for a physical grid, especially in lateral cervical spine or cross-table exams

The air-gap technique is especially useful in mobile or trauma settings where traditional grid use is limited or impractical.

Grids in Portable and Trauma Imaging

Portable radiography and trauma scenarios present unique challenges. Often performed at the bedside or in the ER, these procedures typically involve thicker anatomy and high scatter environments. While grids are commonly used to improve image quality in these settings, their application must still follow the principles of justification and optimization.

When to Use Grids Portably

• AP abdomen, chest, or pelvis exams with limited ability to collimate or position.

• Large or bariatric patients where scatter volume increases significantly.

• When high diagnostic detail is essential, and contrast would otherwise be degraded.

Even in portable settings, the following precautions should be taken:

• Use grid cassettes with appropriate ratio and frequency.

• Verify SID and beam alignment to prevent grid cut-off.

• Avoid grid use in smaller or pediatric patients unless clinically indicated.

Technologists must exercise judgment: in mobile exams where patient positioning is compromised or anatomical detail is not as critical, skipping the grid may reduce dose without compromising diagnostic value.

Digital Imaging and Grids: A Modern Balance

Digital radiography (DR) systems offer advanced image processing capabilities that can enhance contrast even when no grid is used. This raises an important question: Are grids always necessary in digital imaging?

The answer is nuanced.

Benefits of Grids in DR

• Even with powerful post-processing, scatter still degrades raw data before it reaches the receptor.

• Grids improve the signal-to-noise ratio, especially in exams involving large body parts or high kVp techniques.

Challenges in DR

• DR’s wide dynamic range can hide overexposure, leading to “dose creep”.

• Technologists may rely on software to “fix” poor contrast, rather than optimizing technique or limiting grid use.

The best approach? Use grids only when needed, and rely on the combination of:

• Good positioning

• Tight collimation

• Correct exposure factors

• Sensible use of digital enhancements

This strategy honors both the technical advantages of DR and the safety principles of dose reduction.

Pediatric Imaging and Grid Avoidance

In pediatric radiography, avoiding unnecessary radiation is a top priority due to the increased radiosensitivity of developing tissues. Most pediatric protocols omit grid use, even for thicker anatomy, because:

• Children produce less scatter than adults.

• Pediatric anatomy is typically thinner, making contrast loss less pronounced.

• Grid use increases dose without significant image quality benefit in many pediatric exams.

Instead, dose management in pediatric imaging focuses on:

• Optimized technique charts tailored to size and age.

• High-sensitivity digital receptors that perform well without grids.

• Dedicated pediatric protocols with preset exposure and post-processing parameters.

By following these principles, technologists can produce high-quality pediatric images with minimal exposure—and without the need for a grid.

Conclusion: Grid Use with Purpose and Precision

Grids are a powerful tool in radiographic imaging—but with great power comes great responsibility. When used correctly, they enhance image contrast and ensure diagnostic clarity. When misused or overused, they needlessly raise patient dose and contradict the core values of radiologic safety.

The key to responsible grid use lies in:

• Knowing when grids are truly needed

• Choosing the appropriate grid ratio for the exam

• Employing alternatives like tight collimation or air-gap technique when possible

• Avoiding grid use in pediatric and low-scatter situations

• Maintaining proper alignment and positioning to prevent repeats

Every decision about grid use should be driven by a balance between image quality and radiation safety. In this way, technologists uphold the ALARA principle—not only as a regulation, but as a daily commitment to patient care.

Grids should not be automatic—they should be intentional. Because in diagnostic imaging, the best outcomes come not just from technology, but from the technologist’s knowledge, skill, and judgment.