Which statement correctly describes the relationship between crystal quality and the beam nonuniformity ratio (BMR)?

• A. BMR is unaffected by crystal quality
• B. Higher quality crystals lead to lower BMR
• C. Higher BMR results in less discomfort
• D. Lower quality crystals reduce BMR

Answer: (B)

Crystal quality directly affects how evenly the beam is produced across the field. BMR, or beam nonuniformity ratio, quantifies how much the exposure varies from one part of the beam to another; a lower BMR means a more uniform beam. When crystals are high quality, they have fewer defects and more uniform absorption and scintillation, leading to a consistent light output and less variation in the beam. This reduces nonuniformity, lowering the BMR. If crystal quality is poorer, defects and irregularities cause uneven conversion and more scatter, increasing the beam’s nonuniformity and raising the BMR. So, higher quality crystals lead to lower BMR.