WE‐D‐18A‐04: How Iterative Reconstruction Algorithms Affect the MTFs of Variable‐Contrast Targets in CT Images

• Published in: Medical physics (Lancaster) Vol. 41; no. 6Part29; pp. 498 - 499
• Main Authors: Dodge, C.T., Rong, J., Dodge, C.W.
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01.06.2014
• Subjects: 60 APPLIED LIFE SCIENCES; ALGORITHMS; BEAM PROFILES; CAT SCANNING; COMPARATIVE EVALUATIONS; Computed tomography; CYLINDRICAL CONFIGURATION; Electric measurements; FILTERS; Germanium; IMAGE PROCESSING; ITERATIVE METHODS; Medical image reconstruction; Modulation transfer functions; PATIENTS; POLYSTYRENE; RADIOLOGY AND NUCLEAR MEDICINE
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.4889413

Purpose: To determine how filtered back‐projection (FBP), adaptive statistical (ASiR), and model based (MBIR) iterative reconstruction algorithms affect the measured modulation transfer functions (MTFs) of variable‐contrast targets over a wide range of clinically applicable dose levels. Methods: The Catphan 600 CTP401 module, surrounded by an oval, fat‐equivalent ring to mimic patient size/shape, was scanned on a GE HD750 CT scanner at 1, 2, 3, 6, 12 and 24 mGy CTDIvol levels with typical patient scan parameters: 120kVp, 0.8s, 40mm beam width, large SFOV, 2.5mm thickness, 0.984 pitch. The images were reconstructed using GE's Standard kernel with FBP; 20%, 40% and 70% ASiR; and MBIR. A task‐based MTF (MTFtask) was computed for six cylindrical targets: 2 low‐contrast (Polystyrene, LDPE), 2 medium‐contrast (Delrin, PMP), and 2 high‐contrast (Teflon, air). MTFtask was used to compare the performance of reconstruction algorithms with decreasing CTDIvol from 24mGy, which is currently used in the clinic. Results: For the air target and 75% dose savings (6 mGy), MBIR MTFtask at 5 lp/cm measured 0.24, compared to 0.20 for 70% ASiR and 0.11 for FBP. Overall, for both high‐contrast targets, MBIR MTFtask improved with increasing CTDIvol and consistently outperformed ASiR and FBP near the system's Nyquist frequency. Conversely, for Polystyrene at 6 mGy, MBIR (0.10) and 70% ASiR (0.07) MTFtask was lower than for FBP (0.18). For medium and low‐contrast targets, FBP remains the best overall algorithm for improved resolution at low CTDIvol (1–6 mGy) levels, whereas MBIR is comparable at higher dose levels (12–24 mGy). Conclusion: MBIR improved the MTF of small, high‐contrast targets compared to FBP and ASiR at doses of 50%–12.5% of those currently used in the clinic. However, for imaging low‐ and mediumcontrast targets, FBP performed the best across all dose levels. For assessing MTF from different reconstruction algorithms, task‐based MTF measurements are necessary.