HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Boone, J. M. Articles by Wootton-Gorges, S. L. Search for Related Content PubMed PubMed Citation Articles by Boone, J. M. Articles by Wootton-Gorges, S. L.

Dose Reduction in Pediatric CT: A Rational Approach¹

¹ From the Department of Radiology, University of California Davis Medical Center, Research Imaging Center, 4701 X St, Sacramento, CA 95817. Received April 25, 2002; revision requested June 21; final revision received September 24; accepted November 5. Supported in part by grants from the California Breast Cancer Research Program (7EB-0075) and the National Cancer Institute (R01-CA89260). Address correspondence to J.M.B. (e-mail: jmboone@ucdavis.edu).

View larger version (38K): [in a new window]   Figure 1. Graph shows patient width (W, ) and thickness (T, ) as a function of patient diameter. (W and T are defined geometrically in the inset image, along with the equivalent diameter, Diaeq.) These data demonstrate that the relative proportions of width and thickness remain approximately constant among patients of different size. Identity = line of identity (where x = y).

View larger version (77K): [in a new window]   Figure 2. Scatterplots show CT noise as a function of milliampere seconds for four tube voltages. In each plot, the six data sets (in ascending order) correspond to PMMA cylinders measuring 10, 13, 16, 20, 25, and 32 cm in diameter. CT noise increases at low milliampere second values and for larger-diameter cylinders. These noise data were used as denominators for the CNR measurements in this study.

View larger version (24K): [in a new window]   Figure 3. Graphs show CT contrast enhancement (in Hounsfield units) as a function of patient diameter for four tube voltages. Except in C, symbols ( = 80 kVp, = 100 kVp, = 120 kVp, = 140 kVp) correspond to physical measurements of iodine contrast on CT scans, and solid lines represent computer-simulated results. Symbols represent the average of four measurements, each of which was obtained from a different CT image. A, Graph shows that the contrast of iodine (ie, a 0.5% solution of an iodine-based contrast agent) is highest at lower tube voltages and decreases with increasing patient diameter owing to beam hardening. B, Graph shows contrast between PMMA and water. C, Graph shows contrast between muscle and adipose tissue (ie, soft-tissue contrast) as calculated with the computer model.

View larger version (38K): [in a new window]   Figure 4. Graph shows the CTDI per 100 mAs as a function of patient diameter for four tube voltages, given a 4 x 5-mm transverse acquisition (20-mm nominal collimation). The doses measured in the PMMA phantoms at the edge and at the center are shown. The lines (solid lines for edge data, dotted lines for center data) represent the computer-fit CTDIw values, which were used to interpolate dose values between patient thicknesses.

View larger version (24K): [in a new window]   Figure 5. A, Graph shows the relative radiation dose necessary to achieve constant CNR as a function of patient diameter. The dose necessary to achieve a constant CNR for smaller section thicknesses (dotted lines) must be doubled for 2.5-mm sections and quadrupled for 1.25-mm sections. B, Graph shows the relative milliampere second values required to achieve constant CNR. The dotted lines show the milliampere second values necessary to achieve a constant CNR with 2.5- and 1.3-mm section thicknesses. The ordinate axes of both graphs are logarithmic; this allows display of data over a much larger range of values. The data points represented by the symbols (and the solid line) were averaged over three spectra (100, 120, and 140 kVp) and the two contrast types (ie, soft tissue and iodine). Dose values (in A) and milliampere second values (in B) were normalized to unity for a 28-cm-diameter patient and a 5-mm section thickness. The gray area surrounding the curves corresponds to ±2 SD from the mean (ie, the 95% CI). The crosshairs (centered at patient diameter = 28 cm, dose multiplication factor = 1.0) indicate that these data sets have been normalized to unity at this point.