title: A simple approach to measure computed tomography (CT) modulation transfer function (MTF) and noise-power spectrum (NPS) using the American College of Radiology (ACR) accreditation phantom.
abstract: OBJECTIVE
  To develop an easily-implemented technique with free publicly-available analysis software to measure the modulation transfer function (MTF) and noise-power spectrum (NPS) of a clinical computed tomography (CT) system from images acquired using a widely-available and standardized American College of Radiology (ACR) CT accreditation phantom.
  
  
  METHODS
  Images of the ACR phantom were acquired on a Siemens SOMATOM Definition Flash system using a standard adult head protocol: 120 kVp, 300 mAs, and reconstructed voxel size of 0.49 mm × 0.49 mm × 4.67 mm. The radial (axial) MTF was measured using an edge method where the boundary of the third module of the ACR phantom, originally designed to measure uniformity and noise, was used as a circular edge. The 3D NPS was measured using images from this same module and using a previously-described methodology that quantifies noise magnitude and 3D noise correlation.
  
  
  RESULTS
  The axial MTF was radially symmetrical and had a value of 0.1 at 0.62 mm(-1). The 3D NPS shape was consistent with the filter-ramp function of filtered-backprojection reconstruction algorithms and previously reported values. The radial NPS peak value was ∼115 HU(2)mm(3) at ∼0.25 mm(-1) and dropped to 0 HU(2)mm(3) by 0.8 mm(-1).
  
  
  CONCLUSIONS
  The authors have developed an easily-implementable technique to measure the axial MTF and 3D NPS of clinical CT systems using an ACR phantom. The widespread availability of the phantom along with the free software the authors have provided will enable many different institutions to immediately measure MTF and NPS values for comparison of protocols and systems.
authors: Sackler School of Medicine, Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel. saul.friedman@gmail.com
authors: Saul N
authors: SN
authors: Friedman
authors: George S K
authors: GS
authors: Fung
authors: Jeffrey H
authors: JH
authors: Siewerdsen
authors: Benjamin M W
authors: BM
authors: Tsui
mesh_terms: D000068:Accreditation; D000328:Adult; D006801:Humans; D019047:Phantoms, Imaging; D059629:Signal-To-Noise Ratio; D012955:Societies, Medical; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*
references: Phys Med Biol. 1978 May;23(3):446-54
references: 674361
references: Med Phys. 2008 Dec;35(12):5510-29
references: 19175110
references: Radiology. 2011 Jul;260(1):248-56
references: 21436086
references: Med Phys. 2008 Dec;35(12):5317-27
references: 19175091
references: Med Phys. 2004 Sep;31(9):2423-42
references: 15487722
references: Phys Med Biol. 2007 Jul 21;52(14):4027-46
references: 17664593
references: Med Phys. 1998 Jan;25(1):102-13
references: 9472832
references: Med Phys. 1976 Jul-Aug;3(4):233-6
references: 785200
references: Med Phys. 2002 Nov;29(11):2655-71
references: 12462733
references: Radiology. 1969 Aug;93(2):257-72
references: 5822701
references: Med Phys. 2012 Jul;39(7):4115-22
references: 22830744
references: Med Phys. 2008 Oct;35(10):4443-9
references: 18975691
references: Med Phys. 2009 May;36(5):1700-10
references: 19544787
references: J Nucl Med Technol. 2007 Dec;35(4):213-25; quiz 226-8
references: 18006597