For imaging the lumbar spine, which description best matches ideal collimation?

• A. Collimation limited to the lumbar region with small margins
• B. Collimation extended to include the thoracic region
• C. Collimation only to the sacrum
• D. Collimation to the entire abdomen

Answer: (A)

Focusing the beam tightly on the area of interest is essential to minimize radiation dose and improve image quality by reducing scatter. For imaging the lumbar spine, collimation should cover just the lumbar region with small margins so the entire lumbar vertebrae and lumbosacral junction are included without clipping. This reduces exposure to unnecessary tissues in the thorax or abdomen and keeps scatter low, which enhances contrast. Extending the field to the thoracic region or the entire abdomen would unnecessarily increase dose and degrade image quality with more scatter, while limiting the field to just the sacrum would miss the upper lumbar anatomy. Therefore, collimation limited to the lumbar region with small margins is the best description.