An X-ray grid is a device used in radiographic imaging to improve the contrast of the image by
reducing the amount of scattered radiation that reaches the image receptor. It consists of a
series of lead strips that are angled to allow primary X-rays to pass through while absorbing
scattered X-rays that may degrade the quality of the image.
Grids are widely used in radiography, but they are not necessary for every exam. heir use generally requires increased radiation exposure to maintain image quality, and improper alignment can introduce artifacts such as grid cutoff, particularly in portable imaging. This article covers when a grid is typically used, when it may not be necessary, and what grid use means for dual-energy X-ray imaging.
When is it necessary to use an X-ray grid?
A grid is typically used when scatter would noticeably reduce image contrast. Scatter increases with body part thickness, field size, and kVp.
Thickness guidelines vary. ASRT’s 2025 Best Practices in Digital Radiography uses 12 cm for adults, and older CRCPD guidance suggests more than 13 cm above 70 kVp. Treat these as starting points. Grid use also depends on anatomy, projection, technique, the detector and system, and your department’s protocols.
How does an X-ray grid improve contrast?
Scatter happens when X-rays change direction inside the body. Scattered photons still reach the detector, but they add a haze that lowers contrast and adds noise. Digital processing can adjust brightness, but it cannot fully remove the effect of scatter.
When properly aligned, a grid improves image contrast by absorbing much of the scattered radiation before it reaches the detector while allowing most primary X-rays to pass through. This can improve the visibility of anatomical detail, particularly in examinations where scatter is significant.
What is grid cut-off in radiology?
Grid cut-off occurs when a grid unintentionally absorbs part of the primary X-ray beam, reducing the amount of useful radiation that reaches the image receptor. This is usually due to improper alignment of the grid or using the wrong type of grid for the X-ray technique.
The result can be reduced or uneven receptor exposure, which may appear as lighter areas or loss of image information.
There are four common types of grid cut-off that can occur when using an X-ray grid:
- Off-level: The grid is tilted relative to the beam, or the tube is angled across the grid strips. Exposure drops across the whole image.
- Off-center: The central ray isn’t centered to the grid. Exposure drops across the image.
- Off-focus: The source-to-image distance (SID) is outside the grid’s focal range. Exposure drops toward the edges.
- Upside-down: A focused grid is placed with its tube side facing the detector. Exposure drops sharply toward the edges.
What is the main effect of grid cut-off?
The main effect of grid cut-off is unintended absorption of the primary X-ray beam by the grid. When the grid is misaligned or used outside its intended geometry, some primary X-rays are blocked before reaching the detector.
Possible effects of grid cut-off include:
- Reduced or uneven exposure across the image
- Loss of image information in affected areas
- Increased visible noise in digital images if processing compensates for reduced detector exposure
- Asymmetry between different areas of the image that may obscure or mimic findings
- Repeat imaging if the image is not diagnostically acceptable
How does the use of a grid affect radiation exposure to the patient?
A grid absorbs some primary radiation along with scatter, so the exposure usually has to increase to produce the same signal at the detector. How much depends on grid ratio, kVp, and body part. When scatter is significant, that trade-off may be worthwhile because improved contrast can help avoid an inadequate image and the need for repeat imaging. When scatter is limited, or when the grid is misaligned, the additional exposure associated with grid use may provide less benefit.
Which X-rays commonly use a grid?
Grids are commonly used in the following imaging techniques:
- Abdomen and pelvis: thick anatomy with high scatter
- Spine, hips, and shoulders: commonly used in adult imaging, depending on patient thickness and technique
- Chest: often used in the department at high kVp; portable chest use varies with patient size and protocol
When might you not need a grid? (2026 Update)
When scatter is already low, a grid can add exposure without providing a meaningful improvement in image quality.
Grids are often not needed for:
- Extremities such as hands, wrists, feet, and ankles
- Many knee exams, depending on patient thickness
- Many pediatric exams, with the decision based primarily on patient size and anatomy
- Some portable chest exams, depending on patient size technique, equipment, and departmental protocol
Some projections, such as certain lateral cervical spine views, may use an air-gap technique instead of a grid to reduce scatter reaching the detector.
Grids in portable and bedside X-ray (2026 Update)
Grid alignment is hardest at the bedside. In a fixed room, the tube and grid are mechanically aligned. In a portable exam, the technologist lines them up by eye, often with the detector tilted in a soft mattress and a patient who cannot be moved. Small errors in angle, centering, or distance can cause cut-off, and repeating the exam is not always simple.
As a result, grid use for portable chest imaging varies between sites. Leaving the grid off avoids cut-off but leaves more scatter in the image. Low-ratio grids with a wide focal range, a measured SID, and clear protocols can help. Some systems offer scatter correction software. Evidence suggests these tools can improve image quality and may provide an alternative to a physical grid in some portable imaging situations, although performance can vary with patient size and imaging conditions.
Do I need a grid for dual-energy X-ray imaging?
Dual-energy X-ray imaging can be acquired using different approaches. Two common methods are:
Dual-exposure: Two exposures at low and high kVp, typically taken a fraction of a second apart. Motion between exposures can cause misregistration artifacts. These systems are mostly installed in fixed rooms and are typically used with a grid. Sequential acquisition and system requirements can make this approach less practical for bedside imaging.
Single-exposure: A layered detector captures dual-energy information from one exposure, so there is no gap between images. Scatter can still affect image quality, and grid use can follow many of the same considerations as a standard radiographic exam.
Reveal 35C is designed to produce dual-energy images in fixed or portable settings with or without a grid, so the grid decision can follow your protocol for the patient and exam. Thicker anatomy may still benefit from a grid.
Reveal™ 35C uses SpectralDR® technology with a multilayer detector design to capture spectral information from a single X-ray exposure. From that exposure, the system generates a conventional DR image, a bone-selective image, and a soft-tissue image in which the visibility of overlying or underlying anatomy is reduced.
Because the spectral information is acquired simultaneously, there is no temporal gap between separate low- and high-energy exposures, avoiding the misregistration that can occur when a patient moves between sequential acquisitions.
This can support mobile imaging workflows in settings such as emergency departments and ICUs, where patient positioning and repeat acquisitions may be more challenging.
Frequently Asked Questions (2026 Update)
Does an X-ray grid increase radiation exposure?
Usually, yes. The grid absorbs some primary radiation, so exposure typically increases to keep image quality. When scatter is high, the trade-off is often worth it.
Do portable X-rays need a grid?
It depends on patient size, the exam, and the protocol. Many portable chest exams are done without one, while larger patients may benefit. When a grid is used, careful alignment is essential to avoid grid cut-off.
Do digital X-rays still need a grid?
Often, yes. Digital processing adjusts brightness but can’t fully eliminate the effects of scatter.
Can dual-energy X-ray be done without a grid?
It depends on the method. Dual-exposure systems are generally used with a grid. The single-exposure detector Reveal 35C ais designed to work with or without one, allowing grid use to follow the imaging protocol and clinical situation.
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