100 days with scans of the same Catphan phantom on the same CT scanner

Abstract

Quality control (QC) of CT scanners is important to evaluate image quality and radiation dose. Different QC phantoms for testing image quality parameters on CT are commercially available, and Catphan phantoms are widely used for this purpose. More data from measured image quality parameters on CT are necessary to assess test methods, tolerance levels, and test frequencies. The aim of this study was to evaluate the stability of essential image quality parameters for axial and helical scans on one CT scanner over time. A Catphan 600 phantom was scanned on a Philips Ingenuity CT scanner for 100 days over a period of 6 months. At each day of testing, one helical scan covering the entire phantom and four axial scans covering four different modules in the phantom were performed. All images were uploaded into Image Owl for automatic analysis of CT numbers, modular transfer function (MTF), low‐contrast resolution, noise, and uniformity. In general, the different image quality parameters for both scan techniques were stable over time compared to given tolerance levels. Average measured CT numbers differed between axial and helical scans, while MTF was almost identical for helical and axial scans. Axial scans had better low‐contrast resolution and less noise than helical scans. The uniformity was relatively similar for axial and helical scans. Most standard deviations of measured values were larger for helical scans compared to axial scans. Test results in this study were stable over time for both scan techniques, but further studies on different CT scanners are required to confirm that this also holds true for other systems.

An Automated Measurement of Image Slice Thickness of Computed Tomography

“…The slice thickness value (FWHM) First row is for slice thickness of 5 mm and second row is for slice thickness of 10 mm. As mentioned, the slice thickness measurement on CT can be performed using several types of phantom [9][10][11][12][13]. The AAPM CT performance phantom has one advantage over other the phantoms.…”

“…Due to its complexity, quality control of CT scanners must be periodically carried out [7,8]. A special phantom is usually used, such as the CatPhan phantom [9,10], the ACR CT phantom [11], or the AAPM CT performance phantom [12,13]. The phantoms contain various inserts to quantify the parameters of scanners such as CT number linearity, spatial and contrast resolution, and slice thickness.…”

“…The method of slice thickness testing depends on the types of phantoms used. In the ACR CT phantom, the slice thickness measurement is performed on the axial image by counting the number of discrete wires at the top and bottom [9,12]. In the CatPhan phantom, the full-width at half maximum (FWHM) of the profile for each wire ramp is measured then a trigonometric conversion is calculated based on the known ramp [10].…”

Automation of slice thickness measurements in computed tomography images of AAPM CT performance phantom using a non-rotational method

“…In the ACR accreditation phantom, slice thickness measurements are carried out on axial images by counting the number of discrete lines at the top and bottom. 12 While in the AAPM CT performance phantom, slice thickness is measured as the width of stair image objects. 11 The measurements are generally carried out by a manual method (i.e.…”

Impact of ROI Size on the Accuracy of Noise Measurement in CT on Computational and ACR Phantoms

“…The noise level is generally characterized by the standard deviation (SD) of pixel values in a region of interest (ROI) placed in a homogeneous region [19][20][21]. For quality control (QC), noise is usually measured on a standardized homogeneous phantom, such as the American College of Radiology (ACR) CT accreditation phantom [22], Catphan phantom [23], and others [24]. However, noise characterization by using its image SD can only determine the amount of noise level, not the type of noise or image texture.…”