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DOI: 10.1148/rg.262055138
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CT Dose Reduction and Dose Management Tools: Overview of Available Options1

Cynthia H. McCollough, PhD, Michael R. Bruesewitz, RT(R) and James M. Kofler, Jr, PhD

1 From the Department of Radiology, Mayo Clinic College of Medicine, 200 First St SW, Rochester, MN 55905. Presented as an education exhibit at the 2004 RSNA Annual Meeting. Received June 28, 2005; revision requested August 5; revision received November 8 and accepted November 9. C.H.M. receives research support from GE Healthcare and Siemens Medical Solutions; both other authors have no financial relationships to disclose.

Figure 1
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  		Figure 1.  Graph of relative attenuation values (top) according to table position (in millimeters from the initial position) and associated body region (bottom) shows strong variations in attenuation, by almost three orders of magnitude, according to body region and projection angle. Relative attenuation values, which reflect the sum of x-ray absorption along an imaginary line through the patient, vary with gantry rotation from the anteroposterior direction (black line) to the lateral direction (gray line).

 

Figure 2
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  		Figure 2.  Illustration of the concept of angular dose modulation, in which the tube current (mA) (vertical axis) is varied as the x-ray tube rotates around the patient (horizontal axis), shows greater variation in the thorax than in the abdomen.

 

Figure 3
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  		Figure 3.  Graph of tube current (in milliamperes) superimposed on a CT projection radiograph illustrates the concept of longitudinal dose modulation, with variation of the tube current along the z-axis. The curve is determined by using attenuation data from the CT projection radiograph and the manufacturer-specific algorithm.

 

Figure 4
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  		Figure 4.  Graph of tube current (mA) superimposed on a CT projection radiograph shows the variation in tube current as a function of time (and, hence, table position along the z-axis) at spiral CT in a 6-year-old child. An adult scanning protocol and an AEC system (CareDose 4D; Siemens Medical Solutions) were used with a reference effective tube current–time product of 165 mAs. The mean effective tube current–time product for actual scanning was 38 mAs (effective tube current–time product = tube current–time product/pitch).

 

Figure 5
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  		Figure 5.  Curves show the relationship between the tube current–time products (in milliampere-seconds) that are used for abdominal (abd) and pelvic versus chest CT examinations at the authors’ institution and the patient’s lateral width (in centimeters) at the level of the liver (20). HVL = half-value layer.

 

Figure 6
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  		Figure 6a.  Clinical CT examination of the abdomen and pelvis. (a) CT projection radiograph (topogram). (b, c) Axial CT images at the levels of the liver (b) and pelvis (c). The patient’s lateral width was 30 cm (measured from the topogram at the level of the liver). The reference effective tube current–time product for 5-mm-thick sections was 240 mAs, and the effective tube current–time product that would have been used according to the institutional technique chart was 120 mAs. The AEC system automatically adapted to the small patient size, as shown by the image quality in b (actual effective tube current–time product, 88 mAs) and c (actual effective tube current–time product, 122 mAs).

 

Figure 6
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  		Figure 6b.  Clinical CT examination of the abdomen and pelvis. (a) CT projection radiograph (topogram). (b, c) Axial CT images at the levels of the liver (b) and pelvis (c). The patient’s lateral width was 30 cm (measured from the topogram at the level of the liver). The reference effective tube current–time product for 5-mm-thick sections was 240 mAs, and the effective tube current–time product that would have been used according to the institutional technique chart was 120 mAs. The AEC system automatically adapted to the small patient size, as shown by the image quality in b (actual effective tube current–time product, 88 mAs) and c (actual effective tube current–time product, 122 mAs).

 

Figure 6
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  		Figure 6c.  Clinical CT examination of the abdomen and pelvis. (a) CT projection radiograph (topogram). (b, c) Axial CT images at the levels of the liver (b) and pelvis (c). The patient’s lateral width was 30 cm (measured from the topogram at the level of the liver). The reference effective tube current–time product for 5-mm-thick sections was 240 mAs, and the effective tube current–time product that would have been used according to the institutional technique chart was 120 mAs. The AEC system automatically adapted to the small patient size, as shown by the image quality in b (actual effective tube current–time product, 88 mAs) and c (actual effective tube current–time product, 122 mAs).

 

Figure 7
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  		Figure 7a.  Clinical CT examination of the chest, abdomen, and pelvis. (a) CT projection radiograph (topogram). (b–e) Axial CT images at the levels of the upper thorax (b), middle thorax (c), liver (d), and pelvis (e). The patient’s lateral width was 43 cm (measured from the topogram at the level of the liver). Reference effective tube current–time product for 5-mm-thick sections was 240 mAs, and the effective tube current–time product that would have been used according to the institutional technique chart was 340 mAs. Actual effective values used by the AEC system were 95 mAs (b), 101 mAs (c), 369 mAs (d), and 205 mAs (e). The AEC system automatically adapted both to the larger patient size and the lower-attenuating regions of the body, as shown by the comparable image quality in b–e.

 

Figure 7
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  		Figure 7b.  Clinical CT examination of the chest, abdomen, and pelvis. (a) CT projection radiograph (topogram). (b–e) Axial CT images at the levels of the upper thorax (b), middle thorax (c), liver (d), and pelvis (e). The patient’s lateral width was 43 cm (measured from the topogram at the level of the liver). Reference effective tube current–time product for 5-mm-thick sections was 240 mAs, and the effective tube current–time product that would have been used according to the institutional technique chart was 340 mAs. Actual effective values used by the AEC system were 95 mAs (b), 101 mAs (c), 369 mAs (d), and 205 mAs (e). The AEC system automatically adapted both to the larger patient size and the lower-attenuating regions of the body, as shown by the comparable image quality in b–e.

 

Figure 7
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  		Figure 7c.  Clinical CT examination of the chest, abdomen, and pelvis. (a) CT projection radiograph (topogram). (b–e) Axial CT images at the levels of the upper thorax (b), middle thorax (c), liver (d), and pelvis (e). The patient’s lateral width was 43 cm (measured from the topogram at the level of the liver). Reference effective tube current–time product for 5-mm-thick sections was 240 mAs, and the effective tube current–time product that would have been used according to the institutional technique chart was 340 mAs. Actual effective values used by the AEC system were 95 mAs (b), 101 mAs (c), 369 mAs (d), and 205 mAs (e). The AEC system automatically adapted both to the larger patient size and the lower-attenuating regions of the body, as shown by the comparable image quality in b–e.

 

Figure 7
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  		Figure 7d.  Clinical CT examination of the chest, abdomen, and pelvis. (a) CT projection radiograph (topogram). (b–e) Axial CT images at the levels of the upper thorax (b), middle thorax (c), liver (d), and pelvis (e). The patient’s lateral width was 43 cm (measured from the topogram at the level of the liver). Reference effective tube current–time product for 5-mm-thick sections was 240 mAs, and the effective tube current–time product that would have been used according to the institutional technique chart was 340 mAs. Actual effective values used by the AEC system were 95 mAs (b), 101 mAs (c), 369 mAs (d), and 205 mAs (e). The AEC system automatically adapted both to the larger patient size and the lower-attenuating regions of the body, as shown by the comparable image quality in b–e.

 

Figure 7
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  		Figure 7e.  Clinical CT examination of the chest, abdomen, and pelvis. (a) CT projection radiograph (topogram). (b–e) Axial CT images at the levels of the upper thorax (b), middle thorax (c), liver (d), and pelvis (e). The patient’s lateral width was 43 cm (measured from the topogram at the level of the liver). Reference effective tube current–time product for 5-mm-thick sections was 240 mAs, and the effective tube current–time product that would have been used according to the institutional technique chart was 340 mAs. Actual effective values used by the AEC system were 95 mAs (b), 101 mAs (c), 369 mAs (d), and 205 mAs (e). The AEC system automatically adapted both to the larger patient size and the lower-attenuating regions of the body, as shown by the comparable image quality in b–e.

 




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