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DOI: 10.1148/rg.266065063
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Relationship between Noise, Dose, and Pitch in Cardiac Multi–Detector Row CT1

Andrew N. Primak, PhD, Cynthia H. McCollough, PhD, Michael R. Bruesewitz, RT(R), Jie Zhang, PhD and Joel G. Fletcher, MD

1 From the CT Clinical Innovation Center, Department of Radiology, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905. Recipient of a Certificate of Merit award for an education exhibit at the 2005 RSNA Annual Meeting. Received April 12, 2006; revision requested May 30 and received July 6; accepted July 10. A.N.P., C.H.M., J.Z., and J.G.F. receive research grants from Siemens Medical Solutions, Malvern, Pa; C.H.M. also receives a research grant from GE Healthcare, Waukesha, Wis; J.G.F. has an educational license from GE Healthcare and participates in a CME course sponsored by E-Z-Em, Lake Success, NY; M.R.B. has no financial relationships to disclose.

Figure 1
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  		Figure 1a.  Graphs of the interpolation algorithm used to generate planar data from the measured spiral data. The dotted lines show the center of every detector row, whereas the solid lines indicate the detector boundaries. (See the text for additional details.)

 

Figure 1
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  		Figure 1b.  Graphs of the interpolation algorithm used to generate planar data from the measured spiral data. The dotted lines show the center of every detector row, whereas the solid lines indicate the detector boundaries. (See the text for additional details.)

 

Figure 1
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  		Figure 1c.  Graphs of the interpolation algorithm used to generate planar data from the measured spiral data. The dotted lines show the center of every detector row, whereas the solid lines indicate the detector boundaries. (See the text for additional details.)

 

Figure 1
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  		Figure 1d.  Graphs of the interpolation algorithm used to generate planar data from the measured spiral data. The dotted lines show the center of every detector row, whereas the solid lines indicate the detector boundaries. (See the text for additional details.)

 

Figure 2
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  		Figure 2a.  Noise and dose versus tube current–time product and effective mAs for noncardiac (a, b) and cardiac (c, d) spiral CT modes at four different pitch (p) values and two different gantry rotation times (0.33 seconds and 0.37 seconds). The left y axis corresponds to noise curves; the right y axis corresponds to dose curves. Note that in cardiac mode, noise is dependent on tube current–time product and not on pitch (c). CTDIvol =Volume CT Dose Index.

 

Figure 2
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  		Figure 2b.  Noise and dose versus tube current–time product and effective mAs for noncardiac (a, b) and cardiac (c, d) spiral CT modes at four different pitch (p) values and two different gantry rotation times (0.33 seconds and 0.37 seconds). The left y axis corresponds to noise curves; the right y axis corresponds to dose curves. Note that in cardiac mode, noise is dependent on tube current–time product and not on pitch (c). CTDIvol =Volume CT Dose Index.

 

Figure 2
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  		Figure 2c.  Noise and dose versus tube current–time product and effective mAs for noncardiac (a, b) and cardiac (c, d) spiral CT modes at four different pitch (p) values and two different gantry rotation times (0.33 seconds and 0.37 seconds). The left y axis corresponds to noise curves; the right y axis corresponds to dose curves. Note that in cardiac mode, noise is dependent on tube current–time product and not on pitch (c). CTDIvol =Volume CT Dose Index.

 

Figure 2
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  		Figure 2d.  Noise and dose versus tube current–time product and effective mAs for noncardiac (a, b) and cardiac (c, d) spiral CT modes at four different pitch (p) values and two different gantry rotation times (0.33 seconds and 0.37 seconds). The left y axis corresponds to noise curves; the right y axis corresponds to dose curves. Note that in cardiac mode, noise is dependent on tube current–time product and not on pitch (c). CTDIvol =Volume CT Dose Index.

 

Figure 3
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  		Figure 3a.  (a) Anthropomorphic cardiac phantom with small calcified cylinders used for calcium quantitation (arrows). (b) Axial image shows the water-equivalent cylindrical insert used for noise versus tube current–time product measurements (arrow).

 

Figure 3
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  		Figure 3b.  (a) Anthropomorphic cardiac phantom with small calcified cylinders used for calcium quantitation (arrows). (b) Axial image shows the water-equivalent cylindrical insert used for noise versus tube current–time product measurements (arrow).

 

Figure 4
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  		Figure 4a.  Visual demonstration of the relationships between noise, dose, and pitch. Cardiac phantom images are shown for low and high pitch values. (a) Noncardiac images obtained at the same effective mAs have the same noise. (b) Cardiac images obtained at the same effective mAs do not have the same noise (but do have the same dose). (c) Conversely, cardiac images obtained at the same tube current–time product (not effective mAs) do have the same noise (but do not have the same dose). CTDIvol = Volume CT Dose Index, SD = standard deviation.

 

Figure 4
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  		Figure 4b.  Visual demonstration of the relationships between noise, dose, and pitch. Cardiac phantom images are shown for low and high pitch values. (a) Noncardiac images obtained at the same effective mAs have the same noise. (b) Cardiac images obtained at the same effective mAs do not have the same noise (but do have the same dose). (c) Conversely, cardiac images obtained at the same tube current–time product (not effective mAs) do have the same noise (but do not have the same dose). CTDIvol = Volume CT Dose Index, SD = standard deviation.

 

Figure 4
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  		Figure 4c.  Visual demonstration of the relationships between noise, dose, and pitch. Cardiac phantom images are shown for low and high pitch values. (a) Noncardiac images obtained at the same effective mAs have the same noise. (b) Cardiac images obtained at the same effective mAs do not have the same noise (but do have the same dose). (c) Conversely, cardiac images obtained at the same tube current–time product (not effective mAs) do have the same noise (but do not have the same dose). CTDIvol = Volume CT Dose Index, SD = standard deviation.

 

Figure 5
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  		Figure 5.  Diagram of an ECG-gated spiral CT scan with pitch that is too high for the heart rate. Continuous anatomic coverage of the heart is not possible because of the volume gaps between the images reconstructed from the consecutive cardiac cycles. R = R wave, Recon = reconstruction.

 

Figure 6
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  		Figure 6.  Percentage of area stenosis versus rotation time for a moving stenotic vessel phantom scanned on 16– and 64–detector row CT systems with coronary CT angiography protocols and multiple gantry rotation times (0.33, 0.42, and 0.5 seconds). The measurements were performed for 0.6-, 0.75-, and 1-mm section widths. (See the text for additional details.)

 

Figure 7
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  		Figure 7.  Calcium mass score measured in a rotating insert of an anthropomorphic cardiac phantom scanned on 16– and 64–detector row CT systems with CAC protocols and multiple gantry rotation times (0.33, 0.37, 0.42, and 0.5 seconds). HA = hydroxyapatite concentration in milligrams per cubic centimeter; the diameter of the calcification is given in millimeters. (For example, 400 HA 3 mm corresponds to 400 mg/cm3 HA density and a 3-mm-diameter cylinder.)

 




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