Estimation of the two‐dimensional presampled modulation transfer function of digital radiography devices using one‐dimensional test objects

Abstract

Purpose:The modulation transfer function (MTF) of medical imaging devices is commonly reported in the form of orthogonal one-dimensional (1D) measurements made near the vertical and horizontal axes with a slit or edge test device. A more complete description is found by measuring the two-dimensional (2D) MTF. Some 2D test devices have been proposed, but there are some issues associated with their use: (1) they are not generally available; (2) they may require many images; (3) the results may have diminished accuracy; and (4) their implementation may be particularly cumbersome. This current work proposes the application of commonly available 1D test devices for practical and accurate estimation of the 2D presampled MTF of digital imaging systems. Methods: Theory was developed and applied to ensure adequate fine sampling of the system line spread function for 1D test devices at orientations other than approximately vertical and horizontal.Methods were also derived and tested for slit nonuniformity correction at arbitrary angle. Techniques were validated with experimental measurements at ten angles using an edge test object and three angles using a slit test device on an indirect-detection flat-panel system [GE Revolution XQ/i (GE Healthcare, Waukesha, WI)]. The 2D MTF was estimated through a simple surface fit with interpolation based on Delaunay triangulation of the 1D edge-based MTF measurements. Validation by synthesis was also performed with simulated images from a hypothetical direct-detection flat-panel device. Results: The 2D MTF derived from physical measurements yielded an average relative precision error of 0.26% for frequencies below the cutoff (2.5 mm −1 ) and approximate circular symmetry at frequencies below 4 mm −1 . While slit analysis generally agreed with the results of edge analysis, the two showed subtle differences at frequencies above 4 mm −1 . Slit measurement near 45• revealed radial asymmetry in the MTF resulting from the square pixel aperture (0.2 mm × 0.2 mm), a characteristic which was not necessarily appreciated with the orthogonal 1D MTF measurements. In simulation experiments, both slit-and edge-based measurements resolved the radial asymmetries in the 2D MTF. The average absolute relative accuracy error in the 2D MTF between the DC and cutoff (2.5 mm −1 ) frequencies was 0.13% with average relative precision error of 0.11%. Other simulation results were similar to those derived from physical data. Conclusions: Overall, the general availability, acceptance, accuracy, and ease of implementation of 1D test devices for MTF assessment make this a valuable technique for 2D MTF estimation.

Assessing the in vitro optical quality of presbyopic solutions based on the axial modulation transfer function

“…Some measuring devices dedicated to MTF estimation calculate the radial average MTF obtained in the sagittal and tangential directions. 7 Based on the MTF, several metrics 3,6,8-10 have been developed. These metrics include the average modulation (the mean value of modulation at a range of frequencies), the area under the MTF, the Strehl ratio by means of the MTF (the ratio of the area under the actual MTF curve with the area under the diffraction-limited MTF curve), and the cutoff spatial frequency (the spatial frequency at which the modulation reaches or approaches zero).…”

Mamografi Sistemlerinde İlgi Alanı, Türev ve İnce Gruplama Seçimlerinin Modülasyon Transfer Fonksiyonunun Üzerine Etkileri

“…Şekil 5'te farklı ilgi alan seçimlerinde ESF' lerin nasıl değiştiği incelenmiştir. Bu incelemenin yapılma sebebi, farklı kare ilgi alanlarında ve kare dışındaki ilgi alanlarında görüntüdeki düşük frekans bilgisinin (saçılan x-ışın etkilerini) grafiklere olan etkisini gözlemleme isteğidir [13]. Kullanılan veriler için ilgi alan seçimlerine göre grafiklerin genlik değerlerinin değişmediği ancak görüntüdeki piksel değerlerinin, piksellerin kenardan olan uzaklıklarına göre değiştiği gözlenmiştir.…”

“…Ayrıca literatürde gürültü gidermek için çeşitli yöntemler MTF hesaplamalarında kullanılmaktadır. Örneğin ESF verilerini gaussian ağırlıklı polinoma fit edilmesi [11,13], median filtrelenmesi [3],…”

A hybrid simulation framework for computer simulation and modelling studies of grating-based x-ray phase-contrast images

“…The 1D detector presampling MTF was measured for the grating stepping direction in the image using an implementation of the well-established oversampling technique (Fujita et al 1992, Samei et al 1998, Buhr and Neitzel 2003, Marshall 2006) via an edge test object. The 2D distribution was then formed assuming an isotropic MTF, which is a good approximation following (Wells and Dobbins 2012). A test object with a sharp, straight edge was positioned in front of G 1 and the edge rotated slightly (between 1° and 4°) to the x axis.…”