High-ratio grid considerations in mobile chest radiography.

Area of Science:

• Radiologic Technology
• Medical Imaging Physics
• Diagnostic Radiology

Background:

• Mobile chest radiography often omits grids or uses low-ratio, misaligned grids.
• A novel mobile radiography automatic grid alignment system (MRAGA) ensures accurate focal spot-to-grid alignment.

Purpose of the Study:

• To evaluate the trade-offs of using high-ratio grids in mobile chest radiography.
• To assess image quality at a fixed patient dose with precise focal spot alignment.

Main Methods:

• Utilized modified ANSI chest phantoms (medium and large) with contrast targets.
• Compared five high-ratio grids (10:1-15:1, aluminum and fiber interspace) against nongrid exposures.
• Employed MRAGA for alignment and computed radiography for image acquisition.
• Quantified contrast-to-noise ratio (CNR) and CNR improvement factor (k(CNR)).

Main Results:

• High-ratio grids increased CNR by 4%-65% compared to nongrid images at the same phantom dose.
• Image quality improvement was more pronounced in larger phantoms and mediastinal targets.
• Fiber interspace grids generally yielded superior results over aluminum interspace grids.
• k(CNR) showed minimal dependence on kVp or grid ratio in the lung, but decreased with increasing kVp in the mediastinum.

Conclusions:

• Accurate grid alignment with MRAGA enables high-ratio grids to enhance mobile chest radiography image quality without dose increase.
• Fiber interspace grids demonstrated better performance than aluminum interspace grids.
• Specific fiber grids (13:1 for medium, 15:1 for large phantoms) provided optimal results.