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Nelson R, Harkin S, Iball G. Use of a 3D camera for automated patient positioning for chest-abdomen-pelvis CT scans: Effect on positioning accuracy and patient dose. Radiography (Lond) 2024; 30:1060-1067. [PMID: 38733956 DOI: 10.1016/j.radi.2024.04.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2023] [Revised: 03/21/2024] [Accepted: 04/17/2024] [Indexed: 05/13/2024]
Abstract
INTRODUCTION 3D positioning cameras that automate the positioning of patients with respect to the CT isocentre have been developed and are in common use in CT departments. This study aimed to compare the performance of radiographers and a 3D camera system with respect to positioning accuracy and the effect on patient radiation dose for chest-abdomen-pelvis scans. METHODS Patient positioning and dose data obtained from a dose management system was evaluated over a two-month period for patients positioned with (CAMon) and without (CAMoff) the positioning camera. Median vertical and lateral offset values were compared between the groups whilst doses were evaluated as a function of patient water equivalent diameter (WED) for the thorax and abdomen-pelvis acquisitions for both cohorts. RESULTS Radiographers demonstrated high levels of positioning accuracy, however significant improvements in median vertical offset were identified for the CAMon cohort for both thorax (8 mm vs. 17 mm (p = 0.001)) and abdomen-pelvis (7 mm vs. 16 mm (p = 0.003)) scans. The percentage of patients positioned within 5 mm of the isocentre was 39.0% and 16.1% for the CAMon and CAMoff cohorts. For CAMoff scans, 77.4% of patients were positioned below the isocentre, but this was reduced to 45.8% for CAMon scans. No significant changes in dose as a function of WED were identified related to the camera use (thorax: p = 0.569, abdomen-pelvis: p = 0.760). CONCLUSION Use of a 3D camera delivered significant improvements in the accuracy and reproducibility of patient positioning when compared with radiographers. IMPLICATIONS FOR PRACTICE Improvements in positioning accuracy were observed at the research site and hence positioning camera use has the potential to become standard practice in CT to help ensure appropriate doses are delivered to patients according to their size.
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Affiliation(s)
- R Nelson
- Radiology Department, Jubilee Wing, Leeds General Infirmary, Leeds, LS1 3EX, UK.
| | - S Harkin
- Radiology Department, Jubilee Wing, Leeds General Infirmary, Leeds, LS1 3EX, UK.
| | - G Iball
- Faculty of Health Studies, University of Bradford, Bradford, BD7 1DP, UK.
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Valentin B, Kamp B, Henke J, Ljimani A, Appel E, Antoch G, Steuwe A. Influence of tube and patient positioning in thoracoabdominal CT examinations on radiation exposure-towards a better patient positioning. JOURNAL OF RADIOLOGICAL PROTECTION : OFFICIAL JOURNAL OF THE SOCIETY FOR RADIOLOGICAL PROTECTION 2023; 43:031512. [PMID: 37619552 DOI: 10.1088/1361-6498/acf384] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2023] [Accepted: 08/24/2023] [Indexed: 08/26/2023]
Abstract
Although iso-centric patient positioning is enormously important in computed tomography (CT), it is complicated in thoracoabdominal imaging by the varying dimensions of the body. Patient positioning can affect the appearance of the patient on the localiser. Positioned too close to the x-ray tube, a patient appears considerably more voluminous. The goal of this study is to assess the difference in radiation exposure of combined chest and abdomen CT scans between scans with prior 0°- and 180°-localisers in conjunction with patient positioning. In this IRB-approved retrospective study, patients who had two routine thoracoabdominal CT scans on the same CT scanner, one with a prior 0°- and one with a prior 180°-localiser, were included. To evaluate the radiation exposure of the thoracoabdominal CT examination regarding the tube position during the localiser, volumetric computed tomography dose index (CTDIvol), size-specific dose estimate (SSDE), patient diameter and positioning within the iso-centre for three positions (heart, abdomen, femur level) were compared with regard to the tube position during the prior localiser. CT examinations of 114 patients were included. Despite similar patient weight and diameter between the two examinations, SSDE and CTDIvolwas significantly larger (up to 73%) with 180°-localisers. Patient offset from the iso-centre ranged between -9 mm at the centre slice (abdomen level) to -43 mm at the most caudal slice at the pelvis (femur level), causing a significant magnification (p < 0.001) on 180°-localisers with a subsequent increase of the apparent attenuation. The results of this study emphasise the use of 0°-localisers in thoracoabdominal CTs, since 180°-localisers caused patient magnification with subsequent increase in radiation exposure. The advantage of 180°-localisers, namely reducing the dose in thyroid and breast, is eliminated if the dose of the CT scan increases significantly in the abdomen and pelvis.
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Affiliation(s)
- Birte Valentin
- University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Dusseldorf D-40225, Germany
| | - Benedikt Kamp
- University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Dusseldorf D-40225, Germany
| | - Jan Henke
- University Dusseldorf, Medical Faculty, Department of Nuclear Medicine, Dusseldorf D-40225, Germany
| | - Alexandra Ljimani
- University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Dusseldorf D-40225, Germany
| | - Elisabeth Appel
- University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Dusseldorf D-40225, Germany
| | - Gerald Antoch
- University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Dusseldorf D-40225, Germany
| | - Andrea Steuwe
- University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Dusseldorf D-40225, Germany
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Al-Hayek Y, Zheng X, Hayre C, Spuur K. The influence of patient positioning on radiation dose in CT imaging: A narrative review. J Med Imaging Radiat Sci 2022; 53:737-747. [PMID: 36280573 DOI: 10.1016/j.jmir.2022.09.027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Revised: 09/21/2022] [Accepted: 09/29/2022] [Indexed: 11/29/2022]
Abstract
BACKGROUND AND PURPOSE Although it is fundamental for optimal scanner operation, it is generally accepted that accurate patient centring cannot always be achieved. This review aimed to examine the reported knowledge of the negative impact of patient positioning on radiation dose and image quality during CT imaging. Furthermore, the study evaluated the current optimisation tools and techniques used to improve patient positioning relative to the gantry iso-center. METHODOLOGY A comprehensive search through the databases PubMed, Ovid, and Google Scholar was performed. Keywords included patient off-centring, patient positioning, localiser radiograph orientation, radiation dose, and automatic patient positioning (including synonyms). The search was limited to full-text articles that were written in English. After initial title and abstract screening, a total of 52 articles were identified to address the aim of the review. No limitations were imposed on the year of publication. RESULTS Vertical off-centring was reported in up to 95% of patients undergoing chest and abdominal CT examinations, showing a significant influence on radiation dose. Depending on the scanner model and vendor, localiser orientation, bowtie filter used, and patient size, radiation dose varied from a decrease of 36% to an increase of 91%. A significant dose reduction was demonstrated when utilising an AP localiser, aligning with the trend for radiographers to off-center patients below the gantry iso-centre. Utilizing a 3D camera for body contour detection allowed for more accurate patient positioning and promoted further dose reduction. CONCLUSION Patient positioning has shown significant effects on radiation dose and image quality in CT. Developing a good understanding of the key factors influencing patient dose (off-centring direction, localiser orientation, patient size and bowtie filter selection) is critical in optimising CT scanning practices. Utilising a 3D camera for body contour detection is strongly recommended to improve patient positioning accuracy, image quality and to minimise patient dose.
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Affiliation(s)
- Yazan Al-Hayek
- School of Dentistry and Medical Sciences, Faculty of Science and Health, Charles Sturt University, Wagga Wagga, NSW, 2650, Australia; Department of Medical Imaging, Faculty of Applied Health Sciences, The Hashemite University, Zarqa, 13133, Jordan.
| | - Xiaoming Zheng
- School of Dentistry and Medical Sciences, Faculty of Science and Health, Charles Sturt University, Wagga Wagga, NSW, 2650, Australia.
| | - Christopher Hayre
- Department of Medical Imaging, College of Medicine and Health, University of Exeter, Devon, UK.
| | - Kelly Spuur
- School of Dentistry and Medical Sciences, Faculty of Science and Health, Charles Sturt University, Wagga Wagga, NSW, 2650, Australia.
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Automated patient centering of computed tomography images and its implementation to evaluate clinical practices in three hospitals in Indonesia. POLISH JOURNAL OF MEDICAL PHYSICS AND ENGINEERING 2022. [DOI: 10.2478/pjmpe-2022-0024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Abstract
Purpose: This study aims to develop a software tool for investigating patient centering profiles of axial CT images and to implement it to evaluate practices in three hospitals in Indonesia.
Methods: The evaluation of patient centering accuracy was conducted by comparing the center coordinate of the patient’s image to the center coordinates of the axial CT image. This process was iterated for all slices to yield an average patient mis-centering in both the x- and y-axis. We implemented the software to evaluate the profile of centering on 268 patient images from the head, thorax, and abdomen examinations taken from three hospitals.
Results: We found that 82% of patients were mis-centered in the y-axis (i.e., placed more than 5 mm from the iso-center), with 49% of patients placed 10–35 mm from the iso-center. Most of the patients had a tendency to be placed below the iso-centers. In head examinations, patients were more precisely positioned than in the other examinations. We did not find any significant difference in mis-centering between males and females. We found that there was a slight difference between mis-centering in adult and pediatric patients.
Conclusion: Software for automated patient centering was successfully developed. Patients in three hospitals in Indonesia had a tendency to be placed under the iso-center of the gantry.
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DeWeese L, Griglock T, Moody A, Mehlberg A, Winters C. The Improvement of Patient Centering in Computed Tomography Through a Technologist-Focused Education Initiative. J Digit Imaging 2022; 35:327-334. [PMID: 35022923 PMCID: PMC8754066 DOI: 10.1007/s10278-021-00580-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Revised: 11/19/2021] [Accepted: 12/28/2021] [Indexed: 12/01/2022] Open
Abstract
Proper patient centering is fundamental to the operation of CT. Misalignment of the patient is known to have a negative impact on image quality and dose. The purpose of this study was to improve patient centering in CT and examine the efficacy of several educational methods that could be implemented at any clinical site. The IRB determined the study was not human subjects research, and oversight was waived. Three interventions were examined. The first intervention involved a discussion on patient centering at a staff meeting. As the second intervention, an educational presentation was developed and delivered to CT technologists addressing the physics behind the importance of patient centering in CT. As the third intervention, individual technologist centering performance reviews were conducted by the modality supervisor. Clinical scan data was collected for each study period via a cloud-based software to examine the efficacy of each intervention in terms of lateral and vertical offset. The mean vertical offset of the baseline data was -1.97 cm. After the staff meeting, the mean vertical offset decreased to -1.60 cm (p < 0.001). Following the educational presentation, the mean vertical offset decreased to -1.14 cm (p < 0.001). After the technologist performance reviews, the mean vertical offset decreased to -0.86 cm (p < 0.001). This research examined a quality improvement initiative to improve patient centering at our institution which focused on communication and education. Through this initiative, the mean vertical positioning error decreased, the percentage of exams within 0-1 cm of isocenter increased, and the percentage of exams misaligned by greater than 3 cm decreased. This work has shown that patient centering can be improved with education.
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Affiliation(s)
- Lindsay DeWeese
- Department of Diagnostic Radiology, Oregon Health & Science University, Portland, OR USA
| | - Thomas Griglock
- Department of Diagnostic Radiology, Oregon Health & Science University, Portland, OR USA
| | - Alexander Moody
- Department of Diagnostic Radiology, Oregon Health & Science University, Portland, OR USA
- University of Texas Health Science Center at San Antonio, San Antonio, TX USA
| | - Aaron Mehlberg
- Department of Diagnostic Radiology, Oregon Health & Science University, Portland, OR USA
- Naval Medical Center Portsmouth-Tricare Portsmouth, Portsmouth, VA USA
| | - Celeste Winters
- Department of Diagnostic Radiology, Oregon Health & Science University, Portland, OR USA
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Precise and Automatic Patient Positioning in Computed Tomography: Avatar Modeling of the Patient Surface Using a 3-Dimensional Camera. Invest Radiol 2019; 53:641-646. [PMID: 29762259 DOI: 10.1097/rli.0000000000000482] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVES The aim of this study was to evaluate the accuracy of a 3-dimensional (3D) camera algorithm for automatic and individualized patient positioning based on body surface detection and to compare the results of the 3D camera with manual positioning performed by technologists in routinely obtained chest and abdomen computed tomography (CT) examinations. MATERIALS AND METHODS This study included data of 120 patients undergoing clinically indicated chest (n = 68) and abdomen (n = 52) CT. Fifty-two of the patients were scanned with CT using a table height manually selected by technologists; 68 patients were automatically positioned with the 3D camera, which is based on patient-specific body surface and contour detection. The ground truth table height (TGT) was defined as the table height that aligns the axial center of the patient's body region in the CT scanner isocenter. Off-centering was defined as the difference between the ground truth table height (TGT) and the actual table position used in all CT examinations. The t test was performed to determine significant differences in the vertical offset between automatic and manual positioning. The χ test was used to check whether there was a relationship between patient size and the magnitude of off-centering. RESULTS We found a significant improvement in patient centering (offset 5 ± 3 mm) when using the automatic positioning algorithm with the 3D camera compared with manual positioning (offset 19 ± 10 mm) performed by technologists (P < 0.005). Automatic patient positioning based on the 3D camera reduced the average offset in vertical table position from 19 mm to 7 mm for chest and from 18 mm to 4 mm for abdomen CT. The absolute maximal offset was 39 mm and 43 mm for chest and abdomen CT, respectively, when patients were positioned manually, whereas with automatic positioning using the 3D camera the offset never exceeded 15 mm. In chest CT performed with manual patient positioning, we found a significant correlation between vertical offset greater than 20 mm and patient size (body mass index, >26 kg/m, P < 0.001). In contrast, no such relationship was found for abdomen CT (P = 0.38). CONCLUSIONS Automatic individualized patient positioning using a 3D camera allows for accurate patient centering as compared with manual positioning, which improves radiation dose utilization.
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Paolicchi F, Bastiani L, Negri J, Caramella D. Effect of CT Localizer Radiographs on Radiation Dose Associated With Automatic Tube Current Modulation: A Multivendor Study. Curr Probl Diagn Radiol 2019; 49:34-41. [PMID: 30704769 DOI: 10.1067/j.cpradiol.2018.12.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2018] [Revised: 12/15/2018] [Accepted: 12/31/2018] [Indexed: 11/22/2022]
Abstract
OBJECTIVES To assess the influence of the CT localizer radiograph on the automatic tube current modulation system of 7 CT scanners produced by 4 different CT manufacturers. METHODS The influence of the localizer orientation, table height, tube current and tube potential values on the radiation dose of the related CT scan were evaluated. Images were acquired by using an anthropomorphic phantom positioned in the CT gantry isocenter as well as from -6 cm to +6 cm vertically to the isocenter. RESULTS Vertical movement of the CT table height affected the radiation dose in all scanners using anterior-posterior or a posterior-anterior localizer orientation albeit differently, depending on the manufacturer; only in 1/7 scanner no influence was observed. The latero-lateral localizer orientation proved to be more effective in limiting the influence of the vertical miscentering in all scanners. Changing localizer's tube voltage influenced the scan radiation dose in scanners produced by two manufacturers, while no significant effect was observed in scanners produced by the other two manufacturers. No significant dose variation was observed in 6/7 scanners when changing the localizer's tube current. CONCLUSION Localizer radiograph shows a significant influence on the radiation exposure but with different outcomes depending on the manufacturer of the CT scanner. Radiologists and radiographers should have a thorough understanding of these differences to assure patients the best examination in terms of radiation dose and image quality.
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Affiliation(s)
- Fabio Paolicchi
- Department of Diagnostic and Interventional Radiology, University of Pisa, Pisa, Italy.
| | - Luca Bastiani
- Institute of Clinical Physiology, National Research Council, Pisa, Italy
| | - Jacopo Negri
- Department of Radiology, Macerata General Hospital, Macerata, Italy
| | - Davide Caramella
- Department of Diagnostic and Interventional Radiology, University of Pisa, Pisa, Italy
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Kaasalainen T, Mäkelä T, Kortesniemi M. The effect of vertical centering and scout direction on automatic tube voltage selection in chest CT: a preliminary phantom study on two different CT equipments. Eur J Radiol Open 2018; 6:24-32. [PMID: 30619916 PMCID: PMC6298908 DOI: 10.1016/j.ejro.2018.12.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Revised: 12/11/2018] [Accepted: 12/11/2018] [Indexed: 12/11/2022] Open
Abstract
Purpose To determine the effect of patient's vertical off-centering and scout direction on the function of automatic tube voltage selection (ATVS) and tube current modulation (TCM) in chest computed tomography (CT). Methods Chest phantom was scanned with Siemens and GE CT systems using three clinical chest CT protocols exploiting ATVS and a fixed 120 kVp chest protocol. The scans were performed at five vertical positions of the phantom (-6 to +6 cm from the scanner isocenter). The effects of scout direction (posterior-to-anterior, anterior-to-posterior, and lateral) and vertical off-centering on the function of ATVS and TCM were studied by examining changes in selected voltage, radiation dose (volume CT dose index, CTDIvol), and image noise and contrast. Results Both scout direction and vertical off-centering affected ATVS. The effect differed between the vendors for the studied geometry, demonstrating differences in technical approaches. The greatest observed increase in CTDIvol due to off-centering was 91%. Anterior-to-posterior scout produced highest doses at the uppermost table position, whereas posterior-to-anterior scout produced highest doses at the lowermost table position. Dose varied least using lateral scouts. Vertical off-centering impacted image noise and contrast due to the combined effect of ATVS, TCM, structural noise, and bowtie filters. Conclusions Patient vertical off-centering and scout direction affected substantially the CTDIvol and image quality in chest CT examinations. Vertical off-centering caused variation also in the selected tube voltage. The function of ATVS and TCM methods differ significantly between the CT vendors, resulting in differences in CTDIvol and image noise characteristics.
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Affiliation(s)
- Touko Kaasalainen
- HUS Medical Imaging Center, Helsinki University Central Hospital, Finland.,Department of Physics, University of Helsinki, Finland
| | - Teemu Mäkelä
- HUS Medical Imaging Center, Helsinki University Central Hospital, Finland.,Department of Physics, University of Helsinki, Finland
| | - Mika Kortesniemi
- HUS Medical Imaging Center, Helsinki University Central Hospital, Finland.,Department of Physics, University of Helsinki, Finland
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Rigsby CK, McKenney SE, Hill KD, Chelliah A, Einstein AJ, Han BK, Robinson JD, Sammet CL, Slesnick TC, Frush DP. Radiation dose management for pediatric cardiac computed tomography: a report from the Image Gently 'Have-A-Heart' campaign. Pediatr Radiol 2018; 48:5-20. [PMID: 29292481 PMCID: PMC6230472 DOI: 10.1007/s00247-017-3991-x] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Revised: 08/21/2017] [Accepted: 09/12/2017] [Indexed: 12/28/2022]
Abstract
Children with congenital or acquired heart disease can be exposed to relatively high lifetime cumulative doses of ionizing radiation from necessary medical imaging procedures including radiography, fluoroscopic procedures including diagnostic and interventional cardiac catheterizations, electrophysiology examinations, cardiac computed tomography (CT) studies, and nuclear cardiology examinations. Despite the clinical necessity of these imaging studies, the related ionizing radiation exposure could pose an increased lifetime attributable cancer risk. The Image Gently "Have-A-Heart" campaign is promoting the appropriate use of medical imaging studies in children with congenital or acquired heart disease while minimizing radiation exposure. The focus of this manuscript is to provide a comprehensive review of radiation dose management and CT performance in children with congenital or acquired heart disease.
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Affiliation(s)
- Cynthia K Rigsby
- Department of Medical Imaging #9, Ann & Robert H. Lurie Children's Hospital of Chicago, Departments of Radiology and Pediatrics, Northwestern University Feinberg School of Medicine, 225 E. Chicago Ave., Chicago, IL, 60611, USA.
| | - Sarah E McKenney
- Division of Diagnostic Imaging and Radiology, Children's National Medical Center, Washington, DC, USA
| | - Kevin D Hill
- Department of Pediatrics, Duke University Medical Center, Durham, NC, USA
| | - Anjali Chelliah
- Division of Pediatric Cardiology, Columbia University Medical Center and New York-Presbyterian Hospital, New York, NY, USA
| | - Andrew J Einstein
- Division of Cardiology, Departments of Medicine and Radiology, Columbia University Medical Center and New York-Presbyterian Hospital, New York, NY, USA
| | - B Kelly Han
- Department of Pediatrics, Children's Heart Clinic at The Children's Hospitals and Clinics of Minnesota, Minneapolis, MN, USA
| | - Joshua D Robinson
- Division of Pediatric Cardiology, Ann & Robert H. Lurie Children's Hospital of Chicago, Departments of Pediatrics and Radiology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
| | - Christina L Sammet
- Department of Medical Imaging #9, Ann & Robert H. Lurie Children's Hospital of Chicago, Departments of Radiology and Pediatrics, Northwestern University Feinberg School of Medicine, 225 E. Chicago Ave., Chicago, IL, 60611, USA
| | - Timothy C Slesnick
- Department of Pediatrics, Emory University School of Medicine, Children's Healthcare of Atlanta, Atlanta, GA, USA
| | - Donald P Frush
- Department of Radiology, Duke University Medical Center, Durham, NC, USA
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Marsh RM, Silosky MS. The effects of patient positioning when interpreting CT dose metrics: A phantom study. Med Phys 2017; 44:1514-1524. [PMID: 28133763 DOI: 10.1002/mp.12137] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Revised: 01/19/2017] [Accepted: 01/20/2017] [Indexed: 11/08/2022] Open
Abstract
PURPOSE Review of dose metrics as part of the routine evaluation of CT protocols has become commonplace and is required by the Joint Commission and the American College of Radiology for accreditation. Most CT quality assurance programs include a review of CTDIvol and/or SSDE, both of which are affected by changes in mAs and kV. mAs, and sometimes kV, are largely determined by the Tube Current Modulation (TCM) functions of the scanner. TCM, in turn, relies on localizer scans to provide an accurate estimate of patient size. When patient size estimates are inaccurate, TCM and SSDE calculations are affected, leading to errors in both. It is important that those who are involved in reviewing CT dose indices recognize these effects to properly direct quality improvement initiatives. METHODS An anthropomophic phantom was scanned on four clinical CT scanners using AP and PA localizers and the institution's routine abdomen protocol. Scans were repeated with the phantom at various heights relative to scanner isocenter. For each height, the projected phantom width, as shown by the localizer scans, was measured and normalized by the width of the helical scan. After each localizer scan, the TCM algorithm determined the mAs to be used for the helical scan. The scanner-reported average CTDIvol was recorded for each helical scan, and the SSDE was calculated from the projected phantom size and the scanner-reported CTDIvol at each phantom height. Last, the phantom was augmented with a lipid-gel bolus material to simulate different body mass distributions and investigate the effect of differing body habitus on projected phantom size. The results were considered in the context of optimizing dose in CT imaging, with particular attention paid to the effect on dose to breast tissue. RESULTS Vertical mis-positioning of the phantom within the scanner led to errors in estimated phantom size of up to a factor of 1.5. These effects were more severe when localizers were acquired in the PA orientation compared with the AP orientation. Minification effects were more pronounced for AP localizers. As a consequence of inaccuracies in estimated phantom size, TCM resulted in changes in CTDIvol and SSDE of as much as a factor of 4.4 and 2.7, respectively. The effect was more pronounced when the TCM function used data from the PA, rather than the AP, localizer. CONCLUSIONS Proper patient positioning plays a large role in the function of TCM, and hence CTDIvol and SSDE. In addition, body mass distribution may affect how patients ought to be positioned within the scanner. Understanding these effects is critical in optimizing CT scanning practices.
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Affiliation(s)
- Rebecca M Marsh
- Department of Radiology, University of Colorado School of Medicine, Aurora, Colorado, 80045, USA
| | - Michael S Silosky
- Department of Radiology, University of Colorado School of Medicine, Aurora, Colorado, 80045, USA
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Saltybaeva N, Krauss A, Alkadhi H. Effect of Localizer Radiography Projection on Organ Dose at Chest CT with Automatic Tube Current Modulation. Radiology 2016; 282:842-849. [PMID: 27548276 DOI: 10.1148/radiol.2016160384] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Purpose To calculate the effect of localizer radiography projections to the total radiation dose, including both the dose from localizer radiography and that from subsequent chest computed tomography (CT) with tube current modulation (TCM). Materials and Methods An anthropomorphic phantom was scanned with 192-section CT without and with differently sized breast attachments. Chest CT with TCM was performed after one localizer radiographic examination with anteroposterior (AP) or posteroanterior (PA) projections. Dose distributions were obtained by means of Monte Carlo simulations based on acquired CT data. For Monte Carlo simulations of localizer radiography, the tube position was fixed at 0° and 180°; for chest CT, a spiral trajectory with TCM was used. The effect of tube start angles on dose distribution was investigated with Monte Carlo simulations by using TCM curves with fixed start angles (0°, 90°, and 180°). Total doses for lungs, heart, and breast were calculated as the sum of the dose from localizer radiography and CT. Image noise was defined as the standard deviation of attenuation measured in 14 circular regions of interest. The Wilcoxon signed rank test, paired t test, and Friedman analysis of variance were conducted to evaluate differences in noise, TCM curves, and organ doses, respectively. Results Organ doses from localizer radiography were lower when using a PA instead of an AP projection (P = .005). The use of a PA projection resulted in higher TCM values for chest CT (P < .001) owing to the higher attenuation (P < .001) and thus resulted in higher total organ doses for all investigated phantoms and protocols (P < .001). Noise in CT images was lower with PA localizer radiography than with AP localizer radiography (P = .03). The use of an AP projection allowed for total dose reductions of 16%, 15%, and 12% for lungs, breast, and heart, respectively. Differences in organ doses were not related to tube start angles (P = .17). Conclusion The total organ doses are higher when using PA projection localizer radiography owing to higher TCM values, whereas the organ doses from PA localizer radiography alone are lower. Thus, PA localizer radiography should be used in combination with reduced reference tube current at subsequent chest CT. © RSNA, 2016 Online supplemental material is available for this article.
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Affiliation(s)
- Natalia Saltybaeva
- From the Institute for Diagnostic and Interventional Radiology, University Hospital Zurich, Raemistrasse 100, 8091 Zurich, Switzerland (N.S., H.A.); and Computed Tomography Division, Siemens Healthcare, Forchheim, Germany (A.K.)
| | - Andreas Krauss
- From the Institute for Diagnostic and Interventional Radiology, University Hospital Zurich, Raemistrasse 100, 8091 Zurich, Switzerland (N.S., H.A.); and Computed Tomography Division, Siemens Healthcare, Forchheim, Germany (A.K.)
| | - Hatem Alkadhi
- From the Institute for Diagnostic and Interventional Radiology, University Hospital Zurich, Raemistrasse 100, 8091 Zurich, Switzerland (N.S., H.A.); and Computed Tomography Division, Siemens Healthcare, Forchheim, Germany (A.K.)
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