Computer Tomography scan artifacts, Slides of Radiology

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Ct ARTIFACTS

They can arise from

Physics of X-rays

• (^) Patient motion
• (^) Hardware/equipment limitations
• (^) Image reconstruction errors
• (^) Operator technique
• (^) Artifacts reduce image quality, diagnostic accuracy, and may mimic or obscure pathology.

Beam Hardening Artifact

Cause

• (^) X-ray beams contain photons of various energies.
• (^) As the beam passes through the patient, low-energy photons are absorbed first, leaving a “harder” (higher energy) beam.
• (^) This causes nonlinear attenuation, especially through dense materials (bone, contrast media).
• (^) 🔹 Appearance
• (^) Cupping artifact: Center of a homogeneous object appears less dense than edges.
• (^) Streaks or dark bands between dense structures (e.g., skull base, dental fillings).

HOW TO REMOVE THIS ARTIFACT

• (^) ✅ Use pre-filtration (bowtie filters) to harden the beam before it enters the patient.

✅ Proper calibration and water correction phantom scans.

✅ Avoid scanning two dense bones in the same plane when possible (e.g., raise chin in head CT).

Metal Artifacts

🔹 Cause

• (^) Metallic implants (dental fillings, prostheses, surgical clips) cause:
  • (^) Photon starvation (metal blocks X-rays)
  • (^) Beam hardening
  • (^) Scatter
  • (^) Streaking in reconstructed images

🔹 Appearance

• (^) Bright and dark streaks radiating from metallic objects.
• (^) Often seen in dental, hip, or spine regions.

Correction / Removal

• (^) ✅ Use Metal Artifact Reduction (MAR) software.
• ✅ Apply Dual-energy CT (reconstructs at higher keV levels).
• ✅ Use thin slices and high kVp (1️⃣ 2️⃣ 0– 1️⃣ 4️⃣ 0 kVp).
• ✅ Proper patient positioning (avoid metal in the scan plane).
• ✅ Replace removable metal (e.g., dentures, jewelry) before scanning.

Correction / Removal

✅ Shorten scan time (use faster scanners or spiral CT). ✅ Instruct patient to hold breath during scanning. ✅ Use immobilization aids. ✅ ECG gating for cardiac CT. ✅ Sedation for uncooperative or pediatric patients if necessary.

Partial Volume Artifact

Cause

• (^) When a voxel contains more than one tissue type, CT averages the densities.
• (^) Common at boundaries between bone and soft tissue or air and tissue.

🔹 Appearance

• (^) Blurring or incorrect attenuation values at edges (e.g., bone–soft tissue interface).

Correction / Removal

✅ Use thin slices (smaller voxel size). ✅ Optimize reconstruction algorithms. ✅ Position anatomy of interest at center of slice. ✅ Use multiplanar reformation (MPR) to confirm unclear regions.

Correction / Removal

• (^) Perform detector calibration regularly.
• ✅ Replace defective detector elements.
• ✅ Use built-in ring correction algorithms.
• ✅ Ensure homogeneous phantom calibration before clinical scanning.

Presented By:

• (^) Syed Dawood Zahoor (9050)
  • (^) Jawad Ali (901️⃣ 5)
• (^) Abdullah Nasir (9086)
• (^) Saeedullah (8980)
• (^) Tabinda Javed (91️⃣ 5 4️⃣ )