Consequences of the Patient's Mis-centering on the Radiation Dose and Image Quality in CT Imaging – Phantom and Clinical Study

Súkupová, Lucie; Vedlich, Daniel; Jírů, Filip

doi:10.13189/ujmsj.2016.040304

Cited by 16 publications

(6 citation statements)

References 9 publications

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“…The results by Kalra et al (2009) concur with these results [26]. Furthermore, a study by Sukupova et al (2016) found that within 100 mm of vertical off-centring, there was no substantial change in the CT number; however, with 140 mm or more vertical off-centring, a 20 HU change was recorded [31]. These ndings can be explained whereby the amount of off-centring required to cause a CT number change for a ROI will depend on the alignment of phantom geometry and the bowtie lter size.…”

Section: Vertical Off-centring and Phantom Sizesupporting

confidence: 81%

The Impact of Vertical Off-Centring, Tube Voltage and Phantom Size on CT Numbers: An Experimental Study

Al-Hayek

Spuur

Davidson

et al. 2021

Preprint

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Objectives: This pilot experimental study explores the effect of vertical off-centring on CT numbers in combination with various tube voltages and phantom sizes.Methods: A CIRS Model 062 Electron Density and Combined Head and Body phantom underwent imaging using a Siemens Emotion 16-slice CT and GEMINI GXL scanners. Uniformity was evaluated as a function of vertical off-centring (20, 40, 60, and 80 mm above the gantry iso-centre) using different phantom sizes and tube voltage for ROI positions across the X and Y axis of each phantom. CT number change was assessed by comparing the measured values between anterior (upper) versus posterior (lower) ROIs.Results: The results showed that vertical off-centring and phantom size could account for 92% of the recorded variance and resultant CT number change. The uniformity test recorded a maximum change of 27.2 and 14 HU for peripheral ROIs at 80 mm phantom shift above the gantry iso-centre using the GEMINI GXL and Siemens scanners, respectively. The absolute CT number differences between anterior and posterior ROIs were 13.7 for the 30 cm phantom and 4.8 for the 20 cm phantom at 80 mm vertical off-centring. The most remarkable differences were observed at lower tube voltages.Conclusions: It is essential to highlight the significance of optimal patient centring for CT examinations and the consequences of CT numbers variation on clinical decision making. Phantom off-centring and ROI location have been demonstrated to affect CT number uniformity in this pilot experimental study. This was more evident at peripheral phantom areas, lower tube voltages and larger phantom size.

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Section: Vertical Off-centring and Phantom Sizesupporting

confidence: 81%

The Impact of Vertical Off-Centring, Tube Voltage and Phantom Size on CT Numbers: An Experimental Study

Al-Hayek

Spuur

Davidson

et al. 2021

Preprint

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“…Several studies have investigated the effect of off‐centring on dose and image quality. 8 , 14 , 16 , 18 , 21 , 22 , 24 The importance of these studies aligns with the fact that off‐centring in clinical practice is alarmingly commonplace with one study reporting 95% of patients undergoing thoracic or abdominal CT examinations were vertically off‐centred. 17 A retrospective study of 549 patients by Toth and Ge reported a mean lateral positioning error of 0.0 mm, and from −66 to 34 mm in the vertical direction.…”

Section: Discussionmentioning

confidence: 89%

“… 16 Another study showed a mean value of off‐centring (−43 mm) with the minimum and maximum off‐centring from −88 mm to 16 mm. 24 Studies based on visual estimate centring have shown that patients were off‐centred by a mean of 22, 16 23, 8 25.6 17 and 25‐35 mm 18 below gantry iso‐centre. It is clear from the literature that the centre of mass of the patient tends to be positioned below the scanner centre of rotation, rather than above.…”

Section: Discussionmentioning

confidence: 99%

0° vs. 180° CT localiser: The effect of vertical off‐centring, phantom positioning and tube voltage on dose optimisation in multidetector computed tomography

Al-Hayek

Zheng

Davidson

et al. 2021

J of Medical Radiation Sci

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Introduction: Patient positioning is an essential consideration for the optimisation of radiation dose during CT examinations. The study objectives seek to explore the effects of vertical off-centring, localiser direction (0°and 180°), and phantom positioning (supine and prone) on radiation dose, using three different tube voltages in multidetector computed tomography (MDCT) imaging. Methods: The trunk of a PBU-60 anthropomorphic phantom was imaged using a Discovery CT750 HD -128 slice (GE Healthcare). Images employing 0°and 180°localisers were acquired in supine and prone orientation for each combination of vertical off-centring (AE100, AE60 and AE30 mm) and different tube voltages (80, 120 and 140 kVp), using the system's automatic tube current modulation (ATCM) function. The displayed volume CT dose index (CTDI vol ) and dose length product (DLP) were recorded. Results: With incremental table off-centring of AE100 mm, the dose at 120 kVp in the supine position ranged from 63% to 196% (0°localiser) and from 66% to 191% (180°l ocaliser) as compared to iso-centre. While in the prone position, the dose ranged from 62% to 195% (0°localiser); and 62% to 193% (180°localiser), with a notable dose increase at higher tube voltages. Dose variation and vertical off-centring showed a significant relationship for both 0°and 180°localisers (r = 0.94 and 0.96, respectively, P < 0.001). The CTDI vol variation between supine and prone phantom positions at AE100 mm off-centring was 0.22 mGy (2.9%), and 0.19 mGy (2.3%) when the 0°and 180 °localisers were utilised, respectively. Conclusions: Phantom off-centring and localiser direction evidenced large dose variation. It is recommended that the 0°localiser is employed during CT examinations, in order to minimise the potential additional radiation dose which may result from off-centring and the use of lower tube voltages where clinically appropriate.

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“…Cao et al [28] reported that misalignment of the phantom led to an increase in noise and a CT number error of up to 20%. Sukupova et al [29] reported that misalignment by >140 mm resulted in a change in CT number by 20 HU. A recent phantom study by [30] also reported that a deviation of 4.3 HU was obtained from a misalignment of 80 mm with a low-tube voltage.…”

Section: Discussionmentioning

confidence: 99%

“…However, misalignment up to 10 mm does not cause significant artifacts to appear. Several studies have reported that misalignment can cause changes in image noise and dose at certain position within the phantoms or patients [29][30][31][32][33]. Further studies are needed on the influence of misalignment on the emergence of artifacts.…”

Section: Discussionmentioning

confidence: 99%

Algorithm development for automatic laser alignment assessment on an ACR CT phantom and its evaluation on sixteen CT scanners

Anam,

Amilia,

Naufal

et al. 2023

Biomed. Phys. Eng. Express

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Purpose. The aim of this study is to develop software to automatically assess the laser alignment on the ACR CT phantom and evaluate its accuracy on sixteen CT scanners. Methods. Software for an automated method of laser alignment assessment on the ACR CT phantom was developed. Laser alignment assessment was based on the positions of the ball-bearing markers at the edge of the ACR CT phantom. The automatic assessment was performed using several steps, including segmentation to acquire the coordinates of the ball-bearing markers and determination of the distances between lines connecting them with lines through the center of the image. A comparison of the results from the automatic method with those from the manual method was performed. The manual measurements were carried out using MicroDicom Viewer. A Mann–Whitney U test was performed to determine the statistical difference between both methods. The evaluation was performed on images of the ACR CT phantom scanned with 16 CT scanners from 5 different CT manufacturers. Results. The results confirmed that our software successfully segments the ball-bearing markers and determines the laser alignment assessment on the ACR CT phantom. Evaluation of the algorithm with images from the 16 CT scanners revealed that the difference between the results from automatic and manual methods were about 0.2 mm with a p value of around 0.7 (no statistical difference). Misalignment in the y-axis was larger than the misalignment in the x-axisfor the majority of the scanners tested. It was found that the phantom tended to be placed 2 mm higher than the iso-center. Conclusions. Software to automatically assess CT laser alignment with the ACR CT phantom was successfully developed and evaluated. The automatic assessment was comparable to manual assessment. In addition, the automatic method was user independent and fast.

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Consequences of the Patient's Mis-centering on the Radiation Dose and Image Quality in CT Imaging – Phantom and Clinical Study

Cited by 16 publications

References 9 publications

The Impact of Vertical Off-Centring, Tube Voltage and Phantom Size on CT Numbers: An Experimental Study

The Impact of Vertical Off-Centring, Tube Voltage and Phantom Size on CT Numbers: An Experimental Study

0° vs. 180° CT localiser: The effect of vertical off‐centring, phantom positioning and tube voltage on dose optimisation in multidetector computed tomography

Algorithm development for automatic laser alignment assessment on an ACR CT phantom and its evaluation on sixteen CT scanners

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