An experimental comparison of detector performance for computed radiography systems

Abstract

The intrinsic resolution, noise, and signal-to-noise transfer characteristics of five commercial digital computed radiography (CR) systems were compared using identical experimental methods. The reader/screen combinations evaluated were Agfa ADC-Compact/MD-10, Agfa ADC-Compact/MD-30, Agfa ADC-Solo/MD-10, Agfa ADC-Solo/MD-30, Lumisys CR-2000/MD-10, Fuji FCR-9501 (HQ)/ST-Va, Kodak CR-400/GP-25, and Kodak CR-400/HR. Measurements were made at 70 and 115 kVp with 19 mm added aluminum filtration. The presampled modulation transfer functions (MTFs) of the systems were measured using an edge method. The noise power spectra (NPS) were determined by 2D Fourier analysis of uniformly exposed radiographs. The frequency-dependent detective quantum efficiencies (DQEs) were computed from the MTF, NPS, exposure measurements, and computational estimates of the ideal signal-to-noise ratios. Using 70 kVp and 0.1-0.12 mm pixel sizes, spatial frequencies of 2.1, 2.0, 2.2, 1.9, 2.0, 2.0, 2.3, 2.3, and 3.5 cycles/mm were measured at 0.2 MTF for the eight reader/screen combinations, respectively. Using 70 kVp, 7.74 x 10(-8) C/kg (0.3 mR), and 0.1-0.12 mm pixel sizes, DQE(0.15) values of 20.3%, 22.9%, 24.6%, 28.6%, 22.2%, 30.0%, 29.5%, and 17.3% were obtained for the eight combinations, respectively. The corresponding values at 115 kVp were 15.9%, 18.5%, 21.5%, 21.8%, 15.3%, 23.1%, 22.3%, and 13.8%, respectively. The findings of the study demonstrate the pixel size, orientation, beam quality, screen, and reader dependencies of image quality in CR systems. The physical performance of the systems having standard-resolution screens demonstrated similar resolution performance but more notable variations in DQE. The one high-resolution screen tested had reduced DQE and increased MTF at high frequencies.

Local and global 3D noise power spectrum in cone‐beam CT system with FDK reconstruction

“…The noise power spectrum ͑NPS͒ does this and provides information on the noise components for different spatial frequencies. It can be used to predict detection performance 14,15 and the system detective-quantum-efficiency. [16][17][18][19] In addition, the noise variance, the detectability ͑SNR͒, and the correlation in the noise can be determined from the NPS.…”

The noise power spectrum in CT with direct fan beam reconstruction

“…Compared to the variance, the noise power spectrum ͑NPS͒ can more fully describe the noise including correlation introduced by filtering and other processing steps. The NPS enables comparison of signal and noise at each spatial frequency, it can be used to predict detection performance, 9,10 and it is needed to compute the system DQE. 11,12 Since the pixel value variance can be estimated by integrating the NPS over all frequencies, the NPS is a more powerful metric for analyzing CT performance.…”

Accurate MTF measurement in digital radiography using noise response

“…[1][2][3][4] Although the methods used to measure the MTF have changed slightly over the past several decades, [5][6][7][8][9][10][11][12][13][14] the underlying premise has remained a constant: A precisely machined object or test device is imaged and the subsequent response of the detector is used to obtain the MTF using several steps, which generally include determination of the line spread function ͑LSF͒, taking the Fourier transform of the LSF, and use of various noise reduction and fitting techniques. 6,11,12,[15][16][17][18][19][20] The slit 11 and edge 12 response methods are the two most commonly used and accepted techniques for measurement of the MTF, with the edge-response method being preferred ͑with adoption by the IEC͒ ͑Ref.…”