Efficient use of automatic exposure control systems in computed tomography requires correct patient positioning

Guðjónsdóttir, Jónína; Svensson, Jon; Campling, S.; Brennan, Patrick C.; Jónsdóttir, Birna

doi:10.3109/02841850903147053

Cited by 56 publications

(35 citation statements)

References 15 publications

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“…To get optimal matching with the bowtie filter and accurate AEC control, patients should not be off‐centered in the CT scanner 17 , 18 , 19 , 20 . While this work does not support mispositioning patients in the CT scanner, it does provide a methodology to determine how near isocenter anatomy must be in order to achieve a particular resolution.…”

Section: Discussionmentioning

confidence: 99%

Improvement in CT image resolution due to the use of focal spot deflection and increased sampling

Rubert

Szczykutowicz

Ranallo

2016

J Applied Clin Med Phys

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When patient anatomy is positioned away from a CT scanner's isocenter, scans of limited diagnostic value may result. Yet in some cases, positioning of patient anatomy far from isocenter is unavoidable. This study examines the effect of position and reconstruction algorithm on image resolution achieved by a CT scanner operating in a high resolution (HR) scan mode which incorporates focal spot deflection and acquires an increased number of projections per rotation. Images of a metal bead contained in a phantom were acquired on a GE CT750 HD scanner with multiple reconstruction algorithms, in the normal and HR scan mode, and at two positions, scanner isocenter and 15 cm directly above isocenter. The images of the metal bead yielded two‐dimensional point spread functions which were averaged along two perpendicular directions to yield line spread functions. Fourier transforms of the line spread functions yielded radial and azimuthal modulation transfer functions (MTFs). At isocenter, the radial and azimuthal MTFs were averaged. MTF improvement depended on image position and modulation direction. The results from a single algorithm, Edge, can be generalized to other algorithms. At isocenter, the 10% MTF cutoff was 14.4 cycles/cm in normal and HR mode. At 15 cm above isocenter, the 10% cutoff was 6.0 and 8.5 cycles/cm for the azimuthal and radial MTFs in normal mode. In HR mode, the azimuthal and radial MTF 10% cutoff was 8.3 and 10.3 cycles/cm. Our results indicate that the best image resolution is achieved at scanner isocenter and that the azimuthal resolution degrades more significantly than the radial resolution. For the GE CT750 HD CT scanner, the resolution is significantly enhanced by the HR scan mode away from scanner isocenter, and the use of the HR scan mode has much more of an impact on image resolution away from isocenter than the choice of algorithm.PACS number(s): 87.57.Q‐

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Section: Discussionmentioning

confidence: 99%

Improvement in CT image resolution due to the use of focal spot deflection and increased sampling

Rubert

Szczykutowicz

Ranallo

2016

J Applied Clin Med Phys

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“…However, the overall radiation dose even with the use of AEC still relies on proper patient centering in the gantry (Gudjonsdottir et al 2009). …”

Section: Discussionmentioning

confidence: 99%

Thyroid Radiation Dose to Patients from Diagnostic Radiology Procedures over Eight Decades

Chang¹,

Miller

Lee

et al. 2017

Health Physics

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This study summarizes and compares estimates of radiation absorbed dose to the thyroid gland for typical patients who underwent diagnostic radiology examinations in the years from 1930 to 2010. We estimated the thyroid dose for common examinations, including radiography, mammography, dental radiography, fluoroscopy, nuclear medicine, and computed tomography (CT). For the most part, we observed a clear downward trend in thyroid dose over time for each procedure. Historically, the highest thyroid doses came from the nuclear medicine thyroid scans in the 1960s (630 mGy), full-mouth series dental radiography (390 mGy) in the early years of the use of x-rays in dentistry (1930s), and the barium swallow (esophagram) fluoroscopic exam also in the 1930s (140 mGy). Thyroid uptake nuclear medicine examinations and pancreatic scans also gave relatively high doses to the thyroid (64 mGy and 21 mGy, respectively, in the 1960s). In the 21st century, the highest thyroid doses still result from nuclear medicine thyroid scans (130 mGy), but high thyroid doses are also associated with chest/abdomen/pelvis CT scans (18 and 19 mGy for male and females, respectively). Thyroid doses from CT scans did not exhibit the same downward trend as observed for other examinations. The largest thyroid doses from conventional radiography came from cervical spine and skull examinations. Thyroid doses from mammography (which began in the 1960s) were generally a fraction of a mGy. The highest average doses to the thyroid from mammography were about 0.42 mGy, with modestly larger doses associated with imaging of breasts with large compressed thicknesses. Thyroid doses from dental radiographic procedures have decreased markedly throughout the decades, from an average of 390 mGy for a full-mouth series in the 1930s to an average of 0.31 mGy today. Upper GI series fluoroscopy examinations resulted in up to two orders of magnitude lower thyroid doses than the barium swallow. There are considerable uncertainties associated with the presented doses, particularly for characterizing exposures of individual identified patients. Nonetheless, the tabulations provide the only comprehensive report on the estimation of typical radiation doses to the thyroid gland from medical diagnostic procedures over eight decades (1930–2010). These data can serve as a resource for epidemiologic studies that evaluate the late health effects of radiation exposure associated with diagnostic radiologic examinations.

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“…By tailoring the examination to the individual patient, diagnostic image quality can be maintained with significant dose reduction beyond empiric settings [32, 69,70]. The anatomy scanned should be limited as closely as possible, and patient positioning can also reduce dose (such as moving female breasts away from the scan field of view) [71].…”

Section: Radiation Dose In Coronary Ct Angiographymentioning

confidence: 99%

Coronary CT Angiography for the Detection of Obstructive Coronary Artery Disease

Maurovich-Horvat

Ghoshhajra

Ferencik

2010

Curr Cardiovasc Imaging Rep

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Contemporary CT scanners offer high temporal and spatial resolution, permitting visualization of the rapidly moving heart and coronary arteries. The imaging of coronary artery lumen and detection of obstructive coronary artery disease is feasible with 64-detector-row and higher generation CT scanners. The diagnostic accuracy of coronary CT angiography as compared to invasive coronary angiography is good (sensitivity of 85%-100%, specificity of 85%-99%). The major strength of coronary CT angiography is the high negative predictive value (96% to 99%) that permits excluding significant coronary artery stenosis with high accuracy, when optimal image quality is achieved. Therefore, coronary CT angiography is an appropriate diagnostic test for a selected patient population with a low to intermediate probability of coronary artery disease.

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Efficient use of automatic exposure control systems in computed tomography requires correct patient positioning

Cited by 56 publications

References 15 publications

Improvement in CT image resolution due to the use of focal spot deflection and increased sampling

Improvement in CT image resolution due to the use of focal spot deflection and increased sampling

Thyroid Radiation Dose to Patients from Diagnostic Radiology Procedures over Eight Decades

Coronary CT Angiography for the Detection of Obstructive Coronary Artery Disease

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