Evaluation of Non-Uniform Image Quality Caused by Anode Heel Effect in Digital Radiography Using Mutual Information

Anode heel effects are known to cause non-uniform image quality, but no method has been proposed to evaluate the non-uniform image quality caused by the heel effect. Therefore, the purpose of this study was to evaluate non-uniform image quality in digital radiographs using a novel circular step-wedge (CSW) phantom and normalized mutual information (nMI). All X-ray images were acquired from a digital radiography system equipped with a CsI flat panel detector. A new acrylic CSW phantom was imaged ten times at various kVp and mAs to evaluate overall and non-uniform image quality with nMI metrics. For comparisons, a conventional contrast-detail resolution phantom was imaged ten times at identical exposure parameters to evaluate overall image quality with visible ratio (VR) metrics, and the phantom was placed in different orientations to assess non-uniform image quality. In addition, heel effect correction (HEC) was executed to elucidate the impact of its effect on image quality. The results showed that both nMI and VR metrics significantly changed with kVp and mAs, and had a significant positive correlation. The positive correlation is suggestive that the nMI metrics have a similar performance to the VR metrics in assessing the overall image quality of digital radiographs. The nMI metrics significantly changed with orientations and also significantly increased after HEC in the anode direction. However, the VR metrics did not change significantly with orientations or with HEC. The results indicate that the nMI metrics were more sensitive than the VR metrics with regards to non-uniform image quality caused by the anode heel effect. In conclusion, the proposed nMI metrics with a CSW phantom outperformed the conventional VR metrics in detecting non-uniform image quality caused by the heel effect, and thus are suitable for quantitatively evaluating non-uniform image quality in digital radiographs with and without HEC.

ANODE HEEL EFFECT ATTENUATION IN LUMBAR SPINE RADIOGRAPHY: CAN THE USE OF ALUMINIUM FILTERS IMPROVE CLINICAL PRACTICE OF RADIOGRAPHERS?

Purpose: The aim of this study was to design an aluminium-based filter to reduce the anode heel effect in lumbar spine radiographs. Methods: Initially, lumbar spine examinations were observed in a public imaging department to determine the standard exposure parameters. Then, the characterization of the anode heel effect was made using the Unfors Xi R/F detector and based on the data collected, aluminium filters were designed with a wedge shape, with thicknesses ranging from 0.1 to 4.0 mm. The assessment of the entrance skin dose (ESD) reduction was performed on the anthropomorphic phantom, with and without filters, using the universal dosimeter UNIDOS E equipped with an ionization chamber. Lastly, the image quality assessment was performed with the Pehamed Phantom Digrad A+K and image quality surveys were applied to radiographers and radiologists. Results and Discussion: Uniformity of the beam was achieved, especially with the filter number 2, which presents a significant variation of 9% between cathode and anode side. This filter contributes to ESD reduction of 35% and 36% for AP and lateral projection, respectively. Also, according to the radiographers and radiologists, it improves the image quality of lumbar spine radiography. Conclusion: The use of aluminium filters can be advantageous in the clinical practice of radiographers when carrying out lumbar spine radiographs, since it allows to standardize the anode heel effect, reducing the radiation dose to the patient and without compromising the image quality.

Anode heel effect application with step wedge against effect of signal to noise ratio in computed radiography

It was researched on the application of Anoda Heel Effect (AHE) with a step wedge on the effect of Signal To Noise Ratio (SNR) on Computed Radiography (CR) has been carried out. This research was conducted on a 21 step wedge with two treatments, namely the application of AHE and without the application of AHE. This measurement is repeated three times on radiographs to obtain a total image of six images (without the application of AHE as many as three images and with the application of AHE as many as three images). The results of taking radiographs using AHE and without AHE were measured using the RadiAnt Dicom Viewer program. The SNR value on the step wedge image without the AHE application has an average of 26.89. The SNR value on the step wedge image using AHE is 60.54. The results of the correlation test (Pearson correlation test) on the SNR showed that there was a significant and very strong effect of the application of AHE on the step wedge on the SNR in CR (p-value <0.001 and the R-value ranging from 0.600 to 0.799).

Pengaruh Variasi Tegangan Tabung Sinar-X terhadap Signal to Noise Ratio (SNR) dengan Penerapan Anode Heel Effect menggunakan Stepwedge

It has been conducted research to determine the effect of X-ray tube voltage variation (kV) on Signal to Noise Ratio (SNR) values by applying the Anode Heel Effect using stepwedge with the addition of 1.5 mm thickness each step. The stepwedge used was 1.5-31.5 mm. The X-ray tube voltage variations used were 40, 50, 60, 70, 80, and 90 kV. Analysis of the effect of X-ray tube voltage variation on SNR values is determined using IMB SPSS Statistics 26 with a simple regression test. The test results showed that variations in X-ray tube voltage affect SNR values, where the greater the variation in X-ray tube voltage then the SNR value would get smaller. The optimal SNR value of 72.685 was obtained at a tube tension of 40 kV and a stepwedge thickness of 27.0 mm.

Impact of Patient Alignment on Image Quality in C-Arm Computed Tomography – Evaluation Using an ACR Phantom

Purpose To evaluate the influence of patient alignment and thereby heel effect on the image quality (IQ) of C-arm flat-panel detector computed tomography (CACT). Materials and Methods An ACR phantom placed in opposite directions along the z-axis (setup A and B) on the patient support was imaged using CACT. Image acquisition was performed with three different image acquisition protocols. The images were reconstructed with four convolution kernels. IQ was assessed in terms of high contrast using the modulation transfer function (MTF) and low contrast by assessing the image noise, signal-to-noise ratio (SNR) and contrast-to-noise ratios (CNR) as well as the reliability of density measurements. Furthermore, the dose intensity profiles were measured free-in-air. Results The MTF in setup B is higher than the MTF measured in setup A (p < 0.01). The image noises measured in setup A for the air and bone inserts were higher compared to those measured in setup B (p > 0.05). Opposite behavior has been observed for the polyethylene, water-equivalent and acrylic inserts. The SNR for all inserts is inversely related to the image noise. A systematically increasing or decreasing trend of CNR could not be observed (p > 0.05). The intensity profile measured by the detector system free-in-air showed that the anode heel effect is perpendicular to the z-axis. Conclusion The patient alignment has a minor influence on the IQ of CACT. This effect is not based on the X-ray anode heel effect but is caused mainly by the non-symmetrical rotation of CACT. Key Points: Citation Format