CT Collimators explained 📐 Pre-patient vs Post-patient collimation — know the difference In CT scan, collimators are used to shape and restrict the X-ray beam, helping to control dose and improve image quality. 🔹 Pre-patient collimator • Positioned before the patient • Restricts the primary X-ray beam • Determines slice thickness • Helps reduce unnecessary radiation exposure 🔹 Post-patient collimator • Positioned after the patient (before detectors) • Restricts scattered radiation • Improves